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1998 Part 3     Front Cover (1998 - Part 3)    No author information available Summary: Not available         Table of Contents (1998 - Part 3)    No author information available Summary: Not available         Superconducting electronics coming to market    A.I. Braginski Summary: Superconducting electronic (SCE) products have been commercially available for over 25 years. However, the market remained extremely small. A conservative estimate of the total 1997 volume gives, approximately, US$ 30 million. Until 1997, LTS SQUID systems, mostly for biomagnetic research, represented the dominant share. High-temperature superconductivity (HTS) hadn't yet had any real impact on the market. However, in 1998 HTS filter subsystems for wireless telecommunication receiver front end represent a small, but rapidly growing segment of the market. This paper gives highlights of technical achievements and progress in SQUIDs, and in SCE for wireless, while emphasizing obstacles to and opportunities for much larger markets. A summary of an industry survey conducted prior to writing the paper is also included. Most other SCE products and the identified potential new products, LTS and HTS, represent very small niches having little chance for major growth. These are not discussed. A notable exception is single flux quantum digital electronics. It does not command any market share today, but still has the largest long-term potential for a very large market in telecommunications and in massive data processing.         Recommended directions of research and development in superconducting electronics    J.M. Rowell Summary: For some time, work has been continuing within the U.S.A. on a "Technology Roadmap for the Superconducting Electronics Industry". A similar roadmap exercise is underway in Europe, and in Japan, recently announced research projects in superconductivity involved a detailed planning process. However, the U.S. Roadmap is not complete, and a consensus of industry opinion has not yet been reached on its recommendations. This manuscript should be regarded as a distillation of inputs from many sources, heavily weighted with the author's own prejudices. He suggests that a system level view of superconducting electronics technology should lead to revisions of today's research priorities. In particular, the importance of the cryocooler and cryopackage in each system has broad implications, even affecting the directions of materials and device research.         Application of TBCCO based HTS devices to digital cellular communications    A.P. Jenkins, D. Dew-Hughes, D.J. Edwards, D. Hyland and C.R.M. Grovenor Summary: Linear microstrip resonators suffer from high peak current density inside the resonators which limit the power handling characteristics and hence their use in cellular transmitter applications. To realise higher power filter and combiner networks for cellular applications it is possible to use two dimensional microstrip resonators (such as disks) to equalise the internal current distribution. We have designed and tested such microstrip resonators, fabricated from TBCCO 2212 thin films deposited by RF sputtering onto 50 mm diameter LaAlO/sub 3/ substrates. The R/sub s/ of such films has been measured at 5.5 GHz using a sapphire dielectric resonator and shown to be less than 1 m/spl Omega/ scaled to 10 GHz and at 80 K. The power handling of disk resonators designed for operation in the PCS and DCS1800 cellular bands has been shown to be superior to that of linear resonators fabricated from similar material. The operation of such devices using high power levels and realistic signals encountered in 2/sup nd/ generation digital cellular systems (e.g., DQPSK and GMSK) will be presented. The application of these devices to 3/sup rd/ generation wide band CDMA systems will also be discussed.         Performance of superconducting dual mode resonators with different input/output feedline angles    Sang Yeol Lee, Joo Hyung Park and Dal Ahn Summary: High-temperature superconducting (HTS) dual mode ring resonators have been fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on MgO substrates. Epitaxial YBCO superconducting thin films were deposited on MgO substrates by pulsed laser deposition (PLD). The transition temperature of YBCO thin films were 85-88 K. Dual mode ring resonators are patterned using YBCO superconducting films by conventional photolithography and wet-etching process. The opposite side of the substrate has been made up the ground plane with two layer metal films (Ti/Ag) deposited by e-beam and thermal evaporation. Two types of dual mode ring resonators were fabricated with different input and output feedline angles of 60/spl deg/ and 100/spl deg/. The frequency response shows the resonant center frequency of about 8.5 GHz and stringent narrow bandwidths. These types of dual mode ring resonators could be utilized for dual mode resonator based filters for satellite communications.         HTS power filters for output multiplexers in satellite communications    A. Baumfalk, H. Chaloupka, S. Kolesov, M. Klauda and C. Newmann Summary: The paper reports on advances in the development of high temperature superconducting 40 MHz bandwidth four-pole bandpass filters with elliptic frequency response for 3.4-4.2 GHz (extended C-band) output multiplexers of communication satellites. By employing the concept of "edge-current-free" disk and ring resonators the filters possess a small size but can handle 60 W transmitted power with sufficiently low insertion loss and intermodulation. Measurements of the unloaded Q-factor and power handling as function of the temperature, performed at single disk resonators made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on LaAlO/sub 3/ and sapphire substrates indicate the conditions under which the required Q-factor of about 1.5/spl middot/10/sup 5/ and sufficiently low nonlinear response up to an oscillating power of 15 kW can be obtained. Approaches for shifting the resonant frequencies of unwanted modes relative to the resonant frequency of the employed TM/sub 010/-mode are outlined and shown to be necessary for the envisaged multiplexer applications.         Effects of the finite HTS film thickness on the resonant frequency of the axially symmetric TE/sub 01/spl delta// mode of a parallel plate dielectric resonator    Sang Young Lee, H.J. Kwon, J.H. Suh, J.H. Lee, Jung Hur and V.B. Fedorov Summary: An axially symmetric TE/sub 01/spl delta// mode of a parallel plate dielectric resonator is studied for investigating effects of the film thickness (t) of high-temperature superconductor (HTS) films on the mode resonant frequency (f/sub 0/). A sapphire-loaded cylindrical cavity resonator with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) endplates and mode f/sub 0/ of about 19 GHz has been prepared and its unloaded Q (Q/sub 0/) and f/sub 0/ are investigated at temperatures below the critical temperature of YBCO. From theoretical analysis, it appears that f/sub 0/ changes by less than 0.4% for different t's when the ratio of t to the London penetration depth (/spl lambda/) is more than 10/sup -2/. Meanwhile, from experiments, significant dependence of f/sub 0/ on the gap distance (s) between the sapphire rod and the top endplate is observed with f/sub 0/ changing by about 1 GHz (/spl sim/5%) from 19.578 GHz to 18.648 GHz, as s increases from 0 to 1 mm at 77 K. The experimental values of f/sub 0/ are observed to agree well to the calculated f/sub 0/. Applicability for tunable high-Q resonators is described.         Design and fabrication of coplanar YBCO structures on lithium niobate substrates    E. Rozan, C. Collado, A. Garcia, J.M. O'Callaghan, R. Pous, L. Fabrega, J. Rius, R. Rubi, J. Fontcuberta and F. Harackiewicz Summary: YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) with low RF losses has been successfully deposited onto lithium niobate (LNO) to improve the performance of electrooptic Mach-Zender modulators. Epitaxial, c-axis oriented superconducting YBCO thin films have been grown on X-cut LNO single crystals with a yttria-stabilized zirconia (YSZ) buffer layer by RF magnetron sputtering. This buffer layer is needed to obtain good superconducting properties of the YBCO grown. Numerical tools have been developed to analyze CPW structures based on YBCO/YSZ/LNO trilayers, and they indicate that YSZ thickness has to be kept to the minimum necessary for good YBCO growth. With this restriction, the RF losses of YBCO/YSZ/LNO samples have been measured. The results from these measurements are used to quantify the performance enhancement in a Mach-Zender modulator using YBCO electrodes.         Fine tuning of high Q HTS shielded resonators using HTS coated SrTiO/sub 3/ pucks    L. Hao, J.C. Gallop, D. Lacey and L. Davis Summary: The combination of very low loss dielectric single crystal materials (such as sapphire) with a HTS shielding enclosure has led to the achievement of high Q resonators operated in the temperature range 40 K-70 K which show great promise for frequency standard applications. A number of problems remain to be solved. We have already reported how high frequency stability with minimum temperature control may be achieved by means of composite dielectric pucks, the components having opposite signs for their temperature coefficients of permittivity. A second requirement for a frequency standard is that it should possess a specified frequency. Here we report implementation of electronic tuning of a sapphire dielectric puck resonator by using a SrTiO/sub 3/ (STO) tuning element situated in the evanescent field region outside the sapphire puck. In addition the same structure may be used when the sapphire and STO elements act as weakly coupled resonators so that the resonant frequency becomes a very sensitive function of temperature, allowing the possibility of very high resolution thermometry.         Properties of SNS Josephson junctions fabricated by 200 keV oxygen implantation into YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//    F. Kahlmann, A. Engelhardt, J. Schubert, W. Zander, C. Buchal and J. Hollkott Summary: The properties of SNS Josephson junctions in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films have been investigated, which were fabricated by oxygen irradiation at 200 keV through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500/spl deg/C in an oxygen atmosphere, the implanted region has a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of <15 K. Close to the coupling temperature the critical current shows a nearly complete modulation in an applied magnetic field. This indicates a homogeneous current distribution in the junctions and therefore a homogeneous defect distribution throughout the implanted and subsequently annealed region of the superconducting microbridges. Over the entire temperature range of Josephson coupling, the junctions exhibit resistively shunted junction like I-V characteristics with additional excess current. Furthermore, the exponential dependence of the critical current on temperature is in good agreement with conventional superconductor-normal-superconductor proximity effect theory.         High-Tc Josephson junctions on micro V-shape groove prepared by focused ion beam    N. Yutani, K. Suzuki and Y. Enomoto Summary: For Josephson junctions using a narrow groove on a substrate etched by a focused ion beam (FIB), there is a strong relation between junction properties and groove shapes. We have developed the FIB milling method which has flexibility to produce a variety of different groove shapes. V-shape grooves with different sizes (width=215-594 nm, depth=27-92 nm) have been formed with the same slope angle on the MgO [100] substrate. The top surface profile of the 300 nm thick YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) film had the same V-shape as the grooves on the substrate, but the YBCO groove widths were 110 nm narrower than the FIB groove widths. The 3 /spl mu/m width junctions fabricated on these grooves showed RSJ type I-V curves without exception and had the average of critical current (Ic) values of 0.520 mA at 4.2 K.         Asymmetrical FIB junctions as components for HTS SFQ circuits    Y. Mizuno, K. Miyahara, J.G. Wen, T. Utagawa and Y. Enomoto Summary: High-temperature superconductor (HTS) Josephson junctions have been formed on asymmetrical V-shape grooves etched by a Ga focused-ion beam (FIB). The asymmetrical groove is made by tilting the substrate during FIB etching. Transmission electron microscopy (TEM) shows a tilted V-shape groove and two clear grain boundaries in the NBCO film. The I-V characteristics of the junctions are controlled by the dose amount of Ga ions and the NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO) film thickness. The inductance of the lines was estimated to be 0.5 pH//spl mu/m for the film thickness of 200 nm for the characteristics of a SQUID fabricated with the asymmetrical FIB junctions.         Electrical properties of electron and ion beam irradiated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//    W.E. Booij, C.A. Elwell, E.J. Tarte, P.F. McBrien, F. Kahlmann, D.F. Moore, M.G. Blamire, N.H. Peng and C. Jeynes Summary: An electron beam with sufficient energy can be used to create a high quality Josephson junction in a single layer of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The number of junctions thus produced is severely limited by the serial nature of the technique. An alternative method to create similar high quality Josephson junctions without such a serious throughput limitation is possibly the combination of high resolution masking and ion irradiation. For this reason we have studied the electrical properties of both electron and proton irradiated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// in some detail. It was found that the resistivity of electron beam irradiated barriers of intermediate length (200 nm) are strongly influenced by a proximity effect when the irradiated material has a finite T/sub c/. At higher electron doses the superconducting properties are fully suppressed and the electrical behaviour is dominated by a Variable Range Hopping mechanism.         Fabrication of YBaCuO junctions by the irradiation of focused ion beam    H. Shiga, Y. Soutome and Y. Okabe Summary: We have fabricated Josephson junctions in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBaCuO) thin films by the irradiation of focused ion beam (FIB). We used Be/sup 2+/ ions with the energy of 200 keV. When the fluence of Be/sup 2+/ ions was 1.2/spl times/10/sup 16/ ions/cm/sup 2/, the I-V characteristics of the junctions at 4.2 K showed RSJ-like characteristics with the excess current. The I/sub c/R/sub n/ product of the junctions was 1.1 mV at 6.3 K. Shapiro steps up to 20th step could be observed by the irradiation of 8.47 GHz microwave at 6.3 K. The magnetic modulation curve of the junction at 4.2 K was similar to the Fraunhofer pattern. These characteristics remained unaltered after preservation in a desiccator for 6 months.         Fabrication of HTS Josephson junctions on substrates prepared by focused ion beam system    I. Jin, C.-H. Chen, S.P. Pai, B. Ming, D.J. Kang, T. Venkatesan, F. Machalett, K. Edinger, J. Orloff and J. Melngailis Summary: YBCO Josephson junctions were fabricated by using a Focused Ion Beam (FIB) of 20-nm diameter gallium ion beam. We first made trenches of 100-nm width and 300-nm depth on LaAlO/sub 3/ (LAO) substrates that were covered by 100-nm chromium (Cr) conducting layer. After removing the conducting layer by chemical etching, YBCO followed by a gold layer was pulsed laser deposited in-situ. The deposited YBCO was disconnected over the trenches and the gold layer filled the trenches and made connections between the separated YBCO so that it formed SNS junctions. We observed proximity coupling up to 86 K.         Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions    L. Ozyuzer, N. Miyakawa, J.F. Zasadzinski, Z. Yusof, P. Romano, C. Kendziora, P. Guptasarma, D.G. Hinks and K.E. Gray Summary: Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV=2/spl Delta/ as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d(x/sup 2/-y/sup 2/) (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T/sub c/=62 K, the Josephson current is measured as a function of junction resistance, R/sub n/, which varied by two orders of magnitude (1 k/spl Omega/ to 100 k/spl Omega/). I/sub c/R/sub n/ product is proportional to the 0.47 power of I/sub c/ and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T/sub c/=62 K) to the underdoped regime (T/sub c/=70 K), the average I/sub c/R/sub n/ product increases as does the quasiparticle gap. The maximum I/sub c/R/sub n/ is /spl sim/40% of the /spl Delta//e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.         Two-stage S-band DC SQUID amplifier    G.V. Prokopenko, D.V. Balashov, S.V. Shitov, V.P. Koshelets and J. Mygind Summary: A 6 mm/spl times/6 mm chip comprising two identical DC SQUID based amplifiers (SQAs) has been designed, fabricated and tested as a two-stage RF amplifier in a frequency range 3.5-4.0 GHz. Each SQA consists of a double washer type DC SQUID with novel integrated input resonant circuit. The reflection coefficient of both input and output of the SQA has been measured in the two stage configuration. To avoid SQA saturation at the wide band noise tests a tunable 40 MHz bandpass YIG-filter has been used. The following parameters of the two-stage SQA have been measured at the 3.65 GHz: gain of (17.5/spl plusmn/1) dB, 3 dB bandwidth of about 250 MHz, and noise temperature (4.0/spl plusmn/0.5)K what corresponds to intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.6 /spl mu//spl Phi//sub 0/Hz/sup -1/2/ and energy sensitivity /spl epsiv//sub i//spl ap/75 /spl planck/ (7.8/spl middot/10/sup -33/ J/Hz). If the measured RF mismatch between the input/output of SQA and source signal/post-amplifier is taken into account a gain of (20.5/spl plusmn/1.5) dB and noise temperature as low as (2.5/spl plusmn/1.0) K (intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.4 /spl mu//spl Phi//sub 0/Hz/sup -1/2/, energy sensitivity /spl epsiv//sub i//spl ap/47 /spl planck/) can be estimated.         Advanced version of two-stage dc SQUID-based amplifier    D.E. Kirichenko, A.B. Pavolotskij, I.G. Prokhorova, O.V. Saigirev, R. Mezzena, S. Vitale, Y.V. Maslennikov and A.V. Beljaev Summary: An advanced version of a two stage dc SQUID-based low frequency amplifier and its measured signal and noise parameters are presented in this report. An effective input inductance of about 2.9 /spl mu/H, a SQUID's inductance of about 11 pH, an effective coupling k/sup 2/ of about 0.24 and a white noise level of about 0.87 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ at 4.2 K were achieved. The gradiometric scheme, a modified distributed damping filter and a modified geometry of coupling transformers have been used to suppress the influences of the external noise and resonances in the SQUID microstructure.         A ring-weak link superconducting quantum electron interferometer    I.N. Zhilyaev and S.G. Boronin Summary: Properties of a new superconducting quantum election interferometer are investigated. This new interferometer has only one tunnel junction as compared to a classical SQUID which has two junctions. Our measurements have shown that the amplitude of resistance oscillations versus the magnetic field increases as the temperature is lowered.         Noise analysis of the double-loop SQUID with unshunted junctions    M. Kiviranta and H. Seppa Summary: The unshunted (un) SQUID is a two-junction device whose Josephson junctions are damped at high frequencies only. Single-valued rather than hysteretic behaviour on the negative resistance region is obtained by using a voltage bias rather than a current bias. We have studied numerically the noise properties of the un SQUID with a double-loop (dl) washer configuration, in which the SQUID inductance is capacitively split into two loops. Our simulations with /spl beta//sub c/=0.7 and /spl beta//sub l/=0.5-3 suggest that noise level in the un dl SQUID depends more weakly on the device parameters than in the un SQUID. The best energy resolution obtained in the smooth area of the IV curves is /spl epsiv//spl ap/5k/sub B/T/spl radic/(LC) but in narrow pockets in the non-smooth region /spl epsiv//spl ap/3k/sub B/T/spl radic/(LC) is approached.         A 1-MHz low noise preamplifier based on double relaxation oscillation SQUIDs    A.W. Hamster, M.J. van Duuren, G.C.S. Brons, J. Flokstra and H. Rogalla Summary: A low noise and wideband preamplifier based on Double Relaxation Oscillation Superconducting Quantum Interference Devices (DROSs) has been realized. A major advantage of a DROS is that it can be operated in a simple flux modulation. So far, biomagnetic measurements performed in our group required only a limited bandwidth smaller than 100 kHz. Other applications, like for instance readout of radiation and particle detectors, demand a larger bandwidth. In this paper, we will discuss our efforts aimed at increasing the operational bandwidth of a DROS in flux locked loop. Presently, a flux locked loop scheme with a -3 dB bandwidth of 1.45 MHz has been built. With this system a white flux noise of 8 /spl mu//spl Phi//sub 0///spl radic/Hz was measured with a 1/f-corner frequency of 10 Hz. The slew rate was 2.5/spl middot/10/sup 5/ /spl Phi//sub 0//s. With the mutual input inductance of 6.7 nH, an input current noise of the preamplifier of 2.5 pA//spl radic/Hz was found and a current slew rate of 80 mA/s. We will discuss the suitability of our DROS-based preamplifier for readout of cryogenic particle detectors based on superconducting tunnel junctions.         Smart SQUIDs based on relaxation oscillation SQUIDs    M.J. van Duuren, G.C.S. Brons, J. Flokstra and H. Rogalia Summary: Smart SQUIDs based on double Relaxation Oscillation SQUIDs (DROS) and a superconducting up-down counter have been developed. DROS and counter form a flux locked loop on one single chip. The DROS output consists of a series of pulses that controls the two up and down write gates of the counter. The pulsed output structure of the DROS constitutes the internal clock for this single-chip device. Several prototypes were built with a clock frequency of 100 MHz, a linear operation flux range of about 2.5 /spl Phi//sub 0/, and a white noise level of 6.5 /spl mu//spl Phi//sub 0///spl radic/Hz. The smart SQUID is in principle a promising device for application in multichannel SQUID systems.         Design of series SQUID array suppressing Josephson oscillation interference between element-SQUIDs    F. Hirayama, N. Kasai and M. Koyanagi Summary: We have designed and fabricated single-stage series SQUID arrays usable for current amplifiers with filtering resistors in its input coil. From experimental results, it was revealed that filtering in each SQUID in the array successfully suppressed the interference between element-SQUIDs. An array with 1000 SQUIDs showed relatively smooth flux-voltage curves, large voltage swing (/spl sim/50 mV) and current-voltage conversion coefficient (/spl sim/1000 V/A).         First results for a novel superconducting imaging-surface sensor array    R.H. Kraus Jr., E.R. Flynn, M.A. Espy, A. Matlashov, W. Overton, M.V. Peters and P. Ruminer Summary: A superconducting imaging-surface system was constructed using 12 coplanar thin-film SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter lead imaging-plane. Some measurements included two additional sensors on the "back" side of the superconducting imaging-plane to study the field symmetry for our system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been used to: (a) understand the noise characteristics of the dewar-SQUID imaging plate arrangement, (b) to verify the imaging principle, (c) measure the background rejection factor of the imaging plane, and (d) compare superconducting materials for the imaging plane. A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shape and absolute values of the measured and predicted curves agree very well indicating the system Is behaving as a gradiometer in accordance with theory. The output from SQUIDs located behind the imaging surface that sense background fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded form the background sensors by more than a factor of 1000. Measurement of the symmetry of sensor sensitivity to uniform fields exactly followed theoretical predictions.         Continuous feedback operation of a two-stage dc SQUID system    I. Jin and F.C. Wellstood Summary: We report on the continuous feedback operation of a two-stage dc Superconducting Quantum Interference Device (SQUID) system in which one SQUID works as a low-noise preamplifier to read out a second low-noise sensor SQUID. We first flux-locked the readout SQUID and measured the characteristics of the sensor SQUID, including its current-voltage characteristics, current-flux characteristics, and noise spectrum. We then investigated how the two SQUIDs could work together by simultaneously flux-locking both the sensor and the readout SQUIDs. With this two-SQUID flux-locking scheme, we recovered the noise spectrum of the sensor SQUID to within 4%. We discuss how to understand and optimize the two-stage SQUID feedback system.         A concept for a submillimeter-wave single-photon counter    R.J. Schoelkopf, S.H. Moseley, C.M. Stahle, P. Wahlgren and P. Delsing Summary: We discuss the design for a submillimeter-wave photometer, using a combination of superconducting and single-electron devices, which would have high quantum efficiency, very low noise-equivalent powers, and eventually even submicrosecond timing resolution. The absorption of above-gap photons occurs in a small strip of superconducting Al, whose normal-state resistance can be matched efficiently to an antenna of a higher gap (Nb) superconductor. The quasiparticles produced by photon absorption are then confined via Andreev reflection, and forced to tunnel through a small SIS tunnel junction. The tunneling time is much shorter than the known (>10 /spl mu/s) quasiparticle recombination time, so collection efficiency will be high. The device sensitivity would be limited by the small subgap current in the high-quality Al/AlO/sub x//Al tunnel junction at temperatures (100 mK) well below T/sub c/. Scaling based on the larger junctions used in X-ray detector applications suggests that the total dark current can be <0.1 pA, or of order 10/sup 5/ electrons/second, corresponding to an NEP of less than 10/sup -19/ W//spl radic/Hz at 500 microns (600 GHz). The photocurrent will be measured using a fast single-electron transistor (RF-SET), which allows a shot-noise-limited performance even for the very small currents delivered from this low capacitance and high impedance SIS junction. Results of initial fabrication and dc characterization of an integrated photodetector are also given.         Fabrication of superconducting bilayer transition edge thermometers and their application for spaceborne X-ray microcalorimetry    F.M. Finkbeiner, T.C. Chen, S. Aslam, E. Figueroa-Feliciano, R.L. Kelley, M. Li, D.B. Mott, C.K. Stahle and C.M. Stahle Summary: The transition between normal conduction and superconductivity in superconducting materials can be exploited as a highly sensitive thermometer. Transition temperatures can be tailored through the selection of materials, their component cases of more than one material. Two bilayer configurations, Ag/Al and Au/Mo, are examined, including details of preparation, testing, and encountered difficulties. Proposed designs for spaceflight detector applications are discussed.         Thermal and optical tuning of the resonant frequency in YBCO thin films    Shinho Cho and Cheon Lee Summary: The modulation in the resonant frequency of superconducting passive devices fabricated with YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films has been investigated as a function of temperature and optical pulse energy. The frequency-domain measurements are performed in a closed-cycle refrigerator in a temperature range of 20 to 80 K. The optical excitation consists of a 70 psec laser pulse train at 532 nm from an actively mode-locked Nd:YAG laser. The measured optical pulse energy dependence of the resonant frequency is described by f=f/sub p0/|1-a(P/P/sub c/)/sup 2/| where P/sub c/ is the critical optical pulse energy beyond which resonance has disappeared. As for the dependence on temperature, the resonant frequency can be expressed by f=f/sub T0/|1+2/spl lambda/coth(t//spl lambda/)/d|/sup -1/2/ where the magnetic penetration depth is given by a quadratic dependence on temperature, /spl lambda/=/spl lambda//sub 0/|1-(T/T/sub c/)/sup 2/|/sup -1/2/.         High frequency detector response from an array of HTSC bicrystal Josephson junctions    K.Y. Constantinian, A.D. Mashtakov, G.A. Ovsyannikov, Kiejin Lee and I. Iguchi Summary: YBaCuO Josephson junction arrays, fabricated on MgO bicrystal substrates were studied in wide frequency range at 7-26 GHz, 45-120 GHz, and at submillimeter 470-510 GHz waves. Subharmonic fractional Shapiro steps have been observed with amplitudes increasing with frequency of applied microwaves. Mm and submm wave harmonic and subharmonic selective detector response signals were registered when dc magnetic field was applied.         A Nb single crystal X-ray detector read out by superconductive tunnel junctions    M.L. van den Berg, F.B. Kiewlet, M.P. Bruijn, O.J. Luiten, P.A.J. de Korte, J. Martin and R.P. Huebener Summary: We have fabricated a prototype imaging X-ray detector, consisting of Al/AlOx/Al/Nb superconductive tunnel junctions sputtered directly on a high purity Nb single crystal with an RRR/spl ap/15000. Such a detector in principle offers a high energy resolution, combined with a high quantum efficiency, a large detection area and imaging capabilities. The quasiparticle collection efficiency and consequently the X-ray response of the detector is still very poor due to the large thickness of the crystal (120 /spl mu/m), but agrees with proximity theory. By irradiation with a focused electron beam of a Low Temperature Scanning Electron Microscope, the spatial and temporal response of the detector has been determined. The derived diffusion coefficient is two orders of magnitude smaller than expected on the basis of the RRR.         The effect of thermal noise on the operation of DC SQUIDs at 77 K-a fundamental analytical approach    B. Chesca Summary: A rigorous analytical analysis of DC SQUIDs having reduced inductance smaller than 1//spl pi/ and operating in the presence of thermal fluctuations has been developed. On the basis of the Fokker-Planck equation the expressions for the output voltage across the Josephson junctions and the circulating current in the SQUID loop were found. This reduces the problem of finding all important SQUID characteristics (current-voltage curves, dynamic resistance, transfer function, and energy sensitivity) and their optimization to a simple exercise of elementary mathematics. As expected, the present analytical approach gives unique insights and significantly contributes to understand the physics related to the effects of large thermal fluctuations on system's operation.         Imaging of vortices and 1/f noise sources in YBCO dc SQUIDs using low-temperature scanning electron microscopy    S. Keil, R. Straub, R. Gerber, R.P. Huebener, D. Koelle, R. Gross and K. Barthel Summary: Abrikosov- and Josephson-Vortices trapped in bicrystalline YBa/sub 2/Cu/sub 3/O/sub 7/ washer dc SQUIDs containing regular arrays of micrometer holes (antidots) have been directly imaged using a standard scanning electron microscope equipped with a liquid nitrogen cryostage. The signal generation is based on the electron-beam-induced local displacement of vortices, which is detected as a flux change in the SQUID loop. This technique allows one a simple visualization of vortices with a spatial resolution of /spl ap/1 /spl mu/m, at variable temperature and magnetic field. The magnitude of the vortex signal is a direct measure of the amount of flux a vortex couples into the SQUID hole. In addition to the static local distribution of vortices, this technique can provide information on the dynamic behaviour of vortices trapped in the SQUID loop, by using the beam as a local perturbation and measuring the low-frequency noise induced by vortex motion.         Reduction of 1/f-noise in HTS-SQUIDs by artificial defects    P. Selders, A.M. Castellanos, M. Vaupel and R. Wordenweber Summary: We report on the detection of matching effects between antidot and vortex lattices in rf SQUIDs that clearly demonstrate, that antidots can strongly reduce the low-frequency 1/f noise in active superconducting devices. Square lattices of holes (antidots) with diameters of 0.25-2 /spl mu/m and lattice parameters ranging from 0.5 to 50 /spl mu/m are patterned into optimized sputtered YBa/sub 2/Cu/sub 2/O/sub 7-/spl delta// thin films without deterioration of superconducting properties. First, a special experimental set-up consisting of an antidot lattice in flip-chip configuration with a bicrystal rf-SQUID is used for the demonstration of the principle of noise reduction by antidots. Matching effects between vortex and antidot lattice in form of minima in the noise spectra are observed, indicating that thermally activated hopping of vortices can strongly be reduced by antidots. Second, antidots are directly patterned into step-edge rf-SQUIDs. For large antidot lattice parameters (50 /spl mu/m) no degradation of the SQUID parameters can be measured. However, matching effects and noise reduction due to the presence of the antidots can not be observed in this first attempt. The results are discussed in terms of multiquanta, possible solutions and suggestions for improvements are given.         HTS SQUID application as a quantum roulette noise thermometer    L. Hao, J.C. Gallop, R.P. Reed, D.A. Peden and J.C. MacFarlane Summary: We describe a cryogenic primary thermometer called the Quantum Roulette Noise Thermometer (QRNT), which is based on flux quantisation in a HTS superconducting ring. The basis of the QRNT is that the flux state of a double junction SQUID ring (in thermal contact with a heat bath whose temperature is to be measured) is allowed to evolve freely. The flux state is repeatedly interrogated to establish a probability distribution from which the absolute temperature may be derived. The QRNT is in principle dissipationless and has the potential to provide high accuracy with short measuring time. The QRNT prototype device which employs a YBCO thin film on an MgO bi-crystal substrate has been designed and fabricated. The superconducting ring of overall dimensions 6 mm/spl times/8 mm is broken by two grain boundary Josephson junctions of size 5 /spl mu/m/spl times/3 /spl mu/m. The state of the junctions is switched between superconducting and resistive by means of small currents applied to a superconducting strip line located near the junctions. A dc SQUID, which is used to read out the flux state of the QRNT ring, is operated at 77 K while the QRNT device can be set at any desired temperature above 10 K. Ongoing experimental measurements are described with reference to the expected theoretical predictions.         System demonstration of a superconducting communication system    S. Yorozu, Y. Hashimoto, H. Numata, S. Nagasawa and S. Tahara Summary: We report on the first complete system-level demonstration of a superconducting digital communication system. In today's digital computer and communication systems, managing data flow is a major challenge as the systems have to deal with a huge amount of information. A superconductor device may solve this problem. There have been several attempts to make superconducting switching core circuits, but there have been no complete system-level demonstrations. We have built such a system to demonstrate the efficiency of superconducting devices used in a communication system. Our system is focused on parallel processor communication, and consists of PCs as the processor elements at the three nodes, three interface boxes, and a superconductive chip immersed in a 4.2-K cryostat. The interconnection chip operation is essentially packet switching that was designed with a pipeline ring architecture. The interface box consists of parallel-serial converters, serial-parallel converters, a FIFO output buffer, and a level conversion circuit. The network system operates successfully at approximately 100 MHz, and the clock frequency is restricted by the speed of the interface ICs, not by that of the superconductive chip. We also confirmed the 2-GHz operation of the switching chip, and estimate that the total throughput of the system ran be increased to more than 10 Gbps.         Dewar-to-dewar data transfer at GHz rates    J.X. Przybysz, J.D. McCambridge, P.D. Dresselhaus, A.H. Worsham, E.J. Dean, J.P. Sage and T.J. Weir Summary: Digital circuits have been developed to interface superconductive electronic chips with high speed 50-/spl Omega/ transmission lines. Digital data at 1 Gigabit per second was transferred through a Josephson chip in a first cryostat to another Josephson chip in a second cryostat. The chips were connected by more than 3 meters of 50-/spl Omega/ transmission line. No semiconductor amplifiers were used in this data path. A Hewlett Packard data source provided the original data to the first chip, which converted it to SFQ data. Output interface circuits were driven by a 2-GHz external clock to latch series strings of 10 junctions and drive 2-Gbps data into a 50-/spl Omega/ cable. In the second cryostat, a latching three-junction interferometer with a two-turn control line converted the input signal to latched data and switched an MVTL OR-gate output. This demonstration showed that low-power Josephson digital circuits can be integrated into multichip digital subsystems that can pass data at high rates without the use of power-hungry semiconductor amplifiers.         High data rate switch with amplifier chip    R.D. Sandell, J.W. Spargo, M. Leung and S.R. Whiteley Summary: A critical component for high bandwidth communications links is a digital switch. Desirable features of a digital switch include: high input/output bandwidth, high channel count, scalability, low latency and interchannel skew. Superconductive circuits, with simultaneous high speed and low power advantages (even including the requisite cryocooler) have been applied to a highly scaleable crossbar switch, useful in supercomputer networks, massively parallel processing (MPP), and high data rate telecommunications. We report here on the testing of a 16/spl times/16 switch chip based on the switch chip component of the highly scaleable crossbar system. We have successfully transmitted multi-Gb/s data through this superconducting switch, with packet destination addressing decoded from the header of the data packet. The data are transmitted to a separate superconducting amplifier chip, mounted on a superconducting multi-chip module with the switch. The switch is a crossbar architecture, voltage state design, and operated to beyond 3 Gb/s. The amplifier is a clocked latching stack of Josephson junctions. Output of the amplifier at 6.2 Gb/s is 7.0 mV, which facilitates the interface of the module to its users. BER of the two-chip assembly is 10/sup -9/ or less above 2 Gb/s.         Single flux quantum components for packet switches    V.K. Kaplunenko, V.V. Borzenets, S.J. Berkowitz and N.B. Dubash Summary: A superconducting front-end receiver operating in a wide frequency band from 10 to 40 Gb/s could increase the throughput of packet switches. Rapid Single Flux Quantum logic, which has the advantage of high-speed operation at medium integration levels, was used to build receiver components: a multiple bit-rate clock recovery circuit and a demultiplexer. Only 16 heading bits of the packet were required to read the clock frequency in a range from 22.5 to 45 Gb/s. Preliminary experiments showed single bit-rate clock recovery cell operation up to 35 GHz and /spl plusmn/17% bias current margins for a 1:2 demultiplexer. The interface between the receiver and semiconductor components is discussed.         Effects of oxygen content on YBCO Josephson junction structures    J.P. Sydow, M. Berninger, R.A. Buhrman and B.H. Moeckly Summary: The high degree of crystal stress and strain present at, and in the vicinity of, high angle grain boundary (GBJ), ramp edge Co doped SNS (Co-SNS), or interface engineered junctions (IEJ) can lead to localized and highly non-uniform regions of basal plane oxygen loss in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO). These oxygen inhomogeneities will, to a greater or lesser degree, affect or cause the superconducting weak link behaviour demonstrated by these types of junctions. In order to examine the impact of the localized oxygen micro/nanostructure on the weak link behaviour of these three junction technologies, we have utilized ozone anneals to provide a partial pressure of atomic oxygen far in excess of that produced by standard O/sub 2/ anneals.         Flux trapping and magnetic field dependence of critical currents in narrow YBCO step edge junctions    E.E. Mitchell, C.P. Foley, K.-H. Muller, K.E. Leslie and D.L. Tilbrook Summary: We have studied narrow (0.8-18 /spl mu/m wide) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// step edge junctions in moderate applied magnetic fields as high as B/sub a//spl sim/25 mT. The magnetic field dependence of the junction critical current, I/sub c/, resembles a Fraunhofer diffraction pattern for all the junctions studied, although the field values of the pattern minima are modified due to the planar geometry. At 77 K these narrow junctions exhibit abrupt discontinuities in the I/sub c/(B/sub a/) pattern due to jumps in I/sub c/. These jumps are most likely due to sudden changes in the position of an individual vortex in close proximity to the junction. The I/sub c/(B/sub a/) patterns show hysteretic behaviour for applied fields B/sub a/>1-2 mT at 77 K, and the magnitude of this hysteretic behaviour appears to plateau for B/sub a/>/spl sim/12 mT, depending on junction width.         High-T/sub c/ superconducting step-edge junction on sapphire fabricated by non-etching technique    A.D. Mashtakov, G.A. Ovsyannikov, I.V. Borisenko, K.Y. Constantinyan, I.M. Kotelyanskii and D. Erts Summary: We have produced step-edge Josephson junctions on steps in an epitaxially grown CeO/sub 2/ layer on r-cut sapphire. The epitaxial CeO/sub 2/ layer is deposited at high temperature through a MgO/CeO/sub 2/ micromask. The optimum orientation of the step flank (FS) for grain boundary junction was determined on the basis of known experimental data of YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) film growth on tilted substrates and from analyses of bicrystal grain boundaries formed in YBCO films along the boundary between the FS and planar substrate. Atomic force microscopy (AFM) observations of the steps in which the FS was parallel to the [110]CeO/sub 2/ plane show that the slope angles is in a range from 50/spl deg/ to 70/spl deg/ that correspond to [111] and (221)CeO/sub 2/ crystallographic planes. The results of dc and microwave measurements of obtained high-T/sub c/ step-edge junction are presented.         Stability and uniformity of planar high temperature Josephson junctions fabricated using nanolithography and ion damage    A.S. Katz, S.I. Woods, R.C. Dynes and A.G. Sun Summary: We have investigated the room temperature stability and the critical current uniformity of planar thin film YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions. The junctions were fabricated using electron-beam lithography to define a stencil structure followed by ion damage from a conventional 200 keV ion implanter. Using this technique, we have fabricated junctions with weak link lengths of 20-100 nm that showed classical dc and ac Josephson effects at 77 K. By a suitable choice of damage and stencil width, these devices may be tuned to operate at any temperature between 1 K and the bulk transition temperature, and they may be placed anywhere on a wafer, providing a high degree of flexibility for circuit applications. Results obtained over several months showed a high level of room temperature stability, and the uniformity of the junctions was maintained.         Intrinsic Josephson junction array with typical tunneling characteristics in oxygen-deficient YBaCuO thin films    H.B. Wang, J. Chen, K. Nakajima and T. Yamashita Summary: In our experiments, YBaCuO films were deposited onto [100]MgO substrates by pulsed excimer laser ablation and annealed in low-pressure oxygen to make them oxygen deficient. The films, which were c-axis oriented with transition temperatures around 50 K, were then fabricated into mesa-like devices with an a-b plane area of a few square microns. Important features of our device are its novel microwave coupling and reduced leakage current between the top and bottom electrodes. By ramping the bias current up and down repeatedly and measuring the dc current-voltage curves, we successfully observed typical intrinsic Josephson effects such as hysteresis, voltage jumps of a few millivolts, as well as dozens of branches with regular voltage intervals. The observed microwave response, in the range of a few to 110 GHz, indicates that these oxygen-deficient YBaCuO intrinsic Josephson junctions may find many millimeter-wave and submillimeter-wave applications.         I-V characteristic of a single intrinsic tunnel junction on Bi-2223 thin film    A. Odagawa, M. Sakai, H. Adachi and K. Setsune Summary: We report the successful fabrication of a single intrinsic Josephson junction on a (Bi,Pb)-Sr-Ca-Cu-O thin film and investigate the current-voltage characteristics. Mesa structures are fabricated on the smooth surface of a high-quality thin film. The current-voltage characteristic along the c-axis shows a large distinct hysteresis and the superconducting gap edge structure. The estimated gap is about 75 mV at 4.2 K and is comparable with results of scanning tunneling spectroscopy. The obtained current-voltage curve is explained quite well by assuming d-wave symmetry for the superconducting order parameter neglecting nonequilibrium effects. We have observed voltage steps in the current-voltage characteristic induced by microwave irradiation. The voltage step shifts to higher voltages with increasing irradiation power. It is proposed that this behaviour is caused by fluxon motion.         High resolution ADC using phase modulation-demodulation architecture    S.V. Rylov, D.K. Brock, D.V. Gaidarenko, A.F. Kirichenko, J.M. Vogt and V.K. Semenov Summary: We report successful demonstration of a fully operational integrated superconducting ADC system based on a phase modulation/demodulation architecture. It consists of a high-resolution ADC chip with a multiple-channel race arbiter and integrated bit-pipelined decimation filter, an interface electronics block converting the ADC output to standard ECL form at sampling rates up to 200 MHz, and a computerized test station performing data acquisition, processing and display in real time. We have demonstrated a fully functional 14-bit ADC chip with 2-channel race arbiter and 16-bit decimation filter with 1:64 decimation ratio operating at 11.2 GS/s. By using additional decimation filtering of the ADC output at room temperature we demonstrated its dynamic programmability and resolution-bandwidth tradeoff. The measured ADC performance (on effective bits) was competitive with the best semiconductor high-resolution ADCs.         A superconductive flash digitizer with on-chip memory    S.B. Kaplan, P.D. Bradley, D.K. Brock, D. Gaidarenko, D. Gupta, Wen-Quan Li and S.V. Rylov Summary: Recording transient physical phenomena such as short electromagnetic pulses requires a very wide-band digitizer. We have successfully designed, fabricated, and tested a superconductive flash digitizer circuit using Nb trilayer technology. The digitizer consists of a 6-bit flash analog-to-digital converter (ADC), a set of on-chip switches to start and stop data acquisition, and a bank of acquisition shift-registers for on-chip memory. A 5-MHz clock reads the data out to room-temperature electronics for analysis. We have used this digitizer to acquire multi-GHz sine waves. We have also recorded the details of short single pulses containing both a short rise time (/spl sim/100 ps) and structure with greater than a 10 GHz instantaneous bandwidth.         Superconducting delta ADC with on-chip decimation filter    V.K. Semenov, Y.A. Polyakov and T.V. Filippov Summary: Last year we presented the first fully operational superconducting Analog-to-Digital Converter (ADC) with on-chip Digital Signal Processing (DSP). Here we review this device and introduce completed and prospective innovations required to exceed the performance of the best semiconductor counterparts. The ADC chip contains 2 basic parts: a "fundamental" ADC operating at about 20 GHz sampling rate and a digital decimation filter which attenuates high-frequency noise components and reduces the sampling rate to match it with the bandwidth of an input signal. Our short term goal is to achieve 14 bits Spurious Free Dynamic Range (SFDR) for 60 MHz signal bandwidth by using the standard 1000 A/cm/sup 2/ Nb-trilayer fabrication technology commercially available at HYPRES, Inc.         A 16-bit serial analog-to-digital converter module with optical output    D. Gupta, D.V. Gaiarenko and S.V. Rylov Summary: A high-resolution analog-to-digital converter (ADC) is needed for a variety of applications including readout electronics for infrared detectors in focal-plane arrays. The heat load of input/output (I/O) cables between the cryogenic environment (4 K) and room temperature dominates the power consumption of such an ADC. To reduce the number of outputs originating from the chip a 16-bit serial ADC has been developed. Further reduction of the heat load and more robust signal transmission can be achieved by extracting the serial ADC output using an optical fiber coupled to a laser diode. A compact module (5.75 in/spl times/2.1 in /spl times/1.1 in) has been prototyped to package the ADC chip and a laser diode.         Superconducting microstrip resonator investigated by FDTD electromagnetic field simulator    Y. Okazaki, K. Suzuki and Y. Enomoto Summary: We developed an electromagnetic field simulator based on Finite Difference Time Domain method (FDTD) to investigate a superconducting microstrip resonator. We simulated the temperature dependence of the resonant frequency in order to confirm the availability of the FDTD simulator against superconducting filters. Moreover, we simulated the high power behavior of the superconducting microstrip resonator.         Observation of supercurrent distribution in YBCO thin film devices by photoexcited THz radiation    M. Hangyo, S. Shikii, M. Yamashita, T. Kondo, M. Tonouchi, M. Tani and K. Sakai Summary: A new method of imaging supercurrent distribution in high-T/sub c/ superconducting film devices using the photoexcited THz radiation is proposed and demonstrated. The images are obtained by scanning focused femtosecond Laser pulses on superconducting film devices with detecting the THz radiation. The characteristic distribution of the transport and persisting currents is obtained and interpreted in terms of the Bean critical state model.         Frequency following imaging of electric fields from resonant superconducting devices using a scanning near-field microwave microscope    A.S. Thanawalla, B.J. Feenstra, Weosheng Hu, D.E. Steinhauer, S.K. Dutta, S.M. Anlage, F.C. Wellstood and R.B. Hammond Summary: We have developed a scanning near-field microwave microscope that operates at cryogenic temperatures. Our system uses an open-ended coaxial probe with a 200 /spl mu/m inner conductor diameter and operates from 77 to 300 K in the 0.01-20 GHz frequency range. In this paper, we present microwave images of the electric field distribution above a Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ microstrip resonator at 77 K, measured at several heights. In addition, we describe the use of a frequency-following circuit to study the influence of the probe on the resonant frequency of the device.         Quality factor and intermodulation product of superconducting coplanar wave guides with slots in a DC magnetic field    G. Benz, T.A. Scherer, M. Neuhaus and W. Jutzi Summary: Superconducting coplanar wave guides may easily be fabricated and combined with surface mounted semiconductor devices. The current density distribution is calculated to determine the microwave losses for different miniaturised cross sections and edge shapes. The calculated and measured quality factors are in good agreement at low power and zero external magnetic field perpendicular to the film. The influence of moats or slots in the CPW stripes on the measured quality factor and intermodulation product as a function of the external magnetic field is discussed in terms of critical superconducting current density.         Magnetic shielding analysis of axisymmetric HTS plate by flux flow creep model    A. Kamitani, S. Ohshima and T. Yokono Summary: The magnetic shielding performance of the high-Tc superconducting (HTS) plate is numerically investigated by assuming the flux flow creep model as a constitutive relation representing a mixed state. In order to reduce the number of variables, both the axisymmetry of the plate shape and the isotropy of the applied magnetic field are introduced. Under these assumptions, the shielding factor and the damping coefficient are calculated as functions of time and the frequency of the applied magnetic field. The results of computations show that an increase in the frequency will weaken the time dependence of the shielding factor and will enhance the shielding performance. In addition, the magnetic shielding performance in the low-frequency range and in the high-frequency range is shown to be strongly influenced by the flax creep and the flux flow, respectively.         Attenuation analysis of superconducting transmission line using two dimensional Time-Dependent-Ginzburg-Landau equation    S. Yoshimori, A. Kobayashi and M. Kawamura Summary: Using the two dimensional Time-Dependent-Ginzburg-Landau equation, we analyzed the relationship between the propagation power and the attenuation of a superconducting microstrip line. An analytical solution was derived by the iteration method under the assumptions that the propagation mode was the TEM mode and that the vector potential exponentially decayed in the superconductor. In the case of a Nb-SiO/sub 2/-Nb structure microstrip line at 4.2 K, the power attenuation increased about 30% when the propagation power increased 20 dB at frequencies greater than 400 GHz.         Copper composition dependence of the structure and microwave properties in Y-Ba-Cu-O films    T. Yoshitake, W. Hattori and S. Tahara Summary: The correlation between the copper composition and the microwave properties of YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) films is studied using coplanar waveguide resonators at 5 GHz. The c-axis lattice constant increases and the axial ratio b/a-the degree of orthorhombicity-decreases as the copper composition of the YBCO films decreases. The microwave properties of these films correlate well with these structural changes. The films with copper-rich composition have a low surface resistance R/sub s/ of 60 /spl mu//spl Omega/ at 50 K and a short magnetic penetration depth /spl lambda//sub L/(0) of 200 nm. The values of these quantities increase with decreasing copper composition. The films with less copper also show a gradual decrease in R/sub s/ below T/sub c,zero/, which is different from the tendency expected from the two-fluid model. These unusual microwave properties can be explained by the inhomogeneous superconductor model in which the regions with locally lowered T/sub c/ are distributed in the YBCO phase. The copper deficiencies that occurred in the films with less copper composition cause these inhomogeneities and thus they are an important cause of high R/sub s/ values of these YBCO films.         Superconducting thin-film transformers at microwave frequencies    A.H. Miklich, J.X. Przybysz, T.J. Smith, S.P. Benz and T.E. Harvey Summary: We describe the use of thin-film superconducting transformers at frequencies up to 20 GHz. Transformers with turns ratios of 2, 4, and 7 were fabricated out of Nb and tested in a liquid-He Dewar. The measured S-parameters showed considerably less bandwidth than predicted based on consideration of the lumped element inductances of the circuit elements. We present an alternative model for the transformer where each part of the patterned circuit is treated as a distributed element (a transmission line). Despite the simplicity of the model, simulations using it agree well with the measured data without using any fitted parameters. These simulations take only a few minutes to compute on a typical workstation, making the model well suited as a design tool.         A superconducting RF resonator in HF range and its multi-pole filter applications    E. Gao, S. Sahba, Hui Xu and Q.Y. Ma Summary: We report a new RF resonator that operates at high frequency (HF, 3-30 MHz) of electromagnetic spectrum. The resonator is fabricated on a double-sided HTS (YBCO) thin film on a single 2" LAO substrate. The resonator is of smaller size and has a higher Q-value than conventional copper resonators. At temperatures below 77 K the Q-value of the resonator is above 40,000. A 3-pole filter is made by using 3 of this resonator which demonstrates a low insertion loss. This report will discuss the design, fabrication, RF characteristics (return and insertion loss), and the Q-value of the devices in detail. The simulated model of the RF characteristics of the devices will also be given.         Thick film YBCO receive coils for very low field MRI    S.J. Penn, N. McN. Alford, D. Bracanovic, A.A. Esmail, V. Scott and T.W. Button Summary: Superconducting receive coils can be used to improve the signal to noise ratio of a MRI system. The greatest improvement is seen in cases where it is the coil noise dominates the noise. This is the case for low field MRI where surface coils are used. The properties of large area (100 mm square) YBCO thick film coils designed for a compact very low field MRI system are reported. The properties are compared with copper and silver mimics.         Microwave radiation and sensing of Josephson junction with the log-periodic toothed trapezoid antenna of high T/sub c/ superconducting films    Kwang-Yong Kang, Insang Song, Yeon Su Ha, Seok-Kil Han, Gun Yong Sung, I-Hun Song and Gwangseo Park Summary: Using high temperature superconducting thin films, we designed and fabricated Josephson junctions associated with a log-periodic toothed trapezoid antenna. Microwave self-radiation from the Josephson junction was measured by using both a superheterodyne receiver at the center frequency of 22 GHz and an external waveguide system. In the case of junction incorporated with an antenna structure, there was a significant increase of power by an order of magnitude with respect to a junction without antenna. Under the 22 GHz irradiation, we observed distinctive Shapiro steps in the I-V measurement, which allowed as estimating the received power of the junction. The received power of the junction with an antenna exhibited as a large increase as that of a self-radiation. Our results indicate that a Josephson junction with an antenna is very effective for the microwave coupling between Josephson junction and free space. The combined device can be used either for a high power microwave source or for a high sensitive sensor.         Superconducting patch array antenna on both-side YBCO thin film for satellite communication    M.I. Ali, K. Ehata and S. Ohshima Summary: Investigated results on direct-fed circularly polarized (CP) microstrip antennas for "Direct Broadcast Satellite" (DBS) system at 12 GHz have been reported. A full-wave microwave circuit simulator based on the method of moments and capable of handling the microwave surface impedance was used in theoretical analysis of the antennas. Antennas were fabricated from both normal conductor (copper) and superconductor (YBCO) for comparison. The measured results on resonant frequency, return loss, gain, bandwidth and axial ratio have been presented along with some design data. The antennas showed good axial ratio and bandwidth. In the comparison of gain, superconducting antennas showed a remarkable improvement over their metal counterparts. The gain of a 4-element array fabricated on both-side superconducting film was found 3.6 dB higher than that of copper array. Therefore, this antenna configuration is expected to be used in DBS system.         Examination on power handling capability of superconducting patch antenna    K. Ehata, M.I. Ali, M. Kusunoki and S. Ohshima Summary: Measured results of power handling capability characteristics of superconducting patch antenna and it's improvement are reported. A direct-fed patch antenna is fabricated by YBa/sub 2/Cu/sub 3/O/sub y/ thin film with 50 nm thickness. The gain of the antenna does not change with the applied power up to 26.3 dBm at 12.3 K, but drop of the gain is observed more than 26.5 dBm. It is found by electromagnetic analysis that this gain drop occurs due to huge current concentration in the direct-fed patch. However, this current concentration can be reduced using the gap-coupled feed, and breakdown power is expected to be three times larger than that of direct feed.         Characteristics of a highly sensitive magnetic sensor constructed of a thick HTS film    M. Itoh, M. Ishidoh, K. Mori and T. Minemoto Summary: For use in constructing highly sensitive magnetic sensors, the present authors have been studying the preparation of thick Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films. In this research, thick YBCO film was fabricated as the magnetic sensor, constructed to retain a residual resistance R/sub res/ at the boiling point of liquid nitrogen (77.4 K). The resistance R/sub ms/ of the magnetic sensor, in the transition region /spl Delta/T, is found to be highly sensitive to the applied magnetic field B/sub ex/, where /spl Delta/T is the region of temperatures between the resistance drop T/sub c//sup onset/ and residual resistance T/sub c//sup res/ temperatures. Under temperature conditions of 77.4 K, the value of R/sub ms/ for this sensor (1.5 mm in width, 67 mm in length, and 280 /spl mu/m thick) for an applied B/sub ex/ of 80/spl times/10/sup -4/ T, increased by factor of 5.8 times greater than that in the absence of a magnetic held. In addition, no evidence was found of the existence of hysteresis in the R/sub ms/ vs B/sub ex/ characteristics for weak values of B/sub ex/. The present paper examines the fabrication conditions and magnetic responses of the highly sensitive sensor constructed of a thick YBCO film.         YBCO SQUIDs fabricated by field-emission electron beam source    S.-J. Kim, J. Chen, Y. Mizugaki, K. Nakajima and T. Yamashita Summary: We report the applicability of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) SQUIDs fabricated by field-emission electron beam source. The junctions show hysteresis and self-resonance steps related to a high frequency resonance in the dc SQUID loop at a voltage V/sub res/=/spl Phi//sub 0//2/spl pi/(LC/2)/sup 1/2/ around 0.3 T/sub c/. The noise spectrum of the SQUIDs was measured with dc-bias schemes at different temperatures and showed values around 10/sup -4/ /spl Phi//sub 0//Hz/sup 1/2/ down to frequencies of 10 Hz at 40 K. The influence of magnetic flux, operating temperatures and flux-voltage transfer factor (|dV/d/spl Phi/|) were investigated. We also tested inverter operation of a dc-biased Josephson logic gate composed of an rf SQUID and a dc SQUID to realize logic circuit performance. Operation of the inverter has been successfully demonstrated although the operating temperature is low, around 10 K.         Hg,Re)1212 bicrystal grain boundary Josephson junctions and dc SQUIDs    A. Tsukamoto, K. Takagi, Y. Moriwaki, T. Sugano, S. Adachi, K. Tanabe and A. Kandori Summary: Bicrystal grain boundary junctions and dc SQUIDs are fabricated using c-axis oriented (Hg,Re)-1212 thin films grown on 24/spl deg/ SrTiO/sub 3/ bicrystal substrates, The junctions exhibit supercurrents up to a temperature close to the film T/sub c/ of 118 K and RSJ-like current-voltage characteristics. A large I/sub C/R/sub n/ product of 400-460 /spl mu/V is observed at 77 K in some junctions. The dc SQUIDs show a field-induced periodic voltage up to 111 K. The 18 pH-SQUID exhibit voltage modulation depths as large as 90 /spl mu/V (at 77 K), 27 /spl mu/V (at 97 K), and 1-2 /spl mu/V (at 110 K). The SQUID with a feedback coil is operated in a flux-locked loop scheme and shows flux noise of 10/sup -3/ /spl phi//sub 0//Hz/sup 1/2/ at 1 Hz.         Passivation of YBCO dc-SQUIDs using polymerized hexamethyldisilasane    A. Kramer, L. Mex, C. Francke, J. Muller and S. Kittelberger Summary: A passivation layer was developed to protect YBCO-devices like flux transformers and SQUIDs against deterioration due to moisture, atmospheric carbon dioxide and oxygen diffusion. The passivation layer is deposited by the polymerization of the silicon organic compound hexamethyldisilasane (HMDS-N) in a plasma enhanced chemical vapor deposition (PECVD) process. AFM investigations confirm that films of 100-150 nm thickness cover YBCO structures without any pinholes and with good step coverage. Electrical transport measurements of passivated YBCO tracks and junctions exposed to humidity and CO/sub 2/ show the excellent passivation properties of the films. No degradation in the critical parameters such as the critical current I/sub c/, the normal resistance R/sub n/ and the flux modulation depth /spl Delta/V is observed on step edge dc-SQUIDs. Investigations of the oxygen diffusion relaxation times show that they are much larger for the passivated samples than in samples without an overlay.         Characterization of grain boundaries in YBa/sub 2/Cu/sub 3/O/sub y/ bicrystal junctions [SQUIDs]    Hsiao-Wen Yu, Ming-Jye Chen, Hong-Chang Yang, S.Y. Yang and H.E. Horng Summary: I-V, V-/spl Phi/ characteristics and atomic force images of grain boundary Josephson junctions fabricated on SrTiO/sub 3/ bicrystal substrates were investigated. The half integer Shapiro steps and I/sub c/ versus B curves show evidence of the inhomogeneous current distribution along the grain boundary junction. The dc SQUID formed on the grain boundary shows the expected V-/spl Phi/ curve. The AFM images, R-T curves and I/sub c/R/sub n/ product reveal sequential destructive deterioration of the junction originating from the underlying grooved substrate. The results are discussed.         Planar SQUID gradiometers fabricated on 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/ bicrystals    C. Carr, A. Eulenburg, E. Romans, C.M. Pegrum and G.B. Donaldson Summary: HTS dc SQUID gradiometers have been fabricated on 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/ bicrystal substrates with slots and flux dams in the SQUID washers. The spatial response of such devices has been measured experimentally and compared with modelled results. Single layer devices, in terms of gradient sensitivity, have characteristics that deviate only slightly from idealized first order gradiometers. The low frequency flux noise of these devices is discussed with particular emphasis on both the unshielded properties and the effect of various cooldown procedures on the noise.         High T/sub c/ dc SQUID utilizing bicrystal junctions with 30 degree misorientation angle    K. Enpuku, T. Minotani, F. Shiraishi, A. Kandori and S. Kawakami Summary: Performances of high T/sub c/ dc SQUID utilizing bicrystal junctions with 30/spl deg/ misorientation angle have been studied. Junction resistance R/sub s/=10 /spl Omega/ and critical current I/sub 0/=10-20 /spl mu/A can be obtained rather easily at T=77 K with this technology. As a result, voltage modulation depth as high as 50 /spl mu/V, and flux noise as low as 5 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ obtained for the 100 pH-SQUID. The measured values of the voltage modulation depth agree reasonably well with the numerical simulation, while the measured values of the flux noise are about 2 or 3 times larger than the simulation. The reason for the high noise level is discussed by taking into account imperfection of junctions.         Fabrication and characterization of 45/spl deg/ a-axis tilt grain boundary YBa/sub 2/Cu/sub 3/O/sub 7-x/ Josephson junctions and dc SQUIDs    F. Tafuri, F. Carillo, L. De Nunzio, F. Lombardi, F.M. Granozio, A. di Chiara, G. Testa, A. Monaco and E. Sarnelli Summary: YBa/sub 2/Cu/sub 3/O/sub 7/-/sub x/ junctions and dc SQUIDs have been realized by employing 45/spl deg/ a-axis tilt grain boundaries through a fabrication procedure based on the biepitaxial technique. YBa/sub 2/Cu3O/sub 7-x/ grows mainly oriented [103] on SrTiO/sub 3/ and [001] on the MgO seed layer. A wide characterization of the tilt junctions and SQUID properties has been carried out. High values of the I/sub C/R/sub N/ quality factor and of the magnetic flux-to-voltage transfer parameter have been obtained, The observed phenomenology confirms differences from the one typical of 45/spl deg/ c-axis tilt grain boundary junctions and gives important information on the nature of the current steps appearing at finite voltages in the current-voltage characteristics. These devices could also have some impact on experiments designed to study the symmetry of the order parameter, exploiting their microstructure and anisotropic properties. A maximum speed of Josephson vortices as calculated from the voltage step values, of the order of 2 10/sup 6/ m/sec is obtained, which encourages high frequency applications.         Low thermal leakage coaxial cable for HTS devices    H. Kubota and H. Takeuchi Summary: A high temperature superconductor (HTS) filter has been developed recently. It is cooled by a small cryocooler and is operated at 70 Kelvin (K) in a vacuum chamber. Coaxial cables are used for the high frequency transmission line between the filter in lower temperature and other circuits at room temperature. Because HTS filters are typically used in low-loss applications, there is an important subject to optimize electrical loss and thermal leakage in the transmission line. The usual semirigid coaxial cables have a small amount of loss; they conduct too much outside heat into the HTS filter. We have developed our own coaxial cables to optimize both electrical and thermal performance. The outer conductor of this new coaxial cable was made of plated thin copper film and was designed to have an optimum thickness of 0.005 mm. SMA connectors are fitted carefully to both ends of the coaxial cable. The new coaxial cable that is 1.68 mm in diameter and 100 mm in length is evaluated. The evaluation result found the electrical insertion loss to be 0.175 dB at 2.0 GHz and thermal leakage to be 48 mW from 300 K to 77 K. We have also developed an HTS receiving filter subsystem for a CDMA base station using our own coaxial cables. We obtained excellent results.         Characteristics of YBCO SQUIDs with step-edge and biepitaxial grain boundaries    S.Y. Yang, C.H. Chen, H.E. Horng, W.L. Lee and H.C. Yang Summary: Some characteristics of YBCO SQUIDs with step-edge and biepitaxial grain boundaries were investigated. V-I curves of the step-edge SQUIDs can be described by the RSJ-like model with a linear relationship between the critical current I/sub c/ and temperature T, whereas the typical I/sub c/-T curve for the biepitaxial SQUIDs concaved upward at temperatures near the critical temperature. The V-I curves of both kinds of the step-edge and the biepitaxial SQUIDs under microwave irradiation revealed integral Shapiro steps. Furthermore, the voltages of the step-edge SQUIDs were well modulated by the applied magnetic field. And also, the typical Fraunhofer diffraction of the I/sub c/-/spl Phi/ curve was observed for the single junction in the step-edge SQUIDs. On the other hand, the magnetic field modulated voltage oscillation was also found for the biepitaxial SQUIDs. All the details will be discussed in this report.         Technology for YBa/sub 2/Cu/sub 3/O/sub 7/ SNS- and SIS-Josephson junctions    K.-O. Subke, S. Krey, H. Burkhardt, A. Bartold and M. Schilling Summary: Ramp-edge Josephson junctions from the high-temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ require a multilayer preparation process. In order to increase the reproducability of the junction characteristics we investigate the subprocesses using statistical methods for the design of experiments. The optimization of the process parameters enables us to prepare ramp-edge Josephson junctions with PrBa/sub 2/Cu/sub 3/O/sub 7/ as barrier material which exhibit tighter barriers. Adapting the growth conditions for YBa/sub 2/Cu/sub 3/O/sub 7/ on MgO films we prepared Josephson junctions with a 10 nm MgO barrier.         Fabrication of high IcRn YBCO ramp junctions using Ga doped Pr-Ba-Cu-O barriers at 65 K    R. Hu, H.W. Chan, J.M. Murduck, M. Sergant, C.L. Pettiette-Hall, J. Bulman and J.L. Luine Summary: Yttrium Barium Copper Oxide ramp junctions have been fabricated via off-axis rf magnetron sputtering using Praseodymium Barium Copper Gallium Oxide as a barrier material. Optimal wafer processing conditions and junction behavior as a function of barrier thickness are presented. IcRn values of 500 microvolts at 65 K have been achieved with a two step deposition/anneal process using Praseodymium Barium Copper Gallium Oxide as the barrier. This junction process has been demonstrated on 2 inch wafers.         Frequency down conversion and AC Josephson effect in HTS ramp-type junctions on MgO substrates    A.H. Sonnenberg, L. Amatuni, G.J. Gerritsma and H. Rogalla Summary: We report on the characterization at high frequencies of DyBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film ramp-type junctions with a PrBa/sub 2/Cu/sub 3/O/sub 7-x/ barrier fabricated on MgO substrates using a thin SrTiO/sub 3/ buffer layer. Josephson emission has been detected over a wide temperature range from 4.2 K to 85 K at millimeter wavelengths using a sensitive receiver. Measured spectrum characteristics, emitted power and linewidth are well described by theoretical models. Signal frequency down conversion has been carried out in two different modes using external and internal local oscillators. Wide band electronically tunable Josephson emission allowed us to achieve the frequency down conversion in a very sensitive self-oscillator-mixing mode up to 2.5 THz. For the first time, for any type of Josephson junction, self-oscillator mixing has been achieved at ambient temperatures as high as 80 K.         Properties of high-T/sub c/ ramp-edge junctions with a Ga-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// barrier    I-Hun Song, Eun-Hong Lee, Insang Song and Gwangseo Park Summary: We have fabricated high-T/sub c/ ramp-edge junctions with a Ga-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) barrier in the trilayer geometry of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///YBa/sub 2/Cu/sub 2.79/Ga/sub 0.21/O/sub 7-/spl delta///YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on LaAlO/sub 3/ single crystals. Interface resistances of the junctions were drastically reduced by using in-situ RF plasma cleaning treatment. The cross-sectional images of the interface of the junctions were analyzed by high resolution transmission electron microscopy. The temperature dependences of critical currents and junction resistances were consistent with the behavior predicted by the conventional proximity effect. The critical currents of the Ga-doped junctions were less sensitive to the variation of the barrier thickness compared to those of the other junctions. The increase of the barrier resistivity by Ga-doping resulted in an enhancement of the I/sub c/R/sub n/ values, up to 320 /spl mu/V at 60 K.         High-temperature superconducting edge-type Josephson junctions with modified interfaces    T. Satoh, M. Hidaka and S. Tahara Summary: A new process is presented for fabricating uniform high-temperature superconducting edge-type Josephson junctions. The junctions were fabricated by an in situ process using low-/spl epsi/ LaSrAlTaO material for both the insulator layer and the substrate. The LaSrAlTaO layer played a role as a mask for in situ edge fabrication. This process contained no intentional barrier deposition process. These junctions however showed resistively and capacitively shunted junction like current-voltage characteristics and an excellent uniformity. These junctions showed small spreads in the critical current as low as 1 /spl sigma/=8% for 100 junctions at 4.2 K.         Interfacial microstructures in ramp type multilayer Josephson junctions studied by TEM    J. Gao, Y. Yang and J.L. Sun Summary: The microstructures of high T/sub c/ ramp type Josephson junctions were studied by using transmission electron microscopy. The work was emphasized at the interfacial defects and the influence of the ramp slope. The results show that for the ramp slope angles of 15/spl deg//spl sim/40/spl deg/, the epitaxy was still remained through all layers at the ramp region without the formation of big grain boundaries. No amorphous layers and secondary phases were observed at the barrier interfaces. For a gentle ramp junction, small misoriented grains appeared in some portions of the barrier. The substrate ramp formed during the ion etching process had little influence on the growth of the upper layers. In junctions with a steep ramp, defects increased near the interface, although the epitaxy of the barrier was of good quality. The results demonstrate that the slope angle of the junction ramp is an important factor that influences the performance of the Josephson junctions.         Magnetic field behavior of SNS edge Josephson junctions    J.B. Bulman Summary: Measurements of the response of critical current of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///PrBa/sub 2/Cu/sub (3-x)/(Ga)/sub x/O/sub 7-/spl delta///YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// SNS edge Josephson junctions to external magnetic field reveal periodic dependence of critical current on magnetic field. Theoretically the shape of critical current versus magnetic field for uniform current flow across the junction should resemble a Fraunhofer diffraction pattern. Using analysis of depth of modulation as an indication of how well the experimental modulation pattern fits the diffraction model, our experiments show a correlation between the depth of modulation and the type of junction. RSJ-like I-V curves, with their sharp concave upward curvature and I/sub ex//I/sub c/<1, correlated with larger depth of modulation than flux flow-like I-V curves with their rounded concave downward curvature and I/sub ex//I/sub c/>1. Also the response of single junctions as a function of temperature is analyzed.         Very large YBa/sub 2/Cu/sub 3/O/sub 7/-Josephson-junction-arrays    H. Burkhardt, O. Brugmann, A. Rauther, F. Schnell and M. Schilling Summary: Arrays with YBa/sub 2/Cu/sub 3/O/sub 7/-Josephson junction ramp-edge geometry and on bicrystal substrates were investigated. The ramp-edge Josephson junctions were prepared in arrays of three, five and seven junctions in series and in a mixed array with a very large number of up to two million on one chip. First measurements are presented. On bicrystal substrates Josephson junctions were prepared up to 105 Josephson junctions in series. They show scaled current-voltage characteristics and Shapiro-steps under influence of microwave radiation.         Superconducting modulators for high dynamic range delta-sigma analog-to-digital converters    A. Hodge Worsham, D.L. Miller, P.D. Dresselhaus, A.H. Miklich and J.X. Przybysz Summary: Superconducting digital circuits are capable of producing high dynamic range analog-to-digital converters (ADCs). We present sigma-delta architectures using large (>100) oversampling ratios to give signal-to-noise ratios of greater than 100 dB in simulation. Three distinct designs, using two distinct mechanisms for feedback, are presented. All of the designs use only shunted junctions, and are therefore compatible with HTS SNS junctions. Simulations are presented for a modulator which creates feedback pulses by SQUID lobe-crossings, a modulator which uses the transresistance of a SQUID for feedback, and a modulator which uses threshold crossings in both the first and second loops for feedback.         A new design approach for RSFQ logic circuits based on the binary decision diagram    N. Yoshikawa, H. Tago and K. Yoneyama Summary: We will propose a new design approach for single-flux-quantum (SFQ) logic circuits based on a binary decision diagram (BDD). The BDD is a way to represent a logical function by using a directed graph, which is composed of nodes having one input (root) and two outputs (branches). The node has binary states internally which can be controlled from outside, and it switches a messenger entering from the root into one of two branches depending on the internal state. It has been proven that any combinational logic can be represented by this basic element. We will show that the BDD is effectively implemented by an SFQ circuit, where the node is replaced with an SFQ D/sub 2/ flip-flop. Important features of the BDD SFQ logic circuit are simplicity of circuit structure, self-timed nature and high modularity. We have designed a BDD SFQ adder and showed that the junction count and latency are smaller than that of the conventional RSFQ adder.         Application of credit-based flow control to RSFQ micropipelines    D.Y. Zinoviev and M. Maezawa Summary: Traditional micropipelines based on handshaking mechanisms are simple and reliable, but their throughput is limited by the round-trip flight time between two consecutive micropipeline stages. We propose an RSFQ implementation of a micropipeline with simple credit-based flow control that can hide the round-trip latency and significantly improve the throughput. In this paper, we present numerically calculated and experimentally measured throughput for several types of RSFQ credit-controlled micropipelines (including the special case of a micropipeline with only one credit), and their critical comparison.         Clock-driven on-chip testing for superconductor logic circuits    Y. Hashimoto, S. Yorozu, H. Numata and S. Tahara Summary: We have developed and demonstrated a clock-driven on-chip testing (CDOT) method for high-speed testing of superconductor logic circuits. This testing method uses an on-chip signal-pattern generator (SPG) driven by a clock signal. The SPG is based on a feedback shift register, in which a complement output of the last-stage D-flip-flop is fed back to the first-stage D-flip-flop. Thus, SPG generates a periodic signal-pattern when a clock signal is applied to it. The advantages of this testing method are that: (a) no external control signal is needed; (b) a simple SPG that consists of only D-flip-flops is used; (c) it is easy to extend to multi-bit testing. This greatly simplifies high-speed testing and design of test circuits. We have applied this method to the high-speed testing of the ring interface (RIF) circuit, which is an elemental circuit in our superconducting ring-network system. We have designed a test circuit, consisting of the RIF circuit and a 12-bit on-chip test-pattern generator, with resistor-coupled Josephson logic (RCJL). The test circuit includes about 1,400 Josephson-junctions. It has been fabricated using Nb/AlO/sub x//Nb Josephson-junction technology. As the result of the high-speed testing, full operation of the RIF circuit at 1-GHz clock frequency and proper operation of a sending part of the RIF circuit at 2-GHz clock frequency have been successfully verified.         Cryogenic packaging for multi-GHz electronics    T.S. Tighe, G. Akerling and A.D. Smith Summary: To meet the packaging needs of current superconducting electronics, we have developed high speed multi-chip modules (MCMs), flexible ribbon cabling and press-contact surface mounts. We describe these new technologies and include techniques for high reliability, high-yield assembly. In addition, we present electrical and thermal characterizations of a system which incorporates these new technologies. Electrical characterization includes multi-GHz insertion loss and digital-data transmission measurements. We have performed extensive thermal modeling using SINDA software and have experimentally verified these simulations. We present the results and their general applicability to these new cryogenic packaging technologies.         Superconducting transition-edge microcalorimeters for X-ray microanalysis    G.C. Hilton, D.A. Wollman, K.D. Irwin, L.L. Dulcie, N.F. Bergren and J.M. Martinis Summary: We have developed high-performance X-ray microcalorimeters based on superconducting transition-edge sensors. These superconducting detectors, which are cooled by a compact adiabatic demagnetization refrigerator mounted on a scanning electron microscope, provide significant new capabilities for X-ray microanalysis. The performance characteristics of these detectors are nearly ideal for many applications in X-ray microanalysis, attaining an energy resolution of 3-4 eV at a counting rate of 500 s/sup -/ and an effective collection area of 4 mm/sup 2/. The excellent energy resolution enables measurements of chemical shifts in X-ray spectra caused by changes in electron binding energy due to chemical bonding. Another important application of these detectors is analysis of contaminant particles and defects for the semiconductor industry. We present data demonstrating the analysis of particles on Si wafers, including 0.3 /spl mu/m tungsten particles and 0.1 /spl mu/m alumina particles.         Wavelength dependent photoresponse in YBCO thin-film systems    S.T. Ruggiero, M.P. Mischke, C.E. Tanner, A.J. Wilson, L.R. Vale and D.A. Rudman Summary: We present results on the photoresponse of YBCO narrow-line structures with deliberately broadened resistive transitions. We have explored the photoresponse of these systems as a function of temperature, bias current and power at wavelengths of 0.670, 0.850 and 10.6 /spl mu/m and at frequencies from 3 to 10/sup 5/ Hz at 0.670 /spl mu/m. The response was bolometric in nature in the vicinity of T/sub c/ (R=30 V/W). However, the response below T/sub c/ shows significant enhancement at 0.670 /spl mu/m. The wavelength regime of the enhancement suggests the participation of transient photodoping of the material or related phenomena.         On the concept of a normal metal hot-electron microbolometer for space applications    L. Kuzmin, D. Chouvaev, M. Tarasov, P. Sundquist, M. Willander and T. Claeson Summary: We present a theoretical analysis and experimental evaluation of a hot-electron microbolometer with normal metal absorber for ultrasensitive detecting infrared and submillimeter waves. The basic version of the antenna coupled microbolometer makes use of a hot-electron effect in the thin film resistive strip and Andreev reflection of hot electrons at SN interface between the strip and superconducting antenna. A value of NEP=5/spl middot/10/sup -18/ W/Hz/sup 1/2/ for the thermal fluctuation noise and the thermal time constant t=0.2 /spl mu/s at 300 mK have been estimated for one of the realized devices with thermal conductance G/spl ap/6/spl middot/10/sup -12/ W/K. At 100 mK, the thermal conductance has been decreased to G/spl ap/7/spl middot/10/sup -14/ W/K, that gives estimations for the thermal NEP=2/spl middot/10/sup -19/ W/Hz/sup 1/2/ and the time constant t=5 /spl mu/s. An advanced version of the microbolometer includes also additional SIN junctions connected to the resistive strip for electronic cooling the absorber. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.         New type detectors of particles and radiation based on HTSC materials    S.G. Gevorgyan and A.A. Movsisyan Summary: We developed an open-flat coil preparation technology allowing to make coils with high Q-factor values. It permits to develop a new measuring device based on a tunnel diode oscillator with such nontraditional open-flat coil. Such devices are very sensitive to the small changes of distances between the metallic planes and the coil's flat surface. The resolution is about (3-4) /spl Aring/. It permits to study small changes of the magnetic penetration depth in HTSC with the same resolution. New method allow to detect the S/N transitions of both the spherical shape single tin (Sn) grains with diameters up-to (2-3) /spl mu/m and 0.5 /spl mu/m thick and 4 /spl mu/m/spl times/5 /spl mu/m YBCO films. Such high resolution permits to use such devices in various areas of science and technology. Particularly, they may be used for the creation of a new detectors of particles and radiation based on HTSC materials. The basic principles and few designs of new detectors are presented suitable for various applications. The sensitivities achieved are: about 10/sup -11/ W/cm/sup 2/ for the visible spectrum radiation; about 0.1 mOe/cm/sup 2/ for the magnetic fields, and 0.1 /spl mu/A/cm/sup 2/ for the currents in HTSC films. Possible directions of the further improvement of the devices' features and also improvement of detectors' parameters are also suggested.         Imaging detectors based on the response of anisotropic layered materials    A.M. Gulian, D. Van Vechten, K.S. Wood, G.G. Fritz, J.S. Horwitz, M.S. Osofsky, J.M. Pond, S.B. Qadri, R.M. Stroud, J.B. Thrasher, V.O. Vartanyan, A.S. Kuzanyan, V.R. Nikogosyan and A.L. Gyulamiryan Summary: The inherent properties of naturally layered materials such as the high-temperature superconductors cause a transient voltage when a light pulse is absorbed. The amplitude is proportional to the absorbed energy. Observable pulses arise in the HTS materials even at room temperature. A phenomenological model of the effects consistent with our observations on the first generation of sensors will be discussed along with recent results regarding sensitivity to single photons, array geometry and readout, and energy resolution.         Fabrication technology for high-density Josephson integrated circuits using mechanical polishing planarization    H. Numata, S. Nagasawa, M. Tanaka and S. Tahara Summary: A mechanical polishing planarization (MPP) process is developed with an endpoint detection method. MPP makes it possible to form self-aligned contacts on small junctions and to decrease parasitic inductance. It can also control the thickness of the insulation layers precisely. MPP was used to fabricate a 22 /spl mu/m/spl times/22 /spl mu/m vortex transitional memory cell and the cell operated correctly. The reliability of interlayer insulation was increased for 64-Kbit memory cell arrays fabricated using MPP. It is concluded that MPP is an effective technology for fabricating high-density Josephson circuits.         Manufacturability of superconductor electronics for a petaflops-scale computer    L.A. Abelson, Q.P. Herr, G.L. Kerber, M. Leung and T.S. Tighe Summary: Ultra-low power and ultra-high speed single-flux-quantum electronics is an enabling near-term technology solution for petaflops-scale computers. The proposed Hybrid Technology Multi-threaded (HTMT) petaflops computer architecture includes computational modules operating at 100 GHz and an I/O throughput of 32 Petabits/s. Due to fundamental time-of-flight and power dissipation limitations of semiconductor ICs, superconductor ICs at an integration level of 100 k gates/cm/sup 2/ are proposed for the HTMT computation modules. In this paper, we discuss the manufacturability of superconductor-based computation modules, including the IC foundry process, packaging, and data link out of the cryopackage. We focus on the critical technical challenges that exist in each of these areas and present a technology roadmap to achieve the HTMT requirements.         Very small critical current spreads in Nb/Al-AlOx/Nb integrated circuits using low-temperature and low-stress ECR PECVD silicon oxide films    Xiaofan Meng, A. Bhat and T. Van Duzer Summary: We have developed a new Nb/Al-AlOx/Nb IC process with very small critical current spread. Low-temperature and low-stress ECR (Electron Cyclotron Resonance) PECVD (Plasma Enhanced Chemical Vapor Deposition) silicon oxide films have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputtered silicon oxide. Since ECR PECVD silicon oxide films have superiority in quality over e-beam evaporated silicon monooxide films and extremely low damage to underlayers compared to sputtered films, our Nb/Al-AlOx/Nb IC quality and yield have been improved greatly. The critical current spreads (maximum to minimum) are less than 1%(/spl sigma/<0.2%) on chip and less than 4%(/spl sigma/<0.7%) cross a four-inch wafer for 5 /spl mu/m/spl times/5 /spl mu/m junctions. Even for high critical current density (/spl sim/10 kA/cm/sup 2/) small junctions (1.5 /spl mu/m x 1.5 /spl mu/m) the on-chip spread is only about 4%(/spl sigma/<0.7%). High quality Nb/Al-AlOx/Nb ICs have been fabricated and demonstrated.         Rapid single flux quantum T-flip flop operating up to 770 GHz    W. Chen, A.V. Rylyakov, V. Patel, J.E. Lukens and K.K. Likharev Summary: Rapid Single Flux Quantum (RSFQ) T-flip flops (TFFs) operating up to 770 GHz have been demonstrated at 4.2 K. The devices, consisting of either resistively shunted or unshunted Josephson junctions, are fabricated using a planarized Nb/AlO/sub x//Nb trilayer process. Electron beam lithography is used to pattern all levels with a minimum junction area less than 0.1 /spl mu/m/sup 2/. Critical current densities of 0.5 mA//spl mu/m/sup 2/ and 2.5 mA//spl mu/m/sup 2/ are used for the shunted (tested at 1.8 K) and unshunted devices (tested at 4.2 K) respectively. The input and output frequencies of the TFFs are obtained from the input and output voltages by the Josephson relation. The output voltage is exactly half of the input voltage when the divide-by-two operation is correct.         Processing and characterization of high Jc NbN superconducting tunnel junctions for THz analog circuits and RSFQ    V. Larrey, J.-C. Villegier, M. Salez, F. Miletto-Granozio and A. Karpov Summary: A generic NbN Superconducting Tunnel Junctions (STJ) technology has been developed using conventional substrates (Si and SOI-SIMOX) for making THz spectrometers including SIS receivers and RSFQ logic gates. NbN/MgO/NbN junctions with area of 1 /spl mu/m/sup 2/, Jc of 10 kA/cm/sup 2/ and low sub-gap leakage current (Vm>25 mV) are currently obtained from room temperature sputtered multilayers followed by a post-annealing at 250/spl deg/C. Using a thin MgO buffer layer deposited underneath the NbN electrodes, ensures lower NbN surface resistance values (Rs=7 /spl mu//spl Omega/) at 10 GHz and 4 K. Epitaxial NbN [100] films on MgO [100] with high gap frequency (1.4 THz) have also been achieved under the same deposition conditions at room temperature. The NbN SIS has shown good I-V photon induced steps when LO pumped at 300 GHz. We have developed an 8 levels Al/NbN multilayer process for making 1.5 THz SIS mixers (including Al antennas) on Si membranes patterned in SOI-SIMOX. Using the planarization techniques developed at the Si-MOS CEA-LETI Facility, we have also demonstrated on the possibility of extending our NbN technology to high level RSFQ circuit integration with 0.5 /spl mu/m/sup 2/ junction area, made on large area substrates (up to 8 inches).         Electrical tuning of passive HTS microwave devices using single crystal strontium titanate    I. Wooldridge, C.W. Turner, P.A. Warburton and E.J. Romans Summary: Over the last few years several groups have fabricated High Temperature Superconducting (HTS) thin film microwave devices which have included a ferroelectric thin film layer in their design. The electric field dependence of the ferroelectric promises desirable in-situ tuning of the frequency response. Here we present the results of our experiments on the tuning of a coplanar HTS resonator using single crystal strontium titanate (STO). We have patterned a simple coplanar resonator device onto Y-Ba-Cu-O thin films deposited on [100] magnesium oxide substrates. Careful consideration of the size, position and biasing of these high permittivity STO crystals with respect to the planar device allows us to minimise the perturbance to the plain resonators response whilst at the same time maximising the degree to which we are able to tune the device. We have also performed a series of capacitance measurements on our STO crystals to obtain reliable data for the dependence of the permittivity on temperature, applied bias and crystallographic orientation.         Fabrication of superconducting delay line with GaAs Schottky diode    K. Koh and K. Hohkawa Summary: We improved the fabrication process of superconductor/semiconductor devices based on epitaxial liftoff (ELO) technology by using polyimide film in place of Apiezon wax. We investigated the process conditions and fabricated basic GaAs devices. We also succeeded in bonding a GaAs Metal-Semiconductor-Metal photodiode on YBCO micro-strip-line that is formed on an SrTiO/sub 3/ substrate. The basic characteristics of this photodiode are measured and the results have confirmed that the ELO process using polyimide film is feasible for fabricating superconductor/semiconductor functional devices.         Next generation Nb superconductor integrated circuit process    L.A. Abelson, R.N. Elmadjian and G.L. Kerber Summary: We have developed our next generation Nb integrated circuit process which offers higher performance, particularly for SFQ-type logic, and increased density compared to our present 2000 A/cm/sup 2/ foundry process. The new process is based on our existing Nb foundry process, but has been optimized to utilize more of the sub-micron alignment and exposure capabilities of our optical lithography tools. Minimum linepitch and junction size have been reduced to 2.5 /spl mu/m (from 4 /spl mu/m) and 1.75 /spl mu/m (from 2.5 /spl mu/m), respectively, and J/sub c/ has been increased to 4000 A/cm/sup 2/. These goals have been achieved by an overall reduction in layer thicknesses, implementation of SF/sub 6/ dry etch for metal line definition, and optimization of the photolithography process. The new process offers lower inductance wiring and substantially lower parasitic circuit inductances compared with the existing Nb foundry process. In this paper, we discuss these improvements and report parametric test data for devices fabricated in this process.         A 10 GHz digital amplifier in an ultra-small-spread high-J/sub c/ Nb/Al-AlOx/Nb integrated circuit process    A. Bhat, Xiaofan Meng, S. Whiteley, M. Jeffery and T. Van Duzer Summary: We describe a Josephson amplifier fabricated in a high-J/sub c/ process, which is operational to speeds of at least 10 GHz, the highest reported for a voltage-state amplifier. The amplifier converts /spl sim/200 /spl mu/V digital signals to /spl sim/5 mV at 10 GHz and could be used as an interface between two superconducting systems. The bit-error-rate of the circuit was /spl sim/5/spl times/10/sup -12/ at 5 GHz, the lowest reported; bit-error-rate measurements at 10 GHz were not possible. A high-J/sub c/ process which was used to fabricate the amplifier was developed at UC Berkeley with extremely low I/sub c/ spreads; at /spl sim/9.4 kA/cm/sup 2/ /spl sigma/ as low as 0.6% was observed. At /spl sim/10 kA/cm/sup 2/, the typical junction linear dimensions are 1.5 /spl sim/ 2 /spl mu/m, sizes for which it is not possible-with available tools-to make reliable vias that are smaller than the junction. We use a nonplanarized junction process, where the via for contact of a wiring layer to a junction can be larger than the junction.         Evaluation of critical current density of Nb/Al/AlO/sub x//Nb Josephson junctions using test structures at 300 K    K.K. Berggren, M. O'Hara, J.P. Sage and A. Hodge Worsham Summary: We have designed and fabricated test structures that allow the determination of the critical current density and processing run-out of low T/sub c/ Josephson junctions based only on room-temperature measurements. We demonstrated that the 300 K tunneling conductance of a junction barrier is proportional to the critical current at 4.2 K. This testing technique greatly reduced the time required to characterize a process wafer. In one demonstration we tested hundreds of devices across a 150-mm-diameter wafer in less than an hour. In another we used a selective niobium anodization process with only two mask levels to determine the critical current density of a Nb/AlO/sub x//Nb trilayer within a day of its deposition. We have also used automated probing stations to decrease testing delays further and thus to improve process cycle time.         Machine-aligned fabrication of submicron SIS tunnel junctions using a focused ion beam    R.B. Bass, J.Z. Zhang and A.W. Lichtenberger Summary: The objective of our research is to develop a machine-aligned technique for the definition and insulation of Nb/Al-AlO/sub x//Nb superconducting-insulating-superconducting (SIS) tunnel junctions with areas as small as 0.2 /spl mu/m/sup 2/. The fabrication of such ultrasmall area planar SIS junctions had previously only been achieved using electron beam lithography (JPL). Typical techniques for the fabrication of micron-scale SIS junctions involve a self-aligned resist lift-off process. The resist pattern is used to define both the junction counter-electrode and the insulation field that separates the wiring layer from the base electrode. The wiring layer contacts the junction counter-electrode through a via in the insulation field that is created during resist liftoff. In our process, the junction is defined and insulated in separate steps; a via through the insulation layer to the junction is aligned and defined using a gallium focused ion beam with nanometer spot-size. Such small area SIS junctions have potential applications in high frequency SIS mixer circuits. They may also be used in experiments to investigate quantum coherence in superconducting circuits and may even serve as the key elements in future superconducting quantum computers.         Unexpected geometrical anodization effect in the fabrication of Nb/Al-oxide/Nb junctions    H.H. Huang, J.Z. Zhang, A.W. Lichtenberger and R.E. Miller Summary: In our research on the fabrication of Nb/Al-oxide/Nb mixer elements, we have discovered an unexpected effect which is attributable to the geometry of the mixer. We have found that the electrical quality of anodically sealed junctions fabricated in our laboratory depends strongly on the geometry of the base electrode. For example, it is possible to design a series array of junctions using two geometries of base electrode features and obtain poor junction electrical characteristics with one type of base feature and excellent characteristics with the other. The role of Nb film stress, junction size and placement on the base electrode feature, wiring interconnection process and anodization conditions in this effect have been studied.         Self-shunted Nb/AlO/sub x//Nb Josephson junctions    V. Patel and J.E. Lukens Summary: We describe the fabrication and properties of high critical current density (J/sub c/) Nb/AlO/sub x//Nb Josephson junctions with deep-submicron dimensions. The junctions are fabricated using a planarized process in which all levels are patterned using a combination of optical and electron-beam lithography. The base and counter electrodes are defined by reactive ion etching using quartz etch masks to give a minimum feature size of 0.2 microns. For J/sub c/=2.1 mA//spl mu/m/sup 2/ and junction area less than 0.1 /spl mu/m/sup 2/ the devices are self-shunted and exhibit nonhysteretic I-V characteristics. A small hysteresis in the larger junctions is caused by heating in the electrodes.         Novel method for fabricating deep submicron Nb/AlO/sub x//Nb tunnel junctions based on spin-on glass planarization    A.B. Pavolotsky, T. Weimann, H. Scherer, J. Niemeyer, A.B. Zorin and V.A. Krupenin Summary: A novel method for the fabrication of sub-1-/spl mu/m Nb/AlO/sub x//Nb tunnel junctions has been developed, that is based on spin-on glass planarization. The Nb/AlO/sub x//Nb sandwich and the Nb wiring layer are structured by reactive ion etching using e-beam lithography. The insulation between the base electrode and the wiring layer is realized by planarised spin-on glass. Single electron transistors with junction areas of 0.3 /spl mu/m/spl times/0.3 /spl mu/m and linear arrays of junctions with sizes down to 0.5 /spl mu/m/spl times/0.5 /spl mu/m have been fabricated and measured.         Sub /spl mu/m Nb/AlO/sub x//Nb Josephson junctions fabricated by anodization techniques    R. Dolata, T. Weimann, H.-J. Scherer and J. Niemeyer Summary: Technological processes for the fabrication of Nb/AlO/sub x//Nb Josephson junctions with areas as small as 0.04 /spl mu/m/sup 2/, based on anodization techniques, are investigated. A cross strip process requiring only two masks is compared with a standard three mask etching and anodization process. Details of the fabrication processes as well as the electrical characterization at 4.2 K and 30 mK of tunnel junctions fabricated by the different methods are presented. Limitations and applications of the two different processes are discussed.         Characterization of NbN/AlN/NbN tunnel junctions    Z. Wang, H. Terai, A. Kawakami and Y. Uzawa Summary: We report on tunneling properties and interface structures for high-quality NbN/AlN/NbN tunnel junctions fabricated on ambient temperature MgO substrates. Junction quality and electrical parameters were systematically investigated in a very wide range for current density. The junctions show a very good junction quality with a high gap voltage, large I/sub c/R/sub N/ product, and large R/sub sg//R/sub N/ ratio as the current density varied from 100 A/cm/sup 2/ to above 100 kA/cm/sup 2/. The average barrier heights of the NbN/AlN/NbN tunnel junctions are calculated from the barrier thickness dependence of the critical current density. We found that the current density has two distinct types of dependency on the AlN barrier thickness, corresponding to two average barrier heights in different regions for the current density.         Overdamped niobium-nitride junctions for 10 K operation    H. Akaike, R. Oke, T. Aoyama, A. Fujimaki and H. Hayakawa Summary: We have fabricated overdamped NbN/NbNx/NbN Josephson junctions with the IcR product of 0.64 mV and the critical current density Jc of 1.2 kA/cm/sup 2/ at 10 K. The NbNx barriers are formed by plasma nitridation of the surface of the superconductive NbN base electrodes. Although the junctions show small-hysteretic characteristics at 4.2 K, they change to overdamped ones with increasing temperature. We obtained the over-damped junctions with the Jc ranging from 0.05 kA/cm/sup 2/ to 3.3 kA/cm and the IcR product ranging from 0.11 mV to 0.64 mV at 10 K. The junction characteristics are discussed from a viewpoint of the dependence of Ic on temperature. On the other hand, small hysteretic characteristics at 4.2 K enable us to evaluate Ic spread using a series of junctions. The standard deviation, 1-4 was 2.9% for a series of 64 junctions with an area of 5/spl times/5 /spl mu/m/sup 2/ at 4.2 K.         Characteristics of junctions and resistors fabricated using an all-NbN superconductor integrated circuit foundry process    G.L. Kerber, L.A. Abelson, R.N. Elmadjian and E.G. Ladizinsky Summary: Trilayer NbN/MgO/NbN tunnel junctions and Mo and NbN/sub x/ resistors fabricated over a NbN ground plane form the basis of a high performance, 10 K, superconductor integrated circuit foundry process. To produce high yield LSI and VLSI superconductor integrated circuits requires predictable device characteristics, stable, well-characterized, thin film deposition processes, and control of critical dimensions (CD). In this paper, we discuss improvements in thin film deposition processes, device characteristics, and CD control. Repeatable trilayer characteristics have been achieved through the use of feedback control of critical MgO and NbN sputtering parameters. Run-to-run variations in MgO film thickness have been reduced to less than /spl plusmn/1.0% (1/spl sigma/) using a novel computer feedback control technique. Improvements in MgO deposition uniformity and CD control of junction size have reduced across wafer I/sub c/ nonuniformity to less than /spl plusmn/10% (3/spl sigma/) and 100 junction array I/sub c/ nonuniformity on 0.5 cm chips to /spl plusmn/2% (1/spl sigma/). We report on the electrical characteristics of junctions and resistors and on component spreads and stability of our NbN foundry process.         Low T/sub c/ superconductive circuits fabricated on 150-mm-diameter wafers using a doubly planarized Nb/AlO/sub x//Nb process    K.K. Berggren, E.M. Macedo, D.A. Feld and J.P. Sage Summary: We have used a doubly planarized all-refractory technology for superconductive electronics (DPARTS) process to fabricate mixed-signal circuits that have more than 200 junctions per circuit and operate at 2 GHz. A 150-mm-diameter wafer can produce more than 400 chips, each 5 mm on an edge. The junctions had a critical current density of 1.7 kA/cm/sup 2/. The wafers were evaluated at room temperature, both in- and post-process. In-process testing was used to detect parameter shifts during processing, while post-process testing used an automated testing station to test more than 3500 structures across each completed wafer and thus establish a large set of statistical data for studying the spread and targeting of parameter values. The circuits were fabricated in a class-10 clean room in which 0.25 /spl mu/m CMOS and CCD devices were also produced. The DPARTS process could also be used for sub-/spl mu/m fabrication, as it includes optical lithography with an i-line stepper; chemical-mechanical planarization at two levels; a self-aligned via process; and dry, anisotropic etching for all metal etching and via definition steps. The use of 150-mm-diameter wafers ensures that this process will be able to exploit technological advances in the standard silicon tool set as improvements become available. The results demonstrated here are a necessary precondition to yielding large volumes of superconductive electronic circuits containing devices with sub-/spl mu/m dimensions.         Transmission line high-T/sub c/ dc-SQUIDs    S. Kuriki, H. Oyama, E. Maruyama, A. Hayashi, S. Hirano, D. Suzuki and M. Koyanagi Summary: Because of high permittivity of SrTiO/sub 3/ (STO) substrate, YBCO high-Tc SQUIDs have distributed impedance. Based on the simulation by the analytical method to calculate the I-V characteristic, we have designed and fabricated YBCO dc SQUIDs that have a transmission-line-like geometry of thin parallel strips with a wide slit between them. The geometrical parameters were determined to give high modulation voltage. The fabricated SQUIDs had a white noise of (0.5-1.0)/spl times/10 /spl Phi//sub 0//Hz/sup 1/2/. We also designed a direct coupling magnetometer, in which the transmission line SQUID was located within the hole of the pickup coil. On a small substrate area of 5 mm/spl times/10 mm, the fabricated magnetometer had an effective area of 0.22 mm/sup 2/. The field noise of about 100 fT/Hz/sup 1/2/ was obtained in the white noise region.         Investigation of multiple SQUID arrangements in single layer high T/sub c/ magnetometers    V. Schultze, V. Zakosarenko, R. Ijsselsteijn, J. Ramos and H.-G. Meyer Summary: Single layer high T/sub c/ dc SQUID sensors on bicrystal substrates were investigated. Special attention was paid to achieve a large flux-to-voltage transfer function in order to ensure stable operation of the SQUID electronics and to get low flux noise even in disturbed environment. Josephson junctions on 30/spl deg/ bicrystal were tested as well as sub-/spl mu/m junctions an 24/spl deg/ bicrystals. The steep edges achieved by sub-/spl mu/m patterning increased the resistance of the superconducting structures against large external fields. The design for large flux-to-voltage transfer functions focused on multiple de SQUID arrangements. For magnetometers with a directly coupled pickup-loop three junction SQUIDs show no advantage compared to standard two junction SQUIDs, but the series connection of two ordinary dc SQUIDs does. Although for magnetometers with inductively coupled pickup-loop twenty SQUIDs in series were used the effect on the flux-to-voltage transfer coefficient was poor, due to differences in the critical current and inductance of individual SQUIDs. The sensitivity of the whole magnetometer achieved with inductively coupled single layer pickup-loops is much smaller than with directly coupled ones. For the latter a pickup-loop formed as a conventional square washer shows better results compared to a slotted square.         Low-noise integrated SQUID electronics operating in liquid nitrogen    V. Zakosarenko, J. Kunert, V. Schultze, H.-G. Meyer, R. Gross and F. Nitsche Summary: Directly coupled electronics for a dc SQUID was developed as a fully integrated circuit designed for operation at liquid nitrogen temperature. It was fabricated on the base of BiCMOS technology. The parameters of the model used for the design were extracted from the measurements of resistors, capacitors, and all types of transistors (npn, pMOS and nMOS) possible in this technology at 77 K. The npn transistors are favorable for the input stage as they have lower noise level. Up to 1280 transistor cells were connected in parallel to decrease the noise. Such a macro transistor has a white noise level of 160 pV/Hz/sup 1/2/ and power dissipation of 7 mW. The entire flux locked loop electronics containing a preamplifier built of two macro transistors and operational amplifier as an integrator has been tested with a high T/sub c/ SQUID. The flux locked loop operated stable. The white noise level corresponds to the expected value. It is determined mainly by the intrinsic noise of the SQUID itself.         Second-order dc SQUID gradiometer from single layer of high temperature superconducting film    Soon-Gul Lee, Yunseok Hwang, Byung-Chang Nam, Jin-Tae Kim, Yong Ki Park and Gun Yong Sung Summary: We developed a new design of the planar-type single-layer second-order SQUID gradiometer. The device consisted of 3 parallel-connected pickup loops, each of which is directly coupled to the step-edge junction dc SQUID. The device was made from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7/ film patterned by photolithography with ion milling technique. Response of the device to various field distributions was tested, with 3 identical wire-wound coils coupled to each loop. Balancing was achieved by using a small piece of superconductor placed in the center loop. The gradiometer responded sensitively to the second-order field gradient, but did not respond to a uniform field or the first-order gradient. Measured off-balance was about 0.6% for the uniform field and 1.4% for the first order gradient.         Slotted high-T/sub c/ dc SQUID magnetometers    A.B.M. Jansman, M. Izquierdo, J. Flokstra and H. Rogalla Summary: Recently, it was observed that the low frequency noise of slotted SQUIDs is not affected when cooling them down in magnetic fields up to 0.05 mT. This behavior is ascribed to the fact that magnetic vortices are expelled out of the narrow strips into the slots. Thus 1/f noise by hopping of vortices in the superconducting structure is eliminated. Here we present a systematic investigation on a series of slotted high-T/sub c/ dc SQUIDs. The number of slots varies from zero to eight. A model is developed that provides values for the effective area and inductance of the slotted washers and the current distribution within the slotted SQUIDs. The model can explain the experimentally observed maximum in the effective area for four slots very well. The observed agreement with respect to the modulation depth supports the theoretical values for the inductance. The white noise of the slotted SQUIDs is higher than expected, while the expected rise of low frequency noise for field cooled solid washer SQUIDs was not observed.         Low-frequency noise in field-cooled, directly coupled magnetometers    H.-M. Cho, R. McDermott, B. Oh, K.A. Kouznetsov, A. Kittel, J.H. Miller Jr. and J. Clarke Summary: We have studied the low-frequency noise properties of high-T/sub c/ directly coupled magnetometers involving dc Superconducting Quantum Interference Devices (SQUIDs) connected to four different types of pickup loop. Two of the pickup loops have a solid-washer design, while the other two comprise structures with narrow (4 /spl mu/m) linewidths. The devices were fabricated from YBCO thin films laser deposited on bicrystal substrate. The noise properties of the magnetometers cooled and maintained in static magnetic fields were measured at 77 K. The pickup loop contributes to the 1/f noise of field-cooled devices solely through vortex motion at tapered outer edges; this noise was eliminated by repatterning the edges to make them sharp. We demonstrate that solid-film washers can be replaced with narrow-linewidth structures without any loss in effective area.         The inverse problem in the magnetic diffraction of Josephson junctions    D.L. Tilbrook Summary: The determination of the critical current distribution in a Josephson junction is an important practical problem which is potentially capable of providing information about the local junction morphology. One possible approach is based on the magnetic diffraction pattern of the Josephson junction. Since the magnetic diffraction pattern may be expressed as the modulus of the Fourier transform of the current distribution in the junction, the problem of determining the current distribution is equivalent to retrieving the phase information which is lost when taking absolute values. This paper constitutes an analysis of this inverse problem specifically in relation to the determination of the current distribution from the magnetic diffraction pattern. Algorithms developed for similar inverse problems from other fields are examined to determine their applicability to this problem. It is proved that in some special cases the problem may be solved uniquely. In more general cases the density of possible solutions is studied to determine the conditions under which a unique solution might be found by an extension of the experimental procedure.         Two methods for a first order hardware gradiometer using two HTS SQUIDs    M.A. Espy, E.R. Flynn, R.H. Kraus Jr. and A.N. Matlashov Summary: Two types of first order electronic gradiometers have been developed using high temperature superconducting (HTS) SQUIDs. Gradiometry is accomplished in hardware by either 1) subtracting the output of the signal and background SQUIDs in a summing amplifier (parallel technique) or 2) converting the inverted background SQUID output to a magnetic field at the sensor SQUID (series technique). Balance levels achieved are 2000 and 1000 at 20 Hz for the parallel and series methods respectively. Balance level as a function of frequency is presented. Balance level for hardware gradiometry is limited by time delays from the electronics and how well the signal amplitudes are matched. A simple algorithm that allows one to estimate the limit on balance level from these factors is presented and compared with data.         Operating conditions for a pulse-quantized AC and DC bipolar voltage source    S.P. Benz, C.J. Burroughs, T.E. Harvey and C.A. Hamilton Summary: We have developed an accurate ac and dc bipolar voltage source based on the quantized pulses of Josephson junctions. A factor-of-6 increase in output voltage over previous unipolar waveforms is achieved by generating bipolar waveforms where arrays of junctions are biased with both a broadband two-level digital code and a sine wave. We use simulations to determine the optimum operating conditions as a function of frequency and as a function of the phase difference between the digital code and the sinusoidal drive.         RSFQ multiplexer and demultiplexer    L. Zheng, N. Yoshikawa, J. Deng, X. Meng, S. Whiteley and T. Van Duzer Summary: An 1:8 RSFQ demultiplexer (DEMUX) and an 8:1 RSFQ multiplexer (MUX) were designed, simulated and optimized to operate at about 20 GHz. Both the inputs and outputs of the DEMUX are complementary dual-rail signals. The basic 2-bit DEMUX module is a self-clocked dual-rail T flip-flop. This DEMUX has a simpler structure than an earlier version of a data-driven-self-timed (DDST) DEMUX developed in our laboratory; however its simulated dc bias margin is (-20%, +20%), which is lower than the more complex device (-29%, +29%). The MUX takes lower data rate single-rail inputs and combines them sequentially into a single output. The complementary output is recovered from the output itself to facilitate interfacing to other dual-rail circuits on chip. The calculated dc bias margin is (-30 %, +28%). Circuit functionality is verified for the 2-bit MUX and the 2-bit DEMUX at low speed. An on-chip high-speed test system is designed to evaluate operation of the MUX and DEMUX at 20 GHz. The circuits are fabricated using a 1 kA/cm/sup 2/ niobium process at both UCB and HYPRES.         An interface circuit for a Josephson-CMOS hybrid digital system    M. Suzuki, M. Maezawa, H. Takato, H. Nakagawa, F. Hirayama, S. Kiryu, M. Aoyagi, T. Sekigawa and A. Shoji Summary: For broadband data communication between Josephson and CMOS digital systems, amplification of small Josephson-output signals and synchronization between the systems are important issues. We present an interface circuit for a Josephson-CMOS hybrid digital system. The interface circuit consists of a parallel-in-parallel-out (PIPO) circuit and built-in Josephson-MOS amplifiers. The PIPO circuit, implemented based on 4JL latching logic technology, performs synchronized data transfer between the Josephson and CMOS circuits. The Josephson-MOS amplifiers consists of stacked Josephson junctions (Suzuki stacks) and MOS inverters which are monolithically integrated on a chip. The circuits have been designed, fabricated and tested. We have successfully confirmed correct operation of the circuits.         New fabrication process elements of phase-mode logic circuits    T. Onomi and K. Nakajima Summary: We present the phase-mode circuits based on new fabrication process elements for high-density circuit integration. Nb/AlN/sub x//Nb overdamped junctions without external resistive shunts are applied to the phase-mode circuits. The area of a bias feed resistor can be reduced by a replacement of the metallic resistor by the junction normal resistance. As a miniaturization method of an inductance, the effective inductance of a Josephson junction is used. The phase-mode circuits based on these new integration methods have been fabricated by Nb integration technology. Various aspects which are brought about by these fabrication technologies are discussed.         Monte-Carlo yield analysis [of Josephson circuits]    M.W. Johnson, Q.P. Herr and J.W. Sparge Summary: Speed, integration scale, and production cost of digital electronics are all constrained by circuit yield. This is true in any technology, In Josephson circuits, parameter variations figure prominently into the yield equation. Extensive statistical data exist for processes such as TRW's Nb and NbN technologies; yield calculation is a way to relate these data to circuit performance. To determine parametric yield using Monte Carlo, any and all circuit parameters are treated as Gaussian random variables. This kind of yield calculation has now been incorporated into the MALT optimization utility. As a worked example, we analyze a stacked SQUID amplifier design. The technique reveals circuit dynamics that are difficult to uncover by other means.         Single photon imaging X-ray spectrometers    K. Segall, C.M. Wilson, L. Li, A.K. Davies, R. Lathrop, M.C. Gaidis, D.E. Prober, A.E. Szymkowiak and S.H. Moseley Summary: We have developed superconducting, single-photon imaging X-ray detectors with an energy resolution of 26 eV FWHM at 6 keV and a spatial resolution of 0.5 /spl mu/m over an effective area of 18 /spl mu/m/spl times/100 /spl mu/m. The energy resolution is among the best reported for this kind of detector and is within a factor of /spl ap/4 of its theoretical limit. The calculated absorption efficiency of the detector is 28%. Scaling to larger areas and higher quantum efficiency appear possible. We discuss the device design and readout along with possible sources of resolution broadening.         High resolution tunnel junction extreme ultraviolet detectors limited by quasiparticle counting statistics    S. Friedrich, J.B. le Grand, L.J. Hiller, J. Kipp, M. Frank, S.E. Labov, S.P. Cramer and A.T. Barfknecht Summary: Superconducting tunnel junctions (STJs) can be used as high-resolution high-count rate photon detectors. They are based on the measurement of the excess quasiparticle tunneling current caused by the absorption of a photon in one of the junction electrodes. We have fabricated Nb-Al-AlO/sub x/-Al-Nb tunnel junction detectors with different sizes and characterized them in synchrotron experiments. We present a study of the detector performance in the energy band between 50 and 1000 eV. For photon energies below 70 eV, the intrinsic device resolution of the best STJ devices agrees with the theoretical limit set by the statistics of the charge generation and tunneling processes.         High resolution X-ray and infrared detectors using magnetic penetration depth thermometers    C.J. Yeager, F. Finkbeiner, P.J. Shirron and M.J. DiPirro Summary: We are developing a high-resolution X-ray detector using a magnetic penetration depth thermometer (PDT). A PDT uses the strong temperature dependence of the magnetic penetration depth of a superconducting film. PDTs were originally developed for use at liquid helium temperatures and achieved resolutions on the order of 2 nK. The low intrinsic heat capacity and high sensitivity make it potentially useful for X-ray microcalorimetry. Using a superconducting bilayer film of aluminum and silver, a PDT can be developed to work at 100 mK or lower. A detector with a 1 mm pixel would be background limited and have an intrinsic resolution better than 2 eV out of 6 keV. Higher resolutions could be achieved for lower energy sources, making this technique useful as an infrared bolometer. Results of the current work will be presented along with analysis of design issues.         Quantum efficiency and time-domain response of superconducting NbN hot-electron photodetectors    K.S. Il'in, M. Currie, M. Lindgren, I.I. Milostnaya, A.A. Verevkin, G.N. Gol'tsman and R. Sobolewski Summary: We report our studies on the response of ultrathin superconducting NbN hot-electron photodetectors. We have measured the photoresponse of few-nm-thick, micron-size structures, which consisted of single and multiple microbridges, to radiation from the continuous-wave semiconductor laser and the femtosecond Ti:sapphire laser with the wavelength of 790 nm and 400 nm, respectively. The maximum responsivity was observed near the film's superconducting transition with the device optimally current-biased in the resistive state. The responsivity of the detector, normalized to its illuminated area and the coupling factor, was 220 A/W(3/spl times/10/sup 4/ V/W), which corresponded to a quantum efficiency of 340. The responsivity was wavelength independent from the far infrared to the ultraviolet range, and was at least two orders of magnitude higher than comparable semiconductor optical detectors. The time constant of the photoresponse signal was 45 ps, when was measured at 2.15 K in the resistive (switched) state using a cryogenic electro-optical sampling technique with subpicosecond resolution. The obtained results agree very well with our calculations performed using a two-temperature model of the electron heating in thin superconducting films.         Soft X-ray performance of superconducting tunnel junction arrays    P. Verhoeve, S. Kraft, N. Rando, A. Peacock, A. van Dordrecht, R. den Hartog, D.J. Goldie, R. Hart and D. Glowacka Summary: A number of 6/spl times/6 element arrays of Ta-based superconducting tunnel junctions have been manufactured for photon counting applications with moderate energy resolution in ground-based optical astronomy. The individual array elements show low leakage, uniform responsivity across the array, good simultaneous Josephson current suppression and minor crosstalk between adjacent pixels. The same arrays have been characterized in the soft X-ray range (E=270-1500 eV). The base electrode response shows good energy resolving power (E//spl Delta/E/spl ap/140). Unwanted spectral features originating from other parts of the detector can be largely eliminated by rise-time filtering. Modifications in the layering are necessary in order to improve the soft X-ray detection efficiency.         Hilbert-transform spectroscopy with high-T/sub c/ Josephson junctions: first spectrometers and first applications    Y.Y. Divin, U. Poppe, K. Urban, O.Y. Volkov, V.V. Shirotov, V.V. Pavlovskii, P. Schmueser, K. Hanke, M. Geitz and M. Tonutti Summary: First laboratory prototypes of Hilbert-transform spectrometers have been developed. To meet the requirements of Hilbert-transform spectroscopy, high-T/sub c/ Josephson junctions with RSJ-like behavior have been fabricated on twin-free NdGaO/sub 5/ bicrystal substrates. The operation of the spectrometers has been demonstrated from 60 GHz up to 2.25 THz. The first out-of-lab application of Hilbert-transform spectrometers has been successfully demonstrated at the TESLA Test Facility linear accelerator at DESY (Hamburg). The spectra of coherent transition electromagnetic radiation from electron bunches have been measured and a bunch length of /spl sigma//sub t/=1.2 ps has been derived from these spectra. The market perspectives for Hilbert spectrometers have been estimated.         High-T/sub c/ bolometers with silicon-nitride spiderweb suspension for far-infrared detection    M.J.M.E. de Nivelle, M.P. Bruijn, P.A.J. de Korte, S. Sanchez, M. Elwenspoek, T. Heidenblut, B. Schwierzi, W. Michalke and E. Steinbeiss Summary: High-T/sub c/ GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(GBCO) superconducting transition edge bolometers with operating temperatures near 90 K have been made with both closed silicon-nitride membranes and patterned silicon-nitride (SiN) spiderweb-like suspension structures. As a substrate silicon-on-nitride (SON) wafers are used which are made by fusion bonding of a silicon wafer to a silicon wafer with a silicon-nitride top layer. The resulting monocrystalline silicon top layer on the silicon-nitride membranes enables the epitaxial growth of GBCO. By patterning the silicon-nitride the thermal conductance G is reduced from about 20 to 3 /spl mu/W/K. The noise of both types of bolometers is dominated by the intrinsic noise from phonon fluctuations in the thermal conductance G. The optical efficiency in the far infrared is about 75% due to a goldblack absorption layer. The noise equivalent power NEP for FIR detection is 1.8 pW//spl radic/Hz, and the detectivity D* is 5.4/spl times/10/sup 10/ cm /spl radic/Hz/W. Time constants are 0.1 and 0.6 s, for the closed membrane and the spiderweb like bolometers respectively. The effective time constant can be reduced with about a factor 3 by using voltage bias. Further reduction necessarily results in an increase of the NEP due to the 1/f noise of the superconductor.         HTS edge junction dependence on base electrode edge smoothness    J. Murduck, C.L. Pettiette-Hall, R. Hu, O. Salazar, M. McGerr, K. Daly and J. Luine Summary: A series of experiments were performed in a Taguchi experimental matrix to examine and compare critical fabrication process factors in junction electrical performance. Factors such as angle of HTS deposition by pulsed laser deposition (PLD), pre-cleaning and annealing dwell time prior to epitaxial depositions, and angle of film edges created by ion milling were examined. The most critical factor influencing junction performance was the inherent morphology and smoothness of the base electrode. Based on this we focused on improving base electrode film smoothness. Using this approach we reduced junction excess current by a factor of 5 to 10 as confirmed by subsequent wafer fabrications, improved technique was then integrated into our two-inch wafer process which incorporates automated stepping equipment providing deep sub-micron layer-to-layer alignment capability.         Interface-engineered YBCO edge junctions    B.H. Moeckly, K. Char, Yi. Huang and K.L. Merkie Summary: We have fabricated all YBCO edge junctions which do not require the deposition of an interlayer or barrier material. Rather, through appropriate high-temperature vacuum annealing and in-situ ion plasma treatments, we have modified the junction interface in such a way as to lead to reliable weak link behavior. These devices display RSJ-type I-V characteristics with excellent magnetic field modulation. I/sub c/R/sub n/ values over the range 0.5 to 3 mV and corresponding R/sub n/A values of 6/spl times/10/sup -8/ to 1.2/spl times/10/sup -9/ /spl Omega/-cm/sup 2/ at 20 K are easily attained by varying the process, which is not possible in most high-T/sub c/ junction technologies. These junctions can also be very uniform and appear to be quite stable. We have observed an unusual response to applied microwave radiation. We have investigated the microstructure of these junctions using transmission electron microscopy (TEM). Results of these analyses lead us to believe these junctions are feasible as the basic components of a high-T/sub c/ circuit technology.         High-resistance HTS edge junctions for digital circuits    B.D. Hunt, M.G. Forrester, J. Talvacchio and R.M. Young Summary: We have investigated factors affecting the resistance of edge-geometry HTS weak links, including SNS junctions with Co-doped Y-Ba-Cu-O as a normal metal interlayer. We have also studied devices with no deposited interlayer in which the weak link is produced by ion beam surface damage or by controlled disorder near the base electrode-counterelectrode interface. For each of these weak links several parameters, including the base electrode material and the deposition conditions of the normal metal and counterelectrode, are found to have strikingly large effects on device resistance. Controlling these factors has enabled the fabrication of high-quality, high-resistance (/spl ap/1 Ohm) SNS edge junctions with one-sigma I/sub c/ spreads down to 6% in 10-junction series arrays. The junctions without deposited interlayers exhibit electrical characteristics and parameter spreads approaching the best results obtained with the Co-YBCO SNS devices.         Characterization of ramp-type Josephson junctions with a Co-doped PrBaCuO barrier    J. Yoshida, S. Inoue, T. Hashimoto and T. Nagano Summary: Current transport mechanism in Go-doped PrBaCuO barriers was investigated for ramp-type junctions. The junction characteristics were extremely sensitive to a slight variation in the substrate temperature and the oxygen atmosphere during the heating process for the subsequent barrier layer deposition. Such sensitivity was related to the thermodynamic stability of YBaCuO. The conductance of junctions fabricated under the optimized conditions exhibited an exponential dependence on the barrier layer thickness at low temperatures, and the decay length was estimated to be around 1 nm. Characteristic power law dependence of junction conductance on temperature was confirmed for these junctions, indicating that resonant tunneling and hopping conduction via a small number of localized states were predominant. Clear Josephson characteristics were observed for junctions with a barrier thinner than 11 nm. We found that the experimental I/sub c/ versus barrier thickness relation was also explained well by resonant tunneling models.         Fabrication and properties of Nd-Ba-Cu-O/Pr-Ba-Cu-O/Nd-Ba-Cu-O ramp-edge junctions    G.A. Alvarez, M. Becht, T. Utagawa, K. Toma, U. Kawabe, F. Wang, Y. Li, F. Saba, M. Sato and K. Tanabe Summary: We present recent results on the fabrication process of NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO) ramp-edge junctions with a PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (PBCO) barrier by pulsed laser deposition (PLD). We also describe the fabrication of high T/sub c/ Superconductor-Normal metal Superconductor (SNS) junctions in an edge geometry with integrated ground planes and insulators. The process incorporates five layers which includes an integrated high T/sub c/ ground plane with a low /spl epsiv//sub r/ interlevel dielectric layer of CeO/sub 2/ deposited by Metal Organic Chemical Vapour Deposition (MOCVD). We have used YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) single crystals as a groundplane. It was confirmed that NBCO layers could be incorporated in the multilayer structure without substantial degradation. Process modifications necessary to reach our fabrication goals are outlined.         Development of ramp-edge SNS junctions using highly stable normal-metal barrier materials    Q.X. Jia, Y. Fan, C. Kwon, C. Mombourquette, D. Reagor, R. Cantor, J.P. Zhou, Y. Gim, C. Jones, J.T. McDevitt and J.B. Goodenough Summary: By using a cation-modified and corrosion-resistant compound of (Pr/sub y/Gd/sub 0.6-y/)Ca/sub 0.4/Ba/sub 1.6/La/sub 0.4/Cu/sub 3/O/sub 7/ (y=0.4, 0.5, and 0.6) as normal-metal barrier materials, high-temperature superconducting Josephson junctions have been fabricated in a ramp-edge superconductor/normal-metal/superconductor (SNS) configuration. We have tuned the Pr substitution level in order to achieve the optimal electrical resistivity of the barrier layer for high-performance SNS junctions. The junctions fabricated with these normal-metal barriers show well-defined RSJ-like current vs voltage characteristics at liquid-nitrogen temperature. The junction performance is mainly controlled by the N-layer instead of the interface. We have also fabricated dc superconducting quantum interference devices based on ramp-edge SNS technology with these normal-metal barriers. The ratio of peak-to-peak voltage modulation of the superconducting quantum interference devices to the I/sub c/R/sub n/ product is more than 30%.         Systematic investigation of ramp edge junction using Ca-doped and Ga-doped PBCO barrier    M. Horibe, N. Hayashi, K.-I. Kawai, M. Maruyama, A. Fujimaki and H. Hayakawa Summary: We have investigated systematically the characteristics of ramp edge junctions with Ca- and Ga-doped PBCO barriers. The localized state density g and/or the volume of the state v in the barriers are increased by Ca-doping and decreased by Ga-doping. Ca-doping reduces the I/sub c/R/sub n/ products, and Ga-doping enhances the I/sub c/R/sub n/ products, though the dominant transport mechanisms are direct tunneling for the junctions having I/sub c/R/sub n/ greater than 1 mV. The change in the I/sub c/R/sub n/ products can be interpreted in terms of the proximity effect at the interface states formed by hybridization between the localized states in the barrier and conduction electron states of electrodes. The ideal superconductor-insulator interface at the junction interfaces is required to enhance I/sub c/R/sub n/ products.         Long term stability of YBCO-based Josephson junctions    L.R. Vale, R.H. Ono, J. Talvacchio, M.G. Forrester, B.D. Hunt, M.S. Dilorio, K.-Y. Yang and S. Yoshizumi Summary: We report on a study of long term aging in three different types of YBa/sub 2/Cu/sub 3/O/sub 7-x/ Josephson junctions. Junction aging will affect the choices made in integrating this technology with actual applications. The junction types used in this study are (a) Co-doped barrier edge SNS junctions, (b) noble-metal SNS step-edge junctions, and (c) bicrystal junctions which are either unpassivated or passivated in situ with a normal metal shunt or an epitaxial insulator. While all the junctions show degradation, for some the long term survival rate is encouraging.         Operation of HTS dc-SQUID sensors in high magnetic fields    M.I. Faley, U. Poppe, K. Urban, E. Zimmermann, W. Glaas, H. Halling, M. Bick, H.-J. Krause, D.N. Paulson, T. Starr and R.L. Fagaly Summary: For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson junctions, HTS films prepared at optimized conditions with a high oxygen pressure dc-sputtering technique, a capsulation with a heater, and a proper dc-SQUID layouts. DC-SQUIDs tested in magnetic fields up to about 1 kG demonstrate no reduction of the critical current. A model is proposed, which gives a satisfactory explanation of the experimental results. With the use of a digital feedback a dynamic range of about 160 dB was achieved. Highly sensitive devices were prepared with flip-chip flux antennas. For the magnetometers a resolution of about 40 fT//spl radic/Hz was obtained in unshielded environment.         Low-noise Y-Ba-Cu-O flip-chip dc SQUID magnetometers    J. Ramos, A. Chwala, R. Ijsselsteijn, R. Stolz, V. Zakosarenko, V. Schultze, H.E. Hoenig, H.-G. Meyer, J. Beyer and D. Drung Summary: We have prepared low-noise flip-chip SQUID magnetometers by using dc SQUIDs with large flux-to-voltage transfer functions and superconducting flux transformers. The dc SQUIDs have a square washer geometry and are prepared on a SrTiO/sub 3/ bicrystal substrate with a misorientation angle of 30/spl deg/. The maximum peak-to-peak flux modulated voltage varies typically between 20 and 60 /spl mu/V for a SQUID inductance of 80 pH. The YBa/sub 2/Cu/sub 3/O/sub 7-x/ flux transformers are prepared on a SrTiO/sub 3/ single crystal polished on both sides. The preparation process of the flux transformers involves the deposition of YBCO and SrTiO/sub 3/ layers by pulsed laser ablation and pattern definition by ion beam etching. The flip-chip magnetometers are encapsulated and robust to temperature cycling. We operate the magnetometers in magnetically shielded and in unshielded environment by using a direct-coupled read-out electronics. The field sensitivity of the magnetometers is equal to 2.2 nT//spl Phi//sub 0/. The field resolution of the magnetometers is typically <40 fT/Hz/sup 1/2/ at 1 kHz and about 100 fT/Hz/sup 1/2/ at 1 Hz inside shielding. The suitability of these devices for geophysical applications is shown by Transient Electromagnetics measurements.         Operation of rf SQUID magnetometers with a multi-turn flux transformer integrated with a superconducting labyrinth resonator    Y. Zhang, H.R. Yi, J. Schubert, W. Zander, H.-J. Krause, H. Bousack and A.I. Braginski Summary: This paper demonstrates a design of a planar multi-turn flux transformer integrated with a superconducting labyrinth resonator serving as the planar tank circuit for a radio frequency (rf) superconducting quantum interference device (SQUID) magnetometer. All structures were patterned from 200 nm-thick epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films grown on 10/spl times/10 mm/sup 2/ LaAlO/sub 3/ substrates. A double-hole washer SQUID had one hole coupled to the input coil of the labyrinth resonator and the other hole coupled to the input coil of the multi-turn flux transformer using a flip-chip configuration to form a magnetometer. This resonator has a good high-frequency coupling to the double-hole rf SQUID, thus securing its optimum operation. For the voltage-to-flux (transfer function) coefficient, a value of 300-500 /spl mu/V//spl Phi//sub 0/ was obtained. A SQUID magnetometer with an inductance of 210 pH exhibited white flux noise of 11.5 /spl mu//spl Phi//sub 0///spl radic/Hz at 77 K. This corresponded to a white magnetic field noise of 11.5 fT//spl radic/Hz.         Noise properties of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junction array magnetometers    S. Krey, O. Brugmann, H. Burkhardt and M. Schilling Summary: We have fabricated magnetometers based on the magnetic field dependence of the critical current of 24/spl deg/ bicrystal Josephson junctions from the high temperature superconductor (HTS) YBa/sub 2/Cu/sub 3/O/sub 7/. The field sensitivity is increased with additional flux focusers up to /spl part/I/sub c///spl part/B=130 A/T. Because the voltage modulation and signal-to-noise ratio increases with the number of junctions, serial arrays of up to 105 junctions are employed. At 77 K we obtain a transfer function of /spl part/V//spl part/B=7500 V/T and a white noise level of /spl radic/S/sub B/=1.2pT//spl radic/Hz for the largest array. The 1/f noise component from critical current fluctuations in the junctions is suppressible by a simple flux modulation scheme.         Mechanisms controlling interface-properties in high-T/sub c/ superconductors    H. Hilgenkamp and J. Mannhart Summary: Influences of the predominant d(x/sup 2/-y/sup 2/)-symmetry of the order parameter and of bending of the electronic band structure on the superconducting and normal state transport characteristics of interfaces involving high-T/sub c/ superconductors are discussed. It will be shown that these generic properties of the high-T/sub c/ cuprates are important factors for many characteristic aspects of interfaces in these materials, such as the angular dependencies of the critical current density, the normal state resistivity and consequently the I/sub c/R/sub n/-product of grain boundaries, the comparatively large contact-resistances between superconductors and normal-metals, and the small values of the Stewart-McCumber parameter /spl beta//sub c/ leading to the overdamped current-voltage characteristics.         Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ bicrystal grain boundary Josephson junctions    U. Schoop, S. Kleefisch, S. Meyer, A. Marx, L. Alff, R. Gross, M. Naito and H. Sato Summary: The study of the detailed influence of the order parameter (OP) symmetry on the properties of high temperature superconducting (HTS) Josephson junctions still is a key issue. Whereas the hole doped HTS such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO), or La/sub 1.85/Sr/sub 0.15/CuO/sub 4-/spl delta// (LSCO) are known to have a dominating d-wave component of the OP, there is significant evidence that the electron doped material Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ (NCCO) has an s-wave symmetry of the OP. Therefore, we have studied the electrical transport properties of [001] tilt NCCO bicrystal grain boundary Josephson junctions (GBJs) with misorientation angles between 7/spl deg/ and 36.8/spl deg/ and compared them to those of the hole doped HTS. For the NCCO-GBJs an exponential decay of the critical current density J/sub c/ with increasing misorientation angle as well as a scaling of the characteristic junction voltage V/sub c//spl prop/J/sub c//sup p/ was found very similar to what is observed for the hole doped HTS. This strongly suggests that the OP symmetry is not the key parameter controlling the characteristic properties of HTS-GBJs. In contrast, they are most likely related to the presence of a disorder induced, insulating grain boundary barrier which is similar for both the d- and s-wave HTS.         Microstructural defects in bicrystal substrates and their influence on yttrium barium copper oxide grain boundary Josephson junctions    J.W.P. Hsu, E.B. McDaniel, A.L. Campillo, S.C. Gausepohl, M. Lee, R.A. Rao and C.B. Eom Summary: Using a near-field scanning optical microscope (NSOM), we found non-uniformly distributed microstructural defects near the fusion boundary of bicrystal substrates. These defects depict themselves as circular dark spots in the optical transmission images. We attribute these optical features to near-surface voids at the boundary previously found in transmission electron microscopy studies. Our results show a direct link between the presence of these defects and the superconducting properties of the YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) grain boundary Josephson junctions (GBJJs). We find that junctions that are fabricated over highly defected regions of the bicrystal substrates have lower critical temperatures and currents. The positions of defects across a junction also play a role in determine the device characteristics. Strain fields associated with these defects are most likely responsible for affecting YBCO film growth locally and junction performance. We employ an NSOM to survey these microstructural defects in bicrystals of various tilt angles and of different materials that are commonly used for fabrication of YBCO GBJJs. We find that these defects and their strain fields are the result of the bicrystal fusion process and are not intrinsic to the materials.         Interactions between bicrystal Josephson junctions in a multilayer structure    H.Q. Li, R.H. Ono, L.R. Vale, D.A. Rudman and S.H. Liou Summary: We have fabricate and studied a variety of devices based on stacked YBa/sub 2/Cu/sub 3/O/sub x/ bicrystal Josephson junctions in a multilayer structure. The proximity of the junctions in the two layers produces a large number of effects based on interactions between the junctions. Voltage locking and current locking were observed in the stacked junctions. The voltage locking is due to the ac path provided by a SrTiO/sub 3/ layer between the stacked junctions. The current locking is likely the result of a Josephson vortex interaction.         Design and performance of a velocity-matched broadband optical modulator with superconducting electrodes    K. Yoshida, T. Uchida, S. Nishioka, Y. Kanda and S. Kohjiro Summary: The performance of a LiNbO/sub 3/ optical modulator employing superconducting electrodes as a transmission line for a traveling-wave signal has been studied theoretically as well as experimentally. In the case of velocity matching between signal and optical waves using a shielding plane on top of a coplanar waveguide, numerical calculations of the attenuation constants of both superconducting and normal-conducting transmission lines indicate that the performance of the optical modulator can be far superior to that using normal-metals with respect to the figure of merit of bandwidth/driving-voltage. Microwave operation of a velocity-matched traveling-wave-type optical modulator with superconductor electrodes (NbN) has been successfully demonstrated. In the frequency range between dc and 26.5 [GHz] it is shown that the obtained modulation depth is in good agreement with the theoretically expected one.         Measurements of YBCO parametric amplifiers    J. Luine, A.D. Smith, A. Sun, E. Dantsker and K. Daly Summary: For applications where extremely low-noise amplifiers are demanded, RF SQUID parametric amplifiers offer significant capabilities. We present results on the first RF SQUID parametric amplifiers (paramp) fabricated using TRW's YBCO integrated circuit process technology. TRW's paramps consist of thousands of RF SQUIDs distributed along and coupled to /spl sim/7 cm coplanar transmission lines. We demonstrate two important paramp functions: adjustable true time delay of RF signals and frequency upconversion of 0 to 1 GHz base band signals to side bands of the /spl sim/10 GHz pump. When the input and output impedances are different the correct figure of merit is upconversion transimpedance gain, shown to be proportional to pump frequency and independent of base band frequency, thereby providing wide band signal amplification. Finally, the spur-free dynamic range for these first paramps is inferred from measurement and modeling to be /spl sim/82 dB-/spl radic/Hz.         Current noise of contacts to YBa/sub 2/Cu/sub 3/O/sub 7/ high T/sub c/ superconducting platelets through the transition region    Yuping Chen, G.L. Larkins Jr., C.M. Van Vliet and Y. Vlasov Summary: We describe noise measurements in the frequency range 10 Hz-1 MHz on indium contacts to YBCO layers with a LaAlO/sub 3/ substrate. The spectra are of the 1/f/sup /spl alpha// type with /spl alpha/=1.2 above T/sub c/ and 1.15 below T/sub c/. Above T/sub c/ there is burst noise, although the averaged spectra are stable and reproducible, The voltage noise versus temperature, for a fixed current, shows a sharp dip at the transition temperature T/sub c/=85 K, but is otherwise largely constant. The normalized noise S/sub v//V/sup 2/ goes as [R(T)]/sup -2/, which is indicative for 1D switching-percolation noise ("p-noise"), predicted previously, but not hitherto observed. This noise is of importance for low-frequency superconducting devices, such as bolometers and pyroelectric detectors, and for microwave devices where mixing with a carrier occurs. Current models of high T/sub c/ conductance-noise are reviewed and discussed.         Investigation of coaxial cable properties for HTS filters    H. Takeuchi and Y. Kubota Summary: To decrease thermal leakage in coaxial cables, we have developed a novel coaxial cable for HTS filters. We call it the "thin outer conductor coaxial cable". The outer conductor of this new cable was made of copper film and was designed to have an optimum thickness of 0.005 mm by the simulation and experimentation of thermal and electrical performance. Coaxial cables that are 1.68 mm in diameter and 90 mm in length have an insertion loss of 0.17 dB at 2.0 GHz. Impedance analysis of the connector joint was evaluated with TDR, and we obtained results for detailed explanations of breakdown in electrical performance. The coaxial cable was tested for low temperature properties and underwent the heat cycle test; however, performance deterioration could not be found.         Preparation of ramp-edge Josephson junctions with natural barriers    A. Fujimaki, K. Kawai, N. Hayashi, M. Horibe, M. Maruyama and H. Hayakawa Summary: We have demonstrated ramp-edge Josephson junctions using high temperature superconductors without depositing artificial barriers. We use a surface barrier formed naturally during an etching process by an Ar ion beam. The resistivity of the barrier, which is evaluated in the Nb/Au/YBCO structures, changes over 4 orders in accordance with the gas pressure in the vacuum annealing executed before the deposition of the counter-electrode. All the junctions having YBCO/barrier/YBCO structure exhibit RSJ-like current-voltage characteristics over the entire temperature range of operation. Fraunhofer-like modulation patterns are observed with a very small amount of excess current even at low temperatures except for large junctions. The temperature dependence of J/sub c/ and R/sub u/A are similar to those in HTS grain boundary junctions. Since the junction parameters are controlled by the total pressure during the vacuum annealing, the junctions made through this procedure have a potential for circuit applications.         Fabrication of YBa/sub 2/Cu/sub 3/O/sub 7/ ramp-type junctions by interface treatments    R. Dittmann, J.-K. Heinsohn, A.I. Braginski and C.L. Jia Summary: We have investigated ramp-type junctions with barriers fabricated by interface treatments instead of epitaxially grown barrier layers. In our approach, YBa/sub 2/Cu/sub 3/O/sub 7/ ramps were treated with Ar ions in a Kaufmann-type source and subsequently annealed prior to the deposition of the top electrode. The I-V curves of the junctions as well as the power dependence of the Shapiro step height can be well described by the RSJ-model. At 77 K the critical current density is 10 kA/cm/sup 2/, and the critical voltage is about 30 /spl mu/V. The strong modulation of the critical current with external magnetic field indicates the formation of a homogeneous barrier layer at the interface. The temperature dependence of critical current and normal resistance suggests a metallic barrier as interface layer.         Properties of rough interfaces in superconductors with d-wave pairing    A. Golubov and M.Yu. Kupriyanov Summary: Theoretical model of a rough interface in a superconductor with d-wave symmetry of the order parameter is proposed. The surface roughness is introduced by means of a surface layer with small electronic mean free path. The proximity effect between such a layer and a bulk d-wave superconductor is studied theoretically in the framework of the quasiclassical Eilenberger theory. It is shown that as a result of strong scattering in the interlayer the d-wave component of the order parameter near the interface is reduced while the s-wave component localized near the interface is generated. Angular and spatial structure of the pair potential and the electronic density of states near the interface is calculated. The interplay of the zero-energy (midgap) and finite-energy bound states leads to peculiarities in the energy dependence of the angle-averaged density of states. We argue that the model is relevant for the description of rough interfaces in high T/sub c/ superconductors. In the framework of the present approach we calculate the Josephson critical current for several types of junctions with rough interfaces.         Fabrication of YBaCuO wiring for YBaCuO trilayer junctions    H. Sato, H. Akoh, T. Onizawa, K. Hohkawa, A. Tomioka and U. Kawabe Summary: We have investigated the advancement of the trilayer junction fabrication process toward the YBaCuO/PrBaCuO/YBaCuO trilayer junctions with the YBaCuO wiring layers. Run-to-run variation of J/sub c/ was obtained to be factor three for the YBaCuO junctions with Au wiring layer on the two substrates. We found that c-axis oriented YBaCuO films with T/sub c/ of 85 K were developed on an [110] SrTiO/sub 3/ substrates with CeO/sub 2//MgO buffer layers. From these results, we have attempted to fabricate YBaCuO trilayer junctions with the YBaCuO wiring layer.         BaTbO/sub 3/ as a new material for insulation and junction barriers in High-T/sub c/ devices    U. Poppe, R. Hojczyk, C.L. Jia, M.I. Faley, W. Evers, F. Bobba, K. Urban, C. Horstmann, R. Dittmann, U. Breuer and H. Holzbrecher Summary: It is shown that BaTbO/sub 3/ has a high degree of chemical and structural compatibility with YBa/sub 2/Cu/sub 3/O/sub 7/ and that this new material has many properties beneficial for different device applications. The growth morphology of several YBa/sub 2/Cu/sub 3/O/sub 7//BaTbO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ multilayer films was investigated by high-resolution transmission electron microscopy (HRTEM). Depending on the deposition temperature two types of interface between YBa/sub 2/Cu/sub 3/O/sub 7/ and BaTbO/sub 3/ were found. At relatively high deposition temperatures the misfit strain is mainly restricted to a narrow (smaller 1 nm) interface layer, whereas at lower temperature a semi coherent interface with well-localized misfit dislocations was observed. By /sup 18/O//sup 16/O tracer experiments it was shown that significant oxygen diffusion in a BaTbO/sub 3/ layer is possible at temperatures below 500/spl deg/C. The diffusion rate is much higher than in conventionally used insulators like e.g. SrTiO/sub 3/ and even higher than in YBa/sub 2/Cu/sub 3/O/sub 7/. Insulating properties of BaTbO/sub 3/ were successfully tested for crossovers in multilayer devices. Furthermore field effect devices and Josephson junctions using BaTbO/sub 3/ as dielectric or barrier material have been investigated. The ramp-type Josephson junctions included chemically as well as ion beam etched ramp-edges. In both cases the normal resistance decreases with decreasing temperature for a barrier thickness of 10 nm. For chemically etched junctions well defined Shapiro steps and characteristic voltage of about 0.2 mV at 77 K were observed.         Improvement of the sandwich junction properties by planarization of YBCO films    M. Maruyama, K. Yoshida, M. Horibe, A. Fujimaki and H. Hayakawa Summary: We have improved the properties of c-axis-oriented YBCO/PBCO/YBCO trilayer junctions using planarization of YBCO films. The root-mean-square value of the film roughness reduces to less than 60% of that of an as-grown film. The junctions made through the planarization exhibit RSJ-like current-voltage characteristics even for 20-nm-thick PBCO interlayers. The characteristic voltage is 0.16 mV at 50 K, which is remarkably improved compared to that of junctions without the planarization.         Fabrication and characterization of high quality NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///Sr/sub 2/AlTaO/sub 6//NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///Sr    Yijie Li, F.M. Saba, J.G. Wen and K. Tanabe Summary: High quality epitaxial Sr/sub 2/AlTaO/sub 6/ (SAT) and Sr/sub 2/AlNbO/sub 6/ (SAN) insulator films as well as the related trilayers of NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO)/SAT/NBCO and NBCO/SAN/NBCO have been successfully grown on SrTiO/sub 3/ [100], LaAlO/sub 3/ [100], and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(YBCO) [001] single crystal substrates by pulsed laser deposition (PLD). The top and bottom NBCO layers have a T/sub c/0 of 87-90 K and J/sub c/>10/sup 6/ A/cm/sup 2/ at 77 K, measured by four-probe and dc magnetization methods. X-ray diffraction and transmission electron microscopy analyses reveal that the deposited trilayers have an all-epitaxial structure and abrupt interface without interdiffusion. We also measured the dielectric properties of SAT layers using the patterned structures on YBCO [001] single crystal substrates. Our results show that SAT and SAN can be used as insulator layers on YBCO single crystal substrate in high-T/sub c/ superconducting multilayer processing including NBCO films.         Improvement of SrTiO/sub 3/ thin film surface polished by chemical mechanical planarization for HTS multilayer device    H. Takashima, N. Terada and M. Koyanagi Summary: In order to improve the superconducting and insulation properties of the HTS multilayer structure, we have introduced Chemical Mechanical Planarization (CMP) into the fabrication process. While the surface roughness of the upper SrTiO/sub 3/ (STO) film due to the precipitates on the base YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) film was decreased less than 1/10 by CMP and those of the edge angle of the patterned base films was reduced from 90 to less than 1 degree, the as-polished surface crystallinity was amorphous as observed by RHEED. For improvement of the crystallinity, the surface was annealed to show pattern with clear streaky spots. The top YBCO stripline in the crossover structures had a T/sub c/ of 89 K and J/sub c/ of more than 1.0/spl times/10/sup 6/ A/cm/sup 2/ at 77 K. The insulation resistivity between two YBCO layers at 77 K was 7/spl times/10/sup 8/ /spl Omega/cm.         Josephson junctions with hysteretic current voltage characteristics at high temperatures    P.F. McBrien, R.H. Hadfield, W.E. Booij, A. Moya, M.G. Blamire, E.J. Tarte, J. Clark and C.M. Pegrum Summary: The properties of bicrystal Josephson junctions with external capacitors are reported. It was found that the hysteresis in the current voltage (IV) characteristic was very sensitive to the wavelength of the Josephson oscillation in the dielectric and thermal noise suppression of the critical current. A McCumber parameter /spl beta//sub c/ of 1.2 at 65 K has been achieved. In addition intrinsic grain boundary capacitance has been found to give a large /spl beta//sub c/ value of 9.6 at 4.2 K.         Effects of capacitive shunt on the current-voltage characteristics of high T/sub c/ Josephson junctions    Soon-Gul Lee, Yunseok Hwang and Yunsung Huh Summary: We have studied hysteresis of the grain boundary YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions with Au film shunt capacitors. The capacitive shunt clearly developed hysteresis in the current-voltage curves of the junctions. However, the McCumber parameter /spl beta//sub c/, obtained from data was much smaller than the calculated values. The reason is believed to be due to the fact that the capacitive reactance was dominated by the kinetic inductance of the bridge and the series resistance of the Au film connecting the two capacitors structured on both sides of the electrodes. Using a superconducting capacitor built directly on the bridge will enhance the hysteresis. More study is needed on the inductive shunt in the junction.         Automation of SQUlD nondestructive evaluation of steel plates by neural networks    C. Hall Barbosa, A.C. Bruno, M. Vellasco, M. Pacheco, J.P. Wikswo Jr. and A.P. Ewing Summary: This paper presents a method for automation of SQUID nondestructive evaluation (NDE) using neural networks, exempting the need for a trained technician, necessary to most of the usual NDE methods. An LTS-SQUID susceptometer, with a 16 mm diameter planar concentric gradiometer, was used to image flaws in steel samples from the bottom of an oil storage tank. Natural and artificial corrosion pits of various sizes were present in the samples, and a vertical magnetic field of 0.5 mT was applied by a superconducting magnet concentric with the gradiometer coils. A finite element model was used to simulate the magnetic signals due to the flaws, yielding training sets for the artificial neural networks. A neural system composed of two cascaded networks was developed to preprocess and analyze the magnetic signals. The first network removes a distortion that occurs in the experimental magnetic signal, and the second network detects the presence of flaws, and also assesses their severity. The trained neural networks were successfully tested with the experimental data obtained with the SQUID system.         The bulk high-Tc superconducting fluxgatemeter for nondestructive evaluation    M. Miyazaki, H. Nakane and H. Adachi Summary: A high-T/sub c/ superconductive fluxgate magnetic sensor utilizing sintered YBa/sub 2/Cu/sub 3/O/sub 7-x/ core is constructed and applied to detect a flaw in an aluminum plate. The magnetic sensor successfully works in an unshielded environment. An electric current was supplied to an aluminum plate directly. A slit (0.2 mm width, 30 mm length), which is considered as a flaw, on an aluminum plate is successfully detected with this sensor, even though the slit is covered with another aluminum plate. The sensor can detect the flaw with its direction perpendicular to the electric current in the sample. It's supposed that the sensor can determine the length of the flaw larger than the diameter of the detection coil. These results suggest that the sensor has a potential for nondestructive evaluation of non-magnetic metals such as aluminum alloys, and also for their multi-layered structures.         Development of an electromagnetic microscope using HTS SQUIDs    W.N. Podney Summary: Superconductive quantum interference devices (SQUIDS) offer new technology for eddy current evaluation of materials. Their high resolution at low frequencies enables arrays of small pickup loops that can give images of millimeter fatigue cracks, corrosion, and inclusions deep inside materials and structures, nondestructively. High temperature superconductors can bring the arrays into common use. They enable packaging them in a hand-held, refrigerated instrument, without cryogenic encumbrances. The instrument would be a hand held, electromagnetic microscope for eddy current evaluation of materials.         Low input coil inductance SQUIDs for cryogenic current comparator applications    J. Sese, A. Camon, C. Rillio, M.G.H. Hiddink, L. Vargas, M.J. van Duuren, G.C.S. Brons, J. Flokstra, H. Rogalla and G. Rietveld Summary: Dc SQUIDs with an optimal input coil inductance have been developed for a Cryogenic Current Comparator (CCC) that is used for the calibration of electrical standards. We studied a series of SQUIDs with input inductances in the range from 20-160 nH. The electrical properties like input current noise and flux to voltage transfer have been investigated. The CCC is an overlapping tube configuration and the tube itself is used as the pick-up coil of the flux transformer circuit of the SQUID. The coupling between CCC and flux transformer is in this case ideal and should have an optimal value when the effective overlapping tube inductance, typically in the range from 10-100 nH, equals that of the SQUID input coil (flux transformer theory). To compare with theory, sensitivity measurements on the SQUID-CCC have been performed in a special set-up where the effective overlapping tube inductance can be modified placing the CCC in a superconducting shield at various distances.         Micro-imaging system using scanning DC-SQUID microscope    T. Morooka, S. Nakayama, A. Odawara, M. Ikeda, S. Tanaka and K. Chinone Summary: A micro-imaging system in a low temperature environment has been developed for the study of superconducting films and magnetic films and for the inspection of superconducting integrated circuits. The system consists of a micro DC-SQUID, a cryostat, a precise scanning stage, and a computer. Two different types of micro DC-SQUIDs were designed. One was a magnetometer (Bz) with a one-turn pick-up coil with a diameter of 10 /spl mu/m, and the other was a gradiometer (dBz/dx) with a planar first-order derivative pick-up coil. Each micro DC-SQUID was integrated on a 3 mm /spl times/3 mm Si chip using thin Nb film fabrication technology. Preliminary experiments were made using the system and several magnetic images were obtained. We present observations of a thin superconducting Nb film pattern by applying the Meissner screening and the magnetic domains of a thin garnet ((YBi)/sub 3/(FeAl)/sub 5/O/sub 12/) film.         A SQUID picovoltmeter working at 77 K    T. Eriksson, J. Blomgren, D. Winkler, T. Holst and Y.Q. Shen Summary: A SQUID picovoltmeter working at 77 K has been constructed with a bandwidth of 37 kHz. The white noise of the picovoltmeter was 32 pV//spl radic/Hz with the input shorted. For an optimal source resistance of 0.8 /spl Omega/ the noise temperature was 46 K. The picovoltmeter was constructed from a multilayer high-T/sub c/ SQUID-magnetometer coupled to the signal source via a 10-turn copper coil. The mutual inductance between the coil and the SQUID washer was 0.7 nH. To reduce the noise contributions of the first-stage room temperature amplifier, additional positive feedback (APF) was used together with direct read-out electronics. As a demonstration, the current-voltage characteristics of another SQUID was measured with the picovoltmeter.         Experimental and numerical results of electromagnetic nondestructive testing with HTc SQUIDS    A. Ruosi, G. Pepe, G. Peluso, M. Valentino and V. Monebhurrun Summary: We present here recent results on detection of surface and subsurface artificial features in Al-Ti planar structures, to show current performance of our eddy-current nondestructive evaluation system based on HTc SQUIDs. The anomalous magnetic fields generated by flaws with known electromagnetic characteristics have been modeled by three-dimensional codes based on finite element method and volume integral formulation and developed for the investigated problem. Both numerical solutions have correctly predicted the shape of the complicated magnetic field response which is mainly the result of the shape of the defect, the geometry of the inducing coil and the characteristics of the SQUID gradiometer.         SQUID microsusceptometry in applied magnetic fields    L.R. Narashimhan, C.K.N. Patel and M.B. Ketchen Summary: We describe the design and construction of a planar dc SQUID susceptometer to characterize microcrystallites as a function of temperature from 0.3 K to 4 K in magnetic fields exceeding 280 G. Eliminating the need for magnetic shielding permits broader application of SQUIDs to characterization of small spin ensembles. We present temperature- and field-dependent magnetic susceptibility data on crystallites mounted directly on the surface of a SQUID chip. Large, in-plane static fields are applied through an external coil while perpendicular fields up to 2 G can be applied by a series-wound on-chip field coil. Paramagnetic, antiferromagnetic, and superconducting transitions have been resolved on samples of order 20 to 50 /spl mu/m (30 to 500 picomoles, /spl sim/5/spl times/10/sup 16/ emu/Hz/sup 1/2/.) We discuss the effects of sample shape and location on the spin calibration of the assembled susceptometer.         Ultralow temperature SQUIDs for primary thermometry    S.L. Thomasson and C.M. Gould Summary: We have designed and constructed a primary thermometry system for operation from 4.2 K to temperatures well below 0.65 K, the bottom of the International Temperature Scale (ITS-90). The system is composed of a thin-film resistive-SQUID (R-SQUID) and a dc SQUID readout amplifier fully integrated on a single chip. We have fabricated our SQUIDs using Ti/Pd/Au shunt resistors, which remain normal conductive down to mK temperatures. Thermal and electrical constraints demand that the readout amplifier to the R-SQUID has a low system noise. We used a dc SQUID series array in a direct readout flux-locked loop scheme to achieve a system bandwidth in excess of 1 MHz with a white noise level less than 1 /spl mu//spl Phi//sub 0///spl radic/Hz.         Design of high resolution HTS-SQUID magnetometers for biomagnetic imaging    A. Moya, F. Baudenbacher, J.P. Wikswo Jr. and F.C. Wellstood Summary: To image the magnetic fields produced by action, injury and development currents in isolated living tissue or small animal preparations one requires a field sensitivity of a few hundred fT//spl radic/Hz together with a sub-millimeter spatial resolution. The design constraints of HTS bicrystal SQUID magnetometers with sub-millimeter resolution are analyzed in order to maximize field sensitivity. The desired combination of sensitivity and spatial resolution can be achieved by a multiloop magnetometer of 600 /spl mu/m in diameter. The authors' calculations predict a magnetic field sensitivity of 120 fTHz/sup -1/2/ for sensors with more than five loops. Decreasing the sensor size to 300 /spl mu/m results in a field sensitivity of 320 fTHz/sup -1/2/ requiring four loops.         Three-dimensional network of inductively coupled Josephson junctions as a vectorial magnetic field sensor    T. Di Matteo, J. Paasi, A. Tuohimaa and R. De Luca Summary: We study the response of a current biased three-dimensional cubic network of inductively coupled Josephson junctions for different directions of the applied magnetic field by means of numerical simulations. We discuss the feasibility of these systems to be used as sensitive vectorial magnetic field sensors.         Depinning of single vortices in niobium thin film dc supercond interference devices by rf demagnetisation    J. Gail, M. Muck and C. Heiden Summary: To test the influence of an rf magnetic field on pinning and depinning of single vortices in thin niobium films we prepared dc SQUIDs with a square loop of 1 /spl mu/m line width and a hole size of 20 /spl mu/m/spl times/20 /spl mu/m. On one side the niobium strip widens to an area of 5 /spl mu/m/spl times/5 /spl mu/m, which is large enough for the pinning of at least one vortex. The motion of the trapped vortices from one pinning site to another generates flux changes in the SQUID loop and can thus be detected by the SQUID. We report on measurements of two level fluctuations caused by vortices hopping between different pinning sites. The investigations were made in a temperature range from 2.8 K to 4.5 K. By measuring the time, for which a vortex remains in one of the pinning sites, one can deduce the difference of the pinning energies and the activation energy for hopping between the pinning sites. By the use of a high frequency demagnetisation process the vortex can be forced to change the pinning site or to leave the superconductor, depending on the power and the frequency of the rf field.         Flux/voltage calibration of axial SQUID gradiometers using an optimization procedure    C. Hall Barbosa, E. Andrade Lima, A.C. Bruno, A.P. Ewing and J.P. Wikswo Jr. Summary: A straightforward experimental procedure for calibration of axial SQUID gradiometers has been developed, based on numerical optimization techniques. A dc current carrying wire of finite length, whose magnetic field spatial distribution is well known, was scanned by a SQUID system at several lift-off distances. Initially, theoretical magnetic field parameters such as lift-off and scanning tilt angles were numerically optimized in order to match the normalized shapes of experimental and theoretical signals. After that, the calibration factor can be easily found as the ratio between the two non-normalized signals. Once the calibration factor was obtained, an experimental validation was made by using a current-carrying copper sheet and by comparing the calibrated experimental signal with a model prediction, leading to good results. The overall procedure is easily implemented and can be modified to account for different SQUID systems and gradiometer geometry.         SQUID gradiometer measurement system for magnetorelaxometry in a disturbed environment    J. Schambach, L. Warzemann, P. Weber, R. Kotitz and W. Weitschies Summary: A SQUID measurement system for magneto-relaxometry (MRX) in disturbed environment is presented. It was developed for the determination of the distribution of magnetic nanoparticles in large objects like animals. The system is based on a thin film LTS SQUID gradiometer with a baseline of 5 mm and a field gradient sensitivity of about 30 fT/cmHz/sup 1/2/. The entire system is PC-controlled and includes a nonmagnetic x-y stage. A Helmholtz coil of 80 cm diameter allows the magnetization of the samples with fields up to 7 mT. First measurements in a disturbed environment are presented.         Subpicosecond measurements of the response of Josephson transmission lines to large current pulses    M. Currie, R. Sobolewski and T.Y. Hsiang Summary: Josephson transmission lines (JTLs) are commonly used as signal interconnects in single-flux quantum (SFQ) circuits. They are also used, however, to transform arbitrary waveforms into SFQ pulses. Here we use a low-temperature electro-optic sampling system with subpicosecond resolution to observe the response of a JTL to a picosecond input pulse. Previously, this system has been used to directly observe SFQ pulses on niobium transmission lines. In our experiment, niobium metal semiconductor-metal (MSM) photodiodes were connected to 3, 4, 19, and 20-stage JTLs. The MSM photodiodes provided picosecond pulses to excite the JTL. The JTL bias and input pulse amplitude were varied to observe fluxon interaction and time delay of the JTL stages. Observed JTL behavior is dominated by dipolar oscillations radiated from the first stages of the JTL. By varying the values of line inductance and junction capacitance, thus changing the oscillation periods, these oscillations were traced to the coupling of the junction capacitance and line inductance. This is a new feature of the JTL that has thus far not been observed or incorporated into simulations. Our results could have significant implications on the limit of SFQ circuits.         Delay insensitive RSFQ circuits with zero static power dissipation    S. Polonsky Summary: Total power dissipation in RSFQ circuits consists of two parts, dynamic and static. Dynamic power is dissipated in Josephson junctions performing useful logical and data transmission operations. This dissipation is fundamental and proportional to the data rate (at 4 K, of the order of 10/sup -18/ Joule per bit). Static power is dissipated in resistors used by RSFQ circuits to distribute dc bias current between Josephson junctions. This part of dissipation is not intrinsic to RSFQ circuits and in principle can be eliminated. The goal of this work is to show that Delay Insensitive (DI) RSFQ primitives can be modified so that resistors are no longer required in the dc power supply distribution network, so that the on-chip static power dissipation is absent. In this report we present the schematics for such primitives, define the class of circuits that allow resistor-free current distribution network, and formulate the requirements to the design of this network.         Pulse jitter and timing errors in RSFQ circuits    A.V. Rylyakov and K.K. Likharev Summary: We have carried out measurements of bit error rate (BER) of Rapid Single-Flux-Quantum (RSFQ) XOR gates with various nominal dc power supply voltages (from 0.1 V to 1.0 mV), operating at speeds up to 25 GHz. (For these gates, implemented using HYPRES' standard, 3.5-/spl mu/m, 10 /spl mu/A//spl mu/m/sup 2/ Nb-trilayer process, this speed is close to maximum.) A special on-chip RSFQ test circuit allowed high-speed measurements of BER in the range from 10/sup -9/ to 10/sup -13/ to be carried out. As a result of these experiments, a new type of thermal-fluctuation-induced digital errors in RSFQ circuits has been identified. These "timing" errors arise at high speed due to time jitter of data and clock pulses. We have developed a simple theory of these errors which allows a fair description of the experimental data. The theory shows that in some cases the timing errors may be an important factor limiting speed performance of RSFQ circuitry. Nevertheless, our XOR gates could operate at 25 GHz with BER below 10/sup -13/ at the standard temperature (4.2 K) at any dc power supply voltage in our range. For the lowest voltage (0.1 Volt) the calculated static power dissipation in the gate was as low as 23 nanowatts, lower than the unavoidable dynamic dissipation (43 nanowatts).         Short-term frequency stability of RSFQ ring oscillators    C.A. Mancini and M.F. Bocko Summary: The temporal stability of the clock signal has a profound effect on the performance of synchronous RSFQ digital systems. Short-term clock fluctuations, or clock jitter, can severely degrade system performance due to the hazard of timing constraint violations. Successful large-scale RSFQ digital systems will require highly stable multi-Gigahertz on-chip clock sources. To meet this need, methods for characterizing and measuring the short-term stability of such sources are required. In this paper we identify the relevant figure of merit to characterize and compare various clocks: the cycle-to-cycle standard deviation of the clock periods. We have developed experimental techniques for the measurement of this figure of merit and applied it to the characterization of an RSFQ ring oscillator. The experimental results are compared with results from a stochastic circuit simulator. We determined the value of jitter to be 1.52% at 10 GHz.         A NRZ-output amplifier for RSFQ circuits    R. Koch, P. Ostertag, E. Crocoll, M. Gotz, M. Neuhaus, T. Scherer, M. Winter and W. Jutzi Summary: Interfaces between RSFQ circuits in the Return-to-Zero (RZ) and semiconductor circuits in the Non-Return-to-Zero (NRZ) mode are developed for data transmission at about 10 GHz clock frequencies reducing the errors owing to a finite sampling jitter of conventional room temperature equipment. A prototype of a NRZ output interface with the Nb-Al/sub 2/O/sub 3/-Nb technology has been simulated, implemented and successfully tested at 100 MHz. The interface can easily be combined with a superconducting pulse amplifier for NRZ output signals in the range of several mV. Corresponding simulations and a layout of the amplifier are presented.         New logic circuits based on SFQ signals    F. Furuta, Y. Suzuki, E. Oya, S. Matsumoto, H. Akaike, A. Fujimaki, H. Hayakawa and Y. Takai Summary: We propose new logic circuits based on Single Flux Quantum logic with Resettable Latch (SFQ-RL). This new logic enables us to initialize the whole circuit and realize an inverter easily. This initialization function is needed for general state machines, in addition, suppressing the failed operation caused by a trapped flux in storage loops. SFQ-RL logic consists of three primitives of gates, "Latch (L)-gate", "Copy(C)-gate" and "OR (O)-gate". L-gate is a kind of flip-flop gate. The difference from a conventional RSFQ latch, "RS-FF" is that L-gate can be reset without emitting an output pulse using "Initialize" pulse. Our numerical simulation shows that the bias margin of L-gate is /spl plusmn/8%. C-gate and O-gate correspond to "Splitter" and "Confluence Buffer" in RSFQ logic, respectively. Every logic function can be realized by only the three primitives. We confirmed the operations, "AND" and "OR" with reasonable margins and speeds by the numerical calculation. We have experimentally demonstrated the logic function such as OR based on SFQ-RL logic. We confirmed the normal operation of the gate with the bias margin of /spl plusmn/25.9%.         Design and implementation of an RSFQ switching node for petaflops networks    S. Yorozu, D.Yu. Zinoviev and G. Sazaklis Summary: This work is part of a project to design a petaflops-scale computer using a hybrid technology multi-threaded architecture (HTMT). A high-bandwidth low-latency switching network (CNET) based on RSFQ logic/memory family comprises the core of the superconductor part of the HTMT system, interconnecting 4,096 processors. We present a preliminary low-level design and partial experimental implementation of a multi-credit RSFQ network switching node with the estimated throughput of 7/spl middot/10/sup 10/ 85-bit-parallel packets per second, service latency of 109 ps, and dissipated power of 4.6 mW.         RSFQ-based D/A converter for AC voltage standard    H. Sasaki, S. Kiryu, F. Hirayama, T. Kikuchi, M. Maezawa, A. Shoji and S.V. Polonsky Summary: Digital to analog converters based on the Josephson effect are promising for voltage standards, because they produce voltage steps with ultimate precision and stability. In this paper, we describe a project to develop a Josephson D/A converter designed for synthesizing a sinusoidal waveform with metrological accuracy. The D/A converter is based on RSFQ (Rapid Single Flux Quantum) logic circuits, and consists of a frequency multiplier (FM), a pulse distributor (PD), and a number of voltage multipliers (VMs). Each VM circuit, corresponding to the n-th bit digital code, multiplies the number of SFQ pulses by a factor of 2/sup n/. By gating the input SFQ pulses from the FM to the VMs using the PD circuits, a programmable output voltage is obtained. Possible sources of uncertainties in the measurement of the rms value of the synthesized sine wave are discussed.         RF applications of high temperature superconductors in MHz range    Q.Y. Ma Summary: High quality, low noise RF devices (resonators and filters) in MHz range have been designed, fabricated, and tested. The devices were designed using either interdigital capacitor or spiral structures and made from two inch HTS wafers. Applications of these devices to magnetic resonance imaging (MRI) and RF communication are reviewed. Substantial gain in signal-to-noise ratio (SNR) using HTS coils for both proton and sodium MRI on animals and humans at field strength of 0.5 T-3 T are demonstrated. HTS single-pole and three-pole bandpass filters operated at 77 K are built. Multi-pole bandpass filters in MHz range are successfully made on two-inch, single layer HTS wafer. A three-pole filter with a center frequency of 18 MHz has shown a low insertion loss of 0.7 dB at 77 K.         HTS microwave devices and subsystems with pulse tube refrigerators    Yusheng He, Yuan Zhou, Jingtao Liang, Hong Li, Luwei Yang, Wenxiu Zhu, Jinghui Cai, Aisheng He, Zhonglin Gong, Peiheng Wu, Yijun Feng, T.W. Button, P.A. Smith, M.J. Lancaster, F. Wellhofer and C.E. Gough Summary: Two new types of pulse tube refrigerators with optimized cooling power of 6 W at 77 K have been designed and fabricated. Experiments show that vibration of the pulse tube refrigerators is at least an order of magnitude smaller than that of Stirling coolers. Two microwave devices, a HTS cavity and a HTS miniature lumped band-stop filter, were integrated with the refrigerators and operated successfully, which demonstrated the potential application of these integrated devices and the refrigerator as practical HTS sub-systems.         High-Q dielectric resonator devices at cryogenic temperatures    N. Klein, S. Schornstein, I.S. Ghosh, D. Schemion, M. Winter and C. Zuccaro Summary: Dielectric resonators machined from various single crystalline materials exhibit a strong increase of quality factor upon cooling to cryogenic temperatures. As an example, single crystalline lanthanum aluminate prepared by the Verneuil crystal growing technique exhibits a variation of the loss tangent with temperature at 4 GHz from 8/spl middot/10/sup -6/ at 300 K to about 2/spl middot/10/sup -6/ between 77 K and 120 K. As an application, we have developed a dielectric dual-mode filter for satellite communication based on two degenerated modes in a hemisphere machined from lanthanum aluminate. Employing aperture coupling between adjacent hemispheres, we have built a C-band quasielliptic four-pole filter for use in output multiplexers of future cryogenic satellite transponders. Our filter with a centre frequency of 3.72 GHz and a bandwidth of 32 MHz exhibits an in-band insertion loss of -0.04 dB below T=120 K corresponding to an unloaded quality factor of 87,000. No degradation of the filter performance was observed up to power levels of 180 watts. Our results indicate the great potential of cryogenic dielectric resonator devices for future communication satellites up to Ka-band frequencies.         High-temperature superconductor filters: modeling and experimental investigations    I.B. Vendik, V.V. Kondratiev, D.V. Kholodniak, S.A. Gal'chenko, A.N. Deleniv, M.N. Goubina, A.A. Svishchev, S. Leppavuori, J. Hagberg and E. Jakku Summary: 10-pole HTS microstrip band-pass filters with central frequency 1.75 GHz have been designed, manufactured, and investigated without any trimming in the linear and nonlinear regimes. A high filter performance with insertion loss not more than 0.5 dB and power handling capability up to 10 W of input power at T=60 K has been observed. Different commercial and home-made software were used to simulate the filter characteristics.         A K-band (HTS,gold)/ferroelectric thin film/dielectric diplexer for a discriminator-locked tunable oscillator    F.A. Miranda, G. Subramanyam, F.W. Van Keuls and R.R. Romanofsky Summary: The performance of a K-band conductor/ferroelectric thin film/dielectric tunable diplexer that is being developed as a critical part of a discriminator-locked tunable oscillator will be discussed. This diplexer consists of two K-band (18 to 22 GHz), two-pole YBCO/SrTiO/sub 3//LaAlO/sub 3/ bandpass filters coupled to the microwave signal input port through a 50 /spl Omega/ power splitter. When tested independently at 77 K and varying bias of /spl plusmn/400 V, these filters exhibited a passband frequency shift greater than 1.7 GHz, while maintaining a non-deembedded insertion loss near 2.0 dB. Electromagnetic modeling results for the diplexer indicate that varying the dielectric constant of the SrTiO/sub 3/ from 3000 (/spl sim/77 K) to 500 (/spl sim/300 K) will shift the diplexer's "cross-over" frequency from 19 to 21 GHz, with only minor variations in insertion loss. Measurements at 298 K of this diplexer circuit using a gold/SrTiO/sub 3// LaAlO/sub 3/ structure resulted in non-deembedded insertion losses of 3.3 dB and 2.5 dB at the filters' maxima at 20.65 and 22.43 GHz, respectively, with a cross-over frequency at 21.07 GHz. These room temperature results are consistent with modeling. The measured characteristics of YBCO/SrTiO/sub 3//LaAlO/sub 3/ diplexers at cryogenic temperatures will be presented.         Modulation and demodulation of 2 GHz pseudo random binary sequence using SFQ digital circuits    P.D. Dresselhaus, E.J. Dean, A. Hodge Worsham, J.X. Przybysz and S.V. Polonsky Summary: The high speed and low power needed for Spread Spectrum communications leads to a desirable application of digital superconductivity. Low temperature Nb/AlOx/Nb digital Single Flux Quantum (SFQ) circuits have been designed and fabricated in our facility, which compose critical subcircuits of the superconductive Spread Spectrum Modem. Four- and 6-bit Pseudo Random Binary Sequence (PRES) generators with output latching amplifiers have been produced and operated at up to 5.4 GHz. On chip modulation and de-modulation of these PRES codes have been performed with time resolution of less than one chip of the code. High-speed off-chip data was XORed with the on-chip PRES at up to 3.7 GHz to produce the modulated pattern. Rapid synchronization allows the code to start within one clock cycle of being fully reset, and the latching output amplifier gives enough power to do real time room temperature measurements of high-speed SFQ circuits.         Full operation of a three-node pipeline-ring switching chip for a superconducting network system    S. Yorozu, Y. Hashimoto, H. Numata, M. Koike, M. Tanaka and S. Tahara Summary: We report on the full circuit operation of a switching core chip for a superconducting network system. Our network fabric is a pipeline-ring architecture. Our ring network has a unidirectional data flow. This configuration provides increases of switching performance in two ways: a larger throughput means that many cells can occupy the ring bus at the same time, and a shorter operation time means that the bus occupation control only needs to check whether the data exists on the connected local part of the bus. The circuit consists of three ring interface circuits (RIFs), a slot repeater (SR) circuit, and superconducting interconnections. Each RIF has an address. The main functions of the switching circuit are the following: (a) decoding of packet addresses and routing, (b) arranging the blocking of data between incoming data from the processor and network, and (c) redefining (changing the validity) of slots. We designed the circuit with a voltage-level bipolar-powered logic family. There are about 4300 Josephson junctions in the whole circuit and it measures about 3.3 mm/spl times/2.5 mm. We successfully tested these functions and demonstrated data exchange in the whole circuit. We were also able to confirm correct operation up to 2-GHz clock frequency by using an on-chip self-testing method.         Temperature-dependent bit-error rate of a clocked superconducting digital circuit    Q.P. Herr, M.W. Johnson and M.J. Feldman Summary: We measured the bit-error rate (BER) of an RS latch, a clocked SFQ circuit. A digital error-detection circuit was used to detect BER in the range unity to 10/sup -13/; below 10/sup -7/, the circuit was operated with a 12 GHz on-chip clock. BER was measured as a function of control current; both positive and negative control current was applied, leading to two distinct modes of error incidence. The error function curves extrapolate to 10/sup -80/ for optimal control current at a temperature of 5.5 K. Measurements were repeated over the range 3-7 K. Comparison to theoretical error-function estimates of BER indicate that the noise is strictly thermal.         Bit error rate measurements for GHz code generator circuits    E.J. Dean, P.D. Dresseihaus, J.X. Przybysz, A.H. Miklich, A. Hodge Worsham and S.V. Polonsky Summary: A new method of analyzing bit error rates (BERs) for SFQ circuits and their outputs at GHz speeds will be presented. This method was used to test four- and six-bit pseudorandom code generators. The code generators were operated in free-run mode, i.e., without a synchronization (Reset) pulse. This enabled us to conduct BER testing to much lower levels than when the code generator is operated in Reset mode. The SFQ circuit output was amplified with a superconducting output latch to give voltage levels suitable for display on a sampling scope. The GHz output data was analyzed by external computer software; this permitted extended tests without user supervision. With the code generators operating in free-run mode, they routinely gave bit error rates (BERs) in the 10/sup -11/ range; the best BER recorded was 1.1*10/sup -13/ (2 errors in /spl sim/2.5 hours) at 2 GHz. We have successfully tested these code generators at frequencies in excess of 3.5 GHz with BERs in the 10/sup -10/ range as well.         High-frequency crosstalk in superconducting microstrip waveguide interconnects    M. Currie, R. Sobolewski and T.Y. Hsiang Summary: A low-temperature electro-optic sampling system was implemented to study the crosstalk of picosecond pulses between niobium microstrip interconnects. This system has been used to perform noninvasive, nodal testing on superconducting integrated circuits. We have characterized the crosstalk arising from the crossing of two microstrip waveguides. This is representative of high-speed interconnects in VLSI technology in which one signal line must cross above another. The measured crosstalk signal showed the capacitive nature of the coupling, thereby providing the material's dielectric permittivity at high frequencies. Our results have provided feedback for improving computer simulations of superconducting electronic circuits.         COOL-0: Design of an RSFQ subsystem for petaflops computing    M. Dorojevets, P. Bunyk, D. Zinoviev and K. Likharev Summary: We discuss a preliminary design of a Rapid Single-Flux-Quantum (RSFQ) subsystem for general-purpose computers with petaflops-scale performance. The subsystem is being developed at Stony Brook within the framework of the Hybrid Technology MultiThreading (HTMT) project. COOL-0 design is based on 0.8-/spl mu/m RSFQ technology which enables the implementation of superconductor processing elements (SPELLs) operating at clock frequencies up to 100 GHz pipelined cryo-memory (CRAM) with 30 ps cycle time and interprocessor network (CNET) with a bandwidth of 30 Gbps per channel. The main architectural challenge is an almost 1,000-fold speed difference between the RSFQ processors and room-temperature SRAM comprising the second level of the HTMT memory hierarchy. The proposed solution to the problem is hardware support for two-level multithreading and block transfer techniques in SPELLs. Our preliminary estimates show that an RSFQ subsystem with 4 K SPELLs and a 4-Gbyte CRAM may be sufficient to achieve the performance close to 0.5 petaflops for computationally intensive program kernels. COOL-0 would occupy a physical space of about 0.5 m/sup 3/ and dissipate power as low as 250 Watts (at helium temperature). These numbers present a dramatic improvement compared to a hypothetical purely-semiconductor petaflops-scale computer.         RSFQ front-end for a software radio receiver    E.B. Wikborg, V.K. Semenov and K.K. Likharev Summary: We present results of a preliminary analysis of possible front-ends of a software defined radio base station receiver containing superconductor Rapid Single-Flux-Quantum (RSFQ) components. The main component of such a front-end, an oversampling analog-to-digital converter (ADC) with expected internal clock rate up to 20 GHz has already been developed and fabricated with commercially available 3.5-/spl mu/m, 1-kA/cm/sup 2/ niobium-trilayer technology. Simulations show that, even with such crude feature size, the superconductor ADC components can outperform their semiconductor counterparts.         A superconductive multi-hit time digitizer    O.A. Mukhanov, A.F. Kirichenko, J.M. Vogt and M.S. Pambianchi Summary: We are developing an all-digital, high-speed, low-power superconductive multi-hit time digitizer based on a RSFQ time-to-digital converter (TDC). The advantages of this TDC, as compared to semiconductor TDCs, include excellent single, as well as multi-hit time resolution and extremely low power dissipation. Each TDC channel consists of a 14-bit superconductive counter based on toggle flip-flops with destructive readouts, a 9-word shift register-based FIFO memory, and a parallel-to-serial converter with output driver. To facilitate external control and data interfacing of the TDC, we have been developing a VXI-bus interface. Its low-power dissipation allows the TDC to be directly integrated with cooled front-end detectors, including optical detectors, eliminating cable bandwidth limitations.         A fully integrated 16-channel RSFQ autocorrelator operating at 11 GHz    A.V. Rylyakov, D.F. Schneider and Yu.A. Polyakov Summary: We present the results of low- and high-speed testing of a fully integrated all-digital one-bit RSFQ autocorrelator for short-millimeter and submillimeter wave spectrometry applications. The 16-channel device, complete with a 16/spl times/9 array of binary counters, on-chip double-oversampling quantizer and on-chip clock was operational at clock speeds of up to 11 GHz. The total number of Josephson junctions in the design was 1672, while the estimated total power dissipation was less than 0.1 mW. For high-speed testing of the device we have developed a specialized 16-channel room-temperature interface capable of real-time data acquisition at a 16 Mbps-per-channel output rate. Extensive high-speed on-chip testing of the autocorrelator has also been performed, both in analog and digital modes, in the latter mode with an additional on-chip clock controller. All chips were fabricated in HYPRES' standard 3.5 /spl mu/m-10 /spl mu/A//spl mu/m/sup 2/ Nb-trilayer process. We also present a new concept of a 128-channel autocorrelator system built on 8 independent identical chips with approximately 2,500 Josephson junctions per chip, i.e. within the reach of the present-day fabrication technology.         First realization of a tracking detector for high energy physics experiments based on Josephson digital readout circuitry    S. Pagano, V.G. Palmieri, A. Esposito, O. Mukhanov and S. Rylov Summary: We have designed and realized a prototype of a high energy particle microstrip detector with Josephson readout circuits. The key features of this device are: minimum ionizing particle sensitivity, due to the use of semiconductive sensors, fast speed and radiation hardness, due to the use of superconductive circuitry, and current discrimination, which allows the use of several types of semiconductors as detector (Si, GaAs, CVD-diamond) without loss in performances. The Josephson circuitry, made by a combination of RSFQ and latching logic gates, realizes an 8-bit current discriminator and parallel to serial converter and can be directly interfaced to room temperature electronics. This device, which is designed for application as vertex detector for the Compass and LHC-B accelerator experiments, has been tested with small radioactive sources acid will undergo to a test beam at the CERN SPS facility with 24 GeV/c protons. Current results and future perspectives will be reported.         High-speed decimation filter for delta-sigma analog-to-digital converter    Y.P. Xie, S.R. Whiteley and T. Van Duzer Summary: A 12-bit digital filter is designed for an A/D converter system with sampling speed of 16 GHz. Data stream of 16 Gbit/s from delta-sigma modulator will pass through a 1:4 demultiplexer. Four identical 12-bit digital filters are used to catch the data streams from the demultiplexer for 4 Gbit/s in each channel. The 12-bit superconductive digital filter is designed with modified variable threshold logic (MVTL) gates. A novel XOR gate is designed and used in this circuit to reduce circuit complexity and improve performance. Progress of high speed testing results is presented. The filter comprises 584 Josephson junctions and consumes about 1 mW power.         Conduction across the interface between a superconductor and a spin polarized metal    R.J. Soulen Jr., M.S. Osofsky, B. Nadgorny, T. Ambrose, P.R. Broussard, M. Rubinstein, J. Byers, C.T. Tanaka, J. Nowack, J.S. Moodera, G. Laprade, A. Barry, M.D. Coey, Y.M. Mukovskii, D. Shulyatev and A. Arsenov Summary: We have studied Andreev reflection in point contacts formed between several low T/sub c/ superconductors and various spin polarized normal metals. We have also developed a theoretical model for the phenomenon. There is good accordance between theory and experiment.         Spin-polarized quasiparticle injection into YBCO    I. Jin, Z. Chen, T. Wu, S.P. Pai, Z. Dong, S.B. Ogale, R. Ramesh, T. Venkatesan, M. Johnson, E. Finley, F.A. Hegmann and M.R. Freeman Summary: FET-type devices have been fabricated by using trilayers of Nd/sub 0.7/Sr/sub 0.3/MnO/sub 3/LaNiO/sub 3/ (NSMO) or LaNiO/sub 3/ (LNO) (gate)/LaAlO/sub 3/ (LAO) (barrier)/YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) (channel) in order to investigate effect of quasiparticle injection into YBCO. Here, NSMO and LNO were used as gate electrodes for injection of spin-polarized and spin-unpolarized quasiparticles into the superconducting channel, respectively. When injecting along the c-axis of YBCO, the critical current was suppressed with spin-polarized quasiparticles 30 times more efficiently than with spin-unpolarized quasiparticles. Differential current gain, defined as a differential change of the critical current to injection current change, has been achieved up to /spl sim/16 for c-axis YBCO. If the response time is limited by quasiparticle relaxation time of /spl sim/10 ps, the device may be useful for fast electronics. Preliminary high-speed measurements indicate that part of the critical current suppression may be caused by quasiparticle injection, not all by heating. When injecting along a-axis, no significant dependence on quasiparticle polarization was observed. Other superconductors such as Pr/sub 1.85/Ce/sub 0.15/CuO/sub 4/ (PCCO) and PbIn have been tested in similar devices for comparison.         Introduction of ramp-type technology in HTS quasiparticle injection devices    R. Moerman, D. Veldhuis, G.J. Gerritsma and H. Rogalla Summary: Injection of quasiparticles with an energy larger than the superconducting gap into a superconducting strip results in breaking of Cooper-pairs and hence the suppression of the superconducting properties. Experiments using planar injection devices made of HTS materials with various barrier materials showed current gains varying from 2 up to 15 at 77 K. By changing the junction size and therefore the superconducting volume the current gain could be increased. A further reduction of the junction volume is very difficult using the planar device geometry. However, by applying the ramp-type technology it is possible to reduce the junction volume by at least one order of magnitude and a further increase in current gain is expected. Another advantage of this technology is the formation of in-situ barriers and electrodes and hence a better control of the junction characteristics should be possible, also the compatibility with the processes involved making RSFQ devices can be interesting for later applications. We have fabricated ramp-type injection devices, using various types of barriers. Characterization of these devices has been performed and the results of these experiments will be presented and discussed.         HTS quasiparticle injection devices with large current gain at 77 K    C.W. Schneider, R. Moerman, D. Fuchs, R. Schneider, G.J. Gerritsma and H. Rogalla Summary: Recent progress on the development of planar QP-injection devices using YBCO and STO as an epitaxial injection barrier will be discussed. The main problem for HTS injection devices is to grow reliably a well defined, ultra-thin tunneling barrier suitable for QP tunneling. For this purpose, we used inverted cylindrical magnetron sputtering to first optimize the smoothness of our YBCO films by controlling tightly an relevant sputtering conditions. We are able to prepare smooth [001] YBCO films on [001] STO substrates on a routine basis with an average roughness varying between 1 and 2 nm. With these flat YBCO films both planar as well as grain boundary junctions were fabricated using epitaxial STO barriers between 2 and 8 nm thick and a 50 nm of Au counter electrode. Planar junctions with 6 nm STO barriers were in most cases fully insulating, in some cases, a current gain of up to 7.4 at 77 K was obtained. For 3 nm STO barriers, the highest current gain was 15 at 81 K. The injection results also show a scaling behavior with junction size. Based on the present materials development and device understanding, we consider a current gain of up to 20 at 77 K possible.         Quasiparticle injection into YBCO four terminal Josephson devices    F. Lombardi, Z.G. Ivanov, T. Claeson and U. Scotti di Uccio Summary: A four terminal Josephson device, based on quasiparticle injection into an YBCO step edge Josephson junction was analysed. Two injector junctions are defined on both sides of the step edge junction using native Au/YBCO barrier. The Josephson critical current is reduced by increasing the injection current. The results are explained in terms of a non equilibrium state of the YBCO electrode under quasiparticle injection.         Transformation of electric energy into sound energy in Josephson junctions    G.I. Urushadze Summary: Charge fluctuations of superconducting and normal carriers exist in Josephson junction, connected with the thermal activation processes. These fluctuations excite damping acoustic fluctuations in the electrodes across the junction. Application of the current causes the decrease of damping while at the current of definite value damping disappears completely. After further increase of current the acoustic fluctuations become unsteady their amplitudes start to increase and if at this regime the sound wave passes through the junction it is amplified. This paper deals with the physical basis of the sound wave amplification by Josephson junction with introduction of relaxation time of the coherent phase (CP) as the output of a self-consistent solution of the Fokker-Planck equation. The problem deals with a wide bound of frequencies and other parameters. The question of experimental measurement of the lifetime of Josephson junction in metastable state is also discussed.         Sound wave amplification in non-stationary Josephson effect    G.I. Urushadze and Z.Z. Toklikashvili Summary: We have investigated the longitudinal sound wave interaction with Josephson transition. The coefficient of sound amplification in single Josephson junction and in the stack of Josephson-coupled layered structures (BSCCO) have been determined.         Superconducting electrometer based on the resistively shunted Bloch transistor    S.V. Lotkhov, H. Zangerle, A.B. Zorin, T. Weimann, H. Scherer and J. Niemeyer Summary: We have fabricated the Bloch transistor shunted on-chip by a small-sized Cr resistor with R/sub s/=1 k/spl Omega/. The Bloch transistor normally consists of two small Josephson junctions connected in series, which in our case have been replaced by two superconducting interferometer loops, each with two junctions in parallel. A capacitively coupled gate is supplied to control the induced charge of the small intermediate electrode (island) of the transistor. The measured I-V curves show no hysteresis and correspond to the operation of a effective Josephson junction at the high-damping and strong-noise limits. The critical current of the system was found to be close to its nominal value, that is in accordance with the electromagnetic environment theory. The I-V curves were modulated by the gate with a period of e and a maximum swing of about 2 /spl mu/V. Such rather moderate modulation results from the Josephson-to-charging energies ratio, E/sub J//E/sub C//spl ap/9, in our sample being far from its optimum value (/spl ap/0.3+1).         High performance packaging system for superconducting electronics    D. Gaidarenko and R. Robertazzi Summary: We demonstrate a packaging system/test probe suitable for testing complex, large scale superconducting integrated circuits with thousands of Josephson junctions. The cryopackage is designed to work with a 1 cm superconducting die, with liquid He immersion cooling using a standard storage dewar. The package has 80 high-speed input-output lines (DC to 20 GHz) which connect the chip to room temperature electronics. The tip of the cryopackage, containing the chip, is shielded from the ambient magnetic field with two mumetal cylinders and contains a built-in coil, which provides in-situ degaussing of the inner shield. To clear flux trapped in the chip being tested, the probe contains a novel gas manifold and a system of heaters. During the defluxing operation, a heater evaporates liquid helium inside the chip enclosure, the expanding vapor purging the liquid from the sample cell and warming the chip above its transition temperature. Once the chip is defluxed, the liquid helium is allowed back into the cell, at a rate slow enough to avoid trapping flux in the chip while it is cooled. The process can be automated and does not require any movement of the probe once inserted in the dewar.         Sequential read-out architecture for multi-channel SQUID systems    A. Matlashov, R.H. Kraus Jr., M. Espy, P. Ruminer, L. Atencio and A. Garachtchenko Summary: We describe a novel multi-channel sequential SQUID read-out technique that requires fewer wires than conventional units and also simplifies the electronics significantly. We designed and experimentally tested the sequential read-out electronics with up to 8 channels using LTS 8/spl times/8 mm/sup 2/ magnetometers with better than 3 fT//spl radic/Hz field resolution. We have investigated noise performance, amplitude-frequency characteristics, and cross-talk of the sequential read-out electronics for 2, 4, and 8 channels. We observed field resolution better than 4 fT//spl radic/Hz, 6 fT//spl radic/Hz, and 9 fT//spl radic/Hz for 2-, 4-, and 8-channel versions, respectively. We observed 10 kHz frequency bandwidth for the 8-channel version using 200 kHz modulation frequency. Cross-talk better than -90 dB was measured for this system. A single-channel simulation was used to estimate the field resolution for systems with up to 128 channels. We found that the expected field resolution can be better than 15 fT//spl radic/Hz, 20 fT//spl radic/Hz, and 30 fT//spl radic/Hz for 32-, 64-, and 128-channel systems, respectively, with the sequential read-out technique.         Baseline distance optimization for SQUID gradiometers    A. Garachtchenko, A. Matlashov, R.H. Kraus Jr. and R. Cantor Summary: We optimized the baseline length of SQUID-based symmetric axial gradiometers using a computer simulation. The signal-to-noise ratio (SNR) was used as the optimization criteria. We found that in most cases the optimal baseline is not equal to the depth of the primary source, rather it has a more complex dependence on the gradiometer balance and the ambient magnetic noise. We studied both first and second order gradiometers in simulated shielded environments and second order gradiometers in a simulated unshielded environment. The noise source was simulated as a distant dipolar source for the shielded case. We present optimal gradiometer baseline lengths for the various simulated situations.         Highly balanced gradiometer systems based on HTS-SQUIDs for the use in magnetically unshielded environment    J. Borgmann, A.P. Rijpma, H.J.M. ter Brake, H. Rogalla and P. David Summary: Two different concepts for gradiometer formation were tested applying high-temperature rf SQUIDs operated at 77 K in liquid nitrogen. All gradiometer systems are fully based on magnetometers. The first concept applies a compensating magnetometer at different positions to actively cancel the magnetic field at the location of other magnetometers. These magnetometers were arranged in an axial direction. In parts, a system of superconducting plates was used to align the relative magnetic orientation of the magnetometers. The outputs of these sensors were used to form a highly balanced electronic gradiometer. The second concept is based on electronic noise cancellation. A set of three magnetometers arranged in an axial direction was used to form an electronic second-order gradiometer. Different types of reference systems based on HTS-SQUID magnetometers and fluxgate sensors were applied to the gradiometer signal for achieving a high common mode rejection of the environmental disturbances. The performance of the different systems is demonstrated in a magnetically unshielded environment as well as in a shielded environment and the common mode rejection of homogeneous magnetic fields is measured. To demonstrate the performance of the systems, biomagnetic measurements have been performed in shielded and unshielded environments.         HTS SQUID magnetometer with SQUID vector reference for operation in unshielded environment    D.F. He, H.-J. Krause, Y. Zhang, M. Bick, H. Soltner, N. Wolters, W. Wolf and H. Bousack Summary: Using a HTS rf SQUID vector reference, we demonstrated magnetically unshielded operation of an HTS rf SQUID magnetometer. The reference consists of three magnetometer SQUIDS oriented in x, y and z directions. The sensing SQUID magnetometer is z-oriented and positioned at (baseline) distance of 8 cm from the z-reference. A balance (common mode rejection) better than 4000 was achieved by electronic adjustment of the subtraction coefficients of the reference rf SQUID channels in the homogeneous field of large Helmholtz coils. With 3.5 mm diameter washer rf SQUIDs, the magnetic field sensitivity of the magnetometer was 220 fT//spl radic/Hz at frequencies greater than 100 Hz in unshielded environment. A frequent task in nondestructive evaluation of materials is the determination of the magnitude and size of ferrous inclusions in non-magnetic metal alloys. As a preliminary test, we used the magnetometer for the detection of ferrous particles in unshielded environment. A magnetized 10 mg particle was identified from a distance of 80 mm by a scan of its remanent field. Magnetocardiograms (MCG) measurements are also performed.         Comparison of low noise cooling performance of a Joule-Thomson cooler and a pulse-tube cooler using a HT SQUID    R. Hohmann, C. Lienerth, Y. Zhang, H. Bousack, G. Thummes and C. Heiden Summary: Due to their intrinsic low mechanical vibration level both, Joule-Thomson refrigerator and Pulse-Tube refrigerator are promising candidates for low noise cooling of high-T/sub c/ SQUIDs. We report here on a test comparing the performance of a commercial Joule-Thomson cooler and a single stage Pulse-Tube cooler used to operate one and the same HT rf SQUID under comparable conditions in shielded environment. In order to reduce vibrations the cold stages of both cooler systems were connected by flexible plastic lines of several meters length with their compressors. Operated in a liquid nitrogen cryostat, the white field noise of the SQUID was 40 fT//spl radic/Hz at frequencies above 30 Hz. A slightly higher white noise (about 60 fT//spl radic/Hz) was observed for operation with either of the two coolers. This is probably due to the vicinity of superinsulation to the SQUID. The Joule-Thomson cooler produced a somewhat higher low frequency excess noise below 30 Hz and some characteristic noise bands at intermediate frequencies (ca. 100 Hz-500 Hz). The Pulse-Tube cooler led to a spectrum of lines at multiples of the pulse frequency (4.6 Hz). Both effects could be attributed (using cross correlation measurements) to residual mechanical vibrations of the cold heads of both coolers.         Design and preliminary results from a high temperature superconducting SQUID milliscope used for non-destructive evaluation    M.A. Espy, L. Atencio, E.R. Flynn, R.H. Kraus Jr. and A. Matlashov Summary: We present the design and preliminary results from a SQUID 'milliscope'. The device was designed for nondestructive evaluation (NDE) as part of the Enhanced Surveillance Program at Los Alamos National Laboratory. A high temperature superconducting (RTS) SQUID sensor is used to map magnetic fields induced in the sample. Eddy currents are induced in the conducting sample by a wire coil designed to produce minimal magnetic field at the SQUID when no sample is present. The features of interest are characterized by anomalies in the induced magnetic field. The goal of the instrument is sensitivity to small features generally buried under several intervening layers (/spl sim/1-20 mm) of conducting and/or nonconducting materials and robustness of design (i.e. the ability to operate in a noisy, unshielded environment). The device has primarily focussed on specific NDE problems such as the ability to detect buried "seams" in conducting materials and quantify the width of these seams. We present the design of the instrument, and some data to demonstrate its capabilities.         SQUIDs as detectors in a new experiment to measure the neutron electric dipole moment    M.A. Espy, A. Matlashov, R.H. Kraus Jr., P. Ruminer, M. Cooper and S. Lamoreaux Summary: A new experiment has been proposed Los Alamos National Laboratory; to measure the neutron electric dipole moment (EDM) to 4/spl times/10/sup -28/ ecm, a factor of 250 times better than the current experimental limit. Such a measure of the neutron EDM would challenge the theories of supersymmetry and time reversal violation as the origin of the observed cosmological asymmetry in the ratio of baryons to antibaryons. One possible design for this new experiment includes the use of low temperature superconducting (LTS) SQUIDS coupled to large (/spl sim/100 cm/sup 2/) pick-up coils to measure the precession frequency of the spin-polarized /sup 3/He atoms that act as polarizer, spin analyzer, and detector for the ultra-cold neutrons used in the experiment. The method of directly measuring the /sup 3/He precession signal eliminates the need for very uniform magnetic fields (a major source of systematic error in these types of experiments). It is estimated that a flux of /spl sim/2/spl times/10/sup -16/ Tm/sup 2/ (0.1 /spl Phi//sub 0/) will be coupled into the pick-up coils. To achieve the required signal-to-noise ratio one must have a flux resolution of d/spl Phi//sub SQ/=5/spl times/10/sup -6/ /spl Phi//sub 0//Hz/sup 1/2/ at 10 Hz. While this is close to the sensitivity available in commercial devices, the effects of coupling to such a large pick-up coil and flux noise from other sources in the experiment still need to be understood. To determine the feasibility of using SQUIDs in such an application we designed and built a superconducting test cell, which simulates major features of the proposed EDM experiment, and we developed a two-SQUID readout system that will reduce SQUID noise in the experiment. We present an overview of the EDM experiment with SQUIDs, estimations of required SQUID parameters and experimental considerations. We also present the measured performance of a single magnetometer in the test cell as well as the performance of the two SQUID readout technique.         A one tenth scaled magnetically shielded room of double cylindrical HTS combined with ferromagnetic metals    S. Haseyama, M. Kojima, S. Shibuya, H. Nakane and S. Yoshizawa Summary: This paper deals with a cylinder with both ends closed and a hole at the middle point on the side of both cylinders. The holes can be aligned to permit the examinee to enter or exit the double cylindrical MSR (Magnetically Shielded Room). An MSR one tenth the size of a human body was made. The diameter and length of the cylinder were 250 mm and 350 mm, respectively. The size of the hole was 90 mm/spl times/180 mm. The material used for this MSR was mainly high T/sub c/ superconductor with a coating of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ 100 /spl mu/m thick. The ends of the MSR were plated with permalloy. To detect the inner magnetic fields at various points of the MSR, 33 sensors with three-dimensional sensitivity were placed at one closed end. The ratio of the internal to external field strength was measured by applying external magnetic fields parallel and perpendicular to the door. The readings of the ratios obtained were 10/sup -2/ to 10/sup -3/ in the parallel and 10/sup -3/ to 10/sup -4/ in the perpendicular case.         HTS scanning SQUID microscope cooled by a closed-cycle refrigerator    E.F. Fleet, S. Chatraphorn, F.C. Wellstood, S.M. Green and L.A. Knauss Summary: We have developed a scanning SQUID microscope which uses a commercially available closed-cycle refrigerator to cool a YBa/sub 2/Cu/sub 3/O/sub 7/ bi-crystal dc SQUID to about 77 K. The system allows magnetic imaging of samples which are at room temperature and pressure with spatial resolutions of 50 /spl mu/m or better. It is more compact and requires less maintenance than a more conventional liquid-nitrogen cooled system, while delivering equal sensitivity. In order to reduce the SQUID-sample separation while maintaining vacuum thermal isolation of the SQUID, the sensor is separated from the sample by a 25 /spl mu/m thick, optically transparent window. The noise spectrum of our SQUID shows a 1/f spectrum below 500 Hz with 72 pT//spl radic/Hz field sensitivity at 10 Hz, and a white noise level of 20 pT//spl radic/ Hz.         High-frequency clock operation of Josephson 256-word/spl times/16-bit RAMs    S. Nagasawa, H. Numata, Y. Hashimoto and S. Tahara Summary: A Josephson 256-word/spl times/16-bit RAM that includes a power circuit has been developed to enable high-frequency clock operation. This RAM consists of a 4/spl times/4 matrix array of 256 RAM blocks, impedance-matched lines, and signal amplifiers. A power-supply circuit, composed of a transformer and a Josephson regulator, is included in each 256 RAM block. Fail bit maps for the 256 RAM block were measured, and perfect operation with a 100% bit yield was obtained. The 256 RAM block functioned up to a clock frequency of 1.07 GHz. We succeeded in feeding a large high-frequency current of more than 2 A into the entire 256-word/spl times/16-bit RAM. The 256-word/spl times/16-bit RAM therefore functioned up to a clock frequency of 620 MHz.         Case study in RSFQ design: fast pipelined parallel adder    P. Bunyk and P. Litskevitch Summary: We present a design for parallel pipelined carry-lookahead Kogge-Stone 32and 64-bit integer adders with the traditional concurrent flow timing scheme, and the results of its gate-level logical simulation using a VHDL model, with parameters reduced from the physical-level simulation of RSFQ cells. The design uses only five different types of bit processing blocks and is easily scalable to any length of the operands. The multi-pulse logic representation together with interchanging logical polarity between pipeline stages is used to simplify the design of the blocks, which contain only two types of clocked RSFQ gates: an inverter and a D-flip-flop. Simulations show that in the absence of thermal fluctuations and random parameter spread the clock frequency of the adder implemented in the projected 0.8 /spl mu/m Nb-trilayer technology could be as high as 150 GHz. However, an approximate account of these factors shows that in order to achieve a 99% adder fabrication yield and a 10/sup -25/ adder error rate the maximal frequency should be reduced to 60 GHz for 1.5% Josephson junction spread and to 52 GHz for 3% spread. Adder latency is close to 260 ps for 32 bits and 320 ps for 64 bits. We plan to re-design the adders to increase their speed.         Timing jitter and bit errors in a 64-bit circular shift register    A.M. Herr, M.J. Feldman and M.F. Bocko Summary: The bit-error rate of a 64-bit single-flux-quantum circular shift register, operating at a clock frequency of 10-16 GHz was measured. Error incidence depends on the values of the clock and data bias currents and on the clock frequency. Timing violation arising from thermal jitter is the dominant error mechanism. The jitter per JTL stage is estimated to be 290 fs based on the error rate data. This corresponds to a noise temperature of 8-9 K.         Numerical studies of interchip pulse transmission for complex RSFQ systems    H. Toepfer, T. Lingel, F.H. Uhlmann and M. Aoyagi Summary: As the complexity of superconducting digital systems increases, the necessity of a careful design of interconnecting structures becomes more and more evident. Especially in the communication between chips, discontinuities are inevitable. Deriving a high frequency characterization of critical regions is therefore a crucial step for a design-oriented microwave modeling. We employed the finite-difference time-domain technique based on the discretization of Maxwell's equations for the numerical analysis of typical interconnect components, e.g. flip chip connection pads, vias, and transmission line discontinuities. The peculiar properties of superconductors are taken into account by incorporation of the London equations and the two-fluid model into the numerical scheme. Computer simulations have been carried out for various arrangements. Their results show in the time-domain how the shape of a rapid single flux quantum (RSFQ) pulse is affected by passing a discontinuity in the interchip signal path. Furthermore, frequency domain characterizations are obtained in terms of scattering parameters providing information about the bandwidth of the structure under investigation.         SFQ data processing with set/reset information    H. Kodaka, T. Hosoki, M. Kitagawa and Y. Okabe Summary: We propose a new class of SFQ logic circuits. In this new approach, an SFQ pulse represents the transition between "zero" and "one". By using these two bits of information, a one-to-one correspondence between input and output can be realized. Since the correspondence is then the same as in semiconductor circuits, this method permits logic design without clock elements. In order to carry out this logic, we propose the most fundamental element, a new DC/SFQ converter. A computer simulation and low-speed test were performed. Both results showed that this converter operates correctly with a wide margin. Moreover, this converter also provides the basis for many other logic elements such as AND, OR, and XOR.         Experimental investigation of Cherenkov flux-flow oscillators    V. Kurin, A. Yulin, E. Goldobin, A. Klushin, H. Kohlstedt, M. Levitchev and N. Thyssen Summary: This paper is devoted to the experimental investigation of a new class of superconducting microwave oscillators based on Cherenkov radiation from Josephson vortices. Samples consisting of a long Josephson junction embedded in a dispersive transmission line with space-periodical inhomogeneities were fabricated and tested. We report observation of new resonances on the I-V curve of the system and present the first radiation measurements in the 80-120 GHz frequency range.         Design and fabrication of Cherenkov flux-flow oscillator    A.M. Baryshev, A.V. Yulin, V.V. Kurin, V.P. Koshelets, S.V. Shitov, A.V. Shchukin, P.N. Dmitriev and L.V. Filippenko Summary: The Josephson Flux-Flow Oscillator (FFO) has been used as an on chip local oscillator at frequencies up to 650 GHz. The FFO linewidth of about 1 MHz was measured in the resonant regime V<915 /spl mu/V for niobium-aluminum oxide-niobium tunnel junctions, while considerably larger values were reported at higher voltages. To overcome this fundamental linewidth broadening we propose a novel on chip Cherenkov radiation flux-flow oscillator (CRFFO). It consists of a long Josephson junction and a superconducting slow wave transmission line that modifies essentially the junction dispersion relation. Two SIS detectors are connected both to the long Josephson junction and the transmission line to evaluate available microwave power. The output power coming both from the long junction and the transmission line is estimated at different bias conditions.         Vortices in HTS junctions and SQUIDs    R.G. Humphreys Summary: Three different problems of a vortex penetrating a superconducting thin film have been addressed. It has been shown that the flux coupled from a vortex into a pickup loop or SQUID washer can be obtained from knowledge of the current distributions which flow in the absence of a vortex, a much easier calculation. Results are given for the case of the SQUID washer. The current distribution for a vortex near a circular hole in a film has been found in the strong shielding limit, and the force on the vortex deduced. The current distribution of a Josephson vortex penetrating a planar junction, such as a bicrystal junction, has been calculated. The form of the Josephson vortex is different from that usually assumed, with a long range tail. The size of the Josephson vortex is typically a factor of two larger than that obtained by taking the conventional expression in terms of the Josephson penetration depth.         Subharmonic locking in Josephson junctions    M. Cirillo, V. Merlo, D. Winkler and N. Thyssen Summary: We have designed and tested a coplanar waveguide configuration which allows for coupling and detection of microwave radiation to planar and stacked Josephson junctions structures. The design is particularly versatile for experiments such as phase-locking of Josephson oscillations to external signals and detection of low frequency components in the waveform of a pumped junction. Using this design we have measured subharmonic phase-locking in long Josephson junctions and performed a first quantitative check of the existing theoretical models.         Resistive states of superconducting hot-electron bolometer mixers: charge-imbalance vs. hotspot    D. Wilms Fleot, E. Miedema, J.J.A. Baselmans, T.M. Klapwijk and J.R. Gao Summary: We present a study of the resistive behavior of hot-electron bolometers in two different regimes. At bath temperatures near the critical temperature and under the condition of a low current density, the behavior can be understood in terms of charge-imbalance, Andreev reflection, and the superconducting proximity effect. At lower temperatures, a high current density and the application of LO power result in the formation of a resistive electronic hotspot. We propose to interpret heterodyne downconversion as the result of the length oscillation of the hotspot at the intermediate frequency.         An 800 GHz NbN phonon-cooled hot-electron bolometer mixer receiver    J.H. Kawamura, C.-Y.E. Tong, R. Blundell, D. Cosmo Papa, T.R. Hunter, G. Gol'tsman, S. Cherednichenko, B. Voronov and E. Gershenzon Summary: We describe a heterodyne receiver developed for astronomical applications to operate in the 350 /spl mu/m atmospheric window. The waveguide receiver employs a superconductive NbN phonon-cooled hot-electron bolometer mixer. The double sideband receiver noise temperature closely follows 1 kGHz/sup -1/ across 780-870 GHz, with the intermediate frequency centered at 1.4 GHz. The conversion loss is about 15 dB. The receiver was installed for operation at the University of Arizona/Max Planck Institute for Radio Astronomy Submillimeter Telescope facility. The instrument was successfully used to conduct test observations of a number of celestial sources in a number of astronomically important spectral lines.         Heterodyne measurements of a NbN superconducting hot electron mixer at terahertz frequencies    P. Yagoubov, M. Kroug, H. Merkel, E. Kollberg, J. Schubert, H.-W. Hubers, G. Schwaab, G. Gol'tsman and E. Gershenzon Summary: The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 1300 K at 650 GHz, 4700 K at 2.5 THz and 10000 K at 3.12 THz. The measurements were performed at 4.5 K ambient temperature. The amount of local oscillator (LO) power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain measured at 650 GHz is -9 dB, the total conversion gain is -14 dB.         Submillimeter-wave mixing and noise in HTS Josephson junctions    M. Tarasov, E. Stepantsov, D. Golubev, Z. Ivanov, T. Claeson, O. Harnack, M. Darula, S. Beuven and H. Kohlstedt Summary: A Josephson quasioptical detector comprising YBaCuO junction on bicrystal MgO substrate, integrated log-periodic Au antenna, MgO extended hyperhemisphere lens attached to the substrate and 1.4 GHz cold amplifier with cold circulator has been designed, fabricated and experimentally studied. We fabricated several integrated Josephson junctions 1-2 /spl mu/m wide which at 4.2 K demonstrate RSJ IV curves with critical currents 100-300 /spl mu/A and normal resistance of 10-20 /spl Omega/. The noise temperature (T/sub N/) at 4.2 K and 330 GHz measured by a hot/cold load method in fundamental mixing mode with external BWO local oscillator brings T/sub N/=1100 K for the junction shunted by low-inductance resistive shunt and T/sub N/=1400 K without shunting. At bath temperatures of 20-40 K the noise temperature was in the range 1500-3000 K, at 50 K the noise temperature was below 2000 K, and at 60-70 K increased over 3000 K in the frequency range 310-586 GHz. The noise temperatures measured in the self-pumping mode vary between 580-2300 K with dc bias in the range 0.1-0.5 mV. The linewidth of Josephson oscillations has been extracted from a selective detector response and IF noise voltage dependence. The measured excess noise can be attributed to shot noise and multiple Andreev reflection in pinholes with Ss'S structure. We observed small subharmonic steps in IV curve and noise dependencies, which are typical for SNS junctions.         HTS mixers based on the Josephson effect and on the hot-electron bolometric effect    O. Harnack, S. Beuven, M. Darula, H. Kohlstedt, M. Tarasov, E. Stephansov and Z. Ivanov Summary: We report on our experimental studies of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers. Mixers based on high-T/sub c/ bicrystal Josephson junctions have been fabricated, and noise, conversion efficiency, and receiver bandwidth measurements have been performed in the frequency range between 90 and 550 GHz. The dependence of the mixer performance on the operation temperature has been studied. High-T/sub c/ HEB mixers have been fabricated on MgO and sapphire substrates. We successfully sized the dimensions of the effective device volume down and managed to fabricate 50-60 nm long devices. In such short structures phonon diffusion into the normal metal electrodes should significantly improve the mixer performance.         On-chip integration of HTS Josephson oscillator and mixer    S. Beuven, M. Darula, O. Harnack, K. Karlovsky and H. Kohlstedt Summary: We report on the experimental realization of a sub-mm wavelength oscillator based on HTS Josephson junctions integrated on-chip with detector Josephson junction-mixer. Detector and oscillator are coupled via a microstripline. The oscillator is a 2-dimensional (2D) network (array) of 20 HTS step-edge junctions. The array is biased in parallel, i.e. all junctions of the network are oscillating with the same frequency. Effective pumping of the Josephson mixer was possible up to several hundred GHz. The best results, i.e. significant depression of the critical current and steep Shapiro steps up to the 4th order, were obtained between 150 GHz and 200 GHz. Power transfer was detectable up to frequencies around 1.15 THz.         Superconducting chip receivers for imaging application    S.V. Shitov, V.P. Koshelets, A.B. Ermakov, L.V. Filippenko, A.M. Baryshev, W. Luinge and Jian-Rong Gao Summary: Experimental details of a unique superconducting imaging array receiver are discussed. Each pixel contains an internally pumped receiver chip mounted on the back of the elliptical microwave lens. Each chip comprises a quasi-optical SIS mixer integrated with a superconducting flux-flow oscillator (FFO) both fabricated from the same Nb/AlO/sub x//Nb trilayer on a silicon substrate. Properties of the integrated lens antenna were studied using an externally pumped reference SIS mixer which showed antenna sidelobes below /spl sim/17 dB and a receiver double side band noise temperature, T/sub RX/(DSB), below 100 K within the frequency range 460-500 GHz that is close to the quantum noise. For the imaging array T/sub RX/(DSB)=150 K has been measured at 500 GHz using the internal flux-flow oscillator as a local oscillator (LO). A balanced SIS mixer was tested showing T/sub RX/(DSB)<100 K within the range of 480-510 GHz using the internal LO. A computer system was developed to control simultaneously the dc bias of the SIS mixer and the frequency and power provided by FFO. The system also performs automatic optimization of the receiver noise temperature.         Characterization of the bandwidth performance of distributed junction arrays    Sheng-Cai Shi, T. Noguchi, J. Inatani, Y. Irimajiri and T. Saito Summary: The bandwidth performance of distributed junction arrays is investigated in this paper. Firstly, the mixing behavior of distributed junction arrays is numerically analyzed with the help of an equivalent circuit model. Secondly, the mixing performances of two respective distributed junction arrays using five and ten junctions are measured. Experimental results are discussed in detail.         A HTS rf SQUID vector magnetometer for geophysical exploration    M. Bick, G. Panaitov, N. Wolters, Y. Zhang, H. Bousack, A.I. Braginski, U. Kalberkamp, H. Burkhardt and U. Matzander Summary: We report on a highly sensitive rf SQUID vector (x, y, z) magnetometer system operating at 77 K and suitable for electromagnetic geophysical exploration. We achieved stable long-term operation of all three channels during field trials outside magnetic shielding in urban and rural environments. With sensors on 10/spl times/10 mm/sup 2/ substrates, the white noise level in earth's field was 40 fT//spl radic/Hz above 100-300 Hz, in all three channels. The new system meets the high requirements for slew rate (>2 mT/s), dynamic range (>130 dB) and bandwidth (20 kHz) which must be fulfilled in geophysical measurements, especially the TEM (transient electromagnetic) method. We also present results of geophysical TEM field trials over various test sites. We obtained good reproducibility of SQUID data and a good correlation between output signals of reference induction coils and the derivative of SQUID signals. Results from TEM measurements indicate that for late time signals, originating from deeper geological structures, the SQUID magnetometer provides a better signal-to-noise ratio than an induction coil.         Field trials using HTS SQUID magnetometers for ground-based and airborne geophysical applications    C.P. Foley, K.E. Leslie, R. Binks, C. Lewis, W. Murray, G.J. Sloggett, S. Lam, B. Sankrithyan, N. Savvides, A. Katzaros, K.-H. Muller, E.E. Mitchell, J. Pollock, J. Lee, D.L. Dart, R.R. Barrow, M. Asten, A. Maddever, G. Panjkovic, M. Downey, C. Hoffman and R. Turner Summary: Since December 1992, CSIRO and BHP have been field trialing rf HTS SQUID magnetometers for mineral prospecting applications. Ten field trials in widely varying environments(from -16/spl deg/C to +40/spl deg/C ambient temperatures) in mostly remote locations saw the development of a system which can be operated in many configurations including ground based and airborne Transient ElectroMagnetics (TEM). The magnetometer system has been developed to a point where, at late times in TEM applications, the SQUID system has a higher signal-to-noise level than the competing traditional coil technology. In some trials, a SQUID magnetometer detected anomalies at later times than were observed with the coil system, indicating an enhanced ability to detect highly conductive targets. This paper reviews development of our 3-axis SQUID magnetometer. SQUID systems as B field sensors have advantages over coils which are dB/dt type sensors. We will discuss the importance of these advantages for mineral prospecting in regions with a conducting soil cover or overburden typical of the Australian landscape.         High-performance high-T/sub c/ SQUID sensors for multichannel systems in magnetically disturbed environment    F. Ludwig, J. Beyer, D. Drung, S. Bechstein and T. Schurig Summary: We have fabricated and characterized high-T/sub c/ SQUID sensors that are suited for operation in multichannel systems in magnetically disturbed environment. Utilizing the superior properties of our 30/spl deg/ SrTiO/sub 3/ bicrystal junctions, we are able to fabricate high-performance single-layer direct-coupled SQUID magnetometers. System noise levels down to 24 fT Hz/sup -1/2/ and typical 1/f corners of 4 Hz/sup -1/2/ were obtained for devices having a 9 mm/spl times/9 mm pickup loop and a nominal SQUID inductance of 100 pH. To protect the SQUIDs from moisture, they are hermetically encapsulated in a ceramic housing. A thick film resistor integrated on the chip carrier allows one to heat the SQUID device above T/sub c/ in order to release trapped magnetic flux. For the operation of our low-noise SQUIDs, a compact direct-coupled read out electronics with a preamplifier voltage noise of 0.4 nV Hz/sup -1/2/ and 100 kHz bias reversal was developed. Sensor dynamics and linearity were investigated with regard to the operation in magnetically disturbed environment. The maximum system bandwidth and slew rate of our bias reversal electronics were 1 MHz and about 5/spl times/10/sup 5/ /spl Phi//sub 0//s, respectively. For signal frequencies /spl les/50 Hz/sup -1/2/, a minimum total harmonic distortion of -118 dB was measured, dominated by nonlinearities in the read-out electronics. A new magnetometer design with improved noise performance in magnetically disturbed environment is presented.         Nondestructive evaluation of wires using high-temperature SQUIDs    H. Weinstock, N. Tralshawala and J.R. Claycomb Summary: A method using SQUID magnetometry and low-frequency current injection has been developed to detect defects during the fabrication of single and multi-strand wire, especially superconductive NbTi/Cu wire.         Aircraft wheel testing with machine-cooled HTS SQUID gradiometer system    R. Hohmann, M. Maus, D. Lomparski, M. Gruneklee, Y. Zhang, H.-J. Krause, H. Bousack and A.I. Braginski Summary: For eddy current detection of deep-lying flaws in large aircraft wheels, an automated airplane wheel inspection system using a HTS SQUID gradiometer sensor is being developed. Wheel drums made of aluminum alloys have to be tested frequently since they are subject to enormous dynamic loads and very high braking temperatures at landing. For economic reasons, testing should be performed from the outside without removing the inner ferromagnetic keys which fit the brake system. In order to operate the sensor in hostile environments such as airport maintenance hangars, a planar rf double hole SQUID gradiometer was used. SQUID cooling is performed by a closed cycle Joule-Thomson cryocooler, equipped with flexible plastic gas lines. The wheel testing is being performed on an automated test stand with the wheel slowly rotating and a robot with the SQUID enclosure scanning stepwise along the wheel axis. Additional signals due to inner cracks of 10 mm length, penetrating 25 percent of the 10 mm thick wall, are easily identifiable in the periodic signal background due to the presence of ferromagnetic keys. In comparative measurements, the prototype SQUID system clearly exhibited advantages over conventional techniques, with optimization reserve still at hand.         Inspection of aircraft parts with high remanent magnetization by eddy current SQUID NDE    M.v. Kreutzbruck, U. Baby, A. Theiss, M. Muck and C. Heiden Summary: We have developed an eddy current NDE system based on HTS rf SQUIDs as magnetic field sensors. Due to their high field sensitivity even at very low frequencies, SQUIDs are especially suitable for applications where a large eddy current penetration depth is required. We have used 3 GHz rf SQUIDs in our system made from YBCO thin films with a field resolution of about 1 pT//spl radic/(Hz) and a high dynamic range, more than 140 dB//spl radic/(Hz) in unshielded environment. With this system we could detect deep lying (up to 26 mm) cracks in test samples and original aircraft parts. Measurements made on the same sample showed an improvement in the signal to noise ratio of up to 3 orders of magnitude for cracks deeper than 13 mm, when comparing a conventional eddy current NDE unit with our SQUID system. Test objects containing ferromagnetic structures with a high remanent magnetization (often more than 1 mT), like aircraft wheels or steel bolts in part of the aircraft wing, very often cause instabilities of the flux locked loop operation of the SQUID. To prevent unlocking, we have developed a new background field compensation scheme. Special compensation electronics takes care of slowly varying magnetic fields of up to 1 mT/s and enabled us to perform eddy current measurements in presence of slow (<30 Hz) background field variations of up to 5 mT.         Standard method for detection of magnetic defects in aircraft engine discs using a HTS SQUID gradiometer    Y. Tavrin, M. Siegel and J. Hinken Summary: We have developed a new high sensitive magnetic method for non-destructive testing (NDT) of small ferrous inclusions in aircraft engine discs. The measuring method is based on a second order gradiometer using three thin film Superconducting Quantum Interferometer Devices (SQUIDs) as magnetic sensors. The high balance of the gradiometer setup with a base length of 60 mm insures that the measuring system is extremely stable against external disturbances without having a magnetic shield. At the same time the resolution of the local magnetic field is high, about 130 fT/Hz/sup 1/2/. The system is suitable for NDT of technical components, especially for tests into large depth of parts with large size. Using this new method, the location, depth and size of magnetic inclusions in non-magnetic alloys can be determined. The method is used as a standard testing procedure in production quality control of aircraft engine discs.         Radio frequency bias current scheme for dc superconducting quantum interference device    Y. Zhang, D.F. He, N. Wolters, R. Otto, K. Barthels, X.H. Zeng, H.R. Yi, H.-J. Krause, A.I. Braginski and M.J. Faley Summary: We have developed a radio frequency bias current scheme with reversal frequency up to 50 MHz for dc superconducting quantum interference devices (SQUIDs). The SQUID and the readout electronics, were connected via a quarter wavelength (/spl lambda//4) transmission line. This transmission line not only transported the SQUID signal, but also served as the resonant matching circuit. For a dc SQUID of inductance 115 pH (loop size 75/spl times/75 /spl mu/m/sup 2/), we measured a flux noise of 33 /spl mu//spl phi//sub 0///spl radic/Hz at 77 K in the flux locked loop configuration. The corner frequency of 1/f noise was less than 0.5 Hz.         Digital and analog measurements of HTS SFQ RS flip-flops and shift register circuits    Y.H. Kim, J.H. Kang, G.Y. Sung, J.H. Park, J.M. Lee, K.R. Jung, C.H. Kim, T.S. Hahn and S.S. Choi Summary: We fabricated reset-set (RS) flip-flops and shift registers by using YBCO bicrystal junctions and tested their operations by using a computer-controlled digital measurement set-up and an analog measurement set-up. The RS flip-flop circuits operated successfully at temperatures up to 71 K. The RS flip-flop circuit was observed over 600 computer-generated clock cycles with nearly no errors. The circuits were reset or set during each clock cycle. By using an analog measurement technique, we operated the RS flip-flop circuits at frequencies of up to 500 Hz. Since our probe was not designed for high speed operation, the test speed was limited to this frequency. Although we could not operate the shift register completely, we observed flux propagation in the shift register.         Design and fabrication of a voltage divider utilizing high-T/sub c/ ramp-edge Josephson junctions with a ground plane    T. Hashimoto, S. Inoue, T. Nagano and J. Yoshida Summary: Circuit operation of a voltage divider utilizing YBa/sub 2/Cu/sub 3/O/sub x//Co-doped PrBa/sub 2/Cu/sub 3/O/sub y//YBa/sub 2/Cu/sub 3/O/sub x/ ramp-edge Josephson junctions with a ground plane was demonstrated for the voltage region of 0-400 /spl mu/V at 12.5 K, where the maximum voltage corresponds to /spl sim/200 GHz internal Josephson oscillation. This voltage was around the critical current-normal resistance (I/sub c/R/sub n/) product of 420 /spl mu/V. In the design of the voltage divider, a transmission line model was adopted for an inductance loop because of the large dielectric constant of the insulation layer interposed between the ground plane and the wiring serving as a loop inductance. In the fabrication of the circuit, a SrTiO/sub 3//Co-doped PrBa/sub 2/Cu/sub 3/O/sub y//SrTiO/sub 3/ multilayer insulation and four-directional ramp-edge junction process using a photoresist reflow technique were adopted.         HTS SFQ T-flip flop with directly coupled readout    A.G. Sun, D.J. Durand, J.M. Murduck, S.V. Rylov, M.G. Forrester, B.D. Hunt and J. Talvacchio Summary: The authors report the design, fabrication, and test results of single flux quantum (SFQ) toggle flip flop circuits. These circuits, investigated as building blocks of an HTS counting ADC, feature a directly coupled readout junction stack similar to those used in LTS RSFQ circuits. The directly coupled circuit delivers higher readout voltage, hence potentially higher operating speed than magnetically coupled alternatives. The circuits were fabricated using two multilayer HTS SNS junction integrated circuit technologies (one at Northrop Grumman and the other at TRW) featuring three YBCO depositions. Initial testing demonstrated toggling of a T-flip flop in response to SFQ pulses generated by integrated dc/SFQ converters. The readout voltage is shown to approach 40% of the junction I/sub C/R/sub N/ product, and as high as 100 /spl mu/V at 65K. Test results are compared with predicted fabrication process parameter requirements. To increase margins and tolerance to process parameter variations, improvements to the design have been made using JSpice and MALT.         A reentrant delay-line memory using a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// coplanar delay-line    W. Hattori, T. Yoshitake and S. Tahara Summary: The rapid growth in telecommunication traffic demands a higher-speed asynchronous transfer mode (ATM) switching system. At present, the upper limit of the system clock rate is determined by the maximum clock rate of conventional semiconductor memory devices, such as the register files used in ATM cell buffer storage. This is because the maximum clock rate of these register files is restricted by the propagation delay time between each register stage. Since a reentrant superconducting delay-line memory avoids this restriction using an analogue delay given by the superconducting delay line, we have proposed that this memory should be used in high-speed ATM cell buffer storage. Recently, we fabricated a 10-/spl mu/m-wide 37-cm-long YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// coplanar delay-line. This line had a delay of approximately 2.8 ns. Using this coplanar delay-line and an assembly of commercially available integrated circuits, we successfully developed superconducting delay-line memory. This memory operates as a 32-bit buffer storage at a clock rate of 10 GHz, which is several times faster than the register files. This result shows that the superconducting delay-line memory is a powerful candidate for high-speed ATM cell buffer storage.         C-axis microbridges for rapid single flux quantum logic    P.J. Hirst, T.G. Henrici, I.L. Atkin, J.S. Satchell, J. Moxey, N.J. Exon, M.J. Wooliscoft, T.J. Horton and R.G. Humphreys Summary: The c-axis microbridge (CAM) junction technology has an inherently low inductance due to its groundplaned geometry which should be well suited to SFQ logic applications. However, the critical currents of the conventional (2 /spl mu/m diameter) CAM technology are too high. Experiments with optical lithography have shown that junctions of /spl sim/0.5 micron dimension are required. A new process using electron beam lithography has been developed. The junction statistics even at this early stage of development look promising. To confirm the validity of the rest of the design and fabrication technology a CAM based RS Flip-Flop has been fabricated which shows the correct traversal of the state graph at 45 K.         Investigation for the basic characteristics of HTS SFQ logic gate    K. Saitoh, T. Utagawa and Y. Enomoto Summary: The characteristics of a simple logic gate which consists of an rf-Superconducting QUantum Interference Device (SQUID) and dc-SQUID has been investigated in connection with the Single-Flux-Quantum (SFQ) logic operation and Josephson junction characteristics. The Josephson junctions were made of Neodymium Barium Copper Oxide thin film employing Focused Ion Beam technology. We confirmed the generating SFQ in the rf-SQUID and simultaneous read-out by the dc-SQUID up to 50 K. It has been found that the temperature dependence of output voltage level decreased more rapid than that of critical current normal resistance product. The origin of the discrepancy was studied using a phenomenological model of the Josephson junction and numerical simulation.         Limitations on HTS single flux quantum logic    J. Satchell Summary: There is widespread interest in transferring Single Flux Quantum (SFQ) logic from niobium technology to a suitable HTS technology. The higher operating temperature results in increased noise and associated errors. We have developed numerical methods to study noise induced errors and how they depend on circuit parameters. A simple picture holds for all the circuits studied to date. The error probability shows an error function (integrated Gaussian) distribution. The width of the distribution is circuit dependent, but is 1 to 4 times the noise contribution of a single junction, and the noise free (deterministic) margin corresponds to the point where the error probability is 0.5. The distributions are frequently asymmetric, and minimum error rate does not occur for a design centered between the deterministic margins. A stochastic optimizer has been developed that allows us reoptimize circuits for conditions when noise induced margin narrowing is important. We have used this to study the influence of layout induced stray inductance on the feasibility of HTS circuits using the T flip-flop as an example. Stray inductance appears to be as important as junction reproducibility, and significant improvements are needed to allow high operating temperatures.         Application of a cryogenic vector network measuring technique in a high-speed digital test    K. Shimaoka, M. Nemoto, S. Tokunaga, I. Yoshida, A. Fujimaki and H. Hayakawa Summary: The result of a digital transmission test of a YBa/sub 2/Cu/sub 3/Ox/MgO/Au microstrip line to coplanar waveguide transmission line converter is reported. It was fabricated in order to introduce a microwave design technology for high-speed digital testing. The performance was verified using a cryogenic vector network measuring technique. The transmission characteristics of the microstrip line to coplanar waveguide transmission line converter was almost the same as YBa/sub 2/Cu/sub 3/Ox/MgO/Au microstrip line at frequencies from 40 MHz to 10 GHz at 30 K. The bit error rate was analyzed using a 2/sup 23/-1 pseudo random binary signal at 3 GHz. The degradation of the bit error rate caused by the microstrip line to coplanar waveguide transmission line converter and the measuring system itself are discussed using the Q factor of the signal obtained from the bit error rate analysis and the transmission characteristics obtained by the vector network measurement.         Measurement of the error rate of single flux quantum circuits with high temperature superconductors    B. Ruck, Yonuk Chong, R. Dittmann, A. Engelhardt, B. Oelze, E. Sodtke, M. Siegel, W.E. Booij and M.G. Blamire Summary: The determination of bit error rates in single flux quantum logic circuits operating at temperatures well above the temperature of liquid helium is essential since the question of stability against thermal noise arises. We determined experimentally the static and for the first time the dynamic error rate at temperatures of about 40 K with the help of simple test circuits. The static error rate has been investigated using two different circuits with bicrystal junctions in either single-layer or multilayer configuration. In both cases the internal state of a storage loop was observed by a dc-SQUID. A ring oscillator based on a Josephson transmission line allowed us to measure the dynamic error rate of a Josephson comparator at high frequencies. This circuit has been fabricated using junctions by focused-electron-beam irradiation. It is specially suited for the detection of seldom occurring switching errors.         MM and sub-MM properties of ramp-type Josephson junctions on MgO with STO buffer layers    H. Myoren, J. Chen, T. Yamashita, L. Amatuni, A.H. Sonnenberg, G.J. Gerritsma and H. Rogalla Summary: We have successfully fabricated ramp-type junctions on MgO substrates using an SrTiO/sub 3/ (STO) buffer layer. The observed I/sub c/R/sub n/ product for the junctions on MgO with STO buffer layer were about 2 mV at 4.2 K and 0.1 mV at 60 K. The junctions clearly showed Shapiro steps under irradiation of MM-waves and sub-MM-waves. We observed Josephson emission at 50 GHz from a junction on a MgO substrate with STO buffer layer at 17 K. We have also confirmed mixing in the self-oscillating mode using MM-wave and sub-MM-wave signals.         Development of a compact system for high-resolution X-ray detection using a SQUID amplifier    T. Ikeda, H. Kato, K. Kawai, H. Miyasaka, T. Oku, W. Ootani, C. Otani, H. Sato, R.M. Shimizu, H. Watanabe, H. Nakagawa, H. Akoh, M. Aoyagi and T. Taino Summary: A compact system for an STJ-based high resolution X-ray detection system using a SQUID amplifier has been developed. A noise level of less than 4.8 mV at the SQUID output pulse height of 1.2 V for Nb-based STJ signals was achieved in the temperature range of 1.7-4.2 K with good reproducibility under an external magnetic field of about 0.01 Tesla, which was applied to suppress the Josephson current of the STJ. The results show the possibility of constructing a compact STJ-based X-ray detection system with an 'on-site' low noise SQUID preamplifier.         Fabrication and characterization of infrared and sub-mm spiderweb bolometers with low-T/sub c/ superconducting transition edge thermometers    F.B. Kiewiet, M.P. Bruijn, H.F.C. Hoevers, A.C. Bento, W.A. Mels and P.A.J. de Korte Summary: Spiderweb bolometers with a superconducting transition edge thermometer combine a high sensitivity and absorption efficiency for far infrared and sub-mm radiation with a low susceptibility to high energetic particles. They are among the most promising detectors today for future astronomy applications. In this paper we present our fabrication process for a fully integrated bolometer consisting of absorber, thermometer and suspension structure, based on micromachining of a silicon nitride membrane and various thin film deposition and etching steps. The optimization of Ti/Au transition edge thermometers is described, as well as electrical measurements on a fully integrated bolometer, indicating an electrical noise equivalent power of 2/spl times/10/sup -17/ W//spl radic/Hz at an operating temperature of 270 mK.         Niobium Josephson junction bolometers for optical detection in the visible-infrared region    R. Monticone, V. Lacquaniti, R. Steni, M. Rajteri, M.L. Rastello, L. Parlato and G. Ammendola Summary: The response of Nb Josephson junctions fabricated on different substrates, silicon and amorphous glass, is measured under optical illumination at several conditions of light intensity and light chopping frequency. The linearity of the response on the optical power extends over five orders of magnitude. The signal of the junction on silicon is 2 orders of magnitude lower than that of the junction on amorphous glass, but at least one order of magnitude faster, as the time constant of a directly irradiated junction on silicon is lower than 10 /spl mu/s. The signal dependence on chopping frequency of the junction on amorphous glass is typical of a strong thermal coupling between film and substrate, while for the junction on silicon it depends mainly on the thermal boundary resistance between film and substrate.         Heat transport across the interface between normal metal and d-wave superconductor    I.A. Devyatov, M.Yu. Kupriyanov, A.A. Golubov, L. Kuzmin and M. Willander Summary: Heat conductance and heat current across normal metal/d-wave superconductor (NID) interface are calculated in the framework of quasiclassical equations. The calculations are performed for different values of boundary transparencies and crystal axis orientation. It is shown that in contrast to N/s-wave boundary the heat conductance of transparent (D=1) NID interface is considerably larger and has a nonactivated form. Electronic heat current across NID structures is also calculated for different interface models taking into account the midgap states and the possibility of generating a gapless s-wave state in the vicinity of rough NID interface. It is shown that NID junctions cannot compete with analogous NIS devices in microrefrigerating and bolometer applications.         Thermal boundary resistance of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ multilayer strip    D. Robbes, N. Cheenne, J.-F. Hamet and J.P. Rice Summary: The present work deals with measurements of the thermal resistance at the boundary between a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(YBCO) thin film and its substrate. Above the film's critical temperature (T/sub c/) the YBCO strips were heated by Joule effect. We used a method based on the third harmonic generation of the voltage across the strips. At high frequency of the heating current, the deduced thermal resistance is dominated by the boundary effect. We used that method to evaluate the possible enhancement of the thermal insulation between the upper layer (YBCO thicker film) and the MgO substrate when ten 2/spl times/8 nm thick YBCO/STO bi-layers are deposited between them. The strips were 600 /spl mu/m long and 40 /spl mu/m wide. The thermal resistance was measured at various frequencies and temperatures above T/sub c/, both for a single layer taken as a reference sample and for a multilayer sample. Below T/sub c/, we used optical heating of the strips to evaluate the insulation effect obtained with multilayered sample. The ratio of thermal conductances was close to 11, thus demonstrating the insulation enhancement obtained with the multilayered structure. The effect could lead to antenna-coupled microbolometers with improved performances.         Nb/Al-AlOx/Nb edge junctions for distributed mixers    R.S. Amos, A.W. Lichtenberger, C.E. Tong, R. Blundell, S.-K. Pan and A.R. Kerr Summary: We have fabricated high quality Nb/Al-oxide/Al/Nb edge junctions using a Nb/SiO/sub 2/ bi-layer film as the base electrode, suitable for use as traveling wave mixers. An edge is cut in the bi-layer with an ion gun at a 45 degree angle using a photoresist mask. The wafer is then cleaned in-situ with a physical ion gun clean followed by the deposition of a thin Al (a1) film, which is then thermally oxidized, an optional second Al (a2) layer, and a Nb counter electrode. It was found that devices with an a2 layer resulted in superior electrical characteristics, though proximity effects increased strongly with a2 thickness. The counter electrode is defined with an SF/sub 6/+N/sub 2/ reactive ion etch, using the Al barrier layer as an etch stop. The Al barrier layer is then either removed with an Al wet etch to isolate the individual devices, or the devices are separated with an anodization process. Various ion gun cleaning conditions have been examined; in addition, both wet and plasma etch bi-layer edge surface pre-treatments were investigated. It was found that edge junctions with large widths (i.e., those more suitable for traveling wave mixers) typically benefited more from such treatments. Initial receiver results at 260 GHz have yielded a DSB noise temperature of 60 K.         Comparison between high-T/sub c/ superconducting microstrip filters and normal conducting counterparts    Dong-Chul Chung, Kyung-Kuk Park, Sung-Jin Park, Byoung-Sung Han and Jong-Sun Hwang Summary: In this paper the comparative study of HTS microstrip filter and gold counterpart is reported in terms of insertion loss, transmission characteristics, bandwidth and other various characteristics. Practically full procedures from the preparation of each thin films to fabrication procedure of each devices and experimental results are given for both HTS microstrip filter and gold counterpart. The filters used in this work, were based on the use of non-uniform microstrip line type, which is a stepped impedance resonator as a filter element. The superconducting microstrip filter used in this work was fabricated on MgO substrates using YBCO (YBa/sub 2/Cu/sub 3/O/sub 7-x/) superconducting thin films by pulsed laser deposition technique and also, the gold filter with the same dimensions was fabricated on the same substrate by thermal evaporation technique. Then gold thin films of the same thickness were evaporated on the other sides of each filter for the ground plane. Comparison results between HTS filter and gold filter show that a usable filter can be made by using this architecture.         Design and implementation of a lumped-element multipole HTS filter at 15 MHz    Hui Xu, E. Gao, S. Sahba, J.R. Miller, Q.Y. Ma and J.M. Pond Summary: We have designed a three-pole bandpass filter operating at 15 MHz. The parameters of the filter include high Q, narrow band, low insertion loss and a return loss of 20 dB. The filter was fabricated from double-sided YBCO thin film on a two inch LAO substrate. The design utilizes individual HTS lumped elements (interdigital capacitors and meander line inductors) to realise the poles of the filter. The design and modeling of the filter are discussed in detail. Experimental results from the S-parameter measurements will be presented. Good agreement has been found between the simulation results and experimental data.         A miniaturized interdigital microstrip bandpass filter    Kao-Cheng Huang, D. Hyland, A. Jenkins, D. Edwards and D. Dew-Hughes Summary: A 2.4 GHz three-stage microstrip bandpass filter was designed using a miniaturized interdigital capacitor structure to reduce the configuration in size. The filter was simulated by a finite element method software and then fabricated using TBCCO superconducting films on 20 mm/spl times/20 mm/spl times/0.5 mm MgO substrates. It was generated by photolithographic and wet etching process and packaged in a brass box. The bandwidth is 4% and the passband insertion loss of the filter was measured to be -0.4 dB at 77 K. The return loss is better than -8 dB. In particular, this filter has a sharper performance at its edge of fundamental pass band.         Thin film HTS passive microwave components for advanced communication systems    Jia-Sheng Hong, M.J. Lancaster, R.B. Greed, D. Voyce, D. Jedamzik, J.A. Holland, H.J. Chaloupka and J.-C. Mage Summary: This paper presents results of thin film high temperature superconducting (HTS) passive microwave components recently developed for advanced communication systems, which include miniature resonators, narrow-band bandpass and bandstop filters, couplers and duplexers. The components are fabricated using YBCO thin films on either MgO or LAO substrates. Excellent performances have been achieved.         Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films for microstrip filters    M. Zeisberger, M. Manzel, H. Bruchlos, M. Diegel, F. Thrum, M. Klinger and A. Abramowicz Summary: High performance narrowband bandpass filters are required in satellite communication systems. Especially HTS filter banks are particularly attractive because of their low insertion loss and sharp filter skirts needed in input multiplexers. Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ thin films on 2"-LaAlO/sub 3/-substrates and 10/spl times/10 mm/sup 2/-sapphire substrates were prepared using a two step technology. A Tl-free precursor film is prepared by sputtering. The Tl-incorporation is performed by annealing in a Tl/sub 2/O loaded atmosphere. The best films show surface resistances below 100 /spl mu//spl Omega/ at 77 K and 4 GHz. Two-pole bandpass-filters with a center frequency of 4 GHz and a bandwidth of 17.5 MHz using dual-mode ring resonators have been fabricated from the films on LaAlO/sub 3/. The measured passband shape achieved with tuning elements is in good agreement with the specifications of the design.         Hairpin-line/half-wave parallel-coupled-line narrowband bandpass filters using high temperature superconducting thin films    Hyung Kuk Yoon, Young Joong Yoon, Joo Hyung Park and Sang Yeol Lee Summary: In this paper, hairpin-line and hybrid hairpin-line/half-wave parallel-coupled-line filters using High-Temperature Superconducting (HTS) thin films are proposed. The proposed structures provide more compact size than conventional parallel-coupled-line filters and hybrid hairpin-line filters reduce the spurious modes due to the surface waves in the hairpin-line filters. The designed filters using HTS have low loss, small size and narrow bandwidth characteristics with the minimum number of poles in comparison with the normal metal microstrip line filters. The 3 pole filters centered at 14.25 GHz with the bandwidth of less than 1% were designed and fabricated. These operating characteristics are simulated and fabricated using HTS and compared with the normal metal microstrip line filters.         Design and performance of miniaturized superconducting coplanar waveguide filters    K. Yoshida, K. Sashiyama, S. Nishioka, H. Shimakage and Z. Wang Summary: Design and performance of coplanar waveguide (CPW) microwave filters using high Tc superconducting films have been studied. The bandpass filter made of CPW requires the coating of only one side of the substrate with a superconductor, and the width of the CPW filter can be uniformly reduced in scale without changing its characteristic impedance, leading to a miniaturized filter by adopting the meanderline geometry. In order to realize the miniaturized filter we investigate the interdigital gap with strong coupling and the modeling of the corner bend. It is shown that the size of the filter can be greatly reduced by introducing CPW with a meanderline geometry. Experiments of a prototype miniaturized CPW filter with its computer-simulated performance have been presented.         A compact narrowband HTS microstrip filter for PCS applications    Hong Teuk Kim, Byoung-Chul Min, Young Hwan Choi, Seung-Hyun Moon, Seung-Min Lee, Byungdu Oh, Jin-Taek Lee, Ikmo Park and Chull-Chai Shin Summary: We have fabricated a compact narrowband microstrip hairpin-comb filter for PCS applications by patterning double-sided YBCO films prepared by pulsed laser deposition on a 50-mm-diameter, 0.5-mm-thick LaAlO/sub 3/ wafer. To achieve the desired performance with the size limitation, folded half-wavelength resonators are all oriented in the same direction. We design the filter with the aid of a commercially available full-wave EM simulator, ENSEMBLE, which is based on the method of moments. The 11-pole filter has a 0.6 dB minimum insertion loss and 11.5 MHz bandwidth at 1.778 GHz, and shows a very sharp skirt and strong stopband characteristics. The measurement data are in good agreement with the simulated result.         Coplanar quarter-wavelength resonator filters fabricated by the superconducting sol-gel films    H. Kanaya, H. Senoh, T. Kaneyuki and I. Awai Summary: High temperature superconducting Y-Ba-Cu-O films were prepared on MgO polycrystal substrates by the sol-gel process. The average transition temperature and the surface resistance are 83 K and 2.8 m/spl Omega/ (at 30 K and 9.9 GHz, input power =-10 dBm), respectively. We fabricated a YBCO coplanar waveguide (CPW) quarter-wavelength (/spl lambda//4) resonator around 2 GHz (the length of the resonator is one half as long as that of the popular half-wavelength (/spl lambda/1/2) resonator) and compared its RF properties with that of a /spl lambda//2 resonator. Moreover, 2-pole CPW bandpass filter using YBCO sol-gel film was constructed with capacitively coupled /spl lambda//4 resonators. It has a narrow fractional bandwidth (3.60%) at 30 K.         Investigation of Nd-Ce-Cu-O planar tunnel junctions and bicrystal grain boundary junctions    S.I. Woods, A.S. Katz, T.L. Kirk, M.C. de Andrade, M.B. Maple and R.C. Dynes Summary: We have fabricated planar c-axis Pb/NCCO junctions and in-plane NCCO bicrystal grain boundary junctions. The Pb/NCCO junctions exhibit single-step elastic tunneling and sustain hysteretic Josephson supercurrents, evidence that NCCO has an s-wave component to its superconducting order parameter. Tunneling spectroscopy on high-resistance Pb/NCCO junctions reveals a semi-gap of 3-4 meV in the density of states of NCCO and evidence for phonon coupling to NCCO quasiparticles. The grain boundary junctions were made by laser ablating thin NCCO films onto yttrium-stabilized-zirconia bicrystal substrates and sustain supercurrents that modulate in applied magnetic field and show resistively-shunted-junction I-V characteristics.         Characteristics of bi-crystal grain boundary junctions with different tilt angles for digital circuit applications    Gun Yong Sung, Jeong Dae Suh, Kwang Yong Kang, Jun-Sik Hwang, Soon-Gil Yoon, Moon Chul Lee and Soon Gul Lee Summary: We have characterized bi-crystal grain boundary junctions with various tilt angles, i.e., 24/spl deg/, 30/spl deg/, 36.8/spl deg/, and 45/spl deg/ for digital applications. A simple rapid single-flux-quantum (RSFQ) logic circuit has been fabricated using a single layer high-T/sub c/ superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin film structure with 4 bi-crystal grain boundary Josephson junctions. The circuit includes one readout superconducting quantum interference devices (SQUID) and one storage SQUID. We have focussed upon the readout SQUID properties, including J/sub c/, R/sub n/A, and I/sub c/R/sub n/, as a function of the tilt angles of the grain boundary junctions. The 24/spl deg/-tilt grain boundary junctions were the best candidates for the simple digital circuits among the bi-crystal grain boundary junctions of the tilt angle from 24/spl deg/ through 45/spl deg/. The response of the readout SQUID was demonstrated by an input signal through the storage SQUID at 82 K.         Comparative study of electron and laser beam scanning for local electrical characterization of high-T/sub c/ thin films and junctions    P.M. Shadrin, Y.Y. Divin, S. Keil, J. Martin and R.P. Huebener Summary: The development of spatially resolved methods for an electrical characterization of thin films and junctions is essential for further progress in physics and applications of high-temperature superconductors. Two methods, electron beam and laser beam scanning, are used to get the high-resolution electrical images. In this paper we present the results of the comparison of electron- and laser-induced responses of the same high-T/sub c/ Josephson junctions. Using a laser-beam-induced thermoelectric response at room temperature and its odd-symmetric behavior across the grain boundaries, we were able to visualize the grain boundary faceting in bicrystal high-T/sub c/ Josephson junctions with the resolution of /spl sim/0.1 /spl mu/m.         Conductivity and microwave response of YBaCuO Josephson junctions on YSZ bicrystal substrate    D.V. Meledin, A.P. Lipatov, A.A. Verevkin, V.A. Ilyin, V.A. Serjantov and A.A. Naumov Summary: We have studied conductivity and microwave response of single YBaCuO Josephson junctions (JJ) and their one-dimensional serial arrays. The I-V characteristics, conductivity, differential resistance and detector response of microwave radiation with frequencies F=134 and 550 GHz were measured in the temperature range from 4.2 to 88 K. Total conductivity of YBaCuO JJ was in general determined by the RSJ model with deviations affected by the influence of localized states forming around a bicrystal boundary. Microwave response of YBaCuO JJ contains two components: the Josephson component that predominates at low bias voltage, and observed at high bias voltage component due to the microwave-induced increase of the probability of inelastic resonant quasiparticle tunneling through several localized states, where response voltage changes its sign.         Bicrystal submicrometer Josephson junctions and dc SQUIDs    R. Ijsselsteijn, H. Elsner, W. Morgenroth, V. Schultze and H.-G. Meyer Summary: Submicrometer Josephson junctions and dc SQUIDs with such junctions have been prepared on symmetrical 24/spl deg/ bicrystal substrates and were electrically characterized. The submicrometer structures are patterned using e-beam lithography and a C/Ti/e-beam resist mask system. Junctions with dimensions down to about 350 nm show no degradation of their superconducting properties at 77 K, when patterned at low temperatures. Series connections of directly coupled SQUIDs with large (110-160 pH) coupling-inductance, prepared with 0.5 /spl mu/m wide junctions show flux-to-voltage transfer function values up to 100 /spl mu/V//spl Phi//sub 0/. For these SQUIDs, typical white noise levels of 10 /spl mu//spl Phi//sub 0///spl radic/Hz are measured at 77 K.         Flux motion in YBCO biepitaxial Josephson junctions    H.H. Sung, S.Y. Yang, H.E. Horng and H.C. Yang Summary: We have measured the current-voltage characteristics of overdamped long YBa/sub 2/Cu/sub 3/O/sub 7/ biepitaxial Josephson junctions. The velocity-matching step was observed in the current-voltage characteristics with an applied magnetic field. The presence of velocity-matching steps suggests that the biepitaxial Josephson junction is formed around a dielectric-like barrier between superconducting grains. Anomalous subharmonic voltage steps were found under microwave irradiation. The relations between anomaly steps and fluxon motion are discussed.         High current gain HTS Josephson vortex flow transistors    P.A.C. Tavares, E.J. Romans and C.M. Pegrum Summary: We have fabricated discrete Josephson vortex flow transistors from yttrium barium copper oxide thin-films on 24 degree strontium titanate bicrystals. The devices have an asymmetric design with the control current fed through an independent control line. We have measured high current gains, in excess of 20 at 77 K for a range of several devices, and substantially higher at lower temperatures. The performance at 77 K has been studied and compared with theoretical simulations, which have included the effects of noise.         A discrete HTS Josephson flux-flow structure with gain at 77 K    T. Nguyen, G.A. Daniels, J.B. Beyer and J.E. Nordman Summary: We have developed flux-flow devices based on parallel arrays of HTS bi-crystal grain-boundary Josephson junctions (GBJs) with current gains well above unity (1.6-1.8) at 77 K. The symmetric control characteristics are similar to those of the LTS SuperCIT with the critical current maximum at zero control current and decreasing linearly with increasing control currents. Our design featured a control line that is defined by a parallel array of long slots in the base electrode. The slots confined the control current to within 2 /spl mu/m of the grain-boundary junctions resulting in tight coupling of the control fields to the junction array. Furthermore, the slots allowed the bias current to remain uniform as it crossed the control line into the base electrode. This combination was necessary to produce SuperCIT-like control characteristics as well as useful current gains in single-layer device structures. Device transresistance and usable output voltage range (typically 0.2-0.3 /spl Omega/ and 0.1 mV, respectively, for YBCO devices at 77 K) were limited by the low intrinsic shunt resistance and I/sub c/R/sub n/ product of the bi-crystal GBJs. Better device characteristics can be expected with improved junction qualities.         Gain-frequency characteristics of transistors based on flux flow in hysteretic long Josephson junctions (LJJ)    M.A. Ketkar, J.B. Beyer and J.E. Nordman Summary: Transistors based on one dimensional flux flow in hysteretic long Josephson junctions (LJJ) and deriving output from the spatial average over the length can be modeled as a section of transmission line. Time domain analyses made on these transmission line sections with both the ends terminated with typical resistance values reveal a fundamental gain-frequency relationship unique to all devices whose output voltage is equal to the spatial average over the length of the junction. The maximum frequency of a transistor depends on the transit time of carriers and the parasitic elements. The analysis shows that the frequency response of a flux flow transistor is related but not equal to the inverse of the transit time of fluxons. Secondly the step response of these transmission line sections varies linearly with time, which indicates a slew rate limitation. The slew rate that affects the high frequency response of a flux flow device is shown to be a function of the critical current density of the junction and material parameters. Analysis made on niobium-lead junctions indicates that the slew rate peaks at an optimum current density level. The results of these analyses and performance comparisons are presented.         Interaction induced by nonuniform self-fields in stacks of two long Josephson junctions    G. Carapella, G. Costabile, N.F. Pedersen and S. Sakai Summary: We fabricated and tested devices consisting of two long stacked Josephson junctions with direct access to the intermediate electrode, whose thickness is smaller than London penetration depth /spl lambda//sub L/. The electrodes are patterned so that the junctions can be independently biased in the overlap configuration. In the absence of an external magnetic field, we measured the critical current of one junction in the stack as a function of the bias current in the other junction, while the latter was either in the zero voltage state or in the McCumber state. The results indicate that mutual interaction takes place anyway, i.e. when both the junctions or only one of them is in the zero voltage state. To account for the observed phenomena we propose a model that takes into account the nonuniform self-fields generated by the bias currents in this special three-terminal device.         Narrow long Josephson junctions    Yu. Koval, A. Wallraff, M. Fistul, N. Thyssen, H. Kohlstedt and A.V. Ustinov Summary: Long Josephson junctions of width down to less than 0.3 /spl mu/m are fabricated using electron beam lithography. The junctions are made in niobium-aluminum-oxide trilayer technology using cross-linked PMMA for insulation. We measured the fluxon penetration field, the magnetic field period of the critical current modulation, and the Fiske step voltages of the junctions. A strong dependence of these quantities on the junction width is observed. Assuming a general-type relation between the spatial derivative of the phase and the spatial variation of the magnetic field along the plane of the junction, we derive a scaling relation between the measured quantities depending on the junction width. The derived relation is consistent with the experimental data.         Range of chaotic state in the Josephson junction driven by a pulse train signal    A. Takada, S. Kacchi, T. Furukawa and T. Kuwahara Summary: The parameter dependence of the onset of chaos which appears as the devil's staircase on the current-voltage curve in the Josephson junction driven by a pulse train signal is studied based on an analog circuit simulation. In this study, hysteresis parameter /spl beta/ and reduced frequency /spl Omega/ are regarded as significant. It is suggested that from the viewpoint of these parameter dependencies there is no remarkable difference in the range of chaotic states in the junction if compared to a monochromatic-signal-driven junction, meaning that operation above the junction plasma frequency is desirable to avoid chaos. The rf-amplitude dependence of the onset of chaos is also roughly surveyed.         Experimental realization of a 3D integrated RSFQ T-flip-flop using stacktrons    B. Ruck, R. Schmitz, N. Thyssen, B. Hermanns, H. Kohlstedt and S. Lomatch Summary: Superconducting circuits based upon Rapid Single Flux Quantum (RSFQ) Logic are an interesting approach for future digital electronics with clock frequencies in the range of 100 GHz. Our intention is to increase the integration density of such circuits. Therefore we have successfully fabricated and tested an RSFQ-circuit based on a new kind of stacked three terminal device, henceforth called a "stacktron". A stacktron consists of two vertically arranged all-niobium tunnel junctions, each separately shunted by a thin film resistor, and an access to the intermediate niobium layer. An RSFQ frequency divider (T-flip-flop) including two stacktrons has been tested up to 20 GHz. As a shunt resistor we used Pd/Au, so that /spl beta//sub c/<1 and the IV-curve is nonhysteretic. The junctions showed a current density of approximately 250 A/cm/sup 2/. The I/sub c/R/sub n/-product was 100 /spl mu/V. These first steps toward a three dimensional (3D) RSFQ architecture will be discussed in the framework of highly integrated and complex RSFQ-circuits.         Niobium tunnel junctions with multi-layered electrodes    P.N. Dmitiriev, A.B. Ermakov, A.G. Kovalenko, V.P. Koshelets, N.N. Iosad, A.A. Golubov and M.Yu. Kupriyanov Summary: The current-voltage characteristics of the niobium - aluminum oxide niobium tunnel junctions have been studied systematically and are compared with numerical simulations based on the microscopic theory of the proximity effect. The thickness of the base niobium layer is varied from 35 to 500 mm while the thickness of the aluminum layer is kept constant (about 9 nm). In a separate series of experiments the aluminum thickness is varied from 2 to 30 nm for two fixed thicknesses of the base electrode: 50 and 200 nm. The appropriate conditions for a full suppression of the so called "knee" structure at the gap voltage in the current-voltage characteristic are experimentally determined and theoretically interpreted in the framework of the microscopic theory. The influence of the additional aluminum layer in a composite base electrode on the properties of the tunnel junction have been studied in dependence on the aluminum thickness and distance of this layer from the barrier. The obtained results demonstrate that the current-voltage characteristics of tunnel junction can be engineering by an appropriate layer thickness of compound base electrode.         Non-equilibrium experiments in LTS Josephson double tunnel devices [Nb/Al/AlO/sub x//Nb]    G. Ammendola, G.P. Pepe, G.P. Peluso, G. Peluso, A. Barone, L. Parlato, E. Esposito, E. Monticone and M. Rajteri Summary: Superconducting Tunnel Junctions (STJ) are promising devices as a next generation of nuclear and optical detectors. Non-equilibrium experiments can provide useful information on the behaviour of a perturbed superconductor. Among possible nonequilibrium sources, we used quasi-particle injection in three-terminal double tunnel junction devices and a laser pumping source. We investigated the effect of perturbed conditions on sub-harmonic gap structures, which are present in I-V characteristics of high quality Nb-based STJs. Experimental results concerning the change of the energy gap measured at V=2/spl Delta//2e show features which can not be completely explained in terms of simple heating effects.         Energy level quantization in underdamped niobium Josephson junctions [Nb/AlO/sub x//Nb]    B. Ruggiero, C. Granata, E. Esposito, V.G. Palmieri, M.G. Castellano, C. Cosmelli, M. Russo and P. Silvestrini Summary: Macroscopic quantum effects in Josephson systems have recently attracted interest in the scientific community both for the physics involved and in view of applications. Here we present experiments on the presence of energy level quantization at temperatures above the classical-quantum regime crossover temperature in different Josephson junctions. This has been possible by extending the measurements of the escape rate out of the zero-voltage state at higher sweeping bias rate (dI/dt up to 100 A/sec) in order to induce nonstationary conditions in the energy potential describing the junction dynamics. Our measurements allow us to obtain as fitting parameter the "effective" resistance to be used in the RSJ model which is compatible with the subgap resistance at very low voltage. The very low dissipation level obtained at low temperatures renders our results quite interesting in view of applications in the quantum limit.         Characterization of individual noise sources in high-temperature superconductor Josephson junctions    T. Kemen, A. Marx, L. Alff, A.D. Koelle and R. Gross Summary: High temperature superconductor (HTS) Josephson junctions usually show a large amount of low frequency 1/f noise. This 1/f noise is caused by fluctuations of the junction critical current I/sub c/ and normal resistance R/sub n/ which are anti-phase correlated. These fluctuations originate from random fluctuations of the occupation number of charge traps in an insulating barrier. We have studied the magnetic field dependence of the normalized fluctuations in HTS grain boundary junctions to obtain information on possible spatial correlations between individual traps. Our experiments suggest that there are no spatial correlations between the noise causing traps on a length scale larger than a few 100 nm. Furthermore, the temperature and voltage dependence of the characteristic times of individual traps has been investigated. Here, for the first time we found clear evidence for a transition from a thermally activated to a tunneling like behavior of individual traps at low temperatures.         Characteristics of noises in high-temperature YBCO Josephson junctions    H.E. Horng, S.Y. Yang, J.T. Jeng, J.M. Wu, J.H. Chen and H.C. Yang Summary: In this work, the characteristics of the noises for high-temperature YBCO Josephson junctions and SQUIDs were studied. The noise power spectrum densities showed complicated behaviors, which may be attributed to many causes. In order to realize the contributions of these causes to the noise, the noise power spectra were detected at various bias currents. Thus, the noises owing to the critical current fluctuation, resistance fluctuation or apparent flux motion can be investigated. By comparing these noise power spectra under the different conditions, the origins of the noises for the junctions and SQUIDs can be clarified.         Low-frequency noise of YBCO/Au junctions    Y. Xu, J.W. Ekin and C.C. Clickner Summary: We have fabricated ex-situ c-axis YBCO/Au junctions with low contact resistivities. These devices exhibit large low-frequency resistance fluctuations. At room temperature the junction noise spectrum is 1/f like. At liquid nitrogen temperature (77 K) and lower, the noise spectrum depends sensitively on the bias current, with certain bias levels producing clear two-level fluctuation behavior. The normalized resistance noise for these junctions at temperatures below 77 K has an average value of 2 to 3/spl times/10/sup -5/(Hz)/sup -1/2/. We discuss practical issues related to junction noise properties.         The current-phase relation in high-T/sub c/ YBaCuO Josephson junctions    E. Ii'chev, V. Zakosarenko, R.R.J. Ijsselsteijn, V. Schultze, H.-G. Meyer, H.E. Heonig and H. Topfer Summary: The current-phase relation (CPR) of YBa/sub 2/Cu/sub 3/O/sub 7-x/ step-edge as well as 36/spl deg/ and 45/spl deg/ grain boundary Josephson junctions (GB JJs) has been investigated experimentally in the temperature range between 4.2 K and 85 K. The junctions were incorporated into a washer-shaped superconducting ring with inductance L=80-300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency between 9 and 40 MHz. The CPR has been obtained from the measurement of the impedance of the phase-biased junction. It is shown, that deviations from harmonic behavior of the apparent CPR for step-edge JJs can be explained by the influence of thermal noise. The CPR of 36/spl deg/ GB JJ were found to be very nearly sinusoidal in the measured temperature range. The CPR of 45/spl deg/ GB JJs were found to be nonsinusoidal at low temperatures. The reasons of this behavior are discussed.         Intermodulation measurements in superconducting meander lines    Shinho Cho and Cheon Lee Summary: The intermodulation measurements are used to study the nonlinear effects in high-T/sub c/ microstrip meander lines at microwave frequencies. The superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ (YBaCuO) thin films were grown by laser ablation on both sides of lanthanum alumite substrates and the microstrip pattern was defined using photolithography. The meander line is elicited by two microwave signals from two sweep oscillators at both frequencies of 4.70052 GHz and 4.69952 GHz over temperature range of 19 to 86 K. The measured harmonic signals show a gradual decrease in transmission and disappear as the critical temperature is reached. As for the dependence on the input power the transmission (A) of the third-order harmonic signals at 19 K shows a linear dependence on the input power (P), A(P)=1.30P-61 in the range of 12.5-17.0 dBm.         An HTS transceiver for third generation mobile communications    R.B. Greed, D.C. Voyce, D. Jedamzik, J.S. Hong, M.J. Lancaster, M. Reppel, H.J. Chaloupka, J.C. Mage, B. Marcilhac, R. Mistry, H.U. Hafner, G. Auger and W. Rebernak Summary: Future third-generation mobile communication systems will require improved sensitivity and selectivity to support the growth in multi-media services, increased coverage, longer talk time and larger numbers of subscribers. The paper describes a transceiver for use in mobile and personal communications base transceiver stations (BTS). Key components of the transceiver are fabricated using thin film high temperature superconductor technologies to achieve, in the receiver chain, enhanced sensitivity and selectivity and, in the transmitter chain, reduced combiner losses and increased selectivity. Cryo-packaging techniques, which provide a long between-service interval are described. The cryogenic r.f. module encapsulation design features novel r.f. and thermal interconnects which obviates the need for long lossy input cables. In-situ tuning methods allow the HTS filters to be optimised at the operating temperature, 60 K, and in vacuum. The transceiver incorporates an integrated miniature Stirling-cycle cooling engine designed for a 5-watt heat lift at 60 K, over an ambient temperature range of -40/spl deg/C to +65/spl deg/C. The control electronics are driven directly from the BTS d.c. supplies. The input power requirement to the cryo-cooler and drive electronics is <250 watts. The design of the cooler is arranged to provide an inherent balance, virtually eliminating vibration. Multiple r.f. transceivers are integrated with a single cryocooler, and together with bypass switching, alarms and lightning protection, are contained within a single mast-head mounted weatherproof housing.         Transmit filters for wireless basestations    A.C. Anderson, Hui Wu, Zhengxiang Ma, P.A. Polakos, P.M. Mankiewich, A. Barfknecht and T. Kaplan Summary: Transmit filters for PCS basestation applications will be required to handle peak power levels up to hundreds of watts. To achieve this goal, filters based on high temperature superconductor patch resonators have been investigated. Among these, circular resonators operating in the TM/sub 010/ mode, due to its radial current flow, are particularly promising. However, the large size of these resonators places limits on the frequency and number of poles of planar filters. As an alternative, we have designed and tested 3-pole filters based on the vertical coupling of stripline circular resonators. For operation in the PCS frequency range each resonator was fabricated from two double-sided YBCO films deposited on 2-in. lanthanum aluminate substrates. The measured Q of these resonators at 50 K and 2 GHz was higher than 100,000 and is limited by the dielectric losses of the substrate. The measured circulating power of above 1 MW at 50 K extrapolates to power handling, for a 9-pole, 1% bandwidth filter, of more than 1 kW. A 1.2% bandwidth, 3-pole filter based on this design has been characterized, and does not show any power dependence up to 72 W, the limit of our test setup.         Superconducting filters for wireless communications: a reappraisal    D.G. Smith and V.K. Jain Summary: Since 1992, several U.S. companies have developed high temperature superconducting (HTS) filters with low insertion loss and high Q-factors for wireless applications. With the promise of HTS filters to provide increased basestation sensitivity (leading to increased range for rural basestations), better interference rejection, and improved quality of cellular and PCS services, predictions of a large market were made, Booz Allen first studied this emerging market in 1995, when the technology was still relatively new. Today, representatives of many of the leading U.S. wireless service providers and equipment manufacturers are familiar with the capabilities of HTS filters, now frequently combined with cryogenic LNAs. In addition, incumbent technologies have improved, and possible alternative solutions developed. Using Booz Allen's proven market characterization approach, this paper re-examines the requirements of the cellular/PCS market and includes order-of-magnitude estimates of market sizes for the rural range extension case. Drivers of adoption, competing technologies, emerging market trends, new innovations, and the impact of cryocooling are all considered. We conclude that the domestic U.S. market may be slower to develop than earlier estimates predicted, and consider strategies for HTS filter vendors to grow the market.         Development of superconductive microwave filters for mobile communications and filter banks    B. Marcilhac, Y. Lemaitre, D. Mansart and J.C. Mage Summary: The development of superconductive microwave filters connected to the use of cooled electronics is now in the critical phase of system integration. All the different steps of filter development, design and fabrication must be controlled, reproducible and technically realisable by conventional microelectronics tools. We developed filters for mobile communications and filter banks with the goal of optimising these aspects. Lanthanum aluminate substrates were chosen instead of magnesium oxide or sapphire substrates. The fabrication of double-side sputtered film on 2" diameter wafer was optimised and stabilised resulting in very low insertion loss. To eliminate the time-consuming operation of tuning the filter with screws, the complete designs were modelled by EM software. Exact agreement has been obtained between modelling and measurements. Results on a 10-pole 1.75 GHz bandpass filter with 5% bandwidth and on a 5-pole 9.1 GHz passband filter with 0.5% bandwidth are presented.         HTS AMPS-A and AMPS-B filters for cellular receive base stations    E.R. Soares, K.F. Raihn, A.A. Davis, R.L. Alvarez, P.J. Marozick and G.L. Hey-Shipton Summary: The multiple, interleaved pass band nature of the AMPS cellular system provides an excellent opportunity for high performance HTS filter technology for base station reverse link applications. The 25 MHz spectrum is divided into 4 unequal bands, 2 each for the A and B operators. For AMPS-A, the two band pass filters are connected in parallel, while for AMPS-B a band pass filter is cascaded with a band reject filter. All band pass filters have finite transmission zeros and the band reject filter is designed to have an equal ripple stop band. The design and performance of high selectivity filters for this application is described.         Evaluation of HTS sub-systems for cellular basestations    D. Jedamzik, R. Menolascino, M. Pizarroso and B. Salas Summary: The application of High Temperature Superconductors (HTS) has led to the development of new sub-systems for cellular basestations used in network infrastructures. They offer performance advantages in terms of sensitivity and selectivity as well as a reduction in size, which allows them to be installed on top of the antenna mast. Results are presented for an HTS-system, which was designed to interface to GSM-1800 basestations. The measured performance parameters of an HTS subsystem and a conventional system have been implemented into a network-planning tool to assess the advantages in the improved system performance for network operators. Both macro cellular environments, deployed to serve rural areas with a low user density and an urban condition, with macro plus microcellular environment with a high subscriber density have been evaluated. The results show, that the network operator can choose to employ different advantages, for example a reduction in the number of basestations in rural areas by 24%, or an increased capacity in urban areas with a simultaneous reduction of carriers by 30%.         Flux quantum sigma-delta analog-to-digital converters for rf signals    D.L. Miller, J.X. Przybysz, A.H. Worsham and E.J. Dean Summary: The sigma-delta architecture is the method of choice for analog-to-digital converters (ADCs) for high dynamic range applications. This architecture uses oversampling and precise feedback to generate a shaped spectral distribution of the quantization noise. Subsequent digital filtering suppresses out-of-band quantization noise, yielding a large signal to in-band noise ratio. A unique advantage of superconducting electronics is the availability of the flux quantum to provide quantum mechanically accurate feedback at GHz rates. Josephson digital technology extends sigma-delta ADCs from MHz sampling rates to GHz sampling rates, from kHz signal bandwidths to MHz signal bandwidths, with comparable or better dynamic range when compared to semiconductor implementations. This paper presents circuits for Josephson sigma-delta ADCs, including single-loop and double-loop modulators operating at sampling rates up to 2 GHz, and circuits for quantized feedback. The first demonstration of double-loop noise shaping is also presented.         Extraction of impacts of fabrication spread and thermal noise on operation of superconducting digital circuits    V.K. Semenov, Yu.A. Polyakov and Wei Chao Summary: We have developed a procedure to investigate and distinguish several disturbing influences on an RSFQ circuit such as thermal noise, flux trapping and fabrication spread. The procedure is applied to a slightly modified RSFQ shift register with 3 independent dc biases, which are common for all cells. One of the biases performs a special function. Nominally it is equal to zero and used only to create a controllable effect on the operation of the circuit. The impact of different factors is extracted from their interference with the special bias. It has been found that the influence of thermal noise in the best samples fabricated at HYPRES, Inc. is comparable with that of fabrication spread even for low (/spl sim/4 K) operational temperature.         CNET: design of an RSFQ switching network for petaflops-scale computing    L. Wittie, D.Yu. Zinoviev, G. Sazaklis and K. Likharev Summary: This work is part of a project to design a petaflops-scale computer using a Hybrid Technology Multi-Threaded (HTMT) architecture. In the core of the superconductor part of the HTMT system there should be a high-bandwidth low-latency RSFQ switching cryonetwork (CNET) connecting 4.096 computing modules with each other and with room-temperature semiconductor components. In this report, we present a preliminary study of three simplified, "flat" models of the CNET, each for two alternative architectures: banyan network and pruned high-dimensional mesh. The results indicate that with the speed and space limitations accepted in the HTMT concept, CNET will be able to provide a cross-sectional bandwidth of about 2/3 packets per computing module per network clock cycle (in the present design, 32 ps).         Self-timed parallel adders based on DI RSFQ primitives    Y. Kameda, S.V. Polonsky, M. Maezawa and T. Nanya Summary: We present two versions of self-timed pipelined parallel carry-look-ahead adders. The adders are designed based on delay-insensitive (DI) rapid single-flux-quantum (RSFQ) primitives. Basic binary gates employ dual-rail encoded data, which include timing information in themselves. One version uses wave pipelining and the other delay-insensitive pipelining with a request-acknowledge data transfer protocol. We show simulation results of 4 to 32-bit adders and their sensitivity to delay variations. Two design schemes are compared in terms of area, speed, robustness, interface and design process for large systems.         High-speed asynchronous data multiplexing/demultiplexing    A.F. Kirichenko Summary: High-speed data acquisition and communication systems require fast multiplexing and demultiplexing of data. We are developing novel multiplexer/demultiplexer circuits using a dual-rail approach. A single cell of the demultiplexer is a toggle type B flip-flop. The demultiplexer operates at 95 GHz and its performance does not depend on the demultiplexing ratio. The dual-rail technique avoids racing between data and clock signals. The multiplexer circuit is based on RS type B flip-flops and works up to 60 GHz. The circuits are implemented in HYPRES' standard Nb process with a critical current density of 1.0 KA/cm/sup 2/.         A novel approach to chip-to-chip communication using a single flux quantum pulse    M. Maezawa, H. Yamamori and A. Shoji Summary: A novel approach to chip-to-chip communication for RSFQ technology is proposed. The main idea is to fabricate Josephson junctions on a substrate for multi-chip packaging, which equips the substrate as well as the chip with built-in active drivers and receivers. The driver on the chip is connected directly to the receiver on the substrate through a connector which can be considered as a lumped circuit element. Because the circuit is free from the impedance matching constraint, broadband chip-to-chip data transfer with wide operating margins will be realized. We have designed, simulated and optimized a chip-to-chip single flux quantum (SFQ) pulse transfer circuit. For a connector inductance of 20 pH, the bias current margins and the maximum throughput have been calculated to be /spl plusmn/24% and above 50 Gb/s, respectively.         Modeling of a long Josephson junction coupled to SFQ elements    Yongming Zhang Summary: By combining a long Josephson junction (LJJ) with single-flux-quantum (SFQ) circuits, new digital applications for long junctions can be explored. To fully investigate the dynamics of the hybrid LJJ/SFQ circuits, a numerical model was developed for an unshunted long junction coupled to shunted SFQ Josephson transmission line (JTL) through superconducting strips. The model is based on a one-dimensional array of Josephson junctions that is described by a set of discrete sine-Gordon equations. Simulations support our experimental observation that the first zero-field step can exist when the LJJ is terminated by SFQ elements. The influences on the first zero-field step by the self-inductance, the critical current, and the shunt resistance of JTL cells are studied in detail. Simulation also confirms that each 4/spl pi/ phase leap at the end of the long junction creates two separated SFQ pulses after several overdamped JTL cells.         Magnetoencephalogram systems developed at KIT    H. Kado, M. Higuchi, M. Shimogawara, Y. Haruta, Y. Adachi, J. Kawai, H. Ogata and G. Uehara Summary: We have developed new systems for magnetoencephalography (MEG). The pick up coil is a coaxial type first-order gradiometer with 50-mm base line. The magnetic field resolution of the system is about 4 fT/Hz/sup 0.5/ or 0.8 (fT/cm)/Hz/sup 0.5/ in white noise region. The unique feature of the system is the gantry-free horizontal dewar, which is fabricated through what we call "ship-in-a-bottle approach". Less than 10-liter/day liquid helium consumption for the 100-liter capacity is realized. One of the merits of the horizontal dewar is that a small room is sufficient for installation because of the low height (0.89 m) of the dewar. Another merit is that the patient can be measured in lying position which is more relaxing compared to the conventional vertical type.         Synthetic gradiometer systems for MEG    A.A. Fife, J. Vrba, S.E. Robinson, G. Anderson, K. Betts, M.B. Burbank, D. Cheyne, T. Cheung, S. Govorkov, G. Haid, V. Haid, C. Hunter, P.R. Kubik, S. Lee, J. McKay, E. Reichl, C. Schroyen, I. Sekachev, P. Spear, B. Taylor, M. Tillotson and W. Sutherling Summary: This paper will describe features and performance of low-T/sub c/ whole-cortex MEG systems which utilise synthetic gradiometers to achieve a high level of environmental noise cancellation. The near field MEG sensitivities achieved through use of synthetic gradiometers typically range from 3 to 7 fT//spl radic/Hz above 1 Hz in moderately shielded rooms and less than 10 fT//spl radic/Hz above a few Hz in open environments. This performance has been observed for fixed vertical and also adjustable MEG systems which can tilt between vertical and horizontal orientations.         A vector magnetometer module for biomagnetic application    M. Burghoff, H. Schleyerbach, D. Drung, L. Trahms and H. Koch Summary: Multichannel SQUID systems are widely used for biomagnetic research. Commonly, these instruments measure one component of the magnetic vector field or one gradient of vector field. We have designed a vector magnetometer module allowing the recording of orthogonal vector components. The module is designed as a cube with one liquid helium cooled SQUID mounted at each of its six faces. The mean values of signals from SQUIDs of opposite faces are estimates for the magnetic field components in the center of the cube. Due to Maxwell's third equation, the signals of the six SQUIDs can be combined to yield zero. This allows an on-line check of the SQUID performance. The features of the vector magnetometer module are illustrated by cardiac measurements. 3D graphics allow direct inspection of the magnetic field vector. The cube is designed to be used as a basic module of a multichannel SQUID system for biomagnetic application.         Neuromagnetic SQUID measurement in a superconducting magnetic shield    H. Ohta, M. Aono, T. Matsui, Y. Uchikawa, K. Kobayashi, K. Tanabe, S. Takeuchi, K. Narasaki, S. Tsunematsu, Y. Koyabu, Y. Kamekawa, K. Nakayama, T. Shimizu, Koike, K. Hoshino, H. Kotaka, E. Sudoh, H. Takahara, Y. Yoshida, K. Shinada, M. Takahata, Y. Yamada and K. Kamijo Summary: A superconducting magnetic shield of high-Tc superconductor Bi(Pb)SrCaCuOx has been constructed whose diameter is 65 cm and length is 160 cm respectively. We have successfully observed somatosensory evoked magnetic fields coming out from human brains in the superconducting magnetic shield stimulating the median nerves of patients by current pulses. We made a 64-channel whole-head SQUID magnetometer of SNS (Superconductor/Normal metal/Superconductor) junctions. The sensitivities of the dc-SQUID of mesoscopic SNS junctions are around 5 fT//spl radic/(Hz) even in rather unfavorable surroundings. The magnetic shield can reduce a magnetic field to around -80 dB or 10/sup -4/ even at as low a frequency as 0.05 Hz.         High-Tc SQUID systems for practical use    P. Seidel, F. Schmidl, S. Wunderlich, L. Dorrer, T. Vogt, H. Schneidewind, R. Weidl, S. Losche, U. Leder, O. Solbig and H. Nowak Summary: Planar thin film DC-SQUID gradiometers with small base length (4...6 mm) were optimized for application in different measurement systems. The field gradient noise of these planar DC-SQUID gradiometers in unshielded environment is better than 5 pT/cm/spl radic/(Hz) (at 1 Hz, 77 K). Other components of these systems like electronics, cryostats, scanning equipment, and data analysis software are discussed. An industrial system for nondestructive evaluation and a clinical system for bedside investigations on cardiac infarction are demonstrated as examples of starting cooperation between university and small companies interested in application of superconductivity.         High-resolution measurement by a high-T/sub c/ superconductor sampler    M. Hidaka, T. Satoh, M. Koike and S. Tahara Summary: We measured a signal current waveform by using a high-T/sub c/ superconductor (HTS) sampler with a 1-ps delay between every sampling point. The maximum time differential obtained in the measured waveform was 12 /spl mu/A/ps with a 2.5-/spl mu/A current sensitivity at 25 K. This result guarantees that the sampler is able to measure current waveforms correctly when their maximum time differential is less than 12 /spl mu/A/ps. The superior temporal response was achieved by using high-speed single-flux-quantum pulses generated in the HTS circuit. A unique feature of the sampler is that it directly measures the current with picosecond and microampere resolutions. Measurement of current flowing through wiring in a semiconductor large-scale integrated circuits is a promising application for the HTS sampler.         Fabrication of QFP devices from Au/SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ structures    H. Hasegawa, Y. Tarutani, T. Fukazawa and K. Takagi Summary: Quantum Flux Parametron (QFP) devices were fabricated from Au/SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ structures based on bicrystal grain boundary junctions. The junction connected to a load inductor in series was utilized as a sampling gate which reads out the load current. External fluxes were applied to two closed loops separately in the QFP by using two independent activation lines in order to reduce the load inductance. A multiplexer consisting of a couple of the QFPs and the sampling junction was fabricated and was tested at 6.5 K.         Picosecond response of optically driven Y-Ba-Cu-O microbridge and Josephson-junction integrated structures    R. Adam, M. Currie, R. Sobolewski, O. Harnack and M. Darula Summary: We report our studies on single-picosecond electrical pulse excitation and detection in YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) transmission lines containing microbridges and grain-boundary Josephson junctions. The structures were patterned in YBCO films grown by laser ablation on MgO bicrystals and consisted of 20-/spl mu/m-wide coplanar lines, separated by a 20-/spl mu/m-wide gap. Each transmission line contained a 5-/spl mu/m-wide and 10-/spl mu/m-long microbridge and a 5-/spl mu/m-wide grain-boundary weak link, and was overlaid with 50 nm of Au to improve its high frequency properties. Using a Ti:sapphire laser, we excited the microbridge with 100-fs-wide 400-nm-wavelength optical pulses and studied response of our test structures, utilizing a cryogenic electro-optic sampling system. We directly observed 2.1-ps-wide pulses generated by YBCO microbridges, as well as the single-picosecond Josephson junction response. The junction response depended directly on the current bias and its polarity with respect to the excitation electrical pulse, and exhibited single-flux-quantum-like characteristics. Our test structures can be regarded as examples of all-YBCO ultrafast optoelectronic circuits.         Monte Carlo and thermal noise analysis of ultra-high-speed high temperature superconductor digital circuits    M. Jeffery, P.Y. Xie, S.R. Whiteley and T. Van Duzer Summary: We model the high temperature superconductor (HTS) rapid single flux quantum (RSFQ) toggle (T) flip-flop including process variations and thermal noise. A Monte Carlo method is used to calculate the theoretical yield of the circuit at speeds ranging from 1-83 GHz and for various process parameter spreads. Thermal noise is also included in the simulations and we calculate bit error rates at 1-150 GHz as a function of temperature. Our results demonstrate quantitatively the difference between HTS layouts with and without parasitic inductance. Furthermore, our simulations suggest that using the existing HTS process with a 250 /spl mu/V I/sub c/R/sub n/ product the T flip-flop operating temperature should be below 40 K in order to obtain bit error rates less than 10/sup -6/ at gigahertz speeds.         High temperature superconducting multilayer multichip module: fabrication and high speed characterization    P.R. Anderson, A.W. Lindner, P.M. Chau and A.D. Smith Summary: Superconductivity is attractive for high performance multichip modules (MCMs) for increasing wiring density while eliminating attenuation and dispersion caused by wiring resistance. However, multilayer HTS structures have been difficult to fabricate. A methodology and materials set was developed to fabricate a multilayer structure with superconducting traces in the X-Y planes and normal metal interconnects in the Z-plane. A simple, multilayer circuit was designed to characterize the high-speed digital waveform characteristics and pulse integrity. Design guidelines were employed to maintain constant impedance through multiple transmission lines. The circuit was modeled on a 3D simulator with a one nanosecond rise-time pulse. The goal was to correlate the modeled and measured data with respect to the pulse integrity and impedance. Eye-diagrams were produced using a one-gigahertz pulse train. In addition, thermal cycling was performed on the structures to identify if any thermal expansion mismatches occurred. Electrical tests were performed before and after the cycling to verify circuit integrity. The data from the thermal cycling will be discussed.         HTS scanning SQUID microscopy of active circuits    E.F. Fleet, S. Chatraphorn, F.C. Wellstood and L.A. Knauss Summary: We have used a high-T/sub c/ scanning SQUID microscope to image semiconductor circuits operating in air at room temperature. Our microscope uses a commercially available 77 K refrigerator to cool a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// dc SQUID. The system maintains vacuum isolation of the SQUID even when it is separated from a room-temperature sample by about 30 /spl mu/m. When operated in this manner, the SQUID has a magnetic field sensitivity of 20 pT//spl radic/Hz above 500 Hz. By inverting the magnetic field images to generate two-dimensional current density distributions, we localize current paths to within /spl plusmn/36 /spl mu/m at SQUID-sample separations of 150 /spl mu/m. We present images and discuss the spatial resolution obtained with this technique.         High-T/sub c/ SQUID microscope study of the effects of microstructure and deformation on the remanent magnetization of steel    T.J. Shaw, K. Schlenga, R. McDermott, J. Clarke, J.W. Chan, S.-H. Kang and J.W. Morris Jr. Summary: We have studied the effects of heat treatment and mechanical stress on the remanent magnetization of ferromagnetic steels using a high-transition-temperature (HTC) Superconducting QUantum Interference Device (SQUID) microscope. Samples were prepared by different heat treatments, which produced varied microstructures, and different rolling treatments, which produced varied levels of deformation. The samples were subsequently magnetized in fields of 50 mT, and the remanent magnetization was measured by rastering the sample over the SQUID using a two-dimensional (2D) translation stage with a scanning range of 50 mm/spl times/50 mm. With a separation between the SQUID and sample of approximately 0.5 mm, this produced a 2D magnetic field image due to the local remanent magnetization of the sample. In addition, microstructural information was determined using optical imaging, allowing us to correlate the effects of heat treatment and mechanical stress on local remanent magnetisation with detailed microstructural information. Since the strength and integrity of steels can be well predicted from microstructural information, correlation of this information with the 2D remanent magnetization images could lead to an effective method for the non-destructive evaluation of ferromagnetic steels through a simple measurement of remanent magnetization.         A scanning SQUID microscope for samples at room temperature    J. Dechert, M. Mueck and C. Heiden Summary: We report on the development of a scanning SQUID microscope for measurements of samples at room temperature. A thin film niobium DC-SQUID is used with conventional read-out electronics. It is placed above the thin bottom window of a fiberglass cryostat, allowing us to realize a distance of about 75 /spl mu/m between SQUID and sample. The evaporation rate for the liquid helium was about 0.3 1/h. Because the effective SQUID area can easily be brought below 10 /spl mu/m/sup 2/, the obtainable spatial resolution of such a scanning SQUID microscope is limited mainly by the distance between SQUID and sample. The sample is moved under the cryostat with a computer controlled XY-stage. Provisions are made for quick sample changes which are important for the practical application of such a device.         A variable temperature scanning SQUID microscope    A.Ya. Tzalenchuk, Z.G. Ivanov, S. Pehrson, T. Claeson and A. Lohmus Summary: We present a design of a scanning SQUID microscope (SSM) operating in a temperature range between about 5 K (2 K with pumping) and 100 K.         Application of high performance LTS SQUID systems in gravitational experiments    W. Vodel, H. Koch, S. Nietzsche, J.V.Z. Glyscinski, R. Neubert, M. Pilz, H. Dittus, S. Lochmann, C. Mehls and D. Lockowandt Summary: The design of a Galilean-type free-fall experiment to test Einstein's equivalence principle at an improved level of sensitivity is described. Two test bodies of different material fall down from a height of 109 m inside of an evacuated drop tube (Drop Tower Facility Bremen, Germany). Their possible relative displacement is measured using LTS DC SQUID based position sensors. Experiences and results of this experiment meet directly the current STEP project of NASA/ESA to test the Equivalence Principle in space at a level of one part in 10/sup 18/. Several issues of the developed measuring system are discussed, above all, the performance of two types of SQUID position sensors. Furthermore some recent results of free fall tests of components of the measuring system at the Bremen Drop Tower are presented.         Measurements of the decoherence time from energy level quantization in Josephson junctions and rf SQUIDs    C. Cosmelli, F. Chiarello, G. D'Agosta, M.G. Castellano and G. Torrioli Summary: We have measured the effective resistance of a Josephson junction and of an rf SQUID cooled at a temperature between 18 mK and 35 mK. From a fit of the data with a simplified solution of the master equation describing the system dynamics we found for both devices an effective resistance R/spl ap/4-5 M/spl Omega/. This value, in the same system cooled at 5 mK, would lead to a decoherence time of approximately 1.1 /spl mu/s allowing one to perform measurements of the Rabi oscillations having a tunneling frequency of the order of few MHz. This value is very promising also for the realization of qu-bits realized by means of Josephson devices.         Superconducting material diagnostics using a scanning near-field microwave microscope    S.M. Anlage, D.E. Steinhauer, C.P. Vlahacos, B.J. Feenstra, A.S. Thanawalla, Wensheng Hu, S.K. Dutta and F.C. Wellstood Summary: We have developed scanning near-field microwave microscopes which can image electrodynamic properties of superconducting materials on length scales down to about 2 /spl mu/m. The microscopes are capable of quantitative imaging of sheet resistance of thin films, and surface topography. We demonstrate the utility of the microscopes through images of the sheet resistance of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film wafer, images of bulk Nb surfaces, and spatially resolved measurements of T/sub c/ of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film. We also discuss some of the limitations of the microscope and conclude with a summary of its present capabilities.         Flux flow oscillators for sub-mm wave integrated receivers    V.P. Koshelets, S.V. Shitov, A.V. Shchukin, L.V. Filippenko, P.N. Dmitriev, V.L. Vaks, J. Mygind, A.M. Baryshev, W. Luinge and H. Golstein Summary: The results of a detailed study of the microwave linewidth of Nb-AlO/sub x/-Nb flux flow oscillators (FFO) are presented. The dependence of the FFO linewidth on the junctions parameters has been measured by using an improved technique based on harmonic mixing in the frequency range 250-600 GHz. Experimental data are compared with theoretical estimates to evaluate the influence of the possible mechanisms responsible for the broadening of the FFO linewidth. The origins of the increased linewidth at the transition from the resonant to the "pure" flux-flow regime are discussed. The results of the linewidth measurements for the FFO locked to an external synthesizer via a wideband feedback loop are presented. The possibility of phase locking of the Josephson oscillator has been demonstrated experimentally. A FFO linewidth as low as 3.3 kHz (determined by the resolution bandwidth of the spectrum analyzer) has been measured at 310 GHz; it is far below the fundamental level given by shot and thermal noise of the free-running tunnel junction.         Analysis of linear branches in the I- characteristics of Josephson junctions    M. Cirillo, V. Merlo and N. Gronbech-Jensen Summary: Resistive branches have often been observed in the current-voltage characteristics of long Josephson junctions. In the present paper we perform a systematic numerical analysis of the generation of these branches when an external magnetic field is applied to the junctions. We show that the linear branches exist only over a limited voltage interval which is determined quantitatively. We also clarify to what extent the linear branches can be attributed to flux-flow effects.         Application of a DC SQUID array amplifier to an electrically small active antenna    J. Luine, L. Abelson, D. Brundrett, J. Burch, E. Dantsker, K. Hummer, G. Kerber, M. Wire, K. Yokoyama, D. Bowling, M. Neel, S. Hubbell and K. Li Summary: We have built and operated a wide band electrically small active antenna consisting of a YBa/sub 2/Cu/sub 3/O/sub 7/ half-loop over ground plane antenna, an LTS (niobium) 200 element DC SQUID array amplifier, and low-noise cryogenic GaAs buffer amplifier. These components were integrated with a liquid He flow cryostat into a portable stand-alone package. Measurements of active antenna response from 50 to 500 MHz were made using a transverse electromagnetic cell to illuminate the half-loop antenna. At frequencies below the observed antenna resonance (250 MHz) the active antenna response is flat thereby exhibiting wide band gain.         1 volt DC programmable Josephson voltage standard    C.J. Burroughs, S.P. Bent, T.E. Harvey and C.A. Hamilton Summary: NIST has developed a programmable Josephson voltage standard (JVS) that produces intrinsically stable voltages that are programmable from -1.1 V to +1.1 V. The rapid settling time (1 /spl mu/s), large operating current margins (2 to 4 mA), and inherent step stability of this new system make it superior to a conventional JVS for many dc measurements. This improved performance is made possible by a new integrated-circuit technology using intrinsically shunted superconductor-normal-superconductor (SNS) Josephson junctions. These junctions operate at lower excitation frequencies (10 to 20 GHz) than a conventional JVS and have 100 times greater noise immunity. The Josephson chip consists of a binary array sequence of 32 768 SNS Josephson junctions. The chip has been integrated into a completely automated system that is finding application in mechanical/electrical watt-balance experiments, evaluation of thermal voltage converters, electron-counting capacitance standards, and metrology triangle experiments.         Improved primary Josephson voltage standard with a new microwave driving source    H.-G. Meyer, G. Wende, L. Fritzsch, F. Thrum, M. Schubert, F. Muller, R. Behr and J. Niemeyer Summary: Several improvements of Josephson voltage standard systems are described. These concern optimized microwave chips for the voltage generation, a new cryoprobe with an attenuation-reduced waveguide and a simplified microwave source. All these improvements contribute to a marketable cryogenic voltage standard.         77 GHz RSFQ counter for DC Josephson voltage standard applications    M.S. Pambianchi, Wenquan Li, J. Coughlin, E. Talej and D.K. Brock Summary: Josephson primary voltage standards require a frequency-locked 77 GHz signal to perform precise frequency-to-voltage conversion. We describe the development of superconducting frequency counters used for microwave source locking in Josephson junction array primary voltage standards, and discuss design challenges and high speed test results. The counters increase the accessibility of Josephson standards by reducing the size, number of components, and cost of these systems.         New microwave circuits for programmable voltage standards using high-temperature Josephson junction arrays    A.M. Klushin, C. Weber, H. Kohlstedt, R.K. Starodubrovskii, A. Lauer, I. Wolff and R. Semerad Summary: New microwave circuits for voltage standard application containing 256 shunted bicrystal junctions were designed and investigated. The series array follows a meander line, which prevents the uniform distribution of microwave current along the array. To overcome this drawback, we are placing the meander parallel to a coplanar waveguide line. This provides parallel feeding of microwave power to series connected junctions. A circuit divided in 8 sub-arrays represents a seven-bit digital-to-analog converter. At a frequency f=27332 MHz and for a constant power each of the segments of the array demonstrated the first current step at 78 K.         High temperature Josephson bicrystal junctions and arrays for metrological applications    C. Weber, A.M. Klushin, S. Beuven, A. Van Der Hart, H. Kohlstedt, R. Semerad and W. Prusseit Summary: Concerning metrological applications of high-temperature superconductor (HTS) Josephson junctions, we investigated the properties of gold shunted bicrystal YBCO junctions on yttria-stabilized zirconia (YSZ) and sapphire substrates. We focus on three important items that are related to the problem of parameter spreads: (a) the control of the shunt resistance-this parameter is dominated by the contact resistivity between the YBCO and the Au-a direct method for the measurement of this crucial parameter was applied; (b) the impact of the shunt resistance and the spread in junction resistance on the tolerable junction size and the frequency working regime for metrological arrays; and (c) the realization of series arrays with a high packing density of junctions using electron-beam-patterning. The parameter spreads are comparable to those of standard lithography processed junctions.         Josephson voltage standard by controlling chaos    E. Abraham, I.L. Atkin and A. Wilson Summary: We apply control of chaos to the rf-biased Josephson junction used in the voltage standard. We show that the technique works successfully, even in the presence of thermal noise. Restrictions on nonlinearity no longer apply and phase locking can be ensured.         Magnetically tunable superconducting resonators and filters    D.E. Oates and G.F. Dionne Summary: Compact, low-loss, tunable filters are needed for overload protection in the front end of many microwave-frequency systems. We have demonstrated magnetically tunable superconducting resonators and filters comprising microwave circuits coupled to ferrite substrates in monolithic structures using niobium at 4 K and hybrid resonator structures using YBCO at 77 K. A three-pole 1% bandwidth filter with 10-GHz center frequency and 1-dB insertion loss is described. In these devices the tunability results from changes in the magnetization of the ferrite rather than changes in the ferrimagnetic resonance frequency as in conventional YIG filters. Tunability data plotted us a function of magnetic field are fitted to the hysteresis theory developed previously and indicate that a tuning range of 13% is achievable. We have demonstrated switching times of less than one microsecond in structures incorporating closed magnetic paths in the form of a circular toroid.         Simultaneous optimization of the linear and nonlinear microwave response of YBCO films and devices    J.C. Booth, J.A. Beall, D.A. Rudman, L.R. Vale, R.H. Ono, C.L. Holloway, S.B. Qadri, M.S. Osofsky, E.F. Skelton, J.H. Claassen, G. Gibson, J.L. MacManus-Driscoll, N. Malde and L.F. Cohen Summary: We present results of a systematic study of the effect of film deposition temperature on both the linear and nonlinear response of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films and devices at microwave frequencies. Measurements of the unpatterned films show that samples grown by pulsed laser deposition at a lower substrate temperature (740/spl deg/C) display a smaller low-temperature residual surface resistance compared to films grown at a higher substrate temperature (780/spl deg/C). However, the same films which display low residual surface resistance also show increased nonlinear effects (measured by third harmonic generation) at all temperatures. Analysis of these results suggests that the increased defects present in the films grown at the lower deposition temperature are responsible for both the lower surface resistance and the higher third harmonic generation observed in these samples. We discuss the consequences of these results for the simultaneous optimization of both linear and nonlinear microwave properties of HTS thin films and devices.         Microwave intermodulation in high-T/sub c/ superconducting microstrip resonators    B.A. Willemsen, B.H. King, T. Dahm and D.J. Scalapino Summary: We present experimental results on microwave intermodulation measurements on a High T/sub c/ Superconducting band-reject microstrip resonator which exhibits unconventional 2:1 intermodulation products. We discuss unusual features of this 2:1 behavior that are uncovered by detailed frequency swept and unbalanced power measurements. We also introduce a phenomenological theory which arises from a nonlinear inductance of the form L=L/sub 0/+/spl alpha/|I| which quantitatively describes the observed response.         YBaCuO disk resonator filters operating at high power    B.A. Aminov, H. Piei, M.A. Hein, T. Kaiser, G. Muller, A. Baumfalk, H.J. Chaloupka, S. Kolesov, H. Medelius and E. Wikborg Summary: We have developed and successfully operated a compact tunable one-pole filter at 2 GHz for transmitter combiners in mobile radio base stations. The concept is based on edge-current free modes in circular symmetric resonators. Unloaded quality factors Q/sub 0/>5.10/sup 5/ were achieved with double-sided 2''-diameter YBaCuO films on Czochralski-grown LaAlO/sub 3/. The dielectric loss tangent limited Q/sub 0/ around 60 K to values below 10/sup 5/. A circulating (transmitted) power of 800 kW (130 W), 700 kW (115 W) and 90 kW (15 W) could be handled in pulsed operation (pulse duration 10 ms, duty cycle 3%) at 23, 45 and 76 K, respectively, without measurable Q-degradation. These results approach the best microwave field performance measured so far with unpatterned films at 19 GHz. The power handling of the filter degraded in proportion to the duty cycle, indicating heating as the dominant limitation. The filter could be tuned by 3% by moving a plunger film by 36 /spl mu/m above the ring-shaped groundplane of the resonator. The CW power handling was not affected by the tuning, but the radiation losses and the maximum achievable power levels were degraded compared to the fixed-frequency filter.         Large non-linear kinetic inductance in superconductor/normal metal bilayer films    J.H. Claassen, S. Adrian and R.J. Soulen Jr. Summary: We study the kinetic inductance in thin superconducting/normal metal (S/N) bilayer films where the penetration depth is greater than the S thickness. Using the two-coil mutual inductance method, we show that it is possible to estimate the dependence of kinetic inductance on sheet current density. It is found that, as expected from Ginzburg-Landau theory, the dependence is very weak in bare superconducting films. However in S/N bilayers of NbN/Al and Nb/Al the kinetic inductance can be smoothly varied over at least a 2:1 range by application of a dc transport current. It is proposed that this novel non-linearity could be exploited in some microwave applications.         Ten-fold tunability of the permittivity of Ba/sub 1-x/Sr/sub x/TiO/sub 3/ in epitaxial multilayers with (Y/Nd)Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta//    Yu.A. Boikov, Z.G. Ivanov and T. Claeson Summary: Dielectric properties of 400-600 nm thick epitaxial layers of SrTiO/sub 3/ and Ba/sub 0.9/Sr/sub 0.1/TiO/sub 3/, inserted between YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// or NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, were investigated as functions of temperature and electric field. The electric field response of the dielectric permittivity of the ferroelectric layer correlated with the Curie point and was considerably higher with Nd based than with Y based superconducting electrodes. Insertion of thin buffer layers improved the tunability and decreased the microwave losses of the Ba doped dielectric.         Fabrication of terahertz YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// hot-electron bolometer mixers    A.W. Kleinsasser, J.B. Barner, M.J. Burns, B.S. Karasik and W.R. McGrath Summary: Superconducting hot-electron bolometer (HEB) mixers are promising heterodyne detectors for THz frequencies. HEB mixers operating at 4 K or below offer the possibility of near-quantum-limited performance without an upper frequency limit imposed by the superconducting energy gap. High temperature superconductor HEB mixers offer very sensitive, low power heterodyne detectors operating at temperatures approaching 90 K for applications requiring closed-cycle refrigeration. We report on recent progress in fabricating and characterizing high-T/sub c/ mixers based on ultra-thin (10-20 nm) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films patterned to submicrometer dimensions (0.1-1 /spl mu/m) and incorporated into 1-3 THz planar mixer circuits.         A hot-spot mixer model for phonon-cooled NbN hot electron bolometric mixers    H. Merkel, P. Khosropanah, P. Yagoubov and E. Kollberg Summary: Based on a one dimensional heat transport equation for the electrons in a super-conducting hot electron bolometer (HEB) a model for a hot spot mixer is see up. The hot spot parameters are applied in a small signal oscillator model predicting IV curves and conversion gain. Besides its normal resistance and its IF bandwidth a HEB around its optimal operating point is sufficiently characterized by its hot spot length as a function of heating power. All mixer properties can be derived from this parameter set.         Transition edge sensors as single photon detectors    A.J. Miller, B. Cabrera, R.M. Clarke, E. Figueroa-Feliciano, S. Nam and R.W. Romani Summary: We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.         A new biasing technique for transition edge sensors with electrothermal feedback    Sae Woo Nam, B. Cabrera, P. Colling, R.M. Clarke, E. Figueroa-Feficiano, A.J. Miller and R.W. Romani Summary: We have developed a new operating mode for superconducting transition edge sensors (TES) used in cryogenic particle detection which use electrothermal feedback (ETF). By using the new technique with the optical photon detectors our group has developed, we have been able to reduce the decay time of the pulses from the detector by more than a factor of five. The technique involves reducing the voltage bias across the tungsten superconducting detector during a pulse. By reducing the voltage during a pulse, there is an additional reduction in joule heating which speeds up the recovery of the detector. In theory, the technique reduces the decay time of the pulses which allows for higher maximum count rates. In addition to a brief theoretical analysis of the benefits of the technique, we present experimental results and analysis demonstrating a pulse decay time reduction by a factor of five.         Optimal choice of material for HEB superconducting mixers    B.S. Karasik, W.R. McGrath and R.A. Wyss Summary: We demonstrate that a potential distinction in ultimate performance of phonon-cooled and diffusion-cooled HEB mixers is not due to the cooling mechanisms but rather due to the different properties of available superconductors. The only available material for a phonon-cooled mixer with sufficiently large IF bandwidth (/spl sim/4 GHz) is NbN, whereas a variety of clean materials (e.g., Nb, NbC, Al) are suitable for a diffusion-cooled mixer. For a readily achievable device length of 0.1 /spl mu/m for example, the diffusion-cooled IF bandwidth can be /spl ges/10 GHz. The requirement of low local oscillator (LO) power can also be more easily met in diffusion-cooled devices by selection of a material with lower critical temperature and low density of electron states. In contrast, the parameters in the NbN-based mixer cannot be widely varied because of the high resistivity and high transition temperature of the material and the necessity of using ultrathin films. Given the limited availability of LO power from compact solid-state sources at frequencies above 1 THz a diffusion-cooled mixer based on aluminum is a very attractive choice for low-background radioastronomy applications.         New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz    E. Gerecht, C.F. Musante, H. Jian, K.S. Yngvesson, J. Dickinson, J. Waldman, P.A. Yagoubov, G.N. Gol'tsman, B.M. Voronov and E.M. Gershenzon Summary: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.         Focused electron beam damaged YBCO Josephson junctions for THz device applications    S.-J. Kim and T. Yamashita Summary: We investigate the high-frequency properties of focused electron beam (FEB) damaged Josephson junctions for THz device applications. The FEB damaged YBCO junctions exhibit the resistively shunted junction (RSJ)-like current-voltage (I-V) curve and the microwave-induced Shapiro steps for all operation temperatures. At 4.2 K, the junctions exhibited the microwave-induced Shapiro steps up to 3 mV in dV/dI-V curves suggesting that the junctions can respond up to about 1.5 THz. To estimate the high frequency performance of the junctions, direct irradiation by a far infrared (FIR) laser at 0.76 THz is carried out and the clear first Shapiro step is observed for the junctions with I/sub C/R/sub N/ product of about 2 mV and at the operation temperature of 6 K.         A broad band low noise SIS radiometer    A. Karpov, J. Blondel, P. Dmitriev and V. Koshelets Summary: A new type of ultra broad band SIS low noise radiometer has been developed. The SIS receiver instantaneous band of about 30% is significantly increased compared to traditional designs. We avoid a restriction related to the limited band of the Intermediate Frequency (IF) low noise amplifier by using a multifrequency heterodyne power source. In this regime the frequency mixing is performed simultaneously in a big number of the subbands and the IF signals are combined in a common amplifier. A low noise operation in this regime is possible due to the quantum nature of the frequency mixing in SIS quasi particle tunnel junctions. The SIS receiver covers 25 GHz band centered at 90 GHz with an equivalent noise temperature of about 50 K. The receiver uses a fixed tuned SIS mixer with Nb/Al Ox/Nb junctions. The critical Josephson current density is about 2.6 KA/cm/sup 2/ and the junction area is of about 1.5 /spl mu/m/sup 2/. The limits to further improvement of the radiometer and the possibilities for extension of the technique to the sub millimeter band are discussed.         Numerical modelling of the diffusion cooling response in superconducting hot-electron mixers    H. Araujo and G.J. White Summary: Superconducting bolometric mixers that exploit hot-electron diffusion over electron-phonon inelastic scattering as the quasiparticle cooling mechanism are rapidly becoming a dominant technology for low-noise terahertz spectroscopy. We report on the results of modelling a microbolometer treated as a distributed element, as a refinement of the simple discrete-element model commonly used so far. The diffusion equation governing the hot-electron subsystem is solved numerically for a submicron niobium bridge, in the limit of local thermal equilibrium. There is reasonable agreement between the present mixer performance calculations and experimental data reported in literature. However, this model seems to overestimate conversion gain, perhaps indicating that the finite time required for energy sharing among hot-electrons inside the bridge should not be disregarded. It is also found, in the frame of this work, that terahertz radiation is dissipated more effectively than dc electrical power, which has implications on how mixer sensitivity is calculated.         Investigation of NbN phonon-cooled HEB mixers at 2.5 THz    G.W. Schwaab, G. Sirmain, J. Schubert, H.-W. Hubers, G. Gol'tsman, S. Cherednichenko, A. Verevkin, B. Voronov and E. Gershenzon Summary: The development of superconducting hot electron bolometric (HEB) mixers has been a big step forward in the direction of quantum noise limited mixer performance at THz frequencies. Such mixers are crucial for the upcoming generation of airborne and spaceborne THz heterodyne receivers. In this paper we report on new results on a phonon-cooled NbN HEB mixer using e-beam lithography. The superconducting film is 3 nm thick. The mixer is 0.2 /spl mu/m long and 1.5 /spl mu/m wide and it is integrated in a spiral antenna on a Si substrate. The device is quasi-optically coupled through a Si lens and a dielectric beam combiner to the radiation of an optically pumped FIR ring gas laser cavity. The performance of the mixer at different THz frequencies from 0.69 to 2.55 THz with an emphasis on 2.52 THz is demonstrated. At 2.52 THz minimum DSB noise temperatures of 4200 K have been achieved at an IF of 1.5 GHz and a bandwidth of 40 MHz with the mixer mounted in a cryostat and a 0.8 m long signal path in air.         A new fabrication technique for ultra-small diffusion-cooled hot-electron bolometers    A.M. Datesman, J.Z. Zhang and A.W. Lichtenberger Summary: Hot-electron bolometers (HEBs) are becoming the technology of choice for heterodyne mixing in the short submillimeter wavelength regime (frequencies above 1 THz). In this paper, we describe a new, versatile, easily variable method of diffusion-cooled HEB fabrication using a focused-ion beam (FIB) microscope. This technique does not require electron-beam lithography or definition of the bolometer element by lift-off.         SINIS Josephson junctions for programmable Josephson voltage standard circuits    H. Schulze, F. Muller, R. Behr, J. Kohlmann, J. Niemeyer and D. Balashov Summary: Nonhysteretic Josephson junctions with a superconductor-insulator-normal metal-insulator-superconductor (SINIS) structure fabricated using the reliable Nb-AlO/sub x/ technology have been used for the design and fabrication of a 1-V inherently stable Josephson voltage standard. The superconducting circuit can be driven at the same microwave frequencies as conventional SIS circuits. The microwave-induced 1-V step is suitable for calibration purposes. The successful operation of the 1-V circuit is due to an internal, phase-locked oscillation of all SINIS junctions which are embedded in a low-impedance strip-line. The microwave power required for exciting the coherent oscillation is very low and allows the integration of low power sources. Even operation without any external microwave source appears to be possible.         Nb-based SNS junctions with Al and TaO/sub x/ barriers for a programmable Josephson voltage standard    V. Lacquaniti, S. Gonzini, S. Maggi, E. Monticne, R. Steni and D. Andreone Summary: We report results achieved in the fabrication of two different Nb-based SNS devices which can be used for the development of a programmable Josephson voltage standard. Junctions with an Al metal barrier, 5 to 100 nm thick, have been fabricated obtaining devices with I/sub C/R/sub N//spl ap/0.5 mV. A second kind of junction has been fabricated using 10 nm thick non-stabilized TaO/sub x/ as a barrier, deposited by bias sputtering. For these devices, using the bias voltage as the main process parameter, I/sub C/R/sub N//spl ap/0.1 mV was obtained. Measurements of the electrical properties of the Nb/Al/Nb and the Nb/TaO/sub x//Nb junctions are reported.         Bias voltage dependence of a flux-sensitive Al/GaAs/Al (SNS) interferometer    J. Kurchinsky, R. Taboryski, J.B. Hansen, M. Wildt, C.B. Sorensen and P.E. Lindelof Summary: We report new results on interferometers based on high transparency superconductor-semiconductor-superconductor junctions composed of Al and highly doped GaAs. The fabricated devices consist of planar dc-SQUID like geometries with an effective flux-sensitive area of about 100-150 /spl mu/m/sup 2/. At zero bias voltage the fabricated interferometers typically exhibit 3% sinusoidal modulation of the conductance as a function of a magnetic field applied perpendicular to the loop. The conductance modulation is caused by resonant Andreev states in the normal GaAs region of the device. With increasing bias voltage of the order of a few microvolts the device is driven out of resonance and the conductance oscillations are extinguished. However, at higher bias voltage corresponding to the superconducting energy gap of Al (178 /spl mu/V) the conductance oscillations reappear but with reduced amplitude.         InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with NbN electrodes    T. Akazaki, J. Nitta and H. Takayanagi Summary: We report on the fabrication of InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with NbN electrodes made by using a DC magnetron sputtering deposition and we describe the device characteristics we obtained. Excellent pinch-off characteristics were obtained even at /spl sim/10 K when NbN electrodes retain their superconductivity. For a 3-/spl mu/m-gate device, the maximum extrinsic transconductance at 10 K was 300 mS/mm, even at the very low drain voltage of 0.2 V. We found that the HEMTs with NbN electrodes, not only have superior characteristics at /spl sim/10 K that exceed the critical temperature of Nb, but are also able to combine with NbN Josephson junctions.         Above-gap differential resistance anomaly in superconductor-constrictions-superconductor contacts    A. Saito, K. Hamasaki, T. Ishiguro, A. Kawakami and Z. Wang Summary: Annealing experiments of high-transmittance Nb-constrictions-Nb (Nb-c-Nb) contacts have been carried out at various temperatures. The constrictions with diameters as small as 10 nm were grown in the thick MgO (or Al/sub 2/O/sub 3/, SiO/sub 2/) layer of an insulating Nb/Insulator/Nb sandwich by applying a high electric field of 0.1-2 V/nm in liquid helium. We observed an above-gap anomaly, i.e., anomalous differential resistance (dV/dI) peaks, only in highly transmissive Nb-c-Nb contacts. These peaks were greatly suppressed by annealing treatments at temperatures as low as 130/spl deg/C for 30 min in air, without degradation of normal resistance R/sub N/ after annealing. When we applied the high field of 0.4 V/nm to such junction at 4.2 K again, the dV/dI vs. V curve almost recovered the original shape before annealing.         Behavior of a charged two-level fluctuator in an Al-AlO/sub x/-Al single-electron transistor in the normal and superconducting state    M. Kenyon, J.L. Cobb, A. Amar, D. Song, N.M. Zimmerman, C.J. Lobb and F.C. Wellstood Summary: We have studied the behavior of a charged two-level fluctuator in an Al-AlO/sub x/-Al single-electron transistor (SET) in the normal state over a temperature range from 85 mK to 3 K. The fluctuator caused the SET's island charge to shift by /spl Delta/Q/sub o/=0.1/spl plusmn/0.025 e with an escape rate out of each state which was periodic in the gate voltage. We compare our results to a model which assumes the fluctuator resides in one of the tunnel junctions and discuss model predictions for when the device is in the superconducting state.         Design investigation of 1D-arrays of metallic single electron tunneling transistors    M. Knoll and F.H. Uhlmann Summary: Starting from the geometry and material constants we calculate the capacitances in metallic single charge tunneling structures using a 3D numerical field computation tool based on the boundary element method. This is exemplified by means of a step-edge cut-off tunnel junction geometry. Beginning with a single junction we further investigate multi-junction single electron transistors and, for the first time, arrays of them. Beside this calculation of the intercapacitance matrix we quantitatively analyze the influence of parasitic background charges. In view of its performance our tool could establish the basis for the evaluation of more complex layouts in single charge electronics.         Charge transfer in 1-D HTS mesoscopic tunneling junction arrays    M.Z. Tong, J.F. Jiang and Q.Y. Cai Summary: The influence of superconducting energy gap on the performance of single electron transistor as electrometer has been studied and was found out to improve its charge sensitivity. This paper mainly deals with 1-D (dimensional) HTS mesoscopic tunneling junction array made up of HTS material Tl-1223 with capacitively coupling to a ground plan. The layered nature of Tl-1223 acts as ideal SIS junctions. The influence enforced by the superconducting energy gap on the static and dynamics of such an array is studied numerically based on the "Orthodox Theory" of single electronics. The charge transfer in the means of solitons introduced by the voltage source attached to the end of the array is also discussed.         The active loads based on capacitively coupled HTSC-single hole transistor    B. Shen, J.F. Jiang and Q.Y. Cai Summary: Starting with the intrinsic current-voltage properties of the capacitively coupled HTSC-single hole transistor (HTSC-SHT), the intrinsic current-voltage properties of all forms of the active loads based on capacitively coupled HTSC-SHT are studied by using a semi-classical model of the single hole tunneling effect. The small signal equivalent circuit of the active loads is also discussed here, and the conclusions are significant to the design of the HTSC-SHT analog circuits.         Fabrication and measurement of metallic single electron transistors    T. Wagner, W. Krech, B. Frank, H. Muhlig, H.-J. Fuchs and U. Hubner Summary: Using the so-called self-aligned in-line technique, we have fabricated single electron transistors based on the metals aluminum, tantalum and chromium. The material deposition was carried out without exception by sputtering. The samples were electrically characterized both in a dilution refrigerator and in a helium-3 cryostat. In case of transistors made completely of (superconducting) aluminum we observed in the modulation characteristics deviations from the predictions of the orthodox theory of sequential quasiparticle tunneling. They are caused by additional current contributions due to Josephson-quasiparticle cycles. Furthermore, we report on the low-temperature behavior of mixed single electron transistors made of tantalum and chromium islands, respectively, between aluminum oxide barriers and external aluminum electrodes.         Fabrication and characterisation of YBCO single grain boundary step edge junctions    C.P. Foley, E.E. Mitchell, S.K.H. Lam, B. Sankrithyan, Y.M. Wilson, D.L. Tilbrook and S.J. Morris Summary: We use ion beam etching techniques to fabricate YBCO step edge junctions (SEJ) on MgO substrates. Argon ion-beam etching (IBE) of the substrate at angles other than at normal incidence is used to define the step height and angle. Thin (/spl sim/300 nm) magnetron sputtered YBCO films are deposited over the step and patterned using microlithography and cold substrate ion-beam etching techniques. The critical current, I/sub c/ of these SEJs can be controlled by varying the angle of the step etched into the substrate. Fabrication techniques are described which produce one grain boundary at the top of the step and include a smooth return path thereby avoiding a second grain boundary at the bottom of the step. At 77 K, the current-voltage (I-V) characteristics show resistively shunted junction behaviour. These junctions routinely demonstrate reasonably large I/sub C/R/sub N/ products (0.1-0.6 mV), making them suitable for applications in high temperature SQUID devices.         Effects of step conditions on the properties of YBCO step-edge Josephson junctions    Yunseok Hwang, Byung-Chang Nam, Moon Chul Lee, Dong Wook Kim, Soon-Gul Lee, In-Seon Kim, Jin-Tae Kim, Yong Ki Park and I-Hun Song Summary: We have studied transition properties of YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions as a function of the angle of the step-line with respect to the major axes of the SrTiO/sub 3/ substrate. Substrate steps were prepared by Ar ion milling with photoresist mask, and the YBa/sub 2/Cu/sub 3/O/sub 7/ film was deposited by pulsed laser ablation and patterned by ion milling to form junctions. The critical temperature of the junctions was independent of the angle. However, the critical current of the junctions showed a modulation with the angle. A maximum was observed for the step-line oriented parallel to the major axes of the substrate and a minimum for the step-line oriented 45/spl deg/ against the axes. The modulation of the critical current is believed to be caused by the difference in the microscopic structure of the epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7/ film at the step and also symmetry of the high Tc superconductor.         Properties of Bi-2212/Bi-22Y2 step-stack Josephson junctions    W. Lopera, E. Baca, M.E. Gomez, P. Prieto, U. Poppe and W. Evers Summary: We have fabricated step-stack Josephson junctions based on high quality epitaxial BSCCO (2212 phase) thin films, deposited on Y-doped bismuth (Bi-22Y2) steps. Bi-2212 and Bi-22Y2 films were grown by a high oxygen pressure dc-sputtering technique. The structural characteristics have been analyzed by X-ray, transmission electron microscopy (TEM), and Rutherford backscattering spectrometry (RBS). Bi-22Y2 steps between 100 and 300 nm high were patterned by photolithography and non-aqueous chemical etching. Junctions were characterized by current-voltage (I-V) measurements under magnetic fields and microwave irradiation. I-V curves have shown a clearly hysteretic weak-link Josephson behavior at different temperatures. The temperature dependence of the critical current in these step-stack junctions has also been analyzed.         Microwave emission due to anisotropic quasiparticle injection into an ErBa/sub 2/Cu/sub 3/O/sub y/ superconductor    K. Lee, E. Kume, H. Yamaguchi, H. Arie, W. Wang and I. Iguchi Summary: We report the observation of microwave emission and the dc measurements on tunnel injection of quasiparticles into a ErBa/sub 2/Cu/sub 3/O/sub y/ (EBCO) thin film using the samples with antenna geometry which are nearly free from the parallel overlapping effect of the injector current and the thin film current. The injector consists of two EBCO/insulator/Au (S/I/N) gate junctions. The samples were fabricated by lift-off photolithography technique. The microwave emission intensity from the junction was measured under the condition of broadband non-resonant matching using a superheterodyne radiometric receiver at frequencies f/sub REC/=36 GHz and 47 GHz. The detected microwave emission power increased nearly linearly with the injection current. The emitted power was greater for the higher receiving frequency. The observed maximum emitted broad band spectrum power at frequency f/sub REC/=47 GHz was about 10 pW for an integrating time of 1 sec. The phenomenon is discussed in terms of the nonequilibrium dynamics together with the ionic nature of oxide superconductor.         Fabrication of Josephson junctions on La-Sr-Cu-O single crystals    Y. Uematsu, H. Myoren, K. Nakajima, T. Yamashita, I. Tanaka and H. Kojima Summary: We have successfully fabricated Josephson junctions on single crystals of La/sub 2-x/Sr/sub x/CuO/sub 4/ (LSCO) high-T/sub c/ superconductor using niobium (Nb) as counter electrodes. A reproducible fabrication process has been established taking into account the surface state of LSCO is dominantly affecting junction properties. The surface state of LSCO has been characterized using XPS. The current voltage curves (IVCs) of Nb/LSCO junctions exhibit RSJ like Josephson junction properties. Due to intrinsic Josephson effect of LSCO, the IVCs branches are first observed for the Nb/LSCO junctions on LSCO mesa whose interfaces are parallel to the ab-plane of LSCO.         Inelastic resonance tunneling in S-Sm-S tunnel structures with s- and d-wave pairing in the electrodes    I.A. Devyatov, D.V. Goncharov, M.Yu. Kupriyanov and A.A. Golubov Summary: Inelastic resonant tunneling via localized states (LS) in an amorphous interlayer located between superconducting banks with s- and d-wave symmetry of the order parameters is studied theoretically. The developed theoretical model is applied to the description of high T/sub c/ Josephson junctions with semiconductor oxide interlayers. It is shown that the calculated form of the current-voltage characteristics and the temperature dependence of the zero bias conductivity fit the experimental data only if anisotropic pairing occurs in the S-banks.         Mechanics of high temperature superconductive Josephson junctions    I.A. Parinov Summary: The strength and fracture resistance problems of Josephson junctions (JJs) defining diminution of effective superconducting area to compare with geometrical one and large parameter spreads are insufficiently studied. With account of thermal expansion anisotropy and other properties of laminated composite structures of the ceramic-ceramic and metal-ceramic types which to be proper for JJs, the set of strength and toughness parameters is computed, fracture features and toughening mechanisms are considered.         Magnetic field splitting of the quasiparticle states in Nd-Ba-Cu-O/Pr-Ba-Cu-O/Nd-Ba-Cu-O planar junctions    G.A. Alvarez, T. Utagawa, K. Tanabe and Y. Enomoto Summary: We report on high quality planar junctions fabricated from well characterized c-axis quasi-homoepitaxial NdB/sub 2/Cu/sub 3/O/sub 7-/spl delta///PrB/sub 2/Cu/sub 3/O/sub 7-/spl delta/// NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(NBCO/PBCO/NBCO) multilayers. C-axis axis tunneling spectroscopy investigations provide evidence of quasiparticle tunneling that is commonly observed for superconductor-insulator-superconductor (SIS) junctions. The tunneling conductance dI/dV of the junctions in parallel magnetic field reveals an anomalous splitting of the superconducting quasiparticle density of states. The magnitude of the splitting was found to be proportional to /spl mu//sub B/H and may be related to the magnetic moment of the quasiparticles.         Fabrication of submicron BSCCO stacked junctions by focused ion beam (FIB)    Yu.I. Latyshev, S.-J. Kim and T. Yamashita Summary: A method for the fabrication of in-plane submicron size intrinsic Josephson junctions by focused ion beam (FIB) has been developed. The method includes double-sided processing of thin layered single crystals by FIB and has been demonstrated on high quality BSCCO (2212) single crystal whiskers. The stacked junctions with in-plane area down to 0.3 /spl mu/m/sup 2/ have been fabricated without deterioration of superconducting transition temperature T/sub c/ and the superconducting energy gap /spl Delta/.         Circuit models for arrays of Josephson oscillators with loads    E. Trias, T.P. Orlando, A.E. Duwel and S. Watanabe Summary: Parallel arrays of underdamped Josephson junctions are interesting due to their ability to produce coherent radiation. For a broad range of array parameters, we find that these arrays have solutions which can be represented as traveling waves with a small number of harmonics. We develop equivalent circuits for the DC and AC response using a harmonic balance technique. The reflection and transmission properties at the boundaries are studied by adding a passive terminating load to the array. We also develop a load criteria for optimal output power to both passive and nonlinear loads.         Maximizing microwave power from triangular Josephson junction arrays    N.C.H. Lin and S.P. Yukon Summary: We investigate the dynamics of N/spl times/N triangular Josephson junction (JJ) arrays and the same arrays where only diamond triangular pairs are retained. The diamond arrays are shown to be more stable and their stability is traced to the dynamical states of a single diamond. Using diamonds with 2 JJ's on each horizontal link is shown to enhance rf output and facilitates the fabrication of arrays with HTS step-edge junctions. The effects of JJ defects and loads on array rf output are also considered.         Linewidth measurement of millimeter wave radiation from a Josephson array source coupled to free space    S. Deus and S. Kiryu Summary: Radiation from a linear array oscillator with a spiral antenna has been coupled out of the dewar through a Teflon window. Both its linewidth and its power have been measured after coupling the radiation through free space into a second dewar. The linewidth has been determined using a SIS mixer with a spiral antenna which was pumped with an 88 GHz phase-locked Gunn oscillator, and also by Josephson mixing of the array itself. The array oscillator has a distributed array structure of 300 resistively shunted junctions which are placed in groups of 6 junctions. It was fabricated on a silicon wafer and has a two-arm spiral antenna. The chip was attached to a silicon lens with an anti-reflection coating. The linewidth of the array oscillator was determined between 158 GHz and 194 GHz, far below its design frequency of 400 GHz. The measured linewidth and power data of the oscillator reveal interesting information about its phaselocking behavior in the operating range far below its design frequency.         Dynamics of arrays of inductively-coupled Josephson junctions    P.A. Warburton and N. Raman Summary: We present the results of our simulations of inductively-coupled overdamped Josephson junction arrays in a vanishingly small external magnetic field. With identical junctions we show that the junctions are always phase locked and that the output power is optimised when the loop inductance is minimised. For nonidentical junctions, however, the junctions may or may not be phase locked. We show that a high loop inductance increases the probability of phase locking, and that the average output power is maximised when the normalised loop inductance is equal to one. The addition of a load inductance external to the array does not affect the probability of phase locking.         On and off-chip detection of radiation from HTS Josephson junction arrays    Kiejin Lee, I. Iguchi and K.Y. Constantinian Summary: We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T/sub c/ Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the dc bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was a series connection of interlocking dc SQUIDs geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.         Two-dimensional Josephson junction network architectures for maximum microwave radiation emission    J. Oppenlander, W. Guttinger, T. Traeuble, M. Keck, T. Doderer and R.P. Huebener Summary: We have investigated experimentally a novel type of self-synchronizing two-dimensional Josephson junction array based on special symmetry breaking network architectures. The measurements confirm the theoretical prediction that in such "selector Josephson networks" the Josephson oscillators mutually synchronize into a coherent in-phase state and that such arrays are capable of emitting maximum coherent microwave power in the entire theoretically expected frequency range. The DC biased oscillator array operates coherently even without a reinjection of the generated microwave by an external load or by a resonator cavity. The selector network possesses a much higher tolerance against imperfections, perturbations and load parameter variations than conventional regular two-dimensional or one-dimensional arrays. The experimental sample has been fabricated in an industrial process using Nb-technology, in effect providing relatively large spreads in the array junction parameters. The measured frequency range goes from 85 GHz up to 380 GHz with a maximum microwave power of 0.16 /spl mu/W matched to a coupled load for an array with only 100 active Nb-AlO/sub x/-Nb junctions.         Experimental investigation of local timing parameter variations in RSFQ circuits    I.V. Vernik, Q.P. Herr, K. Gaij and M.J. Feldman Summary: Circuit parameter variations resulting from the fabrication process affect the timing parameters of rapid single flux quantum (RSFQ) digital circuits. This determines the maximum clock rate and the yield of the circuit. It is generally believed that the global parameter variations (target-to-wafer) are much more significant in this regard than the local parameter variations (on-chip), but there has been little experimental evidence for this. This experiment measures the distribution of local parameter variations of the timing parameter of RSFQ circuits. The experiment consists of a 10 by 10 matrix of nominally identical RSF~ "clock rings" covering an integrated circuit area, a total of 3500 Josephson junctions. Each ring is activated individually, and its frequency is measured with accuracy better than 1%.         Effect of thermal noise on the bit error rate of SFQ devices    J.H. Kang, J.X. Przybysz, A.H. Worsham and D.L. Miller Summary: To measure the effect of thermal noise on switching a Josephson junction to the voltage state a simple SFQ circuit constructed with resistively shunted Nb/AlO/sub x//Nb junctions was used. Based on a good agreement between the measured data and the thermal activation theory, the effect of thermal noise on the bit error rate of SFQ devices was studied, The effective thermal noise temperature of 10 K used to fit the data was higher than the bath temperature of 4.2 K. Careful circuit design to get large critical margins is necessary to achieve high operating temperature of SFQ logic devices.         Simulation and 18 Gb/s testing of a data-driven self-timed RSFQ demultiplexer    N. Yoshikawa, Z.J. Deng, S.R. Whiteley and T. Van Duzer Summary: We have developed a data-driven self-timed (DDST) rapid-single-flux-quantum (RSFQ) demultiplexer (demux) for the interface between on-chip high-speed RSFQ circuits and off-chip low-speed circuits. In order to eliminate the timing issue in a synchronous clocking system we employed the DDST architecture, where a clock signal is localized within a 2-bit basic demux module and dual rail lines are used to transfer the timing information between the modules. A larger demux can be produced simply by connecting the 2-bit modules in a tree structure. The DDST demux was designed for 10 Gb/s operation with sufficient dc bias margin using HYPRES 1 kA/cm/sup 2/ Nb process. We have successfully tested operation of the 2-bit demux up to 18 GHz using the DDST on-chip high-speed test system which was developed in our group.         Investigation of signal isolation and transient characteristics in quantum-flux-parametron (QFP) circuits    Y. Tarutani, H. Hasegawa, T. Fukazawa, A. Tsukamoto and K. Takagi Summary: Quantum-Flux-Parametron (QFP) gates whose input and output are inductively coupled with the next gate are proposed. According to the numerical simulation, the degree of signal isolation is improved and the output signal deformation is suppressed compared to the directly connected QFP gates. Majority gates that are capable of handling input signals much greater than three are improved in their functionality. Characteristics of the QFP gates upon application of an activation current are also investigated by the numerical simulation. The minimum time of the signal propagation between adjacent QFP gates is calculated to be 5 ps.         NbN circuits and packaging for 10 Kelvin IR focal plane array sensor signal processing    M.W. Johnson, D. Durand, L. Eaton, M. Leung, A. Spooner and T. Tighe Summary: Infrared (IR) focal plane array (FPA) imaging signal processing circuits, built in NbN and operating at 10 Kelvin, are presented. An ADC chip and digital signal processing chip are mounted on a 1.25 inch multi-chip module (MCM) with high bandwidth, low impedance interconnect. The populated MCM is designed to be installed into a module housing for operation with the cryogenic IR FPA. The 12-bit NbN SFQ counting ADC, previously used in a single chip version of the IR focal plane array sensor test system, is now implemented in an improved NbN process which includes a ground plane. Considerable attention has been focused on reducing parasitic inductance to compensate for the high characteristic inductance of the NbN films. These design improvements increase operating margins and circuit yield and make the ADC more robust in the presence of external system noise. Data from a bit-serial subtraction circuit to be used for pixel-by-pixel background subtraction is also presented. Finally, the design and electrical qualification of the physical package is described.         Measurement of the energy sensitivity of a superconductive comparator    D.A. Feld, P. Sage, K.K. Berggren and A. Siddiqui Summary: Comparators are a critical component in sigma-delta A/D converters. We have studied experimentally the sensitivity of a quantum flux parametron (QFP) comparator operated over a range of sampling frequencies F/sub S/ from 40 Hz to 40 MHz. In one experimental method, following Ko and Lee, we measure the firing probability of the QFP as a function of applied flux. The sensitivity can be derived from the slope of this curve. In a second method, we measure the sensitivity directly by observing the spectrum of the QFP output while the amplitude of a small sinusoidal applied flux is adjusted to exceed the noise floor by 3 dB. The two methods were found to be in good, but not perfect agreement. The sensitivity was measured as we varied both F/sub S/ and the dock rise time. The spectrum of the quantization noise exhibits, as expected, a flat floor whose level is inversely proportional to F/sub S/. The best energy sensitivity that we observed was for a clock frequency of /spl sim/20 MHz with a 10 ns rise time. The measured sensitivity was about 1500 h (Planck's constant). The readout circuit prevented us from clocking the comparator into the GHz range for even greater sensitivity. We also believe that the comparator could be optimized to improve sensitivity further. The noise floor was low enough that we could observe excess low-frequency noise below 5 Hz. We have not yet determined whether it is intrinsic to the comparator or originates from our test electronics. We hypothesize that the noise floor will continue to fall as F/sub S/ increases until we reach the speed limit of the comparator, at which point successive output samples will no longer be uncorrelated, or until we reach the uncertainty-principle limit (h) in the 100s of GHz range.         First demonstration of correlation in a niobium superconductive programmable binary-analog matched filter    J.P. Sage and D.A. Feld Summary: A complete prototype superconductive programmable binary-analog matched filter for a 2-Gchip/s spread-spectrum modem has been operated for the first time and has performed correlation. We had previously demonstrated functionality of each individual element of the filter. The analog samplers had captured signals with bandwidths in the order of 10 GHz; the binary weighted taps, which utilize the unique quantum mechanical properties of superconductive circuits, had exhibited nondestructive readout as required; and the two digital shift registers, one that stores the binary code pattern and one that controls sampling of the input analog signal in the bank of track-hold cells, had functioned at 2 GHz. Now all of these elements have been operated together in low-frequency tests. A 7-bit (or "chip" in spread-spectrum terminology) pseudo-noise (pn) code sequence was loaded into the reference shift register in each of the seven possible positions while an analog version of the pn code with its amplitude varied over the full bipolar dynamic range of the filter was used as the incoming signal. The filter response peaked as expected when the analog signal and the binary reference were aligned. The peak and sidelobe responses agreed quantitatively with those predicted from calibration measurements made with uniform signals instead of pn codes.         Diagnosis of electric cable insulation by high Tc SQUID    S. Tanaka and K. Inadomi Summary: We have developed the wide band electronics for SQUID and measured short pulse currents simulating a signal in a degraded power electric cable. The SQUID driving electronics had a bandwidth as wide as 1.4 MHz and it could successfully detect currents of 3 /spl mu/A with the width of 120 nsec. These results suggested that SQUIDs can be applied to the partial discharge measurement of power cables.         Magnetic evaluation of HTS magnetic shielding cylinders using an HTS dc-SQUID    K. Mori, T. Minemoto and M. Itoh Summary: For practical applications, an ideal magnetic shielded vessel can be realized by making use of a high-critical temperature superconductor (HTS). Generally, the value of the maximum shielded magnetic flux density B/sub s/ is used to evaluate the magnetic shielding effect of the HTS vessel. Little is known, however, of the characteristics and evaluation procedures used to determine the behavior of the magnetic flux density B/sub in/ within the shielded vessel when exposed to an external magnetic flux density B/sub ex/ of less than the value of B/sub s/. In order to evaluate the behavior of the magnetic field within the Bi-Pb-Sr-Ca-Cu-O cylinder to an applied B/sub ex/ the temporal change of B/sub in/, and the magnetic noise power spectrum (NPS) of B/sub in/ are measured by an HTS dc-SQUID magnetometer and spectrum analyzer. The present paper examines the optimum shielding conditions for constructing an ideal magnetic shielding vessel.         Imaging high-frequency magnetic and electric fields using a high-T/sub c/ SQUID microscope    S. Chatraphorn, E.F. Fleet, F.C. Welistood and R.C. Black Summary: We have used a liquid-nitrogen-cooled scanning SQUID microscope to image room-temperature sources of high-frequency magnetic fields and electric fields. We detect the fields by monitoring their effect on the SQUID modulation depth; high-frequency magnetic fields affect the modulation depth differently than high-frequency electric fields. We briefly describe our system, explain the principle behind detection of magnetic and electric fields, and show images of some simple room-temperature samples in the 0.8-13 GHz frequency range.         Magnetic properties of Ho measured by a scanning SQUID microscope    S.A. Gudoshnikov, A.S. Kalabukhov, S.A. Chupakhin, A.M. Tishin, O.V. Snigirev, J. Bohr, M. Muck, C. Heiden and J. Dechert Summary: We have applied a dc SQUID based microscope to study surface magnetization of a Ho single crystal at 77 K in parallel (up to 0.4 kA/m) and perpendicular (up to 0.1 kA/m) magnetic fields. Magnetization curves and the topographic maps of the magnetic field distribution near the polished surface [0001] of the crystals have been recorded with a spatial resolution better than 50 /spl mu/m. Qualitative evidence for ferromagnetic ordering at the [0001] surface have been found.         Construction and measurements of HTS DC SQUID electronic gradiometer to be used in NDE systems    Jinyoung Kim, Joonhee Kang, Eunhong Lee, I-Hun Song, Junho Gohng and T.S. Hahn Summary: We have designed a non-destructive evaluation system by using an electronic gradiometer constructed with two DC SQUID magnetometers. Typical flux modulation of the SQUIDs used in this work was about 30 /spl mu/V and the noise at 10 Hz was about 14 /spl mu//spl Phi//sub 0///spl radic/Hz. The system includes a non-magnetic stainless steel dewar and a set of coaxial exciting coils, which was used to induce an eddy current in the test piece. The sample motion stage and the SQUIDs were computer controlled and the output data from the electronic gradiometer was obtained by using Labview software.         HTS-dcSQUID gradiometer for nondestructive evaluation    N. Kasai, D. Suzuki, H. Takashima, M. Koyanagi and Y. Hatsukade Summary: We have fabricated a HTS-dcSQUID gradiometer on the basis of a single YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// film for a hand held NDE system. The two loops of the gradiometer are coupled directly to a SQUID arranged at the center of the pickup coil. The gradiometer worked at 77 K and at normal laboratory environment without magnetic shielding. The effect of the small area of the SQUID loop on the performance of the gradiometer was experimentally estimated. The performance of the SQUID gradiometer was investigated by measuring holes in a carbon fiber reinforced plastic plate in a magnetically shielded room.         A direct readout high-T/sub c/ dc SQUID electronics with ac bias and a liquid-nitrogen-cooled preamplifier    S.A. Gudoshnikov, L.V. Matveets, R. Weidl, L. Dorrer, P. Seidel, S.I. Krasnosvobodtsev, A.S. Kalabukhov and O.V. Snigirev Summary: Direct readout dc SQUID electronics based on a liquid-nitrogen-cooled preamplifier and alternating current bias was developed. The preamplifier with an intrinsic voltage noise of 0.18 nV/Hz/sup 1/2/ was used as the first stage of this electronics. A mathematical description of the noise suppression by this electronics was done. Low-frequency noise was reduced by a factor of 6 at 1 Hz by this technique.         High frequency coupling coefficient between the coplanar resonator and radio frequency SQUID    H.R. Yi, Y. Zhang, J.H. Bousack and A.I. Braginski Summary: The coupling coefficient (k/sup 2/) between the superconducting coplanar resonator and the flip chip coupled washer radio frequency SQUID was calculated using computer simulation. The coplanar resonator is formed by two coplanar lines surrounding a flux concentrator with each line having a slit. For a 3 mm/spl times/3 mm washer SQUID with a 100 /spl mu/m/spl times/100 /spl mu/m loop coupled to a coplanar resonator with the slits on opposite sides, we estimated k/sup 2/=7.1/spl times/10/sup -3/. However, if the same SQUID is coupled to a coplanar resonator with parallel slits and with a short circuit at the 90/spl deg/ position with respect to the opening slit, k/sup 2/ of only 0.5/spl times/10/sup -3/ is obtained, which indicates that the k/sup 2/ is strongly dependent on the resonator layout. The simulation also shows that k/sup 2/ is dependent on the SQUID washer size and the separation distance between the washer SQUID and the coplanar resonator.         High-temperature superconducting pickup-loop hysteresis for magnetometer and gradiometer configurations    J.W. Purpura Summary: Magnetic hysteresis of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin-film pickup loops was measured using a single-layer sample design that allowed experiments to characterize both magnetometers and gradiometers. Measurements were performed at 77 K for samples having pickup-loop linewidths ranging from 20 /spl mu/m to 800 /spl mu/m. Magnetometer hysteresis was found to increase with increasing linewidth and increasing amplitude of the applied magnetic field ramp. Gradiometer hysteresis was found to depend primarily on the degree of hysteretic balance between the two individual loops comprising the gradiometer. The dependence of gradiometer hysteresis on applied field amplitude was found to be sample dependent, monotonically increasing in some cases, and exhibiting a local minimum in others.         YBCO-noble metal resistors for HTS Josephson Noise Thermometry    D.A. Peden, J.C. MacFarlane, Ling Hao, R.P. Reed and J.C. Gallop Summary: Noise thermometry based on HTS Josephson devices has the potential to provide an absolute technique for the realisation of the temperature scale in the range 4 K-50 K. A resistor connected as a shunt across a YBCO grain boundary junction forms an HTS Josephson Noise Thermometer. We present experimental results and mathematical models for the resistivity of a noble metal film which connects two strips of superconducting YBCO. Accurate temperature measurement requires the resistor to be no more than 1/1000th of the intrinsic junction resistance. This sets an upper limit of 1 m /spl Omega/ for the value of the shunt resistor, including any contact resistance which exists between the metal and YBCO films. Essential aims are firstly to determine the lowest achievable contact resistivity, and secondly to demonstrate a very small variation with current of the contact resistance. A one dimensional model of the current transfer from superconducting to normal films has been used to define the necessary overlap length and also to investigate the possible influence of current dependent proximity effects at the interface. The model is compared with experimental behaviour of two designs of shunt resistance, one a simple rectangular patch configuration and the other a meander line.         Integrated high-transition temperature SQUID-based voltmeters operated at 77 K    H.C. Yang, J.H. Chen, H.E. Horng, S.Y. Yang and J.T. Jeng Summary: The voltage noise levels of high-T/sub c/ based YBa/sub 2/Cu/sub 3/O/sub 7/ bicrystal SQUIDs and SQUID voltmeters were measured to investigate their noise characteristics. The SQUIDs are of washer type with outer dimension of 90 /spl mu/m/spl times/90 /spl mu/m and inner dimension of 20 /spl mu/m/spl times/20 /spl mu/m. The SQUIDs have a normal inductance of about 60 pH. The integrated modulation and input coils were circular in shape. The modulation coil has a radius of r/sub 2/=80 /spl mu/m and r/sub 1/=60 /spl mu/m while the input coil for voltage measurement has radius r/sub 2/=50 /spl mu/m and r/sub 1/=30 /spl mu/m. Using a dc bins and standard flux locked loop, the spectral density of the voltage noise, S/sub v/, was observed to behave as 1/f at low frequencies and the root mean square flux noise, S/sub /spl Phi///sup 1/2/, is white and has a value of /spl sim/15 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ at 1 kHz. The flux noise levels were reduced to /spl sim/4 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ using the ac bias reversing technique. These data suggest that the dominant 1/f voltage noise was caused by critical current fluctuations. We further demonstrate that the 1/f can be induced by flux motion. The voltage noise levels of the SQUID voltmeters are also reported.         Universal active dc biasing system for a high-T/sub c/ SQUID based on a liquid-nitrogen-cooled preamplifier    N.N. Ukhausky, L. Dorrer, F. Schmidl and P. Seidel Summary: A system for the SQUID active dc biasing was developed and tested. This system provides an opportunity to change the output resistance of the biasing source over a wide range. The white flux-noise of a bicrystal SQUID-gradiometer has been measured in direct readout scheme with three different values of the biasing source output resistance. A maximum level of white noise of 11 /spl mu//spl Phi//sub 0//Hz/sup 1/2/@100 kHz was found in case of maximum output resistance (current-biasing). A white noise of 7,9 /spl mu//spl Phi//sub 0/Hz/sup 1/2/ was measured for the minimum of the biasing source resistance (voltage-biasing). The best level of the flux noise of 6 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ was found at a biasing source resistance close to SQUID normal resistance R/sub n/ (power-biasing). Significant reduction of the cut-off frequency (near 10 kHz instead of 100 kHz) was found for the tested bicrystal SQUID-gradiometers due to the active dc voltage-and power-biasing systems in comparison with the standard current-biasing circuit.         High temperature superconductor transimpedance amplifiers using serially connected bi-crystal junction SQUID arrays    Kin Li, S.P. Hubbell, R. Cantor and M. Teepe Summary: This article discusses the design and measurement of high temperature superconductor transimpedance amplifiers using bi-crystal junction SQUID arrays. The peak to peak modulation voltages of the arrays as a function of their SQUID inductance were measured. The measured transresistance, dV/sub o//dI/sub i/, of a 30-element array of 5-pH SQUIDs was 4 V/A. The voltage modulation depth of the 30-element array was 2 mV and the white noise of the array was 1.0 nV/Hz/sup 1/2/ at 100 kHz. The dynamic range of the array was 120 dB in a one hertz bandwidth. This device has the potential to be used as a broadband amplifier for low impedance sources.         High-T/sub c/ SQUIDs for low-field NMR and MRI of room temperature samples    K. Schlenga, R.F. McDermott, J. Clarke, R.E. De Souza, Annjoe Wong-Foy and A. Pines Summary: We have constructed a high-T/sub c/ SQUID spectrometer to detect NMR signals from samples at room temperature in magnetic fields up to 3 mT. The multiloop SQUID magnetometer has a system noise of about 30 fT/Hz/sup 1/2/ at the relevant frequencies of 2 to 100 kHz. The magnetometer is operated in vacuum at 77 K, and is separated from the sample, which Is less than 1.5 mm away, by a sapphire window. In a magnetic field of 2 mT we can detect the proton spin echo at 86 kHz without signal averaging. This sensitivity enables us to obtain one-dimensional images. In addition, we present data on hyperpolarized /sup 129/Xe, which has an optically pumped polarization of several percent.         Sensitive high-T/sub c/ SQUID magnetometers for unshielded operation    M.S. Dilorio, K. Yang, S. Yoshizumi, S.G. Haupt, D. Haran, R.H. Koch, F.P. Milliken, J.R. Rozen, D.K. Lathrop, S. Kumar, III Trammell and H.S. Summary: We have developed sensitive highly reliable high-T/sub c/ SQUID magnetometers a reproducible SNS junction fabrication process. In order to enable unshielded operation in the earth's field, we have incorporated flux dams into direct-coupled SQUID magnetometers. By using up to four pickup coils in parallel, each with its own flux dam, an effective area of 0.57 mm/sup 2/ has been achieved on 24 mm/spl times/24 mm substrates using 100 /spl mu/m wide pickup coils. We have demonstrated a magnetic field noise sensitivity of 80 fT//spl radic/Hz 10 Hz and 77 K in an externally applied field 60 /spl mu/T. This magnetic field sensitivity unchanged from the zero-field measurement.         Improvement of high T/sub c/ SQUID performance using an integrated resistor    E.J. Tarte, D.J. Kang, W.E. Booij, P.D. Coleman, A. Moya, F. Baudenbacher, S.H. Moon and M.G. Blamire Summary: The performance of high T/sub c/ SQUIDs with resistively shunted inductances have been investigated. We find that the voltage modulation depth /spl Delta/V of shunted 83 pH SQUIDs is significantly larger than that of unshunted SQUIDs with similar parameters and increases with the parameter /spl gamma/=R/sub n//R/sub s/ as expected from theory (R/sub n/ is the junction resistance and R/sub s/ the shunt resistance). We also find that the conventional decrease of /spl Delta/V with SQUID inductance L can be eliminated leaving only the effect of the thermal noise flux. In this way /spl Delta/V=63 /spl mu/V has been achieved for a bicrystal SQUID at 77 K whose screening parameter /spl beta//sub L/=13. Noise measurements performed on this SQUID indicate that the resistor in circuit does not increase the noise.         Broadband SQUID amplifiers for photonic applications    V. Polushkin, D. Glowacka, R. Hart and J.M. Lumley Summary: The dynamics and noise of a dc SQUID (the Superconducting Quantum Interference Device), with the McCumber parameter /spl beta//sub c/=2/spl pi/R/sup 2/l/sub c/C//spl Phi//sub 0/ close to the unity (where I/sub c/, R, C is the critical current, the shunt resistance and the capacitance of the Josephson junctions comprising the SQUID, respectively, /spl Phi//sub 0/=2.07 10/sup -15/ Wb is the magnetic flux quantum) integrated with a planar spiral input coil, have been experimentally studied. The length of the spiral input coil was chosen so as to match its /spl lambda//4 microwave resonance frequency to the plasma resonance frequency of the SQUID. The input coil resonance is found to enhance the overall quality factor Q of the Josephson oscillations in the SQUID and, as a result, to increase the dynamic resistance R/sub d/ and the gradient of the flux-to-voltage characteristics, /spl delta/V//spl delta//spl Phi/, without hysteresis. A dc SQUID with a loop inductance L=30.5 pH, /spl beta//sub c/=0.72, and a 6 turn input coil demonstrated a non-distorted quasi-sinusoidal flux-to-voltage transfer function with an exceptionally large modulation depth of 140 /spl mu/V peak-to-peak. The spectral density of the magnetic flux noise was as low as 3.5/spl times/10/sup -7/ /spl Phi//sub 0//Hz/sup 1/2/ in the double stage configuration, measured at a temperature 4.2 K using direct read out electronics. In combination with an intermediary transformer, the current resolution of the SQUID is as low as 1.25 pA/Hz/sup 1/2/ with an input coil inductance of 100 nH.         Quasiparticle mixing in Ba-K-Bi-O grain boundary junctions    T. Takami, Y. Wada, K. Kuroda, T. Ozeki and K. Hamanaka Summary: A Ba/sub 1-x/K/sub x/BiO/sub 3/ (BKBO) grain boundary junction formed on a MgO bicrystal substrate showed a superconductor-insulator-superconductor (SIS) behavior with a sharp gap structure and a Josephson current. A 270 GHz millimeter wave mixing in a BKBO junction was performed by using the quasi optical technique. A log-periodic antenna, a hyperhemispherical MgO lens and a Teflon lens were used in order to improve coupling for millimeter wave. The IF outputs have some peaks depending on the photon assisted tunneling steps. This is the first time that quasi-particle mixing could be done in an oxide superconductor.         A frequency-domain mixer model for diffusion-cooled hot-electron bolometers    A. Skalare and W.R. McGrath Summary: A new frequency domain hot-electron bolometer (HEB) mixer model is described, which takes into account the non-uniform temperature distribution found in superconducting diffusion-cooled devices. In this model the bolometer is discretized into a finite number of segments, and the non-linear large signal response to local oscillator and DC heating is found by an iterative algorithm. A frequency-domain coupling matrix is introduced to represent small-signal modulations around the large-signal values of temperatures and heat flows inside the device. The coupling matrix and a Norton representation of the mixer DC and intermediate frequency (IF) circuit allows the mixer conversion to be calculated.         Simulation of conversion gain and reflectivity coefficients in heterodyne detector using a superconductor-normal metal-superconductor junction    A.M. Luiz, Y.A. Gorelov and R. Nicolsky Summary: We design a millimeter-wave heterodyne receiver using Superconductor-Normal metal-Superconductor (SNS) junction. We simulate its Current-Voltage Characteristics (CVC) as a function of its relevant physical parameters. Performing computer simulations, we use the negative derivative range of its CVC to calculate the conversion gain and reflectivity coefficients of the proposed device. These parameters show that it should be possible to increase the sensitivity of the SNS mixer and a reflection parametric amplifier may be feasible.         Millimeter- and submillimeter-wave negative resistance SNS mixers    T. Matsui and H. Ohta Summary: We have studied negative-resistance mixers both theoretically and experimentally. The current carried by the bound quasi-particles in the N-region of a mesoscopic SNS weak-link has a dc and cosine components. Current transport in the SNS weak-links is affected by bias-voltages in many experiments. The I-V curves often show complex structures including negative differential resistance which cannot be understood by the simple RSJ model. Supercurrent is directly affected both by the bias voltage and the density of states at the energy gap of superconductor. The supercurrent by the Multiple-Andreev-Reflection is considerably changed across subharmonic gap voltages because of the singularity of the density of state of superconductor near the energy gap. We have done mixer experiment of SNS weak-links and have observed IF peaks at subgap voltages which are caused by the negative differential resistance.         A three photon noise SIS heterodyne receiver at submillimeter wavelength    A. Karpov, J. Blondel, M. Voss and K.-H. Gundlach Summary: An ultra-low noise single sideband SIS receiver has been prepared for radio astronomy at the sub millimeter wavelength /spl lambda//spl ap/0.85 mm. The minimum single sideband receiver noise temperature of 48 K corresponds to 3 h/spl omega//k or equivalent number of 3 photon of noise. The minimum single sideband SIS mixer noise temperature is about 20 K, close to 1.2 h/spl omega//k, or one photon of noise. The Nb/AlOx/Nb junctions with a Josephson critical current density of 9 KA/cm/sup 2/ and with the area of about 0.9 /spl mu/m/sup 2/ were used. The receiver has been tested at the 30 meter IRAM radio telescope in the winter seasons of 1997 and 1998. The observations at the radio telescope are speeded up by a factor of two to three with the new receiver.         Noise of superconductor/normal metal/superconductor mixer based on low voltage negative differential resistance effect    Y. Gorelov and R. Nicolsky Summary: The conversion efficiency was calculated for some type of high-T/sub c/ superconducting junctions, which have negative derivative on current-voltage characteristics. This distinguishing feature can be explained by Andreev reflections in superconductor/normal metal boundaries. In this work it is analyzed a combination of the theoretical predictions of noise, based on noise correlation matrix of the mixer model, and theory of Likharev-Semenov for the thermal noise. The conversion gain is possible in SNS mixers in spite of noise in negative derivative region.         Fabrication of niobium-carbonitride Josephson junctions on magnesium-oxide substrates using chemical-mechanical polishing    S. Kohjiro, H. Yamamori and A. Shoji Summary: We have developed a fabrication technique for narrow NbC/sub x/N/sub 1-x//MgO/NbC/sub x/N/sub 1-x/ junctions on MgO substrates using chemical-mechanical polishing (CMP) for the removal of SiO/sub 2/ insulation layer from the top of junctions. Parameters of CMP have been optimized so that the run-to-run deviation of removal rate for SiO/sup 2/ is less than /spl plusmn/20% and uniformity across a 10 mm/spl times/10 mm area is better than /spl plusmn/20%. Using the optimized CMP, NbC/sub x/N/sub 1-x//MgO/NbC/sub x/N/sub 1-x/ junctions with width of 1-4 /spl mu/m have been successfully fabricated. Fabricated junctions showed no superconducting leakage current and critical current densities of interconnections between the counter electrode and the wiring were larger than 1/spl times/10/sup 8/ A/m/sup 2/. This CMP-based fabrication technique is applicable to SIS mixers and Josephson local oscillators operated near 1 THz.         Detection and storage of femtosecond laser pulse signals by optical magnetic-flux-generation in a YBCO thin film loop    M. Tonouchi, S. Shikii, M. Yamashita, K. Shikita and M. Hangyo Summary: We studied the optical creation and modulation of magnetic flux quanta in a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film loop by observing terahertz emission excited with femtosecond laser pulses. The magnetic flux is created and modulated in the loops with a polarity controlled by means of optical supercurrent modulation. The results suggest a possible application of the superconductive loop as an optical flux-trap memory for the detection and storage of the femtosecond optical signals. The mechanism for the creation of the magnetic flux is discussed in relation to the current distribution in the loop.         Passivation, transition width, and noise for YBCO bolometers on silicon    D.G. McDonald, R.J. Phelan Jr., L.R. Vale, R.H. Ono and D.A. Rudman Summary: We are developing YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thermometers for large area bolometers that include a heater for calibration by the electrical substitution of power. Because YBCO on buffered Si is under mechanical stress and must be very thin to avoid cracking, we find it is electrically sensitive to its passivation layer. For example, passivation by SrTiO/sub 3/ raised the noise in our films by about a factor of 100. An alternative is to first cap the YBCO with Au for passivation, and then add an insulator for electrical isolation. Such devices have a narrower transition width, by a factor of 3.9. A model with a shunt resistor across the superconductor predicts a narrowing of the transition, but by less than the observed amount. The noise equivalent temperatures of our thermometers, about 4 nK Hz/sup -1/2/, are not degraded by the normal metal shunt, although the resistance is decreased. The resistance is decreased. The resistance can be raised using AgAu alloy in place of Au, with equivalent noise performance.         Development of superconducting tunnel junctions with an aluminum-oxide insulation layer for X-ray detection    H. Sato, T. Ikeda, H. Kato, K. Kawai, H. Miyasaka, T. Oku, W. Ootani, C. Otani, H.M. Shimizu, H. Watanabe, H. Nakagawa, H. Akoh, M. Aoyagi, T. Taino, K. Inaba and Y. Kino Summary: Superconducting tunnel junctions (STJ), with a buffer layer between the silicon substrate and junction, are being developed for use as high-resolution X-ray detectors. Aluminum-oxide (Al/sub 2/O/sub 3/) is employed as the buffer layer in order to suppress the phonon mediated background from the Si substrate. The extent of phonon insulation was studied by measuring the X-ray spectra of STJs as a function of buffer layer thickness. The phonon insulation ability of Al/sub 2/O/sub 3/ was compared to that of magnesium-oxide. The Al/sub 2/O/sub 3/ layer should be a good phonon insulator, with the ability to suppress phonons with a single buffer layer.         Response properties at 2.525 terahertz using high-T/sub c/ Josephson junctions on silicon bicrystal substrates    J. Chen, E. Kobayashi, K. Nakajima, T. Yamashita, S. Linzen, F. Schmidl and P. Seidel Summary: Using high-T/sub c/ grain boundary Josephson junctions (GBJJs) made of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// deposited across silicon bicrystal boundary, we successfully demonstrated direct response at frequency as high as 2.525 THz and the operation temperature up to 70 K. Also, the effects of response on polarization of electromagnetic waves and the harmonic mixing properties are investigated. It is found that there is no polarization dependence of the response for our high-quality GBJJs. This result is favorable to the spectroscopy application. At frequency as high as 2.525 THz, the high-order harmonic mixing at zero and finite bias voltage has been demonstrated.         Electronic refrigerators: optimization studies    B. Jug and Z. Trontelj Summary: Electric current flowing through a normal metal-insulator-superconductor (NIS) junction accompanied by the heat transfer from normal metal to superconductor is able to cool electrons in the normal metal electrode below the lattice temperature under certain conditions. The tunneling electric current dependence on biasing voltage at different normal metal electrode electron temperatures is calculated. Refrigerators with one and with two NIS junctions are investigated. Further, the cooling power of SNIS and SINIS refrigerators, its dependence on biasing voltage and on the temperature of normal metal electrode electrons are investigated. With reduced insulator layer thickness the resistivity of a NIS junction decreases. Thus, the cooling power of a refrigerator increases. But simultaneously the probability for Andreev reflections which diminish the efficiency of the refrigerator increases. Therefore, the optimal thickness of the insulator layer needs to be found. A method for calculating an optimal insulator layer thickness based on the introduction of a new function that needs to be minimized is described. Geometrical limits on the influence of Andreev reflection are determined.         Single-photon-counting hotspot detector with integrated RSFQ readout electronics    D. Gupta and A.M. Kadin Summary: Absorption of an infrared photon in an ultrathin film (such as 10-nm NbN) creates a localized nonequilibrium hotspot on the submicron length scale and sub-ns time scale. If a strip /spl sim/1 /spl mu/m wide is biased in the middle of the superconducting transition, this hotspot will lead to a resistance pulse with amplitude proportional to the energy of the incident photon. This resistance pulse, in turn, can be converted to a current pulse and inductively coupled to a SQUID amplifier with a digitized output, operating at 4 K or above. A preliminary design analysis indicates that this data can be processed on-chip, using ultrafast RSFQ digital circuits, to obtain a sensitive infrared detector for wavelengths up to 10 /spl mu/m and beyond, with bandwidth of 1 GHz, that counts individual photons and measures their energy with 25 meV resolution. This proposed device combines the speed of a hot-electron bolometer with the single-photon-counting ability of a transition-edge microcalorimeter, to obtain an infrared detector with sensitivity, speed, and spectral selectivity that are unmatched by any alternative technology.         Non-thermal response of a diffusion-cooled hot-electron bolometer    A.D. Semenov and G.N. Gol'tsman Summary: We present an analysis of a diffusion-cooled hot-electron bolometer in the limiting case of a weak thermalization of non-equilibrium quasiparticles. We propose a new model relying on the non-thermal suppression of the superconducting energy gap by excess quasiparticles. Using material parameters typical for Al, we evaluate performance of the bolometer in the heterodyne regime at terahertz frequencies. Estimates show that the mixer may have quantum limited noise temperature and a few tens of GHz bandwidth, while the required local oscillator power is in the /spl mu/W range due to in-effective suppression of the energy gap by quasiparticles with high energies.         Resolution degradation in X-ray detectors based on superconducting tunnel junctions    R. den Hartog, P. Verhoeve, A. Peacock, A. Poelaert and N. Rando Summary: Despite considerable progress over the past years, the detection of medium-energy X-ray photons (E>1 keV) with STJs near the energy-resolution limit, set by the Fano and tunnel noise, remains an elusive goal. There is presently little doubt that the spatially inhomogeneous response of the STJ is responsible for the degradation of the energy resolution. We review several proposed mechanisms against experimental data for Nb- and Ta-based STJs, of various sizes and in single or array-format. We argue against a single mechanism behind the resolution degradation. The experimental results presented here support a model in which quasi-particles are lost at the edges of the STJ, but also indicate that losses into the leads seriously degrade the energy resolution. Finally, an example is given of how fabrication details may play a role as well.         Multiple flux-flow branches and phase transition of Josephson fluxon lattice in intrinsic Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ stacked Josephson junctions    V.M. Krasnov, N. Mros, A. Yurgens and D. Winker Summary: We experimentally study the c-axis current-voltage characteristics (IVCs) of small area Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ mesas containing only a few intrinsic stacked Josephson junctions (SJJs). In a magnetic field, H, parallel to the ab-plane, a Josephson flux-flow branch (FFB) appears in the IVCs. The FFB consists of multiple closely spaced but distinct sub-branches and exhibit a well defined Fiske step structure. When normalised to the applied magnetic field, the flux-flow branches for different H collapse into two universal curves representing two different Josephson flux-flow regimes characterised by different propagation velocities. A transition between the two regimes occurs within a narrow field interval and may indicate phase transition of the Josephson fluxon lattice in intrinsic SJJs.         Preparation of intrinsic Josephson junctions using Bi-2212 thin films    M. Inoue, M. Yoshida, T. Senzaki, Y. Sugihara, J. Otsuka, K. Ohbayashi, A. Fujimaki and H. Hayakawa Summary: We fabricated intrinsic Josephson junctions 10 /spl mu/m/spl times/10 /spl mu/m in area using Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (Bi-2212) thin films with large grains employing a two-step annealing procedure. The first annealing step at a high temperature in O/sub 2/ is for the growth of crystal grains and the second step at a lower temperature in N/sub 2/ is for the control of the oxygen content in the film. By this method, Bi-2212 thin films with the c-axis critical current density J/sub c/ of 10/sup 1/-10/sup 4/ A/cm/sup 2/ were obtained. A mesa structure was formed on the surface of the annealed film and we measured its electrical properties along the c-axis. The current-voltage characteristics with clear hystereses and multiple branches were observed for the samples with J/sub c/ of /spl sim/10/sup 3/ A/cm/sup 2/ or less. The gap structure was observed in the current-voltage characteristics for low mesas. J/sub c/ and the voltage jump decreased more rapidly with increasing temperature than those predicted by the BCS theory. We could obtain intrinsic Josephson junctions in Bi-2212 thin films with similar properties as in single crystal samples.         Short pulse tunneling measurements of the intrinsic Josephson junctions in Bi-Sr-Ca-Cu-O    M. Suzuki, T. Watanabe and A. Matsuda Summary: We have measured the I-V characteristics of intrinsic Josephson junction stacks fabricated on the surface of a Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// crystal. In order to reduce the Joule heating, which necessarily occurs associated with these measurements, we have reduced the number of junctions in the stack to approximately 10, and then adopted the short pulse measurement method. With these measures, it becomes possible to observe I-V characteristics which have a clear gap structure with slight gap suppression due to current injection. The voltage response analysis indicates that the magnitude of the gap suppression is no greater than 3% at the maximum. The estimated gap parameter is 50 mV for a single junction.         Characteristic temperature dependence of the maximum Josephson current in Bi-Sr-Ca-Cu-O intrinsic junctions    M. Suzuki, T. Watanabe and A. Matsuda Summary: We have measured the temperature dependence of the maximum Josephson current I/sub c/ for 15-30 nm thick stacks comprised of 10 to 20 Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic junctions. It is found that I/sub c/ typically shows little saturation at low temperatures but continues to increase noticeably as temperature decreases towards T=0. This behavior becomes significant as the normal tunneling resistance increases with decreasing oxygen content.         Bi-Sr-Ca-Cu-O intrinsic Josephson junctions fabricated by inhibitory ion implantation    K. Nakajima, N. Yamada, J. Chen, T. Yamashita, S. Watauchi, I. Tanaka and H. Kojima Summary: Intrinsic Josephson junctions were fabricated by silicon (Si) ion implantation into Bi-Sr-Ca-Cu-O (BSCCO) single crystals of 2212 phase grown by the traveling solvent floating zone (TSFZ) method. Si ions with the acceleration energy of 80 keV were implanted into BSCCO. Si-implanted portion of BSCCO turned to insulator and defined junctions precisely. The project range of Si into BSCCO controls thickness of intrinsic junctions. The junction exhibited a typical current-voltage characteristic of the BSCCO intrinsic Josephson junction showing a good uniformity of the critical current and the number of branches is consistent with the depth where Si ions were implanted.         Intrinsic BSCCO Josephson junctions on off-axis substrates    T. Kawahara, T. Ishibashi, H. Kaneko, K. Sato, K. Lee and I. Iguchi Summary: Anisotropic transport and microwave properties of intrinsic Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (2212) Josephson junctions fabricated on off-axis substrates were studied. The twin-free thin film 2212 Josephson junctions have been prepared by molecular beam epitaxy (MBE) on LaAlO/sub 3/ [001] substrates tilted 6/spl deg/ toward the [110] direction, and were patterned into a line shape along [110] LaAlO/sub 3/ with 20 /spl mu/m in width. We found that the anisotropy parameter /spl gamma/ was increased from 76 to 120 by the annealing at temperature of 320-350/spl deg/C in the MBE chamber. The coherent Josephson radiation from stacked 2212 intrinsic junctions and their modulation under applied magnetic field were observed at frequency f/sub REC/=1.7 GHz by using a nonresonant detection method. These results confirmed the occurrence of the mutual phase locking of the stacked series array of intrinsic junctions along the c-axis.         High frequency microwave emission from BSCCO intrinsic junctions    W. Wang, K. Lee, I. Iguchi, K. Hirata and T. Mochiku Summary: We studied the microwave emission properties of very thin mesa structures of high quality Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ (BSCCO) single crystals grown by the traveling solvent floating zone technique. To increase the anisotropy of crystal, the samples were annealed at 400-600/spl deg/C for 1-20 hrs. The mesa height was 15-45 nm, for which 10-30 resistive hysteresis branches in the I-V characteristics might be expected. The emission power from the stack of the intrinsic junctions was measured by a superheterodyne detection technique at receiving frequencies f/sub rec/=12 GHz, 36 GHz and 47 GHz. For the first time, we observed two kinds of emission modes, one may be explained by microwave emission from phase-locked Josephson junctions, and the other may be caused by the injection of quasiparticle current into the layered intrinsic junction system.         Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic Josephson junctions fabricated by a simple technique without photolithography    Y.J. Feng, W.L. Shan, M. Jin, J. Zhou, G.D. Zhou, Z.M. Ji, L. Kang, W.W. Xu, S.Z. Yang, P.H. Wu and Y.H. Zhang Summary: Due to the roughness in the surface of the crystal sample, it is hard to use photolithography in the patterning process of the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic Josephson junction. In this paper, we report a simple technique for fabricating the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic Josephson junctions. In the patterning process, metal masks are used instead of photolithography and argon ion milling is applied to form a small mesa on the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// crystal surface. Real four-probe transport measurements are made on the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic junctions and typical current-voltage characteristics with multi-branch structure have been observed, from which the superconducting gap parameter can be extracted. Additionally, from the strung hysteresis in the I-V characteristics, the capacitance C/sub J/ of the unit intrinsic Josephson junction can be estimated, which is in good agreement with that evaluated from the geometric parameters of the unit junction between the two copper oxide lagers.         Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic junction and its application in harmonic mixing at the millimeter waveband    W.L. Shan, G.D. Zhou, Y.J. Feng, Z.M. Ji, W.W. Xu, S.Z. Yang, P.H. Wu and Y.H. Zhang Summary: In this paper, we report on the successful fabrication and characterisation of the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic junctions. To study the microwave influence of these intrinsic junctions, harmonic mixing was carried out in the millimeter waveband at temperatures ranging from 20 K to 77 K. Up to 68/sup th/ harmonic mixing in the 8 millimeter waveband and 56/sup th/ in the 3 millimeter waveband were clearly observed. The dependence of the intermediate frequency output on the temperature, the signal power and the local oscillator power were studied, and some unexpected features were observed.         Josephson junction phased arrays    S.P. Yukon and N.C.H. Lin Summary: We propose a design for an active antenna array employing 2D triangular Josephson junction (JJ) arrays as oscillators. The oscillators are kept in sync by coupling their flux trains to that of a serpentine discrete JJ transmission line. Adding external magnetic flux to the line between adjacent oscillators induces a phase shift in their rf voltages enabling beam steering.         Radiation emission from triangular arrays of Josephson junctions    P. Caputo, A.U. Ustinov, N.C.H. Lin and S.P. Yukon Summary: The high frequency properties of underdamped Josephson junction arrays consisting of parallel biased triangular cells having a Josephson contact in each branch are studied. At the applied magnetic field corresponding to half a flux quantum in every cell, the junctions transverse to the bias current ("horizontal" junctions) oscillate in phase. The radiation emitted by these junctions is measured using a double-side band superheterodyne receiver in the 80-120 GHz range. It is found that the radiation has a spectral linewidth of about 80 MHz, which is close to that expected from the RSCJ model for the DC biased "vertical" junctions. Our experimental data confirm that both the frequency and the linewidth of the horizontal junction oscillations are controlled by the rotating vertical junctions. In the double row array, when the two rows are simultaneously driven at the same voltage state, we observe a weak radiation peak, which can be explained in terms of a "mixed-mode" dynamics. Numerical simulations that predict this mechanism are in good accord with experiment.         A double junction ring oscillator based on shunted, stacked junctions    S. Lomatch, B. Ruck, R. Schmitz, M. Darula and H. Kohlstedt Summary: We present the design of a double junction ring oscillator, along with initial rf measurements. The ring oscillator design includes the usage of two shunted, stacked junction devices ("Stacktrons") as active switching nodes in the ring. The rf detection circuitry was designed to accommodate both a detector junction for measuring Shapiro steps and a finline antenna for broadband rf. As a motivation for our study, the double junction ring oscillator allows the probe of the multiple flux quantum (MFQ) state, which is a distinct, transient dynamical state resulting from the synchronous switching of nodal junctions in the circuit. Such a state has several possible applications. We quantify the existence of the MFQ state in the ring circuit configuration with numerical simulations, including circuit margins and yield. Finally, we provide a detailed explanation of the coupling circuitry between the ring oscillator and rf detection circuitry.         Phase locking of Josephson junction arrays achieved by a non-traditional bias scheme    G. Filatrella, N.F. Podersen and K. Wiesenfeld Summary: We propose to modify the usual biasing scheme of a two dimensional Josephson junction array by connecting the wires in a special cross-type fashion. Numerical simulations show that a simple two dimensional circuit of Josephson junctions with the new biasing scheme, to the contrary of the traditional scheme, one can achieve a stable frequency locked state without the use of an external load. We also show that four of these circuits can be series connected and that the output voltage is further increased. The new scheme may dramatically improve the performance of Josephson junction microwave oscillators.         Phase locking dynamics in 2D Josephson junction arrays with small inductances    B. Frank, M. Basler, W. Krech, K.Yu. Platov and H.-G. Meyer Summary: Phase locking in a basic two-dimensional hybrid Josephson junction array consisting of two rows and four columns is investigated exploiting the small inductance approximation. The general synchronization dynamics agrees with that of simpler systems. Especially, the junction voltages within the same row oscillate practically in phase unless the external magnetic flux in the loops is near to multiples of a quarter of the flux quantum. In case of a finite flux we have found a stable antiphase regime of both uniform interferometer oscillations whereas in the zero-field limit this locking regime is neutrally stable.         Properties of Josephson array oscillators at the submillimeter wave region    A. Kawakami, Y. Uzawa and Z. Wang Summary: We have developed resistively shunted tunnel junctions with a small parasitic inductance (/spl equiv/100 fH) to improve the high-frequency performance of Josephson array oscillators. Josephson array oscillators with 11 such junctions and Nb microstrip resonators were designed and fabricated to operate at 690 GHz. Shapiro steps induced by Josephson oscillation were clearly observed at the submillimeter frequency region. By comparing the step height with the numerical simulation, we estimated the power of the Josephson oscillator delivered to the load resistor to be about 10 /spl mu/W at 625 GHz. The linewidth of the Josephson array oscillator was also measured using an integrated receiver consisting of two Josephson array oscillators and an SIS mixer. The designed frequency of the receiver was set at 550 GHz. IF output power spectrum was observed when both the oscillators were biased at about 1.17 mV which corresponds to 566 GHz. The composite linewidth of Josephson oscillation was measured about 8 MHz at 4.2 K.         Microwave radiation from zero field singularities in stacks of two long Josephson junctions    G. Carapella, G. Costabile, J. Mygind and N.F. Pedersen Summary: We present experimental results on the radiation emitted from two-stacks of long Josephson junctions with double overlap geometry. Microwave radiation was received from the voltage-locked Zero Field Steps of the c/sup -/ family, corresponding to fluxon-antifluxon pairs oscillating in the stack. It was also received from other current singularities, interpreted as resonances excited by the magnetic field generated by the nonuniform bias currents. In the former case, there is experimental evidence for an appreciable signal, while, theoretically, the net signal produced is expected to be vanishingly small. This event can he explained in terms of a possible delay between the component signals, as the junctions in the stack do not have identical length.         Oscillation spectral linewidth for some phase-locked Josephson-junction arrays    V.K. Kornev and A.V. Arzumanov Summary: High effective autoregressive method has been applied to the calculation of the oscillation line width for the promising phase-locked Josephson-junction arrays. It has been found, that the oscillation linewidth decreases with the number N of Josephson junctions proportionally to N for one-dimensional arrays or even more fast for two-dimensional arrays until number N exceeds the coupling radius. It has been shown that in the case of parallel array inserted into superconducting microstrip line, the phase-locked oscillation state in-phase could be provided by the strong interaction between Josephson junctions and electromagnetic standing wave regardless to applied magnetic field. The necessary amplitude of the standing wave is easy attained at McCumber parameter value /spl beta/>1, when the high-frequency Josephson-junction impedance is small in comparison with the strip-line wave impedance. An extra reduction in the linewidth caused by electromagnetic standing wave impact has also been studied. The results are discussed from viewpoint of the possible applications of the structures as submillimeter wave generators.         Author Index (1998 - Part 3)    No author information available Summary: Not available

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