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2002 Part 1     Front Cover (2002 - Part 1)    No author information available Summary: Not available         Table of Contents (2002 - Part 1)    No author information available Summary: Not available         Conference Information (2002)    No author information available Summary: Not available         The IEEE Council on Superconductivity Awards for Contributions in the Field of Applied Superconductivity (2002 - Part 1)     Summary: Not available         Fabrication of high current density Nb integrated circuits using a self-aligned junction anodization process    G.L. Kerber, L.A. Abelson, K. Edwards, R. Hu, M.W. Johnson, M.L. Leung and J. Luine Summary: We have developed a self-aligned Nb/Al-AlO/sub x//Nb junction anodization process that allows outside junction contacts and relaxed contact alignment. In this process, the junction, rather than the junction contact, becomes the minimum definable feature size. Junction size is limited only by the resolution of the lithography and etch tools, which is 0.65 /spl mu/m in our foundry. The self-aligned junction anodization process allows a significant increase in circuit speed due to the decrease in minimum junction size and increase in junction critical current density without investment in new fabrication tools. This process requires only one additional, noncritical masking step and has no impact on existing design rules. We describe the fabrication and electrical characteristics of lightly anodized junctions and arrays at 8 kA/cm/sup 2/ and the development of new 5 /spl Omega//sq. MoN/sub x/ and 0.15 /spl Omega//sq. Mo/Al resistors. We also discuss the 300 GHz T flip-flop benchmark results from our new 8 kA/cm/sup 2/, 1.25 /spl mu/m Nb integrated circuit process and compare these results to other Nb processes.         High-performance Nb integrated circuit process fabrication    J.M. Murduck, A. Kirschenbaum, A. Mayer, V. Morales and C. Lavoie Summary: For the last 15 years, Nb-based digital circuits were fabricated with 1-2 kA/cm/sup 2/ junctions. However, use of high critical current density Nb junctions coupled with state-of-the-art photolithographic tools greatly reduced parasitic capacitance and increase circuit speed. Our 150 mm-wafer integrated circuit process uses 6 kA/cm/sup 2/ junctions by following a hybrid approach to both optimize wafer throughput and maintain the critical aspects of device fabrication uniformity and reproducibility. Junctions with area less than 0.25 sq./spl mu/m are defined using an in-house production electron-beam system. Other process layers not requiring such resolution are defined with an in-house i-line optical stepper allowing line pitch down to 1 /spl mu/m and layer-to-layer alignment of less than 80 nm. To avoid circuit-limiting parasitic inductance, a chemical mechanical polishing technique is introduced that enables low-inductance 'outside' contacts to our Josephson junctions. In addition, the judicious use of planarization in a fabrication process to decrease circuit inductance are addressed.         Light-anodization process for high-J/sub c/ micron and submicron superconducting junction and integrated circuit fabrication    Xiaofan Meng and T. Van Duzer Summary: We have developed a new approach for high critical current density (J/sub c/) small junction fabrication. The key step is light anodization that forms a thin double-layer of Al/sub 2/O/sub 3//Nb/sub 2/O/sub 5/ oxides around the junction area and on the sidewalls of the junction. This anodization ring is a good dry-etch stop, so the via for the junction contact can be larger than the junction area. The anodization ring can also protect the junction from plasma damage during dry etching and sputtering steps; therefore, it can reduce the junction leakage current and critical-current spread. The new technique is very simple and cost effective compared with the CMP approach. It needs only one additional mask and process step. We have used the technique to fabricate high-J/sub c/ submicron Nb/Al-AlO/sub x//Nb tunnel junctions with very low critical-current spreads. Using this technique, we have also fabricated Nb SQUID's and various Nb digital IC's.         The detection of defects in a niobium tri-layer process    A.A. Joseph, S. Heuvelmans, G.J. Gerritsma and H.G. Kerkhoff Summary: Niobium (Nb) LTS processes are emerging as the technology for future ultra high-speed systems especially in the digital domain. As the number of Josephson Junctions (JJ) per chip has recently increased to around 90000, the quality of the process has to be assured so as to realize these complex circuits. Until now, very little or no information is available in the literature on how to achieve this. In this paper we present an approach and results of a study conducted on an RSFQ process. Measurements and SEM inspection were carried out on sample chips and a list of possible defects has been identified and described in detail. We have also developed test-structures for detection of the top-ranking defects, which will be used for yield analysis and the determination of the probability distribution of faults in the process. A test chip has been designed, based on the results of this study, and certain types of defects were introduced in the design to study the behavior of faulty junctions and interconnections.         Tunneling properties of barriers in Nb/Al/AlO/sub x//Nb junctions    S.K. Tolpygo, E. Cimpoiasu, X. Liu, N. Simonian, Yu.A. Polyakov, J.E. Lukens and K.K. Likharev Summary: We have measured DC I-V curves of niobium-trilayer (Nb/Al/AlO/sub x//Nb) junctions with barriers thermally grown within a broad range of oxygen exposure E=Pt, from 2/spl times/10/sup 5/ to 2/spl times/10/sup 9/ Pa-s, and for applied electric fields ranging from zero all the way up to the breakdown - typically, above 10 MV/cm. The data can be reasonably well fitted by the direct theory assuming trapezoidal barrier profile and using the numerical solution of the Schrodinger equation. (The traditional WKB approximation gives considerable errors for barriers so thin and sharp.) The fitting has shown that with the increase of oxygen exposure, the effective oxide thickness d/sub ef//spl equiv/(m/m/sub 0/)/sup /spl alpha//d where m is the effective mass of the tunneling electron and (/spl alpha//spl ap/0.51) grows from 0.83 to 1.08 nm, while the average barrier height grows from 1.7 to 1.9 eV, and the zero-voltage conductance G/sub 0/ continues to drop as E/sup -1/2/ through all the studied exposure range.         Development toward high-speed integrated circuits and SQUID qubits with Nb/AlO/sub x//Nb Josephson junctions    W. Chen, V. Patel, S.K. Tolpygo, D. Yohannes, S. Pottorf and J.E. Lukens Summary: Our Nb/AlO/sub x//Nb planarized process has been upgraded by adding extra dielectric and Nb wiring layers and the installation of an Inductively Coupled Plasma (ICP) etcher. Much higher quartz etch rates as well as reduced residue are achieved with ICP etch. Etch uniformities of both Nb and quartz are also improved significantly. Damage to Nb during the fabrication process has been investigated. We have found that dry etching in SF/sub 6/ plasma has a significant effect on the quality of Nb films under certain conditions with damage coinciding with the presence of in situ deposited Al.         High quality Nb-based tunnel junctions for high frequency and digital applications    P.N. Dmitriev, I.L. Lapitskaya, L.V. Filippenko, A.B. Ermakov, S.V. Shitov, G.V. Prokopenko, S.A. Kovtonyuk and V.P. Koshelets Summary: A number of new fabrication techniques are developed and optimized in order to fit the requirements of contemporary superconducting electronics. To achieve ultimate performance of integrated submm receivers with operational frequency of 1 THz, tunnel junctions with AlN tunnel barrier having a R/sub n/S value as low as 1 /spl Omega//spl mu/m/sup 2/ have been developed. High quality characteristics of Nb/AlN/Nb tunnel junctions with R/sub j//R/sub n/=16 and R/sub n/S=10 /spl Omega//spl mu/m/sup 2/ have been demonstrated. Electron Beam Lithography (EBL) in combination with Chemical Mechanical Polishing (CMP) has been incorporated to produce Nb/AlN/Nb junctions with 0.03 /spl mu/m/sup 2/ area. A new approach to obtain overdamped Nb/AlO/sub x//Nb tunnel junctions has been proposed and realized. The dependencies of the main parameters of novel junctions on the current density and circuit geometry have been studied. These junctions may have a good potential in Josephson junction arrays and Single-Flux-Quantum applications (RSFQ).         Improved critical-current-density uniformity by using anodization    D. Nakada, K.K. Berggren, E. Macedo, V. Liberman and T.P. Orlando Summary: We discuss an anodization technique for a Nb superconductive-electronics-fabrication process that results in an improvement in critical-current-density J/sub c/ uniformity across a 150-mm-diameter wafer. We outline the anodization process and describe the metrology techniques used to determine the NbO/sub x/ thickness grown. In the work described, we performed critical current I/sub c/ measurements on Josephson junctions distributed across a wafer. We then compared the J/sub c/ uniformity of pairs of wafers, fabricated together, differing only in the presence or absence of the anodization step. The cross-wafer standard deviation of J/sub c/ was typically /spl sim/5% for anodized wafers but >15% for unanodized wafers. This difference in J/sub c/ uniformity is suggestive of an in-process modification from an unknown cause that is blocked by the anodic oxide. It is interesting that small junctions do not see an improvement in I/sub c/ uniformity - apparently the anodization improves only the J/sub c/ uniformity and not the variation in junction size. Control of J/sub c/ is important for all applications of superconductive electronics including quantum computation and rapid single-flux quantum (RSFQ) circuitry.         Ti quadlevel resist process for the fabrication of Nb SIS junctions    W.W. Clark IV, J.Z. Zhang and A.W. Lichtenberger Summary: We have fabricated high quality Nb/Al-oxide/Nb Superconductor-Insulator-Superconductor (SIS) junctions using a Ti-based quadlevel resist process. The quadlevel materials have been carefully chosen to optimize the fluorine-based anisotropic reactive ion etching of Nb and subsequent insulation coverage of the junctions in a self-aligned process. This SIS fabrication process enables excellent control of junction size and is also compatible with Au overlayer junction and junction anodization approaches.         New fabrication process for Josephson tunnel junctions using photosensitive polyimide insulation layer for superconducting integrated circuits    K. Kikuchi, S. Segawa, Eun-Sil Jung, H. Nakagawa, K. Tokoro, H. Itatani and M. Aoyagi Summary: Photosensitive polyimide, synthesized by block copolymerization, is expected to be an excellent insulation layer in LSI circuits in the future. This polyimide has a higher thermal resistance than those of the other organic polymers. It also has good electric properties such as a high break down voltage and a low dielectric constant. We propose a new fabrication process for the Josephson tunnel junction using a photosensitive polyimide. It is possible to simplify the fabrication process of the Josephson tunnel junction, because the photosensitive polyimide is used as the insulation layer instead of conventional inorganic insulation films without an etching process. We fabricated Nb/Al-AlOx/Nb Josephson tunnel junctions using this new process. The junctions show excellent current-voltage (I-V) characteristics with V/sub m/ values more than 80 mV.         Thermal annealing of Nb/Al-AlO/sub x//Nb Josephson junctions    J.V. Migacz and M.E. Huber Summary: We thermally annealed single un-shunted Josephson junctions at temperatures of 110 to 270/spl deg/C for durations of 2.5 to 90 minutes. We also exposed some junctions for three separate 15-minute periods in order to compare the result with that of a continuous 45-minute exposure. After annealing, we measured the changes in junction properties such as critical current I/sub C/, normal state resistance R/sub N/, and junction quality parameter V/sub M/. I/sub C/ decreases with increased exposure, (starting at approximately 125/spl deg/C) and R/sub N/ increases, such that the I/sub C/R/sub N/ product remains roughly constant up to 200/spl deg/C, at which point I/sub C/R/sub N/ also begins to decrease. V/sub M/ declines slightly with increased exposure, but with a large amount of scatter. Samples with interrupted exposures degraded less than if annealed continuously. Based on our results, we find that junctions can tolerate an exposure of up to 90 minutes at temperatures as high as 200/spl deg/C without significant degradation in performance, though allowances will need to be made for shifts in critical current. Junctions exposed for up to 15 minutes at 225/spl deg/C are degraded further but may still function well enough for some applications.         Analysis of the fabrication process of Nb/Al-AlN/sub x//Nb tunnel junctions with low R/sub n/A values for SIS mixers    N.N. Iosad, M. Kroug, T. Zijlstra, A.B. Ermakov, B.D. Jackson, M. Zuiddam, F.E. Meijer and T.M. Klapwijk Summary: We characterize the fabrication process of superconductor-insulator-superconductor junctions (SIS) based on a Nb/Al-AlN/sub x//Nb tri-layer. Utilization of the AlN/sub x/ tunnel barrier, produced by Al nitridation in a nitrogen glow discharge, enables us to produce high quality SIS junctions with low R/sub n/A values (the product of junction resistance and area). Analyzing the correlation of junction resistance and plasma properties, it is concluded that the mechanism of tunnel barrier formation is based on nitrogen implantation into the Al layer with subsequent diffusion of nitrogen, stimulated by plasma heating. The latter process plays a dominant role since R/sub n/A values are well correlated with the power dissipated on the substrate surface. An SIS mixer using this technology and electron-beam lithography has been successfully fabricated.         Characterization of low frequency noise in epitaxial NbN/AlN/NbN tunnel junctions    Z. Wang, A. Saito, A. Kawakami and K. Hamasaki Summary: We measured the low frequency noise characteristics and subharmonic gap structures of epitaxial NbN/AlN/NbN tunnel junctions with different current densities. For all of the junctions, the voltage noise power spectrum S/sub v/(f) showed a frequency dependence that is well described by 1/f behavior. Subharmonic gap structures were clearly observed in the dV/dI-V curves at voltage 2/spl Delta//ne, and the values of n increased with the current density J/sub c/ in the junctions. We estimated the 1/f noise parameter /spl eta/ using the empirical theory of Rogers and Buhrman for the S/sub v/(f), and investigated the correlation between the /spl eta/ and the inverse junction quality 1/Q. We found that the /spl eta/-1/Q relationship for our epitaxial tunnel junctions gave a different behavior for nonepitaxial tunnel junctions. The tunnel barrier properties were investigated by applying a pulse voltage to the junctions at 4.2 K, and measuring the applied voltage dependence of the I-V characteristics and low frequency noise amplitude.         Integrated niobium thin film air bridges as variable capacitors for superconducting GHz electronic circuits    M. Schicke and K.F. Schuster Summary: Superconducting GHz electronics can be improved by variable tuning circuits. We present a low temperature (<150/spl deg/C) process for the fabrication of niobium (Nb) thin film air bridges as variable capacitors, which can be integrated in Nb superconducting electronics. These elements can be applied for on-chip adjustment of filters, resonators and tuning circuits. Measurements and calculations of the electrostatic actuation of the bridges will be compared.         Nb/AlO/sub x//Al/AlO/sub x//Nb double-barrier junctions with high critical current densities: influence of barrier asymmetry    S.K. Tolpygo, A. Brinkman, A.A. Golubov and M.Yu. Kupriyanov Summary: In order to be useful for high speed digital circuit applications, double-barrier SINIS or SIS'IS junctions must be nonhysteretic, possess high critical current densities (j/sub c/>1 kA/cm/sup 2/) and high characteristic voltages V/sub c//spl sim/0.3 mV, where V/sub c/=I/sub c/R/sub sub/ and R/sub sub/ is a characteristic (subgap) resistance damping the junction in the operating range of voltages. This requires high transparencies of barriers and small interlayer thicknesses. Data are presented on fabrication and Josephson properties of SIS'IS junctions with j/sub c/ up to 10 kA/cm/sup 2/ at 4.2 K. It is shown that the asymmetry of double-barrier structure starts playing a major role at high j/sub c/ (i.e., at thin, high transparency barriers) as evidenced by the temperature dependences of the critical current, the value of the current deficit in the I-V characteristics, and the appearance of multiple Andreev reflection peaks in differential conductance of the junctions.         Cross-type submicron Josephson junctions using SNS technology for Josephson voltage standard applications    T. May, M. Schubert, G. Wende, U. Hubner, L. Fritzsch and H.-G. Meyer Summary: We have developed a very simple method for manufacturing submicrometer Josephson junctions (JJs) based on niobium and titanium layers. Together with the use of a microwave circuit consisting of modified coplanar strips this type of JJs offers the possibility of easy integration of several thousand submicrometer junctions in a microwave circuit. Up to this point we have manufactured and successfully tested arrays with 2000 super-/normal-/super-conductor junctions with areas from 0.3 /spl mu/m/spl times/0.3 /spl mu/m to 2.0 /spl mu/m/spl times/2.0 /spl mu/m. First measurements with microwave irradiation showed stable Shapiro steps at voltages up to 40 mV and, thereby, the proper operation of all 2,000 junctions was seen.         Nb/Al/Nb junctions with a wide range of characteristic voltages for superconducting electronic applications    V. Lacquaniti, S. Maggi, R. Steni, C. Cagliero, D. Andreone and R. Rocci Summary: Josephson devices for superconducting electronic applications, such as RSFQ logic circuits and programmable voltage standards, require nonhysteretic junctions with a high speed or a high voltage resolution and hence with characteristic voltages spanning over several orders of magnitude. We present here our recent results on Nb/Al/Nb junctions where, by changing some fabrication parameters such as the thickness and deposition rate of the Al barrier, it is possible to obtain junctions with very different electrical properties. These junctions have characteristic voltages varying from a few tens of /spl mu/V up to more than 1 mV, with critical current densities from 10/sup 3/ up to 10/sup 6/ A/cm/sup 2/.         Accurate Josephson voltage-frequency relation in a granular array of mesoscopic SNS weak links    T. Matsui and H. Ohta Summary: Electron transport in short superconducting weak links is described in terms of multiple Andreev reflections (MAR). According to a recent theory, the current carried by the quasiparticles bound in the N region of a mesoscopic superconductor-normal-superconductor (SNS) weak link consists of dc and cosine components instead of a sinusoidal component. The presence of the dc pair-current component locks the phase relation of the wave function between superconducting grains throughout the series-parallel array of the SNS weak links. We have made a precise measurement of I-V characteristics at 63 K using a constriction in a YBCO polycrystalline film, in which networks of grain boundary Josephson weak links are naturally formed. The measured values of voltage between microwave-induced-current-steps are equal to the theoretical values for a single Josephson element, V/sub n/=n(hf/2e), within an error of 10 ppm. The experimental observation agreed with the theoretical relation to subnanovolt accuracy under irradiation by frequency-modulated millimeter waves. Phase locking of order parameters is thus observed in the array of mesoscopic SNS weak links in the HTS film.         Three-temperature model for hot electron superconducting bolometers based on high-T/sub c/ superconductor for terahertz applications    A. Adam, A. Gaugue, C. Ulysse, A. Kreisler and C. Boulanger Summary: Nowadays, low temperature superconducting hot electron bolometers (LTSC HEBs) are performing really well in the submillimeter wave range. Planar technologies are feasible that can be used for combining bolometer and antenna structures. High temperature superconducting (HTSC) films could also become the next to be used, although it seems that HTSC HEBs cannot reach their LTSC counterparts because of different phonon dynamics. In some previous models, it has been shown, however, that HTSC HEBs should be able to compete with traditional photoconductive detectors in terms of sensitivity. As the substrate temperature was assumed to be constant in these models, we wish to introduce in this paper a more detailed formulation where an extra cooling process (through the substrate) is taken into account. In a first part, simple heat propagation through the substrate is simulated to confirm the theory. The whole detector performance is analyzed in a second part, through a three-temperature model, for different device critical dimensions and thermal parameters. The influence of these characteristics on the lower cutoff frequency and on the maximal responsivity is then discussed. Different ways to improve these detectors are also given.         Speed measurements of diffusion-cooled tantalum bolometers    A. Skalare, W.R. McGrath, B. Bumble and H.G. LeDuc Summary: Thin tantalum films were deposited on silicon wafers using a niobium seed layer to promote alpha-phase growth. These films were patterned into submicrometer size diffusion-cooled bolometers with superconducting transition temperatures of up to 2.35 K and a transition width of about 200 mK. The thermal relaxation times of the devices were determined by measuring the device impedance as a function of frequency and by fitting a theoretical model to the data. Measured relaxation times at low bias voltages range from 0.75 GHz for a 400-nm long device to 6 GHz for a 100-nm device, excluding electrothermal feedback. This should allow sufficiently high instantaneous bandwidths for most low-noise mixer applications in astrophysics.         Study of the IF bandwidth of NbN HEB mixers based on crystalline quartz substrate with an MgO buffer layer    D. Meledin, C.-Y.E. Tong, R. Blundell, N. Kaurova, K. Smirnov, B. Voronov and G. Goltsman Summary: In this paper, we present the results of IF bandwidth measurements on 3-4 nm thick NbN hot electron bolometer waveguide mixers, which have been fabricated on a 200-nm thick MgO buffer layer deposited on a crystalline quartz substrate. The 3-dB IF bandwidth, measured at an LO frequency of 0.81 THz, is 3.7 GHz at the optimal bias point for low noise receiver operation. We have also made measurements of the IF dynamic impedance, which allow us to evaluate the intrinsic electron temperature relaxation time and self-heating parameters at different bias conditions.         Superconducting hot-electron bolometer mixer for terahertz heterodyne receivers    A.D. Semenov, H.-W. Hubers, H. Richter, M. Birk, M. Krocka, U. Mair, Y.B. Vachtomin, M.I. Finkel, S.V. Antipov, B.M. Voronov, K.V. Smirnov, N.S. Kaurova, V.N. Drakinski and G.N. Gol'tsman Summary: We present recent results showing the development of superconducting NbN hot-electron bolometer mixer for German receiver for astronomy at terahertz frequencies and terahertz limb sounder. The mixer is incorporated into a planar feed antenna, which has either logarithmic spiral or double-slot configuration, and backed on a silicon lens. The hybrid antenna had almost frequency independent and symmetric radiation pattern slightly broader than expected for a diffraction limited antenna. At 2.5 THz the best 2200 K double side-band receiver noise temperature was achieved across a 1 GHz intermediate frequency bandwidth centred at 1.5 GHz. For this operation regime, a receiver conversion efficiency of -17 dB was directly measured and the loss budget was evaluated. The mixer response was linear at load temperatures smaller than 400 K. Implementation of the MgO buffer layer on Si resulted in an increased 5.2 GHz gain bandwidth. The receiver was tested in the laboratory environment by measuring a methanol emission line at 2.5 THz.         Application of Hilbert spectroscopy to pulsed far-infrared radiation    V. Shirotov, Y. Divin, U. Poppe, H. Larue, E. Zimmermann, A. Ahmet, H. Halling and K. Urban Summary: We present our results on the development and characterization of a prototype of Hilbert spectrometer, which is intended to operate with pulsed far-infrared radiation. The new prototype consists of high-T/sub c/ Josephson detector in an optical cryostat, analog electronics with the bandwidth of 14 MHz, and a DSP-based data acquisition system, controlling spectroscopic measurements. The specially developed digital data acquisition system gives a possibility to operate in two regimes - with and without integration of the pulsed signal. The tests have been carried out using pulsed 94 GHz radiation with pulse duration of 200 ns and a pulse repetition rate of 1 MHz. A measuring time of 7 ms for a data set of 512 spectral points has been realized. It has been demonstrated, that in a broadband (/spl ap/10 MHz) regime of measurements without integration the developed spectrometer has a dynamic range of external signal power of 17 dB, which can be enhanced by using integration function.         YBCO mid-infrared bolometer arrays    J. Delerue, A. Gaugue, P. Teste, E. Caristan, G. Klisnick, M. Redon and A. Kreisler Summary: A 2/spl times/2 array of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBaCuO) transition edge bolometers has been fabricated on an MgO substrate. The bolometers are of the meander type with line width and line spacing of 40 /spl mu/m. The meander length of a single bolometer is 12.5 mm, covering an area of 1 mm/spl times/1 mm. The voltage responsivity of each pixel, at 10 /spl mu/m wavelength, has been studied as a function of modulation frequency. The array exhibits a uniform response and an electrical noise equivalent power (NEP) of 4.2 /spl times/10/sup -12/ W//spl radic/Hz or an optical NEP of 1 /spl times/10/sup -9/ W//spl radic/Hz. Thermal crosstalk between adjacent pixels has been also studied and first imaging results are presented.         Response time characterization of NbN superconducting single-photon detectors    Jin Zhang, W. Slysz, A. Verevkin, O. Okunev, G. Chulkova, A. Korneev, A. Lipatov, G.N. Gol'tsman and R. Sobolewski Summary: We report our time-resolved measurements of NbN-based superconducting single-photon detectors. The structures are meander-type, 10-nm thick, and 200-nm wide stripes and were operated at 4.2 K. We have shown that the NbN devices can count single-photon pulses with below 100-ps time resolution. The response signal pulse width was about 150 ps, and the system jitter was measured to be 35 ps.         Planar antenna-coupled transition-edge hot electron microbolometer    S. Ali, L.D. Cooley, D. McCammon, K.L. Nelms, J. Peck, D. Prober, D. Swetz, P.T. Timbie and D. van der Weide Summary: We describe a new type of bolometric detector for millimeter and submillimeter wavelengths. The detector is a variant of the Transition Edge Sensor (TES), which has recently been used to build bolometers. In this version of the TES, we couple radiation from a planar antenna to an absorbing normal metal film which is electrically connected to a superconducting thin film. The lateral dimensions of the absorber and TES are /spl sim/10 microns. At low temperatures, the thermal isolation between the electrons and the lattice in the absorber and the superconductor allows the electrons to heat up. We call this device a Transition-edge Hot-electron Microbolometer (THM). These detectors could have numerous advantages for low-background measurements in the far-IR, such as, background-limited sensitivity, short time constant, wide spectral range, immunity to cosmic rays, low microphonic noise and simple readout electronics. We are currently building a low-frequency scale model of the planar antenna to characterize microwave properties of the system.         Experimental study of superconducting hot-electron sensors for submm astronomy    B.S. Karasik, B. Delaet, W.R. McGrath, Jian Wei, M.E. Gershenson and A.V. Sergeev Summary: Relaxation, noise, and spectral properties of micron-size hot-electron sensors made from thin Ti film are studied. Due to the small heat capacity of electrons, the devices are sensitive to single quanta of submm radiation. The sensors can be used for both hot-electron direct detectors (HEDD) and hot-electron photon-counters (HEPC) depending whether electron-phonon relaxation or electron outdiffusion is a dominating cooling mechanism. In an HEDD, the diffusion is blocked by Andreev contacts and the cooling rate is determined by the electron-phonon relaxation. The electron-phonon time in disordered films is long (/spl tau//sub e-ph//spl ap/0.16/spl times/T/sup -4/ /spl mu/s) providing an NEP/spl ap/10/sup -19/ W//spl radic/Hz at 0.3 K and NEP/spl ap/10/sup -20/ W//spl radic/Hz at 0.1 K. The output noise in micron-size bridges follows the predictions of the hot-electron model. In the diffusion mode, the relaxation time of 3 ns has been measured in a 3 /spl mu/m-long device. Smaller size HEPC's would be able to operate with the spectral resolution of 300 GHz at 0.3 K and 100 GHz at 0.1 K and with the photon counting rate in the GHz range. The spectral response of a prototype antenna-coupled Nb HEDD device has been measured and shown to be flat over the range 250-900 GHz.         Fabrication of nanostructured superconducting single-photon detectors    G.N. Gol'tsman, K. Smirnov, P. Kouminov, B. Voronov, N. Kaurova, V. Drakinsky, J. Zhang, A. Verevkin and R. Sobolewski Summary: Fabrication of NbN superconducting single-photon detectors, based on the hotspot effect is presented. The hotspot formation arises in an ultrathin and submicrometer-width superconductor stripe and, together with the supercurrent redistribution, leads to the resistive detector response upon absorption of a photon. The detector has a meander structure to maximally increase its active area and reach the highest detection efficiency. Main processing steps, leading to efficient devices, sensitive in 0.4-5 /spl mu/m wavelength range, are presented. The impact of various processing steps on the performance and operational parameters of our detectors is discussed.         SQUID-based nondestructive evaluation of carbon fiber reinforced polymer    C. Carr, D. Graham, J.C. MacFarlane and G.B. Donaldson Summary: Recent work with HTS SQUIDs in nondestructive evaluation has concentrated on the detection of flaws in aircraft-grade aluminum, with particular emphasis on surface-breaking tears beside rivets. More complex materials are now also being used in aircraft manufacture, with carbon fiber reinforced polymer (CFRP) being one of the most common. Existing technologies such as ultrasound are particularly well suited to the detection of impact-damaged sites and until now there have only been a few reports of eddy current examination of CFRP samples. Here we present results on samples with regions of heat damage, impact damage and with nonmagnetic inserts using eddy current detection techniques. We compare the signal to noise ratio and spatial resolution for a variety of sensors including HTS SQUIDs and gradiometers and conventional induction coils, and discuss variations in detection efficiency with field component measured.         Mobile HTS RF SQUID magnetometer    D.F. He, M. Daibo and M. Yoshizawa Summary: Using a simple compensation method, we developed a mobile HTS RF SQUID magnetometer. The dc and low frequency (below 20 Hz) magnetic field could be compensated very well. With the compensation, the HTS RF SQUID magnetometer remained locked while being swung at large angles in the Earth's field. For frequencies greater than 20 Hz, there was no increase in the flux noise observed after moving the SQUID system in the Earth's field. Using the mobile HTS RF SQUID magnetometer, we constructed an eddy current NDE system, which demonstrated the possibility of detecting defects in ferromagnetic materials.         A four channel HTS SQUID NDE system    S.-M. Lee, H.J. Lee, D.-J. Choi, H.N. Lee and B. Oh Summary: We have constructed an NDE system using an array of four HTS SQUID sensors. The sensor array was fabricated on a SrTiO/sub 3/ bi-crystal substrate. The SQUID pickup loops were held perpendicular to the device under test. The lateral dimension of the SQUID was 20 micrometers and the noise was typically less than 30 pT/Hz/sup 1/2/ at 10 Hz. We used modulation FLL circuits for SQUID readout. The effect by modulation and feedback coupling between adjacent channels was investigated by measuring noise spectrum and output change with and without operating adjacent channels. We applied the system to map the magnetic field generated by current distribution and magnetic inclusions in a working circuit as well as a current carrying metal pattern.         SQUID-NDE method on damaged area and damage degree of defects in composite materials    Y. Hatsukade, M.S. Aly-Hassan, N. Kasai, H. Takashima, H. Hatta and A. Ishiyama Summary: Current detection method was developed to detect damaged area and damage degree of complex defect in electrically conductive composite materials by using superconducting quantum interference device (SQUID) gradiometer. The method was applied to a carbon fiber-reinforced carbon matrix composites (C/Cs) specimen in various damage conditions to investigate the effectiveness of the method. The area and amount of detoured current due to damage in the specimen were successfully detected corresponding to the damage condition. The possibility of the method for classification of the damage condition was discussed.         Nondestructive testing of PEM fuel cells    J.R. Claycomb, A. Brazdeikis, M. Le, R.A. Yarbrough, G. Gogoshin and J.H. Miller Jr. Summary: We report on electric and magnetic nondestructive testing (NDT) of proton exchange membrane (PEM) fuel cells. Fuel cells are electrochemical devices that convert hydrogen and oxygen gas into water, heat and useable electricity. Fuel cell membrane health can affect the cells overall performance and lifetime. We have explored several NDT techniques employing highly sensitive HTS and LTS SQUID and fluxgate magnetometers. Magnetic fields generated by electrochemical currents flowing in the fuel cell are studied in the spatial, time and frequency domain under various operating conditions. Frequency domain electric and magnetic signals are compared under extreme conditions and membrane failure.         Conductivity tomography for non-destructive evaluation using pulsed eddy current with HTS SQUID magnetometer    H.-J. Krause, G.I. Panaitov and Yi Zhang Summary: In standard eddy current nondestructive evaluation, the depth of investigation is restricted to a limited range around the skin depth of the chosen excitation frequency. We developed a pulsed eddy current NDE technique which allows simultaneous analysis of the sample at all depths. The advantage of SQUID magnetometers over induction coil sensors is that the field does not decay as rapidly as its time derivative, allowing for a broader range of investigated depths. Using rectangular excitation pulse trains, eddy currents are induced in the samples. The generated magnetic response field is recorded in off-time between the transmitter pulses by an HTS SQUID magnetometer. The early time data of the transient signal corresponds to the upper layers of the sample, while the late time data deliver information from deep layers. The transient responses are averaged over a number of alternating excitation pulses in order to enhance the signal-to-noise ratio and to eliminate drift. Scan measurements of different aluminum samples are presented. From the measured data, a 3D apparent conductivity image of the sample is calculated by applying a technique known from geophysical data interpretation. From this tomographic conductivity image of the sample, the position and depth of flaws in the material is readily determined.         Multi channel high-T/sub c/ scanning SQUID microscope    J. Matthews, S.Y. Lee, F.C. Wellstood, A.F. Gilbertson, G.E. Moore and S. Chatraphorn Summary: We have constructed and tested a multichannel scanning SQUID microscope. An array of up to 8 high-T/sub c/ YBCO SQUIDs are mounted on a single chip at the end of a 77 K cold finger. Each SQUID loop measures 30 /spl mu/m by 60 /spl mu/m, and the SQUID's are spaced by about 200 /spl mu/m. The normal to the surface of the chip (and the SQUID loop) is aligned parallel to the main scanning direction. A vacuum space and a thin (<25 /spl mu/m) sapphire window separate the SQUID chip from the sample, which is in air at room-temperature. The microscope has been tested by imaging defects in wires and short circuits in computer chips. We discuss the advantages of the multichannel system over the single channel system, as well as some of the obstacles encountered.         Minority carrier diffusion length measurements of semiconductors using a multiwavelength laser SQUID microscope    M. Daibo, T. Kikuchi and M. Yoshizawa Summary: We evaluated single crystal silicon wafers with a p-n junction structure using a laser superconducting quantum interference device (SQUID) microscope. A high temperature superconductor SQUID magnetometer was used to detect photogenerated magnetic signals with an amplitude of several pico-tesla. The relationship between the photogenerated magnetic fields and the wavelengths of the excitation light was investigated. The minority carrier diffusion length was obtained by using a multiwavelength (680 to 850 nm) laser SQUID microscope. The results were found to be in good agreement with those obtained using the probe contacting method. The laser SQUID microscope can enable a truly noncontacting and contamination-free test of equipment with a high spatial resolution, and can enable testers to make quantitative evaluations. While surface pretreatment is necessary in traditional destructive measurements, the laser SQUID method can be used to take immediate measurements without any required pretreatment. These features make this method highly advantageous for monitoring the semiconductor process.         HTS SQUID microscope head with permalloy flux guide    T. Nagaishi, K. Minamimura and H. Itozaki Summary: In order to improve the spatial resolution of an HTS SQUID microscope, permalloy rods with sharpened tip angles of 50/spl deg/ to 170/spl deg/ were placed in front of a SQUID as magnetic flux guides. A current carrying meander line on a printed circuit board with lines and spaces of two widths, 0.3 mm and 0.5 mm, was used as a magnetic field source. The magnetic field distribution was better resolved with the smaller tip angle. Also, a rod with a smaller tip diameter of curvature of 30 /spl mu/m could resolve the magnetic field distribution better than one with a 100 /spl mu/m diameter. It was further found that using a magnetic shield around the magnetic flux guide to suppress the inefficient magnetic field allowed the magnetic field image to be better resolved. The limits of the system's spatial resolution were examined with a 100 /spl mu/m wide meander line. Magnetized laser-printed characters of font size from 2 points to 5 points were also imaged. It was found that this method has a higher magnetic sensitivity and spatial resolution than a large SQUID system, and allows the position and distance from the sample to be adjusted.         LTS SQUID microscope with micron spatial resolution    J. Anderberg, M.S. Colclough, D.B. Crum, Y. Tokura, D.N. Paulson and R.L. Fagaly Summary: We describe a multichannel LTS SQUID microscope with micron spatial resolution. The system achieves micron resolution by the use of small (14 /spl mu/m) detection coils and narrow gap between the coils and the object(s) being scanned. Samples are mounted inside an exchange-gas can at the lower end of a cryogenic probe. This houses all of the cryogenic portions of the microscope and is filled with helium exchange gas. A 5 mm/spl times/5 mm scanning stage is used to scan the sample, which is at cryogenic temperatures. Stepping motors on the scanning stage allow step sizes as small as 0.16 /spl mu/m. The SQUIDs are mounted on a cantilever structure with nine separate detection coils on the end of the structure. Flux noise of the SQUIDs is better than 5 /spl mu//spl Phi//sub o///spl radic/Hz. Sensitivity is better than 100 pT//spl radic/Hz with a bandwidth of dc-10 kHz. Open architecture software provides control of all critical system components, along with data acquisition and analysis. We have demonstrated spatial resolutions better than 2 /spl mu/m. We discuss the impact of the external field coils for susceptibility measurements.         Weld quality evaluation using a high-temperature SQUID array    D.D. Clark, M.A. Espy, R.H. Kraus Jr., A. Matlachov and J.S. Lamb Summary: This paper presents preliminary data for evaluating weld quality using high-temperature SQUIDs. The SQUIDs are integrated into an instrument known as the SQUID Array Microscope, or SAMi. The array consists of 11 SQUIDs evenly distributed over an 7.5 mm baseline. Welds are detected using SAMi by using an on board coil to induce eddy currents in a conducting sample and measuring the resulting magnetic fields. The concept is that the induced magnetic fields will differ in parts of varying weld quality. The data presented here was collected from three stainless steel parts using SAMi. Each part was either solid, included a good weld, or included a bad weld. The induced magnetic field's magnitude and phase relative to the induction signal were measured. For each sample considered, both the magnitude and phase data were measurably different than the other two samples. These results indicate that it is possible to use SAMi to evaluate weld quality.         Nondestructive testing of niobium sheets for superconducting resonators    M. Muck, C. Welzel, A. Farr, F. Schloz and W. Singer Summary: We have developed a LTS SQUID system for eddy-current testing of niobium sheets used to fabricate superconducting resonators for particle accelerators. Since the fabrication of superconducting resonators from planar niobium sheets is very costly, a measurement procedure is required which can test the niobium sheets before the resonator is made. Our system can detect relevant surface damage or inclusions of foreign material having a volume of as small as 10/sup -12/ m/sup 3/ in a test sample made from high-purity niobium. Due to the relatively high frequency of the eddy currents of up to 100 kHz, the system-although employing a magnetometer-can be operated in an unshielded environment. The SQUID readout uses 4 MHz AC-flux modulation; a peak-to-peak dynamic range of 15 fluxquanta is obtained at 100 kHz.         A fully portable, cryocooler-based HTS SQUID NDE instrument    C. Carr, J.C. MacFarlane and G.B. Donaldson Summary: We have recently introduced a novel cryocooler-based HTS SQUID NDE instrument. The system incorporates a closed-cycle cooler that is connected to the inner and outer copper thermal batteries which then allows simultaneous cooling of both masses. Once the inner has been cooled to a temperature of approximately 40 K and the outer to a slightly higher temperature of around 70 K, the connecting "coldfinger" is retracted through a gate valve and the thermal batteries are then maintained in a sealed, vacuum-tight chamber. At this point, the cryocooler can be switched off and fully disconnected from the cryobattery. A sapphire rod is attached to one end of the inner copper thermal mass and this holds the HTS SQUID gradiometer mount. Here we report on the cooldown times for the system and discuss SQUID electrical characteristics at these lower temperatures. Finally we propose a design for the next generation of instrument.         Defect detection in thick aircraft samples based on HTS SQUID-magnetometry and pattern recognition    K. Allweins, G. Gierelt, H.-J. Krause and Mv. Kreutzbruck Summary: SQUID technology has recently evolved to the point that it can be used for industrial applications in Non-Destructive Evaluation (NDE). We present the implementation of an HTS SQUID magnetometer in an eddy current testing system to measure very thick structures in large aircraft. We measured a 62 mm-thick, bolted aluminum sample from the EADS-Airbus, similar to the three-layered outer wing splice that is being proposed for the Airbus A-380. The combination of field sensitivities of a few pT//spl radic/Hz and a large dynamic range of about 140 dB//spl radic/Hz enabled us to detect defects at a depth of up to 40 mm. However a problem was presented by the fact that deep-lying defects which caused small field variations were superimposed on field changes, in their turn caused by current distortions in the vicinity of the titanium bolts. Separation of these two contributions was achieved through parameter optimization based on FEM simulations and signal processing. We report on the possibilities for flaw detection using adapted eddy current excitation.         Gamma ray irradiation tests of high-T/sub c/ SQUID    T. Nagaishi, K. Ara, Y. Morita and H. Itozaki Summary: Gamma ray irradiation tests on high-T/sub c/ SQUIDs were carried out to examine their behavior under nuclear reactor environments. The SQUIDs were made of HoBa/sub 2/Cu/sub 3/O/sub 7-x/ superconducting thin films on SrTiO/sub 3/ substrates. Some were encapsulated in glass fiber reinforced epoxy resin. Gamma ray irradiation was performed with a Co-60 gamma ray source. Irradiation dose rates used were 8.1 to 12.2/spl times/10/sup 3/ Gy/h (1.0 to 1.5/spl times/10/sup 6/ R/h) and the maximum absorption dose was about 10.4 MGy. During and after the irradiation, the noise of the output of the SQUIDs was measured with a power spectrum analyzer. The modulation voltage did not change until a total irradiation dose of about 3 MGy, after which it decreased slightly. We conclude that high-T/sub c/ SQUIDs are resistant to gamma ray irradiation and thus the application of high-T/sub c/ SQUIDs as sensors for reactor component inspection is promising.         Ultimate limits to magnetic imaging    F.C. Wellstood, J. Matthews and S. Chatraphorn Summary: An inverse transformation based on the Fast Fourier Transform (FFT) can be used to convert two-dimensional (2-D) images of magnetic field into corresponding images of the 2-D source currents that generated the field. We discuss the ultimate limits to the spatial resolution that can be obtained in such current density images when information about the sample is incorporated into the inversion process. We discuss the key parameters and compare our theory to experimental data obtained from a high-T/sub c/ scanning SQUID microscope.         Ultra selective HTS bandpass filter for 3G wireless application    G. Tsuzuki, Shen Ye and S. Berkowitz Summary: This paper presents an ultra selective HTS filter that meet existing 3G wireless band. The filter consists of 22 resonators and five cross coupling structures that produce ten transmission zeros near the band edges. A quadruplet cross coupling technique was introduced into the design for the transmission zero implementation. To accommodate twenty-two resonators within a limited wafer size, a compact new topological resonator was also developed. The filter was fabricated using a YBCO thin film on a 2-in MgO wafer. Measured skirt slope has exceeded 30 dB/100 kHz and the filter has a 90 dB out-of-band rejection at 350 kHz from its band edge. This filter surpasses the rejection of an ideal 50-pole Chebyshev filter.         Design method of miniaturized HTS coplanar waveguide bandpass filters using cross coupling    H. Kanaya, J. Fujiyama, R. Oba and K. Yoshida Summary: A new design method of miniaturizing HTS coplanar waveguide bandpass filters using cross coupling is presented. When the size of the filter decreases, the cross coupling between the resonators tends to appear, which causes attenuation poles. In order to control the cross-coupling section, we redesigned the meanderline interval and shape, so that we can design the frequency and number of the attenuation poles. The half-wave length resonator bandpass filter (BPF) is designed by using the 2.5-dimensional electromagnetic field simulator. 7-pole cross-coupled CPW BPF (center frequency of 2 GHz, bandwidth of 15 MHz, ripple of 0.1 dB and two attenuation poles on both sides of pass band) is packed within 6 mm/spl times/10 mm substrate. Simulated performance is in good agreement with the designed one. This BPF has the skirt steepness of 20 dB/MHz (40 dB attenuation), which is the same skirt characteristic of 11-pole Chebyshev BPF. Moreover, we tested YBCO BPF by using our present design theory at cryogenic temperature.         Full-wave 2D and 3D spectral domain analysis of HTS multistrip multilayer lossy structure    I. Vendik, A. Deleniv, M. Gashinova, I. Kolmakov and Y. Kolmakov Summary: The 2D and 3D CAD tools for modeling planar microwave devices are developed. The full-wave 2D analysis based on Method of Moments (MoM) is used for calculation of propagation characteristics of slot- and stripmulticonductor lossy lines embedded in multilayer lossy media. The 3D analysis based on MoM allows considering an arbitrary conductor structure embedded in a multilayered anisotropic media. Two examples of simulation are given. The modeling of the structure consisting of four coupled slots in HTS film based on a bilayered substrate with a tunable upper ferroelectric layer was performed by 2D-analysis. The results of simulation are analyzed for estimation of the insertion loss for each propagation mode. The simulation by 3D-analysis of the HTS microstrip resonator based on ferrite-MgO substrate has been done. The comparison of the HTS microstrip line current distribution simulated by 2D and 3D approaches is implemented and a high accuracy of used models is demonstrated.         Narrow-band filter for the frequency range of 1.9 GHz using double-sided YBCO films on 10-mm-square and 20-mm-square LaAlO/sub 3/ substrates    L.M. Wang, Mao-Yuan Horng, Chen-Chung Liu, Jyh-Haur Tsao, H.H. Sung, H.C. Yang and H.E. Horng Summary: Narrow-band microstrip hairpin-type filters are designed for wireless-communication applications. We have fabricated the high-T/sub c/ superconducting filters by patterning YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) films deposited on 10-mm-square and 20-mm-square, 0.6-mm-thick LaAlO/sub 3/ substrates. The form of hairpin-resonator band-pass filter can be thought of as an alternative version of parallel-couple-resonator filter, except that the open-circuited ends of the resonator are folded back. Our 3-pole 10-mm-square filter has a 2.5-dB maximum insertion loss and 16 MHz bandwidth at 1.94 GHz, while 3-pole 20-mm-square filter has a 0.45-dB maximum insertion loss and 30 MHz bandwidth at 1.94 GHz both with the air-gap height of 3 mm. By mechanically changing the height of air gap between the filter pattern and the top housing plane, the center of frequency of the filter was varied from 1.92 to 2.0 GHz, corresponding to a frequency shift of about 5%. The influences of wafer sizes and housing height on filter performance are discussed.         A 9 pole bandpass filter at 2.7 GHz with Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// coplanar wave guides on a sapphire substrate    S. Wuensch, E. Crocoll, M. Neuhaus, T.A. Scherer, A. Stassen, H.-J. Wermund, W. Jutzi and O. Lochner Summary: A bandpass filter for a 0.6 dB relative bandwidth of 4.5% at 2.67 GHz is implemented with nine end coupled resonators of meander lines with air bridges for ground connections on a 1.7/spl times/3.7 cm/sup 2/ substrate. A single side thermally co-evaporated Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film with a CeO/sub 2/ buffer layer on a sapphire substrate is patterned with an Ar ion beam. Within a bandwidth of 112 MHz at 2.67 GHz the measured insertion loss is smaller than 0.1 dB at 15 K. Filters for a two channel receiver with almost identical transfer functions have been achieved without manual tuning screws. Their characteristics should not be affected by mechanical vibrations on a cold finger.         Extracting the model parameters of high-T/sub c/ superconductor film from the experimental characteristics of microwave resonators and filters    I. Vendik and P. Yudin Summary: A development of CAD of microwave integrated circuits based on high-T/sub c/ superconducting (HTS) films is of high importance. Design of planar HTS microwave devices (filters, multiplexers etc.) is based on a careful simulation of the device characteristics and requires a correct model description of the HTS material. A method of extracting model parameters of HTS film from the experimental characteristics of microwave resonators and filters is considered. It is based on a correct phenomenological model of the HTS film surface impedance and accurate simulation of the microwave resonator (filter). The calculation of the model parameters was realized by Monte Carlo method based on properties of the quasirandom (Halton's) sequences. The set of extracted model parameters is used in the CAD tool for HTS microwave circuits design providing a good agreement between simulated and measured data. A procedure of extracting model parameters of a ferroelectric film from the experimental characteristics is also proposed.         High-T/sub c/ superconducting planar filters with improved performance    I.B. Vendik, M.S. Gashinova, M.N. Goubina, Y.A. Kolmakov, I.A. Kolmakov and G.Y. Zhang Summary: The results of design and investigation of band-pass filters are presented. The filter is based on a set of double-resonator structures. The main constituent of the filter is the pair of coupled resonators in the form of modified hairpins. The combination of coupling inside the pair and between the pairs provides the desired filter performance. The 12-pole filter (17/spl times/22 mm) manufactured on the double-sided YBCO films on LaAlO/sub 3/ substrate exhibited at T=50 K, 0.3 dB insertion loss, 15 dB return loss in 4% pass band (f/sub 0/=1.7475 GHz) and 60 dB out of band rejection. Another band-pass filter is 12-pole quasielliptic filter based on quasilumped resonators. This filter area is 21/spl times/32 mm (MgO). Filter was designed with 902.5 MHz center frequency, 25 MHz bandwidth and 70 dB out of band rejection.         HTS hairpin microstrip filter on r-cut sapphire substrate    F. Aiga, H. Fuke, Y. Terashima, M. Yamazaki, H. Kayano and T. Hashimoto Summary: We have developed a 17-pole high-temperature superconductor thin-film hairpin microstrip filter on r-cut sapphire substrate. We determined the optimum orientation of hairpin resonators on r-cut sapphire substrates, considering the anisotropy of dielectric permittivity. With optimum orientation, the desired frequency response was realized. On the other hand, when the orientation was not the optimum, the frequency response was violently disturbed. The cause of the disturbance of the frequency response was investigated.         Enhanced performance of HTS hairpin type bandpass filter by interdigitated inner poles    K.R. Jung and J.H. Kang Summary: To improve the performance of the hairpin type bandpass filter, we designed a new style hairpin type HTS 2-pole microstrip bandpass filter by using interdigitated inner poles. The filter was designed to operate at 5.8 GHz. The interdigitated inner pole has 29 fingers where each finger had a dimension of 0.4 mm length and 0.1 mm width. The gap distance between the two fingers was 0.1 mm. In simulations, the new style filter showed a significant improvement in the performance over the regular hairpin type filter. To fabricate the filters by using superconductive YBa/sub 2/Cu/sub 3/O/sub 7-x/ films, we deposited the films on the sapphire substrates by using CeO/sub 2/ thin layer as a buffer layer. We used ArF pulsed laser deposition system to fabricate the films. We used ArF to obtain the smoother film surface instead of KrF that has been used more widely. We also rotated the substrates during the film growth to obtain the better film uniformity. Fabricated YBa/sub 2/Cu/sub 3/O/sub 7-x/ films showed a critical temperature of 87.8 K. The packaged filter with the size of 13.7 mm/spl times/3.3 mm showed lower center frequency, narrower bandwidth, and less loss compared to the same size regular hairpin type filter, by 14.5%, 29.6%, 0.55 dB, respectively.         Realization of HTS trisection band pass filter    H.-S. Jhon, Chang Hoon Jeon, Kyoung Bo Han, Seong Sik Myoung, Jong Gwan Yook, Q.X. Jia and Sang Yeol Lee Summary: We report characteristics of a high-temperature superconductor (HTS) bandpass filter with the designed center frequency of 11.8 GHz. An epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting thin films were grown on a MgO substrate using the pulsed laser deposition (PLD) technique. Use of HTS films for microwave applications provides a realization of high performance planar filters with narrow passband and low insertion loss. We have designed and fabricated trisection bandpass filters with the center frequency of 11.8 GHz. In order to reduce the filter size, the filter was designed to have modified hairpin-type coupled lines. The film thicknesses were about 500 nm. Superconducting transition temperatures have shown to be about 89 K. The fractional bandwidth of the HTS filter was about 1.1% and the band rejection ratio was about 296 dB/GHz. Also the performance of superconducting bandpass filter is compared with a copper filter.         HTS microstrip bipin antenna array for broadband satellite communication    Dong-Chul Chung Summary: In this paper we report the broadband antenna array made of high-T/sub c/ superconducting (HTS) thin films. Though HTS antennas have high efficiency and high gain, narrow bandwidth due to the high Q is the major limitation for application of satellite communication and mobile communication. Defining bandwidth as the frequency range over which standing wave ratio (SWR) is 2:1 or less, HTS antenna bandwidths are typically less than 1%. Thus considerable effort has been focused on developing HTS antennas for broadband operation. In this work the HTS antenna array, using the bipin antenna which consisted of two triangle-radiation patches, was designed and fabricated using a YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting thin film on a MgO substrate for broadband operation. Also gold antennas with the same dimension as our HTS antennas were fabricated on the MgO substrate for the comparison. Experimental results for our HTS antenna array and gold counterparts were reported in terms of radiation patterns, return losses, bandwidths and other various characteristics. The center frequency of our HTS antennas was 20.28 GHz and the bandwidth obtained was significant 10%.         Circularly polarized HTS microstrip antenna array    Dong-Chul Chung, Sung-Yul Choi, Young-Ho Ko, Jong-Ha Lee and Min-Hwan Kwak Summary: A four-element, 11.67 GHz, high-T/sub c/ superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system was designed and built on a 0.5 mm thick MgO substrate. One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperatures. The array produced good circular polarization, and the gain of the array at 77 K, relative to a gold array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was -35.79 dB at the resonant frequency of 11.67 GHz and the total effective bandwidth was about 3.4%. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the circularly polarized HTS antenna array.         A self-attenuating superconducting transmission line for use as a microwave power limiter    J.C. Booth, D.A. Rudman and R.H. Ono Summary: We have designed, fabricated, and tested microwave power limiter based on high-temperature superconductor thin-film technology. The power limiter takes the form of a 50 /spl Omega/ coplanar waveguide transmission line that is reversibly driven from the low-loss superconducting state to the high-loss normal state when the microwave currents within the device exceed a critical value. When operated at 70 K, the power limiter displays very low insertion loss in the nonlimiting state (<0.1 dB at 40 GHz), and extremely wide bandwidth (>40 GHz), with constant impedance over the entire microwave range. The maximum power transmitted by the device can be engineered by varying the transmission-line dimensions, and can be further tuned once the device has been fabricated by varying the operating temperature. In the over-power state the device continues to pass a portion of the incident signal, although with reduced linearity. Switching times for the power limiter are estimated to be on the order of microseconds or less, based on both pulsed rf measurements and on measurements using a periodic amplitude-modulated drive signal. We expect this device to be useful for protecting high-performance receiver circuits from over-power conditions without limiting the dynamic range or bandwidth of receiver systems.         Intermodulation distortion and third-harmonic generation in YBCO films of varying oxygen content    D.E. Oates, S.-H. Park, M.A. Hein, P.J. Hirst and R.G. Humphreys Summary: We have measured the nonlinear surface impedance, intermodulation distortion (IMD), and third-harmonic generation (THG) in a series of identically prepared YBaCuO films that have been carefully annealed to produce a controlled oxygen stoichiometry. These are also compared with an unannealed film. The measurements were performed using a stripline-resonator technique as a function of temperature at a fundamental frequency of 2.3 GHz; the IMD tone separation was 10 kHz. We have found that overdoping films with oxygen substantially lowers the IMD relative to optimally and underdoped films. We have also observed differences in the slopes of the THG and IMD, with IMD slope of close to 2:1 while the same film shows THG slope of 3:1. A possible explanation of the differences lies in the different time scales to which IMD and THG are sensitive.         Description of the nonlinear behavior of superconductors using a complex conductivity    J.C. Booth, S.A. Schima and D.C. DeGroot Summary: The origin of the detrimental nonlinear response in high T/sub c/ superconductor (HTS) microwave devices is currently not well understood. In order to help elucidate the origin of these nonlinear effects, we have developed a description of the nonlinear response in superconductors in terms of a current-dependent complex conductivity. We demonstrate that such a treatment can consistently describe the results of power-dependent surface impedance measurements in resonator geometries as well as harmonic generation and intermodulation distortion effects in transmission line geometries. This approach yields a device-independent quantity that describes the nonlinear response of the superconducting material itself, which is suitable for comparisons of different materials and for material optimization. A further benefit of this description of nonlinear effects is that the relative importance of the nonlinear resistive and inductive components of a superconductor can be examined. We use this approach to predict the phase of the nonlinear response in HTS planar transmission lines, and compare our predictions with new phase-sensitive measurements made using a nonlinear vector network analyzer.         Microwave and DC properties of niobium coplanar waveguides with 50-nm linewidth on silicon substrates    W. Jutzi, S. Wuensch, E. Crocoll, M. Neuhaus, T.A. Scherer, T. Weimann and J. Niemeyer Summary: Long superconducting niobium coplanar waveguides (CPW) on silicon wafers have been implemented with inner conductor width, thickness and length of about 50 nm/spl times/250 nm/spl times/3.2 mm, respectively. CPW tapers yield the transition from small to large cross sections for 50 /spl Omega/ coaxial SMA connectors. Microwave properties are measured at 4.2 K via /spl lambda//2-resonators where the inner conductor width w/sub i/ is about half the London penetration depth. Due to the dominant kinetic inductance the measured quality factor is close to an evaluated minimum value for w/sub i/<50 nm. The quality factors of such nanolines with niobium are approximately 150 at 10 GHz, i.e., more than two orders of magnitude larger than with aluminum at the same temperature. An unexpected power dependence of the intermodulation amplitudes and the corresponding dc properties are described.         Phase noise of an HTS resonator operated in the nonlinear regime    S.A. Vitusevich, N. Klein, A.G. Zaitsev and J. Geerk Summary: Nonlinear properties of high-temperature superconducting (HTS) strongly coupled resonators at different input power have been investigated by measurements of the quality factor as a function of input power as well as by generation of the intermodulation distortion (IMD). The double-sided YBCO films on CeO/sub 2/ buffered sapphire demonstrate advanced performance with the microwave surface resistance of /spl sim/0.3 m/spl Omega/ at 8.5 GHz at 77 K and an IMD third-order interception point estimated at P/sub circ//spl ap/70 W. A parallel feedback oscillator was assembled using a transmission type HTS resonator cooled with liquid nitrogen and a room temperature low noise amplifier. Results on the phase noise investigation of the 2.3 GHz oscillator based on HTS resonator operated in the nonlinear regime demonstrated a deviation from the simple model of the phase noise, which predicts an up-conversion of 1/f noise of the amplifier to oscillator phase noise. The latter can be explained by the phase noise introduced additionally due to the nonlinear response of the HTS resonator.         Prediction of nonlinear distortion in HTS filters for CDMA communication systems    C. Collado, J. Mateu, R. Ferrus and J.M. O'Callaghan Summary: HTS materials are known to produce intermodulation and other nonlinear effects, and this may restrict their use in wireless communication systems. While significant efforts are being done to measure and characterize nonlinear properties of HTS materials, there are very few works that relate these properties to system parameters. In this work we attempt to bridge this gap by using harmonic balance algorithms to analyze the nonlinear performance of superconducting filters subject to the WCDMA signals specified by 3GPP for the UMTS wireless system. This is a first step to predict compliance with system parameters like adjacent channel leakage power ratio (ACLR) or error vector magnitude (EVM).         Analysis of dielectric-loaded cavities for characterization of the nonlinear properties of high temperature superconductors    J. Mateu, C. Collado, O. Menendez and J.M. O'Callaghan Summary: This work describes and compares two alternative methods of analyzing dielectric-loaded cavities for measurement of intermodulation distortion in HTS films. One of them is based on assuming a specific type of HTS nonlinearities and developing theoretical equations based on them. The second is based on a numerical approach that can be applied to many types of nonlinearities. Both methods are shown to work on measured data of representative HTS films.         Nonlinear response of Gd-Ba-Cu-O and Y-Ba-Cu-O microstrip resonators on sapphire    A.G. Zaitsev, R. Schneider, G. Linker, B.W. Tao, F. Ratzel, R. Smithey and J. Geerk Summary: HF power-induced nonlinear effects, including the two-tone intermodulation distortion (IMD), were examined by using 2.3 GHz microstrip resonators prepared from double-sided YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) and GdBa/sub 2/Cu/sub 3/O/sub 7-x/ (GBCO) films on CeO/sub 2/ buffered sapphire. Both, the YBCO and the GBCO resonators exhibited similarly high performance with low IMD level. The third-order interception points varied linearly with temperature from P/sub TOI//spl ap/1500 W of the circulating power, P/sub circ/, at 4.2 K to P/sub TOI//spl ap/90 W at 77.4 K. The dependence of the IMD products on the P/sub circ//P/sub TOI/ ratio was found to be the same at all measurement temperatures. Similarly, the variation of the microwave surface resistance /spl Delta/R/sub S/ versus P/sub circ//P/sub TOI/ was found to be temperature-independent. The combination of these dependences provided a universal relation between the power of the IMD signals and /spl Delta/R/sub S/, which was exhibited by both YBCO and GBCO resonators in the entire examined temperature range.         Imaging local sources of intermodulation in superconducting microwave devices    A.P. Zhuravel, A.V. Ustinov, D. Abraimov and S.M. Anlage Summary: This work presents new experimental results on low-temperature (LT) characterization of local RF properties of passive superconducting (SC) microwave devices using a novel laser scanning microscope (LSM). In this technique, a modulated laser beam is focused onto and scanned over the surface of a resonant SC device to probe the spatial distribution of RF current. The highly localized photo-induced change of the kinetic inductance of the SC device produces both a shift of the resonant frequency f/sub 0/ and change of the quality factor Q. An image of these changes is recorded as the laser spot is scanned over the device. We present the first measurements of spatially resolved intermodulation response in a high temperature superconducting (HTS) co-planar waveguide resonator, opening up a new window into the local origins of nonlinearity in the HTS materials.         Intrinsic and extrinsic surface impedance of HTS: T- and H-dependencies    E. Gaganidze and J. Halbritter Summary: The application of HTS is obstructed by high surface impedances and their increases Z(T,f,H/sub rf/) with rf field. To separate intrinsic from extrinsic and rf mode from HTS material properties well characterized films are required. Using TBCCO films and corrosion protected YBCO films well defined material and physical parameter dependencies have been found which for the first time allowed a unique separation of intrinsic surface resistances R/sub int/(T,f,H/sub rf/) from extrinsic residual losses R/sub res/(T,f,H/sub rf/) and shed light onto /spl delta/Z/spl prop/H/sub rf//sup 2/ increases observed in TE/sub 011/ modes. The latter confirms that rf results of TE/sub 01n/-mode end-plate replacements are sensitive tools to study HTS thin film material properties before structuring. Aside from /spl delta/R/sub s/(H/sub rf/)/spl prop/H/sub rf//sup n//spl prop//spl delta/X/sub s/(H/sub rf/), rf measurements in the frequency and time domain yield the ratio r=/spl delta//sub s///spl delta//sub s/ which shows distinct T and f dependencies for various mechanisms and rf modes. r(T,f)/spl ap/1 indicates hysteresis losses of Josephson fluxons governed by the weakest links at the edges of the films, being weighted differently in TE/sub 01n/ and strip-line modes.         An AC magnetizing field biosusceptometer using a SQUID based sensor with additional compensation module    S. Della Penna, C. Del Gratta, F. Cianflone, S.N. Erne, C. Granata, A. Pentiricci, V. Pizzella, M. Russo and G.L. Romani Summary: We present a new SQUID based susceptometer for liver iron concentration (LIC) assessment. The instrument is operated with an inhomogeneous AC magnetizing field. The susceptometer is based on 7 channels, each consisting of a sensing unit and of an additional unit for the compensation of the applied field residual and its variation. Each unit is a second order gradiometer and is coupled to a dc SQUID with a parallel washer configuration. The compensation module output is digitally processed and coupled to the sensing gradiometer by means of an additional feedback path. The estimation of LIC is based on a numerical model of the subject's torso obtained from the segmentation of ultrasound images.         Performance of high-T/sub C/ SQUID magnetometers for application in biomagnetism    In-Seon Kim, K.K. Yu, Y.H. Lee, H.C. Kwon and Y.K. Park Summary: Single layer direct-coupled YBCO SQUID magnetometers have been fabricated and characterized for the purpose of MCG measurements in magnetically disturbed environment. Two types of magnetometers have been designed and fabricated using 10 mm/spl times/10 mm substrates. We could operate the conventional 3-mm-wide solid pickup loop magnetometers more stably than the 12-parallel-line pickup loop magnetometers in laboratory environment. We developed a first-order electronic gradiometer system with the SQUID magnetometers with axial displacement of 80 mm without any mechanical alignment of magnetometers. The system with a software filter using calculation of discrete Fourier transform could record clear magnetocardiogram in a weak magnetic-shield-room.         Integrated SQUID-gradiometer system for magneto-cardiography without magnetic shielding    R. Stolz, V. Zakosarenko, N. Bondarenko, M. Schulz, L. Fritzsch, N. Oukhanski and H.-G. Meyer Summary: First-order planar superconducting quantum interface device (SQUID) gradiometers were fabricated on the basis of the Nb/AlO/sub X//Nb technology developed at IPHT Jena. The gradiometers have two pickup loops each with quadratic dimensions of 2 cm and a baseline of 4 cm, integrated on chip. The intrinsic noise corresponds to a field resolution in one loop better than 3 fT//spl radic/Hz. Because of the high gradiometer balance (>10/sup 5/) the main signals masking a cardiogram are magnetic field gradients caused by nearby sources (laboratory equipment). To suppress the disturbances a second-order gradiometer was realized electronically. In addition, three washer-SQUID's arranged as a three-axis magnetometer were used to improve the disturbance suppression. All SQUID's were operated with directly coupled low-noise high-speed electronics controlled by a computer via a RS232 port. They have an input voltage noise of about 0.33 nV//spl radic/Hz, a 1/f corner frequency of 0.1 Hz and bandwidth of 5 MHz. The SQUID signals were digitized using a commercially available 16-bit ADC and digitally filtered. The system shows stable operation in the laboratory without magnetic shielding. A human cardiogram could be recorded in real time with a signal-to-noise ratio better than 20. First results of the measurement of foetal cardiogram in a magnetically shielded room are discussed.         Off-axis second-order high-T/sub C/ rf SQUID gradiometer for magnetocardiography in unshielded environment    Hong-Chang Yang, Shu-Yun Wang, Jen-Tzong Jeng, Jau-Han Chen and Herng-Er Horng Summary: We study an electronic gradiometer system for magnetocardiography (MCG) in unshielded environments. The electronically balanced gradiometer consists of three high temperature radio-frequency (rf) superconducting quantum interference device (SQUID) magnetometers, arranged in off-axis arrangement with the baseline of 6 cm to form the second order (2nd-order) gradiometer system. A set of coefficients were found to optimize the noise spectrum of the 2nd-order gradiometer via the fast Fourier transform technique by considering both the phase and the amplitude in the subtraction circuit. Besides, the signal of the 2nd-order gradiometer was filtered by notch and low frequency band pass filters. Hence, the field noise spectrum of the 2nd-order gradiometer was reduced to 1.5 pT/Hz/sup 1/2/ at 60 Hz, to 1 pT/Hz/sup 1/2/ at 10 Hz, and to 1.5 pT/Hz/sup 1/2/ at 1 Hz. We perform MCG measurements in unshielded environments. To enhance the signal to noise ratio, the measured MCG signals were averaged according to the simultaneously recorded electrocardiogram signals recorded simultaneously. The MCG measurement was performed over several locations above the thorax of a human being. Our results demonstrate that the off-axis arrangement can offer the flexibility in the design of the SQUID-based multichannel magnetocardiogram.         Adaptive frequency dependent gradiometry applied to SQUID magnetocardiography    M. Bick, G. Panaitov, M. Schiek, Yi Zhang and H.-J. Krause Summary: In the case of magnetocardiography (MCG), gradiometry is a commonly used method to reduce environmental noise. Here, the balance of the gradiometer is one of the main parameters determining the achievable noise reduction. In earlier work, we reported the use of frequency dependent gradiometer coefficients to effectively balance a gradiometer consisting of signal and reference sensors. In this work, the advantages of adaptive determination of these coefficients during a measurement without perturbing the MCG signal are investigated. MCG measurements were recorded with first and second order high temperature SQUID gradiometers inside and outside magnetic shielding. It will be shown that the heart signal is not distorted by applying our software noise reduction technique. Furthermore, by recalculation of gradiometer coefficients during the MCG measurement, an improved signal-to-noise ratio is achieved. The optimum repetition time for coefficient recalculation is determined.         A high-T/sub c/ SQUID based magnetophysiology system    P.E. Magnelind, Z. Ivanov, A.Ya. Tzalenchuk, E.J. Tarte and A. Lohmus Summary: We report on the present status of our high-T/sub c/ SQUID based system for measurements of room temperature samples. The main application of the system is magnetic recordings of signals in nerve tissue, i.e., magnetophysiology. We have fabricated four slotted SQUID sensors of two different designs. The best SQUID sensor shows an intrinsic white noise of 8.2 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ and a corresponding magnetic field noise of 4.5 pT/Hz/sup 1/2/ at 77 K.         High T/sub c/ SQUID system and magnetic marker for biological immunoassays    K. Enpuku, D. Kuroda, T.Q. Yang and K. Yoshinaga Summary: High T/sub c/ SQUID system is developed for the detection of the biological binding-reaction between antigen and its antibody. In this measurement, the antibody is labeled with magnetic nanoparticles, and the magnetic signal from the nanoparticles is measured. The excitation field of a few mT is applied in parallel to the SQUID in order to magnetize the nanoparticles. Due to mechanical misalignment, however, the vertical component of the excitation field couples to the SQUID, and degrades the system performance. In order to solve this problem, we develop two methods. One is the use of a compensation field in the case of the flux dam, and the other is the use of a switch instead of the flux dam. We also develop a magnetic marker utilizing Fe/sub 3/O/sub 4/ nanoparticle with diameter of d=25 nm. The nanoparticle is embedded in the polymer with typical diameter of 80 nm, and COOH is attached around the surface of the polymer. The properties of the marker are discussed.         Detection of magnetic nanoparticles in lymph nodes of rat by high T/sub c/ SQUID    S. Tanaka, H. Ota, Y. Kondo, Y. Tamaki, S. Kobayashi and S. Noguchi Summary: We have proposed a Lymph-node detection system using a high T/sub c/ SQUID gradiometer and ultra-small particles. A rat was injected with a mixture of water diluted superparamagnetic particles. The lymph nodes containing particles were then extracted from the rat. The lymph node samples were measured by a SQUID gradiometer system. We have successfully measured the signal from the lymph node.         Biomagnetic measurements with HTS SQUID magnetometers in moderate shielded environments    Herng-Er Horng, Shou-Yen Hung, Jen-Tzong Jeng, Shu-Hsien Liao, S.-C. Hsu, Ji-Chuu Hwang and Hong-Chang Yang Summary: An HTS SQUID magnetometer for biomagnetic measurements was implemented in a moderate noise shielded environment. The intrinsic noises of the SQUID magnetometer shielded with a tri-layer magnetic shielding cylinder were 50 fT/Hz/sup 1/2/ above 10 Hz and 100 fT/Hz/sup 1/2/ at 0.1 Hz. The moderate shielded environments are constructed of mu-metal layers. With the moderate shielding the magnitude of the QRS complex of a rat specimen was found to be around 10 pT and the signal-to-noise ratio was larger than 10. The requirements for improving biomagnetic measurements in the moderate magnetic shielding are discussed.         Non-invasive assessment of the heart function in unshielded clinical environment by SQUID gradiometry    A. Brazdeikis, Y.Y. Xue and C.W. Chu Summary: Bioelectrical activity of the heart produces minute magnetic fields that may be measured above the torso with superconducting quantum interference device (SQUID) sensors. A new application has been developed which permits noninvasive assessment of the heart function in unshielded magnetically harsh clinical environment. The system incorporates a multichannel SQUID system, a supine nonmagnetic ergometer, a peripheral data interface and software tools for processing magnetocardiographic data. To demonstrate the performance of the method, biomagnetic measurements have been performed both at rest and during physical exercise. Signal processing, signal-to-noise ratio and artifact rejection procedures have been discussed.         HTS SQUID gradiometer using substrate resonators operating in an unshielded environment - a portable MCG system    Yi Zhang, N. Wolters, J. Schubert, D. Lomparski, M. Banzet, G. Panaitov, H.-J. Krause, M. Muck and A.I. Braginski Summary: We have demonstrated and verified the basic feasibility of performing magnetocardiographic (MCG) measurements without magnetic shielding when using a first-order electronic gradiometer with our novel dielectric substrate resonator rf SQUIDs. The setup at the operation site involved adjustment of the gradiometer's baseline length and adaptive balancing. Our experimental portable system was tested in three environments differing in the level of electromagnetic interference.         Applying high-T/sub C/ superconducting quantum interference devices with a room-temperature pickup coil in the measurement of impedance magnetocardiograms    A. Kandori, A. Tsukamoto, D. Suzuki, K. Ogata, Y. Soutome, T. Miyashita, Y. Seki, K. Yokosawa, K. Tsukada and K. Takagi Summary: A high-T/sub C/ superconducting quantum interference device (SQUID) magnetometer - in which a room-temperature pickup coil is used to detect an impedance magnetocardiogram (I-MCG) signal - has been developed. The pickup coil (30-mm diameter) is installed outside the cryostat and is connected to the input coil of the high-T/sub C/ SQUID. The magnetometer's noise level is 150 fTHz/sup -1/2/ (>10 kHz). The magnetometer was used to measure I-MCG signals (about 12 pT), which were obtained by applying an ac current (15 kHz) of constant amplitude (7 mA, peak-to-peak) to a healthy male subject.         SFQ-to-level logic conversion by HTS Josephson drivers for output interface    T. Hato, Y. Ishimaru, N. Harada, M. Horibe, A. Yoshida, Y. Tarutani, K. Tanabe and N. Yokoyama Summary: Latching-type driver circuits integrated with high-temperature superconductivity (HTS) junctions and two types of resistor were fabricated. These circuits could successfully perform latching operation by means of a single-flux-quantum (SFQ) signal input. Ramp-edge-type HTS junctions were fabricated by interface engineering and showed a hysteretic current-voltage characteristics under a temperature of 50 K. The critical current (I/sub c/) of these 5-micron-wide junctions was about 0.2 mA and the I/sub c/R/sub n/ product was about 1.7 mV at 4.2 K. The circuits included two types of resistors, which were made of RF-magnetron-sputtered indium-tin-oxide (ITO) and Au films. A driver with a parallel 2-junction-stack could convert an SFQ pulse, which was transformed through several Josephson transmission lines (JTL's) from a DC/SFQ circuit, to a 2.3-mV level signal.         Improved high-T/sub c/ superconductor sampler circuits using Josephson transmission line buffers    M. Maruyama, M. Hidaka and T. Satoh Summary: We report on an increase of the measurement bandwidth of a high-T/sub c/ superconductor sampler circuit. The circuit composes a waveform measurement system, in which it is cooled by a compact single-stage cryocooler and operates at a temperature of 35-40 K. In the sampler circuit, there exists a sampling jitter due to thermal fluctuation in the critical current of the pulse generator trigger junction. To reduce the jitter, one can overdrive the trigger junction. However, leakage current into the adjacent sampler element due to parasitic inductance is an obstacle to the use of a larger trigger current. We attempted to suppress the leakage current by inserting a Josephson transmission line (JTL) buffer into the sampler circuit. It was found that a trigger current two-times larger than that of the conventional circuit became possible with the addition of a four-stage JTL and that the frequency at which the measured amplitude decreases by 3 dB increased from 7 GHz to 14 GHz. This result suggests that the jitter was suppressed in the sampler circuit with the JTL buffer.         Error correction circuits of comparators based on quasi-one junction SQUID(s) for high temperature superconductor    H. Sugiyama, H. Wakana, S. Adachi, M. Horibe, Y. Ishimaru, Y. Tarutani and K. Tanabe Summary: The conventional quasi-one junction SQUID (QOS) as a comparator must have a loop inductance less than a threshold. Such a small loop inductance cannot be realized in high temperature superconductor (HTS) having larger sheet inductance. We suggest novel comparators based on QOS for HTS material, in which a few circuits are added to the QOS. The comparator operation is shown in analog simulation. It results in high accuracy below the sampling rate of 50 GS/s by use of typical YBCO junction parameters. The comparator operation at extremely high sampling rate over 100 GS/s is also feasible.         HTS multilayer technology for optimal bit-error rate RSFQ cells    D. Cassel, T. Ortlepp, K.S. Ilin, G. Pickartz, B. Kuhlmann, R. Dittmann, H. Toepfer, A.M. Klushin, M. Siegel and F.H. Uhlmann Summary: The operation of Rapid-Single-Flux-Quantum logic (RSFQ) circuits is strongly influenced by thermal noise. Especially for higher temperatures the bit-error rate (BER) is a critical issue. A new design concept focused on improved noise immunity has been developed to reach an optimal BER for high-temperature superconductor (HTS) RSFQ cells. For example, we expect for a T-Flip-Flop (TFF) of our cell library a theoretical improvement of the BER of six orders of magnitude at a temperature of 50 K. To verify the new design approach, we have designed basic RSFQ cells using parameter values derived from our multilayer technology. The process with two superconducting YBCO layers is based on substrates with two bicrystal lines. This paper focuses on the multilayer technology to realize the optimal design parameters. One of the most crucial issues is patterning of small structures on a micron scale, especially the small vias. This new patterning process is described in detail.         Fabrication of interface elements for oxide RSFQ circuits    Y. Tarutani, Y. Ishimaru, H. Wakana, M. Horibe, H. Sugiyama, S. Adachi, Y. Oshikubo, O. Horibe, T. Suzuki, K. Tanabe and U. Kawabe Summary: RSFQ circuit elements were fabricated based on the YBa/sub 2/Cu/sub 3/O/sub 7-x/ ramp-edge junctions and their characteristics were investigated. In particular, two types of interface circuits were designed, fabricated and their amplification functions were evaluated. The interface circuits comprised series array of SQUID's that shared a common inductor each other. Each SQUID was switched between zero voltage state and voltage state by current injection. Input signal was AC Josephson current for the type-one interface circuit. The input signal was an SFQ for the type-two interface circuit. Both interface circuits could successfully be operated. In particular, an output voltage more than 1 mV was obtained for the type-one interface circuit that comprised the stack of five SQUID's.         Oscillation of SFQ pulse in oxide JTL [Josephson transmission line]    Y. Tarutani, H. Sugiyama and K. Tanabe Summary: Characteristics of SFQ signal propagation in oxide circuits were investigated by numerical simulation. The numerical simulation for the SFQ signal propagating in the Josephson transmission line (JTL) was performed by assuming the inductor to be a passive transmission line and by taking into account the high I/sub c/R/sub n/ value of oxide junctions. The SFQ signal was found to oscillate when the inductor length was more than 20 /spl mu/m. The origin of the oscillation and the oscillation conditions were investigated with respect to the Josephson plasma frequency. A shunt resistor connected between an inductor and the groundplane was found to be effective for suppressing the oscillation. The JTL in which shunt resistors are connected may also be used as a delay line.         Evaluation of dynamic range for an HTS sigma-delta modulator with 100-GHz sampling    K. Saitoh, Y. Soutome, T. Fukazawa, F. Furuta and K. Takagi Summary: Circuit simulations were used to study the capability of a high-temperature superconducting (HTS) sigma-delta modulator using interface-engineered-Josephson junctions (IEJ's). The dynamic range was calculated while varying the temperature (T) and input-signal frequency (f/sub 0/), and in the resultant power spectra, correct noise shaping (6 dB/oct) was found. Investigation of the dynamic range in terms of effective number of bits (ENOB) showed that ENOB was 6.7 for f/sub 0/<200 MHz and T<40 K. At higher input-signal frequencies, i.e., 400 MHz40 K.         Improvement of a bit error rate measuring system for high-temperature superconducting circuits    M. Horibe, K. Shimaoka, Y. Tarutani and K. Tanabe Summary: We have evaluated and tried to improve the measurement precision of a bit error rate (BER) measuring system for superconducting circuits equipped with a magnetic shield and a cryocooler. A noise model has suggested that the most effective way of improving BER is to reduce the noise figure of the wideband pulse amplifier (WPA). BER measurement using a 3-Gbps, 2/sup 15/-1 pseudo random binary signal showed that by using low-noise WPA (noisefigure=4 dB) a 12.0-mV output voltage is required to obtain a minimum BER of 1.19/spl times/10/sup -15/ (a 10/sup -7/ improvement over the previous system) for a 50 /spl Omega/ standard microstrip. A BER of a La/sub 0.2/Yb/sub 0.9/Ba/sub 1.9/Cu/sub 3/O/sub x//MgO/Au microstrip-line to coplanar-waveguide transition-line converter (MCC) was also measured. It was found that the minimum BER was 4.87/spl times/10/sup -13/ (a 10/sup -5/ improvement over the previous system) when the output voltage was 23.8-mV. However these measured BER values were larger than those expected by the noise model. The cause of the larger measured BER is discussed. A minimum BER of 3.64/spl times/10/sup -55/ in 14.8-mV output voltage for a 50 /spl Omega/ standard microstrip was obtained when the cryo-cooler was not operated (without the noise from a cryo-cooler).         RSFQ asynchronous serial multiplier and spreading codes generator for multiuser detector    A.Yu. Kidiyarova-Shevchenko, K.Yu. Platov, E.M. Tolkacheva and I.A. Kataeva Summary: Serial multiplier and serial spreading code generators are vital elements of the RSFQ multiuser detector. We have designed different versions of both circuits to achieve maximum speed and at the same time minimize Josephson junction count. Comparison of different serial multipliers architectures supporting signed multiplication favored for asynchronous shifting over zero circuits based on carry save adder and co-flow distribution of the partial product and the clock. A 25-bit spreading code generator supporting parallel input/output has been designed for 4 kA/cm/sup 2/ (TRW) and for 1 kA/cm/sup 2/ (HYPRES) processes. The corresponding maximum simulated clock speed of 52 GHz and 26 GHz and effective device area of 1/spl times/0.12 mm/sup 2/ and 1.9/spl times/0.2 mm/sup 2/.         Flux-1 RSFQ microprocessor: physical design and test results    P. Bunyk, M. Leung, J. Spargo and M. Dorojevets Summary: The Flux-1 chip is an RSFQ implementation of a small general-purpose processing engine with target clock frequency of 20 GHz and over 5000 gates (over 60 K Josephson junctions) connected in an irregular pattern. The scale of this design task forced us to re-think conventional RSFQ design methodology and implement new approaches suitable for digital systems of this level of complexity and beyond. This paper presents lessons learned from the Flux-1 effort, mostly concentrating on chip physical design. Here we discuss our approach to the circuit design and verification of individual gates, gate interconnect using passive transmission lines and use of CAD tools for design automation and verification.         System design approach for RSFQ multiuser detector    K.Yu. Platov, A.Yu. Kidiyarova-Shevchenko, H. Zhao, T. Ottosson and E. Strom Summary: The extraordinary speed of RSFQ circuits is attractive for the implementation of a successive interference canceller, which is one of the most effective types of multiuser detector. We present system design analysis, optimizing the bit error rate performance and targeting a doubling of the uplink capacity. A complete model is considered: a long-code asynchronous code division multiple access (CDMA) system with frequency-selective fading paths, 100 voice equivalent channels per sector and 10 resolvable multipath components. Assuming uniform quantization of input signals, we have shown that the realistic case of heavily loaded systems would require up to ten iterations to achieve reliable detection.         Design and component test of a tiny processor based on the SFQ technology    N. Yoshikawa, F. Matsuzaki, N. Nakajima, K. Fujiwara, K. Yoda and K. Kawasaki Summary: An eight-bit SFQ processor has been designed and some key components have been tested to confirm feasibility of the large-scale SFQ digital circuit. The designed processor is composed of a one-bit ALU, two eight-bit registers with local clock generators, an instruction register, a five-bit program counter, a state controller, and a 32-byte register file. A bit-serial architecture and a distributed local clock architecture, where each register has its own local clock generator, have been employed in order to increase the local clock frequency. The target clock frequency is 16 GHz and 10 GHz for the NEC 2.5 kA/cm/sup 2/ and Hypres 1 kA/cm/sup 2/ Nb processes. On the circuit design level, we have used a data-driven self-timed architecture and a binary decision diagram, which reduce the timing design difficulty in high frequency operation. The processor, which contains 7,300 Josephson junctions, has been designed by using a cell-based design methodology with the assistance of a top-down CAD environment. We have successfully tested some important circuit blocks, including a one-bit ALU, eight-bit registers, and a demultiplexer for register files.         Architectural and implementation challenges in designing high-performance RSFQ processors: a FLUX-1 microprocessor and beyond    M. Dorojevets and P. Bunyk Summary: This paper discusses the major challenges and solutions in designing high-performance superconductor processors in the context of the on-going collaboration between SUNY Stony Brook, TRW, and the JPL (NASA). It presents the architecture and organization of the first 8-bit FLUX-1 RSFQ microprocessor with a target clock frequency of 20 GHz fabricated in TRW's 4 kA/cm/sup 2/, 1.75-/spl mu/m Josephson junction technology in 2001-2002. A new parallel partitioned architecture has been developed for FLUX-1 in order to fill its long processing pipelines with operations, and reduce interconnect delays. The latest version of FLUX-1, called FLUX-1R, with improved circuit design characteristics and decreased power dissipation was fabricated in July 2002. FLUX-1R contains 63,107 Josephson junctions on a 10.35 mm /spl times/10.65 mm die with flip-chip packaging. The chip is currently under testing at TRW.         Single flux quantum packet switch circuits for large-scale communication systems    S. Yorozu, Y. Kameda, Y. Hashimoto and S. Tahara Summary: Large-scale telecommunication systems in the larger nationwide network of the next decade will require routers having a packet switching throughput capacity of over several-tens Tbps. In such future high-end routers, the packet switch, which is the biggest bottleneck of the router, will need higher processing speeds than semiconductor devices. In this paper, we describe an SFQ packet switch architecture that is used in the internal speed-up Banyan network. According to the architecture we have designed and demonstrated a deep-pipelined 2/spl times/2 packet switch logic circuit, which is the key element in a packet switch, by applying two technological advances regarding design methodology and packaging. This circuit is among the largest SFQ random logic circuits yet reported.         Multi-channel time digitizing systems    A. Kirichenko, S. Sarwana, D. Gupta, I. Rochwarger and O. Mukhanov Summary: In this paper we present an overview of a family of Time-to-Digital Converter (TDC) systems developed at HYPRES over the past several years. We have developed three types of RSFQ-based time digitizing systems: an eight-channel multi-hit 30-ps TDC, a two-channel multi-hit 6-ps TDC, and a dual-function multi-hit TDC/ADC. We present results of successful testing of an all-digital TDC up to 33-GHz clock frequency, digitizing at 30-ps time intervals. The eight-channel all-digital TDC chip occupies a 1 cm /spl times/1 cm area with more than 10000 Josephson junctions. For better time resolution, the digital counter-based TDC can be integrated with an analog prescaler. The prescaler improves time resolution to 6 ps and has also been successfully tested. We have also integrated TDC channel with sensitive SQUID to a dual-function ADC/TDC digitizer. An advanced VXI-based interface allows the parallel 8-channel data to be acquired at a read-out clock rate of 100 MHz.         A GHz multi-channel cryogenic test fixture for superconducting integrated circuit testing    M. Aoyagi, K. Kikuchi, Y. Sato, H. Nakagawa, H. Sato, K. Tokoro and H. Akoh Summary: We have designed a cryogenic test fixture for functional testing of digital and analogue superconducting integrated circuits (IC) in the GHz frequency range. The test fixture consists of a ball grid array (BGA) chip carrier, a detachable BGA socket, a coaxial printed wiring board, and 40 long coaxial cables with SMA connectors. The chip carrier has a microstrip wiring and solder balls. On the chip carrier, a superconducting IC chip is connected using Al wire bonding. The wiring board has a coaxial wiring structure. The wiring characteristic impedance of the chip carrier and the print wiring board was designed to be 50 /spl Omega/. In the BGA socket, the BGA chip carrier is electrically connected to the printed wiring board using anisotropic conductive rubber sheet. The coaxial cables are connected to the printed wiring board with soldering. All parts of the system were made with nonmagnetic materials. The high frequency characteristics were partially evaluated by TDR measurement and vector impedance measurement at 4.2 K, 77 K and room temperature.         Ballistic SFQ signal propagation on-chip and chip-to-chip    Q.P. Herr, M.S. Wire and A.D. Smith Summary: We recently reported communication up to 60 Gb/s between digital superconductor chips mounted on a passive carrier, using a novel driver circuit that produces a double-flux-quantum pulse. Here, we answer various practical questions pertaining to chip-to-chip and on-chip communication in greater detail. On-chip, the traditional single-flux-quantum driver is adequate, although margins and bit error rate degrade significantly at the microstrip resonance frequency. Chip-to-chip, using the double-flux-quantum driver, shows little frequency dependence, in spite of 13% reduction of signal current in the chip-to-chip transitions. Appropriate microstrip impedance is in the range 4-8 /spl Omega/ for a 4 kA/cm/sup 2/ Josephson junction IC process. Data includes bit errors rates for pseudo-random data in the range 3-27 Gb/s.         Josephson-CMOS hybrid memory with ultra-high-speed interface circuit    Y.J. Feng, X. Meng, S.R. Whiteley, T. Van Duzer, K. Fujiwara, H. Miyakawa and N. Yoshikawa Summary: In this paper we report our recent progress in realizing a Josephson-CMOS hybrid random-access memory. We have established a 4 K CMOS device model based on low-temperature experimental data on discrete MOS devices. We implemented an ultra-high-speed interface circuit to amplify millivolt-level Josephson input signals to volt-level signals for CMOS circuits. The interface circuit includes a Josephson series-array preamplifier and an ultra-fast hybrid Josephson-CMOS amplifier. Simulation and optimization of the interface circuit have predicted a delay of less than 60 ps. We have designed and fabricated the interface circuit using the 0.25 /spl mu/m National Semiconductor Corporation (NSC) process for the CMOS chip, and the UC Berkeley 6.5 kA/cm/sup 2/ Nb process for the Josephson junction (JJ) chip. The functionality of the interface circuit has been tested and proved by wire-bonding the CMOS chip to the JJ chip. We also demonstrate the design and fabrication of a model 64-kbit Josephson-CMOS hybrid memory; this circuit includes the ultra-high-speed interface, address buffers, word line decoders, 3 T DRAM-type cells, and Josephson sensing circuits; these are fabricated using the 0.25 /spl mu/m NSC CMOS process and the UC Berkeley Nb process. Subnanosecond access time is predicted by a conservative simulation that used a room-temperature model for the CMOS. We plan a stacked-chip structure using very short wire bonding with which we will be able to measure subnanosecond access times.         Experimental demonstration of superconducting bandpass delta-sigma modulator    J.F. Bulzacchelli, Hae-Seung Lee, J.A. Misewich and M.B. Ketchen Summary: Superconducting bandpass delta-sigma (/spl Delta//spl Sigma/) modulators are being developed for direct analog-to-digital conversion of radio frequency signals in the GHz range. Recently we demonstrated operation of a superconducting bandpass /spl Delta//spl Sigma/ modulator with the highest center frequency (2.23 GHz) and sampling rate (up to 45 GHz) reported to date. The test chip used in that experiment includes an integrated acquisition memory, which eliminates the need for very high speed interfacing. This paper describes key implementation details of this complex test chip, which contains 4065 Josephson junctions. The paper also explains how magnetic coupling from large power supply currents can be reduced through the use of optically-isolated current sources with independent grounds. The measured output spectra of the modulator at a 45 GHz sampling rate are presented.         Integration of cryocooled superconducting analog-to-digital converter and SiGe output amplifier    D. Gupta, A.M. Kadin, R.J. Webber, I. Rochwarger, D. Bryce, W.J. Hollander, Young Uk Yim, Channakeshav, R.P. Kraft, Jin-Woo Kim and J.F. McDonald Summary: HYPRES is developing a prototype digital system comprising a Nb RSFQ analog-to-digital converter (ADC) and SiGe amplifiers on a commercial two-stage cryocooler. This involves the detailed thermal, electrical, and mechanical design of the ADC chip mount, input/output (I/O) cables, and electromagnetic shielding. Our objective is to minimize the heat load on the second (4 K) stage of the cryocooler, in order to ensure stable ADC operation. The design incorporates thermal radiation shields and magnetic shielding for the RSFQ circuit. For the I/O cables, the thermal design must be balanced against the acceptable attenuation of RF lines and resistance of DC bias lines. SiGe heterojunction bipolar transistor (HBT) signal conditioning circuits, placed on the first (60 K) stage of the cryocooler, will amplify the mV-level ADC outputs to V-level (e.g., ECL) outputs for seamless transition to room-temperature electronics. Cooling these HBT circuits lowers noise and improves their high-frequency performance. Demonstration of this prototype should lead the way to commercialization of high-speed digital superconducting systems, for such applications as wireless communication, radars, and switching networks.         Characteristics of voltage multipliers for a Josephson D/A converter    F. Hirayama, M. Maezawa, H. Sasaki and A. Shoji Summary: We present design and experimental results of a voltage multiplier (VM) that is a main component of a Josephson D/A converter based on single flux quantum pulses. We have analyzed the VM operation through detailed simulations and have re-designed the circuit. The amplitude of the constant-voltage step for a 64-stage VM with the new design is 80 /spl mu/A at 10 GHz of an input frequency, which is sufficiently large for D/A converter applications.         Feedback-current-injection-type second-order lowpass sigma-delta modulator    S. Hirano, H. Hasegawa, S. Nagasawa, S. Kato, K. Miyahara and Y. Enomoto Summary: In order to establish double-loop feedback design, we have fabricated a prototype superconducting double-loop lowpass sigma-delta modulator. For digital feedback gain, multiple flux quanta are produced by a ladder circuit and carried through Josephson Transmission Lines (JTLs) to the feedback driver. The feedback driver consists of a single Josephson junction or two serially-connected junctions. Direct injection of the pulse current from the JTLs through a low-value resistor drives the feedback driver. The sigma-delta modulator was operated at the sampling frequency of 1.1 GHz and the measured power spectrum showed the noise shaping roughly of 12 dB/octave, which is characteristic of the second-order sigma-delta modulator.         Numerical analysis of superconductive oversampling analog-to-digital converters    A. Fujimaki, K. Nakazono, M. Onogi, K. Okada, A. Sekiya and H. Hayakawa Summary: We have numerically studied oversampling analog-to-digital converters (ADCs) in terms of sensitivity, spurious-free dynamic range, signal-to-noise ratio (SNR) or dynamic range toward the application to a future mobile communication system. These ADCs are based on single-flux-quantum logic. The sensitivity depends on the impedance of the grounded element, while the SNR is less dependent on the architecture of the modulator. A band-pass /spl Sigma/-/spl Delta/ modulator is suitable for digital RF radios due to its high sensitivity. The second-order modulator with a feedback gain of 20 and 50 GHz-operation of the single-loop modulator show the same effect on the improvement of SNR. Further improvement required for the digital RF architecture can be realized by using a multi-bit comparator or by higher operating speed.         RSFQ random logic gate density scaling for the next-generation Josephson junction technology    P. Bunyk Summary: Post-layout automatic analysis of Flux-1 microprocessor, a representative random logic RSFQ chip of more than 5000 gate complexity, allowed us to extract important layout parameters such as gate density, Josephson junction density and gate/wiring/unused area ratios. A scaling model is presented to predict the area required to layout a given number of random logic gates. When applied to Flux-1 chip itself, which occupies 88.6 mm/sup 2/ in the current TRWs 4 kA/cm/sup 2/ J110D technology, this model predicts that it can be shrunk by almost a factor of two in area to 49 mm/sup 2/ if moved to a next-generation J110E technology with 8 kA/cm/sup 2/ junctions. This information enables us to confidently floorplan random logic chips to be implemented in future advanced JJ technologies. It can also provide directions for JJ technology improvements leading to the maximum positive impact on RSFQ chip density.         Design issues for interconnects in densely packaged RSFQ structures    B. Dimov, T. Ortlepp, H. Toepfer and H.F. Uhlmann Summary: The manufacturing process of LTS RSFQ circuits is quite similar to that of the semiconductor chips, thus providing the possibility of an ultra high-density packaging similar to the modern semiconductor logic circuits. However, the miniaturization of the interconnects does not enhance their performance. The present work highlights the impact of the parasitic interactions between the superconductive interconnects on the correct logical functionality and the upper bias current margins of the LTS RSFQ circuits.         The effects of DC bias current in large-scale SFQ circuits    H. Terai, Y. Kameda, S. Yorozu, A. Fujimaki and Z. Wang Summary: The supply of bias current is one of the key problems to be overcome for fully operational large-scale SFQ circuits. Large currents cause various undesirable effects that degrade circuit operation. The magnetic field induced by a large DC bias current affects the operation of several SFQ cells, even with a microstrip-line structure applied for the bias lines. In this paper, experimental results using SQUIDs show that bias-line shielding is the most effective way to reduce the effect of the DC bias current. The operating margins of SFQ cells were also found to be sensitive to the current in the ground plane. The location of a ground bonding should be close to the point of current injection if we wish to avoid undesirable diffusion of current through the ground plane. We confirmed the effectiveness of bias-line shielding and of the location of ground bonding with a circuit composed of about 500 junctions.         Differential SFQ transmission using either inductive or capacitive coupling    M.W. Johnson, Q.P. Herr, D.J. Durand and L.A. Abelson Summary: The bias current requirement for RSFQ circuits is about an ampere per thousand gates. High current increases the thermal load of cables into the cryostat, produces undesirable currents and fields on-chip, and makes efficient power supply difficult. Series-biasing has been proposed, whereby the circuit is divided into blocks powered in series. This requires floating ground planes for each block, and differential signal propagation across ground plane boundaries where the blocks communicate. We have demonstrated transmission of pseudo-random data across a differential link using two distinct approaches, based on magnetic and capacitive coupling. For each circuit, we have measured data rates up to 30 Gb/s and bit error rates down to 10/sup -10/. Bit error rates extrapolate to lower values. Inductive coupling was implemented in TRW's 4 kA/cm/sup 2/ Nb process, capacitive coupling in TRW's 8 kA/cm/sup 2/ process.         Comparison of genetic algorithms to other optimization techniques for raising circuit yield in superconducting digital circuits    C.J. Fourie and W.J. Perold Summary: Novel logic devices in the RSFQ and COSL superconducting logic families are most often sub-optimal. Before such devices can be incorporated into physical designs, they have to be optimized for high theoretical yield, and preferably for highest possible yield. Even simple logic gates can contain numerous inductors, resistors and Josephson junctions. During optimization, it is often needed to adjust all the element values. The search space is therefore very large, and genetic algorithms have been used with success to optimize such gates. The conversion of circuit file to genome for the genetic algorithms is discussed, as well as fitness evaluation through Monte Carlo analysis. Results with both novel and existing logic gates are presented. Other optimization techniques are also discussed in comparison to genetic algorithms.         Bit error rate determination of RSFQ logic cells by means of noise analysis of basic network components    T. Ortlepp, H. Toepfer and F.H. Uhlmann Summary: The influence of thermal noise gives a major restriction in the development of Rapid Single Flux Quantum (RSFQ) logic circuits with high-T/sub c/ superconductors. In the past, we have demonstrated a general way for determining the digital bit error rate and for predicting operation ranges with good noise immunity. The method is based on a single Fokker-Planck equation which includes the full system dynamics. However, the complexity of this equation increases dramatically with the number of Josephson junctions. Our new approach describes a method to divide an RSFQ logic cell into several basic primitives. They can be characterized quickly in terms of switching probability for a lot of different parameters. From these analyses, look-up tables are built-up. We describe how to combine these data in order to achieve the bit-error rate for the whole cell. While saving more than 90% of computation time, the comparison with our previous results for full system analyses shows less than 4% difference. This approach provides for a powerful tool to include the influence of thermal noise into the optimization process of RSFQ logic circuits as well.         Automatic Josephson-transmission-line routing for single-flux-quantum cell-based logic circuits    Y. Kameda and S. Yorozu Summary: In single-flux-quantum (SFQ) circuits, the delay produced by the Josephson transmission line (JTL) is comparable with or larger than the one produced by the logic cells. Therefore, it is difficult to find the routes that satisfy the timing constraints in a large circuit manually. To overcome this obstacle, we propose a two-step automatic JTL routing technology that performs coarse and fine timing adjustments. First, an automatic router draws dummy wires within coarse timing constraints, and then the dummy wires are replaced with JTL cells. Fine timing adjustments are done in the latter step. Some JTL cells in clock and data paths are replaced with faster JTL cells so that clock signals always arrive earlier than data signals at clocked-gates. Two example circuits were designed using the automatic JTL routing technology. One is composed of nearly 600 Josephson junctions. It was experimentally tested up to 35 GHz with on-chip test components. The other is composed of about 4000 Josephson junctions. After the fine timing adjustment, logic simulation showed that it can operate at 20 GHz. We also experimentally confirmed its correct operations at low speed.         Cell based design methodology for BDD SFQ logic circuits: a high speed test and feasibility for large scale circuit applications    N. Yoshikawa, K. Yoda, H. Hoshina, K. Kawasaki, K. Fujiwara, F. Matsuzaki and N. Nakajima Summary: We have proposed a cell-based design methodology for SFQ logic circuits based on a binary decision diagram (BDD) and implemented a BDD SFQ standard cell library using a Hypres Nb process. In this design methodology, any logic function can be implemented by connecting binary switches. Since the circuits are dual rail logic and do not need a global clock, difficulty in the timing design is reduced considerably. In our cell-based design approach, the cell library is composed of only five kinds of basic cells, whose circuit parameters are optimized so as to remove the inter-cell interaction. At the layout level, the cells have the identical size so that circuits can be implemented by simply embedding the basic cells. In this study we have performed an on-chip high-speed test of the BDD SFQ logic circuits. The test system consists of two four-bit data-driven self-timed (DDST) shift registers with a ladder type clock generator. We have confirmed 12 GHz operations of the BDD SFQ logic circuit. We have also examined circuit size dependence of the DC bias margin of large BDD SFQ circuits.         Improved design for parallel multiplier based on phase-mode logic    Y. Horima, T. Onomi, M. Kobori, I. Shimizu and K. Nakajima Summary: For the improvement of the phase-mode parallel multiplier, we propose to use a Booth encoder as a substitute of an AND array. Booth's algorithm is often used for the generation of partial products. The scale of the encoder does not matter for defining its operation frequency because the phase-mode Booth encoder is a pipelined structure. We suggest that the encoder is used as a serial encoder to reduce the number of Josephson junctions (JJ). There are two methods for applying the Booth encoder to the current structure. The first method is shifting multiplicands. The second method is shifting partial products and complementary signals. The total JJ's in both methods are less than the AND array in large scale. The phase-mode Booth encoder with 2.5 kA/cm/sup 2/ Nb/AlO/sub x//Nb junctions can operate over 30 GHz according to the numerical simulations.         Playing the ".ac" card in noise analysis of RSFQ circuits    Q.P. Herr and M.W. Johnson Summary: Noise-induced bit error rate (BER) is an important design constraint for RSFQ circuits. No method, however, has been reported to calculate the BER of real, multi-junction RSFQ gates. We report such a method that requires only the operating margins and the root-mean-square noise current of the device in question. Noise current is determined using the ".ac" analysis card built into SPICE circuit simulators. As usual, operating margins are also determined using SPICE. These quantities determine BER via the error function, as is appropriate for threshold dynamics. The method is general enough to be applied to any RSFQ gate and even exotic circuits such as those that use passive microstrip signal propagation. Comparison to experimental data indicates that BER in RSFQ circuits does indeed arise strictly from thermal noise.         A design approach to passive interconnects for single flux quantum logic circuits    Y. Hashimoto, S. Yorozu, Y. Kameda and V.K. Semenov Summary: We developed a design approach for interface circuits to connect Single Flux Quantum (SFQ) cells by using passive transmission lines (PTL's). In the approach, an interface circuit between a PTL and JTL is optimized to obtain a standard interface circuit, and then, modifications are made to previously designed SFQ cells and the standard interface circuit to connect the SFQ cells by using PTL's. The key point is the use of approximately the same interface circuit with every SFQ cell to maintain the matching condition between the interface circuit and the PTL's. Based on this approach, we designed an interface circuit and a test circuit composed of two D-flip-flops connected using 2-mm-long PTL's via the interface circuits. The impedance of the PTL was 2 /spl Omega/. We achieved high-speed operation of the test circuit up to 35 GHz with a bias margin of -15/+30%.         On using finite segment methods and images to establish the effect of gate structures on inter-junction inductances in RSFQ circuits    C.J. Fourie and W.J. Perold Summary: Several programs exist that calculate inductance in line structures. Some can even handle corners and holes in the ground plane. However, real structures in superconducting electronics are often more complex, and more elaborate techniques are needed to provide a reliable estimate of inductance, especially over very short intra-gate distances. A technique implemented with a modified version of FastHenry is discussed, whereby any inter-junction inductance in RSFQ circuits, in the vicinity of complex three-dimensional structures, junction cover pads and damping resistors, can be estimated. Placement of the reflection plane for the method of images is also discussed, together with the effect of segmentation size, and various results presented.         A novel global self-timing methodology for BSFQ circuits    Chen Kong Teh and Y. Okabe Summary: Recently we have proposed Boolean single-flux-quantum (BSFQ) circuits, which like CMOS circuits directly support Boolean primitives, and do not require local synchronization for their elementary cells as well as for their combinational cells. However, only the cell-level timing description of the BSFQ circuits was considered, which did not specify their global timing strategy in a system-level design. In this paper, we present a novel global self-timing methodology, dual encoding hierarchical pipelining (DEHP), for the locally asynchronous BSFQ circuits. In circuit implementation, a nonvolatile memory cell named ND-DFF and a volatile memory cell named D-DFF have been designed.         Current recycling and SFQ signal transfer in large scale RSFQ circuits    J.H. Kang and S.B. Kaplan Summary: The practical implementation of RSFQ technology in most digital electronics application areas requires much more complexity than the presently developed circuits. There are two important issues in building large-scale RSFQ circuits: 1) the recycling of the bias currents and 2) the transfer of SFQ pulses between circuits located far apart. RSFQ circuits are well known to operate with DC current bias. Even though the DC current biasing is more forgiving than the problematic AC biasing, it can still be a big concern when the circuit size becomes large. Dramatic reduction of the total bias current can be achieved by biasing several RSFQ circuits in series, where each circuit is positioned on a separate ground plane. In this work, we have used magnetically coupled Josephson transmission lines as inputs and outputs of an isolated shift register to show the feasibility of using the concept of serial biasing in current recycling. The circuit was simulated, fabricated with Nb technology, and tested at a temperature of 4.2 K. Test results show that SFQ pulses were transferred into the shift register built on a separate ground plane, clocked through it, and sent out back to the circuit on the original ground plane. We also studied on how to transfer SFQ pulses over an extended length, an important issue in building large RSFQ circuits. We have designed the circuits to test our microstrip line and multichip module approaches. We designed, optimized, fabricated and tested the circuits. Test results show that SFQ pulses can be successfully transmitted over an extensive distance in a chip and between chips.         Design of a superconducting ALU with a 3-input XOR gate    K. Takahashi, S. Nagasawa, H. Hasegawa, K. Miyahara, H. Takai and Y. Enomoto Summary: In order to develop superconducting Digital Signal Processors (DSP's), we have been studying a superconducting 1-bit Arithmetic Logic Unit (ALU). This ALU has the simplest function of AND, OR, ADD (addition), and SUB (subtraction). The ALU operates in a 3-stage pipeline. All logic functions such as AND, OR, and SUM (summation) can be executed within a single stage of the pipeline. In order to achieve the high-speed operation of the ALU, we proposed and designed a novel 3-input XOR gate, which can operate in only one logic stage. Our simulation study showed that all components of the ALU can operate up to 50 GHz. These ALU components were fabricated and tested at low speed. Large bias margins of more than /spl plusmn/37% were achieved. The designed ALU's were laid out and fabricated with an Nb process. The ALU occupied the area of 1200 /spl mu/m /spl times/ 2600 /spl mu/m, which contains 560 Josephson junctions (JJ's).         Design and component test of SFQ shift register memories    K. Fujiwara, H. Hoshina, Y. Yamashiro and N. Yoshikawa Summary: The lack of a high-density and high-speed memory is a serious impediment for realization of large-scale RSFQ digital systems. A shift resister memory, which has high throughput and simple circuit structure, is one candidate to overcome this drawback. We show a design framework of the shift register memory, which is usable for the high-speed register files and the main memories of the RSFQ microprocessor. The proposed system consists of an array of shift registers and a packet decoder that switches a high-speed serial data stream into the specified shift register. The target clock frequency is 16 GHz assuming 2.5 kA/cm/sup 2/ Nb standard process. We have estimated the propagation delay and the circuit area of the data-driven self-timed (DDST) packet decoder. Based on this estimation, we have also evaluated the access time and the area of the memory system. Several key components, including the one-to-two packet switch and the one-to-four DDST packet decoder, were implemented and their correct operations were confirmed.         Design and demonstration of SFQ pipelined multiplier    A. Akahori, M. Tanaka, A. Sekiya, A. Fujimaki and H. Hayakawa Summary: We have designed an SFQ pipeline multiplier using a cell-based design method. The cell-based design method enables us to expand the circuit-scale easily and is essential for the design of large-scale circuits. In the construction of the multiplier, a serial-parallel type was adopted. This type performs the partial products and the summation of the products in a bit-serial form. The multiplier designed here is a 3-bit serial-parallel structure with a seven-stage pipeline and is composed of destructive read-out (DRO) gates, nondestructive read-out (NDRO) gates and carry save serial adders (CSSA's). This circuit was fabricated by the NEC standard process. The number of Josephson Junctions is 1150. We have successfully tested the full operation with a bias margin of /spl plusmn/5.5%.         Implementation and application of first-in first-out buffers    Q.P. Herr and P. Bunyk Summary: First-in, first-out (FIFO) buffers load and unload data using separate clocks that may be incoherent. We explore the application of FIFOs to circular shift registers, serial memory, and data re-clocking. We describe two different FIFO implementations in RSFQ. One employs classic handshaking using the Muller C-element. The other employs physical back-pressure based on repulsion of stored single flux quanta in a JTL. Both implementations use seven Josephson junctions, and a single bias resistor, per cell. The bias resistor can be reduced to an arbitrarily low value, thereby eliminating static power dissipation.         High-speed operation of demultiplexer up to 56 GHz    F. Furuta, K. Saitoh and K. Takagi Summary: A 1-to-4 demultiplexer (DEMUX) was designed based on Single Flux Quantum (SFQ) circuitry and high-speed operation was confirmed using on-chip testing. The circuit was designed with a binary-tree structure to enable high-speed operation. We also investigated timing between clock and data signals in detail. Monte Carlo simulation was applied to vary the design parameters pseudo-randomly and the spread of timing was obtained by circuit simulation. Even if the circuit parameters varied as a result of the fabrication process, proper timing was maintained by optimizing the length of Josephson transmission line. The 1-to-4 DEMUX we fabricated distributed data signals correctly at operating frequencies up to 56 GHz with a bias margin of /spl plusmn/7%.         NbN and Nb SFQ device performance    M.W. Johnson, B.J. Dalrymple, D.J. Durand and J.A. Luine Summary: The static frequency divider is commonly used as a performance benchmark for both superconductor and semiconductor digital device technologies. We present results of a static divide-by-two circuit, an NbN (1 kA/cm/sup 2/) SFQ T-flip-flop (TFF) operating to 97 GHz. Details of the measurement and operating criterion are discussed. Measurements of junction capacitance, a particularly important factor effecting device performance, are presented for TRW's NbN process. Simulations of expected device performance are shown to explain measured performance reasonably well. NbN results are presented alongside a those of a recent 8kA/cm/sup 2/ Nb divider operating at 300 GHz, as well as published Nb TFF results.         On-chip clock oscillator for high precision RSFQ applications    V. Kaplunenko Summary: This paper discusses the possible modifications of the flux-flow oscillator, which is a part of an integrated receiver, for use as a precise clock oscillator in RSFQ circuits. At the price of losing tunability, the flux-flow oscillator can be used at resonance modes. To get higher clock rates, a parallel array of 20 identical under-damped Josephson junctions connected by superconducting micro-strip lines can also be used with an SIS mixer to form a phase-locked loop. The array shows a sharp resonance at 600 GHz, which can be used to make a precise on-chip clock. The linewidth of the emitted power of 150 kHz was estimated from the step differential resistance (free-run stability of 2.5 /spl middot/ 10/sup -7/). To convert frequency down to the desired level the array was matched to an over-damped pair of junctions, which form a precise frequency divider. The divider almost does not add any time jitter, thus the linewidth of 15 kHz can be achieved at 60 GHz. The clock stability can be improved by using an on-chip phase-locked-loop (PLL). The main part of the PLL is a phase detector, which can be based on an RSFQ Josephson sampler combined with an RSFQ fast counter. The suggested circuit probably could not compete with an SIS mixer, but significantly simplifies the circuit, and enables an on-chip RSFQ PLL closed by RSFQ frequency meter and DAC.         Demonstration of decimation filter and high-speed testing of a component of the filter    A. Sekiya, M. Tanaka, A. Akahori, A. Fujimaki and H. Hayakawa Summary: We study decimation filters based on the single-flux-quantum circuit in order to realize over-sampled AD converter. We designed the decimation digital filters using CONNECT cells, a well-developed cell library. We designed a T1 cell, because the T1 cell is the key for the counting-type decimation filter. We confirmed correct operation up to 43 GHz by using an on chip test system. Using the T1 cell, we designed second-order counting-type decimation sinc filters with decimation factors N=2 and N=4. The circuit scale was as high as 2758 junctions. We also confirmed the correct operation of these filters.         Implementation of phase-mode arithmetic elements for parallel signal processing    T. Onomi, Y. Horima, M. Kobori, I. Shimizu and K. Nakajima Summary: We report the preliminary designs and the experimental results of high-speed digital processing elements based on phase-mode logic circuits. The core cell of these elements is a bit-serial adder cell consisting of the ICF gate which is the basic gate of phase-mode logic. Our main target is the application of the logic circuits to Digital Signal Processing. The basic arithmetic operations of DSP are a multiplication and an addition. Basic concept of the phase-mode pipelined parallel multiplier has been proposed previously. We design a 2 /spl times/ 2 AND array block and a 2-bit ripple-carry adder for the primitive parallel pipelined multiplier and also a 2-bit subtractor with a pipelined structure. These processing elements have been fabricated using NEC standard 2.5 kA/cm/sup 2/ Nb/AlOx/Nb process. The low-speed test results of these elements show correct operations. Numerical simulations show that a carry save adder (a 2-bit ripple carry adder) can operate over 10 GHz. We also discuss the prospects of large-scale SFQ DSP based on Nb junction technology.         Two-phase 50 GHz on-chip long Josephson junction clock source    I.V. Vernik and D. Gupta Summary: On-chip, high-frequency clock sources are essential for the future development of superconductor digital circuits and systems. We have developed clock sources for rapid single flux quantum (RSFQ) digital circuits using high-quality long Josephson junction (LJJ) resonant oscillators that offer extremely low jitter. To meet the requirement for time-interleaved clock signals of complementary phase, two-phase 30 and 50 GHz clock sources using LJJ's have been developed with both linear and annular geometry. Unperturbed by reflections from boundaries and collisions among the fluxons (flux quanta), the annular LJJ oscillator has demonstrated superior stability and higher quality factor (>10/sup 6/) than the linear LJJ oscillator. The LJJ oscillator with linear geometry is easier to interface with RSFQ circuitry since it has well-defined boundaries at either end, facilitating a two-phase clock source. On the other hand, multiple clock phases may be derived from an annular LJJ oscillator by connecting interface circuitry at various points around the circular junction, if the interface circuitry does not interfere with the fluxon(s) in the annular junction. Experimental results for two-phase RSFQ clock sources based on linear and annular LJJ oscillators are presented.         A YBCO multilayer process using surface-modified junction technology    Y. Soutome, T. Fukazawa, K. Saitoh, A. Tsukamoto and K. Takagi Summary: We have developed processes for fabricating a YBa/sub 2/Cu/sub 3/O/sub 7-x/-multilayered structure which contains surface-modified junctions and a ground plane. A process of Ar-and-oxygen-ion milling, which was developed for fabricating the ramp-edges of the junctions, was applied to planarization of the structure's insulating layers. A process of milling with 500-V O/sub 2/ ions, which was developed for cleaning the ramp-edge surfaces, was applied to improve the critical current values for via-contacts in the structure. The fabricated junctions exhibited an average I/sub c/R/sub n/ product of 0.7 mV and a 1/spl sigma/-spread in the critical current of about 10% at 30 K. The sheet inductance of the strip-lines in the structure was less than 1.0 pH per square in the range below 60 K. The obtained values for I/sub c/R/sub n/ product, 1/spl sigma/-spread, and sheet inductance allow us to realize the high-speed operation of single-flux-quantum circuits at temperatures from 20 to 40 K.         Ramp-edge junctions with interface-modified barriers fabricated on YBCO thick films    H. Wakana, S. Adachi, H. Sugiyama, Y. Takahashi, T. Sugano, M. Horibe, Y. Ishimaru, Y. Tarutani and K. Tanabe Summary: We fabricated ramp-edge junctions with an interface-modified barrier on YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) liquid phase epitaxy (LPE) thick films. The LPE thick films were used as ground-planes. For the insulating layer between the ground plane and base electrode, a SrTiO/sub 3/ (STO)/(LaAlO/sub 3/)/sub 0.3/-(SrAl/sub 0.5/Ta/sub 0.5/O/sub 3/)/sub 0.7/ (LSAT)/STO multilayer with the dielectric constant of approximately 32 was employed. We fabricated ramp-edge junctions with La-doped YBa/sub 2/Cu/sub 3/O/sub y/ (La-YBCO) and La-doped YbBa/sub 2/Cu/sub 3/O/sub y/ (La-YbBCO) as base and counter electrodes, respectively. The fabricated junctions exhibited resistively and capacitively shunted junction (RCSJ)-like characteristics and typical I/sub c/R/sub n/ products of 2.6 and 1.1 mV at 4.2 and 40 K, respectively. The 1 /spl sigma/-spread in I/sub c/ as small as 8.1% was obtained for 100-junction series-arrays. The use of ground plane reduced the sheet inductance of electrodes to a value of 0.76-0.94 pH/square at 4.2 K.         Interface-engineered junctions with YbBaCuO as the counter-electrode    J. Yoshida, H. Katsuno, K. Nakayama, S. Inoue and T. Nagano Summary: The electric properties of interface-engineered junctions with YbBa/sub 2/Cu/sub 3/O/sub 7/ as the counter-electrode were investigated. The junctions exhibited excellent Josephson characteristics with the critical current density (J/sub c/) ranging from 10/sup 2/ A/cm/sup 2/ to more than 10/sup 6/ A/cm/sup 2/, and the normal resistance (R/sub n/) ranging from 10/sup -6/ /spl Omega/cm/sup 2/ to 10/sup -9/ /spl Omega/cm/sup 2/. The R/sub n/ values varied approximately in accordance with J/sub c//sup -p/, where p was close to 0.25 for low-J/sub c/ junctions and increased gradually up to 0.75 for high-J/sub c/ junctions. The junctions with R/sub n/ exceeding 10/sup -7/ /spl Omega/cm/sup 2/ exhibited dI/dV profiles peculiar to tunneling processes via localized states. The dI/dV profiles of the junctions with lower R/sub n/ were characterized by reproducible fine structures below 15 mV, probably due to multiple Andreev reflections. These results indicate that the crossover from the tunneling regime to metallic weak-links takes place in these junctions depending on the process conditions.         Spread of critical currents in thin-film YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junctions and faceting of grain boundary    P. Shadrin, C.L. Jia and Y. Divin Summary: The statistical distributions of critical currents in series arrays of YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions have been studied by low-temperature laser scanning microscopy. A set of arrays has been fabricated on [110] NdGaO/sub 3/ bicrystal substrates with misorientation angles from 2 /spl times/ 10/spl deg/ up to 2 /spl times/ 26/spl deg/ and patterned to the widths from 1.7 up to 5 micrometers. The critical current values of the individual junctions in the array have been obtained by focusing a laser beam on each junction and measuring the bias current at which the maximum laser-induced voltage response has appeared on the array. The measured critical current distributions have been demonstrated to be close to a log-normal Gauss function. A spread of this distribution has been found to increase with a bicrystal angle. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary topography has been studied by atomic force microscopy. From results of these measurements we suppose that the maximum values of critical current density might be assigned to the symmetrical facets of grain boundary.         Lumped arrays of shunted bicrystal Josephson junctions    A.M. Klushin, K.S. Il'in, M. Siegel, M. Schubert, G. Wende and H.-G. Mayer Summary: We report on the design, fabrication, and investigation of lumped arrays of Josephson junctions embedded into coplanar strip-lines (CPS). The arrays were incorporated into the CPS by meandering a bilayer across the grain boundary. Limitations on junctions packing density are discussed. The dependence of the length of the lumped array on spread of critical currents of junctions in the array was found. The investigated arrays with 431 junctions have shown frequency locking with an external irradiation. Voltage steps up to 20 mV at liquid nitrogen temperature were demonstrated.         Shot noise in YBCO bicrystal Josephson junctions    K.Y. Constantinian, G.A. Ovsyannikov, I.V. Borisenko, J. Mygind and N.F. Pedersen Summary: We measured spectral noise density in YBCO symmetric bicrystal Josephson junctions on sapphire substrates at bias voltages up to 100 mV and T=4.2 K. Normal state resistance of the Josephson junctions, R/sub N/=20-90 /spl Omega/ and I/sub C/R/sub N/ up to 2.2 mV have been observed in the experimental samples. Noise measurements were carried out within frequency bands of 1-2 GHz and 0.3-300 kHz. At bias voltages 10/spl les/V/spl les/60 mV a linear voltage dependence of noise power has been registered, while at V/spl les/5 mV a noticeable noise rise has been observed. The latter may explain the experimentally measured linewidth broadening of Josephson oscillations at mm and submm wave frequencies in high-Tc superconducting junctions. Experimental results are discussed in terms of bound states existing at surfaces of d-wave superconducting electrodes.         Dc- and un-SQUIDs for readout of ac-biased transition-edge sensors    M. Kiviranta, J.S. Penttila, L. Gronberg, H. Seppa and I. Suni Summary: We have developed a set of SQUIDs optimized for readout of ac-biased transition edge sensors. Junction shunts are made of Pd and attached to cooling fins to facilitate low-noise operation at sub-kelvin temperatures. SQUID's have a low loop inductance in order to reach a large natural dynamic range even without negative feedback. The SQUIDs are intended to be used for frequency-domain multiplexing of X-ray calorimeter arrays. Both traditional dc-SQUIDs and novel un-SQUIDs are manufactured. The fabrication process and SQUID design criteria are reviewed.         Electronics for arrays of transition edge sensors using digital signal processing    S. Nam, J. Beyer, G. Hilton, K. Irwin, C. Reintsema and J.M. Martinis Summary: Single-pixel transition-edge sensors (TES) are useful for a variety of applications requiring the detection of photons from sub-millimeter wavelengths to gamma rays. Arrays of TES's are required in the next-generation instruments to continue to be useful. We report on the development and performance of an electronics system used to readout and process signals from arrays of TES detectors. The system utilizes high-performance analog and digital electronics, and digital signal-processing. Because the system digitizes signals early in the signal processing chain, it is possible to implement a digital-feedback system to flux lock a SQUID amplifier and digitally process the detector (feedback) signal.         Inductive superconducting transition-edge photon and particle detector    L. Hao, J.C. MacFarlane, P. Josephs-Franks and J.C. Gallop Summary: We propose a novel type of sensor where the sensitive element is an isolated, passive absorber of extremely low thermal mass, maintained close to its superconducting-normal transition, and strongly inductively coupled to a SQUID sensor. Incoming particles or photons are sensed in terms of a transient change in the inductive coupling, rather than a change in resistance. Energy sensitivity and response time can then be defined by the thermal mass of the absorber and its thermal contact with a substrate, independently of any electrical connections. An ultimate energy resolution of order 10/sup -25/ J/Hz is theoretically estimated, based on the properties of the SQUID and the dimensions of the absorber. Calculations of the thermal properties of the absorber suggest that a response time of 1 ns should be feasible, although in practice this will be limited by the bandwidth of the SQUID amplifier. Proof-of-principle measurements on a prototype device are presented, where a SQUID flux noise level of 4/spl times/10/sup -7/ fluxon/Hz/sup 1// was achieved and laser-induced superconducting-normal transitions of a thin-film Pb-Sn absorber were clearly demonstrated.         A frequency-domain SQUID multiplexer for arrays of transition-edge superconducting sensors    T.M. Lanting, Hsiao-Mei Cho, J. Clarke, M. Dobbs, A.T. Lee, P.L. Richards, A.D. Smith and H.G. Spieler Summary: We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge. Frequency-domain multiplexing can greatly simplify the instrumentation of large arrays by reducing the number of SQUID's (superconducting quantum interference devices) and wires to the low temperature stages. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. Each sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single SQUID. The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.         Noise analysis of gamma-ray TES microcalorimeters with a demonstrated energy resolution of 52 eV at 60 keV    T. Miyazaki, J.N. Ullom, M.F. Cunningham and S.E. Labov Summary: We present recent results from our /spl gamma/-ray transition-edge sensor (TES) microcalorimeters. We have demonstrated an energy resolution of 52 eV at 60 keV with devices composed of a high-purity Sn absorber and a Mo/Cu multilayer thin-film TES. In this paper, we present a detailed noise analysis of these devices and show that the major noise sources are device originated (thermal fluctuation and Johnson noise). Our performance analysis explicitly includes the noise contribution due to the composite geometry of these devices and electro-thermal feedback (ETF).         Imaging analysis of superconducting transition edge sensors for calorimeters    M. Ohkubo, H. Pressler, D. Fukuda, T. Inou, H. Takahashi and M. Nakazawa Summary: The superconducting-transition-edge temperature sensors (TES) for calorimeters operate in an intermediate state within normal-superconducting transition. The spatial profiles of a response to an x-ray microbeam exhibit that normal-superconducting phase separation occurs in an iridium TES with electrothermal feedback, as has been observed in many current-carrying conductors with self-heating. The resistive domain (normal region) in the 500 /spl mu/m-square TES grows as applied bias voltage increases. This observation agrees reasonably well with a one-dimensional model of the self-heating. On the other hand, two-dimensional features are explained by nonuniform supercurrent distribution in the superconducting domain. These findings are important for developing detectors with a large detection area for energy dispersive x-ray spectroscopy.         AC biased TES-based X-ray microcalorimeter with an energy resolution of 6.3 eV at 5.89 keV    J. van der Kuur, P.A.J. de Korte, H.F.C. Hoevers, W.M.B. Tiest, N.H.R. Baars, M.L. Ridder, E. Krouwer, M.P. Bruijn, M. Kiviranta and H. Seppa Summary: Frequency domain multiplexing (FDM) is an attractive option for the readout of imaging arrays of microcalorimeters. The most straightforward implementation of FDM is based on alternating voltage (AC) biasing of the individual microcalorimeters. It is clear that for future applications the performance in terms of energy resolution and count rate capability is crucial. We discuss the consequences of AC bias for the performance of a microcalorimeter, and make a direct experimental comparison between the performance of a TES based microcalorimeter AC and DC bias. Modeling, as well as experiments, show that the performance of the device is is very similar in terms of energy resolution and pulse shapes (100 /spl mu/s effective time constant). The measured energy resolution at 5.89 keV photon energy is 6.3 eV for AC bias at 46 kHz and 5.5 eV for DC bias.         A frequency-domain read-out technique for large microcalorimeter arrays demonstrated using high-resolution /spl gamma/-ray sensors    J.N. Ullom, M.F. Cunningham, T. Miyazaki, S.E. Labov, J. Clarke, T.M. Lanting, A.T. Lee, P.L. Richards, Jongsoo Yoon and H. Spieler Summary: Cryogenic sensors composed of transition-biased superconducting films have demonstrated remarkable sensitivity at /spl gamma/-ray, x-ray, optical, and far-infrared to millimeter wavelengths. However, for these sensors to find widespread application in astronomy and materials analysis, technologies for building and reading out large arrays are required. We are currently developing a frequency-domain multiplexing scheme for the read-out of large numbers of microcalorimeters using a much smaller number of amplifiers. In this scheme, each sensor is biased at an identifying frequency and operated in a series LC circuit to suppress out-of-band noise. Here, we present results demonstrating the undegraded operation of two /spl gamma/-ray sensors multiplexed using this technique. In addition, we provide a series of design rules which relate the minimum bias frequency and the values of the reactive elements in the system to a small number of sensor properties. Finally, we discuss the ultimate limits on the number of sensors that can be measured with a single amplifier.         Performance of 32-channel time-division SQUID multiplexer for cryogenic detector arrays    J. Beyer, P.A.J. de Korte, C.D. Reintsema, S.W. Nam, M. MacIntosh, G.C. Hilton, L.R. Vale and K.D. Irwin Summary: Multiplexed readout is a requirement for the successful deployment of large-scale cryogenic detector arrays in applications ranging from x-ray microanalysis to sub-millimeter astronomy. We report on the development of a time-division SQUID multiplexer (SQUID MUX) to read out one column of a 32/spl times/32 transition-edge sensor (TES) array. The new SQUID MUX has three stages. Individual TES pixels inductively couple to first-stage SQUID's, which are summed and coupled to a second-stage SQUID via a superconducting transformer. The first- and second-stage SQUID's are integrated on the same chip and are operated at the working temperature of the detectors of about 100 mK. The second stage SQUID is read out by a SQUID series array at 4K. Compared to former designs, the new SQUID MUX features a balanced input configuration to reduce crosstalk between read-out channels. In this paper we discuss the SQUID MUX design and analyze the noise and bandwidth performance of the SQUID multiplexer. Multiplexing of test input signals utilizing digital feedback electronics is demonstrated.         A new X-ray microcalorimeter based on a pixelated TES array    D. Fukuda, M. Ohno, H. Takahashi, Y. Kunieda, T. Inou, M. Ohkubo, M. Ataka and M. Nakazawa Summary: We are developing a new x-ray microcalorimeter based on superconducting transition edge sensors (TES) as an imaging sensor. This device has ten pixelated transition edge sensors with Iridium superconductive films. When a constant bias voltage is applied to all pixels, each pixel is operated at slightly different equilibrium temperature. This arises from the different thermal responses between pixels, so that response signal shapes would vary according to the position of the incident x-ray. We have fabricated a prototype of the pixelated array and examined its performance. The position dependency measurements by scanning the collimated x-ray over the device have successfully shown that the device is able to resolve its pixel position. The energy resolution of a test device was 13.1 eV (FWHM) for 3 keV x-rays.         YBCO transition edge sensors used for very low noise thermal control    B. Guillet, D. Robbes and L. Mechin Summary: In electrically substituted radiometers, the ultra low noise control of the temperature is required. In this framework, we present results dedicated to the temperature regulation of copper plates, 3 cm diameter and 1 mm thick, using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) transition edge sensors (TES). One of the TES was used as the active thermometer of the temperature control unit, whereas the two others measured the plate temperature behavior. Two heating resistors were wound along a spiral pattern, just underneath the copper plate, to minimize the heating delay. The correlation between the two TES was clearly highlighted by applying a small heat perturbation through the second distributed resistor, the path of which closely follows that of the main resistor. Calibrated temperature oscillations of 30 /spl mu/K rms @ 10 mHz together with spectral analysis were measured and a temperature resolution in the range of a few /spl mu/K rms was achieved.         T/sub C/ suppression in superconducting films for use in transition edge sensors    S.W. Deiker, G.C. Hilton, K.D. Irwin, W.H. Rippard, S.T. Ruggiero, L.R. Vale and B.A. Young Summary: Transition edge sensor (TES) microcalorimeters have proven their value as photon detectors in several wavelength regimes. The central element of a TES is a superconducting film with a transition temperature designed to be at a specific temperature, usually 100 - 500 mK. These films are typically fabricated by depositing bilayers or multilayers of superconducting and normal metals (e.g., molybdenum and copper) whose relative thicknesses have been engineered to produce the desired superconducting transition temperature (T/sub C/) through the proximity effect. Although these fabrication methods have been widely applied, bilayer and multilayer deposition is often difficult, and care must be taken in controlling thicknesses and surface interface quality. An alternative method is to dope the superconducting film with dilute magnetic impurities in order to suppress its T/sub C/ to the desired temperature. This technique has been used successfully in tungsten, but tungsten films are not well-suited to all TES applications. We have thus undertaken a project to investigate T/sub C/ suppression in molybdenum and aluminum films. We present our results from impurity doping using iron and manganese in these films.         Surface micromachining for transition-edge detectors    G.C. Hilton, J.A. Beall, S. Deiker, J. Beyer, L.R. Vale, C.D. Reintsema, J.N. Ullom and K.D. Irwin Summary: We are developing arrays of high-performance detectors based on superconducting transition-edge sensors (TES) for application in x-ray materials analysis as well as x-ray and sub-millimeter astronomy. In order to obtain the desired thermal time constants, as well as to provide thermal isolation from adjacent pixels, these arrays utilize micromachined thermal-isolation structures. Until recently, we have achieved thermal isolation of single-pixel devices by anisotropic wet etching of the entire Si wafer behind the pixel, leaving the detector supported by a thin Si/sub 3/N/sub 4/ membrane. Limitations of this technique make it undesirable for the fabrication of close-packed arrays. One possible means to achieve thermal isolation of close-packed arrays is surface micromachining. Here, a TES is fabricated on top of a Si/sub 3/N/sub 4/ membrane that is held above the substrate by a small number of support legs. Because the underlying wafer is not thinned or removed, the resulting detector chip is strong and requires no special handling. In this paper we describe the fabrication processes and present preliminary data on the properties of 64-pixel arrays of surface-micromachined TES x-ray detectors.         An Nb-based waveguide SIS distributed mixer employing coplanar inductor loaded microstrip transformer for the 800 GHz frequency band    H. Maezawa, C.E. Tong, T. Noguchi, T. Matsunaga, R. Blundell and Shing-Kuo Pan Summary: We present a novel superconducting waveguide mixer for 800 GHz. In this mixer, a half-wave Nb/Al-AlO/sub x//Nb superconducting-insulator-superconductor (SIS) resonator is integrated with a microstrip superconducting transmission line loaded with coplanar inductors. This hybrid coplanar/microstrip transmission line acts as an impedance matching section between the distributed junction and the waveguide feed point of the mixer mount. We have designed mixers with a simple model which predicts that the insertion loss of the matching network is less than 10 percent up to 840 GHz. Preliminary experimental results show that the resonator can work up to 800 GHz but the parameters of the coplanar inductor loaded microstrip line need to be refined to improve power coupling to the resonator.         Radiation power of NbN-based flux-flow oscillators for THz-band integrated SIS receivers    S. Kohjiro, Z. Wang, S.V. Shitov, S. Miki, A. Kawakami and A. Shoji Summary: To develop an efficient local oscillator (LO) integrated with a SIS mixer operating above the gap frequency of Nb, we have investigated the radiation power P of NbN-based flux-flow-type Josephson oscillators (FFO's). The designed and fabricated chip incorporates FFO's, SIS power detectors (DET's), and their coupling circuits. Both FFO's and DET's consist of epitaxial NbN/AlN/NbN junctions with high critical current density J/sub C/ (15200 nW, enough for the optimum pumping of a SIS mixer with rf-resistance of 50 /spl Omega/, is coupled to DET's for 0.5-0.9 THz. The coupling bandwidth is larger than 20% of its central frequency. In the band, the radiation frequency is tuned by the control current through the FFO of 10-100 mA. The maximum coupling frequency of the present experiment is quantitatively agreed with the theoretical one. The peak power of 1.3 /spl mu/W is detected at 0.76 THz. The dissipated power in a FFO is smaller than 500 /spl mu/W, which is 10/sup -4/ times less than that of semiconductor sources. These results indicate the feasibility of NbN-based FFO's for a practical on-chip LO.         Spectral range of the ac Josephson effect in [001]-tilt YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junctions    Y.Y. Divin, O.Y. Volkov, M.V. Liatti and V.N. Gubankov Summary: We have studied the ac Josephson effect in YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junction by monitoring the voltage dependence of the dc current response /spl Delta/I(V) induced by low-power monochromatic radiation with the frequencies f/sub i/. The intensity of odd-symmetric resonances in the function /spl Delta/I(V) near the voltages V/sub i/=hf/sub i//2e is proportional to the amplitude of Josephson oscillations at the frequency f/sub i/. The resonance intensities have been mapped as a function of the Josephson frequency f/sub i/ in the range from 5 GHz to 5 THz, the junction resistance R/sub n/ in the range from 0.4 to 80 Ohm and junction characteristic voltages I/sub c/R/sub n/ in the range from 5 /spl mu/V to 1.8 mV. The central frequency of the range was scaled with the I/sub c/R/sub n/-product of the junction and it could be shifted from GHz-range to the THz-range by a temperature decrease. The spectral range was limited by an enhanced noise broadening of the Josephson linewidth at low frequencies and by increased dc Joule heating at high frequencies.         A 650 GHz fixed-tuned waveguide SIS distributed mixer with no integrated tuning circuit    C.-Y.E. Tong, R. Blundell, K.G. Megerian, J.A. Stern and H.G. LeDuc Summary: A Superconductor-Insulator-Superconductor (SIS) distributed mixer with no integrated tuning circuit has been designed for use in a fixed-tuned waveguide mixer block. This mixer employs two half-wave SIS resonators connected in series across the feed point of the waveguide circuit. By selecting appropriate dimensions for the resonators, we can obtain proper impedance matching over a reasonable input bandwidth. Since there is no lossy thin film microstrip line in front of the SIS junction, efficient power transfer from the waveguide feed to the mixer element can be achieved. A receiver noise temperature of 185 K at 650 GHz has been measured with a dual 0.33/spl times/16.8 /spl mu/m SIS resonator. The noise temperature remains below 300 K over an input bandwidth of about 10%. This design can be used at much higher frequency where the loss of tuning circuit becomes significant.         An integrated receiver with phase-locked superconducting oscillator    S.V. Shitov, V.P. Koshelets, A.B. Ermakov, P.N. Dmitriev, L.V. Filippenko, V.V. Khodos, V.L. Vaks, P.A. Yagoubov, W.-J. Vreeling and P.R. Wesselius Summary: A submillimeter heterodyne spectrometer employing a superconducting local oscillator is demonstrated for the first time. The sensor chip comprises a quasioptical double-dipole lens-antenna SIS mixer (T/sub RX/=250 K at 380 GHz), a Josephson flux-flow oscillator and a SIS harmonic mixer. Room temperature PLL electronics is used with a reference source at 10 GHz. The PLL bandwidth of 10 MHz and the hold range of 3 GHz are estimated for locking at 32-th harmonic of the reference source. The spectral resolution better than 1 MHz and broadening effect of a spectral line of SO/sub 2/ gas at 326867 MHz are measured with a laboratory gas cell at 300 K at pressure 0.03 - 0.3 mbar using acousto-optical spectrometer.         Design and analysis of an all-NbN SIS mixer using a tuning circuit with two half-wavelength distributed junctions    Y. Uzawa, M. Takeda, A. Kawakami and Z. Wang Summary: We have designed an all-NbN superconductor-insulator-superconductor mixer with a broadband tuning circuit for the terahertz band, which enables the use of junctions with a lower current density. It uses the reactance compensation efficiently produced by two half-wavelength distributed junctions connected by a half-wavelength microstripline. Based on the design and simulated noise performance, a tuning circuit using NbN junctions with a current density of 25 kA/cm/sup 2/ should be able to cover the 780-950 GHz band with an SSB receiver noise temperature below 4hfk/sub B/.         Development of a waveguide NbN-based SIS mixer in the 900-GHz band    M. Takeda, Y. Uzawa, Z. Wang, A. Saito and A. Kawakami Summary: We have designed and fabricated waveguide superconductor-insulator-superconductor (SIS) receivers at 870 GHz with NbN/AlN/NbN tunnel junctions on an MgO substrate. A waveguide probe was incorporated into the mixer chip for a waveguide-to-microstrip transition. As the tuning circuit for the SIS mixer, we designed a resonant distributed junction whose length is one wavelength and critical current density is 20 kA/cm/sup 2/. The mixing properties were calculated based on the quantum theory of mixing. The SSB mixer noise temperature should be less than 100 K and conversion gain larger than -8.0 dB in the frequency range from 840 to 920 GHz. We also observed the resonance steps of the fabricated SIS mixer. The tuning frequency was slightly higher than the designed frequency.         Design of a superconducting MEM shunt switch for RF applications    Y.S. Hijazi, Y.A. Vlasov and G.L. Larkins Jr. Summary: We have designed, simulated and optimized a capacitively shunted RF MicroElectroMechanical (MEM) superconducting switch. The switch consists of a High Temperature Superconducting (HTS) YBa/sub 2/Cu/sub 3/O/sub 7/ coplanar waveguide (CPW) structure with a gold membrane bridge suspended above the center conductor and anchored at the ground planes (air gap 3 /spl mu/m). A thin layer of BaTiO/sub 3/, in the shape of a patch, lies on top of the center conductor and underneath the suspended gold membrane. Under an applied voltage, the gold bridge membrane actuates downwards and collapses on top of the dielectric layer of BaTiO/sub 3/ thereby capacitively shunting the RF signal to ground. Using Sonnet, simulations were conducted to optimize the switch design. An analysis of these results revealed interesting relationships between the switch mechanical and electrical parameters; this paper discusses and analyzes these results, along with measured data.         Fabrication of a superconducting MEM shunt switch for RF applications    Y.S. Hijazi, D. Hanna, D. Fairweather, Y.A. Vlasov and G.L. Larkins Jr. Summary: We have developed a fabrication process for a superconducting MicroElectroMechanical (MEM) shunt switch. The design of the switch has been optimized using Sonnet simulations. The switch consists of a YBa/sub 2/Cu/sub 3/O/sub 7/ Coplanar Waveguide (CPW) transmission line with a gold membrane bridge anchored at the ground planes and suspended above an area of the center conductor covered with BaTiO/sub 3/. Under an applied electric field this membrane bridge actuates downwards and shunts the RF signal to ground. The membrane returns to its original shape when the electric field is removed. In the up position the device exhibits an s/sub 21/ insertion loss of less than 0.25 dB from dc through 900 MHz (most of which is due to radiated loss). In the down position the s/sub 21/ loss in the same frequency range is greater than 30 dB.         Simulation study on the mechanical tuning of high-T/sub c/ superconducting microwave filters    M. Inoue, A. Maehara, H. Mizuno, A. Fujimaki, S. Hontsu, S. Mine and H. Hayakawa Summary: We tried to apply the mechanical tuning method to lumped-element superconducting filters and investigated the tunability by simulation. This tuning method is the same as we previously adopted for tuning microstrip-line-type resonators, i.e., tuning by the displacement of a dielectric floating plate with an actuator above the resonator. We considered band pass filters with a center frequency in a GHz range and a bandwidth of a few tens to a few hundreds MHz. The inductors and the capacitors were designed and simulated using an electromagnetic analysis simulator, Sonnet EM. We assumed MgO for the substrate and the floating plate. We investigated the properties of the filters and their tunability.         Tuning of Y-Ba-Cu-O ring resonators by Sr-Ti-O thin films    M. Adam, D. Fuchs and R. Schneider Summary: Tunable YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) ring resonators were produced to study the nonlinear dielectric properties of SrTiO/sub 3/ (STO) thin films. Epitaxial STO/YBCO double layers were deposited by sputtering on LaAlO/sub 3/ substrates and patterned to coplanar ring resonators. By applying an electric field of 100kV/cm the resonant frequency could be shifted by 5% from 5.13 to 5.38 GHz and the unloaded quality factor, Q/sub 0/, of the resonator increased from 195 to 394. The dielectric properties sensitively depended on the deposition temperature of the STO films which was varied from 710 to 810/spl deg/C. With increasing deposition temperature the relative permittivity, /spl epsiv//sub r/, at 77 K raised from 234 to 424. Annealing the film deposited at 810/spl deg/C in 1 bar oxygen for 2 hours at 1200/spl deg/C resulted in an additional increase to /spl epsiv//sub r/=613. The highest tunability with a 70% reduction of the permittivity at 120 kV/cm was also reached in the annealed film. Although the lowest loss tangent, tan/spl delta/, of 0.006 at 77 K was found for the film deposited at 710/spl deg/C, the annealed film had the best tunability to loss ratio. The measured temperature and electric field dependence of the permittivity and loss tangent could be described by a phenomenological model which elucidates the loss mechanisms in the STO films.         Tunable HTS microwave filters using strontium titanate thin films    B.H. Moeckly, L.S.-J. Peng and G.M. Fischer Summary: High performance HTS microwave filters stand to benefit from the capability to electrically tune their frequency of operation. This function may be performed with tunable dielectric materials such as SrTiO/sub 3/ (STO). We have optimized the growth of STO thin films by pulsed laser ablation and by reactive coevaporation. Loss tangents on the order of 0.001 at 65 K are possible, while maintaining acceptable tunability. We have integrated STO films into lumped-element YBCO microwave resonators and filters in order to tune their center frequencies. We describe methods of doing so, the effect of coupling strength, and the performance of these devices.         Tunable microwave filters using ferroelectric materials    I. Vendik, O. Vendik, V. Pleskachev and M. Nikol'ski Summary: A new design approach for a microstrip tunable filter on a two-layered substrate with BSTO thin films is suggested. The coupling factor of a ferroelectric capacitor connected to the microstrip resonators of the filter is considered to make possible the design of the filter with constant pass band width while tuning. Results of the filter characteristic simulation and measurement are presented. Tunable coplanar resonator on single crystal STO disk is also considered.         Study of mechanically tunable superconducting microwave filter using lumped elements    S. Hontsu, S. Mine, H. Nishikawa, M. Nakamori, A. Fujimaki, M. Inoue, A. Maehara and T. Kawai Summary: We propose a mechanically tunable superconducting microwave filter based on lumped elements composed of planar meander-line inductors (L) and inter-digital capacitors (C). As the first step, we have designed and evaluated a 3-pole Chebyshev bandpass filters with lumped elements using a circuit simulator. It is found that the center frequency, bandwidth and skirt rejection of the filter can be controlled by changing only the capacitance. The L and C elements values are estimated using an electromagnetic simulator. Furthermore, we have fabricated the inter-digital capacitor designed with the above procedure. We have evaluated change of the C values using mechanical tuning as a step toward a tunable superconducting microwave filter.         Superconducting microstrip hairpin filter with BaTiO/sub 3/ patches    G.L. Larkins Jr., R. Socorregut and Y.A. Vlasov Summary: A high temperature superconducting microstrip line hairpin filter with BaTiO/sub 3/ has been designed and fabricated. The design and the filter simulation were done using Genesys software from Eagleware. In order to maximize the quality factor of the filter, the microstrip lines were made of superconducting YBa/sub 2/Cu/sub 3/O/sub 7/. A YBa/sub 2/Cu/sub 3/O/sub 7/ thin film was deposited on a LaAlO/sub 3/ single crystal substrate using pulsed laser deposition. The microstrip line hairpin filter was then patterned and tested at cryogenic temperatures. A BaTiO/sub 3/ thin film was then deposited and patterned to form patches between the resonators. Microwave tests of the filter with and without the BaTiO/sub 3/ patches were performed at low temperatures. The filter has measured center frequency of 1.65 GHz with a bandwidth of 20 MHz. The results show the effect of using BaTiO/sub 3/ patches on top of YBa/sub 2/Cu/sub 3/O/sub 7/. The most current results on the performance of the filter will be presented.         A device with two orthogonal low-T/sub c/ SQUID gradiometers - a comparison of series and parallel gradiometric SQUID's    K. Yokosawa, D. Suzuki, K. Tsukada and A. Tsukamoto Summary: We have developed a planar gradiometric device with two orthogonal SQUID gradiometers integrated on a substrate. In developing this new device, both series- and parallel-type gradiometric SQUID's (without pickup coils) suitable for the same pickup coils were fabricated. The parasitic inductance, parasitic areas, and cross talks of each SQUID were evaluated to compare their performances. Next, to evaluate the effects of changing field on the SQUID's, the critical current reduction and noise increase under an applied magnetic field were measured. These results show that the parallel SQUID is superior to the series SQUID; thus the parallel SQUID was chosen for use in the new single-chip gradiometric device.         SQUID noise as a function of temperature: a survey of three SQUID's    M.A. Espy, A.N. Matlachov, R.H. Kraus Jr. and J.B. Betts Summary: The temperature dependence of SQUID noise was tested over a temperature range from 0.3-4 K for SQUID's of three different manufactures, two designed for user supplied pick-up coils and one a magnetometer. A SQUID-based picovoltmeter, designed to reduce noise contributions for cables and electronics was used to read out the signal from the SQUID being investigated. The data were taken in support of a physics experiment which will use SQUID's to measure the precession frequency of spin polarized /sup 3/He, acting as a comagnetometer with spin polarized ultra cold neutrons (UCN). The final aim of the experiment is to measure the neutron electric dipole moment to 4/spl times/10/sup -28/ ecm. The /sup 3/He and UCN will be in a bath at temperatures <0.5 K. The noise performance of the SQUID's at these temperatures must be well understood before the experiment. The results of the noise studies as a function of temperature are presented for the three SQUID's and their behavior is compared to theoretical predictions based on SQUID parameters.         Spatial frequency response of conventional and non-conventional SQUID gradiometers    E.A. Lima and A.C. Bruno Summary: The gradiometer spatial frequency response is an important performance feature, mainly if one wants to tailor a gradiometer design to specific applications. Because many nonconventional planar gradiometers have been recently built, we extend a two-dimensional filtering model that predicts the spatial frequency response of ordinary planar gradiometers to incorporate those designs, such as directly coupled and flip-chip gradiometers. We also expand the model to obtain the three-dimensional spatial frequency response of conventional wire-wound axial gradiometers. An assessment of a nonconventional planar design with actual parameters is made and the principal features of its spatial frequency response are compared with the ones of typical conventional gradiometer designs.         HTS Current Concentrator for remote sensing of charged particle beams    L. Hao, J.C. MacFarlane, C. Carr and J.C. Gallop Summary: The principle of the cryogenic Current Comparator, well-established at liquid helium temperatures, is demonstrated here using liquid nitrogen temperature components. By incorporating a novel current concentrator structure in the cylindrical YBCO thick-film coating, it is applied to the noninvasive sensing of charged particle beams. The significant design parameters for the effective operation of the current concentrator are examined, and experimental measurements are compared with theoretical predictions. The device has been successfully operated in prototype form with ion and electron beam currents, and its inherent current sensitivity is estimated to cover the range from <0.1 nA-20 mA.         Cryogenic current comparator for absolute measurements of the dark current of superconducting cavities for TESLA    W. Vodel, R. Neubert, S. Nietzsche, K. Knaack, M. Wendt, K. Wittenburg and A. Peters Summary: A new SQUID based measurement system for detecting dark currents, generated by the TESLA (Tera Electron Volt Energy Superconducting Linear Accelerator) cavities is proposed. It makes use of the Cryogenic Current Comparator principle and senses dark currents in the nA range. To reach the maximum possible energy in the TESLA project is a strong motivation to push the gradients of the superconducting cavities closer to the physical limit of 50 MV/m. The field emission of electrons (dark current) of the cavities at strong fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value to compare and classify the cavities. This contribution describes a Cryogenic Current Comparator (CCC) as an excellent tool for this purpose. The most important component of the CCC is a high performance DC SQUID system which is able to measure extremely low magnetic fields, e.g., caused by the extracted dark current. For this reason the SQUID input coil is connected across a special designed pick-up coil for the electron beam. Both the SQUID input coil and the pick-up coil form a closed superconducting loop so that the CCC is able to detect dc currents down to 1 nA//spl radic/Hz. Design issues and the application for the CHECHIA (horizontal test cryostat) cavity test stand at DESY are discussed.         Digital SQUIDs: new definitions and results    V.K. Semenov Summary: Recently we found that several simple SFQ circuits (normally used as ADC comparators) dramatically outperform conventional SQUIDs in time resolution and slew rate. For example, it is possible to reach a resolution of about a few percent of flux quantum by using a single-shot measurement that takes only a few picoseconds. All these SFQ circuits produce during each clock period only one bit of information that indicates whether the applied flux is larger or smaller the threshold. As a result it is natural to call them digital (or logic) SQUIDs. The new sensors can be used to detect a direction of the electrical current induced in a superconductor loop by the external field and digitally compensated by another SFQ devices. This composite device contains two kinds of digital components and also could be called a Digital SQUID. It has a limited practical value with a hundreds MHz clock rate. Fortunately, the clock frequency could be increased to tens of GHz. But in this case the third digital device (a decimation filter) should be added to filter out off-band noise and reduce the output clock frequency. The last device is rather similar to an ADC and also could be called a Digital SQUID. It is easy to show that the last Digital SQUID has a practically unlimited slew rate and dynamic range without suffering significant loss of energy sensitivity of the conventional two-junction SQUID.         High-T/sub c/ SQUID sensors with integrated Earth field compensation    D. Drung and T. Schurig Summary: An encapsulation with integrated field compensation coils for superconducting quantum interference device (SQUID) magnetometers is presented. The capsule is fabricated from printed-circuit board material. In spite of the small capsule size of 18 mm/spl times/16 mm/spl times/4.8 mm, the compensation field at nominal capsule dimensions is homogeneous to about /spl plusmn/2% over the area of the SQUID magnetometer pickup coil of 9 mm/spl times/9 mm. The field homogeneity degrades by about a factor of two for worst-case tolerances in the thickness of the board material or in the positions of the field coils. A low-noise current source was integrated into our microcontroller-based SQUID readout electronics in order to supply the field coils. Compensation fields of up to /spl plusmn/71 /spl mu/T can be produced with only 19 fT//spl radic/Hz excess noise above the 1/f corner at about 2 Hz. The current source has a 10%-90% settling time of 2.2 ms allowing one to compensate the background field dynamically in environments with very large low-frequency field fluctuations or even in slowly moved sensor systems.         A multichannel SQUID magnetometer system based on double relaxation oscillation SQUIDs    Yong-Ho Lee, Hyukchan Kwon, Jin-Mok Kim, Chan-Seok Kang, Kiwoong Kim, In-Seon Kim, Yong-Ki Park and Soon-Gul Lee Summary: We constructed a multichannel superconducting quantum interference device (SQUID) magnetometer system for magnetoencephalogram measurements. The SQUID is based on the double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID and a reference junction, and shunted by a relaxation circuit of a resistor and an inductor. With the high flux-to-voltage transfers, usually larger than 1 mV//spl Phi//sub 0/, simple flux-locked loop circuits could be used for SQUID operation. The SQUID system consists of 37 integrated magnetometers, distributed on a hemispherical surface, and external feedback scheme was used to eliminate magnetic coupling with the adjacent channels. In addition to the 37 signal channels, 8 reference channels were installed to pickup background noise and to apply software gradiometer. The average noise level of the magnetometers is about 3 fT//spl radic/Hz at 100 Hz, operated inside a magnetically shielded room. The magnetometer system was applied to measure auditory-evoked fields.         Operation of a geophysical HTS SQUID system in sub-Arctic environments    K.E. Leslie, R.A. Binks, C.P. Foley, R.G. Thorn, M.J. Roberts, J. Du, E.E. Mitchell, S.K.H. Lam, C.J. Lewis, C. Millar and R.T. Osmond Summary: Transient ElectroMagnetic geophysical prospecting using SQUID sensors has demonstrated potential for improved target detection at late response times compared to conventional coil sensors. We have developed a three-axis, rf SQUID sensor system which has been extensively operated in sub-Arctic conditions by a geophysics contractor. Due to the harsh environmental and operating conditions, the system is designed to operate in sub-zero temperatures (as low as minus 40/spl deg/C) and is ruggedly packaged whilst still remaining quite portable. Auto-tuning of the rf electronics has been implemented by adjusting the rf SQUID control parameters via a microprocessor controller. After a small amount of training, regular field crews have operated two of these systems in the field continuously for periods of months at a time. An example, comparing SQUID B field data to coil dB/dt data, is presented in this paper.         Vector HTS-SQUID system for ULF magnetic field monitoring    Y. Machitani, N. Kasai, Y. Fujinawa, H. Iitaka, N. Shirai, Y. Hatsukade, K. Nomura, K. Sugiura, A. Ishiyama and T. Nemoto Summary: Anomalous magnetic field variations in the ultra low frequency (ULF) band were observed as precursory phenomena of earthquakes. We constructed a portable monitoring system by using HTS-SQUIDs for measuring the ULF environmental vector magnetic field. The operation of the system was verified at Mt. Bandai, an active volcano. The system safely worked over 100 hours on batteries. We have achieved long term monitoring with the system at the National Institute of Advanced Industrial Science and Technology (AIST) from February 7 to March 22 of 2002 using AC power. The measured magnetic field variations were compared with groundwater level, electric field and geo-electric pulse current variations measured at AIST in order to investigate the source of magnetic field radiation found during the long term monitoring.         Archaeometric prospection with high-T/sub c/ SQUID gradiometers    A. Chwala, R. Ijsselsteijn, T. May, N. Oukhanski, T. Schuler, V. Schultze, R. Stolz and H.G. Meyer Summary: Mapping of the Earth's magnetic field or its gradient is a widely used method in archaeological prospection. The use of SQUID's promises to be advantageous for archaeometry, since they combine a high field resolution with a large bandwidth. Compared to conventional Cs vapor sensors SQUIDs can be used for much faster magnetic mapping, allowing, for the first time, the investigation of huge archaeological features in a reasonable time period. We have investigated several SQUID systems for their usability in archaeometry by measuring a Neolithic double ring ditch enclosure. We have used two electronic High Temperature Superconductor SQUID (HTS SQUID) gradiometers with base lengths of about 60 cm and a Low Temperature Superconductor SQUID (LTS SQUID) gradiometer with a base length of 4 cm. Their intrinsic magnetic field resolution was 6 pT/m//spl radic/Hz for the HTS SQUID gradiometers and about 0.1 pT/m//spl radic/Hz for the LTS SQUID gradiometer. In contrast to Cs vapor gradiometers, which measure the gradient of the total magnetic field, SQUID gradiometers measure one component of the gradient tensor. Since measurements have to be performed whilst movement in the background of the Earth's magnetic field, balancing is the limiting factor for the magnetic gradient field resolution of vector gradiometers.         Two dimensional superconducting quantum interference filters    J. Oppenlander, C. Haussler, T. Trauble, P. Caputo, J. Tomes, A. Friesch and N. Schopohl Summary: We have successfully developed a novel superconducting quantum interferometer based on Josephson junction networks with unconventional loop size distribution. For distinct theoretically determined distributions, the magnetic field B dependent dc voltage V(B) of the interferometer possesses a unique delta-peak like characteristics around B=0. Such devices are called Superconducting Quantum Interference Filters (SQIFs). The unique voltage response of SQIFs allows novel applications, e.g., absolute magnetic field sensors, high speed logical switches and non hysteretic low noise amplifiers which can be directly connected to standard room temperature electronics. In this paper we present new experimental and theoretical results on high performance two dimensional Superconducting Quantum Interference Filters (2D SQIFs). Such 2D SQIFs can be used as absolute magnetic field sensors. Our results indicate that due to the scaling behavior of the flux to voltage transfer function and the scaling of the white output noise, a highly sensitive absolute field sensor based on 2D SQIFs can be very small in size.         High-T/sub c/ superconducting quantum interference filters for sensitive magnetometers    V. Schultze, R. Ijsselsteijn, H.-G. Meyer, J. Oppenlander, C. Haussler and N. Schopohl Summary: We present several kinds of Superconducting Quantum Interference Filters (SQIFs) which are all realized with high-T/sub c/ superconductors. All SQIFs use the same configuration of 30 loops of different size. The properties of these SQIF types - serial arrays, parallel arrays, and a combination of both - are discussed concerning their usefulness for magnetometry. These properties are the formation of the desired single voltage peak, its peak voltage and full width at half maximum, and the magnetic field noise. Concerning all parameters an improvement can be achieved with SQIFs of all types compared to a single SQUID.         Digital spatial filter made from a SQUID array    A.C. Bruno, M.A. Espy, D.D. Clark, A.N. Matlashov and R.H. Kraus Jr. Summary: A linear array of high transition temperature SQUID, has been configured to work as digital spatial filters. The SQUID filters can be configured to obtain a desired spatial frequency response. We describe their design using a technique known as Frequency Sampling, which consists of specifying a discrete spatial frequency response for the SQUID array spatial filter. We then apply that sequence to the inverse Discrete Fourier Transform to get the spatial domain gain of each SQUID and the baseline. Several designs for spatial band-pass filters are proposed and checked experimentally. The results show that while keeping or even increasing the noise rejection obtained with conventional gradiometers, the SQUID filters preserve the original signal characteristics of the source.         Dynamic performance of single-stage SQUID current amplifier with varying device parameters    Jin-Mok Kim, Yong-Ho Lee, Hyukchan Kwon and Yang-Sup Song Summary: We have fabricated a single-stage superconducting quantum interference device (SQUID) current amplifier for detecting pulse outputs of a superconducting microcalorimeter. The current amplifier is made of a double relaxation oscillation SQUID (DROS) that provides a high flux-to-voltage transfer of about 1mV//spl Phi//sub 0/ and a large modulation depth of 80 /spl mu/V. Due to the high flux-to-voltage transfer, the voltage output of the DROS is measured directly with a room-temperature dc preamplifier. The bandwidth of the current amplifier is measured to be 1.2 MHz. Typical noise of the DROS current amplifier is about 6 pA//spl radic/Hz.         Optimization of fabrication conditions for multilayer structures with La-doped YBCO groundplane    M. Horibe, H. Wakana, Y. Ishimaru, S. Adachi, Y. Tarutani and K. Tanabe Summary: We have examined and optimized the fabrication conditions for multilayer structures needed in high-T/sub c/ single flux quantum circuits. La/sub 0.2/Y/sub 0.9/Ba/sub 1.9/Cu/sub 3/O/sub x/ (La-YBCO) was chosen as a material for both the groundplane (GP) and base-electrode. The GP-La-YBCO was deposited at 740/spl deg/C by a sputtering method and the optimized 300 nm thick film exhibited a typical average roughness (Ra) of 2 nm. (La,Sr)/sub 2/AlTaO/sub 6/ (LSAT) isolation layer sputter-deposited under the same conditions as the GP-La-YBCO showed good crystallinity and a relatively flat surface (Ra/spl sim/2 nm). For the deposition of La-YBCO base electrode, a slightly lower substrate temperature (720/spl deg/C) resulted in a smooth film surface (Ra/spl sim/2 nm), while higher substrate temperatures led to appearance of precipitates and hollows on the La-YBCO and columnar morphology of the LSAT layer which was revealed by cross-sectional SEM observation. Interface-engineered ramp-edge junctions fabricated on LSAT/GP-La-YBCO multilayer structures exhibited RCSJ-like I-V characteristics with typical I/sub c/R/sub n/ products of 2 mV at 4.2 K. Excellent isolation between the GP and the base electrode better than 10/sup 9/ /spl Omega//cm/sup 2/ was also confirmed.         Effect of lanthanum doping of YBaCuO electrodes on the characteristics of modified-interface edge junctions    T. Satoh, M. Maruyama and M. Hidaka Summary: With the aim of improving the interface-modification process - a standard technique for forming the barrier in high-temperature superconducting Josephson junctions, lanthanum doping of a YBaCuO electrode was successfully attempted in this study. Accordingly, it was confirmed that lanthanum doping significantly affects junction characteristics; that is, it produces a lower critical current density and higher normal state resistance. In other words, lanthanum doping increased the annealing temperature or time for the barrier-formation process. These effects are advantageous for the growth of the counter layer, and for high-temperature processes made after the junction fabrication, such as upper-layer groundplane integration. It was confirmed that the lanthanum doping of the base electrode has a significant effect on the junction characteristics. It was also found that the lanthanum doping produces benefits in terms of higher critical current and normal-state resistance product.         Novel in-situ fabricated Josephson junctions: trilayer on a substrate slope    B. Hogberg and Z. Ivanov Summary: We demonstrate a high-temperature superconductor (HTS) Josephson junction geometry using only in situ interfaces and with the current flowing in the a-b plane of the HTS. The trilayer on a substrate slope (TOSS) junction is a HTS-barrier-HTS structure deposited in situ on top of a pre-etched slope in the substrate. We present initial results on the fabrication and testing of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// TOSS junctions with a Ga-doped PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// barrier. These devices display resistively shunted junction like I-V characteristics with characteristic voltages up to 5 mV at 4.2 K. The TOSS junction concept is of interest for fundamental studies of interfaces in HTS and can also be applied to an integrated circuit technology.         Fabrication of all YBaCuO trilayer Josephson junctions with YBaCuO wiring layer    H. Sato, E. Fujimoto, T. Yamada and H. Akoh Summary: We report a fabrication process of c-axis oriented all YBaCuO trilayer Josephson junctions with YBaCuO wiring layers. The trilayer junctions consisted of YBaCuO (170nm)/PrBaCuO (28 nm)/YBaCuO (170 nm) structures. CeO/sub 2/ films (520nm) and YBaCuO films (1.2 /spl mu/m) were used as insulating layers and wiring layers, respectively. A junction with a dimension of 7 /spl mu/m/spl times/7 /spl mu/m showed a critical current I/sub c/ of 1.6 mA and a junction resistance R/sub n/ of 1.2 /spl Omega/ at 4.2 K. The values of the critical current density and the I/sub c/R/sub n/ product were estimated to be 3.3kA/cm/sup 2/ and 1.9 mV, respectively. Note that the junction exhibited I/sub c/R/sub n/ product of 1.0 mV even at 30 K. From these results, the junction is promising candidate for satisfying the requirements for HTS integrated circuits.         Solution-growth of ultra-thin, insulating layers of zirconia for passivation and tunnel junction fabrication on YBCO thin films    P.J. Hentges, G. Westwood, H. Aubin, W.G. Klemperer and L.H. Greene Summary: Planar tunnel junctions fabricated with multilayers of solution-deposited zirconia as the insulating tunnel barrier on [001]- and [103]-oriented Y/sub 2/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films display tunneling spectra with features as sharp, or sharper, than any planar tunneling spectra reported for YBCO to date. The multilayers of zirconia are deposited onto the thin film surfaces by repeated reaction with tetra-n-propyl orthozirconate in hydrocarbon solution followed by reaction with water in n-propanol solution at ambient temperature. Gap-like peaks are observed for all thin-film orientations, and well-defined zero-bias conductance dips and zero-bias peaks are observed for [001]- and [103]-YBCO surfaces, respectively. Junctions exhibiting the sharpest features do not show field-induced nor spontaneous splittings, consistent with what is predicted for a narrow tunneling cone. The zirconia multilayers appear to stabilize YBCO surfaces with respect to atmospheric degradation, and tunnel junctions fabricated from aged samples of zirconia on YBCO that had been stored for one year at ambient temperature display conductance characteristics comparable to those obtained from freshly prepared samples.         Investigation of properties of stacked-type interface-treated Josephson junctions fabricated with PrGaO/sub 3/ doping process    Y. Yoshinaga, S. Izawa, K. Wakita, T. Kito, M. Inoue, A. Fujimaki and H. Hayakawa Summary: We have investigated how surface morphology of base YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films affects the properties of the stacked-type interface-treated junctions (ITJ) with the PrGaO/sub 3/ (PGO) doping process. In the ITJs, the junction barriers are formed by Ar ion milling and subsequent annealing, without depositing artificial barriers. The PGO doping process was carried out for eliminating excess currents of the junctions. Our results suggest that the YBCO films suitable for the junctions should consist of similar size grains, and do not contain any precipitates. Furthermore, the morphology should not be changed after the Ar ion milling. The nine junctions fabricated on such a film exhibit the averaged critical current density (J/sub c/) on the chip of 9.0/spl times/10/sup 3/ A/cm/sup 2/, the small 1/spl sigma/ spread of 5.6% in the J/sub c/, and the averaged I/sub c/R/sub n/ product on the chip of 1.5 mV with overdamped characteristics at 4.2 K.         A novel multilayer process for HTS SFQ circuit    H. Katsuno, S. Inoue, T. Nagano and J. Yoshida Summary: We have developed a novel multilayer process for HTS-SFQ circuits adopting a NBCO groundplane and tin-oxide isolation layers, and fabricated an HTS-SFQ ring oscillator circuit including 21 Josephson junctions. The junctions on the buried groundplane exhibited excellent Josephson characteristics with a magnetic modulation of I/sub c/ exceeding 90%, and an I/sub c/R/sub n/ product of 0.75 mV at 30 K. The sheet inductance of the wiring layer at 30 K was evaluated to be 1.1 pH for the counter-electrode layer, and 1.3 pH for the base-electrode layer. We confirmed the correct operation of the 10-stage ring oscillator at 20-30 K. The maximum dc output voltage of the ring oscillator was 0.06 mV at 30 K and 0.12 mV at 20 K, indicating the signal delay per stage of 3.4 ps and 1.8 ps, respectively.         In-situ characterization of engineered surfaces of c-YBCO films for sandwich type junctions    N. Terada, K. Ohki, A. Ohtomi, S. Miyanomae, K. Obara, H. Akoh, H. Sato, T. Yamada and E. Fujimoto Summary: In-situ characterization of the surface nature and re-crystallization of c-axis YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films engineered by Ar ion etching and subsequent annealing has been carried out. Effects of kinetic energy of the Ar ions and annealing conditions have been examined. RHEED and XPS measurements showed that etching with the ion energy above a few hundred eV for longer than 60 sec yielded insulating and amorphous surface layers. Analysis of XPS core signals revealed a deviation of surface composition toward a Y-rich one with an increase of the product of [ion flux] /spl times/ [ion energy] /spl times/ [etching time], whereas thickness and degree of reduction of the amorphous layer were dominated by the kinetic energy of the Ar ions: the higher ion energy resulted in a thicker and less reduced layer. For the amorphous layer created by the 500 eV-beam etching, oxidation-annealing at 630/spl deg/C for 1h is sufficient to convert it into a metallic 123 structure. For the surfaces treated by the 1 keV etching, an insulating feature was conserved even after the annealing of 710/spl deg/C, 1 h or 660/spl deg/C, 3 h. These results mean that the higher energy etching and the shorter subsequent process are desired to properly fabricate barrier layers for the interface-engineered sandwich type of junctions.         Fabrication of YBCO multi-layer wiring with a polished PBCO insulator    Y. Wada, K. Kuroda and T. Takami Summary: In this study we have fabricated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO)/PrBa/sub 2/Cu/sub 3/O/sub 7-x/ (PBCO)/YBCO multi-layer wiring and investigated its properties. We found that a polishing technique is extremely effective in the elimination of precipitates on the films without degradation in film properties. YBCO/polished-PBCO/polished-YBCO crossover with 50 /spl mu/m square of overlap showed resistance of a degree of k/spl Omega/ at 4.2 K while a contact of two YBCO layers through a 10 /spl mu/m square of hole in the PBCO layer exhibited good superconductivity.         Sub-micron thin film intrinsic Josephson junctions    P.A. Warburton, A.R. Kuzhakhmetov, C. Bell, G. Burnell, M.G. Blamire, H. Wu, C.R.M. Grovenor and H. Schneidewind Summary: We have fabricated sub-micron intrinsic Josephson junctions in thin films of Tl-Ba-Ca-Cu-O using two differing techniques suited to different applications. By using lateral focussed ion-beam milling we have created arrays of intrinsic junctions in c-axis oriented films. Such arrays, with areas as low as 0.25 /spl mu/m/sup 2/, display large hysteresis comparable to that observed in single-crystal intrinsic junctions. By using normal focussed ion-beam milling we have created arrays in mis-aligned films grown on vicinal substrates. In arrays of area less than 0.4 /spl mu/m/sup 2/ we observe Josephson phase diffusion and a suppressed critical current, showing that charging effects may be significant in these junctions.         The 0 and pi contact array model of bicrystal junctions and interferometers    V.K. Kornev, I.I. Soloviev, N.V. Klenov, N.F. Pedersen, I.V. Borisenko, P.B. Mozhaev and G.A. Ovsyannikov Summary: The array model of the faceted bicrystal Josephson junctions has been developed more comprehensively. The facet size and the facet critical current dependence on magnetic field are taken in to consideration. The model can be successfully used with high-performance software meant for numerical simulation of the lumped Josephson junction circuits, e.g., PSCAN, WinS. The based on the model results for critical current dependence on applied magnetic field are compared with experimental data for the bicrictal junctions fabricated by dc sputtering at high pressure. Impact of no sinusoidal Josephson current - phase relation on the dc interferometer critical current as a function of magnetic field is analyzed as well.         Lattice-matched, large-grain HTS films for reproducible Josephson junctions    J. Talvacchio, D.A. Kahler, A. Kirschenbaum and J.M. Murduck Summary: Several novel techniques are now available to dramatically increase the grain size of epitaxial Rare-earth-BCO films so they are effectively single crystals. Our motivation is to use single-crystal films for base electrodes of edge SNS junctions to improve their reproducibility. We employed the technique of "tri-phase epitaxy" to grow films by liquid phase epitaxy in a pulsed laser deposition system and examined the surface morphology and crystal structure of the films. We tried several techniques for in-situ monitoring of a Ba-Cu liquid flux on the surface of the film during growth - including resistivity and emissivity measurements - but found that the only way to be certain that we had a liquid phase on the sample surface was from the dendritic crystal patterns that formed after cooling the samples. We observed series of small cracks in the resulting films, presumably due to stress from lattice-match and thermal expansion mismatch with the substrates so we developed a solid solution of YBa/sub 2/Cu/sub 3/O/sub 7/ and NdBa/sub 2/Cu/sub 3/O/sub 7/ to match the lattice of our substrates to better than 0.1%.         Junction characteristics and magnetic field dependencies of low noise step edge junction rf-SQUIDs for unshielded applications    M. Fardmanesh, J. Schubert, R. Akram, A. Bozbey, M. Bick, M. Banzet, D. Lomparski, W. Zander, Yi Zhang and H.-J. Krause Summary: Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO/sub 3/ substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, I/sub c/, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz/sup 1/2/ down to few Hz at 77 K while measured with conventional tank circuits. The I/sub c/ of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.         A high-T/sub c/ second-order gradiometer for use in an unshielded environment    P.P. Broussov, E.J. Romans, C. Carr, G.B. Donaldson and C.M. Pegrum Summary: We have developed a highly balanced five-channel planar high-T/sub c/ second-order SQUID gradiometer. The gradiometer incorporates two long-baseline, first-order single-layer SQUID gradiometers and three orthogonal flux-gate magnetometers used as reference sensors. The outputs of the five channels are combined synthetically on a computer to form a fully balanced second-order gradiometer. We have investigated the use of both time-domain and frequency-domain balancing. We report on the performance of the system when used to measure weak magnetic signals in an unshielded environment.         Long baseline hardware gradiometer based on HTS rf-SQUIDs with substrate resonators    G.I. Panaitov, Yi Zhang, H.-J. Krause, J. Schubert and M. Banzet Summary: We have developed an asymmetric thin film first order gradiometer based on an HTS rf-SQUID. A coupling scheme uses an SrTiO/sub 3/ substrate resonator as an rf-tank circuit which simplifies the gradiometer balancing. Advantage of the technique is that gradiometers with very long baseline can be fabricated. The performance of 13 mm and 33 mm baseline SQUID gradiometers is presented. The gradiometers have been successfully used in applications for nondestructive evaluation of materials.         Is it possible to fabricate a relaxation oscillation SQUID, using high temperature superconductors and grain boundary junctions?    E.J. Tarte, P.F. McBrien, G. Burnell, E.J. Romans, C.M. Pegrum and M.G. Blamire Summary: We discuss whether it would be possible to fabricate Relaxation Oscillation SQUIDs (ROSs) using high temperature superconductors (HTSs). This would require HTS junctions with significant hysteresis at high temperatures and we have attempted to induce this using external capacitive shunts. We achieved McCumber parameter values as large as /spl beta//sub c/=4.5 at 40 K and were able to maintain /spl beta//sub c/>1 to 72 K. However we found that small junction resistances, thermal noise associated with high temperature operation and transmission line resonances in the shunt capacitor limit the value of /spl beta//sub c/. Using the parameters we obtained, we have simulated the performance of a ROS at 60 K and found that voltage pulses were generated. However, the small time averaged voltage across the ROS, would make it impossible to construct a working D-ROS. Despite this, it may be possible to detect the pulses and use them to construct a digital SQUID.         Experimental determination of HTS dc-SQUID amplifier inductance and noise performance    E.E. Mitchell, D.L. Tilbrook, J.C. MacFarlane and C.P. Foley Summary: The inductance L/sub sq/, transimpedance Z, transfer function V/sub /spl Phi// and flux noise S/sub /spl Phi// have been experimentally determined, in open loop mode, for a series of simple dc-SQUID amplifiers which varied only in the length of the loop. The SQUID design had no input flux transformer but included a current path for directly injecting flux into the loop. Correlations between these parameters were obtained which compare favorably with theoretical estimates. We confirm that the best device performance (small S/sub /spl Phi//) is obtained if L/sub sq/ is kept small whilst V/sub /spl Phi// is maximized; the latter was achieved in one device by a novel "ion-beam trimming" technique.         Fabrication and characterization of high-T/sub c/ SQUID magnetometer with damping resistance    M. Matsuda, T. Otowa, T. Matsuura, S. Kuriki, Y. Kawaguchi and K. Takahashi Summary: Effects of damping resistance on current versus voltage (I-V) characteristics for high-T/sub c/ superconducting quantum interference devices (SQUIDs) were studied. In the transverse-type SQUID with coplanar strip lines, parasitic capacitance originating from the large dielectric constant of SrTiO/sub 3/ substrates can induce resonance structures on I-V curves and degrade the modulation voltage. In our simulations, it is shown that the modulation voltage is much improved by using damping resistance. However, the obtained experimental results for our SQUIDs with Au damping do not agree well with those in the simulations. The discrepancy is likely due to existence of the large contact resistance between Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films.         Off-diagonal 2nd-order SQUID gradiometer made from a single layer of high T/sub c/ superconductor film    Soon-Gul Lee, Yunseok Hwang and In-Seon Kim Summary: We developed a transverse second-order SQUID gradiometer from a single layer of high T/sub c/ film, which can measure the off-diagonal element d/sup 2/B/sub z//dxdy of the second-order field gradient. In this design, four-way 'clover-leaf' pick-up loops are coupled directly to a 4-junction dc SQUID in such a way that the coupling polarity of the two diagonal loops is opposite to that of the other two loops. The pickup loops are intrinsically balanced for both uniform field and the 1st-order gradient. We made the device by using a pulsed-laser deposition and Ar ion-milling with photolithography. The entire structure was made on a single crystalline SrTiO/sub 3/ substrate. The gradiometer responded sensitively to the 2nd-order gradient. Induced field focused on the SQUID loop by the screening current flowing along the device perimeter is believed the major off-balancing factor, which can be balanced by adding a closed superconducting loop just outside the device perimeter or merging facing sides of neighboring loops.         YBa/sub 2/Cu/sub 3/O/sub X/ submicron Josephson junctions on bicrystal substrates    I.A. Volkov, M.L. Chuharkin, O.V. Snigirev and M.L. Ranchinski Summary: A technological process based on e-beam lithography and ion beam etching of YBa/sub 2/Cu/sub 3/O/sub X/ (YBCO) film through carbon mask is applied to fabricate a series of YBCO dc SQUIDs on SrTiO/sub 3/ 30/spl deg/-bicrystal substrates. The width of Josephson junctions used in SQUIDs ranges from 0.6 /spl mu/m to 1 /spl mu/m. The character of the temperature dependence of the junctions critical current enables one to confirm the realization of d-wave pairing mechanism as well as the presence of localized states in the grain boundary region. The diffraction pattern of submicron junctions is discussed in relation to their further application in SQUIDs for task of scanning SQUID microscopy in high magnetic fields.         Optimization and passivation of HTS step-edge Josephson junction rf SQUIDs    Jia Du Summary: In this work, various methods of improving the performance and yield of our step-edge junction rf SQUIDs are described. These methods include adjusting the YBCO thin film thickness and trimming of the device parameters by ion beam etching and heat annealing. Significant improvement in SQUID performance and yield was demonstrated by employing these techniques. The effects of passivation of the rf SQUIDs by ex-situ deposition of an amorphous-YBCO thin film were also studied. No adverse effects were observed for the noise performance of the devices due to passivation and long-term stability was obtained.         Magnesium diboride superconducting quantum interference devices fabricated by focused ion beam    G. Burnell, E.J. Tarte, K.A. Yates, Dae-Joon Kang, D.A. Ansell, S.H. Moon, H.N. Lee, B. Oh and M.G. Blamire Summary: We have recently developed a technique for fabricating Superconductor-Normal-Superconductor (SNS) junctions in MgB/sub 2/ thin films using a focused ion beam (FIB). These junctions show a strong modulation of the critical current by applied magnetic field and microwaves. We have made Superconducting Quantum Interference Devices (SQUIDs) with directly coupled pick-up loops using this technique which show large voltage modulations (/spl sim/200 /spl mu/V at 6 K) and a white noise level of 15 /spl mu//spl Phi//sub 0/Hz/sup -1/2/ at 5 kHz. In this work we present the latest results from our devices. We are studying the nature of the barrier created by our fabrication process and also report a preliminary Raman scattering and transport measurement study of resistors made with this technique.         Noise, junction characteristics, and magnetic field dependencies of bicrystal grain boundary junction rf-SQUIDs    M. Fardmanesh, J. Schubert, R. Akram, M. Bick, M. Banzet, W. Zander, Yi Zhang and H.-J. Krause Summary: Bicrystal grain boundary (GB) Josephson junctions and rf-SQUID's were made of 200 nm thick PLD YBCO films on bi-crystal SrTiO/sub 3/ substrates. The junction characteristics were studied to investigate optimal parameters in the rf-SQUID layout designs and the limits imposed by the technology. The I/sub c/ of 3 to 8 /spl mu/m wide test junctions scaled with the junction widths, showing clear linear RSJ-like I-V characteristics at 77 K. All the junctions showed hysteretic RCSJ-like behavior at very low temperatures. Classical Josephson flux motion type (long junction) nonlinearity in I-V curves of all the junctions was also observed at lower temperatures with systematic dependence on the junction widths. Measurements of the magnetic field dependence of the I/sub c/ of the junctions resulted in junction width dependent well-defined Fraunhofer-pattern like characteristics. The obtained characteristics of the junctions led to feasible criteria for the rf-SQUID layouts with desired device characteristics. Rf-SQUID's were made using designs for optimal performance at 77 K while avoiding large superconducting weak links across the substrate GB. Devices with low noise characteristics and junction field sensitivities proper for operation in environmental background magnetic fields were obtained. A nonsystematic spread of optimal working temperature of the SQUID's were also observed which is associated to the spread of the junction parameters caused by the defects at the GB of substrates.         Structure and formation mechanism of interface-modified layer in ramp-edge Josephson junctions with La-doped 123-type superconducting electrodes    S. Adachi, H. Wakana, Yuan Wu, Y. Ishimaru, Y. Tarutani and K. Tanabe Summary: Ramp-edge-type Josephson junctions (JJ) with interface-modified barriers were fabricated. Yb/sub 0.9/La/sub 0.2/Ba/sub 1.9/Cu/sub 3/O/sub y/ and Y/sub 0.9/La/sub 0.2/Ba/sub 1.9/Cu/sub 3/O/sub y/ were used for the counter- and base-electrodes, respectively. Reliable junctions with I/sub c//spl sime/1 mA and 1/spl sigma/=6.5-8.0% for 25-100 JJ arrays were reproducibly obtained. For the junctions, the structure and composition of the barrier were investigated using a transmission electron microscope. A rather homogeneous layer with a thickness of a few nm was observed in the barrier region. The layer had a cubic lattice with a/spl sime/0.39/spl times/0.40 nm/sup 2/ and its cationic composition was Ba:La:(Y+Yb):Cu=38:10:20:32. It implies that the barrier consists of a thin layer of a cubic perovskite (Ba,La)(Y,Yb,Cu)O/sub 3/. The existence of La seems to stabilize the cubic perovskite and improve homogeneity of the barrier layer.         Josephson effect in Nb/Au/YBCO heterojunctions    G.A. Ovsyannikov, P.V. Komissinski, E. Il'ichev, Y.V. Kislinski and Z.G. Ivanov Summary: c-axis oriented and 11/spl deg/ tilted YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) thin films were deposited on [110] NdGaO/sub 3/ and (7 10 2) NdGaO/sub 3/ substrates correspondingly. Nb/Au/YBCO heterojunctions were fabricated using photolithography and ion beam milling. I-V curves of the heterojunctions based on tilted YBCO films showed zero bias anomaly conductance peak and large excess current. We observed the second harmonic (/spl prop/ sin 2/spl phi/) of superconducting current in Nb/Au/YBCO heterojunctions in c-axis oriented YBCO films, although sinusoidal superconducting current-phase relation has been measured for heterojunctions in tilted ones. The obtained results are explained by d/spl plusmn/s symmetry of YBCO superconducting order parameter.         Microstructural study in heteroepitaxial YBa/sub 2/Cu/sub 3/O/sub 7//Nd/sub 2/CuO/sub 4/ multi-layers by using electron microscopy    J. Gao, Y.L. Cheung and S.M. So Summary: Neodymium copper oxide Nd/sub 2/CuO/sub 4/ (NCO) has been applied as a buffer material to improve the epitaxy of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) thin films on reactive substrates and as a potential barrier to construct multi-layer junctions. The microstructures and interfaces in heteroepitaxial Nd/sub 2/CuO/sub 4//YBCO multi-layer have been characterized by using an electron microscopy. Cross-sectional images obtained on a transmission electron microscopy (TEM) revealed an atomically sharp boundary between layers, underlining the excellent compatibility of NCO with YBCO. No chemical reaction occurred between film and substrate. It was found that all layers grow highly epitaxially with their c-axis perpendicular to the substrate surface. On the other hand, various defects such as mis-oriented grains and stacking faults were found near the interfaces.         High quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions and junction arrays fabricated by masked proton beam irradiation damage    Nianhua Peng, Dae Joon Kang, C. Jeynes, R.P. Webb, D.F. Moore, M.G. Blamire and I.R. Chakarov Summary: High quality single Josephson junctions and junction arrays with 10 junctions in series have been fabricated using masked proton beam irradiation damage technology. Monte Carlo simulation of the irradiation damage profile underneath the metal mask has been carried out systematically to guide the metal mask structure design. A high resolution and high aspect ratio metal mask opening was fabricated by focused 30 keV Ga ion beam milling. Various nonconducting oxide buffer layers have been investigated for a Ga contamination free mask fabrication. A contamination free irradiation process and subsequent removal of metal mask after ion irradiation are the keys for the improved properties of junctions fabricated with YBCO.         Probing the phase diagram of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// with tunneling spectroscopy    L. Ozyuzer, J.F. Zasadzinski, K.E. Gray, D.G. Hinks and N. Miyakawa Summary: Tunneling measurements are performed on Ca-rich single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (Bi2212), with various oxygen doping levels, using a novel point contact method. At 4.2 K, SIN and SIS tunnel junctions are obtained with well-defined quasiparticle peaks, robust dip and hump features and in some cases Josephson currents. The doping dependence of tunneling conductances of Ca-rich Bi2212 are analyzed and compared to stoichiometric Bi2212. A similar profile of energy gap vs. doping concentration is found although the Ca-rich samples have a slightly smaller optimum T/sub c/ and therefore smaller gap values for any doping level. The evolution of tunneling conductance peak height to background ratios with hole concentration are compared. For a given doping level, the Ca-rich spectra showed more broadened features compared to the stoichiometric counterparts, most likely due to increased disorder from the excess Ca. Comparison of the dip and hump features has provided some potential insights into their origins.         Influence of charging energy on Cooper pair tunneling in Bi-2212 small intrinsic Josephson junctions    T. Kawae, T. Yasuda, S.-J. Kim, K. Nakajima and T. Yamashita Summary: We have investigated the properties of submicron intrinsic Josephson junctions (IJJs) fabricated on Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// liquid phase epitaxy film. The IJJs with junction area S<2 /spl mu/m/sup 2/ showed individual current-voltage curves, which have suppressed 1st branch and unsuppressed other branches. This suppression was observed systematically as an increase the ratio of charging energy and Josephson coupling energy. It is expected that such suppressions are due to charging effect in IJJs.         BSCCO intrinsic Josephson junctions for microwave detection    T. Tachiki, T. Uchida and Y. Yasuoka Summary: Microwave-induced steps were observed in I-V characteristics of intrinsic Josephson junctions fabricated on an overdoped BSCCO single crystal with a weak magnetic field parallel to the c-axis. Voltage intervals between the steps under the irradiation of 12.2, 13.2 and 13.9 GHz microwaves were independent of the microwave power and proportional to the frequency. From the measurement of voltage intervals, it was found that all the junctions in the fabricated junction stack simultaneously produced Shapiro steps, assuming that the steps are Shapiro steps.         Temperature dependence of the low-frequency noise properties in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ intrinsic Josephson junctions    A. Saito, H. Ishida, A. Irie, A. Kawakami, Z. Wang, G. Oya and K. Hamasaki Summary: We have measured the temperature dependence of the low-frequency noise properties across for mesa stacks of intrinsic Josephson junctions (IJJs) in single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (BSCCO) in the absence of an external magnetic field. The measured curves for noise spectrum density S/sub V/(f) showed a 1/f frequency dependence at temperatures in the range from 4.3 K to 150 K except 36 K. We estimated the magnitude of the S/sub V/(f) by using Rogers and Buhrman's empirical theory and Machlup's formula. From the observed curves for S/sub V/(f), we estimated a 1/f noise level /spl eta/ for a BSCCO IJJ biased at a sub-gap voltage of approximately 10/sup -5/ /spl mu/m/sup 2/, and this value was almost completely independent of temperature in the range between 4.3 K and 40 K. We also found that the /spl eta/ values above T/sub c/ were smaller by a factor of approximately 10 than those below T/sub c/. The /spl eta/ value for the BSCCO IJJ is approximately two orders of magnitude greater than for an epitaxial NbN/MgO/NbN tunnel junction biased above-gap voltage. We consider that the observed variation in the noise level with temperature is not interpretable in terms of a magnetic origin and the 1/f noise in a BSCCO IJJ may be somehow associated with stress or defects in the BiO and/or SrO layers act as tunnel barriers.         RF-induced steps in intrinsic Josephson junctions in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/    A. Irie, Y. Kurosu and G. Oya Summary: We have investigated the RF-induced steps in intrinsic Josephson junctions in mesa-shaped Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ single crystals. By applying RF signal in the frequency range 2-20 GHz to the mesa, two types of responses were observed depending on the frequency of the applied microwave. One is the Shapiro step response observed at the frequencies above the Josephson plasma frequency for surface junction. Another is the microwave-induced vortex flow response for surface and inner junctions. We found that the junction size is also the key condition for the observation of Shapiro steps together with the frequency of applied microwave.         Ion implantation effects on tunneling properties of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8+y/ intrinsic Josephson junctions    K. Nakajima, J. Watanabe, Hua-Bing Wang, Jian Chen and T. Yamashita Summary: We propose a feasible method to modify the tunneling properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/ (Bi-2212) intrinsic Josephson junctions(IJJ's) using silicon ion implantation. The implantation is performed on 150 nm-height mesas at an acceleration voltage of 80 keV with doses ranging from 1/spl times/10/sup 13/ to 5/spl times/10/sup 15/ ions/cm/sup 2/. The critical current of IJJ's rapidly decreases with increasing doses, while the critical temperature hardly changes. The small amount of Si impurities affect on the interlayer coupling but not the gap of the CuO/sub 2/ bilayers. The RF response of a Si-implanted IJJ is demonstrated and reveals clear Shapiro steps as the plasma frequency decreases.         Josephson voltage standard circuit operation with a pulse tube cooler    G. Wende, M. Schubert, T. May, L. Fritzsch, H.-G. Meyer, G. Thummes, Y. Kucukkaplan, L.M. Qiu, J. Kohlmann, J. Niemeyer, H. Hofmeister and J. Scheerer Summary: For a more wide-spread use of Josephson voltage standards, cryogen-free operation, by means of an appropriate closed-cycle refrigerator, is highly desirable. In this work we present a low-noise pulse tube cooler (PTC) that is capable to cool the voltage standard circuits to temperatures below 4 K. As a low loss dielectric waveguide with a very small thermal conductivity a Teflon strip was used for the microwave transmission. The matched transition from the WR12 rectangular waveguide to the Teflon strip and vice versa was made using special exponential tapers. Programmable 1 Volt 14 bit SINIS and 10 Volt SIS arrays assembled in the PTC operated well, i.e., demonstrated a similar performance to that measured in liquid helium. The Josephson junction arrays were integrated in coplanar strips instead of the commonly used microstriplines for the microwave transmission lines. The 1 Volt SINIS array contained 8192 Josephson junctions (JJs). It generated an inherently stable Josephson voltage step of 1.19 V at a driving microwave frequency of 70 GHz. The step width was 150 /spl mu/A and the critical current of the junctions was 550 /spl mu/A. Similar results were obtained under liquid helium cooling conditions. In another experiment a 10 Volt voltage standard chip with 19700 SIS JJs was installed. It was possible to generate stable Shapiro steps at the 10 V level.         Operation of a NbN-based programmable Josephson voltage standard chip with a compact refrigeration system    A. Shoji, H. Yamamori, M. Ishizaki, S.P. Benz and P.D. Dresselhaus Summary: A refrigeration system was designed and constructed for realizing a liquid-He-free programmable Josephson voltage standard. The system is equipped with a two-stage Gifford-McMahon cooler, a thermal-radiation shield, a magnetic-field shield and semi-rigid coaxial cables to supply microwave power to a chip. The performance of the system was examined by use of a NbN-based 8-bit digital-to-analog converter (DAC) chip designed as a 1 V programmable voltage standard. When operated at 8.5 K on the cryocooler, constant-voltage steps with amplitudes greater than 1 mA were observed for every segment of junction arrays on the chip.         4 K cryocooler implementation of a DC programmable voltage standard    C.J. Burroughs, R.J. Webber, P.D. Dresselhaus and S.P. Benz Summary: NIST and HYPRES, Inc. have been collaborating to develop a 1 Volt DC programmable Josephson voltage standard (PJVS) that operates on a closed-cycle refrigerator. The goal of this work is to construct a platform that will allow the chip to work at 4 K without liquid helium, thereby making the system more convenient and eliminating the need for users to handle liquid cryogens. In our existing PJVS systems, the Josephson chip temperature is the only parameter that is not computer controlled. The addition of a cryocooler will allow automated warming and cooling of the Josephson device and enable an intrinsic voltage standard system in which every control function is automated, and the only required user input is the desired output voltage. The cryocooler package is designed to allow PJVS chips to be easily interchanged between the cryocooler and liquid helium cryoprobes.         Zero-crossing Shapiro step in a three-junction SQUID magnetically coupled with two phase-shifted RF signals    Y. Mizugaki, Jian Chen, S. Nishikata, K. Sugi, K. Nakajima and T. Yamashita Summary: We demonstrate a zero-crossing Shapiro step in a three-junction SQUID (3J-SQUID) coupled with two phase-shifted RF signals. The operation is based on periodic flux quantum transitions in the 3J-SQUID under the zero- and negatively-biasing conditions. A test circuit is fabricated using a Nb/AlO/sub x//Nb junction technology. When we feed RF signals up to 10.5 GHz, we observe a Shapiro step crossing the zero-current axis at the voltage position of the 1st order. The experimental current-voltage characteristics are quantitatively reproduced by simulation. Zero-crossing conditions for the DC offset flux and the RF power are obtained experimentally, which is also confirmed by simulation. A programmable Josephson voltage standard is discussed as one of the possible applications.         Stacked SNS Josephson junction arrays for quantum voltage standards    P.D. Dresselhaus, Yonuk Chong, J.H. Plantenberg and S.P. Benz Summary: NIST is using and developing superconductor-normal metal-superconductor (SNS) Josephson arrays for both programmable DC and AC voltage standards. Increasing the output voltage is difficult because the output voltage per junction is small; hence series arrays with large numbers of junctions are needed. The best way to generate higher voltages and achieve the best operating margins for the broadband drive signals is by densely packing the junctions into shorter arrays. NIST has been working on stacked SNS junctions to achieve this goal. By stacking junctions in the array, more junctions may be placed per length, while preserving a lumped microwave element. In this paper we introduce our results on stacked SNS junctions using MoSi/sub 2/ and Ti as barrier materials. These barriers were chosen because they can be reactive-ion etched (RIE) in contrast to our standard PdAu barriers, which must be wet etched. Using RIE, alternating layers of barrier material and Nb may be etched in a single step. We indirectly quantify the junction uniformity in the arrays by measuring the current range of the constant-voltage steps when the arrays are biased with a microwave drive.         Dynamic features of the phase-biased single-Cooper-pair transistor    W. Krech, D. Born, T. Wagner, M. Grajcar, E. Il'ichev and H.-G. Meyer Summary: We have studied dynamic properties of a special Josephson charge qubit. The device consists of a single-Cooper-pair transistor (with capacitive gate) closed by a superconducting inductive loop. The phase bias is implemented by an external flux that threads the loop. Restricting ourselves to a two-band model, we have derived analytical expressions for the oppositely circulating ring currents in terms of gate charge and phase bias. They permit the determination of important device characteristics such as critical current, loop parameters, and Josephson inductance. For the purpose of measurements in connection with macroscopic quantum coherence, we investigate the qubit's microwave response within the frame of Bloch equations with phenomenological relaxation rates. We find the (nonlinear) qubit impedance in terms of quality, detuning, and the quantum resistance unit, which reflects the competition between irradiation and dephasing.         Negative-inductance SQUID as the basic element of reversible Josephson-junction circuits    V.K. Semenov, G.V. Danilov and D.V. Averin Summary: It has been known for a long time that the thermodynamic limit k/sub B/Tln2 on the energy dissipation per logic operation can be overcome by physically and logically reversible circuits. However, explicit experimental demonstration of this is still lacking, and would be highly desirable both in its own right and in view of strong interest in inherently reversible quantum computation. In this work, we suggest a new gate, "negative-inductance SQUID", that is suitable for the experimental demonstration of reversible information processing in Josephson-junction circuits, and present results of its theoretical analysis. We also describe layout-level designs of an individual nSQUID and an 8-cell circular shift register made of nSQUIDs.         Triplet superconductors from the viewpoint of basic elements for quantum computers    A.M. Gulian and K.S. Wood Summary: We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing.         Feasibility studies of ultra-small Josephson junctions for qubits    A.Ya. Tzalenchuk, T. Lindstrom, S.A. Charlebois, E.A. Stepantsov, A.M. Zagoskin, Z. Ivanov and T. Claeson Summary: Most proposed realizations of a high temperature superconductor (HTS) qubit require the use of very small Josephson junctions. The properties of bicrystal junctions are especially interesting since they make it possible to implement several types of flux qubits in a relatively simple way. We have developed a technique that allows us to produce high quality sub-micrometer junctions in a reproducible way using bicrystal technology. We have successfully fabricated and characterized a large number of YBCO junctions and SQUIDs with bridge width as small as 0.2 micrometer on 0/spl deg/-3/spl deg/, 0/spl deg/-40/spl deg/ and 0/spl deg/-45/spl deg/ bicrystal STO substrates. The properties of these junctions have been extensively examined at temperatures down to 20 mK. The effects of external magnetic fields on these structures have been investigated. Figures of merit for the proposed qubits were also extracted from these measurements.         Characterization of an LC-isolated Josephson junction qubit    A.J. Berkley, H. Xu, M.A. Gubrud, R.C. Ramos Jr., J.R. Anderson, C.J. Lobb and F.C. Wellstood Summary: The energy states of a well-isolated hysteretic Josephson junction in the "phase" regime can be used as a qubit. The state of the junction can be determined by measuring when the junction switches from the zero-voltage (qubit) state to the running voltage state, since different levels have different switching rates. The experimental challenge is to provide sufficient electrical isolation of the junction from wires that must be attached to provide bias current and to measure switching events. This isolation must be effective at frequencies around the energy level spacing, in our case from 3-8 GHz. We report on the design and measurement of isolated moderate-to-high-Q junctions using a resonant isolation scheme of a series inductance and capacitive shunt. Microwave activation measurements of the Al-AlO/sub x/-Al junctions at 70 mK were used to gauge the isolation effectiveness and to show the effect of current noise from the isolation resonance on the junction coherence.         Analysis of energy level quantization and tunneling from the zero-voltage state of a current-biased Josephson junction    H. Xu, A.J. Berkley, M.A. Gubrud, R.C. Ramos Jr., J.R. Anderson, C.J. Lobb and F.C. Wellstood Summary: We examine resonant activation from the zero-voltage state of a current-biased Josephson junction in the limit of low damping. In this limit, the quantum dynamics of a Josephson junction can be described by a master equation. Our finite temperature analysis includes transitions between any two levels in the potential well and accounts for escape near the top of the well. Our results show that energy level quantization in lightly damped junctions should be observable even for temperatures in the thermal regime, where only classical behavior is observed for junctions with moderate damping. Finally we discuss implications for ongoing experiments in quantum computation.         SFQ control circuits for Josephson junction qubits    V.K. Semenov and D.V. Averin Summary: Devices of three types: magnetic pulse generators, read-out circuits, and digital circuits controlling them are needed to support scalable operation of quantum logic based on the Josephson junction qubits. The most natural framework for implementation of such a classical interface to quantum circuits is provided by the RSFQ technology . In this work, we argue, however, that specific qubit requirements can not be satisfied with the conventional RSFQ approach and describe the necessary modifications. We suggest a new structure of the pulse generator based on two long underdamped Josephson junctions which is characterized by the reduced power consumption and reduced output noise. We also show how to trade off power consumption and speed of the digital control circuits by using Josephson junctions with similar values of the shunt resistors but very different critical currents. Finally, we suggest a new read-out circuit which enables dynamic compensation of the backaction down to the level approaching fundamental quantum-mechanical limit.         An RSFQ variable duty cycle oscillator for driving a superconductive qubit    D.S. Crankshaw, J.L. Habif, Xingxiang Zhou, T.P. Orlando, M.J. Feldman and M.F. Bocko Summary: We design an RSFQ oscillator with a variable duty cycle to drive a superconductive qubit. This design has been optimized to minimize the decoherence when coupled to the superconductive persistent current qubit. A continuous RSFQ ring oscillator reads the contents of a Non-Destructive Read Out memory cell. By using two out-of-phase counters to Set and Reset the cell, we can vary the duty cycle of the pulses read from the memory cell. This train of flux quanta is filtered, then used to drive the persistent current qubit. The precision is sufficient to measure relaxation time and possibly Rabi oscillations.         Isolation filters for macroscopic quantum coherence experiment    P. Rott and M.J. Feldman Summary: One of the main difficulties in observing quantum coherence (MQC) in rf-SQUID based systems is extremely short coherence times. Quantum coherence in macroscopic system is rapidly destroyed by interaction with the environment. This precludes any MQC experiments from using high-speed data acquisition that allows direct evidence of coherent evolution of linear combination of rf-SQUID eigenstates. In order to perform such experiments, isolation structures that effectively shield MQC experimental elements from small-signal interaction with data acquisition circuitry on chip and at the same time allow large signals such as RSFQ pulses to propagate through. We consider design and simulation of series of Josephson junctions with varied parameters as an example of such isolation filters.         An unshunted comparator as a device for quantum measurements    M. Wulf, Xingxiang Zhou, J.L. Habif, P. Rott, M.F. Bocko and M.J. Feldman Summary: The unshunted single-flux-quantum SFQ comparator is described for the first time. Its dynamic behavior is surprisingly similar to the familiar resistively-shunted SFQ comparator. For certain parameter ranges both junctions of the comparator may pulse at the same time to create a reflected anti-pulse. This phenomenon is utilized in a new SFQ comparator design with better coherence properties for qubit readout. Considerations of quantum noise for the unshunted SFQ comparator are discussed.         Thermal design of superconducting digital circuits for milliKelvin operation    T.A. Ohki, J.L. Habif, M.J. Feldman and M.F. Bocko Summary: Niobium based rapid-single-flux-quantum (RSFQ) digital circuits generally operate at temperature 4 K. It is desirable to develop RSFQ circuits for operation at much lower temperatures, in particular to use as control and interface circuitry for superconducting qubits, and eventually for a full scale quantum computer. The total heat load is moderate - current designs generate 0.5 /spl mu/W per bias resistor, so simple RSFQ integrated circuits are easily compatible with commercial helium dilution refrigerators, and this power can readily be reduced by several orders of magnitude for complex future designs - but thermal conductivity will be a bottleneck. We present a simple model of heat flow through standard RSFQ structures. We find that circuits designed for 4 K operation can be used with little or no modification below one Kelvin. At lower temperatures however the heat generated on chip cannot be removed, and the temperature of a working circuit will rise. We suggest fabrication design rule changes to address this problem.         Efficiency of underdamped dc SQUIDs as readout devices for flux qubits    Shao-Xiong Li, Yang Yu, Wei Qiu, Siyuan Han and Z. Wang Summary: The flux state quantum bit (qubit) is promising for a solid state implementation of scalable quantum computing. The simplest flux state qubit consists of an rf SQUID with two fluxoid states, which can be readout with a dc SQUID - the most sensitive magnetic flux detector. Efficient readout with less back-action is desirable for quantum computing. In this work, we report measurements of the switching flux and switching current distributions of under damped dc SQUIDs. The data show that single shot readout of flux qubit with very high efficiency (>99%) can be realized using underdamped hysteretic dc SQUIDs.         Effects of pulse shape on rf SQUID quantum gates    Zhongyuan Zhou, Shih-I Chu and Siyuan Han Summary: Effects of control-signal microwave pulse shapes on rf SQUID quantum gates are investigated. It is shown that the gate operations are mainly affected by microwave pulse area and are independent of pulse shape in the weak field limit.         Banishing quasiparticles from Josephson-junction qubits: why and how to do it    K.M. Lang, S. Nam, J. Aumentado, C. Urbina and J.M. Martinis Summary: Current-biased Josephson junctions are prime candidates for the realization of quantum bits; however, a present limitation is their coherence time. In this paper it is shown qualitatively that quasiparticles create decoherence. We can decrease the number of quasiparticles present in the junctions by two methods - reducing the creation rate with current shunts and increasing the depletion rate with normal-metal traps. Experimental data demonstrate that both methods are required to significantly reduce the number of quasiparticles and increase the system's coherence. We conclude that these methods are effective and that the design of Josephson-junction qubits must consider the role of quasiparticles.         Capacitively coupled Josephson junctions: A two-qubit system    R.C. Ramos Jr., F.W. Strauch, P.R. Johnson, A.J. Berkley, H. Xu, M.A. Gubrud, J.R. Anderson, C.J. Lobb, A.J. Dragt and F.C. Wellstood Summary: We describe how single Josephson junctions can be connected together capacitively to form a two-qubit system. We discuss the general behavior of this system show the energy level dependence on various junction parameters and choice of coupling strengths. We also discuss measurement techniques for reading out both qubits which are relevant to our ongoing experiments.         Coherent Control of Macroscopic Quantum States in a Josephson Junction    Y. Yu, Z. Yu, S. Han and Z. Wang Summary: Rabi oscillation between macroscopic quantum states of superconducting devices has important implications to the foundations of quantum mechanics as well as the development of quantum computing. At low temperature and low damping, a Josephson tunnel junction biased slightly below its critical current constitutes a macroscopic two-level quantum system. Here we report the results of a single-qubit rotation experiment in a NbN/AlN/NbN Josephson tunnel junction. We show that the state of the junction qubit can be controlled by varying the duration of the microwave pulses.         Macroscopic quantum device based on an RF SQUID system    C. Granata, V. Corato, L. Longobardi, S. Rombetto, M. Russo, B. Ruggiero and P. Silvestrini Summary: The growing amount of theoretical interest in the area of quantum computing have stimulated in recent years research with the aim of developing a corresponding technology. Superconducting Josephson systems appear to be among the most promising candidates. We present the characterization of a fully integrated Josephson device consisting of an RF SQUID coupled to a readout system based on a dc SQUID sensor. We report measurements of the dc SQUID performances showing a high intrinsic responsivity and a low flux noise, giving a good signal to noise ratio in the small signal mode. In the classical regime data on the decay rate from the metastable flux states of RF SQUID are also reported. The low dissipation level and the good insulation of the probe from the external noise are encouraging in view of macroscopic quantum experiments. Work is in progress to improve the design of the device to increase its application capability toward the quantum regime.         Tunable transformer for qubits based on flux states    T.V. Filippov, S.K. Tolpygo, J. Mannik and J.E. Lukens Summary: Flux states of an RF SQUID are promising candidates for the implementation of quantum bits (qubits) for quantum computing. Accurate measurements of the flux states, especially in the time domain, require a controllable coupling between a qubit and a readout circuit (e.g., a dc SQUID magnetometer). Since the readout circuit can also be a source of decoherence, such a controllable coupling also allows one to control (minimize) the back action of the magnetometer. For this purpose we suggest a balanced, tunable transformer. This has a gradiometer configuration such that each arm is broken by a small loop containing two Josephson junctions. As a result the inductance of each arm can be adjusted by an applied bias flux. In the symmetrical case there is no coupling between the qubit and the magnetometer while a desired coupling can be achieved by changing the asymmetry of the arms. Similar transformers may be be useful for achieving controllable, lossless coupling that is required between qubits. Theoretical analysis of the noise back action of the transformer as well as preliminary experimental results are presented.         Experimental characterization of the two current states in a Nb persistent-current qubit    K. Segall, D.S. Crankshaw, D. Nakada, B. Singh, J. Lee, T.P. Orlando, K.K. Berggren, N. Markovic, S.O. Valenzuela and M. Tinkham Summary: We present experiments to characterize a Nb persistent-current qubit as a two-state system. The magnetization signal from the qubit is read-out by a DC-SQUID with near single-shot efficiency. Experiments varying SQUID ramp-rate and temperature suggest thermal activation occurs between the two circulating current states. Such data can be used to fit the parameters of the system, in order to characterize its performance as a potential quantum bit.         Superconducting tunnel junction structures designed for qubit realizations    D. Born, T. Wagner, W. Krech, M. Grajcar and U. Hubner Summary: In view of future macroscopic quantum experiments, we have fabricated prototypes of charge qubits (with tunable Josephson coupling and capacitive gate) provided with capacitively coupled readout single-electron transistor electrometers. The devices are prepared by electron beam direct-writing in conjunction with material deposition by sputtering. All leads are made of Al, and the AlO/sub x/ tunnel barriers are generated by local thermal oxidizing of the surface of the base striplines. The island electrodes are made of Al or Nb in a subsequent deposition step. In the case of Nb it is suitable to protect the barriers by a thin sputtered Al film first. The small-area (100 nm/spl times/100 nm) tunnel junctions have capacitances in the order of a few 10/sup -16/ F; their resistances can be adjusted in a wide range from k/spl Omega/ to M/spl Omega/ with an on-chip spread of less than 10%. The (double) superconducting gap energy was determined to be about 0.4 meV for Al and 1.4 meV for Nb, respectively. Measuring the so-called Coulomb staircase, we have demonstrated the operation of both qubit boxes and sub-e electrometers.         Detection properties of slot antenna coupled YBCO microbridges based on vortex motion    T. Nishida, T. Uchida, T. Tachiki and Y. Yasuoka Summary: High-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) microbridges coupled to a slot antenna were fabricated and the video detection properties in the resistive state were investigated under the irradiation of 94 GHz millimeter-waves. A detected voltage dominated by the nonbolometric response due to vortex motion was observed in the vicinity of the critical temperature. From measurements of the polarization dependence of the detected voltage, it was found that the detected voltage, based on the vortex motion, was not due to the photon energy but instead to a high frequency current induced in the antenna. I-V characteristics of the device with and without the external magnetic fields were also measured. Detected voltages increased with the vortex velocity and the maximum detected voltage was obtained when the vortex velocity was at its maximum.         Ultrafast carrier dynamics in optically excited YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films diagnosed by a pump-and-probe terahertz experiment    H. Wald, P. Seidel and M. Tonouchi Summary: A pump-and-probe terahertz emission technique is reported to investigate the nonequilibrium process of ultrafast generation and relaxation of hot quasiparticles and their recombination to form Cooper pairs in superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films following femtosecond laser excitation. Subpicosecond electromagnetic pulses emitted by an YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// microbridge change after an excitation of the material due to an additional laser pulse, the so-called pump pulse. The modulation of the emitted terahertz pulse amplitude is used to measure the time resolved evaluation of the hot carrier excitation and relaxation after a time delay to the pump laser pulse. The results are compared to terahertz pump-and-probe experiments on GaAs photoswitches and can be explained by avalanche Cooper pair breaking, supercurrent modulation followed by carrier acceleration and Cooper pair recombination accompanied with deceleration of the supercurrent carriers.         Optically and thermally tunable superconducting transmission lines    Shinho Cho, Chang-Sik Son and Jonghun Lyou Summary: Using the method of time-domain optoelectronic sampling spectroscopy, we have tuned the ultrafast electrical pulse propagating through YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) transmission lines as a function of temperature and optical pulse energy. Electrical pulses are generated by photoconductively shorting charged semiconducting optical switches with 70 psec optical pulses at 532 nm. The optically generated and detected electrical pulses have frequencies extending up to 100 GHz. The superconducting transmission lines are microstrip spiral lines on the LaAlO/sub 3/ substrates. By varying the optical pulse energy from 0 to 23 pJ, the delay time through the 66-mm-long superconducting line is tuned by 54 psec at 55 K and shows a quadratic dependence on the optical pulse energy. As for the 250 mm-long transmission line, the delay of 69 psec is observed as the temperature increases from 26 K to 63 K.         Design and performance of superconducting circuits for LiNbO/sub 3/ optical modulator and switch    K. Yoshida, Y. Kanda, H. Yoshihara, H. Kanaya, S. Shinkai and M. Ishitobi Summary: The design and performance of a LiNbO/sub 3/ optical modulator and switch, which employ superconducting circuits, have been studied. Based on a novel design method of the booster circuit using superconducting coplanar waveguide transmission lines, we designed a voltage amplifier with center frequency of 10 GHz, bandwidth of 5 MHz, and the voltage gain of 33 dB using an electromagnetic wave simulator. We also designed a high speed optical switch combining optical directional coupler and Mach-Zehnder interferometer. A preliminary experiment with YBCO electrode on MgO substrate flip-chip-bonded on LiNbO/sub 3/ optical waveguide has been made.         Design of HTS coplanar waveguide matching circuit for low noise CMOS-HTS receiver    H. Kanaya, Y. Koga, G. Urakawa and K. Yoshida Summary: For realizing a single chip HTS integrated microwave receiver, a superconducting slot antenna and a Si-CMOS low noise amplifier (LNA) combined with a broad band matching circuit composed of coplanar waveguide (CPW) meanderline resonators has been designed and tested. By applying the filter technique and using admittance inverters (J inverters), we propose a new design method of CPW broadband impedance matching circuit connected to low and high impedance loads such as HTS antenna and CMOS device. Based on the design method, we designed a Chebyshev type impedance matching circuit connecting with slot antenna and CMOS-LNA at 10 GHz center frequency. More over, in order to increase the antenna directivity, we designed 2-dimensional antenna array by folding the slot antenna.         Externally phase-locked flux flow oscillator for submm integrated receivers: achievements and limitations    V.P. Koshelets, S.V. Shitov, P.N. Dmitriev, A.B. Ermakov, A.S. Sobolev, M.Yu. Torgashin, V.V. Khodos, V.L. Vaks, P.R. Wesselius, P.A. Yagoubov, C. Mahaini and J. Mygind Summary: A Josephson flux flow oscillator (FFO) is the most developed superconducting local oscillator for integration with an SIS mixer in a single-chip submm-wave receiver. Recently, using a new FFO design, a free-running linewidth /spl les/10 MHz has been measured in the frequency range up to 712 GHz, limited only by the gap frequency of Nb. This enabled us to phase lock the FFO in the frequency range 500-712 GHz where continuous frequency tuning is possible; resulting in an absolute FFO phase noise as low as -80 dBc at 707 GHz. Comprehensive measurements of the FFO radiation linewidth have been performed using an integrated SIS harmonic mixer. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field has been studied in order to further optimize the FFO design. A new approach with a self-shielded FFO has been developed and experimentally tested.         Properties of a high-T/sub c/ dc SQUID radiofrequency amplifier    A.S. Kalaboukhov, M.A. Tarasov, A. Lohmus, Z.G. Ivanov and O.V. Snigirev Summary: We present an experimental investigation of a radiofrequency amplifier based on a bicrystal high-T/sub c/ dc SQUID designed for the frequency range 500-3000 MHz. The SQUID input coil comprises only one layer of a normal metal forming open-ended microstrip line. Both dc and microwave properties were investigated and analyzed. Maximum power gain was found to be 16 dB at 520 MHz for a SQUID with 8 turn input coil.         Dynamic characteristics of S-band DC SQUID amplifier    G.V. Prokopenko, S.V. Shitov, I.L. Lapitskaya, V.P. Koshelets and J. Mygind Summary: A low-noise RF amplifier based on a dc SQUID (SQA) has been tested in the frequency range 3.0-4.6 GHz in the open-loop configuration. The following parameters have been measured for the single-stage balanced type SQA at 4.0 GHz: gain (12/spl plusmn/1) dB, 3 dB bandwidth of 500 MHz and noise temperature (1.0/spl plusmn/0.25) K. For the nonbalanced type SQA at 4.0 GHz gain was (15/spl plusmn/1) dB, 3 dB bandwidth 200 MHz and noise temperature (0.5/spl plusmn/0.25) K. The improved performance is obtained due to the increased characteristic voltage (/spl ap/420 /spl mu/V) of the small-area (down to 0.7-0.9 /spl mu/m/sup 2/) high-quality Nb-AlO/sub x/-Nb SIS junctions. The saturation power (normalized to 1 GHz) referred to the input at 1 dB gain compression is estimated as /spl ap/55 K*GHz at a bias voltage of 60 /spl mu/V. The reasons for saturation of the SQA are discussed.         An HTS X-band DC SQUID based amplifier: modeling and development concepts    G.V. Prokopenko, S.V. Shitov, I.V. Borisenko and J. Mygind Summary: We present an X-band amplifier concept based on a HTS grain boundary dc SQUID, which allow for extended dynamic range for use with SIS mixers, e.g., as a buffer amplifier in front of an RSFQ ADC, or possibly for satellite and cellular phone communications. The proposed RF design is based on a combination of single-layer slot and coplanar lines forming novel input and output circuits. The following parameters (per stage) are obtained via simulation for central frequency 11 GHz: bandwidth 0.5-1 GHz, power gain 11-12 dB, noise temperature 5-10 K. A saturation product as high as 500-1000 K/spl middot/GHz is estimated for a characteristic voltage of 1-2 mV. The realization of these parameters makes HTS SQA competitive with existing coolable HEMT-amplifiers for radio astronomy and satellite communication.         Superconducting single and phased-array probes for clinical and research MRI    J. Wosik, Lei-Ming Xie, K. Nesteruk, Lian Xue, J.A. Bankson and J.D. Hazle Summary: Significant improvement of the signal-to-noise ratio (SNR) for magnetic resonance imaging (MRI) applications, in which the thermal noise of the rf receiver probe dominates the system noise can be achieved by cooling down a normal metal probe or by using superconductors. In this work, the SNR enhancement expected from using superconductors for single coil and/or phased array designs are calculated, discussed and compared with some experimental results. We also report on the design and fabrication of a 63.8 MHz probe (1.5 Tesla) consisting of patterned, copper or YBCO films deposited on both sides on a 5 cm LaAlO/sub 3/ substrate. The unloaded Q of the normal metal probe at room temperature and at 77 K was about 400 and 1000, respectively, while the YBCO probe exhibited a Q of 40 000 at 77 K. Five-cm diameter probes cooled to 77 K were superior to their identically designed room temperature equivalents, and provided SNR gains at 1.5 Tesla of 3 and 2 times for YBCO and cooled normal metal, respectively. The application of superconducting coils in conjunction with recently developed techniques for significant reduction of MRI acquisition times by using parallel processing with phased array probes is discussed.         HTSC polaronic quasiparticle injection devices with an organic copper (II) phthalocyanine injector    Sunmi Kim, Kiejin Lee, T. Ishibashi, K. Sato and B. Friedman Summary: We report the nonequilibrium effect of polaronic quasiparticle (QP) injection using an organic injector in a high T/sub c/ three terminal device. The organic, copper (II) phthalocyanine (Cu-Pc), used as the injector, is a photoconductor and a p-type semiconductor. The transport properties of Au/Cu-Pc/Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (BSCCO) tunnel junctions were investigated in the dark and under the He-Ne laser (/spl lambda/=632.8 nm) radiation. We observed that the injection of polaronic QP from the organic Cu-Pc film into the BSCCO film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. We could increase the current gain by He-Ne laser excitation of the organic photoconductor injector. The tunneling spectroscopy of a Cu-Pc/BSCCO junction exhibited an enhancement of the zero bias conductance peak under the He-Ne laser excitation. The above phenomena are of importance in developing optically controlled three terminal superconducting devices.         A high temperature superconductor latch    C.H. Hu, J.F. Jiang and Q.Y. Cai Summary: A latch based on High Temperature Superconductor Single-Hole Transistor (HTS-SHT) and High Temperature Superconductor-Normal Conductor-High Temperature Superconductor (HTS-SNS) junction is proposed in this paper. Firstly, we propose an improved HTS-SHT model based on three-state master equation method, which is comparable to Monte Carlo method in precision even in high voltage region of V/sub DD/. Then, we present a theoretical analysis for this proposed latch, where HTS-SHT is described as this improved three-state model and HTS-SNS junction as a simplified model of Ku/spl uml/mmel-Nicolsky (KN) theory. In the proposed latch, HTS-SHT acts as a drive and HTS-SNS junction acts as a load, where we utilize the low-voltage-negative-differential-resistance (LVNDR) effect of HTS-SNS junction, and the clear Coulomb staircase of HTS-SHT having asymmetric junctions.         Planar Josephson junctions fabricated with magnesium diboride films    D.A. Kahler, J. Talvacchio, J.M. Murduck, A. Kirschenbaum, R.E. Brooks, S.B. Bu, J. Choi, D.M. Kim and C.-B. Eom Summary: Josephson junctions were fabricated in three planar configurations using a focused ion beam (FIB) to cut /spl ges/70 nm gaps in MgB/sub 2/ bridges. In two of the approaches - narrowed microbridges where a 0.1 /spl mu/m bridge was left in place after the FIB cut or thinned microbridges where a 20-40 nm-thick film layer remained uncut - we reproduced junction results obtained by other researchers but with I/sub c/(T)>0 at substantially higher temperatures, >32 K. Measurements were made of critical current modulation in an applied magnetic field and I-V curves were measured with the chips exposed to 1-10 GHz radiation. In the third configuration, S-N-S structures were made by filling the gap made by the FIB with a noble metal. This configuration is preferred to S-S'-S since the normal-conductor coherence length of 40-100 nm for a clean metal roughly matches the width of the FIB cut. Junction R/sub n/ measurements showed that ex-situ Au deposited after a low-energy argon ion cleaning was not as effective as in-situ Pt deposition for obtaining low-resistance S-N interfaces.         Fabrication of Josephson junctions with as-grown MgB/sub 2/ thin films    A. Saito, A. Kawakami, H. Shimakage, H. Terai and Z. Wang Summary: We report on the fabrication of as-grown MgB/sub 2/ thin films and MgB/sub 2//AlN/NbN thin film heterostructures having as-grown MgB/sub 2/ thin films. The MgB/sub 2/ thin films deposited by using a carousel-type sputtering system at substrate temperatures T/sub s/ of 252/spl deg/C typically showed a critical temperature of 28 K. The results of XRD measurements of the thin films indicated a c-axis orientation. The surface morphology of the films fabricated at T/sub s/=252/spl deg/C was determined to be very flat and smooth from SEM images. The MgB/sub 2//AlN/NbN trilayer was continuously deposited on sapphire [001] substrates in a single vacuum run. The AlN-barrier and NbN-counter layers were deposited by using DC-reactive magnetron sputtering at ambient substrate temperatures. The junctions were fabricated by using conventional photolithography, reactive ion etching, and electron cyclotron resonance etching techniques. The junctions demonstrated excellent quasiparticle tunneling characteristics having ideal dependence of the normal resistance on the junction area and on the AlN-barrier thickness. Also, the DC magnetic field and temperature dependences of the supercurrent I/sub c/ were measured to investigate the Josephson tunneling behavior in the MgB/sub 2//AlN/NbN junctions. The junction I/sub c/-H curve showed the ideal Fraunhofer pattern.         Josephson effects in MgB/sub 2/ metal masked ion damage junctions    Dae-Joon Kang, N.H. Peng, C. Jeynes, R. Webb, H.N. Lee, B. Oh, S.H. Moon, G. Burnell, N.A. Stelmashenko, E.J. Tarte, D.F. Moore and M.G. Blamire Summary: We have successfully fabricated high quality Josephson junctions in MgB/sub 2/ thin films by a combination of 30 kV focused Ga ion beam nanolithography and 50 keV proton ion beam irradiation. The junctions show resistively shunted junction like current-voltage characteristics with additional excess current. Monte Carlo simulation results for the optimized mask structure and experimental results for the dc and ac Josephson effects are presented. This technique is particularly useful for prototyping devices due to its simplicity and flexibility of fabrication and has a great potential for high-density integration.         Josephson effect in MgB/sub 2//Ag/MgB/sub 2/ step-edge junctions    Jeong-Il Kye, Ho Nyun Lee, Joo Do Park, Seung Hyun Moon and Byungdu Oh Summary: We have made MgB/sub 2//Ag/MgB/sub 2/ junctions using the steps formed on Al/sub 2/O/sub 3/(0001) substrates. The current-voltage characteristics of these superconductor-normal-superconductor (SNS) type Josephson junctions have shown nonhysteretic behavior with some excess current. The measured I/sub c/R/sub n/ values were 1.2 mV at 4.2 K and 0.24 mV at 20 K. We have observed the modulation of critical current under dc magnetic field as well as Shapiro steps under 20 GHz microwave irradiation.         Transport properties of SINIS junctions with high-current density    F. Born, D. Cassel, K. Ilin, A.M. Klushin, M. Siegel, A. Brinkman, A.A. Golubov, M.Yu. Kupriyanov and H. Rogalla Summary: We have fabricated Nb/Al/sub 2/O/sub 3//Al/Al/sub 2/O/sub 3//Nb devices with different current densities using a conventional fabrication process, varying pressure and oxidation time. Patterning of the multilayers was done using standard photolithography and electron-beam lithography. The current density of SINIS junctions was changed in the range from 0.5 kA/cm/sup 2/ to 20 kA/cm/sup 2/. We achieved characteristic voltages up to 0.35 mV. By fabricating sub-/spl mu/m junction with a width from 0.1 /spl mu/m to 0.5 /spl mu/m, we have studied the influence of the asymmetry of barriers on transport properties. By comparing the experimental and theoretical temperature dependence of the characteristic voltage we estimated the barrier transparency and its asymmetry. The comparison shows a good agreement of experimental data with the theoretical model of tunnelling through double-barrier structures in the dirty limit. A new approach for determination of the asymmetry of both barriers based on the measurement of the electrostatic field distribution in the SINIS structure has been developed.         Properties of high-j/sub c/ SINIS junctions    I.P. Nevirkovets, S.E. Shafranjuk, J.B. Ketterson and E.M. Rudenko Summary: Nb/Al/AlO/sub x//Al/AlO/sub x//Al/Nb junctions with high critical current densities, j/sub c/, above 20 kA/cm/sup 2/ were fabricated and characterized. A critical voltage of V/sub c/=1.25 mV and small hysteresis (about 6% of the critical current) at 4.2 K were obtained for j/sub c/=21 kA/cm/sup 2/. Also, devices with a modified geometry, Nb/Al/AlO/sub x//Al/Nb/Al/AlO/sub x//Al/Nb, were fabricated. In these devices, j/sub c//spl cong/50 kA/cm/sup 2/ at 4.5 K, and the temperature dependence of the critical current, I/sub c/(T), is improved (as compared with our earlier results) in that the steep raise of I/sub c/ is shifted toward higher temperatures. We suggest a theoretical model which satisfactory describes the enhanced critical current for these SINS'NIS junctions as compared with ordinary SINIS junctions.         Superconductor-correlated metal-superconductor Josephson junctions: an optimized class for high speed digital electronics    J.K. Freericks, B.K. Nikolic and P. Miller Summary: It has long been conjectured that tuning the barrier of a Josephson junction to lie close to the metal-insulator transition will enhance the switching speed and provide optimal performance. We examine a new class of junctions, so-called SCmS junctions, where the barrier is a correlated metal (or insulator) close to the metal-insulator transition. We show that high I/sub c/R/sub N/ products and moderate temperature derivatives of I/sub c/ can be achieved when the thickness and metallicity of the barrier is properly tuned. We believe these junctions show promise for the fastest speed digital electronics operation.         Critical current control and microwave-induced characteristics of (NbN/TiN/sub x/)/sub n//NbN stacked junction arrays    M. Ishizaki, H. Yamamori, A. Shoji, S.P. Benz and P.D. Dresselhaus Summary: Stacked double and triple Josephson junctions with NbN electrodes and TiN/sub x/ barriers were fabricated for the next-generation 10 V programmable Josephson voltage standard. Because of difficulties in the growth of uniform junctions in a stack with a constant barrier thickness, a stack with carefully engineered thicknesses was grown that exhibited uniform junction properties. The junction arrays on these chips were biased with microwave power at 16 GHz resulting in constant-voltage steps consistent with the total number of junctions in the array, including the multiple junctions in the stacks. The steps had a current range greater than 1 mA at 4.2 K.         An SNS technology process for ramp junction based digital superconducting circuits    D. Hagedorn, M. Khabipov, R. Dolata, F.-I. Buchholz and J. Niemeyer Summary: The SNS (Nb/HfTi/Nb) ramp junction technology process has been improved for digital superconducting circuit operation. DC interferometers were realized on an isolated superconducting ground plane, connections being realized through windows in the insulation layers. The inductances of superconducting Nb striplines (widths w down to the sub-/spl mu/m range) were measured. For a 250 nm SiO/sub 2//Nb-oxide insulation layer, the sheet inductances of striplines were determined at 0.382 /spl plusmn/ 0.009, 0.340 /spl plusmn/ 0.005, and 0.293 /spl plusmn/ 0.008 pH (stripline widths: 1.5, 1.0, 0.54 /spl mu/m) and compared with data calculated by different inductance evaluation programs. The Josephson junctions used in the interferometers exhibit a critical current density of j/sub C/=525 kA/cm/sup 2/ and a characteristic voltage of V/sub C/=95 /spl mu/V. The design of an RSFQ converter circuit was developed on the basis of SNS ramp junction technology. For circuit applications the critical current density j/sub C/ was set to 150 kA/cm/sup 2/.         New thickness control process of oxide barrier for Nb-based tunnel junctions    Ming-Jye Wang, Hong-Wen Cheng, Sing-Lin Wu, Pi-Kuang Chuan and C.C. Chi Summary: The Nb-based superconductor-insulator-superconductor (SIS) tunnel junctions have been broadly used in many applications. The critical current density (J/sub C/), one of the most important parameters of SIS tunnel junction, is usually controlled by the oxygen exposure (E/sub O2/) of the Al oxidation process. R. E. Miller et al. demonstrated the relation between J/sub C/ and oxygen exposure using the SNEP process. However, the value of J/sub C/ still varies with Nb/AlO/sub x/Al/Nb deposition system, even run-to-run process. A new AuAl/sub 2//Al composite, instead of pure Al, has been used in the oxidation process. From the J/sub C/-E/sub O2/ relation, we have demonstrated the oxidation rate of AuAl/sub 2/ is about 400 times lower than that of Al. Using AuAl/sub 2/ layer, two advantages are observed. 1) For low J/sub C/ tunnel junctions, the thickness of AlO/sub X/, or J/sub C/, can be controlled easily by inserting AuAl/sub 2/ layer as a blocking layer in oxidation process. 2) High quality factor tunnel junctions with J/sub C/>100 kA/cm/sup 2/ are achieved by oxidation of AuAl/sub 2/ layer directly.         Digital logic gates using hot-phonon controlled superconducting nanotransistors    Seung-Beck Lee, G.D. Hutchinson, D.G. Hasko, D.A. Williams and H. Ahmed Summary: We describe the fabrication and digital switching operation of a NOR logic gate that uses a single, dual-input superconducting nanotransistor. The nanotransistor is a weak-link device that has integrated hot-phonon injectors to control its critical current. The fabrication process utilizes a self-aligned method, where the two heaters act as a mask for reactive ion etching to define the device pattern. This device is much simpler to fabricate than previously reported superconducting transistors and the principle of operation makes it possible to use a single nanotransistor, with multiple input heaters, as a NOR logic gate, allowing lower power consumption and improved levels of integration.         Microwave enhanced cotunneling in SET transistors    M.H. Manscher, M.T. Savolainen and J. Mygind Summary: Cotunneling in single electron tunneling (SET) devices is an error process which may severely limit their electronic and metrologic applications. An experimental investigation is given of the theory for adiabatic enhancement of cotunneling by coherent microwaves. Cotunneling in SET transistors has been measured as function of temperature, gate voltage, frequency, and applied microwave power. At low temperatures and applied power levels, including also sequential tunneling, the results can be made consistent with theory using the unknown damping in the microwave line as the only free parameter.         Fabricating NIS tunnel junctions on single crystal superconducting substrate by a lithographic process    A.M. Clark, M.L. van den Berg and J.N. Ullom Summary: We present a novel design for a solid-state microrefrigerator using Normal-Insulator-Superconductor (NIS) tunnel junctions. Cooling of the normal electrode is achieved by electrons tunneling into the superconducting electrode, providing a means of continuous refrigeration at temperatures below 300 mK. The slow diffusion of quasiparticles away from the tunnel barrier limits the cooling power of thin film NIS microrefrigerators for two reasons. First, the efficiency of energy removal from the normal electrode is reduced as quasiparticles build up in the superconducting electrode. Second, phonons produced by quasiparticle recombination near the junction can enter and heat the normal electrode. Using single crystals as both the substrate and the superconducting electrode can prevent the accumulation of quasiparticles near the tunnel barrier. A large volume, high purity electrode will allow quasiparticles to rapidly move away from the junction, thereby eliminating the self-heating. We are developing a photolithographic process to fabricate NIS devices on single crystal Al substrates. Presented here are results from test devices with a 50 /spl mu/m /spl times/ 50 /spl mu/m Al-Al/sub 2/O/sub 3/-Cu tunnel junction deposited on SiN substrates.         A multichannel superconducting tunnel junction detector for high-resolution X-ray spectroscopy of magnesium diboride films    S. Friedrich, A. Vailionis, O. Drury, T. Niedermayr, T. Funk, W.N. Kang, Eun-Mi Choi, Hyeong-Jin Kim, Sung-Ik Lee, S.P. Cramer, Changyoung Kim and S.E. Labov Summary: We have built a high-resolution soft X-ray spectrometer using a 3 /spl times/ 3 array of superconducting Nb-Al-AlO/sub x/-Al-Nb tunnel junctions. The detector is cooled to /spl sim/0.1 K by a two-stage adiabatic demagnetization refrigerator while being held at the end of a 40-cm-long detector snout that can be inserted into an experimental chamber. The 0.6 mm /spl times/ 0.6 mm array has an energy resolution of 10-15 eV FWHM for X-ray energies below 1 keV and total count rate capabilities above 100 000 counts/s. We demonstrate the capabilities of the instrument in a study of anisotropy in c-axis oriented MgB/sub 2/ films by near edge X-ray absorption spectroscopy. The absorption fine structure at the B K-edge differs for excitation with X-rays polarized along the c-axis and in the ab-plane of the MgB/sub 2/ film. We discuss the implications of the anisotropy for the density of states in MgB/sub 2/ at the Fermi surface.         Superconducting tunnel junction detectors for extreme ultraviolet applications    C.M. Wilson, L. Frunzio and D.E. Prober Summary: We present measurements of superconducting tunnel junction (STJ) spectrometers optimized for extreme ultraviolet (EUV) energies, between 20-200 eV. The high count rates demands of astronomical applications, such as solar flare studies, uniquely suit STJs as compared to other cryogenic spectrometers. We have simulated EUV measurements with the technique of multiphoton absorption using a pulsed UV laser as a light source. We have demonstrated an energy resolution of 2.15 eV, close to the requirements of the applications. This resolution is limited by amplifier noise. We present predictions of improved resolution based on new amplifier designs.         Physical properties of the superconducting Ta film absorber of an X-ray photon detector    L. Li, L. Frunzio, C.M. Wilson and D.E. Prober Summary: We have developed single-photon 1-D imaging detectors based on superconducting tunnel junctions. The devices have a Ta film with an Al/AlO/sub x//Al tunnel junction on each end and a Nb contact in the center. The best energy resolution of this kind of detector is 13 eV for 5.9 keV X-ray photons. Two devices with different lengths: 500 and 1000 /spl mu/m are measured to study the nonequilibrium quasiparticle dynamics in the superconducting Ta film. The diffusion constant and lifetime of quasiparticles in the Ta films have been derived by fitting the measured current pulses to the model. The comparison of the simulation and measurement results proves that the quasiparticle loss is not primarily due to the Nb ground contact in the center of the Ta absorber, but is due to the uniform nonthermal loss in the Ta film. The Nb ground contact does contribute to the broadening of the energy width in the center of the Ta film.         Nb-based superconducting tunnel junctions as submillimeter-wave direct detectors    S. Ariyoshi, H. Matsuo, C. Otani, H. Sato, H. Shimizu, T. Matsunaga and T. Noguchi Summary: Employing an anodization method into our fabrication process, we have successfully fabricated STJs with size of 4 /spl mu/m in diameter, Josephson critical current density of 1000 A/cm/sup 2/, low leakage current of less than 10 pA at 0.3 K and high fabrication yield of more than 90 percent. These STJs were applied to fabricate submillimeter-wave direct detectors using 12 linearly distributed junctions, each circular junction having a current density of 600 A/cm/sup 2/ and size of 4 /spl mu/m in diameter. Direct detection of submillimeter-waves was measured using a Fourier transform spectrometer, which shows a maximum sensitivity at 440 GHz and a fractional bandwidth of 10 percent.         On-chip coil-integrated STJ using the persistent superconducting current for photon detectors    K. Kikuchi, T. Taino, M. Nanme, H. Nakagawa, M. Aoyagi, H. Sato, H. Akoh, T. Iizuka, H. Myoren, S. Takada, K. Maehata, K. Ishibashi, T. Ikeda, C. Otani, Y. Takizawa, T. Oku, K. Kawai, H. Miyasaka, H.M. Shimizu, H. Kato and H. Watanabe Summary: A superconducting tunnel junction (STJ) is very attractive for use in high-energy-resolution photon detectors because of its small energy gap. To detect a single photon, the Josephson current of the STJ has had to be suppressed by an external magnetic field. We demonstrated an on-chip coil-integrated STJ photon detector, which excludes the external magnetic field, allowing a small device size. A normal-distribution function shape was adopted for the superconducting electrodes, which makes the magnetic field supplied to the STJ small. We devise a new superconducting photon detector by combining the above techniques. A new Josephson switching gate is also integrated on the same detector chip in order to drive an on-chip integrated coil by a persistent superconducting current. This behavior was confirmed experimentally using the technology of the fabrication process of the Nb/Al-AlOx/Nb Josephson tunnel junction.         Nb-Based Superconducting Tunnel Junctions with /spl Beta/-Ta Trapping Layers for Photon Detectors    H. Myoren, Y. Kogure, S. Takada, H. Sato, C. Otani, H. M. Shimizu and K. Maehata Summary: We have successfully fabricated Nb-based superconducting tunnel junctions (STJs) with /spl Beta/-Ta trapping layers. In an Nb//spl Beta/-Ta stacked structure, /spl Beta/-Ta film showed the thickness dependence of critical temperature T/sub c/ in current-voltage (I-V) characteristics due to the proximity effect from Nb films. We fabricated Nb-based STJs with /spl Beta/-Ta trapping layers for X-ray detector working at 0.4 K. We obtained an energy resolution of 52 eV for 5.9 keV X-ray irradiation at 0.4 K. We expect a high energy resolution by optimizing the thickness of /spl Beta/-Ta trapping layers and improving the fabrication process.         Fabrication of tunnel junctions for direct detector arrays with single-electron transistor readout using electron-beam lithography    T.R. Stevenson, Wen-Ting Hsieh, M.J. Li, K.W. Rhee, R.J. Schoelkopf, C.M. Stahle and J.D. Teufel Summary: This paper describes the fabrication of small aluminum tunnel junctions for applications in astronomy. Antenna-coupled superconducting tunnel junctions with integrated single-electron transistor readout have the potential for photon-counting sensitivity at sub-mm wavelengths. The junctions for the detector and single-electron transistor can be made with electron-beam lithography and a standard self-aligned double-angle deposition process. However, high yield and uniformity of the junctions is required for large-format detector arrays. This paper describes how measurement and modification of the sensitivity ratio in the resist bilayer was used to greatly improve the reliability of forming devices with uniform, sub-micron size, low-leakage junctions.         Wideband frequency metrology using high temperature superconducting Josephson junctions    Jian Chen, Y. Kurigata, Huabing Wang, K. Nakajima, T. Yamashita and Peiheng Wu Summary: We have studied the responses of high temperature superconducting (HTS) Josephson junctions to monochromatic and polychromatic electromagnetic irradiations from 50 GHz to 4.25 THz. The highest operating frequency and the maximum value of normalized response are shown to be proportional to the I/sub C/R/sub N/ product of the junction, where I/sub C/ and R/sub N/ are the critical current and normal resistance of the junction, respectively. Using a junction with I/sub C/R/sub N/ of 330 /spl mu/V, direct detections of monochromatic irradiations from 76 GHz to 3.1 THz have been obtained, indicating that fast detectors can be realized to cover around 50 : 1 frequency band by operating only one junction at one temperature. Also reported are the superposition of polychromatic signals, as well as some possible applications of the system.         Estimation of surface resistance for epitaxial NbN films in the frequency range of 0.1-1.1 THz    A. Kawakami, S. Miki, Y. Uzawa and Z. Wang Summary: To improve the performance of superconducting analog devices at frequencies exceeding the Nb gap frequency, we developed a fabrication process to grow epitaxial NbN/MgO/NbN trilayers. To evaluate the RF performance of the trilayers, we fabricated Josephson junctions with an epitaxial NbN/MgO/NbN microstrip resonator. A Josephson junction was placed in the center of the resonator and it was used as both an oscillator and a detector. The width and length of the microstrip resonator were 10 and 1000 /spl mu/m, respectively. Current steps of up to 1.9 mV resulting from coupling with the resonator were observed in the I-V characteristics. We found that the height of the current steps depended on the loss of the resonator. By assuming that the sum of the dielectric loss and the radiation loss is much smaller than the conductor loss, we estimated the surface resistance of the epitaxial NbN thin films. The surface resistance of the epitaxial NbN films was estimated to be approximately 2.6-88 m/spl Omega/ at 0.1-1.1 THz.         Ultrafast superconducting single-photon optical detectors and their applications    R. Sobolewski, A. Verevkin, G.N. Gol'tsman, A. Lipatov and K. Wilsher Summary: We present a new class of ultrafast single-photon detectors for counting both visible and infrared photons. The detection mechanism is based on photon-induced hotspot formation, which forces the supercurrent redistribution and leads to the appearance of a transient resistive barrier across an ultrathin, submicrometer-width, superconducting stripe. The devices were fabricated from 3.5-nm- and 10-nm-thick NbN films, patterned into <200-nm-wide stripes in the 4 /spl times/ 4-/spl mu/m/sup 2/ or 10 /spl times/ 10-/spl mu/m/sup 2/ meander-type geometry, and operated at 4.2 K, well below the NbN critical temperature (T/sub c/=10-11 K). Continuous-wave and pulsed-laser optical sources in the 400-nm-to 3500-nm-wavelength range were used to determine the detector performance in the photon-counting mode. Experimental quantum efficiency was found to exponentially depend on the photon wavelength, and for our best, 3.5-nm-thick, 100-/spl mu/m/sup 2/-area devices varied from >10% for 405-nm radiation to 3.5% for 1550-nm photons. The detector response time and jitter were /spl sim/100 ps and 35 ps, respectively, and were acquisition system limited. The dark counts were below 0.01 per second at optimal biasing. In terms of the counting rate, jitter, and dark counts, the NbN single-photon detectors significantly outperform their semiconductor counterparts. Already-identified applications for our devices range from noncontact testing of semiconductor CMOS VLSI circuits to free-space quantum cryptography and communications.         Physics of HTS natural, artificial and interface engineered junctions    J. Halbritter Summary: In high-T/sub c/ superconductors, being layered, doped Mott insulators, in-plane weak links occur easily in preparation and in growth, and are prone to deteriorate further. CuO-plane weak links are the major obstacles for HTS transport currents, both dc and rf. Weak links are tunnel junctions showing reduced critical Josephson currents j/sub cJ/ (A/cm/sup 2/), enhanced normal R/sub bn/ (/spl Omega/cm/sup 2/) and leakage resistances R/sub bl/(T0.2 nm as tunnel barrier width of height /spl phi//spl ap/2 eV, and with n/sub L//spl ap/10/sup 21//cm/sup 3/ localized states causing R/sub bl//spl prop/1/n/sub L/. For the first time their R/sub bl/, j/sub cJRbn/ and j/sup 2//sub cJRbn/ degradations are quantified by the resonant tunnel model, even for interface engineered junctions (IEJ), in agreement with experimental data. Comparison of HTS junctions with Nb/Nb/sub 2/O/sub 5y/ and Nb/Al/AlO/sub x/(OH)/sub y/ junctions shows ways out of the interface chemistry deadlock.         Author Index (2002 - Part 1)    No author information available Summary: Not available

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