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2000 Part 1     Front Cover (2000 - Part 1)    No author information available Summary: Not available         Table of Contents (2000 - Part 1)    No author information available Summary: Not available         Conference Information (2000)    No author information available Summary: Not available         The IEEE Council on Superconductivity Award for the Continuing and Significant Contributions in the Field of Applied Superconductivity (2000 - Part 1)    No author information available Summary: Not available         Superconductivity: star technology for the 21st century    C.H. Rosner Summary: The author reviews the history of superconductivity. He considers the breakthrough of low temperature superconductors; the progress of high temperature superconductors; the environmental needs of superconductivity and finally the assessment and challenges of future superconducting technology.         SQUID magnetocardiography: status and perspectives    H. Koch Summary: Magnetocardiography (MCG), the magnetic equivalent to electrocardiography (ECG), is one of the most promising major applications of SQUID systems. Recent advances in SQUID-system technology such as improved noise suppression techniques, better field sensitivity (in particular for HTS SQUIDs), real time options, vector magnetometers and novel signal analysis approaches have appreciably reduced the technical constraints that hindered until recently the implementation of MCG into practical clinical use. Although MCG features several obvious advantages compared with ECG, it remains difficult to present convincing clinically attractive results to medical doctors that would initiate a commercial breakthrough for SQUID systems. Recent clinical MCG investigations have, however, revealed several areas of cardiology where MCG could play a significant role. This presentation will summarize the technical achievements and next steps necessary for system innovation, as well as the crucial clinical trials for the future commercial and clinical success of cardiac SQUID-systems.         HTS filter subsystems for wireless telecommunications    B.A. Willemsen Summary: After many years of research and development, HTS filter subsystems for telecommunications are finally being manufactured in volume. Nearly 1,000 HTS filter subsystems are currently deployed worldwide with millions of hours of cumulative operation. An overview of the worldwide effort to commercialize HTS filter subsystems is presented. The essential technology elements required to manufacture HTS filter subsystems are discussed i.e., filters, cryogenic low-noise amplifiers, advanced cryopackaging, cryocoolers and control electronics. Currently sales of HTS filter subsystems are limited to existing analog and digital telephony networks. Planned third generation (3G) systems for wireless telephony and data communications require higher receiver performance to maintain high data rates with even lower-power handsets. The deployment of HTS filter subsystems in these 3G networks may be an excellent opportunity to achieve greater market penetration. Selected results of field trials of HTS filter subsystems are also presented.         NbN multilayer technology on R-plane sapphire    J.-C. Villegirr, N. Hadacek, S. Monso, B. Delnet, A. Roussy, P. Febvre, G. Lamura and J.-Y. Laval Summary: A new NbN multilayer technology has been developed on 3 inch diameter R-plane sapphire substrates, for combining on-chip fast RSFQ circuits with GHz bandwidth optical links, The circuits take advantage of two high quality [110] NbN layers sputtered epitaxially on sapphire at 600/spl deg/C and selectively patterned: a 400 nm thick layer (/spl lambda//sub L//spl sim/250 nm at 6 K) acts for the ground-plane and microbridge photodetectors are made of a 3.5-8 nm thick NbN epilayer with T/sub c/ above 11 K. Innovative dielectrics formed of 10 nm thick MgO sputtered on top of 200 mm SiO/sub 2/ layers are found to improve significantly the superconductivity of NbN junction electrode lines deposited below 300/spl deg/C. Good quality, hysteretic 2 /spl mu/m/sup 2/ area, NbN/MgO/NbN junctions with high J/sub c/ (up to 50 kA/cm/sup 2/) are obtained with very large gap voltage (6.20 mV) and low sub-gap leakage current (V/sub m/>15 mV) at 4.2 K. At 11 K such junctions are found self-shunted (J/sub c//spl sim/10 k4/cm/sup 2/) with R/sub n/I/sub c/ above 0.5 mV and with low J/sub c/ spread in arrays. J/sub c/ can be adjusted (reduced) without any detrimental effect on the junction quality or spread by annealing at 250/spl deg/C.         Overdamped NbN junctions with Nb/AlO/sub x//Nb multilayered barriers    H. Akaike, T. Iwai, Y. Ninomiya, K. Nakamura, A. Fujimaki and H. Hayakawa Summary: This paper describes electrical characteristics of NbN junctions with Nb/Al/sub 2/O/sub 3/-Al/(Nb) multilayered barriers. The junctions show overdamped behavior at 10 K because of Nb working as a normal layer, which enables us to use them as basic elements in single flux quantum (SFQ) circuits. The junctions, with critical current densities J/sub c/'s up to 3.4 kA/cm/sup 2/ and characteristic voltages V/sub c/'s up to 0.20 mV, were obtained by changing the film thicknesses of lower and upper Nb layers and the Al oxidation conditions when using a conventional batch-type sputtering system. The run-to-run variations of J/sub c/ and V/sub c/ were the maximum-to-minimum spreads of /spl plusmn/32% and /spl plusmn/4.3%, respectively. On the other hand, a V/sub c/ of 0.70 mV and a J/sub c/ of 13 kA/cm/sup 2/ were obtained for the junction fabricated by the ultrahigh-vacuum sputtering system. These results show that NbN/Nb/AlO/sub x//Nb/NbN junctions have high potential and can be applicable to high performance 10 K SFQ circuits.         Fabrication of Nb/Al-N/sub x//NbTiN junctions for SIS mixer applications    B. Bumble, H.G. LeDuc, J.A. Stern and K.G. Megerian Summary: We discuss fabrication and characteristics of superconductor-insulator-superconductor (SIS) junctions which typically exhibit a 3.5 mV sum-gap voltage. Junctions have a sub-gap to normal state resistance ratio of R/sub SG//R/sub N/=27 for resistance-area products down to R/sub N/A=8 /spl Omega/ /spl mu/m/sup 2/ and high quality junctions have been produced with RNA products as low as 4 /spl Omega/ /spl mu/m/sup 2/. The device structure incorporates a Nb base electrode, a tunnel barrier formed by plasma nitridation of a thin Al proximity layer, and a NbTiN counter-electrode. Results for all Nb junctions with high current density aluminum-nitride barriers are also shown. Nitridation of the aluminum layer is investigated by control of the dc floating potential on a separate rf driven electrode in the vacuum process chamber. Devices are integrated to a mixer antenna structure incorporating NbTiN as a ground plane. The wire circuit layer can be either normal metal or NbTiN. Annealing results show improved I-V characteristics with increased RNA products. Recent receiver measurements employing these junctions exhibit low noise performance up to 900 GHz.         Low-loss epitaxial NbN/MgO/NbN trilayers for THz applications    A. Kawakami, Z. Wang and S. Miki Summary: To improve the performance of Josephson oscillators and SIS mixers over 700 GHz, we have developed a fabrication process to grow epitaxial NbN/MgO/NbN trilayers by reactive dc-sputtering. Trilayers were fabricated on a single-crystal MgO substrate at ambient temperature. NbN and MgO films were deposited by reactive dc-sputtering with an Nb and Mg target, respectively. The MgO inter-layer thickness was changed up to 480 nm, but, T/sub C/ and 20-K resistivity of the NbN upper-layer showed no remarkable dependency and they were 15.7 K and about 60 /spl mu//spl Omega/cm, respectively. To evaluate the RF performance of the epitaxial NbN films, we fabricated Josephson junctions with a microstrip resonator constructed from an epitaxial NbN/MgO/NbN trilayer. The I-V characteristics of the junction exhibited resonance steps up to 2.5 mV, which suggests that the epitaxial NbN films have low loss up to 1.2 THz.         1/f noise in high current density NbN/AlN/NbN tunnel junctions    Z. Wang, A. Kawakami, A. Saito and K. Hamasaki Summary: Low frequency noise characteristics of epitaxial NbN/AlN/NbN tunnel junctions have been investigated. For all of our junctions with different current densities, the voltage noise power spectrum S/sub v/(f) showed a frequency dependence of 1/f type. The magnitude of the S/sub v/(f) exhibited two distinct types of dependency on the current density and AlN barrier thickness. We consider that this may result from a difference in the crystal structures of the AlN barrier by consulting with the barrier thickness dependence of tunnel barrier heights. We also estimated the 1/f noise parameter /spl eta/ using the Rogers and Buhrman's empirical theory for the S/sub v/(f), and investigated the relationship between the /spl eta/ and the current density J/sub c/ and the tunnel barrier thickness d/sub AlN/. The tunnel barrier was characterized by investigating the /spl eta/-d/sub AlN/ relation. It was found that the /spl eta/-J/sub c/ and /spl eta/-d/sub AlN/ relation in our high current density junctions, i.e, in the epitaxial tunnel junctions, are different from nonepitaxial tunnel junctions.         NbN/TaN/sub x//NbN SNS Josephson junctions by pulsed laser deposition    A.B. Kaul and T. Van Duzer Summary: We have made NbN/TaN/sub x//NbN Josephson junctions with nonhysteretic I-V characteristics that may have potential application for single-flux-quantum logic or SQUID magnetometers. The trilayer growth was done in-situ using pulsed laser deposition. The resistivity of the TaN/sub x/ was varied by the N/sub 2/ pressure during growth from a few hundred micro-ohm-cm at low pressure to a few hundred milli-ohm-cm at pressures up to 300 mTorr. The films were characterized using Rutherford backscattering, X-ray diffraction, and atomic force microscopy. Junction processing was done in the usual trilayer technology. The fabricated Josephson junctions show I/sub c/R/sub n/ values >0.3 mV at 4.2 K. We also observed that at a high laser fluence, NbN films with low a real particulate density and T/sub c//spl sim/16.2 K could be grown on 25/spl deg/C substrates.         Use of a focused ion beam for characterizing SIS circuits    R.B. Bass, W.W. Clark IV, J.Z. Zhang and A.W. Lichtenberger Summary: We have found the use of a Ga/sup +/ based focused ion beam (FIB) system to be very useful in characterizing our superconducting-insulating-superconductor (SIS) fabrication process. This tool enables us to physically carve cross sections in any feature of interest on our wafer which we can then image with an SEM. This process is used to examine and monitor improvements in the coverage of metallization layers over different circuit topography and in the critical "sealing" capabilities of our SiO insulation layer around the perimeter of the Nb junction counter electrode. It has also been used to better establish a submerged trilayer deposition process where the base electrode is imbedded in the quartz substrate. We have also improved our characterization of the tunnel barrier critical current density of our Nb/Al-oxide/Nb trilayer material by obtaining more accurate diameter measurements from FIB sectioned junctions.         Integrated LTc-SQUID magnetometers for multichannel systems    C. Granata, C. Di Russo, A. Monaco and M. Russo Summary: A reliable procedure based on the niobium technology has been developed to fabricate low intrinsic noise Josephson devices. Results concerning both the design and the characterization of fully integrated DC-SQUID magnetometers are reported. Such devices well meet the requirements of multichannel systems for biomagnetic measurements.         Resonances and flux-flow in Josephson junctions    P. Cikmacs, M. Cirillo, V. Merlo and R. Russo Summary: We have studied flux-flow in very long inline Josephson junctions by experiments and numerical simulations. The existence of the phenomenon is evident through the appearance of resistive branches in the current-voltage characteristics. The results are found in very good agreement with the numerical simulations performed on the basis of real experimental parameters. We demonstrate the fundamental difference existing between the experimental evidences of flux-flow and the features generated in the current-voltage characteristic by resonances between em modes in the tunnel barrier and Josephson AC effect.         Superconducting slot antenna with broadband impedance matching circuit    K. Yoshida, T. Takahashi, H. Kanaya, T. Uchiyama and Z. Wang Summary: A superconducting slot antenna with broadband impedance matching circuit has been proposed and studied theoretically. In order to solve the problem of narrow bandwidths peculiar to superconducting small antennas, which originates from the small antenna impedance, we propose a new design theory of the broadband impedance matching circuit for the antenna. Using the theory we designed a three stage impedance matching circuit for a slot antenna using an electromagnetic wave simulator and confirmed the validity of the design theory.         Broadband HTS microstrip antennas for satellite communication    Dong-Chul Chung Summary: The major limitation of high-T/sub c/ superconducting (HTS) microstrip antennas is the narrow bandwidth due to the high Q and thin substrate. Defining bandwidth as the frequency range over which standing wave ratio (SWR) 2:1 or less, HTS antenna bandwidths are typically 0.85% to 1.1%. Thus considerable effort has been focused on developing antennas for broadband operation. In this work the HTS antenna, which consists 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 MgO substrate for broadband operation. The input impedance and other characteristics for this antenna have been calculated using the moment method. Experimental results for our HTS antenna were reported in terms of radiation patterns, return losses, bandwidths and other various characteristics. The bandwidth obtained was a significant 6.7%.         Miniaturized cooling systems for HTS antennas    K. Ehata, K. Sato, M. Kusunoki, M. Mukaida, S. Ohshima, Y. Suzuki and K. Kanao Summary: Two types of miniaturized cooling systems for High-Temperature Superconducting (HTS) antennas were designed and built. In this paper, details of these systems, measured and simulated properties of patch antennas installed in these systems, and results of a seal-off trial for 1 month are reported. Both the systems had portable size and weight and could cool the HTS devices. When a patch antenna with resonant frequency of 4.9 GHz was installed in the 1st cooling system, the radiation pattern of the antenna was strongly focused in the forward direction. This is because the vacuum chamber in which the antenna was packaged influenced the microwaves radiated from the antenna. Due to this effect, the directive gain of the antenna was enhanced by 11.2 dB. In the 2nd system, a seal-off trial was carried out to investigate the airtight property that is necessary for thermal isolation. The temperature of the sample stage could be kept under the critical temperature of YBCO for 1 month without continuous vacuum pumping. The cooling systems developed in this work are expected to promote the practical use of HTS antennas.         Normal and superconductor coplanar waveguides with 100 nm line width    S. Wuensch, G. Benz, E. Crocoll, M. Fitsilis, M. Neuhaus, T.A. Scherer and W. Jutzi Summary: High speed high package density integrated circuits require a hierarchy of interconnections with small and large cross sections where the smallest linewidth approaches the 100 nm range. Attenuation and delay of superconducting interconnections down to the order of the London penetration depth for 50 /spl Omega/ and higher characteristic impedances are compared with normal conducting ones near 20 GHz. Symmetrical coplanar waveguides with polycrystalline aluminum and niobium and c-axis oriented Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// on substrates with a dielectric constant of about 12 are chosen to demonstrate basic properties mainly at 77 K and 4.2 K. Simulated quality factors are checked by measurements down to 1000 nm line width.         Characterization of X-band filter of double-sided Y-Ba-Cu-O film on MgO substrate    K. Suzuki, N. Hasegawa, H. Nakada, T. Suzuki and Y. Enomoto Summary: We investigated the pulsed laser deposition process of double-sided Y-Ba-Cu-O thin films on MgO substrates, the critical current density (Jc) distribution and the microwave surface impedance (Rs) of the films, and the power handling capability by third-order intermodulation distortion (IMD3) measurements using 40 W high power microwave measurement system. A clean flat MgO surface was important for Y-Ba-Cu-O deposition and successfully obtained by three-hour pre-annealing at 1000/spl deg/C in air. To confirm the film process, we designed, fabricated and measured the 11 GHz band-pass 7-pole Y-Ba-Cu-O filter. We also found that the outskirts of the Y-Ba-Cu-O film on MgO substrate were particularly important in Jc quality because the biggest microwave power in filter circuit is allocated in the outskirts of Y-Ba-Cu-O film area.         Local microwave surface resistance variations of the YBaCuO thin films patterned by selective laser irradiation and plasma fluorination    Y.J. Feng, L. Liu, Z.L. Fu, L.Y. Wu, Q.G. Liu, L.X. You, L. Kang, S.Z. Yang, P.H. Wu and S.Z. Wang Summary: In this paper, we have studied the planar patterning of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films by laser irradiation and ion plasma treatment. The laser ablated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films have been modified either by selective laser irradiation or by plasma fluorination in an atmosphere of CF/sub 4/ to pattern microwave devices. Transport measurements and microstructure analysis have been used to study the effects of the selective laser irradiation or plasma fluorination on the superconductivity of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films. A scanning microwave near-field microscopy has been involved to investigate the local microwave surface resistances of the patterned devices. Enhancement of the microwave surface resistance has been found in the treated regions of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films by selective laser irradiation or plasma fluorination. These results would be helpful in evaluating the microwave performance of the devices.         Electrical and thermal modulation of the propagation time in superconducting spiral lines by optoelectronic techniques    Shinho Cho and Cheon Lee Summary: Current and temperature controlled delays in the propagation time of electrical pulses in YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) spiral transmission lines have been investigated by using optoelectronic techniques. The transmission lines are configured in a stripline geometry, where the central strip consists of a thin film of YBCO embedded in LaAlO/sub 3/. The propagation time of electrical pulses through the spiral transmission lines is measured using electrical autocorrelation techniques making use of semiconductor optical switches. The measured propagation time shows a quadratic dependence on the applied current, which is in good agreement with the Ginzburg-Landau theory. As the temperature increases, a gradual increase in pulse width and a delay in the propagation time of electrical pulses are observed. The results are used to determine the actual temperature-dependent function of the magnetic penetration depth of YBCO spiral lines.         Third-order local nonlinear microwave response of YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb thin films    E.E. Pestov, Y.N. Nozdrin and V.V. Kurin Summary: HTS thin films continue to be of interest for passive device applications at microwave frequencies, but nonlinear effects may limit their performance. We report a set of experimental data on local third-harmonic generation at microwave frequencies (0.5 GHz) in YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb thin films from 4.2 K to T/sub c/. For local investigations of the nonlinear response a probe with inductive coupling was developed. The map of the nonlinear microwave response of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film is plotted below T/sub c/ with high resolution. The third-harmonic power is measured as a function of temperature, input power and dc-magnetic field on some places of the film. The temperature dependence demonstrates a peak of nonlinearity below T/sub c/ for YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb films and a minimum of nonlinearity at low temperatures for HTS films. The behavior of the third-harmonic power vs the input power can be described by the power-law with the exponent n/spl sim/1.5-3. The correlation between the depinning current density J/sub p/ and the nonlinear microwave response is also demonstrated.         Nonlinear analysis of disk resonators. Application to material characterization and filter design    J. Mateu, C. Collado and J.M. O'Callaghan Summary: A procedure for the numerical prediction of the microwave nonlinear behavior (intermodulation products, degradation of quality factors, etc.) of TM/sub 010/ disk resonators has been developed. The procedure is based on relating a very general description of HTS nonlinearities with the circuit elements of a nonlinear radial transmission line. This radial transmission line is then analyzed using the harmonic balance algorithm. Successful cross-checks are performed by comparing simulations with theoretical results obtained for a specific model of HTS nonlinearity. The application of this procedure to the determination of nonlinear material parameters from disk resonator measurements is illustrated as well as its use for simulating filters with several inter-coupled disks.         Nonlinear microwave effects in superconducting microstrip resonators based on YBCO thin films    M. Boutboul, H. Kokabi, S. Sautrot, A. Degardin, A. Kreisler and M. Fourrier Summary: Linear microstrip resonators based on YBaCuO thin films made by RF magnetron sputtering on MgO substrates have been characterized with transmission microwave measurements as a function of temperature (from 10 K to T/sub c/) and the incident microwave power (from -30 to 10 dBm). The variation of the resonant frequency with temperature has been used to determine the intrinsic parameters (/spl lambda//sub 0/, T/sub c/) of the thin film using a fitting procedure and appropriate models. For low microwave powers (<-18 dBm), the variation of the quality factor, the insertion loss and the surface resistance do not exhibit any nonlinear effect. For higher microwave powers nonlinear effects appear and the variation of the quality factor has shown that they vary in a different way according to three temperature zones. Various theoretical models have been used to discuss the experimental results. These zones can be correlated to the temperature dependence of the surface resistance, in particular to grain boundaries resistance and to penetration of microwave Josephson vortices into the weak links. Moreover, the variation of the measured surface resistance as a function of the RF surface magnetic field is discussed considering different models.         The role of interfaces in c-axis microbridges    P.J. Hirst, R.G. Humphreys, J.S. Satchell, M.J. Wooliscroft, C.L. Reeves, G. Williams, A.J. Pidduck and H. Willis Summary: The c-axis microbridge (CAM) junction is a c-axis interconnect between two superconducting layers. This is an attractive geometry, with low parasitic inductance suitable for single flux quantum logic circuits. Such junctions can be made by the planarisation of a mesa or growth into a window in the insulator. Typical critical current density (J/sub c/) values of the mesa type junctions are /spl sim/10/sup 5/ A/cm/sup 2/ at 70 K. However, it has been found that the J/sub c/ in the window junctions can be as high as /spl sim/10/sup 6/ A/cm/sup 2/ at 80 K if the window is milled deep into the superconducting base layer. The I-V curves obtained have been modelled using conventional microbridge theory and reasonable agreement with experiment obtained. These results show that the properties of the previous CAM junctions have been determined by a barrier at the grown interface. This places the mesa junctions in the class of 'interface engineered' junctions. Secondary ion mass spectrometry has shown that the ion milled YBCO surface is Y rich, and deficient in Ba and Cu. This is due to the different milling rates of the cations. The effect of the milling and annealing conditions on this interface have been investigated.         Effect of ion beam damage and heat treatment on interface-modified junctions    W.K. Park, H.J. Lee, J.I. Kye, J.H. Yun, S.-M. Lee, S.H. Moon and B. Oh Summary: We have fabricated Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. We irradiated the ramp edge surfaces with ion beams and heat-treated them under various conditions prior to the deposition of counter-electrode layers. After patterning the samples into ramp edge junctions using photolithography and ion beam etching, we measured their electrical properties, such as current-voltage characteristics, magnetic field modulation of the critical current, and microwave response. Some showed resistively shunted junction (RSJ)-type current-voltage (I-V) characteristics, while others exhibited flux-flow behavior, depending on the details of interface treatment. Junctions fabricated using optimized conditions showed fairly uniform distribution of junction parameters. Their I-V curves were RSJ-type, also shown by the microwave-induced constant voltage steps. I/sub c/R/sub n/ values of typical RSJ-type junctions were about 0.07 mV at 77 K.         Fabrication of interface-controlled Josephson junctions using Sr/sub 2/AlTaO/sub 6/ insulating layers    G.Y. Sung and J.H. Kim Summary: We fabricated ramp-edge Josephson junctions with barriers formed by interface treatments instead of epitaxially grown barrier layers. A low-dielectric Sr/sub 3/AlTaO/sub 6/ (SAT) layer was used as an ion-milling mask as well as an insulating layer for the ramp-edge junctions. An ion-milled YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO)-edge surface was not exposed to solvent through all fabrication procedures. The barriers were produced by structural modification at the edge of the YBCO base electrode using high energy ion-beam treatment prior to deposition of the YBCO counter electrode. We investigated the effects of high energy ion-beam treatment, annealing, and counter electrode deposition temperature on the characteristics of the interface-controlled Josephson junctions. The junction parameters such as T/sub c/, I/sub c/, R/sub N/ were measured and discussed in relation to the barrier layer depending on the process parameters.         Fabrication and characterization of Y-Ba-Cu-O and Nd-Ba-Cu-O ramp-edge junctions with an interface-modified barrier    T. Makita, K. Toma, K. Ishikawa, H. Zama, T. Utagawa, U. Kawabe and K. Tanabe Summary: The fabrication process for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) ramp-edge junctions with an interface-modified barrier has been studied. The conditions of electron cyclotron resonance (ECR) ion etching and following annealing treatment were optimized by evaluating the mean roughness of the ramp surface using atomic force microscope (AFM) observation. We could obtain resistively-shunted junction (RSJ) type current-voltage characteristics for the junctions with the counterelectrode YBCO layer deposited at temperatures lower than 720/spl deg/C, while a deposition temperature higher than 755/spl deg/C resulted in a high-J/sub c/ superconducting contact. The junctions exhibited an I/sub c/R/sub n/ product of 1.0-1.9 mV and magnetic field modulation of I/sub c/ more than 90% at 4.2 K. By applying the optimum etching condition to a NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO) base electrode and employing a slightly higher annealing and deposition temperature, YBCO/NBCO ramp-edge Josephson junctions with a similar I/sub c/R/sub n/ product were successfully obtained.         Preparation of ramp-edge interface modified junctions for HTS SFQ circuits    M. Horibe, T. Ito, Y. Inagaki, G. Matsuda, A. Fujimaki and H. Hayakawa Summary: We have studied the properties of ramp-edge interface modified Josephson junctions (IMJs) whose barriers are formed during the etching process and subsequent annealing process. We investigate the effect of process parameters on junction characteristics (I/sub c/, R/sub n/) and obtain an empirical equation concerning their relationship. We select accelerating voltage (V/sub acc/) and etching time (t/sub etch/) for the control of I/sub c/ of IMJs and set the target value of I/sub c/ at 4.2 K to 500 /spl mu/A in this study. This target value can be realized by V/sub acc/=500 V and t/sub etch/=20 min from our empirical equation. We prepare four different samples fabricated in the same conditions, and examine the reproducibility and controllability of I/sub c/. The obtained I/sub c/s are very close to the target value, and the run-to-run spread is confined to about 150 /spl mu/A. The reproducibility and controllability of I/sub c/ are improved compared to our previous data of junctions with artificial barriers.         Investigation of ramp-type Josephson junctions with surface-modified barriers    Y. Soutome, R. Hanson, T. Fukazama, K. Saitoh, A. Tsukamoto, Y. Tarutani and K. Takagi Summary: We have investigated the properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ ramp-edge Josephson junctions with surface-modified barriers produced by Ar-ion irradiation followed by oxygen annealing. The fabricated junctions displayed RSJ-like I-V characteristics and excellent uniformity. The stray capacitance of the junctions was estimated from the ramp-edge structure. The junction capacitance was obtained by subtracting the stray capacitance from the shunting capacitance. We estimated the barrier thickness from the junction capacitance, and found that the critical current density of the junction increased exponentially with decreasing barrier thickness. The relative dielectric constant of the barriers ranged from 13 to 18.         Nb-based SIS mixer in the 800 GHz band    T. Noguchi, H. Maezawa, Sheng-Cai Shi and S. Yamamoto Summary: We have built a waveguide SIS mixer with Nb-based parallel-connected twin junctions at 800 GHz which is above the gap frequency of Nb (690 GHz). Heterodyne mixing was performed at 810 GHz and a receiver noise temperature of 580 K (DSB), which includes noise contributions due to a vacuum window and a beam splitter, was achieved using Nb/AlO/sub x//Nb junctions with Nb striplines. The performance of this mixer is quite good and it is shown that efficient mixing in Nb-based SIS junctions is still possible above the gap frequency, SIS mixers with Al striplines have also been fabricated and good DC I-V characteristics have been observed. Heterodyne measurements of these mixers are now under preparation.         Precision techniques for whole wafer dicing and thinning of superconducting mixer circuits    W.L. Bishop, D.M. Summers and A.W. Lichtenberger Summary: Present designs for millimeter and submillimeter superconducting mixer circuits often require finished quartz wafer thicknesses from a few mils to less than a mil. Typically this is accomplished by first dicing the wafer into individual chips and then thinning each chip separately. In our new process the entire wafer is first diced; however, the cuts are only made two mils deeper than the desired finished chip thickness. An ultra-flat Si wafer is prepared with a 5 /spl mu/m thick Apiezon-W black wax coating on both sides. The quartz wafer is mounted to the Si carrier, cuts side down, which is itself mounted to a stainless steel lapping block. The "stack" of block/Si/quartz is then placed in a tool designed to permit compression of the sandwich to 30 psi at 145C. In this process the quartz wafer is positioned flat with respect to the Si wafer to better than +/-2.5 /spl mu/m. The stack is then lapped and polished through the backside of the wafer, into the cuts to the desired wafer thickness to better than +/-5 /spl mu/m. The Si/quartz bilayer is subsequently removed from the block resulting in a fully diced and thinned quartz wafer.         IF bandwidth and noise temperature measurements of NbN HEB mixers on MgO substrates    S. Miki, Y. Uzawa, A. Kawakami and Z. Wang Summary: We report the fabrication and testing of hot electron bolometric mixers with an ultrathin NbN film as heterodyne receivers operating at terahertz frequencies. We found that the quality of the NbN strip is usually degraded by damage resulting from the fabrication process, and we developed a process for reducing such damage. We also fabricated HEB mixers with a new structure in order to study the IF bandwidth determined by the original quality of the NbN thin films. Investigations at 100 GHz revealed that the widest IF bandwidth of 2.0 GHz was obtained by a mixer based on a 2.8 nm-thick NbN film. An HEB mixer based on the 2.8 nm-thick NbN film was also fabricated and evaluated. The receiver noise temperature at 900 GHz was 780 K, the absorbed LO power was about 400 nW, and the conversion gain was -13 dB.         A two-dimensional hot-spot mixer model for phonon-cooled hot electron bolometers    H.F. Merkel, P. Khosropanah, S. Cherednichenko, K.S. Yngvesson, A. Adam and E.I. Kollberg Summary: A hot spot model for superconducting hot electron bolometers is presented based on a two-dimensional heat transport equation for electrons and phonons including heat trapping due to quasiparticle bandgap gradients. Skin effect concentrates the RF heating in lateral regions of the bridge and the bias current in the center. A reduction in conversion gain compared to a one-dimensional hot spot model is explained by the RF and bias heating profiles not being identical. An experimentally verified increase of the IF bandwidth from 3.5 GHz to 8 GHz when increasing bias voltage is predicted. IV curves, gain and noise are in very good agreement with measurements.         Performance of all-NbN quasi-optical SIS mixers for the terahertz band    Y. Uzawa, A. Kawakami, S. Miki and Z. Wang Summary: We have designed, fabricated, and tested terahertz superconductor-insulator-superconductor (SIS) mixers having a self-compensated NbN/AlN/NbN tunnel junction and an epitaxially grown NbN/MgO/NbN microstripline. The junction as a distributed element was 0.8-/spl mu/m wide and 2.4-/spl mu/m long, and its current density was 50 kA/cm/sup 2/. The microstripline consisted of a 200-nm-thick NbN ground plane, a 180-nm-thick MgO insulator, and a 350-nm-thick NbN wiring layer. An investigation of the mixer in our receiver configuration showed flat noise characteristics from 870 to 960 GHz. The lowest receiver noise temperature of about 550 K was obtained at 909 GHz, including a 9-/spl mu/m-thick Mylar beam splitter loss and other optical losses. These characteristics suggest that SIS mixers with self-compensated NbN/AlN/NbN junctions and NbN/MgO/NbN microstriplines are appropriate for used in wideband and low-noise operations at terahertz frequencies.         Thermal time constant of Nb diffusion-cooled superconducting hot-electron bolometer mixers    D. Wilms Fleet, J.R. Gao, T.M. Klapwijk and P.A.J. de Eorte Summary: We present an experimental study of the intermediate frequency bandwidth of a Nb diffusion-cooled hot-electron bolometer mixer for different bias voltages. The measurements show that the bandwidth increases with increasing voltage. Analysis of the data reveals that this effect is mainly caused by a decrease of the intrinsic thermal time constant of the mixer and that the effect of electrothermal feedback through the intermediate frequency circuit is small. The results are understood using a qualitative model, which takes into account the different effective diffusion constants in the normal and superconducting domains.         Low-voltage negative-resistance mixers of nano-meter SNS junctions    T. Matsui and H. Ohta Summary: The current carried by the bound quasi-particles in the N region of a mesoscopic SNS junction has dc and cosine components. The dc current component is carried by the pair charge (-2e) transferred by a couple of Andreev reflections at both of the NS interfaces. The pair-charge transfers decrease due to reduction of the allowed number, 2/spl Delta//V, of Andreev reflections when the voltage, V, increases. Therefore, the low-voltage negative-differential-resistance is observed on the I-V curves of mesoscopic SNS junction, when the junction is driven by the low impedance voltage-bias source. The supercurrent carried by the quasi-particle in the N-region is sensitive to the external high-frequency fields. In a mixer experiment using the nano-meter SNS junctions of NbN, prominent IF signal peaks are observed at low bias voltage. Each IF signal peak corresponds to the negative differential resistance region at low bias voltage.         Bandwidth of a hot-electron bolometer mixer according to the hotspot model    A.D. Semenov and H.-W. Hubers Summary: The hotspot model has been used to simulate the intermediate frequency bandwidth of a lattice cooled NbN hot-electron bolometer mixer. The results of simulation suggest that with the increase of the bias current, the bandwidth decreases, passes the minimum, and recovers again. The appearance of the bandwidth minimum correlates with experimentally observed noise maximum at the mixer output that drastically reduces the sensitivity of a relevant receiver. At large bias currents the bandwidth exceeds the reciprocal electron cooling time. Since the noise temperature also increases with the bias current, a compromise between the desirable bandwidth and acceptable noise temperature can be reached by varying the bias current.         Sigma-delta A/D converter in HTS ramp edge technology    A.H. Sonnenberg, I. Oomen, H. Hilgenkamp, G.J. Gerritsma and H. Rogalla Summary: We have successfully fabricated and tested a high temperature superconducting sigma-delta A/D converter, The quantizer is a balanced comparator that has been characterized separately in two temperature regimes. The circuits have been fabricated with ramp edge junctions with a PrBaCuCaO-barrier on a buried ground plane. For the current to voltage conversion in the sigma-delta converter we fabricated a 50 mOhm resistor with an in-situ gold layer, The sigma-delta converter has been tested at an internal clock of up to 174 GHz. The signal-to-noise ratio has been measured at a relatively low frequency of 3.4 kHz and was at least 63 dB but most likely higher since the measurement was limited by the noise in the amplifiers, As a first attempt towards the development of a decimation filter we have fabricated and tested a toggle flip-flop. The toggle flip-flop has been tested successfully at 40 K up to a frequency of 33 GHz, which corresponds to 70% of the I/sub c/R/sub n/-product of a reference junction.         A new superconducting device with transistor-like properties    G.P. Pepe, L. Parlato, G. Ammendola, E. Esposito, G. Peluso, A. Barone and N.E. Booth Summary: A superconducting transistor with large current gain and bandwidth at low temperatures would have many applications. We have fabricated and tested a new three-terminal superconducting device with transistor-like properties at an operating temperature of 4.2 K. It is based on a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb and an Al quasiparticle trap which can work either in the superconducting or in the normal metal state. Current amplification factors of up to 2.0 are observed at a temperature of 4.2 K when the Al is superconducting, while large current gains of more than 50 are observed when the Al is in the normal state. The device shows a high degree of unidirectionality. The results can be explained on the basis of the recently proposed QUAsiparticle TRApping TRANsistor, which should have wide applications in detection systems operating at low temperatures.         SQUID systems for macroscopic quantum coherence and quantum computing    P. Carelli, M.G. Castellano, F. Chiarello, C. Cosmelli, R. Leoni and G. Torrioli Summary: Among the various devices proposed as elements of a quantum computer, the rf-SQUID is a very promising candidate. In fact, systems based on this element can be adjusted in situ, can be coupled by means of superconducting transformers, can be prepared individually and measured with superconducting electronics. Moreover, many progresses were made in these years which showed quantum effects in this system. The present paper describes a complete device developed in order to get a direct measurement of the quantum coherent oscillation. The knowledge of this time, together with its limiting factors, is a prerequisite for fabricating a qubit based on rf-SQUIDs.         Imaging defects in Cu-clad NbTi wire using a high-T/sub c/ scanning SQUID microscope    E. Fleet, A. Gilbertson, S. Chatraphorn, N. Tralshawala, H. Weinstock and F.C. Wellstood Summary: We have used a sensitive magnetic microscope based on the dc Superconducting Quantum Interference Device (SQUID) to examine room-temperature samples of Cu-clad NbTi wire. Our SQUID microscope allows the wire (in air at room temperature) to be brought to within about 0.05 mm of the SQUID, although typically the separation is 0.3-0.4 mm. The wires have round or rectangular cross-sections and are about 2 mm across. With the wire aligned parallel to the x-direction in the x-y scanning plane we apply currents of a few mA through the wire at a frequency of a few hundred Hz, and image the x-component of the magnetic field. Defects cause a redistribution of current and corresponding features in the magnetic field image. We show images of wires, and discuss the advantages of using the parallel component of the field.         Magnetic flux guide for high-resolution SQUID microscope    S.A. Gudoshnikov, Y.V. Derquzhkina, P.E. Rudenchik, Y.S. Sitnov, S.I. Bondarenko, A.A. Shablo, P.P. Pavlov, A.S. Kalabukho, O.V. Snigirev and P. Seidel Summary: Magnetic properties of a permalloy needle designed for use in a high-spatial-resolution scanning SQUID magnetic microscope as a magnetic flux guide have been examined. The distributions of the magnetic field normal component over a needle were imaged at 77 K in various applied magnetic fields. Influences of the flux guide on the high temperature superconducting dc SQUID characteristics have been investigated.         SQUID microscope for magnetic structure visualization in magnetoimpedance elements    S.A. Gudoshnikov, P.E. Rudenchik, L.V. Matveets, O.V. Snigirev, B.Ya. Liubimov, N.S. Perov, E.A. Gan'shina, A.S. Antonov, A.L. D'achkov and M.V. Sedova Summary: An attempt to apply a SQUID microscope for visualization of magnetic structure in giant magnetic impedance (GMI) elements was undertaken. The measurements were carried out on the 1/spl times/10/sup -3/ mm thick permalloy strip with the in-plane sizes 6 mm/spl times/0.3 mm. The topography of the vertical component of magnetic field was imaged with a high spatial resolution close to 30/spl times/10/sup -3/ mm over the central part of a sample. The images taken in the applied magnetic field varied over the range /spl plusmn/4 kA/m reveal the domain structure with anisotropy perpendicular to longitudinal sample axis.         HTS SQUID microscope head with sharp permalloy rod for high spatial resolution    T. Nagaishi, K. Minamimura and H. Itozaki Summary: Spatial resolution with a sharp permalloy rod on an HTS SQUID microscope head was investigated. A 5 mm diameter and 10 mm long permalloy rod with one side sharp and one side flat is placed In front of a washer type SQUID with 0.1 mm spacing. A 0.3 mm line and space meander line on a printed circuit board carrying current was used as a magnetic field source. The SQUID microscope head with the sharp permalloy rod scanned two dimensionally on the meander line inside the magnetic shield. The 0.3 mm line and space meander line was resolved. We also demonstrated imaging of laser-printed characters. This method has the advantage of using a washer type SQUID with high magnetic sensitivity, high spatial resolution and facilitating the adjustment of the position and the measurement distance from the sample.         Study of trapped flux in a superconducting thin film-observation by scanning SQUID microscope and simulation    K. Tanaka, T. Morooka, A. Odawara, Y. Mawatari, S. Nakayama, A. Nagata, K. Ikeda, K. Chinone and M. Koyanagi Summary: Flux trapping in superconducting devices, such as Josephson circuits and SQUIDs is a major cause for degradation of device performance. Intentionally made holes and moats in superconducting films were previously found effective in overcoming the effects of flux trapping. Despite the need for a design rule for the arrangement of holes or moats, comparison between experiment and theory of the flux trapping locations has not yet been discussed. We therefore studied the locations of trapped fluxes in a superconducting thin film cooled at a rate of 0.02 K/sec for various external magnetic flux densities from 1 /spl mu/T to 3 /spl mu/T by using a scanning SQUID microscope. Trapped fluxes were observed at positions where holes were prepared in the superconducting film and also at superconducting locations outside the holes. Trapped fluxes outside the holes were orderly arranged regardless of magnetic flux density during cooling. These locations were then compared with those determined by simulations based on a model that considers both the surface barrier effect introduced by Bean and Livingston and the interaction among fluxes. The simulation shows that the potential wells appear below the transition temperature, corresponding to the trapped fluxes outside holes.         Noise and spatial resolution in SQUID microscopy    S. Chatraphorn, E.F. Fleet, F.C. Wellstood and L.A. Knauss Summary: We have used a scanning SQUID microscope to image magnetic field generated by currents in integrated circuits. To obtain current paths in these circuits, we apply a magnetic inversion technique to the magnetic field data. We find that the spatial resolution obtained from this technique is related to the signal-to-noise ratio, the SQUID-sample separation and the data sampling interval. We describe in detail a mathematical model of how these parameters relate to the spatial resolution. Finally, we discuss the limitations of our apparatus, and how to achieve higher spatial resolution.         Investigation of magnetic flux trapping in high-T/sub c/ thin films by scanning SQUID microscope    K. Suzuki, S. Adachi, Yijie Li, T. Utagawa and K. Tanabe Summary: The behavior of flux trapping in NdBa/sub 2/Cu/sub 3/O/sub y/ thin-film patterns with moats surrounding a 160 /spl mu/m square area has been investigated by a scanning superconducting quantum interference device (SQUID) microscope. Magnetic images were taken for moat patterns with three types of configuration and different size after cooling below T/sub c/ in various fields, and the threshold field for complete flux expulsion from the moat-surrounded area was estimated. It was found that the threshold field strongly depends on the size and gap of moats as well as their configuration. The largest enhancement of the threshold field by a factor of approximately seven as compared with that for an isolated square pattern was observed for the continuous moat pattern with broken corners.         Application of microcalorimeter energy measurement to biopolymer mass spectrometry    M.W. Rabin, G.C. Hilton and J.M. Martinis Summary: We have performed electrospray ionization mass spectrometry using a magnetic-sector mass spectrometer of proteins, detecting the ions with a normal-insulator-superconductor microcalorimeter detector. We emphasize the measurement of ion-impact energy as a way to obtain extra information that is unavailable in normal mass spectrometry. Energy measurements are used to discriminate against erroneous ion-strikes, to resolve ambiguities that cannot be resolved by normal mass spectrometry, and to illustrate some of the performance limits of the current detector design.         Field effect in perovskite-type manganite films on high-T/sub c/ superconductor    J. Sakai, A. Kitagawa, T. Tamada, M. Sakai, T. Hirao and S. Imai Summary: Layered-type junctions of perovskite-type manganite Pr/sub 1-x/Ca/sub x/MnO/sub 3-y/ (PCMO; x=0.3, 0.4, 0.5) and high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) were fabricated and their resistivity perpendicular to the plane were measured. A field effect was observed in which the resistivity decreased for 4 orders with 10 V of applied voltage at 30 K. Several oxygen-annealed junctions showed an abrupt drop of resistivity at about 2 V, independently to x, which is considered to be a sign of charge-ordering (CO). Annealing, on the other hand, suppressed the macroscopic resistivity of PCMO films. A field effect at room temperature was also observed.         Three component spinner magnetometer featuring rapid measurement times    K.E. Leslie, R.A. Binks, C.J. Lewis, M.D. Scott, D.L. Tilbrook and J. Du Summary: We describe the fabrication and performance of a spinning rock magnetometer for measuring the intensity and direction of the remanent magnetisation of rock specimens collected in palaeomagnetic surveys. The strength of these fields is measured using a high temperature superconductor (HTS) rf SQUID. Samples are rotated around two orthogonal axes to facilitate the calculation of the three-component remanence vector with a minimum of operator intervention. Measurements of remanence values ranging from 10/sup 1/ to 10/sup -5/ A/m, with errors of 1/spl times/10/sup -5/ A/m, have been achieved in measurement times of 20 s, while operating the instrument in a typical geophysical laboratory environment. In this paper we discuss the design requirements and data processing necessary to achieve a user-friendly system.         Discharge measurements using a HTS-SQUID based amplifier system    T. Eriksson, J. Blomgren and D. Winkler Summary: In the design and development of high voltage insulation systems, partial discharge measurements are often used for system characterization and evaluation. The aim of this work was to investigate the SQUID sensor as an amplifier in a high voltage environment. An HTS SQUID amplifier has been developed and tested under laboratory conditions. Different SQUIDs and a number of different input configurations have been investigated. Preliminary data indicate that the system has a performance similar to a commercial system used as reference. However, calculations and simulations show that the new method has potential for further improvement.         Analysis of the Bloch oscillating transistor    J. Hassel and H. Seppa Summary: The Bloch-oscillating transistor (BOT) is a device where coherent Cooper-pair current in mesoscopic Josephson junctions can be controlled with single-electron tunneling from the base-electrode. We show computational results on the single-junction BOT (sj BOT). Also the double-junction BOT (dj BOT) is introduced. An approximate formula of the device noise temperature is also presented.         A cell-based design approach for RSFQ circuits based on binary decision diagram    J. Koshiyama and N. Yoshikawa Summary: We have proposed a cell-based design approach for rapid single flux quantum (RSFQ) logic circuits. In our design approach, a binary decision diagram (BDD) is used for representation of logical functions in order to reduce the number of gates. We have made a standard cell library, which is composed of only five basic cells. We add one-junction Josephson transmission line (JTL) to the edge of the input and the output node of some basic cells, by which no deterioration of the DC bias margin is observed for the connection of each cell. In the layout level, the size and the position of the input/output node of each cell are equalized. The standard cell circuits were fabricated by NEC 2.5 kA/cm/sup 2/ and Hypres 1.0 kA/cm/sup 2/ Nb standard process and they were tested at low speed.         High-T/sub c/ superconductor sampler system for digital signal waveform measurement    M. Hidaka, T. Satoh, M. Kimishima, M. Takayama and S. Tahara Summary: We are developing a system using a high-T/sub c/ superconductor (HTS) sampler for measuring a 40-Gbps digital signal waveform, which will be used in next generation ultra-high-speed communications. To measure a 40-Gbps digital signal, the sampler bandwidth needs to be more than 120 GHz. The HTS sampler has the potential to achieve this bandwidth. As a first step in developing this system, we have developed a prototype whose target bandwidth is 40 GHz. In the prototype system, the sampler chip is cooled down to 35 K by a single-stage Stirling cryocooler, and the digital signal is transmitted to the sampler chip via a 40-GHz bandwidth assembly line. This system is the first to integrate an HTS device, a cryocooler, and a high-frequency assemble line. A 5.9-Gbps digital waveform was reconstituted by the prototype system with the correct period.         Tolerance of programmable Josephson voltage standard to noise and junction nonuniformity    Kyu-Tae Kim, Hyun Kwon Hong, Jinhee Kim, Kyu Won Lee and Yang Sup Song Summary: Nonhysteretic Josephson junctions array of a very good uniformity is required for realization of programmable Josephson voltage standard. The tolerable nonuniformity of junction critical current in the presence of a Gaussian noise is analyzed with an accuracy requirement of PJVS.         Analog-to-digital converter testing method based on segmented correlations    J.F. Bulzacchelli, Hae-Seung Lee, J.A. Misewich and M.B. Ketchen Summary: The high sampling rates of superconducting analog-to-digital (A/D) converters complicate testing since the output data rates often exceed the capacity of the interface to room-temperature electronics. Capturing the data with an on-chip shift register allows low speed interfacing, but integration limits of current Josephson technology make such an approach impractical for oversampling converters, as the shift register length must be much larger than the oversampling ratio (OSR). In this paper, we describe a scheme in which two segments of the output data stream are captured with a pair of shift registers, whose lengths can be less than the OSR. The number of clock cycles skipped between acquiring the two segments is set by an on-chip programmable counter (from 0 to N, where N is much larger than the OSR). Cross-correlation of the two segments provides an estimate of the output autocorrelation function R[n], over a narrow range of n. By reprogramming the counter, other sections of R[n] can be estimated through successive measurements, allowing assembly of the entire function R[n] (up to n=N). Fourier transformation of R[n] yields a spectrum with the frequency resolution of an N-point FFT. Both low-pass and bandpass A/D converters can be studied with the method.         A general approach for determining the switching probability in rapid single flux quantum logic circuits    T. Ortlepp, H. Toepfer and H.F. Uhlmann Summary: A major restriction in the development of a working Rapid Single Flux Quantum (RSFQ) logic circuit with high-Tc superconductors is given by the influence of thermal noise. This gives reason to ask for a general determination of the digital bit error rate. As other approaches, our method of calculating the switching probability is based on the Fokker-Planck equation. In the past few years the bit error rates for a single Josephson junction, SQUIDs and the comparator were calculated by using this theory. We demonstrate numerical solution of the multidimensional Fokker-Planck equation to calculate bit error rates due to thermal noise for a Toggle Flip Flop circuit. In the present work, we combine thermal noise analysis with the effects of process variations in order to derive rules for designing high-Tc RSFQ logic circuits.         On-chip high-frequency diagnostic of RSFQ logic cells    P. Febvre, J.-C. Berthet, D. Ney, A. Roussy, J. Tao, G. Angenieux, N. Hadacek and J.-C. Villegier Summary: Hilbert Transform spectroscopy is described as a method to analyze the spectrum of pulse trains generated by RSFQ circuits. Simulations are carried out using parameters appropriate for NbN Josephson junctions for both generation and detection of SFQ pulse trains. It is shown that the pulse shape along with the pulse train repetition rate can be extracted through the use of a Josephson junction, used as a spectrometer, and located on-chip with the RSFQ circuit to test.         Time jitter measurement in a circular Josephson transmission line    V. Kaplunenko and V. Borzenets Summary: A Josephson transmission line closed to form a ring was used to measure the time jitter produced by a single shunted Josephson junction. A toggle flip-flop cell was connected to a sampling oscilloscope, and was used to detect the flux quantum arrival time. Time jitter was determined from the variation of this time. The jitter was measured as a function of the number of cycles the flux quantum made in the ring. The reduced jitter produced by a single junction of 0.2 ps/spl radic/n (n-number of junctions passed by the quantum) was measured using Hypres 1 kA/cm/sup 2/ chip fabrication technology. It was found that jitter varies the distance between the quanta with the same rate of 0.2 ps/spl radic/n.         Carbon masks for patterning of YBa/sub 2/Cu/sub 3/O/sub x/ submicron Josephson junctions    I.A. Volkov, A.S. Kalabukhov, O.V. Snigirev and A.N. Zherikhin Summary: We have developed a fabrication process for submicron wide YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) Josephson junctions on bicrystal substrates. The masks patterned in carbon films grown by laser ablation were used for ion beam etching of YBCO films. The carbon deposition parameters providing conservation of critical temperature of YBCO films covered by carbon layers have been found. The test 1.5 to 3 /sub /spl mu//m wide YBCO bridges have been fabricated on single crystal SrTiO/sub 3/ substrates using the developed technology.         Contacts on single crystals grown by liquid phase epitaxy    Y. Enomoto, H. Suzuki, S. Hoshi, T. Izumi and Y. Shiohara Summary: We have fabricated a contact with a small area on a YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) ground plane grown by Liquid Phase Epitaxy (LPE). The contact has a ramped edge structure, which directly connects CuO/sub 2/ planes between the ground plane and lines. After deposition of NdBa/sub 2/Cu/sub 3/O/sub 7-x/ (NBCO) films used for lines, no deterioration is observed in AFM image on the ramped edge in spite of its higher deposition temperature than that of the YBCO thin film. This shows high crystal quality of the YBCO film grown by LPE. Flux flow type current-voltage characteristics are observed with critical current density of 5/spl times/10/sup 4/ A/cm/sup 2/ at 47 K. XRD shows strain caused by lattice mismatch along the boundaries between NBCO and YBCO.         In-plane magnetic field dependence of intrinsic Josephson junctions in Tl-Ba-Ca-Cu-O thin films    P.A. Warburton, O.S. Chana, A.R. Kuzhakhmetov, D.M.C. Hyland, D. Dew-Hughes, C.R.M. Grovenor, Y. Koval and P. Muller Summary: We have fabricated intrinsic Josephson bridges using Tl-Ba-Ca-Cu-O thin films grown on vicinal lanthanum aluminate substrates. Measurements of the lock-in transition allow us align a magnetic field of up to 4 T with the copper oxide planes to better than 0.3/spl deg/. This allows us to study the dynamics of Josephson fluxons in the films. For fields above 1.4 T and at low currents we observe Josephson flux creep. Above a field-dependent threshold current we observe free flow of the fluxons with a flux-flow resistance which is proportional to field. The fluxons reach a field-independent velocity before the jump to the quasiparticle branch occurs. Our results suggest that the development of a sub-mm-wave oscillator using these bridges will require sub-micron patterning.         Random telegraph voltage noise in a Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ intrinsic Josephson junction    A. Saito, K. Hamasaki, A. Irie and G. Oya Summary: Low frequency noise properties have been investigated in mesa-type Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO) intrinsic Josephson junction. The junction area for this mesa was 160 /spl mu/m/spl times/40 /spl mu/m. The mesa showed highly hysteretic current-voltage characteristic at low temperatures, and had seven discrete-resistive-branches. For the noise measurements only at T/spl sim/36 K, we observed a rapid increase in the noise voltage spectrum over our entire bandwidth. Large random telegraph voltage noises (RTVN) were only detected for low bias current region of the BSCCO mesa for current biased on the 4th (I/sub b/=6.0 mA) and 5th (I/sub b/=5.0 mA) resistive-branches, and also not observed for all of voltage region at 4.2 K and low bias voltage region, from 1st to 3rd resistive-branches, at 36 K. The measured S/sub v/(f) had the Lorentzian frequency dependence, as expected from the Machlup formula for random telegraph signal. The possible origin of the large RTVN may be thermal fluctuation of the "switchback" voltage V/sub min/.         Coherent phase locking of high-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub y/ Josephson junctions    H.C. Yang, C.H. Wu, M.J. Chen, J.H. Chen, C.H. Chen, H.W. Yu, J.T. Jeng and H.E. Horng Summary: We measured I-V curves and noise characteristics of high-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub y/ step-edge Josephson junctions and serial junction arrays under microwave irradiation. The junctions were fabricated on step-edge MgO[100] substrates with low step angles (/spl sim/30/spl deg/). The junction array shows the resistively shunted junction (RSJ) behavior for at least 50 junctions and reveals a coherent phase locking under microwave irradiation. The variation of I/sub c/ was 16% for a 150-junctions array distributed along the step-edge line of 1.5 mm in width. The voltage noise, S/sub v/, of the serial junction array scales as the number of junctions, N. The value of S/sub IR/, (S/sub IR/=|(/spl delta/I/sub c//I/sub c/)||(/spl delta/R/R)|), for a single and 50-junctions obtained from the fluctuation measurement is consistent with the result derived from I/sub c/R/sub n//spl prop/(J/sub c/)/sup q/, with q=0.5.         10 K NbN DSP module for IR sensor applications    A.G. Sun, B.J. Dalrymple, D.J. Durand, Q.P. Herr, M.W. Johnson, J.A. Luine and A. Spooner Summary: The authors report significant progress on infrared (IR) focal plane array (FPA) imaging signal processing circuits, built in NbN and operating at 10 K. The improvements to our NbN process are highlighted by the introduction of directly grounded junctions (DGJ). These DGJs substantially reduce parasitic inductance thereby compensating for the high sheet inductance of NbN films. The circuits being developed include a 16-bit SFQ counting ADC and several digital signal processing (DSP) units. We report test results of greatly improved ADC performance, which is the result of both improved designs and fabrication techniques. Signal processing units on individual chips have been designed, fabricated, and tested. They perform functions such as background subtraction, gain and responsivity correction, and data reduction. We report test results of the DSP chips performing these functions. Ultimately, these chips will be integrated on a multi-chip-module (MCM) with high bandwidth, low impedance interconnects and integrated with an IR focal plane array sensor.         Broad band software-defined radio receivers based on superconductive devices    A. Fujimaki, K. Nakazono, H. Hasegawa, T. Sato, A. Akahori, N. Takeuchi, F. Furuta, M. Katayama and H. Hayakawa Summary: We have studied software-defined radios (SDRs) based on superconducting devices. The increasing data rate in mobile communications will require a band-width of up to a few hundred MHz in the future. We have confirmed numerically the broad-band characteristic of oversampled analog-to-digital converters including a lowpass and bandpass modulator. Furthermore, the bandpass modulator constructed without a resistor is found to have sensitivity improved by two orders of magnitude compared to that of the lowpass modulator. This result means that the digital RF radio architecture based on a bandpass ADC is better suited for a future SDR receiver.         SFQ standard cell-based circuit design of an internal link speeded-up Batcher-Banyan packet switch    Y. Kameda, S. Yorozu and S. Tahara Summary: We are developing a single-flux-quantum (SFQ) packet switch for over 1-Tb/s switching systems. Investigation of several switch topologies leads us to select the Batcher-Banyan packet switch because of its simplicity and regularity. The packet switch structure we propose consists of simple 2/spl times/2 unit switches each connected by speeded-up internal links. Numeric simulation showed that the speeded-up links greatly improved the throughput by resolving packet blocking, which is a major drawback of the Banyan switch. High throughput compatible to a crossbar switch was attained by using links whose speed was quadrupled. Moreover, the throughput did not decrease even though the number of input/output ports increased. Taking the speed of SFQ basic gates into account, the cycle time of the 2/spl times/2 unit switch reaches 25 ps, which is sufficient to achieve the 40-GHz operation. If unit switches are connected by quadrupled internal links, the Batcher-Banyan switch can accept the 10-Gb/s external input rate per channel. This indicates that the total throughput of a 128/spl times/128 switch exceeds 1 Tb/s. The unit switch was designed down to the SFQ gate level. To design a large SFQ circuit, we built several "standard" SFQ cells whose shape was square or rectangular with a unit width and height. Such shapes make it easier to place and connect a number of cells. We show some experimental results of testing SFQ standard cells and logic circuits.         FLUX chip: design of a 20-GHz 16-bit ultrapipelined RSFQ processor prototype based on 1.75-/spl mu/m LTS technology    M. Dorojevets, P. Bunyk and D. Zinoviev Summary: We describe the design and implementation of a single-chip microprocessor based on LTS Rapid Single-Flux-Quantum (RSFQ) technology. Two such chips are to be used in a dual-processor module, being developed by a SUNY-TRW collaboration as a spin-off of the HTMT project. Each FLUX chip represents a simple 16-bit 2-way long-instruction-word (LIW) microprocessor with a pipelined instruction memory of 30-bit instructions, decode and issue units, 8 integer ALUs interlaced with 8 registers, and input/output ports through which two FLUX chips can communicate with each other at a 7-GHz communication rate over a multi-layer MCM. The FLUX instruction set consists of /spl sim/25 instructions. High performance is reached with a scalable design featuring (1) a very high clock rate, (2) localized, regular and ultrapipelined processing in registers with very short wires, (3) instruction-level parallelism utilization with bit-level resolution of data hazards. A 16-bit implementation of FLUX processor consists of /spl sim/90,000 Josephson junctions on a /spl sim/10 mm/spl times/15 mm chip area. Our estimates show that the processor will be able to operate at clock frequencies up to 20 GHz when implemented using TRW's 4 kA/cm/sup 2/, 1.75-/spl mu/m Nb-trilayer technology.         A new concept for ultra-low power and ultra-high clock rate circuits    A.H. Silver and Q.P. Herr Summary: Compared with semiconductors, SFQ logic is very fast and dissipates extremely low power. But it does not approach the theoretical power dissipation associated with an SFQ switching event and single gate speed in complex circuits. For large circuits and systems, e.g., petaflops computing, we must reduce on-chip dissipation, achieve faster clocked logic operation, and increase gate density. CMOS logic dissipates the energy required to switch a transistor pair and dissipates no power between switching events. We describe a new SFQ circuit concept that mimics CMOS to achieve ultra-low power dissipation and ultra-high clock rates. This results in physically compact, self-clocked, complementary logic (SCCL), in which clock distribution is frequency-independent. The basic element in this logic family is a simple two-junction comparator. Using TRW's 2 kA/cm/sup 2/ Nb design rules, we simulated basic digital components: shift register, AND, OR, and NOT at 20 GHz. We present the simulated and measured performance.         Demonstration of chip-to-chip propagation of single flux quantum pulses    M. Maezawa, H. Yamamori and A. Shoji Summary: We report experimental results on chip-to-chip transfer of single-flux-quantum (SFQ) pulses using an active multichip module (MCM). Josephson transmitters and receivers are integrated on both a chip and an MCM substrate. An MCM consisting of a 4.8-mm chip and an 8.2-mm MCM substrate was fabricated using a 1.6-kA/cm/sup 2/ Nb-trilayer process and a solder-bumped flip-chip bonding technology. The correct operation of the circuit was confirmed by low-speed testing. Bit-error rate (BER) of the circuit was measured down to 10/sup -5/, and extrapolation of the error-function fits suggested a very small BER, lower than 10/sup -200/, at the optimum bias point. Experimental margins on the bias voltage were as large as /spl plusmn/34%.         Interface circuit using JTLs as control lines of SQUID array    Y. Tarutani, K. Saitoh and K. Takagi Summary: Interface circuits for the RSFQ circuit system were designed, fabricated and their frequency characteristics were investigated. Key elements of the interface circuit were the series array of SQUIDs and a JTL as a control line of the SQUID. The interface circuit was designed to cover the operating frequencies much greater than 10 GHz. A high-frequency signal generator circuit consisting of a ring oscillator, a frequency divider, and an interface circuit was fabricated. High frequency signals produced in the ring oscillator could be detected by using the interface circuit. The h/2e relationship between the oscillation frequency and the ac Josephson voltage was verified.         Modeling superconducting components based on the fabrication process and layout dimensions    W.J. Perold and C.J. Fourie Summary: A procedure is described where the mask dimensions of superconducting components are used in SPICE simulations to predict the performance of a device. Thickness tolerances of the fabrication process, as well as mask bias offsets and mask tolerances are included in the component models. This makes it possible to predict circuit yield by Monte Carlo analyses, which are based on the fabrication process design rules. Model descriptions of all the components used in a standard superconductor multilayer process are given, and the accuracy of the models are verified. The superconducting components that are modeled include microstrip transmission lines, coupled transmission lines, resistors and Josephson junctions. The usefulness of this procedure is demonstrated by simulation results of a stack amplifier, where the yield of the circuit is calculated for the lumped element model and the proposed model, which includes parasitic elements.         Highly miniature HTS microwave filters    Hieng Tiong Su, F. Huang and M.J. Lancaster Summary: Two 3/sup rd/ order HTS quasi-lumped-element Chebyshev bandpass filters were fabricated. The first uses very compact resonators consisting of interdigital capacitors and straight inductors. Currents in the capacitor fingers were included in the inductance evaluation, In the second filter, a meander-line inductor achieves further miniaturisation. Experimental results agree well with full wave simulations. Quasi-elliptic and group delay compensated filters using similar resonators are also discussed and simulated responses are presented.         Active tuning of high frequency resonators and filters    Hui Xu, E. Gao and Q.Y. Ma Summary: In this paper, we present a new electromechanical approach of active control of high temperature superconducting (HTS) resonator and filter center frequency. The design of the tunable devices incorporates piezoelectric bender or tube actuator, which acts as a varactor of the resonance circuit, with YBCO thin film on LAO substrate. The resonator has an unloaded Q of over 18,000 at 77 K and a center frequency of 362 MHz and a tuning range of over 20% with unloaded Q over 10,000. By applying different voltages to the piezoelectric bender, we have tuned the resonance frequency over 30% with a good linearity and high Q. Based on this structure, a two-pole HTS bandpass filter was designed, fabricated and tested. The filter has a tunable center frequency from 17 to 20 MHz while maintaining a 2.5% 3dB bandwidth, and an insertion loss of less than 0.5 dB at 77 K.         Y-Ba-Cu-O thin films on 3" sapphire wafers for microwave devices    R. Aidam, J. Geerk, G. Linker, F. Ratzel, J. Reiner, R. Schneider, R. Smithey, A.G. Zaitsev, E. Gaganidze and R. Schwab Summary: Epitaxially grown large area YBCO films are essential for superconducting high frequency devices, e.g. microstrip filters for telecommunications. Therefore, c-axis oriented, 250 to 500 nm thick YBCO films were simultaneously deposited by sputtering from hollow cylindrical targets on both sides of CeO/sub 2/ buffered 3" sapphire wafers. The lateral homogeneity was analyzed by mapping the surface resistance, R/sub s/, at 145 GHz and 75 K. Values of R/sub s/ below 50 m/spl Omega/ were reached over the whole area. The HF power handling capability was demonstrated by a break down field higher than 10 mT at 8.5 GHz and 77 K. In order to demonstrate the quality of our sputtered films with respect to large area high frequency applications, simple microstrip resonators were patterned by UV photo lithography and wet chemical etching. At a circulating power of up to 1 W, very high unloaded quality factors, Q/sub 0/, of up to 32000 at 4 GHz and 77 K were achieved. Above 5 W, Q/sub 0/ decreased due to the field dependence of R/sub s/. The operation of complex structures was demonstrated by 3 pole and 7 pole bandpass filters operated at 77 K and 2 GHz and 6 GHz, respectively. The filters, tuned by brass tuning elements, showed transmission losses of less than -0.3 dB and reflection losses of more than -17 dB.         Narrow-band 10-pole Y-Ba-Cu-O filter on sapphire substrate    I. Vendik, A. Deleniv, A. Svishchev, M. Goubina, A. Lapshin, A. Zaitsev, R. Schneider, J. Geerk and R. Aidam Summary: In this paper we present the design procedure of HTS bandpass filters on sapphire substrate. The filter with 0.4% fractional bandwidth in S-band was designed using an effective CAD tool, based on spectral domain approach. The filter is based on hairpin resonators exhibiting unloaded Q up to 43000 at T=77 K. The anisotropy of the dielectric permittivity of sapphire substrate and the YBCO film contribution in the propagating characteristics have been taken into account. Substrate characteristics and YBCO film model parameters were extracted from microstrip and hairpin resonator measurements. These parameters were used in the filter simulation procedure.         Micron and submicron Nb/Al-AlO/sub x//Nb tunnel junctions with high critical current densities    Xiaofan Meng, L. Zheng, A. Wong and T. Van Duzer Summary: To increase superconducting IC speed and density, it is necessary to reduce junction size and increase critical current density. We describe the fabrication and properties of high critical current density micron and submicron Nb/Al-AlO/sub x//Nb tunnel junctions. Using a 10:1 reduction wafer stepper with I-line photoresist, we obtained a minimum linewidth of 0.6 /spl mu/m and junctions as small as 0.3 /spl mu/m/sup 2/. The critical current densities can be as high as 20 kA/cm/sup 2/ still with low subgap currents. The measured critical current spreads are small. This is due to the use of low-temperature, low-stress ECR (Electron Cyclotron Resonance)-based PECVD (Plasma Enhanced Chemical Vapor Deposition) SiO/sub 2/ insulation layers and light anodization around junction areas. The junctions have potential applications in very high-speed superconducting digital circuits and submillimeter microwave devices.         Retargeting RSFQ cells to a submicron fabrication process    D.K. Brock, A.M. Kadin, A.F. Kirichenko, O.A. Mukhanov, S. Sarwana, J.A. Vivalda, Wei Chen and J.E. Lukens Summary: There is a desire to move current state-of-the-art niobium Josephson IC fabrication processes (/spl sim/3 /spl mu/m) to smaller sub-micron linewidths in order to realize a decrease in gate size and increase in both speed and packing density. However, cost and time dictates that a way be found to reuse the existing RSFQ gate/cell development that has been done at the 3-/spl mu/m level. Cell retargeting is the process of migrating existing designs to a new technology, with the effort focused on the maximum reuse of existing material. We have investigated a number of issues critical to this process, including both the physical and electrical aspects. Comments are made on methodologies for RSFQ cell retargeting with respect to existing reduced-linewidth JJ fabrication processes. Experimental demonstrations are shown for retargeted RSFQ static digital frequency dividers (toggle flip-flops) operating at 220 GHz, 240 GHz, and 395 GHz.         Fabrication of ultrasmall tunnel junctions by electron beam direct-writing    D. Born, T. Wagner, W. Krech, U. Hubner and L. Fritzsch Summary: Fabrication of miniaturized tunnel junctions based on high-melting metals by the shadow evaporation technique is rather complicated. The thermal load of the suspended bridge mask during metal evaporation is assumed to be the most serious problem. As an alternative we have developed a preparation technique using e-beam direct-writing lithography in conjunction with material deposition by sputtering. To test the preparation process, we have fabricated single electron transistors (SETs) based on the metals Al and Nb, including mixed Al/Nb samples. For SETs made completely of Nb, we preferred Al0/sub x/ to the natural oxide NbO/sub x/ for barrier generation. The yield of functioning samples amounted to about 80%. By means of simple considerations we have estimated the tunnel capacitances to be of the order of a few 10/sup -16/ F, the tunnel resistance spread was less than one order of magnitude.         Fabrication of SIS junctions for space borne submillimeter wave mixers using negative resist e-beam lithography    I. Peron, P. Pasturel and K.-F. Schuster Summary: We report on the development of a new process for the fabrication of Nb/Al-AlO/sub x//Nb tunnel junctions for channel 1 (480-640 GHz) Superconductor-Insulator-Superconductor (SIS) mixers of HIFI, the Heterodyne Instrument for FIRST (Far InfraRed & Submillimeter Telescope). The process is derived from a standard self-aligned lift-off process but uses negative resist electron beam lithography (EBL) for junction definition. The junction area is tightly controlled down to below 1 /spl mu/m/sup 2/ without the complexity of processes using positive electron beam resists. We describe process parameters and experimental results: DC-tests and Fourier Transform Spectrometer (FTS) measurements.         Precise patterning technique for Nb junctions using optical proximity correction    M. Aoyagi, H. Nakagawa, H. Sato and H. Akoh Summary: In the fabrication process of Nb junctions, a precise and reliable lithography technique for a small junction area is needed to realize a wide-operating-margin circuit. We propose a patterning technique for micron or submicron Nb junctions using optical proximity correction (OPC). In the i-line optical lithography process, scattering bars and serifs are added to the photomask patterns for small junction area. Nb junctions ranging in size from 0.5-/spl mu/m square to 2.0-/spl mu/m square were successfully fabricated using this technique. For a square junction pattern, variations of junction critical current and shrinkage of the junction size are improved using OPC.         YBa/sub 2/Cu/sub 3/O/sub 7/ on Y-stabilized ZrO/sub 2/ buffered [100] Si-"T" resonator microwave characteristics    Y.A. Vlasov, J.M. Vargas, P. Brown and G.L. Larkins Jr. Summary: We have successfully fabricated high quality YBa/sub 2/Cu/sub 3/O/sub 7/ microwave "T" resonators on YSZ buffered P-type [100] oriented 53-56 /sup /spl Omega/-/cm silicon. The 40 to 50 nm thick yttria-stabilized zirconia buffer layer was deposited by pulsed dc magnetron sputtering at 830/spl deg/C. The 250 to 400 nm thick YBa/sub 2/Cu/sub 3/O/sub 7/ film was deposited using laser ablation at 760/spl deg/C. Results include Q values in excess of 20,000 at 3.8 GHz on a coplanar "T" resonator at temperatures below 50 K.         HTS microstrip filters using H-type resonators    Dong-Chul Chung and Byoung-Sung Han Summary: We report the characteristics of a high-T/sub c/ superconductor (HTS) bandpass filter with the designed center frequency of 16.5 GHz. A YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting thin film was prepared using the rf-magnetron sputtering deposition technique. The filter used in this work was composed of the "H"-type resonator (non-uniform microstrip lines). This approach has advantages for a considerably high Q-value and the compact filter structure. The impedance ratio of the "H"-type resonator was 0.5 in this work. In the measured responses, this HTS filter showed the insertion loss of -0.4 dB at maximum. The measured center frequency of our HTS bandpass filter was 16.44 GHz and the passband was from 15.91 GHz to 16.97 GHz, a bandwidth of 6.86% with 3 dB in band Chebyshev ripple. Experimental results of our filters were reported in terms of insertion loss, return loss and other various characteristics.         Superconducting half-wave microwave resonator on YSZ buffered Si [100]    J.M. Vargas, P. Brown, T. Khan, Y. Hijazi, Y.A. Vlasov and G.L. Larkins Jr. Summary: We have produced high quality superconducting half-wave microwave resonators on YBCO/YSZ/Si heterostructures. The YSZ was grown on [100] Si by pulsed dc magnetron sputtering at 820/spl deg/C in 37 mTorr Ar/O/sub 2/. YBCO was then deposited on the YSZ/Si by pulsed laser ablation at 760/spl deg/C in 0.5 Torr of O/sub 2/. A coplanar meander-line structure was patterned and its microwave characteristics measured. The results indicate Si to be a definite candidate for microwave applications producing Q values exceeding 50,000 at 4 GHz for T<30 K. The microwave properties compare favorably to those obtained from identical resonators patterned on normal metal and YBCO/LaAlO/sub 3/ at 30 K.         Fixed-frequency and frequency-agile (Au,HTS) microstrip bandstop filters for L-band applications    E.M. Saenz, G. Subramanyam, F.W. Van Keuls, Chonglin Chen and F.A. Miranda Summary: In this work, we report on the performance of a highly selective, compact 1.83/spl times/2.08 cm/sup 2/ (/spl sim/0.72/spl times/0.82 in./sup 2/) microstrip line bandstop filter of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) on LaAlO/sub 3/ (LAO) substrate. The filter is designed for a center frequency of 1.623 GHz for a bandwidth at 3 dB from reference baseline of less than 5.15 MHz, and a bandstop rejection of 30 dB or better. The design and optimization of the filter was performed using Zeland's IE3D circuit simulator. The optimized design was used to fabricate gold (Au) and High-Temperature Superconductor (HTS) versions of the filter. We have also studied an electronically tunable version of the same filter. Tunability of the bandstop characteristics is achieved by the integration of a thin film conductor (Au or HTS) and the non-linear dielectric ferroelectric SrTiO/sub 3/ in a conductor/ferroelectric/dielectric modified microstrip configuration. The performance of these filters and comparison with the simulated data will be presented.         General electromagnetic simulation tool to predict the microwave nonlinear response of planar, arbitrarily-shaped HTS structures    J. Parron, C. Collado, J. Mateu, J.M. Rius, N. Duffo and J.M. O'Callaghan Summary: This work describes a simulation tool being developed at UPC to predict the microwave nonlinear behavior of planar superconducting structures with very few restrictions on the geometry of the planar layout. The software is intended to be applicable to most structures used in planar HTS circuits, including line, patch, and quasi-lumped microstrip resonators. The tool combines Method of Moments (MoM) algorithms for general electromagnetic simulation with Harmonic Balance algorithms to take into account the nonlinearities in the HTS material. The Method of Moments code is based on discretization of the Electric Field Integral Equation in Rao, Wilton and Glisson Basis Functions. The multilayer dyadic Green's function is used with Sommerfeld integral formulation. The Harmonic Balance algorithm has been adapted to this application where the nonlinearity is distributed and where compatibility with the MoM algorithm is required. Tests of the algorithm in TM/sub 010/ disk resonators agree with closed-form equations for both the fundamental and third-order intermodulation currents. Simulations of hairpin resonators show good qualitative agreement with previously published results, but it is found that a finer meshing would be necessary to get correct quantitative results. Possible improvements are suggested.         A refined circuit model of high temperature superconducting spiral coils for MRI    E. Gao and Q.Y. Ma Summary: A high temperature superconducting (HTS) spiral coil for magnetic resonance imaging (MRI) usually contains many turns of thin track patterned on an HTS film. The total length of the coil track is long (up to few meters) in order to meet the requirement of fitting the resonance frequency to that of the MRI scanner, in the range from 4 MHz (0.1 T of magnetic field) to about 100 MHz (high field). It takes too long time for commercially available software to simulate such circuits because of the relatively large size and small track width of the coil. A new computational frequency-domain model is developed for design and analysis of HTS spiral surface coils for application to MRI. The model is faster in the simulation of the resonance frequencies and s-parameters of the HTS spiral coils because some approximations are used for the coils with long track and low resonance frequency. The new model is based on the circuit analyses theory. The 2-inch coils were simulated for a field of 0.5 T. Tuning and matching are studied by using this model.         Fabrication of HTS hairpin type filter with the center frequency of 22 GHz    Cheol-Su Kim, Seok Cheon Song and Sang Yeol Lee Summary: In order to investigate the possibility of the fabrication of millimeterwave HTS devices, we have designed and fabricated hairpin type filters with the center frequency higher than 20 GHz using YBCO superconducting thin films. The use of high-temperature superconducting (HTS) films in microwave applications provides a realization of high performance planar filters with narrow passband and low insertion loss. We have designed and fabricated 3-pole HTS hairpin type bandpass filters with the center frequency of 22 GHz. In order to reduce the filter size, filter was designed consisting of hairpin type coupled lines. Epitaxial YBCO films were grown on a MgO substrate by pulsed laser deposition (PLD). The film thicknesses were about 500 nm. Superconducting transition temperatures have shown to be about 89 K. Filter shows the insertion loss of 2.8 dB and the bandwidth of about 3 GHz at 77 K. Also the performance of superconducting bandpass filter will be compared with the simulation result.         Further development of a future ESM channeliser with high temperature superconducting filters    R.F. Jeffries, R.B. Greed, D.C. Voyce, G. Nudd, R.G. Humphreys and S.W. Goodyear Summary: An important function of an Electronic Warfare Support Measures (ESM) receiver is the acquisition and identification of signals in the Electronic Warfare (EW) environment. Ideally the receiver requires a high probability of intercept. Current receiver types include wide open systems, which suffer from signal overlap, and scanning superheterodyne receivers, which have a low probability of intercept against some signals. The ideal solution is to channelise the search bandwidth with each channel monitored continuously. To obtain high frequency resolution many narrow bandwidth filters are required. If miniature conventional filter technology is utilised the insertion losses become unacceptably high. By using high temperature superconductors (HTS), a channeliser of small size and low loss may be realised. This paper describes the recent design and build of an ESM channeliser with potential for 2-18 GHz operation. It uses eight filter banks, each consisting of twenty superconducting filters with a bandwidth of 100 MHz, contained within a cryogenically cooled dewar. Interconnects from the filter banks to the external rf connectors consist of flexible microtrace circuits.         Spread of critical currents in thin-film YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junctions    P. Shadrin and Y. Divin Summary: A spread of the critical currents in a series array of up to 100 YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junctions has been studied by Laser Scanning Microscopy. The values of the critical current I/sub c/ of individual junctions in the array have been obtained by focusing a laser beam on each junction and measuring the current at which the maximum laser-induced voltage response /spl Lambda/V on the array has appeared. The distribution of critical currents in logarithmic scale was close to a Gaussian one. The I/sub c/-spread has been found to increase with the increase of misorientation angle of bicrystal substrate and the decrease of the width of the junctions in the array.         Capacitance as a probe of high angle grain boundary transport in oxide superconductors    E.J. Tarte, P.F. McBrien, J.H.T. Ransley, R.H. Hadfield, E. Inglessi, W.E. Booij, G. Burnell, M.G. Blamire and J.E. Evetts Summary: We report a series of studies of grain boundary (GB) capacitance for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films grown on SrTiO/sub 3/ (STO) bicrystal substrates. By varying the film thickness and the width of the track containing the GB, we find that the substrate makes no contribution to the capacitance measured using Fiske resonances or hysteresis in most cases. This is due to the frequency dependence of the dielectric properties of SrTiO/sub 3/. We have also found that GB capacitance per unit area c/sub GB/ correlates with the resistance-area product R/sub n/A. For our own GBs and GBs reported in the literature the data is is consistent with c/sub GB//spl prop/(R/sub n/A)/sup -1/. We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling.         Effects of anomalous Andreev reflection in high T/sub c/ layered structures    A.A. Golubov and F. Tafuri Summary: Andreev reflection is investigated in layered anisotropic normal metal/superconductor (N/S) systems in the case of an energy gap in S not negligible respect to the Fermi energy, as probably occurring in high critical temperature superconductors (HTS). We find that in these limits retro-reflectivity, which is a fundamental feature of Andreev reflection, is broken modifying sensitively transport across S/N interfaces. This study is extended to aspects proper of HTS junctions to investigate both the supercurrents in S-N-S Josephson structures and zero bound states in S-N contacts respectively. Such an investigation provides a new insight into the effects that anisotropy determines into the phenomenology of HTS grain boundary junctions.         YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bicrystal grain boundary T/sub c/ microstructure    J.A. Luine, A.M. Klushin and V.Z. Kresin Summary: We use an S/sub /spl alpha//S/sub /spl beta//IS/spl beta//sub S/spl alpha// tunneling/proximity-effect model with measured YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) grain boundary function (GBJ) normalized critical current temperature dependence /spl eta/(T)=I/sub c/(T)I/sub c/(O) to infer microstructural transition temperature profiles T/sub c/(x) for bicrystal GBJs with various misorientation angles /spl theta/. We discuss the rationale for selecting an optimum value for a numerical analysis parameter /spl epsi/ (associated with the S/sub /spl alpha//S/sub /spl beta// interface T/sub c/ discontinuity). We determine the extent to which inferred T/sub c/(x) profiles vary with /spl plusmn/20% rms deviations from nominal values for the fixed input parameters whose a priori values are not precisely known. This sensitivity analysis shows that specified T/sub c/ locations can be determined with /spl les//spl plusmn/1 nm precision for T/sub c/<60 K. Finally, we present new inferred T/sub c/(x) profiles for bicrystal junctions with /spl theta/=24/spl deg/ and 32/spl deg/ and compare these profiles with those of bicrystal JJs with /spl theta/=19/spl deg/ and 36.8/spl deg/ which we previously reported. Our inferred T/sub c/(x) profiles for these functions exhibit a clear correlation with /spl theta/: as /spl theta/ increases so does the extent of the grain boundary region with suppressed T/sub c/. This expected result gives us confidence that our approach should prove useful as a tool for elucidating the structure and properties of high temperature superconductors.         High temperature superconducting ferrite phase shifter with new latching structure    K.S.K. Yeo and M.J. Lancaster Summary: Superconductor ferrite phase shifters are attractive for phased array radar systems. The huge reduction in size and losses mean that smaller systems are possible. This paper reports a new latching structure for a superconducting ferrite phase shifter which is compact in size and has low losses. The total size of the phase shifter is 6.0 cm/spl times/3.0 cm/spl times/2.5 cm including housing. It should be pointed out that two phase shifters can be accommodated in this size. The minimum insertion loss of the designed phase shifter was measured at 0.8 dB. The phase shifter is fabricated using a Yttrium Barium Copper Oxide (YBCO) microstrip meander-line on a one centimetre square low loss sapphire substrate. We press contacted a magnetized ferrite substrate, with a silver ground plane, onto the fabricated YBCO meander-line to obtain non-reciprocal phase shifting. To magnetize the ferrite substrate without causing magnetic field penetration into the high temperature superconductor (HTS), we propose a new latching structure comprising a single ferrite layer with magnetizing coils. This new structure will confine the magnetic field within the ferrite substrate by providing a closed magnetic path. This is achieved by making a large hole at center of the ferrite substrate.         Tuning properties of 2 GHz superconducting microstrip-line filters    H. Fuke, Y. Terashima, H. Kayano, M. Yamazaki, F. Aiga and R. Katoh Summary: We have fabricated a 2 GHz 12-pole superconducting microstrip line filter and a 2-pole electrically tunable filter using interdigital electrodes and dielectric film. The change of the dielectric constant of a SrTiO/sub 3/ film, stacked on the filter, by applying a bias voltage between the electrodes leads to the tunability. The range of the center frequency modulation was 13 MHz (0.7%) at 60 K, 75 kV/cm. The microwave frequency response was improved by modification of the electrode structure. This tuning method is considered to be promising in that individual resonance elements in multi-pole filters can be tuned independently.         Frequency agile microwave devices based on Y-Ba-Cu-O/Sr-Ti-O//La-Al-O structure    B. Marcilhac, D.G. Crete, Y. Lemaitre, D. Mansart, J.C. Mage, K. Bouzehouane, C. Dolin, E. Jacquet, P. Woodall and J.P. Contour Summary: Among the solutions allowing one to design frequency agile microwave devices, Y-Ba-Cu-O/Sr-Ti-O//La-Al-O multilayers can be used to obtain a frequency shift of 10% and individual resonator Q/sub 0/ higher than 1000. A resonator used for the extraction of the material characteristics and as a single clement filter was optimized. The filter design allows the control of the response over the frequency range. Stop-band filters were tested with good agreement between the materials properties and the modeling.         Broadband and low driving-voltage LiNbO/sub 3/ optical modulator with high T/sub c/ superconducting transmission line    K. Yoshida, H. Takeuchi, H. Kanaya, Y. Kanda, T. Uchiyama and Z. Wang Summary: A new design theory is presented of the high-T/sub c/ superconducting broadband booster circuit for a LiNbO/sub 3/ optical modulator. Based on this theory we studied the gain and bandwidth characteristics of the modulator using a transmission line model. We also designed the practical booster circuit using an electromagnetic wave simulator and demonstrated the optical modulator with broadband and high voltage gain as expected from the theory.         Transmission characteristics of HTS microstrip resonators with a ferrite component    T. Nurgaliev, S. Miteva, A. Jenkins and D. Dew-Hughes Summary: Microwave transmission characteristics of HTS microstrip resonators containing a monocrystalline ferrite layer magnetized in an arbitrary direction were calculated using a RCL approach. Dependencies of the resonance frequencies on the external magnetic field strength and the field orientation angles were analyzed and the results of the calculations were compared with the experiment.         Strontium titanate thin films for tunable YBa/sub 2/Cu/sub 3/O/sub 7/ microwave filters    B.H. Moeckly and Y. Zhang Summary: Tunable ferroelectric thin films such as SrTiO/sub 3/ (STO) are promising for a variety of rf applications requiring tunability. We describe the growth and characterization of STO thin films including their dielectric properties, and summarize attempts at reducing the loss tangent of these films. We also discuss their integration with high-temperature superconductor (HTS) microwave filters for trimming purposes.         Enhanced microwave power from triangular arrays of small Josephson junctions    P. Caputo, A.V. Ustinov and S.P. Yukon Summary: We report on high frequency measurements of underdamped Josephson junction arrays consisting of two rows of parallel biased cells. The rf voltage generated on the junctions transverse to the bias current (horizontal junctions) is detected by a room temperature receiver in the W-band. In order to enhance the emitted power, it has been proposed (S.P.Y.) that the single horizontal junction in each cell be replaced by two (or more) horizontal junctions. This geometry has been proven to have better high frequency performance. Here we present comparative measurements of the output power from two row arrays of different geometries. Among the studied configurations, larger power is obtained from an array with square cells and two horizontal Junctions. In this array, the measured output power is up to about 2 times larger than that in the array with only one horizontal junction, and up to 20 times larger with respect to the array with conventional triangular cells. Experimental data are in good qualitative agreement with numerical simulations.         Phase shifting in a Josephson junction active antenna array    S.P. Yukon and F.C. Lin Summary: We present a design for an active antenna array employing triangular Josephson junction (JJ) sub-arrays as rf oscillator sources. The sub-arrays are kept in sync by coupling to a closed serpentine discrete JJ ladder. Phase shifts are introduced by adding external magnetic flux into the JJ ladders between sub-arrays. Phase shifting distortions are minimized by allowing only two contiguous sub-arrays on any row segment.         Superconducting digital electronics    S. Tahara, S. Yorozu, Y. Kameda, Y. Hashimoto, H. Numata, T. Satoh, W. Hattori and M. Hidaka Summary: Superconducting devices have intrinsically superior characteristics to those of semiconductor devices. Presently, we can fabricate more than twenty thousand junctions on one chip using niobium technology. We have demonstrated the operation of a network system with a superconducting interconnection chip using voltage-state logic. Single flux quantum devices are promising for future superconducting applications because the clock frequency of SFQ logic is higher than that of voltage-state. We have proposed a high-end switch based on hybrid architecture using optical devices, semiconductors and SFQ devices. To demonstrate the high-speed operation of SFQ circuits, we developed an arbiter circuit that uses SFQ components and the arbiter circuit operates at 60 GHz. We also have developed a high Tc superconducting (HTS) SFQ sampler system for observing ultra-fast signal waveforms. In addition, we will discuss the prospects of future superconducting devices based on the fabrication technologies we developed.         Transition edge sensor array development    S. Deiker, J. Chervenak, G.C. Hilton, K.D. Irwin, J.M. Martinis, S. Nam and D.A. Wollman Summary: NIST is fabricating multi-pixel arrays of transition edge sensor (TES) microcalorimeter detectors for use in microanalysis and X-ray astrophysics. We have developed both room temperature digital feedback electronics and a successful SQUID multiplexing technology that will be applied to form a practical, expandable system. We are also exploring surface micromachining techniques to enable the fabrication of large-scale, close-packed arrays of TES microcalorimeters.         Dual mode superconducting planar filters based on slotted square resonators    A. Cassinese, A. Andreone, M. Barra, C. Granata, P. Orgiani, F. Palomba, G. Panariello, G. Pica and F. Schettino Summary: A new kind of dual-mode filter based on cross and transverse slotted square resonators is presented. A pair of unequal crossed slots formed on a square patch resonator provides both a reduction of the filter size and a simple and controllable way to couple the two degenerate modes. Transverse cuts opportunely realized on the patch further decrease the operating frequency without any appreciable change in the power handling capability of the device. Three examples of single stage filters operating in C-band with 1% and 10% fractional bandwidth are designed with a commercial 2.5D software and fabricated using Nb and YBa/sub 2/Cu/sub 3/O/sub 7/ films grown on LaAlO/sub 3/ [100] substrates. The filters response is characterized at different temperatures and the insurgence of non-linearity investigated varying the input power and carrying out intermodulation measurements.         Narrowband Y-Ba-Cu-O filter with quasi-elliptic characteristic    I.B. Vendik, A.N. Deleniv, V.O. Sherman, A.A. Svishchev, V.V. Kondratiev, D.V. Kholodniak, A.V. Lapshin, P.N. Yudin, B.-C. Min, Y.H. Choi and B. Oh Summary: The compact meander-shape configuration of planar resonators is suggested for applications in narrowband filters with quasi-elliptic characteristic. The quasi-elliptic frequency response with two transmission zeroes at the edges of the passband is provided by the specific symmetry of the coupled resonators and is controlled by an appropriate choice of the resonator dimensions and the couplings between the resonators. The 12-pole quasi-elliptic filter with 0.5% fractional bandwidth at 1.775 GHz has been designed using meander-line microstrip resonators and manufactured on a double-sided YBCO film on a LaAlO/sub 3/ substrate. The filter exhibited the in-band insertion loss less than 0.5 dB at T=60 K, the return loss of 20 dB, the out-of-band rejection better than 75 dB, and 40 dB/MHz slope of the characteristic.         Miniaturized HTS coplanar waveguide bandpass filters with highly packed meanderlines    H. Kanaya, T. Shinto, K. Yoshida, T. Uchiyama and Z. Wang Summary: Design and performance of miniaturized coplanar waveguide (CPW) bandpass filters (BPFs) using high T/sub c/ superconducting (HTS) films have been studied. In order to realize the miniaturized filters, we coupled highly packed meanderline half-wavelength resonators with interdigital gaps, where admittance inverters (J inverters) were made of interdigital gaps. The exact J values, susceptance slope parameters and the length of the resonators of the meanderline are calculated from the cascade matrix (K-matrix) and scattering matrix (S-matrix) obtained by the 2.5-dimensional electromagnetic field simulator (HP-Momentum). It is shown that the size of the filters can be greatly reduced by introducing CPW with highly packed meanderline geometry (center frequency 2 GHz, fractional band width 15 MHz, ripple 0.1 dB) packed within 10 mm square substrate. Simulated performance was in good agreement with the designed one.         Cross-coupled band-pass filter using HTS microstrip resonators    B.-C. Min, Y.H. Choi, S.K. Kim and B. Oh Summary: We have fabricated microstrip band-pass filters based on the quadruplet geometry using high-temperature superconductor. Every half-wavelength resonator in the filter consists of a loop-like inductor and two patch capacitors at both ends. The inductive coupling in between the loop-like inductors of non-adjacent resonators produces transmission zeros in the frequency response. The transmission zero can be allocated by changing the polarity and the strength of the cross coupling. We have designed a 9-pole filter for personal communication services (PCS) application using combination of a CAD tool and a full-wave analysis EM simulator. We have fabricated filters using double-sided YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films on LaAlO/sub 3/ substrates. The filter has 1.784 GHz center frequency, 11 MHz 3-dB bandwidth, and 0.8 dB insertion loss at 60 K. Due to the transmission zeros near the passband, the steep skirt characteristic is exhibited. The attenuation at 1 MHz away from the edge of the passband is -34 dB.         High-Q cryogenic dielectric resonator filters for C-band and Ku-band frequencies    H.R. Yi and N. Klein Summary: Dielectric resonator filters for C-band and Ku-band were designed and built. The C-band filter was based on the HEM(11/sup /spl delta//) dual-mode of hemispherical resonators machined from BaMgTaO ceramics, which has a dielectric constant of around 24. The Ku-band filter was based on the HEM(11/sup /spl delta//) dual-mode of cylindrical resonators machined from sapphire single crystals. For both filters with cavity made from copper, unloaded quality factors of 30,000 and more than 60,000 were registered at room temperature and 77 K, respectively. For a four-pole quasi-elliptic filter with center frequency of around 3.72 GHz and bandwidth of 36 MHz, the measured insertion loss was 0.17 dB at room temperature and 0.08 dB at 77 K. For a four-pole quasi-elliptic filter with center frequency of 10.76 GHz and bandwidth of 24 MHz, the measured insertion loss was 0.9 dB at room temperature. We also estimated the unloaded quality factor of the C-band filter when the top copper endplate was replaced by a YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting film. In this case the unloaded quality factor was 100,000 at 77 K.         High performance cryogenic packaging for microwave applications of high temperature superconductors    R.B. Greed, R.F. Jeffries, D.C. Voyce, A.J. Barkway, R.G. Humphreys and S.W. Goodyear Summary: For microwave applications employing high temperature superconductor (HTS) technology to be commercially viable, a high performance cryogenic package is essential. Design considerations to minimise the heat leaks from ambient through conduction along the electrical interconnects and through radiation from the package walls, to reduce the size and mass and to reconcile the physical characteristics of the wide range of materials used within the microwave module and cryogenic package are discussed. Fabrication, process and assembly techniques, which play an important role in determining the long-term reliability of any HTS system, are described. Two examples of the design of cryogenic packages, for commercial and military applications, with inherent mechanical and thermal integrity, high reliability and which do not require a regular maintenance regime are presented to illustrate the design techniques being developed.         Preparation of continually graded barriers of YPrBaCuO for HTS Josephson junctions    J. Gao, J.L. Sun and W.H. Tang Summary: We report preparation of a novel barrier structure for high T/sub c/ superconducting multilayer Josephson junctions using a simple composite target technique. Such a barrier consists of Y/sub x/Pr/sub 1-x/Ba/sub 2/Cu/sub 3/O/sub y/ with a continually varied concentration of yttrium. In this barrier no lattice mismatch and other incompatibility problems occur between adjacent layers. Thus the formation of interfacial defects and structural strain can be mostly prevented. The Josephson coupling takes place at the electrically formed interfaces rather than the structural interfaces. A particular feature of these junctions is that the effective thickness of the barrier strongly depends on the measuring temperature and the concentration gradient. The absence of the structural interface in the weak link region greatly enhances the reproducibility and the performance of these junctions.         Y-Ba-Cu-O/Au/Nb ramp-type Josephson junctions    H.J.H. Smilde, H. Hilgenkamp, G.J. Gerritsma, D.H.A. Blank and H. Rogalla Summary: Ramp-type junctions connecting the d-wave superconductor YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and the s-wave superconductor niobium are fabricated using a thin gold layer as a chemical barrier. High critical current densities exceeding 5 kA/cm/sup 2/ are obtained. The normal state resistivity (R/sub n/A) values of the junctions are of the order of 0.1 /spl mu//spl Omega/ cm/sup 2/. The magnetic field behavior of the critical current of junctions oriented in the [10l]- and in the [11l]-direction of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// is explained in terms of a predominant d(x/sup 2/-y/sup 2/) order parameter in the high-T/sub c/ superconductor.         Properties of trilayer SIS junctions with YBa/sub 2/Cu/sub 3/O/sub 7-y/    Y.-S. Jiang, M. Moriya, T. Kobayashi and T. Goto Summary: In this study, we compared the surface configurations of PrGaO/sub 3/ (PGO) and multilayers of PGO and CeO/sub 2/ deposited on YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) thin films. It is found that the multilayers have flatter surfaces than single layers of the same thickness. Furthermore, the voltage-current characteristics of sandwich type SIS junctions with a range of single barrier and double barrier thickness using YBCO electrodes were investigated. Double layer barriers are effective in suppressing electrical short circuits caused by pinholes. The junction with a double barrier of 5 nm PGO and 2.5 nm CeO/sub 2/ shows a Josephson current.         Fabrication of c-axis oriented YBaCuO trilayer junctions with Ar plasma treatment    H. Sato, A. Kaneko, T. Kaneda, T. Yamada, H. Yamamoto, K. Hohkawa and H. Akoh Summary: We have fabricated c-axis oriented YBaCuO/PrBaCuO/YBaCuO trilayer junctions on a LSAT single crystal substrate. Since the c-axis oriented junctions had a smaller critical current density J/sub c/ compare to [103] oriented YBaCuO trilayer junctions, an Ar plasma treatment was carried out. After base electrode deposition, the film sample was bombarded by Ar plasma generated by a RF signal applying the substrate holder. During the process, only Ar gas was supplied, and a substrate temperature was kept at deposition temperature. A typical junction without Ar plasma treatment had a J/sub c/ of 180 A/cm/sup 2/. The junction with Ar plasma treatment, on the other hand, showed J/sub c/ of 1.6 kA/cm/sup 2/, suggesting that the Ar plasma treatment can be used to improve the junction properties.         A prescaler circuit for a superconductive time-to-digital converter    S.B. Kaplan, A.F. Kirichenko, O.A. Mukhanov and S. Sarwana Summary: The high-speed capability of superconductive electronics is being harnessed to develop a time-to-digital converter (TDC) with picosecond time resolution. We have designed and successfully tested prescaler circuits for improving TDC resolution first to 5 ps, and then below. These circuits are designed to act as a vernier for a superconductive TDC that counts clock periods using a binary counter. One prescaler circuit has already demonstrated 5 ps resolution at a clock frequency of 20 GHz.         Design of superconducting single flux quantum decimation filters    H. Hasegawa, T. Hashimoto, S. Nagasawa, H. Suzuki, K. Miyahara and Y. Enomoto Summary: A third-order sine decimation filter was designed for a /spl Sigma/-/spl Delta/ A/D converter with a second-order modulator. The sine filter was formed from multistage decimation structure, which was constructed from the cascade connection of third-order sine filters with a decimation factor of 2. A counter, consisting of single-flux-quantum (SFQ) toggle flip-flops (TFF) with destructive readout, was used to reduce the circuit scale. The sine filter with a decimation factor of 2, which is the circuit that operates at the highest frequency in a multistage decimation structure, operated up to the clock frequency of 18 GHz in a circuit simulation. A sine filter with a decimation factor of 32 was calculated to require 6700 Josephson junctions that consume 1.9 mW.         Demonstration of 17 GHz operation of M-code generator based on SFQ with resettable latch    A. Akahori, N. Takeuchi, N. Mori, Y. Suzuki, F. Furuta, A. Fujimaki and H. Hayakawa Summary: We have experimentally demonstrated high-speed operation of a maximum code length (M-code) generator using the on-chip-testing system. M-code generator was designed by using Single Flux Quantum with Resettable Latch (SFQ-RL) proposed by us, and fabricated by the NEC standard process. The circuit operates up to 17 GHz correctly, while the bias margin decreases at higher frequencies due to the timing-related errors. This circuit based on SFQ-RL has an advantage that the initialization of the whole circuit can be realized easily. We have also confirmed the "flush" operation that the internal state is initialized simultaneously by one SFQ pulse in SFQ-RL.         9 K operation of RSFQ logic cells fabricated by NbN integrated circuit technology    H. Terai and Z. Wang Summary: We report on the fabrication and the operation of all-NbN rapid single flux quantum (RSFQ) circuits. The NbN integrated circuit consists of NbN/AlN/NbN tunnel junctions, Mo resistors, sputtered SiO/sub 2/ insulating layers, and 400-nm-thick NbN ground plane and wiring layer. The circuits were fabricated with the minimum junction size of 2 /spl mu/m/spl times/2 /spl mu/m and the alignment margin of +/-0.5 /spl mu/m. We designed RSFQ logic cells under critical current density of 2.5 kA/cm/sup 2/, sheet resistance of 2 /spl Omega/ and sheet inductance of 1.4 pH. We experimentally investigated dc bias margin of the fabricated RSFQ cells at 9 K. We observed relatively large dc bias margin of more than +/-25% for a pulse splitter, a confluence buffer and an RS flip-flop, while the dc bias margin of a T flip-flop was less than +/-5%. We succeeded to demonstrate the operation of 16-bit concurrent flow shift register at 9 K.         Experimental characterization of bit error rate and pulse jitter in RSFQ circuits    P. Bunyk and D. Zinoviev Summary: Rapid Single Flux Quantum (RSFQ) logic is well-known for its ultra-high switching speed and extremely low power consumption. In this paper, we present two original experiments to demonstrate that it's also a reliable technology and its reliability is sufficient even for such a large-scale system as a proposed petaflops-scale HTMT computer. We have measured the bit error rate (BER) for a circular register of inverters representing a critical path of a 64-bit integer adder, and timing jitter in a 200 Josephson junction (JJ) long transmission line, imitating a branch of a clock distribution tree, both being important and representative building blocks of the HTMT computer. For the adder critical path we have demonstrated the highest clock frequency of 17 GHz, latency of 860 ps and BER of 10/sup -19/ for 3.5 /spl mu/m technology of HYPRES, Inc. The value of timing jitter was 200 fs per JJ for 1.5 /spl mu/m technology of TRW, Inc. These figures are in good agreement with our simulations.         Superconducting latching/SFQ hybrid RAM    S. Nagasawa, H. Hasegawa, T. Hashimoto, H. Suzuki, K. Miyahara and Y. Enomoto Summary: We have developed a 256-bit superconducting latching/SFQ hybrid (SLASH) RAM block as the first step in developing a 16-Kbit SLASH RAM, which enables high-frequency clock operation up to 10 GHz. The SLASH RAM is composed of ac-powered latching devices and dc-powered SFQ devices. The 256-bit SLASH RAM block is composed of 16/spl times/16 matrix array of vortex transitional memory cells, SFQ-NOR decoders, latching drivers, latching sense circuits, and address buffers. The 256-bit SLASH RAM block chips were fabricated and tested. We confirmed that the 256-bit SLASH RAM block functioned successfully.         Pipelined DC-powered SFQ RAM    A.F. Kirichenko, S. Sarwana, D.K. Brock and M. Radpavar Summary: We present the design and test results of components for a superconductor Cryogenic Random Access Memory (CRAM). The 16-Kb RAM design consists of four 4-Kb sub-arrays (blocks) with a 400 ps access time (latency) and a 100 ps cycle time (throughput). Each 4-Kb RAM block comprises a row-accessed 32/spl times/128 memory cell array, bipolar line drivers, row decoders, and column sense circuits. The implementation of specially designed distributed Josephson junctions in the sensing circuits reduces the overall size of the blocks and allows the use of smaller dc control currents.         Phase-mode pipelined parallel multiplier    T. Onomi, K. Yanagisawa, M. Seki and K. Nakajima Summary: We propose a pipelined parallel multiplier in phase-mode logic. The multiplier can be composed of combinations of gates which are the basic devices of the phase-mode logic. Experimental operations of the ICF gate and the Adder cell for the multiplier are reported. The proposed multiplier has a Wallace-tree structure comprising trees of carry save adders for the addition of partial products. This structure has a regular layout, hence it is suitable for a pipeline scheme. In the final stage of multiplication, a fast carry lookahead adder is used for generating a multiplication result. Using a Verilog-HDL simulation, we show that the parallel multiplier with 2.5 kA/cm/sup 2/ Nb/AlO/sub x//Nb junctions can operate over 10 GHz.         Encoders and decimation filters for superconductor oversampling ADCs    T.V. Filippov, S.V. Pflyuk, V.K. Semenov and E.B. Wikborg Summary: Modulators of superconductor ADCs can operate at very high sampling rates, ranging from 20 GHz (today's technologies) to 400 GHz (prospective sub-micron technologies). Such devices are too fast and therefore impractical without other superconductor devices capable of processing the data streams at such rates. We discuss various structures of such devices, in particular demultiplexers and decimation filters. We also analyze possible hybrid devices, in which only the front stages contain superconductor components. Encoders and decimation comb filters for single-comparator and time-interleaved modulators were designed, fabricated (at HYPRES, Inc.) and successfully tested. The most recent designs of the decimation filters have a unique modular structure, which allows an assembly of various comb filters handling clock frequencies of about 20 GHz (for a 1 kA/cm/sup 2/ fabrication technology).         Circuit improvements for a voltage multiplier    V.K. Semenov and Yu.A. Polyakov Summary: A voltage (or flux) multiplier is a device which multiplies applied SFQ pulses. Due to the quantum nature of an SFQ pulse the device can be used as a voltage (or flux) amplifier with a fundamentally accurate (integer) gain. Earlier we showed that the device can be used for improvement of dc and ac voltage standards. Recently we have found that a long voltage multiplier can display complex dynamic behavior, which can lead to undesirable collective oscillations. This report is devoted to theoretical optimization and experimental investigation of long voltage multipliers connected in series for dc current. Experimentally we have obtained accurate current steps with about 0.1 V voltage drop for a 5 mm/spl times/5 mm chip fabricated in Nb technology and tested at 4 K.         Superconducting second-order sigma-delta modulators utilizing multi-flux-quantum generators    T. Hashimoto, H. Hasegawa, S. Nagasawa, H. Suzuki, K. Miyahara and Y. Enomoto Summary: We have been developing a superconducting second-order sigma-delta analog-to-digital converter with a large bandwidth and a large dynamic range for software radio applications. In a superconducting second-order sigma-delta modulator utilizing a passive integrator and single-flux-quantum (SFQ) feedback, gain to compensate the large attenuation in the passive integrator of the modulator is required to obtain a large dynamic range. In this paper, a second-order modulator utilizing multi-flux-quantum (MFQ) generators creating the needed gain is reported and the design and experimental test results of the elementary circuits including a comparator, a first-order modulator, and the MFQ generator are described. The digital outputs of the comparator and the first-order modulator were experimentally evaluated, where the input dependence of the comparator switching probability and the noise-shaping properties of the modulator were clearly observed. The low speed operation of the MFQ generator creating three SFQ pulses was experimentally confirmed. The other circuits were also tested at low frequencies.         Small scale integrated technology for HTS RSFQ circuits    M. Huang, P.V. Komissinski, A.Yu. Kidiyarova-Shevchenko, M. Gustafsson, E. Olsson, B. Hogberg, Z. Ivanov and T. Claeson Summary: A technology for fabrication of YBCO ramp junctions on a superconducting ground plane is developed and evaluated. The technology is based on a two-layer, S-I, structure or on a four-layer, S-I-S-I, structure grown in situ with YBCO superconductor and with multilayer insulator of PBCO/STO/PBCO. Ramps for junctions, via connections and crossovers are formed by Ar ion milling under rotation and the ramp angle is less than 30/spl deg/ for all directions. A 20-25 nm thick Ga-doped PBCO was used as a barrier for Josephson junctions. One additional YBCO layer, for junction top electrodes and wiring, is deposited and patterned. Surface roughness of multilayers is characterized by AFM and is related to the junction parameters. Transport properties of junctions, via connections and crossovers are evaluated.         AC voltage-biased superconducting bolometer for a frequency-domain SQUID multiplexer    J. Yoon, J. Clarke, J.M. Gildemeister, A.T. Lee and P.L. Richards Summary: We demonstrate that a voltage-biased superconducting bolometer (VSB), read out with superconducting quantum interference device (SQUID), can be biased with a sinusoidal voltage. We show that the load curves taken with AC- and DC-bias are nearly identical indicating that there is no identifiable degradation in the performance of the bolometer due to the AC bias. We discuss the use of a frequency-domain SQUID multiplexer with an array of VSB's that are AC-biased.         Fabrication and characterization of hot-electron bolometers for THz applications    M. Frommberger, P. Sabon, M. Schicke, F. Mattiocco and K.F. Schuster Summary: Superconducting properties of Nb and NbN thin films for application in diffusion and phonon cooled Hot-Electron Bolometers have been systematically investigated. The materials were sputtered on fused quartz substrates in a wide thickness range. DC-measurements of the Nb films allow us to predict the intermediate frequency bandwidth of a hot-electron bolometer mixer device for a given design. To improve the characteristics of the NbN thin films, we used a 15 nm MgO seed layer.         Nb superconducting hot electron bolometer mixers coupled with microstrip lines    W.F.M. Ganzevles, P. Yagoubov, J.R. Gao, T.M. Klapwijk and P.A.J. de Korte Summary: The measured direct and heterodyne response of a quasi-optically coupled superconducting Nb hot-electron bolometer mixer (HEBM) at 2.5 THz is reported. This mixer exploits a novel coupling circuit in which the microstrip line transformer is used to feed the rf signal from the twin slot antenna to the microbridge. The microstrip line is made of Au/SiO/sub 2//Al. Using a Fourier transform spectrometer, the frequency response of such a device is measured. We find a peak response at a frequency of 1.9 THz, which is 20% lower than predicted, and a bandwidth of 1.6 THz as we expect. By applying 2.5 THz radiation from a far infrared laser, we measure an uncorrected noise temperature T/sub N,rec/ of 4200 K.         Fabrication and properties of an ultrafast NbN hot-electron single-photon detector    G. Gol'tsman, O. Okunev, G. Chulkova, A. Lipatov, A. Dzardanov, K. Smirnov, A. Semenov, B. Voronov, C. Williams and R. Sobolewski Summary: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film's supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.         Ultrafast YBCO photodetector based on the kinetic-inductive process    C. Williams, Y. Xu, R. Adam, M. Darula, O. Harnack, J. Scherbel, M. Siegel, F.A. Hegmann and R. Sobolewski Summary: We make use of the nonequilibrium kinetic-inductive effect in epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films to demonstrate an ultrafast, high-sensitivity, broadband photodetector. The photoresponse of a 5-/spl mu/m-wide, 10-/spl mu/m-long, 100-nm-thick YBCO microbridge embedded in a 20-/spl mu/m-wide coplanar strip transmission line was measured using a >1-THz, submillivolt-sensitivity electro-optic sampling system. We performed a comprehensive study of the optical power and wavelength dependency on the YBCO photodetector response. The quantum coherence Rothwarf-Taylor model together with the hot-electron relaxation effect were used to explain the measured data and to extract the number of generated quasiparticles for each absorbed photon, revealing the intrinsic quantum yield of our device to be /spl sim/450. The amplitude, response time, and the intrinsic gain of the YBCO photoresponses were observed to be spectrally flat over the tested range of 390 nm to 810 nm.         Terahertz spectral analysis by ac Josephson effect in high-T/sub c/ bicrystal junctions    Y. Divin, O. Volkov, V. Pavlovskii, U. Poppe and K. Urban Summary: A prototype of a terahertz Hilbert-transform spectrum analyzer based on a high-T/sub c/ Josephson junction integrated into a Stirling cooler has been developed. The detector response of YBa/sub 2/Cu/sub 3/O/sub 7-x/ Josephson grain-boundary junctions to monochromatic radiation with the frequency f in the range from 60 GHz to 5 THz has been studied. Odd-symmetric resonances near the voltages V=hf/2e in the responses /spl Delta/I(V) of these junctions to radiation with different frequencies f have been observed in a decade of spectral range for any operating temperature between 30 to 85 K. Decreasing the junction temperature from 85 to 30 K by a Stirling cooler, the spectral analysis could be made in two decades of spectral range. A resolving power /spl delta/f/f/spl sim/10/sup -3/ has been shown in the terahertz spectral analysis with the low-resistive Josephson junctions. As an example of application of this analyzer, an optimization of the single-line operation of a far-infrared optically-pumped CH/sub 3/OH laser has been demonstrated.         THz-spectroscopy with YBa/sub 2/Cu/sub 3/O/sub 7/-Josephson junctions on LaAlO/sub 3/-bicrystals    F. Ludwig, J. Menzel, A. Kaestner, M. Volk and M. Schilling Summary: For the detection and spectral characterization of transition radiation in the operation of the linear accelerator at the TESLA test facility (TTF) we employ Hilbert-transform spectroscopy with Josephson junctions from high-temperature superconductors (HTS). The Josephson junctions with integrated wideband antennas from HTS are prepared on symmetric 24/spl deg/ LaAlO/sub 3/ bicrystal substrates. The set-up is optimized for low insertion loss over a wide frequency range from 50 GHz to about 2 THz. The HF-characterization is made by microwave Hilbert-transform spectroscopy with a far-infrared laser at 762 GHz and 1.2 THz. The spectral reconstruction of pulsed radiation in dependence of measuring time, signal-to-noise ratio, system noise, junction output voltage and repetition rate of pulsed radiation is deduced from simulation measurements of the Josephson junction response. For the spectral measurement of a single pulse we recommend quasi-optical time delay structures and high repetition rates of generated pulses.         Fabrication and characterization of a cryogenic AC-DC converter    E. Monticone, U. Pogliano and E. Bennici Summary: At present, the AC voltage measurements at the 1 mV level are limited by the low sensitivity of the AC-DC transfer devices. We report the fabrication and characterization of a transition edge sensor on a silicon nitride membrane to perform direct measurements in this voltage range. The sensor consists of a Cr strip where AC power is dissipated and a superconducting-Nb thin film biased into its resistive transition that measures the temperature change. Deposition parameters of Cr film are chosen in order to have a resistance close to 50 ohm that minimize the mismatching with the AC supply. By second and third harmonic methods a thermal conductance of 6/spl middot/10/sup -6/ W/K and a time constant of 4 ms are evaluated for a device on a membrane of 3.5/spl times/3.5 mm/sup 2/. Analysis of the data indicates that a reduction of the noise equivalent power of 4-5 order of magnitude on that of traditional thermal converter is feasible.         Sub-picowatt precision radiometry using superconducting transition edge sensor bolometers    J.A. Chervenak, E.N. Grossman, C.D. Reintsema, K.D. Irwin, S.H. Moseley and C.A. Allen Summary: We describe a cryogenic radiometric calibration system suitable for high sensitivity, low background power bolometers. The system uses a variable temperature blackbody source capable of temperatures of 4 to 20 K, whose output covers the sub-millimeter wavelength regime. The detector is an eight-channel, filled-focal-plane array of superconducting transition edge sensor (TES) bolometers. The system is designed to test components of the optical system such as polarizers, filters and stray light suppressors as well as the performance of the detector array elements. The bolometer response to incident submillimeter radiation is measured and compared to the calculated output of the source seen by the bolometer.         Operation of Nb/Al superconducting microstrips as radiation detectors    M. Greco, V. Lacquaniti, S. Maggi, E. Menichetti and G. Rinaudo Summary: We have developed superconducting Nb/Al microstrip detectors. These devices appear to be very attractive due to their low sensitivity to radiation damage and aging, and to their high energy resolution. The samples are fabricated by superposing a 2 mm/spl times/2 mm Al area on a 5 /spl mu/m wide, 100 /spl mu/m long Nb strip. The thickness of each film is between 50 and 200 nm. We present the results of both steady and dynamical tests on Nb/Al bilayers, after irradiation with a /sup 241/Am alpha-source. We show that the performance of Nb/Al bilayers is better than that of single Nb strip devices.         A superconductor high-resolution ADC    O.A. Mukhanov, V.K. Semenov, W. Li, T.V. Filippov, D. Gupta, A.M. Kadin, D.K. Brock, A.F. Kirichenko, Y.A. Polyakov and I.V. Vernik Summary: This paper presents the development of an Analog-to-Digital Converter (ADC) based on a low-temperature superconductor (Nb) chip and room-temperature interface modules for applications in digital receivers for communications, radars, and electronic warfare. The ADC design, MATLAB/sup TM/ simulations, and experimental results of single- and two-tone tests are described.         Wide bandwidth oscillator/counter A/D converter    M.W. Johnson, B.J. Dalrymple, D.J. Durand, Q.P. Herr and A.H. Silver Summary: We present theory and performance data on oscillator/counter A/D converters fabricated in TRW's Nb process. Circuits with junction critical current density of 2 kA/cm/sup 2/ are discussed. This simple, low power A/D converter architecture is uniquely enabled by the wide bandwidth voltage-controlled oscillator (VCO) and compatible, ultra-fast superconductor single-flux-quantum (SFQ) divide-by-two flip-flops. The measured signal-to-noise ratio (SNR), frequency response, and signal distortion are discussed within the framework of a basic theory of performance as well as time-domain simulations. Noise contributions from quantization error, aperture jitter, and thermal noise are included. The measured signal-to-noise ratio (SNR) is shown to be within a few dB of theoretical performance over more than two decades of frequency. The frequency response is shown to fit well to the expected function through 1 GHz of signal frequency. Harmonic distortion is shown to be consistent with the non-linearity in the front-end's DC I-V characteristic which is subject to design improvement. This architecture extends to higher performance using a multi-junction VCO. Measured two-junction VCO SNR shows essentially the theoretical improvement over that of a single junction.         AC coupling technique for Josephson waveform synthesis    S.P. Benz, C.J. Burroughs and P.D. Dresselhaus Summary: We demonstrate a new bias technique that uses low-pass and high-pass filters to separate the current paths of the sampling and signal frequencies in a Josephson waveform synthesizer. This technique enables the output voltage of the array to be directly grounded by removing the low-frequency common mode signal that previously prevented direct measurement of the array voltage with low-impedance instruments. We directly measure the harmonic spectra of 1 kHz and 50 kHz synthesized sine waves. We also use a thermal transfer standard to compare the rms voltages of synthesized sine waves at frequencies from 1 kHz to 50 kHz. Finally, we describe a new circuit that should enable a significant increase in output voltage by allowing several distributed arrays to be biased in parallel at high frequency, while combining their low frequency output voltages in series.         50 GHz RSFQ pseudo-random number generator design    X. Zhou, S. Xu, P. Rott, C.A. Mancini and M.J. Feldman Summary: Simple RSFQ gates can be very robust, and operate up to high clock speeds in simulation. Larger RSFQ circuits are generally much more limited in clock speed. We believe that this is partly due to less than optimal choice of the timing inter-connections between gates. Timing design is especially problematic for circuits including data loops (feedback). We have developed a new technique for timing design of RSFQ data loops which may be called "balanced skew clock scheduling." It involves equalizing the minimum clock period between every pair of gates. Mathematical analysis proves the optimality of this scheme and reveals the global timing constraints unique to RSFQ data loops. We used this technique for the design of a simple useful clocked RSFQ circuit, a four-bit pseudo-random number generator (PRNG). Constructed from our standard library cells for a 3.5 /spl mu/m 1000 A/cm/sup 2/ Nb-trilayer process, the PRNG worked up to 50 GHz in Jspice simulation.         60 Gbps throughput demonstration of an asynchronous SFQ-pulse arbitration circuit    S. Yorozu, Y. Kameda and S. Tahara Summary: We demonstrated the experimental operation of a single flux quantum (SFQ) pulse arbitration circuit for rapid single flux quantum (RSFQ) digital applications. The circuit arbitrates two asynchronous incoming signals with the internal clock signal, and produces two signals with a time difference. The circuit consists of two data latches and a clock generator based on a ring oscillator. We fabricated the circuit using NEC's 2-/spl mu/m standard fabrication technology, and tested it in two ways. Firstly we tested throughput characteristics. From measurements of the average voltage of output Josephson Junctions, we confirmed that the throughput was indeed controlled by the clock signal up to around 60-GHz. Secondly we tested the arbitration function. The test used a new testing circuit connected with output side of the arbitration circuit. This circuit consists of a confluence buffer, a splitter and three SFQ/DCs, and was capable of monitoring output signals and their arrival time difference. We changed the difference in arrival times of the input signals to the arbiter circuit, and observed two output signals with the test circuit. The observed signals show that they always sent out with time difference, and we thus confirmed the correct operation of the circuit even for pairs of input signals with the same arrival time.         Low error operation of a 4 stage single flux quantum shift register built with Y-Ba-Cu-O bicrystal Josephson junctions    J.H. Park, J.H. Kang, T.B. Jung, K.R. Jung, C.H. Kim, Y.H. Kim, S.S. Choi and T.S. Hahn Summary: We fabricated a 4 stage single flux quantum shift register with YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) bicrystal Josephson junctions and demonstrated the circuit's low error operation by using a computer controlled digital measurement set-up. The circuit was operated at 65 K. Binary data sequences of "1000", "1010", "1011," and "1111" were successfully loaded and shifted in the circuit. The two read SQUIDs placed next to each side of the shift register were used to sense all the individual data states. By operating the circuit with the proper current pulses, we observed no errors during 16 hours, which is equivalent to 21,000 error-free data shifts. We also found that temperature dependent inductance and junction critical currents limit the operating temperature range of the circuit, and the effective thermal noise temperature can be lower than 100 K.         Highly sensitive uncooled magnetometers: State of the art. Superconducting magnetic hybrid magnetometers, an alternative to SQUIDs?    D. Robbes, C. Dolabdjian, S. Saez, Y. Monfort, G. Kaiser and P. Ciureanu Summary: We discuss the performances of highly sensitive magnetometers using flux gates, as well as magnetotransport effects (magnetoresistance - AMR/GMR and magnetoimpedance - GMI). Soft magnetic materials operating at room temperature or cryogenic temperatures are involved in these effects. We report on their performances (sensitivity, bandwidth, etc.) with emphasis on their noise properties. The latter often fall to 1-10 pT//spl radic/Hz even for active areas as low as 1-2 mm/sup 2/. Amorphous magnetic flux guides are often used to enhance the field sensitivity of micro-devices. Their replacement by superconducting concentrators, which could lead to much larger gain factors, is discussed. This review, together with new results, confirms a new research field which could lead to highly sensitive, low noise, superconducting-magnetic hybrid magnetometers.         Design and performance of an HTS current comparator for charged-particle-beam measurements    L. Hao, J.C. MacFarlane, D.A. Peden, R.A.M. Lee, J.C. Gallop and C. Carr Summary: Superconducting direct current comparators are well established for operation at liquid helium temperatures. We have begun investigations into HTS Cryogenic Current Comparator designs, which incorporate a flux concentrator and readout SQUID also made from HTS. This work aims to produce a system capable of high accuracy, non-invasive, measurements of an ion or electron beam current in the range /spl sim/10 nA to 1 mA. We outline a proposal for a precise determination of the faraday fundamental constant, using purely physical systems, and employing an HTS CCC for charged particle beam current measurement. In addition estimates of the potential current sensitivity are reported, based on measurement results of a prototype system, and proof-of-principle measurements of ion beam currents are described. The design and construction of a robust, compact cryogenic unit suitable for further, more realistic, field trials are discussed.         A new idea for a solid-state microrefrigerator operating near 100 mK    J.N. Ullom, M.L. van den Berg and S.E. Labov Summary: We propose a new design for a solid-state microrefrigerator based on Normal-Insulator-Superconductor (NIS) tunnel junctions. These devices are a promising means of providing continuous refrigeration from 0.3 to 0.1 K without vibration or moving parts. Previously, the area and cooling power of NIS refrigerators have been limited by heating of the superconducting electrode. This problem can be overcome by using a superconducting single crystal as both the substrate and superconducting electrode of the NIS junction. In this paper, we briefly explain the benefits of our new design and describe experimental progress towards building such a device.         Aluminum hot-electron bolometer mixers at submillimeter wavelengths    A. Skalare, W.R. McGrath, P.M. Echternach, H.G. LeDuc, I. Siddiqi, A. Verevkin and D.E. Prober Summary: Diffusion-cooled aluminum hot-electron bolometer (HEB) mixers are of interest for low-noise high resolution THz-frequency spectroscopy within astrophysics. Al HEB mixers offer operation with an order of magnitude less local oscillator power, higher intermediate frequency bandwidth and potentially lower noise than competing devices made from other materials. We report on mixer experiments at 618 GHz with devices fabricated from films with sheet resistances in the range from about 55 /spl Omega/ down to about 9 /spl Omega/ per square. Intermediate frequency bandwidths of up to 3 GHz were measured (1 /spl mu/m long device), with absorbed local oscillator power levels of 0.5 to 6 nW and mixer conversion up to -21.5 dB. High input coupling efficiency implies that the electrons in the device are able to thermalize before escaping from the device. It was found that the long coherence length complicates mixer operations due to the proximity of the contact pads. Also, saturation at the IF frequency may be a concern for this type of device, and warrants further studies.         A new noise source in superconducting tunnel junction photon detectors    C.M. Wilson, L. Frunzio, K. Segall, L. Li, D.E. Prober, D. Schiminovich, B. Mazin, C. Martin and R. Vasquez Summary: We report on the development of an "all-in-one" detector that provides spectroscopy, imaging, photon timing, and high quantum efficiency with single photon sensitivity: the optical/UV single-photon imaging spectrometer using superconducting tunnel junctions. Our devices utilize a lateral trapping geometry. Photons are absorbed in a Ta thin film, creating excess quasiparticles. Quasiparticles diffuse and are trapped by Al/AlO/sub x//Al tunnel junctions located on the sides of the absorber. Imaging devices have tunnel junctions on two opposite sides of the absorber. Position information is obtained from the fraction of the total charge collected by each junction. We have measured the single photon response of our devices. For photon energies between 2 eV and 5 eV we measure an energy resolution between 0.47 eV and 0.40 eV respectively on a selected region of the absorber. We see evidence that thermodynamic fluctuations of the number of thermal quasiparticles in the junction electrodes leads to current noise that far exceeds the expected shot noise of the dc bias current. We believe that this may limit the resolution of our present generation of detectors at the operating temperature of 0.22 K.         Hot electron effect in terahertz hybrid devices    B. Leone, J.R. Gao, T.M. Klapwijk, B.D. Jackson, W.M. Laauwen and G. de Lange Summary: We analyse both the direct current and submillimeter pumped current-voltage characteristics of a hybrid superconductor-insulator-superconductor terahertz mixer consisting of a Nb tunnel junction integrated with NbTiN tuning striplines. We find that the presence of the Nb/NbTiN interface gives rise to a hot electron effect. The assumption of an equilibrium electron temperature, as distinct from the phonon temperature, allows a complete understanding of the processes involved. The impact of the hot electron effect on superconducting terahertz detectors is discussed.         NbTiN/SiO/sub 2//Al tuning circuits for low-noise 1 THz SIS mixers    B.D. Jackson, N.N. Iosad, G. de Lange, A.M. Baryshev, W.M. Laauwen, J.-R. Gao and T.M. Klapwijk Summary: Waveguide SIS mixers in which Nb/Al-AlO/sub x//Nb tunnel junctions are integrated with NbTiN/SiO//sub 2//Al tuning circuits are shown to yield receiver noise temperatures as low as 565 K at 970 GHz. Analyzing the noise and gain of one such receiver, it is shown that the NbTiN ground plane is low-loss (<0.6 dB) at 970 GHz. These results are in good agreement with results obtained previously with a quasi-optical mixer incorporating a similar tuning circuit. A decrease in sensitivity above 1 THz is attributed to increasing loss in the NbTiN.         Low-noise biomagnetic measurements with a multichannel dc-SQUID system at 77 K    H.-J. Barthelmess, M. Halverscheid, B. Schiefenhovel, E. Heim, M. Schilling and R. Zimmermann Summary: Directly coupled dc-SQUID magnetometers made from the high-temperature superconductor (HTS) YBa/sub 2/Cu/sub 3/O/sub 7/ on symmetric 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/-bicrystals have been optimized for low-noise operation in static magnetic fields. These magnetometers are encapsulated, for reliable operation in liquid nitrogen. In our small glass cryostat, allowing even mobile applications, up to 24 magnetometers can be mounted in three levels for gradiometer arrangements. With first-order gradiometers an external noise suppression of more than a factor of 100 is achieved. In a magnetically shielded chamber we find a typical noise /spl radic/S/sub B/ (77 K, 10 Hz) of less than 50 fT//spl radic/Hz and low-noise magnetocardiograms are recorded. Due to the low noise of the dc-SQUID sensors also electrically stimulated magnetoencephalography measurements were possible.         Application of high T/sub c/ SQUID magnetometer to biological immunoassays    K. Enpuku, T. Minotani, M. Hotta and A. Nakahodo Summary: A high T/sub c/ SQUID system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. Design and set up of the system is described. Minimum detectable amplitude of the magnetic flux is 0.6 m/spl Phi//sub 0/ for the measurement bandwidth from 0.2 Hz to 5 Hz when we use a magnetometer. The system noise does not increase when the magnetic field of 0.8 mT is applied in parallel to the SQUID. An experiment to measure the antigen-antibody reaction shows that the sensitivity of the present system is 10 times better than that of the conventional method using an optical marker. When a gradiometer is used, the system noise decreased by a factor of 5, compared to the case of the magnetometer. This improvement indicates the usefulness of the gradiometer to suppress the residual environmental noise in the present system. Magnetic markers that have remanent magnetic moment are also studied in order to increase the signal.         Application of high Tc SQUID magnetometer for sentinel-lymph node biopsy    S. Tanaka, A. Hirata, Y. Saito, T. Mizoguchi, Y. Tamaki, I. Sakita and M. Monden Summary: The basic performance of a nanoparticle detection system for lymph node used with a high-Tc superconducting quantum interference device (SQUID) was investigated. Ultra-small iron oxide particles of 360 pg could be detected with spacing of 1 mm between the SQUID magnetometer and the particles. When the space was widened to 40 mm, the detectable weight of the particles was increased and was 1.6 /spl mu/g.         Reduction of non-periodic environmental magnetic noise in MEG measurement by continuously adjusted least squares method    Y. Adachi, M. Shimogawara, M. Higuchi, Y. Haruta and M. Ochiai Summary: We developed a signal processing method named CALM (Continuously Adjusted Least squares Method) to reduce the non-periodical low-frequency noise during magnetoencephalography (MEG) measurements. With this method, we have successfully measured motor related cortical fields (MRCF) under daytime heavy urban noise.         SQUID gradiometry for magnetocardiography using different noise cancellation techniques    M. Bick, K. Sternickel, G. Panaitov, A. Effern, Y. Zhang and H.-J. Krause Summary: Magnetocardiographic (MCG) measurements in unshielded environment require efficient noise cancellation techniques. We have applied two software gradiometry methods to analyze the time series of signal and reference data recorded outside magnetic shielding with high temperature superconducting quantum interference device (HTS SQUID) based gradiometers. One method uses adaptive frequency dependent gradiometer coefficients determined in the Fourier domain to subtract the reference from the signal data. The other method combines recently developed techniques for nonlinear projection with properties of the wavelet transform to extract noise in state space. The analyzed MCG data sets showed improved signal-to-noise ratios for both methods as compared to the data recorded with the electronic gradiometer. In this way, it is possible to increase the bandwidth from 130 Hz for our electronic gradiometer to 250 Hz without using any additional filtering.         Improvement of a technique for localization of steel needles in humans using a SQUID magnetometer    C.H. Barbosa, E.C. Monteiro, E.A. Lima, S.F. Santos, E.G. Cavalcanti and P.C. Ribeiro Summary: A technique was previously developed, based on magnetic field measurements, to localize hypodermic and sewing needles lost in the human body, with the purpose of surgical extraction. The measurements are performed using a SQUID magnetometer, which detects the magnetic field associated with the remanent magnetization of the needle. The technique allowed easy surgical localization of the needles with good precision in all six clinical cases studied so far. The procedure greatly decreases the surgery time for foreign body extraction, and also reduces the generally high odds of failure. This paper presents an improvement of the original algorithm, which is now independent of any constant magnetic field component, thus overcoming the main experimental difficulty usually found, namely that a SQUID system does not measure absolute fields.         High-T/sub c/ superconducting surface coil for 2 tesla magnetic resonance imaging of small animals    J. Wosik, F. Wang, L.-M. Xie, M. Strikovski, M. Kamel, K. Nesteruk, M. Bilgen and P.A. Narayana Summary: The performance of small-volume Magnetic Resonance Imaging (MRI) depends on the system noise determined by noise of a probe and/or of a preamplifier (not by the body noise). Several demonstrations confirmed that, for selected applications, high-T/sub c/ superconductor MRI receiver coils have superior properties to those of comparable copper coils. We report on the outstanding performance of modified twin horseshoe YBCO rf surface probes in a 2 Tesla scanner operating at 77 K. They were used for MR imaging of spinal cord injuries in rats and for imaging of brain of small animals. The probes were designed with a virtual ground plane, thus reducing the coil-to-ground dielectric losses and making its resonant frequency less sensitive to the body proximity. Each coil was fabricated using large area 500 nm thick double-sided YBa/sub 2/Cu/sub 3/O/sub x/ films deposited on sapphire r-cut substrates. We compare the performance of the 2 Tesla high critical temperature superconductor (HTS) probe with that made of a copper coil. Designing and cryo-packaging of HTS MRI probes is discussed.         X-ray single photon 1-D imaging spectrometers    L. Li, L. Frunzio, C. Wilson, K. Segall, D.E. Prober, A.E. Szymkowiak and S.H. Moseley Summary: We have developed superconducting single-photon 1-D imaging X-ray detectors with an energy resolution of 13 eV FWHM at 6 keV and 1-D spatial resolution of 0.25 /spl mu/m over a length of 20 /spl mu/m in an effective area of 20/spl times/100 /spl mu/m/sup 2/. The energy resolution along the 200 /spl mu/m long absorber is 36 eV. The energy resolution of 13 eV is among the best reported for this kind of detectors and is within factor of 2 of its theoretical limit. The signals are read out by low-noise current amplifier with a dc voltage bias. The electronic noise measured by injecting pulses is 8 eV FWHM at 6 keV. By cooling the feedback resistor the current noise is reduced from 160 fA/Hz/sup 1/2/ to 90 fA/Hz/sup 1/2/.         Development of submillimeter-wave camera for Atacama Submillimeter Telescope Experiment    H. Matsuo, S. Ariyoshi, H. Akahori, M. Takeda and T. Noguchi Summary: Submillimeter-wave focal plane arrays based on superconducting direct detectors are designed to be used on a new 10-m submillimeter-wave telescope in Chile. Niobium tunnel junctions with low leakage current coupled to antenna structures can be sensitive submillimeter-wave direct detectors when high quantum efficiency and low leakage current are realized. Inhomogeneous distributed junctions coupled to log-periodic antennas can be used to realize this. Input coupling of better than 50% is calculated with a bandwidth of more than 60 GHz using low current density inhomogeneous distributed junctions. Their measured leakage current of 5 pA and their shot-noise limited operation suggests that noise equivalent power of less than 10/sup -17/W/Hz/sup 0.5/ at operating temperature of 0.9 K could be achieved.         RF single electron transistor readout amplifiers for superconducting astronomical detectors of X-ray to sub-mm wavelengths    T.R. Stevenson, A. Aassime, P. Delsing, R. Schoelkopf, K. Segall and C.M. Stahle Summary: We have made Radio-Frequency Single-Electron Transistors (RF-SETs) with large input gates, and tested performance and modes of operation with the goal of using such devices as on-chip amplifiers for a variety of high impedance cryogenic photodetectors. We achieved /spl ap/100 kHz of closed-loop bandwidth for charge-locked-loop and transimpedance amplifier feedback configurations, and have combined amplifier outputs using a form of wavelength division multiplexing. With our choice of SET junction resistance, a 0.5 fF input gate capacitance gave a cotunneling-degraded charge noise of 1/spl times/10/sup -4/ e//spl radic/Hz, but a fairly low input voltage noise of 30 nV//spl radic/Hz.         Spatially resolved study of superconducting tunnel junctions X-ray detectors by low temperature scanning synchrotron microscopy    H. Pressler, M. Ohkubo, M. Koike, T. Zama, D. Fukuda and N. Kobayashi Summary: A low temperature scanning synchrotron microscope (LTSSM) has been developed for spatial analysis of superconducting tunnel junction X-ray detectors. One and two-dimensional images of the detector response to X-rays were measured by scanning the junctions kept at a working temperature of about 0.4 K with a highly collimated synchrotron radiation beam. The collimation was performed by inserting a pinhole mounted on a scanning unit into the synchrotron radiation in the range of 3-6 keV. The spatial resolution of the LTSSM is between 5 and 10 micrometer. The present results indicate a large discrepancy between the experimental spatial response and a quasiparticle diffusion and edge-loss model. The LTSSM plays an important role in the development of cryogenic X-ray detectors.         A microstrip-coil integration on superconducting tunnel junctions for X-ray detection    T. Taino, H. Nakagawa, M. Aoyagi, H. Sato, H. Akoh, K. Maehata, K. Ishibashi, T. Ikeda, C. Otani, W. Ootani, T. Oku, H. Kato, K. Kawai, H.M. Shimizu, Y. Takizawa, H. Miyasaka and H. Watanabe Summary: We report the first demonstration of X-ray detection by using a Superconducting Tunnel Junction (STJ) with a microstrip-coil. The STJ was fabricated based on Nb/Al/AlO/sub x//Nb integration process technology using a 2 /spl mu/m design rule. Magnetic field was applied into the STJ by the microstrip-coil to suppress the dc Josephson current instead of the conventional electromagnet. The output waveform was successfully observed by irradiation of 5.9 keV X-ray under a condition of microstrip-coil current of 20 mA at 0.4 K.         A high-resolution X-ray detection system using STJ and SQUID amplifier    T. Ikeda, H. Kato, H. Sato, K. Kawai, H. Miyasaka, T. Oku, W. Ootani, C. Otani, H.M. Shimizu, Y. Takizawa, H. Watanabe, H. Nakagawa, H. Akoh, M. Aoyagi and T. Taino Summary: We succeeded in separating the STJ upper electrode events from other electrode events. This study is for X-ray spectroscopy of slow ions. With a SQUID amplifier, it is clearly seen that the upper electrode signal has a sharp peak with a narrow base, while the other has a relatively gentle peak with a wide base. The difference in signal width was used to separate the upper electrode events from other electrode events. Then the X-ray spectroscopy of slow highly charged ions was carried out at RIKEN. The results are shown here.         Spectral features of substrate phonon events obtained by illuminating superconducting tunnel junctions with X-rays    C. Otani, T. Ikeda, H. Kato, K. Kawai, H. Miyasaka, T. Oku, W. Ootani, H. Sato, H.M. Shimizu, Y. Takizawa, H. Watanabe, H. Nakagawa, H. Akoh, M. Aoyagi and T. Taino Summary: The pulse height spectra of the substrate phonon events obtained with superconducting tunnel junctions (STJs) were examined. We compared the spectra for STJs with and without a 50-nm-thick buffer layer of aluminum-oxide on the sapphire substrate under X-ray illumination. We found-that the spectral difference was concentrated in the high-energy tail of the component, corresponding to the events absorbed within a thin skin. The effective thickness of this skin was estimated to be about 3 /spl mu/m by using the amount of difference in the spectra. We explain that the spectral difference could be caused by the selective attenuation of high-frequency phonons in the substrate and buffer layer.         Detection of heavy ions using Nb-based superconducting tunnel junction    H. Sato, T. Ikeda, K. Kawai, H. Miyasaka, T. Oku, W. Ootani, C. Otani, H.M. Shimizu, Y. Takizawa, H. Watanabe, K. Morimoto, F. Tokanai, H. Akoh, H. Nakagawa, M. Aoyagi and T. Taino Summary: The superconducting tunnel junction (STJ) is one of the most promising devices to use as a fast detector for heavy ions. The energy deposited due to the passage of a heavy ion through an STJ forms a region called a hot spot, where the superconductivity of the region is broken. As a result, a reduction of the critical current (I/sub c/) in the STJ occurs. If the bias current exceeds this reduced I/sub c/, the output voltage from the STJ switches from 0 V to its gap voltage, which is recognizable as a signal due to the heavy ion passage. Nb-based STJs were fabricated for this heavy ion detector and an experiment was performed at the RIKEN Ring Cyclotron Facility to investigate the response to heavy ions. Instantaneous switching to the voltage state of the STJ in response to the decrease in I/sub c/ induced by a heavy ion beam was successfully observed by introducing /sup 40/Ar particles with a kinetic energy of 95 MeV/nucleon into the STJ.         Imaging sub-millimeter waves in planar cryoelectronic circuits by scanning laser microscopy    D. Abraimov, A.V. Ustinov and S.V. Shitov Summary: Low temperature scanning laser microscopy (LTSLM) is demonstrated to be capable of imaging sub-THz electromagnetic fields in cryoelectronic integrated structures. This method allows one to evaluate the spatial distribution of time-averaged field amplitudes with a resolution of about one micrometer for samples with characteristic dimensions of order millimeters. Using LTSLM, cryoelectronic devices with both passive and active superconducting elements can be characterized. Local heating of superconducting structures by a laser beam introduces extra loss for the propagating and standing sub-millimeter waves. We present LTSLM images of two-dimensional 400 to 500 standing GHz wave patterns in integrated superconducting receiver chips.         Development of superconducting tunnel junctions for ultra soft X-ray detectors    Y. Takizawa, T. Ikeda, T. Oku, C. Otani, K. Kawai, H. Sato, H.M. Shimizu, H. Miyasaka, H. Watanabe, W. Ootani, H. Akou, H. Nakagawa, M. Aoyagi and T. Taino Summary: Nb-based superconducting tunnel junctions (STJs) with Al trapping layers have been developed for X-ray detectors. One applications for STJs is a low energy radiation detector having energy resolution and a high photon counting rate. STJs have good potential in the band of energies from 40 eV up to 1 keV, because STJs materials have good absorbing properties in this region. The energy resolution was measured by using the Photon Factory beamline BL-12A of High Energy Accelerator Research Organization (KEK) in Japan, and for 200 eV photon, 11 eV Full Width Half at Half Maximum (FWHM) with a 20/spl times/20 /spl mu/m/sup 2/ junction were achieved. In this article, the fabrication technique and preliminary results of measuring the response for this band of energies are reported.         Effects of parasitic capacitance in a magnetically-coupled voltage multiplier    S. Kiryu, M. Maezawa, H. Sasaki, F. Hirayama and A. Shoji Summary: Effects of parasitic capacitance in a magnetically-coupled voltage multiplier (VM) are described. We found that parasitic capacitance between SQUIDs and JTLs in a VM decreases its operating margin. We also found that separation of electric grounds for the output terminal of a VM from those for the JTLs is effective to improve the operating margin. Using this method, a 64-stage VM was fabricated and well-defined output voltage was obtained.         Magneto-optical modulator for superconducting digital output interface    R. Sobolewski and J.-R. Park Summary: We propose an ultrafast magneto-optic (MO) modulator for the SFQ-to-optical digital interface. Our MO modulator is based on the Faraday effect and consists of a microwave microstrip line (MSL) with a polarization-sensitive MO active medium and a fiber-optic cw light delivery. The light modulation occurs in parallel to the magnetic field and perpendicular to the rf signal propagation. The low characteristic impedance of MSL, together with the superconducting ground plane, ensures that the magnetic-field component of the electromagnetic signal is uniform and effectively "focused" across the length of the modulator. For several different MO devices of the above geometry, we have numerically calculated magnetic-field distributions inside the MO material and verified that the H field was uniform over the width of the top electrode. The input modulation current was assumed to be 1 mA-the realistic upper current-output value for the Nb-based SFQ circuit. Taking EuSe as the MO material at 4.2 K, we obtained H=2.51 Oe for a device with 100-/spl mu/m-wide top electrode and characteristic impedance of 4.4 /spl Omega/. The H magnitude could be further increased to as much as 60 Oe for a macroscopic device with the 5-mm-long optical interaction distance, yielding the 36/spl deg/ phase retardation and /spl sim/10% modulation depth in the single-pass-type device. The most desired configuration for the MO modulator was found to be a Mach-Zehnder design. The Mach-Zehnder interferometer increases the device sensitivity, making it very attractive for direct, SFQ-to-optical digital I/O interface.         High-speed interchip data transmission technology for superconducting multi-chip modules    D. Gupta, W. Li, S.B. Kaplan and I.V. Vernik Summary: We have developed an interchip data transmission scheme through passive transmission lines on a multi-chip-module (MCM) carrier and 100-/spl mu/m solder bump bonds. In rapid single flux quantum (RSFQ) logic, digital data are in the form of single flux quantum (SFQ) pulses. A reliable scheme for transmission of SFQ pulses through non-superconducting solder bumps between chips through a passive MCM substrate is yet to be established. Therefore, we have devised a scheme that converts SFQ pulses into toggles in a voltage waveform for interchip transmission. Data in the form of SFQ pulses are reconstructed from this voltage waveform using a sensitive quantizing pulse receiver. Our objective is to eliminate the need for amplification of the transmitted signal. This is achieved by increasing the receiver sensitivity. However, a sensitive receiver, a dc SQUID, may produce more than one SFQ pulse for each rising/falling edge of the voltage waveform. A simple circuit, pulse resurrection logic (PRL), is employed to discard any extra SFQ pulses. Together with the sensitive quantizer, the PRL circuit makes our scheme error tolerant. We have demonstrated the receiver operation using 3-/spl mu/m Nb RSFQ circuits at frequencies up to 20 GHz.         Component development for a 16 Gb/s RSFQ-CMOS interface system    N. Yoshikawa, T. Abe, Y. Kato and H. Hoshina Summary: We have been developing an RSFQ-CMOS interface system. The system consists of three modules: a 1 to 32 bit DDST demultiplexer which converts a 16 Gb/s SFQ data input into a 32-channel 500 Mb/s output, asynchronous stacked-SQUID amplifiers which amplify an SFQ data input into a 5 mV voltage level output, and 77 K CMOS amplifiers which amplify a 5 mV voltage level input into a 5 V output at 500 MHz. We have implemented the asynchronous stacked-SQUID amplifier and the 77 K CMOS amplifier using the HYPRES 1 kA/cm/sup 2/ Nb process and the ROHM 0.6 /spl mu/m CMOS process, respectively. It was demonstrated that the 24-stage asynchronous stacked-SQUID amplifier amplifies an SFQ data input into a 2.0 mV voltage level at 600 MHz. The 77 K CMOS amplifier was shown to amplify a 5 mV voltage level input into 5 V at 500 MHz from the simulation, and a 175 mV voltage input into 3.5 V at 90 MHz from the experiment.         Microfabricated transition-edge X-ray detectors    G.C. Hilton, J.M. Martinis, K.D. Irwin, N.F. Bergren, D.A. Wollman, M.E. Huber, S. Deiker and S.W. Nam Summary: We are developing high performance X-ray detectors based on superconducting transition-edge sensors (TES) for application in materials analysis and astronomy. Using our recently developed fully lithographic TES fabrication process, we have made devices with an energy resolution of 4.5/spl plusmn/0.1 eV for 5.9 keV X-rays, the best reported energy resolution for any energy dispersive detectors in this energy range. These detectors utilize micromachined thermal isolation structures and transition-edge sensors fabricated from Mo/Cu bilayers with normal-metal boundary conditions. We have found the normal-metal boundary conditions to be critical to stable and reproducible low noise operation. In this paper we present details of fabrication and performance of these devices.         Gamma-ray spectrometers using superconducting transition edge sensors with external active feedback bias    D.T. Chow, M.L. van den Berg, A. Loshak, M. Frank, T.W. Barbee Jr. and S.E. Labov Summary: We are developing X-ray and gamma-ray spectrometers with high absorption efficiency and high energy-resolution for X-ray and gamma-ray spectroscopy. They are microcalorimeters consisting of a bulk Sn absorber coupled to a Mo/Cu multilayer superconducting transition edge sensor (TES). We have operated these microcalorimeters with an external active feedback bias to linearize the detector response, improve the count rate performance, and extend the detection energy range. We measured an energy resolution of 120 eV FWHM for 60 keV incident gamma-rays with no degradation of resolution from active bias. We present X-ray and gamma-ray results and operation of this detector design in both bias modes.         Noise and energy resolution of X-ray microcalorimeters    P.A.J. de Korte, W.M. Bergmann Tiest, M.P. Bruijn, H.F.C. Hoevers, J. van der Kuur, W.A. Mels and M. Ridder Summary: Two type of sensor geometries of voltage-biased X-ray microcalorimeters with a phase-transition thermometer have been built and tested. Both devices show, in addition to the well-known noise sources of thermal fluctuation noise or phonon noise from the heatlink to the bath and Johnson noise from the thermometer resistance, also thermal fluctuation noise from the thermometer itself. In both cases however the measured energy resolution is limited by other sources. The energy resolution of the asymmetric lateral type of sensor, 12 to 15 eV @ 5.9 keV, is limited by a position dependent heatleak of the absorber to the bath. The energy resolution of the symmetric lateral sensor, 6.8+/-0.3 eV FWHM @ 5.9 keV, is limited by excess noise at frequencies below 1000 Hz. The origin of this noise component is unknown so far.         Fabrication and characterization of superconducting X-ray calorimeters with transition edge sensors    T. Morooka, K. Tanaka, S. Nakayama, A. Nagata, K. Chinone, M. Ukibe, F. Hirayama, M. Ohkubo, M. Koyanagi, T. Mizuki, T. Hikosaka, U. Kawabe and T. Nemoto Summary: We have developed superconducting calorimeters using transition edge sensors (TESs) for industrial X-ray microanalysis. To obtain high count rate, high reliability, and high energy resolution, a large format array of the sensors and an integration of a TES calorimeter and a SQUID amplifier are required. A novel calorimeter fabrication process has been established, in which a micro-machining technology using a silicon-on-insulator wafer was applied. A 4-pixel Au/Ti TESs calorimeter was fabricated using this process. SQUID amplifiers suitable for the calorimeter have also been designed and fabricated. It is expected to achieve a count rate per pixel of 7.1 kcps. The expected energy resolution including the SQUID contribution was estimated at 17-21 eV. It has been confirmed that the SQUID contribution for the current noise of our calorimeter can almost be ignored. It has also been confirmed that an array of 14 or more pixel are required that to achieve an effective count rate of more than 100 kcps.         Fabrication of Mo/Au transition-edge sensors for X-ray spectrometry    N. Tralshawala, R.P. Brekosky, M.J. Li, E. Figueroa-Feliciano, F.M. Finkbeiner, M.A. Lindeman, C.M. Stahle and C.K. Stahle Summary: We present fabrication details of our Mo/Au X-ray microcalorimeters, which are being developed as one of the candidate high resolution spectrometers for the Constellation-X mission. We have reproducibly fabricated Mo/Au transition-edge sensors with Tc's of /spl sim/100 mK on etched silicon nitride membranes and connected via superconducting Nb leads. Our single pixel devices have, so far, attained resolution of 3.7 eV at 3.3 keV. We also discuss our plans for fabrication and testing of fully functional multi-pixel array of X-ray microcalorimeters.         Superconducting transition-edge bolometer in a resistive and in an inductive mode    H. Seppa Summary: We analyze the energy resolution of a superconducting transition-edge bolometer (STEB) biased with an ac current. We will show that the ac readout method enables us to utilize STEB either monitoring the change in dissipation due to the change in temperature or the change in inductance owing to the increased in number of quasiparticles.         Small area Y-Ba-Cu-O thin films for applications in hot-electron bolometers    L.R. Vale and R.H. Ono Summary: We are investigating the use of very thin, small area YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films on Si substrates for application in hot-electron bolometers. Hot-electron bolometers produced from high-T/sub c/ materials will be favored over their low-temperature counterparts in applications of radio astronomy and atmospheric physics where the higher operating temperatures provide distinct advantages. Devices on Si can help advance this technology for bolometric space applications, where a substrate is needed with good thermal conductance and excellent IR performance. Based on our experience with YBCO bolometers and YBCO film growth on Si, we have begun a study of sub-micrometer scale devices. Our typical YBCO films grown on Si by pulsed laser deposition have critical temperatures of 86 K and critical currents of 1-3/spl times/10/sup 6/ A/cm/sup 2/ at 77 K for YBCO microbridges 45 nm thick. We have made 1-2 /spl mu/m wide microbridges from YBCO films of 25 nm to 45 nm thick. These microbridges show reduced critical temperatures of 71 K to 81 K, respectively, related to the processing sequence that produces the microbridges.         YBaCuO mid-infrared bolometers: Substrate influence on inter-pixel crosstalk    A. Gaugue, P. Teste, J. Delerue, A. Gensbittel, A. De Luca, A. Kreisler, F. Voisin, G. Klisnick and M. Redon Summary: A theoretical modelling approach has been developed, allowing the prediction of the response of YBaCuO bolometers forming an elementary array and the thermal crosstalk between adjacent pixels. Two models are described, a 2D analytic model and a 3D numerical model. The latter takes into consideration the thermal boundary resistance between the substrate and the heat sink. The predicted responses are compared with those of a 2/spl times/2 YBaCuO bolometer array deposited on MgO substrate and tested at 10 /spl mu/m wavelength.         High-temperature superconducting edge-type Josephson junctions with modified interface barriers    T. Satoh, J.-G. Wen, M. Hidaka, S. Tahara, N. Koshizuka and S. Tanaka Summary: This paper describes recent results on the fabrication, electrical characteristics, and microstructure of high-temperature superconducting edge-type Josephson junctions with modified interface barriers. The barriers are formed by surface modification of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// base layer. This process involves structural and chemical modification by ion irradiation and crystallization by annealing. The junctions showed resistively and capacitively shunted junction-like current-voltage characteristics and excellent uniformity. The spread in the critical current for one hundred junctions was smaller than 1/spl sigma/=10% at 4.2 K. The uniformity is now approaching 1/spl sigma/=5%. The junction characteristics have remained the same after two-year room-temperature storage. They also showed no change after high-temperature processing at about 700/spl deg/C. High-resolution transmission electron microscopy revealed that both the crystal structure and chemical composition in relatively thick barriers are different from those of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//.         Transport properties of [100] tilt and twist biepitaxial Y-Ba-Cu-O junctions    E. Sarnelli, F. Carillo, G. Testa, F. Lombardi, F.M. Granozio, F. Ricci, U. Scotti di Uccio and F. Tafuri Summary: The effects of the order parameter symmetry and the interface grain boundary orientation on the transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ biepitaxial grain boundary junctions have been investigated. 45/spl deg/ [100] tilt and twist junctions on SrTiO/sub 3/ [110] and MgO [110] substrates by employing respectively MgO and SrTiO/sub 3/ as seed layers have been fabricated. More complex junctions by using CeO as seed layers have also been fabricated and analyzed. The analysis of experimental data points towards a predominant d-wave symmetry of the superconductive order parameter.         Nanometer scale masked ion damage barriers in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//    D.-J. Kang, R. Speaks, N.H. Peng, R. Webb, C. Jeynes, W.E. Booij, E.J. Tarte, D.F. Moore and M.G. Blamire Summary: Josephson junctions have been formed in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// by ion implantation though apertures in 450 nm thick Au masks using 50 keV H implants with fluences up to 5/spl times/10/sup 18/ cm/sup -2/. The mask apertures were milled with a focused 30 keV Ga ion beam giving a best measured electrical junction length of about 70 nm. Resistively shunted junction behavior has been observed over a wide temperature range (about 10 K). Shapiro steps have also been measured on these devices. The influence of possible Ga contamination is discussed.         Analysis of I/sub c/ spreads in interface engineered junctions    J. Yoshida, S. Inoue, H. Sugiyama and T. Nagano Summary: We have investigated the electrical properties of interface engineered junctions fabricated under various process conditions to clarify the possible origin of the spreads in I/sub c/ and R/sub n/ values. We found that in most cases, the I/sub c/R/sub n/, values of junctions on a wafer scaled with the square root of I/sub c/. The distribution of both the junction I/sub c/ and R/sub n/ were expressed well by the log-normal distribution function with their /spl sigma/ values being different by a factor of two. These results indicate that Cooper pairs and quasiparticles in the junctions transfer through different transport channels, i.e., direct tunneling for the former and resonant tunneling for the latter, and that a variation in the tunnel barrier thickness among junctions dominates the spreads in the I/sub c/ and R/sub n/ values. In contrast, we could not observe a universal scaling relation between I/sub c/R/sub n/, and I/sub c/ among junctions processed under different conditions. This indicates that the I/sub c/ variation due to process conditions originates from something other than a simple barrier-thickness variation.         Study on fabrication conditions of the interface-treated trilayer junctions    M. Maruyama, K. Yoshida, T. Kito, T. Furutani, Y. Yoshinaga, M. Horibe, M. Inoue, A. Fujimaki and H. Hayakawa Summary: We have investigated the effects of fabrication conditions on the properties of the interface-treated trilayer Josephson junctions. In the junctions, barriers are formed by ion milling, followed by annealing. We controlled the accelerating voltage for the milling process and the gas pressure for the annealing process. Josephson currents were observed in the junctions fabricated under various conditions. It was found that higher accelerating voltage contributes to the reduction of leakage paths in the barriers. However, clear dependence of the Josephson currents on the conditions was not observed in contrast to the results for the ramp-edge junctions.         Characterization of HTS SFQ circuits using interface-engineered Josephson junctions    K. Saitoh, Y. Soutome, T. Fukazawa, Y. Tarutani and K. Takagi Summary: We fabricated and tested high-temperature superconducting (HTS) rapid-single-flux-quantum (RSFQ) circuits using interface-engineered Josephson junction (IEJ). The characteristics of high-speed operation were examined by voltage-divider operation based on the toggle-flip-flop circuit. An operation at 155 GHz was obtained at 15 K and the proper functioning of the voltage divider was observed up to 27 K. Temperature dependence of the maximum operation speed was analyzed by circuit simulation with thermal-noise sources. To achieve higher speed operation using a Josephson junction with a higher I/sub c/R/sub n/ product, we also fabricated an RSFQ balanced comparator using IEJ; proper switching characteristics of the circuit was confirmed up to 190 GHz at 30 K. The bias condition dependencies were studied based on the circuit simulations in the relationship of the I/sub c/R/sub n/ product. The results of circuit simulation indicate that a Josephson junction with an I/sub c/R/sub n/ product of more than 0.7 mV is required for high-speed operation (100 GHz) in high-temperature range (30-40 K). We believe that the IEJ is a promising junction candidate for realizing high-speed operation in a high-temperature range.         Influence of La-doping of YBa/sub 2/Cu/sub 3/O/sub 7/ on transport properties of interface-engineered ramp-edge junctions    J.-K. Heinsohn, R. Dittmann, J. Rodriguez Contreras, J. Scherbel, A. Klushin and M. Siegel Summary: We have investigated the influence of La-doping of the YBa/sub 2-x/La/sub x/Cu/sub 3/O/sub 7/ (YBCO) thin film electrodes on dc and ac Josephson properties of ramp-edge junctions with interface-engineered barriers. Non-doped optimized junctions exhibit critical current densities, j/sub c/, of 5/spl middot/10/sup 4/ A/cm/sup 2/ and normal sheet resistances, R/sub N//spl middot/A, of 3/spl middot/10/sup -9/ Ohm/spl middot/cm/sup 2/ at 77 K. The transport properties of junctions with x=0.03 La-doping are quite similar to those of non-doped junctions. La-doping of x=0.05 and x=0.07 leads to an increase of R/sub N//spl middot/A and decrease of j/sub c/ by about one order of magnitude. Devices with j/sub c/<10/sup 4/ A/cm/sup 2/, which are operating in the short junction limit exhibit current-voltage characteristics without any excess current and 100% modulation of critical current in external magnetic field. The current voltage characteristics exhibit well defined Shapiro steps. The dependence of current-step height on microwave current can be described in the resistively-shunted junction model. The strong changes in the temperature dependencies of j/sub c/ and R/sub N//spl middot/A suggest different electrical transport properties for junctions fabricated with non-doped and La-doped YBCO. The temperature dependence of the critical current and the normal resistance allows us to draw conclusions to the transport properties of our junctions.         On-orbit status of the High Temperature Superconductivity Space Experiment    M. Nisenoff and W.J. Meyers Summary: The High Temperature Superconductivity (HTS) Space Experiment (HTSSE-II) successfully achieved orbit 23 February 1999 with the launch of the Advanced Research and Global Observation Satellite (ARGOS). It contains eight HTS components and subsystems. Developed by various industrial and government laboratories in the 1992 to 1994 time frame, they were integrated with a closed cycle refrigerator into the HTSSE-II payload during 1995. The monitoring of the on-orbit performance of the HTS devices began in May 1999. After a brief description of the HTSSE program, the performance characterization of the HTSSE-II devices will be presented.         Development of space qualifiable HTS communication subsystems    R.R. Mansour, T. Romano, S. Ye, S. Peik, T. Nast, D. Enlow, C. Wilker and J. Warner Summary: The paper presents the measured results of a C-band 60-channel superconductive input multiplexer integrated with pulse tube space-qualified cryocoolers. The multiplexer is developed to duplicate the requirements of the INTELSAT 8 program. The channel filters are self-equalized 10-pole HTS planar structures designed with drop-in cryogenic ferrite circulators and isolators. The paper presents details on RF design, packaging and cryocooler integration. It demonstrates that at least 50% reduction in mass and 50% reduction in size can be achieved by replacing the INTELSAT 8 C-band dielectric resonator input multiplexer with a superconductive multiplexer.         Progress in low noise cooling performance of a pulse-tube cooler for HT-SQUID operation    C. Lienerth, G. Thummes and C. Heiden Summary: Previously it was shown that Joule-Thomson- and pulse tube coolers (PTC) are attractive candidates for low noise cooling of HT-SQUIDs. Tests of a highly sensitive HT-SQUID that was mounted directly on the cold tips of these coolers revealed discrete peaks in the flux noise spectrum which were attributed to pressure wave-induced vibrations of the coolers. A first additional noise reduction for the PTC was achieved by using Ti-V-Al tubes instead of stainless steel for the regenerator and pulse tube. Further reduction was obtained by mounting the sensor on a separate platform that was thermally connected to the cold tip by use of a flexible copper link. The remaining amplitude of axial vibrations at the cold platform was measured to be about 0.5 /spl mu/m as compared to 6.0 /spl mu/m without vibration compensation. We report on the tests of different methods of vibration compensation for the PTC, using a sensitive rf HT-SQUID magnetometer with coplanar resonator showing an intrinsic noise of 45 fT//spl radic/Hz at frequencies above 100 Hz and 110 fT//spl radic/Hz at 10 Hz. Measurements of the flux noise spectrum of the HT-SQUID using the new PTC cold head will be presented.         Submillimeter superconducting integrated receivers: Fabrication and yield    L.V. Filippenko, S.V. Shitov, P.N. Dmitriev, A.B. Ermakov, V.P. Koshelets and J.-R. Gao Summary: Fabrication procedure and yield analysis of superconducting integrated receivers is reported. These chip receivers, apart from the quasi-optical SIS mixers, contain internal local oscillators and associated rf and dc interfaces. Due to both complexity and design requirements of the integrated circuit, certain restrictions are applied to the standard Nb/Al/Al/sub x/O/sub y//Nb SNEAP process. To obtain accurate area for micron-size SIS junctions and thickness for multi-layer SiO/sub 2/ insulation, a few solutions and modifications were developed. The possibility of transferring this fabrication process worldwide has been proven experimentally.         SIS receivers for millimeter and submillimeter-wave detection    D. Andreone, L. Brunetti, V. Lacquaniti, R. Steni and J.R. Thorpe Summary: In this work we report the current status in our development of sensitive heterodyne detectors for efficient down-conversion of submillimeter-wave signals to D-band. These detectors use the strong non-linearity of Nb/Al-AlO/sub x//Nb tunnel junctions and employ preferably quasi-optical techniques to couple local-oscillator and radio-frequency signals to the superconducting junctions via a log-periodic antenna and hyper-hemispherical lens combination. Several devices have been fabricated and tested.         X-ray and optical photon counting detector using superconducting tunnel junctions    B. Delaet, P. Feautrier, J.-C. Villegier and A. Benoit Summary: The properties of Superconducting Tunnel Junctions (STJ) make them very suitable for low light level astronomical observations. STJ detectors could be used to improve the sensitivity of such a system to be implemented on ground based telescopes. We have developed a modified version of the "SNEP" fabrication process for making Nb/Al-AlO/sub x/-Al/Nb and Ta/Al-AlO/sub x/-Al/Ta/Nb STJ's. These junctions show a very low sub-gap leakage current at 0.1 K. They use a double thin aluminum trapping layer and a Nb or Ta absorber grown epitaxially on a R-plane sapphire substrate. A new experimental set-up has been completed to achieve photon counting performances for the X-ray and for optical-near infrared wavelengths. An original, room temperature, charge sensitive preamplifier has been built for this purpose and tested with a /sup 55/Fe X-ray source. The 6 keV peak of this source can be observed in the measured spectrum. Photon counting ability in the near infrared at 0.78 /spl mu/m is also demonstrated.         Development of practical soft X-ray spectrometers    G. Brammertz, P. Verhoeve, A. Peacock, D. Martin, N. Rando, R. den Hartog and D.J. Goldie Summary: Cryogenic soft X-ray imaging spectrometers are currently being developed for applications in the fields of astronomy and material sciences. In this paper we present experiments on optimized single devices, which show measured energy resolutions of 4.6 eV, 8.1 eV and 20.5 eV at 525 eV, 1.5 keV and 6 keV respectively. These energy resolutions combined with a quantum efficiency of more than 40% in the energy range from 0.5 to 2 keV together with a count rate capability of 15 kHz demonstrate the overall good performance of single Superconducting Tunnel junctions (STJs). Assembling these optimized single devices in a matrix read-out would provide the practical basis for a soft X-ray imaging spectrometer.         Superconducting integrated receiver as 400-600 GHz tester for coolable devices    S.V. Shitov, M. Levitchev, A.V. Veretennikov, V.P. Koshelets, G.V. Prokopenko, L.V. Filippenko, A.B. Ermakov, A.M. Shtanyuk, H. Kohlstedt and A.V. Ustinov Summary: A laboratory-purpose submillimeter wavelength receiver is developed and tested. The device can in situ detect the spectrum of an rf source working below 100 K within the frequency range 400-600 GHz. A sample is placed close to the receiver sensor; both are in vacuum inside the probe stick and cooled by liquid helium in the standard transport dewar. The quasioptical sensor design is based on the superconducting integrated receiver chip; its noise temperature below 300 K was measured at /spl ap/500 GHz with a variable-temperature black body. The output level of the tester is suitable for the direct readout by a spectrum analyzer. Details of the design and main test data are reported.         Line-splitting in high-resolution superconducting tunnel junction EUV detectors    S. Friedrich, L.J. Hiller, M.F. Cunningham and S.E. Labov Summary: We have developed high-resolution Nb-Al-AlO/sub x/-Al-Nb tunnel junction extreme ultra-violet (EUV) detectors. In the energy range between 25 and 70 eV, we have measured an energy resolution of 2.2 eV full-width at half maximum (FWHM). The energy resolution degrades significantly in the energy range between /spl ap/80 and /spl ap/230 eV where the Nb absorber is partially transparent and some of the photons are absorbed in the Al trap layers. We have for the first time observed a distinctly different response for photons absorbed in the Nb and the Al layer of the same junction electrode. We have modeled this effect with Monte-Carlo simulations of the charge generation process in superconducting multilayers.         A data acquisition system for test and control of superconducting integrated receivers    A.B. Ermakov, S.V. Shitov, A.M. Baryshev, V.P. Koshelets and W. Luinge Summary: A data acquisition system for the Integrated Receiver Test and Control ("IRTECON") was developed and tested with the single-chip quasioptical receiver containing a planar double-dipole antenna SIS mixer and FFO as a local oscillator. The basic system includes a controlling computer with two acquisition cards, an analogue bias supply and GPIB linked peripheries. The system collects and analyzes I-V data of the FFO and SIS mixer, tunes their regimes over the receiver frequency range. The possibility to optimize automatically the receiver noise temperature is realized. This system can be adopted to control a wide range of SIS-based receiving system such as an imaging receiver on remote location.         A 200-300 GHz single sideband SIS mixer for radio astronomy    A. Karpov, J. Blondel, D. Billon-Pierron and K.-H. Gundlach Summary: We present an ultra broadband low noise single sideband (SSB) SIS mixer developed for 200-300 GHz radio astronomy receivers. The mixer uses two Nb/AlO/sub x//Nb junctions. Image band rejection by 20 dB is provided in the entire 200-300 GHz band using a mechanical tuning of the single noncontacting backshort in the mixer. The SIS receiver SSB noise temperature is close to 50 K in the main part of the band. A speed-up of the observations at radio telescopes by a factor 2-3 is expected with the new receiver.         Heat sources in electronic refrigerators    B. Jug and Z. Trontelj Summary: Tunneling electric current through the normal metal-insulator-superconductor junction is accompanied with heat flow out of normal metal when properly voltage biased. The phenomenon enables cooling of electrons and phonons (under special conditions) in the region below 1 K. At lower bath temperatures two parasitic heat sources decrease refrigerator performance. (i) Due to tunneling of hot electrons from a normal metal electrode to a superconductive one an excess quasiparticle density appears in the superconductor which results in tunneling of electrons back to the normal metal and consequently the normal metal electron temperature increases. This phenomenon is called back tunneling. (ii) Second heat source is the Cooper pair formation: the part of energy released by the formation of Cooper pairs in a superconductor is dissipated in a normal metal. Both contributions are calculated-by considering quasiparticle behavior in the junction region and no free parameters are introduced. Diffusion, tunneling and back tunneling of quasiparticles in the superconductor in equilibrium are considered to calculate temperatures of electrons and phonons in the normal metal electrode. This detailed model explains the increase of normal metal electron temperatures above the bath temperature at lower bath temperatures.         Advanced Stirling cryogenic unit for cooling of a highly sensitive HTS/Hall-magnetometer used in a system for nondestructive evaluation    G. Kaiser, U. Bohm, A. Binneberg, S. Linzen and P. Seidel Summary: The invention of a new type of highly sensitive HTS/Hall-magnetometer which can be produced in large quantities with excellent reproducibility and operated with relatively simple non-feedback electronics offers the possibility for the development of unexpensive commercial systems for nondestructive evaluation. In order to meet the market requirements a cryogenic sub-system based on an AIM SL200 split Stirling cryocooler is currently under development at ILK Dresden (Institut fur Luft- und Kaltetechnik Dresden). In this contribution we will discuss the particular advantages of the new magnetometer concerning cryocooler operation. The design of the cryogenic test unit will be presented.         Sidelobes suppression in normal-distribution-shaped Josephson tunnel junctions    K. Kikuchi, H. Myoren, T. Iizuka and S. Takada Summary: We have studied normal-distribution-shaped Josephson tunnel junctions for STJ (superconducting tunnel junction) photon detector applications. By employing a normal-distribution function to the shape of the superconducting electrodes sidelobes of the Josephson current were entirely suppressed with a small magnetic field. This behavior was confirmed experimentally by using Nb/AlO/sub x//Nb Josephson tunnel junctions. There were no oscillatory sidelobes in the Josephson current dependence on the magnetic field. Experimental results were in good agreement with theoretical ones. The Josephson current was efficiently suppressed by an external magnetic field of about 0.5 mT at 4.2 K, which is less than one tenth that of other shaped junctions. In the experiment at 0.3 K, Fiske steps due to the resonances were not observed by suppression with a magnetic field of about 1 mT.         Quantum Roulette Noise Thermometer: Progress and prospects    R.A.M. Lee, L. Hao, D.A. Peden, J.C. Gallop, J.C. MacFarlane and E.J. Romans Summary: A novel form of primary thermometer called the Quantum Roulette Noise Thermometer (QRNT) has been fabricated and is presently undergoing feasibility studies. This device utilises flux quantisation in a high temperature superconducting ring interrupted by two closely spaced, parallel, Josephson junctions. Several devices have been fabricated and different methods investigated for measuring the statistical distribution of trapped flux states. We report the results of these endeavours with emphasis on a method for suppressing I/sub c/ by applying an r.f. field to the junctions.         SQUID detection of magnetic fields produced by chemical reactions    J. Claycomb, M. Nersesyan, D. Luss and J.H. Miller Jr. Summary: We report on the detection of chemomagnetic fields produced by solid state combustion and liquid-solid reactions. Magnetic time series and noise spectra are recorded with high-T/sub c/ SQUID magnetometers. The moving reaction zone, ion convection, ion diffusion all cause macroscopic ionic currents, which generate electric and magnetic fields. A simple electromagnetic model describes the relation between a moving charge distribution associated with the combustion wave and the resulting magnetic field. Certain reactions exhibit power law behavior in the noise spectra and probability distributions of magnetic field peak amplitudes, consistent with self-organized criticality.         Resistance bridge based on the cryogenic current comparator in a transport dewar    E. Bartolome, A. Camon, J. Sese, C. Rillo, J. Flokstra, G. Rietveld and H. Rogalla Summary: An optimized resistance bridge based on the Cryogenic Current Comparator (CCC) with SQUID readout has been developed. The bridge can be used for routine secondary resistance calibrations as well as for the traceability of 100 /spl Omega/ to the quantum Hall resistance. The CCC-SQUID, shielding and wiring are mounted in a telescopic insert, fitted in a low-evaporation rate, transportable liquid He dewar, with an autonomy of around 1 month. A difference compensator method is used to balance the bridge. A new, more reliable and self-standing bridge electronics has been fabricated and tested. An uncertainty in the comparison of resistors at least one order of magnitude better than room temperature CCs is expected.         High-T/sub c/ SQUID gradiometer for mobile magnetic anomaly detection    T.R. Clem, D.J. Overway, J.W. Purpura, J.T. Bono, R.H. Koch, J.R. Rozen, G.A. Keefe, S. Willen and R.A. Mohling Summary: The prototype for a nitrogen-cooled high-T/sub c/ SQUID gradiometer has been developed and is being evaluated for magnetic anomaly detection of underwater targets in mobile surveys. The prototype's design is based on the concept of the Three-Sensor Gradiometer (TSG). In the TSG approach, balance of two independent SQUID magnetometers is more difficult to attain than for conventional low-T/sub c/ gradiometers in which signal subtraction occurs prior to a single SQUID stage. Experiments have been conducted using a platform-motion simulator to evaluate performance of this gradiometer for mobile operation. Sensor configuration, experimental procedures, approaches for improved performance, and empirical results are reported. Interesting results of predictions to estimate detection range obtained from matched-filter calculations are included. The paper concludes with description of current preparations for a sea test of this sensor and a perspective of future developments.         Electronic gradiometer using HT/sub c/ SQUIDs with fast feedback electronics    A. Matlashov, M. Espy, R.H. Kraus Jr., K.R. Ganther Jr. and L.D. Snapp Summary: An electronic gradiometer was built using a HTS SQUID magnetometer array. A SQUID magnetometer in the center of the array was used to pick up background noise, and the output signal fed back to other magnetometers to cancel background noise. Fast feedback electronics were built for the background channel with a slew rate about 10/sup 7/ /spl Phi//sub 0//sec and 10 MHz small signal bandwidth. Two other magnetometers of the array were connected to pcSQUID/sup TM/ electronics with 5/spl times/10/sup 4/ /spl Phi//sub 0//sec slew rate using the AC bias mode to decrease 1/f noise. The output signals from these two magnetometers were input to a summing amplifier resulting in a gradiometric output signal without background channel noise. Constructing the gradiometer with different magnetometers on the array enables us to vary the baseline from 0.75 mm to 7.5 mm with 2/spl times/10/sup -12/ T//spl radic/Hz field resolution in an unshielded laboratory environment. This variable-baseline gradiometer can be used for NDE, biomagnetism and other applications.         Improved direct-coupled dc SQUID read-out electronics with automatic bias voltage tuning    D. Drung, S. Bechstein, K.-P. Franke, M. Scheiner and Th. Schurig Summary: A low-noise wideband read-out electronics for dc superconducting quantum interference devices (SQUIDs) is presented. The preamplifier which is directly connected to the SQUID has white voltage and current noise levels of 0.4 nV//spl radic/Hz and 6.2 pA//spl radic/Hz with 1/f corners at 0.2 Hz and 13 Hz, respectively. The SQUID can be operated with both dc bias and ac bias of up to 250 kHz. In the latter case, a special circuit synchronously detects the ac bias component at the preamplifier output and automatically removes it by tuning the bias voltage. An in-system programmable microcontroller is used to control all functions of the SQUID system via a serial RS-485 interface. It also generates the ac bias clock and sets the SQUID working point via low-noise D/A converters. The read-out electronics has been used to operate low-noise SQUID magnetometers. Noise levels down to 35 fT//spl radic/Hz and 0.9 fT//spl radic/Hz with 1/f corners at about 2 Hz have been achieved with thin-film SQUID magnetometers operated at 77 K and 4.2 K, respectively. With static bias a high bandwidth of up to 6 MHz was achieved without affecting the noise level. With 100 kHz bias reversal the rms noise increased by about 3% when increasing the system bandwidth from 100 kHz to 1.4 MHz. The system slew rate was 0.4 /spl Phi//sub 0///spl mu/s to 2.3 /spl Phi//sub 0///spl mu/s. A short integrator reset time of <1 /spl mu/s allows one to increase the dynamic range utilizing the periodicity of the SQUID voltage vs. flux characteristic.         Magnetic detection of a surface ship by an airborne LTS SQUID MAD    M. Hirota, T. Furuse, K. Ebana, H. Kubo, K. Tsushima, T. Inaba, A. Shima, M. Fujinuma and N. Tojyo Summary: A three-axis LTS SQUID magnetometer was fabricated as a Magnetic Anomaly Detector (MAD) onboard an aircraft. A magnetometer measuring magnetic total field, which is rotational invariant, is suitable for performing distant target detection in unshielded mobile operation. To configure the magnetometer, several requirements for the SQUID magnetometer had to be considered such as ultra wide dynamic range above 150 dB, extremely accurate linearity and orthogonality of the three-axis. The magnetic vector component with the sufficient dynamic range was obtained by synthesizing the SQUID output voltage and the counts of SQUID's flux-voltage (/spl Phi/-v) periodicity. The magnetic total field was obtained from the three magnetic vector components using our scalar composition algorithm that corrects the non-orthogonality and so on. The compensation algorithm with quadratic form of permanent, inductive and eddy-current magnetism was used to suppress the magnetic noise caused by the platform manoeuver. Our SQUID MAD was designed to implement the procedures mentioned above in real-time. The SQUID MAD was equipped in the tail boom of the aircraft and its performance was evaluated in the flight tests. We confirmed that our SQUID MAD provided extremely high sensitivity in flight by suppressing the magnetic noise, and successfully detected a distant surface ship.         Effect of repetitive transmitter signals on SQUID response in geophysical TEM    G. Panaitov, M. Bick, Y. Zhang and H.-J. Krause Summary: Results of SQUID application in geophysical time domain transient electromagnetic (TEM) measurements are presented. We analyze peculiarities of SQUID TEM recordings, comparing them to data of commonly used induction coil. Two significant effects have been observed with the SQUID TEM system which are less pronounced or not observed in corresponding reference coil data. We consider a model for SQUID TEM measurements, taking into account the effect of repetitive transmitter signals which gives a possible explanation for these effects.         An HTS SQUID picovoltmeter with a flip-chip flux transformer    J. Blomgren, T. Eriksson and D. Winkler Summary: An HTS SQUID picovoltmeter was constructed, which in two different configurations gave a voltage noise of e/sub n/=3.2pV//spl radic/Hz and a current noise of i/sub n/=310 pA//spl radic/Hz, and a voltage noise of e/sub n/=75 pV//spl radic/Hz and a current noise of i/sub n/=10 pA//spl radic/Hz, respectively. The low frequency noise was reduced to below 1 Hz using bias current reversal. The SQUID is coupled to the input coil via an intermediate flip-chip flux transformer. Measurements were performed to determine the input coil to SQUID mutual inductance for different input coil configurations.         HTS dc SQUID systems for geophysical prospection    V. Zakosarenko, A. Chwala, J. Ramos, R. Stolz, V. Schultze, H. Lutjen, J. Blume, T. Schuler and H.-G. Meyer Summary: We describe the use of high T/sub c/ flip-chip dc SQUID magnetometers in systems for several geophysical prospection methods. For use in the Transient Electro Magnetics (TEM) method, a one-channel SQUID magnetometer system (vertical field component) was adapted to rough conditions in the field. We report on measurements in South Africa over a geophysically interesting target in real production mode. Transients up to 200 ms could be recorded, which is about a factor of 100 more than with conventional coils. For investigation of the magnetic field gradient a two-channel system, built as a first-order electronic gradiometer with a baseline up to 1 m, was designed and manufactured. It can be used, e.g., for surface exploration or for archeometry. The system can be moved in the Earth's magnetic field. We achieve a common mode rejection of 100. The reasons for the imbalance and the possibility of further improvement of the system are discussed.         Microwave induced steps in RF-field-driven DC SQUID and its potential applications    T. Kondo, Y. Mizugaki, J. Chen, K. Nakajima and T. Yamashita Summary: We have been studying an RF-Field-driven DC SQUID (RFDS) that exhibits RF-induced-current-steps larger than those of single junctions at lower normalized frequency and a strong selection rule for the step orders which depends on the external DC magnetic field. In RFDS, even order steps are dominant in the absence of DC magnetic field. Contrarily, a DC magnetic field of a half flux quantum dominantly enhances odd order steps. Therefore the output of an RFDS can be switched between two voltage levels corresponding to the RF-induced-step by an external DC field input for a certain bias condition. We carried out numerical simulations to characterize the switching properties of the RFDS for various bias conditions, including RF circulating currents and DC bias current.         Active supercurrent control in superconductor/ferromagnet heterostructures    R.J. Kinsey, G. Burnell and M.G. Blamire Summary: Several recent papers predict that the critical temperature of superconducting/ferromagnet heterostructure can be controlled by varying the exchange field of the ferromagnet within the superconductor, providing a means of controlling the superconducting properties. This paper reports the first experimental observation of this effect: we show that the critical temperature and critical current of a Nb/Co bilayer can be controlled by a small magnetic field, on the order of a few tens of kA/m. In these devices, the suppression of T/sub c/ is minimised at the coercive field of the Co layer implying that with a sufficiently fine domain structure the net exchange field in the superconductor is reduced. These structures offer the potential for active control of the superconducting properties in both low and high T/sub c/ materials through the application of very small magnetic fields.         Properties of asymmetric high critical temperature dc SQUIDs    G. Testa, S. Pagano, E. Sarnelli, C.R. Calidonna, M.M. Furnari and M. Russo Summary: Asymmetries between the two Josephson junctions of a dc-SQUID have always been considered undesirable spurious effects, responsible for the degradation of the device performance. However, it was recently demonstrated that a suitable choice of the asymmetric configuration can lead to magnetic flux noise values lower than symmetric ones. The numerical analysis was performed by using parameters typical of low-Tc SQUIDs, operating at the liquid helium temperature. In this paper, the analysis has been extended to high critical temperature dc SQUIDs, operating at the liquid nitrogen temperature. Also in this case, asymmetric SQUIDs show the best performance in terms of both flux to voltage transfer coefficient V/sub /spl Phi// and magnetic flux noise S/sub /spl Phi//. In order to optimize the device performance, the dependence of SQUID properties on damping resistance and normalized SQUID inductance has been computed for both symmetric and asymmetric configurations.         Voltage-flux-characteristics of asymmetric dc SQUIDs    J. Muller, S. Weiss, R. Gross, R. Kleiner and D. Koelle Summary: We present a detailed analysis of voltage-flux V(/spl Phi/)-characteristics for asymmetric dc SQUIDs with various kinds of asymmetries. For finite asymmetry /spl alpha//sub I/ in the critical currents of the two Josephson junctions, the minima in the V(/spl Phi/)-characteristics for bias currents of opposite polarity are shifted along the flux axis by /spl Delta//spl Phi/=/spl alpha//sub I//spl beta//sub L/ relative to each other; /spl beta//sub L/ is the screening parameter. This simple relation allows the determination of /spl alpha//sub I/ in our experiments on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// dc SQUIDs and comparison with theory. Extensive numerical simulations within a wide range of /spl beta//sub L/ and noise parameter /spl Gamma/ reveal a systematic dependence of the transfer function V/sub /spl Phi// on /spl alpha//sub I/ and /spl alpha//sub R/ (junction resistance asymmetry). As for the symmetric dc SQUID, V/sub /spl Phi// factorizes into g(/spl Gamma//spl beta//sub L/)/spl middot/f(/spl alpha//sub I/,/spl beta//sub L/), where now f also depends on /spl alpha//sub I/. For /spl beta//sub L//spl lsim/5 we find mostly a decrease of V/sub /spl Phi// with increasing /spl alpha//sub I/, which however can only partially account for the frequently observed discrepancy in V/sub /spl Phi// between theory and experiment for high-T/sub c/ dc SQUIDs.         Performance of high-T/sub c/ dc SQUID magnetometers with resistively shunted inductances compared to "unshunted" devices    F. Kahlmann, W.E. Booij, M.G. Blamire, P.F. McBrien, N.H. Peng, C. Jeynes, E.J. Romans, C.M. Pegrum and E.J. Tarte Summary: We have investigated resistively shunted direct-coupled high-T/sub c/ dc SQUID magnetometers with different inductances. At T=77 K, good quantitative agreement was observed between the measured maximum voltage modulation depth and calculated values based on the theoretical predictions by Enpuku et al. (1995) whereas the white magnetic flux noise at 10 kHz of all four devices was found to be a factor of 2.3 higher than predicted. The lowest white magnetic field noise of 153 fT/Hz/sup 1/2/ was obtained for the magnetometer with an inductance of 100 pH and an outer dimension of the pickup loop of just 3 mm. The combined theoretical and experimental results suggest that although similar magnetic field noise values can he obtained for inductances up to 200 pH, the minimum value of the unshunted case cannot be improved upon. However, the maximum voltage modulation depth could be increased significantly at little cost to the noise compared to an unshunted device.         Study of Y-Ba-Cu-O dc SQUID devices with resistively shunted inductances    Y.Q. Shen, P.R.E. Petersen and T. Holst Summary: A number of dc SQUIDs with different inductance values have been fabricated in YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on MgO substrates. Resistors prepared in Au thin films have been applied as shunt resistors for the SQUID inductance loop. Characterisation and noise measurement have been carried out on these SQUIDs. The results are in agreement with theoretical predictions of Enpuku et al. The use of shunt resistors has improved the performance of the SQUIDs with high inductance, and made it less dependent on the critical current of the junctions, which is not always reproducible. Furthermore, high SQUID inductance increases the coupling efficiency of magnetic flux, for example in terms of a better inductance matching between the SQUID and the pick-up loop in a directly coupled magnetometer. Based on this study, SQUID devices such as magnetometers and gradiometers with high field responses have been designed and tested.         Direct detection of vortex motion in high-T/sub c/ grain boundary junctions    S. Hirano, H. Oyama, M. Matsuda, T. Morooka, S. Nakayama and S. Kuriki Summary: Using a superconducting thin-film coil and Nb-based SQUID, the flux generated by vortices in a field-cooled (10 /spl mu/T) wide bicrystal YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grain boundary junction (GBJ) was measured directly at 77 K. At and above a small threshold field change, random switching noise was observed, with switching heights corresponding to long-distance movement of vortices over 20 to 500 /spl mu/m within the GBJ, driven by the shielding current. The vortex movement was suppressed to lengths of less than 1 /spl mu/m by making slots in the GBJ. From these results, we estimated the flux noise of a directly coupled dc SQUID magnetometer with a weak link in its pick-up coil.         Low-frequency noise reduction in Y-Ba-Cu-O SQUIDs by artificial defects    P. Selders and R. Wordenweber Summary: We demonstrate, that extremely simple arrangements of few antidots in HTS rf-SQUIDs can significantly reduce the 1/f noise in ambient field down to the level of zero-field noise. The onset field B/sub on/ at which the low-frequency noise starts to increase, is shifted from B/sub on//spl ap/8 /spl mu/T without antidots to B/sub on//spl ap/40 /spl mu/T with antidots for field cooled measurements and to B/sub on//spl ap/25 /spl mu/T for zero field cooled experiments. The geometric arrangements of the antidots are obtained from the analysis of the current distribution in the washer and the position of penetrating vortices in the case of zero field cooled experiments.         Fabrication of RS flip-flops using Y-Ba-Cu-O ramp-edge junctions and their operation    J.H. Park, J.H. Kim, G.Y. Sung, C.H. Kim, K.R. Jung, J.H. Kang and T.S. Hahn Summary: We fabricated single flux quantum RS flip-flop circuits by using ramp-edge Josephson junctions and tested their performance. The junctions were constructed with two Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) electrodes and a barrier layer. As barrier materials we used cobalt-doped YBCO. To insulate between YBCO layers we used Sr/sub 2/AlTaO/sub 6/ (SAT) thin films. We also fabricated RS flip-flop circuits by using YBCO ground planes to reduce the inductance of YBCO film. The fabricated Josephson junctions showed typical RSJ-like current-voltage (I-V) characteristics above 50 K. We could successfully demonstrate the correct operation of the RS flip-flop circuits at the temperatures near 50 K. We used a computer controlled digital measurement set-up to test the circuits. The RS flip-flop circuit fabricated on a ground plane showed more definite set and reset states on the voltage-flux (V-/spl phi/) modulation curves of the read SQUID than those of the circuit made without ground plane. This may be attributed to the shielding effect by a YBCO ground plane.         A latching-type driver circuit using capacitively-shunted HTS ramp-edge-type junctions    T. Hato, N. Harada, Y. Ishimaru, A. Yoshida and N. Yokoyama Summary: We developed a latching-type driver using capacitively shunted high-temperature superconductivity (HTS) junctions for Single-Flux-Quantum (SFQ)-semiconductor output interfaces and fabricated it using ramp-edge-type HTS junctions. Assuming a junction IcRn product of 2 mV, a circuit simulation shows that the driver can produce an output of about 8 mV from an SFQ input pulse with a sufficiently short rise time for an interface clock operation of several gigahertz. HTS junctions were fabricated using the interface engineering method, and capacitors were made from an Indium oxide insulator (the dielectric constant was about 23 at 20 K) sandwiched by YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) electrodes. The hysteresis of the I-V characteristics of the junctions increased by increasing the area of capacitance. The latching operation of the driver was observed with an output voltage of up to 3 mV.         Quasi-particle injection devices for interfaces between superconductors and semiconductors    H. Shiga and Y. Okabe Summary: We have fabricated an injection type 3-terminal device for interface between superconductor and semiconductor circuits using a high temperature superconductor. When quasi-particles are injected from the Au electrode to a YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) bridge, superconductivity of the bridge area is weakened and I/sub c/ of the bridge decreases. Therefore, we can easily make the bridge in resistive state by injecting sufficient amount of current I/sub inj/. The length, width, and thickness of the bridge are 20 /spl mu/m, 10 /spl mu/m, and 100 nm, respectively. The Au-YBCO contact area is 200 /spl mu/m/sup 2/. When the bridge became resistive, the resistance was about 100 /spl Omega/. The current gain |/spl Delta/I/sub c///spl Delta/I/sub inj|/ was as high as 9. However, the contact resistance was about 17 /spl Omega/, which is 200 times as large as the required value for the operation as an interface device. This shortcoming might be overcome by appropriate annealing.         Frequency locking of Josephson junctions in a surface wave resonator    A.M. Klushin, E. Goldobin, G.A. Melkov, O.M. Ivanjuta, Y.V. Eghorov, K. Numssen and M. Siegel Summary: We report on the design, fabrication, and investigation of a series array of Josephson junctions embedded into the surface wave resonator. The resonator is fabricated by using Au-YBa/sub 2/Cu/sub 3/O/sub 7/ bilayer on yttria-stabilized zirconia bicrystal substrate. The arrays were incorporated into the resonator by meandering the bilayer across a grain boundary. The circuit design and the excitation of the proper resonant mode provides series dc biasing and parallel ac biasing of the JJs array. Experimental results show that microwave current is distributed uniformly along the whole 8 mm long array. In the vicinity of the resonant frequency, almost no difference between the microwave currents in the junctions was found.         Fabrication of ultra-small and long intrinsic Josephson junctions on Bi-2212 single crystal whiskers    Sang-Jae Kim, Y.I. Latyshev, T. Yamashita and S. Kishida Summary: We report successful fabrication of small and long intrinsic Josephson junctions (IJJs) using Bi-2212 single crystal whiskers. The stacks of IJJs were made by 3-D focused-ion-beam (FIB) etching method. First a microbridge was patterned in a required junction width by etching into the substrate normal direction. By tilting the sample stage up to 90/spl deg/, two grooves on the bridge were, then, etched from the lateral direction in order to create the required junction size. For in-plane area of 0.01 /spl mu/m/sup 2/, Bi-2212 stacks showed no critical current. We also fabricated 3-D IJJs consisting of small and long stacks on the same chip.         Terahertz-frequency waveguide NbN hot-electron bolometer mixer    J. Kawamura, C.-Y.E. Tong, R. Blundell, D.C. Papa, T.R. Hunter, F. Patt, G. Gol'tsman and E. Gershenzon Summary: We have developed a low-noise waveguide heterodyne receiver for operation near 1 THz using phonon-cooled NbN hot-electron bolometers. The mixer elements are submicron-sized microbridges of 4 nm-thick NbN film fabricated on a quartz substrate. Operating at a bath temperature of 4.2 K, the double-sideband receiver noise temperature is 760 K at 1.02 THz and 1100 K at 1.26 THz. The local oscillator is provided by solid-state sources, and power measured at the source is less than 1 /spl mu/W. The intermediate frequency bandwidth exceeds 2 GHz. The receiver was used to make the first ground-based heterodyne detection of a celestial spectroscopic line above 1 THz.         Dynamic range of frequency-selective response of high-T/sub c/ Josephson detector to millimeter-wave radiation    V. Shirotov, Y. Divin and K. Urban Summary: We have studied a voltage dependence of the response /spl Delta/I(V) of high-T/sub c/ Josephson detector to millimeter-wave radiation as a function of power of incident radiation. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions with the resistances R/sub n/=0.5-1.5 Ohm and the I/sub c/R/sub n/-product in the range 0.16-0.25 mV at 80 K have been fabricated for this study. Gunn oscillator with the frequency f=86 GHz and a set of calibrated attenuators with total attenuation of 80 dB have been used for the measurements. The dynamic range, i.e. the range of power of electromagnetic radiation at which the response of the detector is directly proportional to radiation power, was found to be around 40 dB above the noise-equivalent power for frequency-selective response at voltages V near hf/2e and >45 dB for the broadband response at low voltages.         Noise and conversion efficiency of aluminum superconducting hot-electron bolometer mixer    I. Siddiqi, A. Verevkin, D.E. Prober, A. Skalare, B.S. Karasik, W.R. McGrath, P. Echternach and H.G. LeDuc Summary: We report on microwave measurements of superconducting aluminum hot-electron bolometers (Al HEBs). Diffusion-cooled Al HEB mixers are good candidates for space-borne applications in the Terahertz frequency range since they are predicted to have small local oscillator (LO) power requirements, intermediate frequency (IF) bandwidths /spl gsim/10 GHz, and a noise temperature lower than that of Nb and NbN HEB mixers. Mixer measurements were made at an LO frequency /spl sim/30 GHz, with an IF in the range 0.1 to 7.3 GHz. For T<0.8 K, a magnetic field H=0.1-0.3 T was applied to suppress the superconductivity in the contact pads, and partly in the bridge. For a 0.6 /spl mu/m long device, we measure an IF bandwidth of 4 GHz, a conversion efficiency /spl eta/=-8 dB, and a mixer noise temperature T/sub M//spl gsim/4 K, DSB (T/sub mixer/=T/sub output noise//2/spl eta/). These results are shown to be in quantitative agreement with simple theoretical predictions.         NbN hot electron bolometric mixers for terahertz receivers    M. Kroug, S. Cherednichenko, H. Merkel, E. Kollberg, B. Voronov, G. Gol'tsman, H.W. Huebers and H. Richter Summary: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.         Design and demonstration of fundamental logic circuits based on a single-flux-quantum gate with a resettable latch    N. Takeuchi, A. Akahori, N. Mori, Y. Suzuki, F. Furuta, A. Fujimaki and H. Hayakawa Summary: We have confirmed the importance of the tolerance design for obtaining correct operation in larger-scale Single Flux Quantum (SFQ) logic circuit. Experimental results show that the bias margin of SFQ/dc converter is considerably enhanced by employing tolerance design. The primitives of Single-Flux-Quantum-logic with Ressettable Latch (SFQ-RL) are designed to have high tolerance. As a result, relatively complex circuits based on SFQ-RL including 4-bit Shift Register, 3-Input Majority circuits, binary counter operate correctly with sufficient bias margins. These circuits are fabricated in NEC's standard process using 2.5 kA/cm/sup 2/ Nb/AlOx/Nb junction technology.         New BSFQ circuit designs with wide margins    Chen Kong Teh and Y. Okabe Summary: Recently we have proposed novel Boolean Single-Flux-quantum (BSPQ) circuits, which just like CMOS circuits support Boolean primitives directly, and do not require local synchronization for each operation cell. However, previous BSFQ AND, OR, and XOR cells suffered from problems with narrow margin, where their critical margins hardly exceeded /spl plusmn/10% due to low flux gain. Furthermore, while being suitable for combinational circuits, previous BSFQ NOT cells had initialization problems in sequential circuits. In this paper, new versions of these circuits with simulated margins beyond /spl plusmn/30% are proposed. Moreover, a Muller C-element, an error canceller, a destructive read-out (DRO), and a demultiplexer are also newly created. The operation time, parameter margins, and circuit size of these BSFQ cells are comparable to those of the conventional RSFQ cells.         New phase-mode logic gates with large operating regions of circuit parameters    T. Onomi, K. Yanagisawa and K. Nakajima Summary: We propose new phase-mode logic gates with large operating regions of circuit perimeters. In the phase-mode logic, logic circuits are realized by combination of ICF (INHIBIT controlled by fluxon) gates. The function of the ICF gate can be achieved by the two gates which are an INHIBIT gate and an AND gate. These two gates are fabricated by NEC 2.5 kA/cm/sup 2/ Nb/AlOx/Nb standard process and successfully demonstrated. A Monte-Carlo calculation is used for evaluating yields of the gates. From 1000 calculations for each gates, we show that each yield of the INHIBIT gate and the AND gate does not decrease with increasing /spl sigma/=7% and /spl sigma/=9% which are the standard deviations of the parameter spreads. A realization of high-reliability LSI circuits will be expected by using these gates.         RSFQ time digitizing system    A.F. Kirichenko, S. Sarwana, O.A. Mukhanov, I.V. Vernik, Y. Zhang, J. Kang and J.M. Vogt Summary: We have developed a high-performance time digitizer system using a superconductor technology for high-energy and nuclear physics detector instrumentation, CMOS chip diagnostics, and military applications. The system consists of an 8-channel, RSFQ multi-hit Time-to-Digital Converter (TDC) integrated into a single system with a semiconductor VXI interface and control modules. The Digitizer operation and output digital data analysis are performed and fully controlled using custom PC-based LabVIEW/sup TM/ software. This all-digital TDC contains eight 9-hit, 14-bit, 20-GHz TDC channels on a 1 cm /spl times/1 cm chip. The TDC chip is capable of operation in Common Start and Common Stop modes. The VXI digitizer part comprises a 200 MS/s, 8-channel data receiver module, a TDC control module, and a commercial VXI-PCI link. The data receiver module converts data into ECL format. The TDC control module based on Xilinx CPLD technology sorts this data and also controls the superconductive RSFQ chip operation by producing all necessary control and readout signals. We present results of operation and experimental performance evaluation of this system.         Spread spectrum data transfer from dewar to dewar at 2 gigachips per second    J.X. Przybysz, E.J. Dean, P.D. Dresselhaus, D.L. Miller, A.H. Worsham and S.V. Polonsky Summary: Spread spectrum data modulation, transmission, and demodulation has been demonstrated between SFQ chips in separate dewars. The baseband demonstration consisted of modulating (encoding) data with a spreading code, transmitting the coded data to a Receiver and demodulating (decoding) the data using an identical spreading code. The Transmitter code was produced by a 2 GHz, 4-bit SFQ pseudorandom sequence generator creating a 15-chip spreading code, which modulated a /spl sim/133 MHz data source. This data was output by a 10/spl times/ superconducting latch providing /spl sim/8 mV of AC drive. This signal was fed through 50-/spl Omega/ coaxial cable to a SFQ Receiver chip in a separate dewar. No amplification of the AC signal between the dewars was needed, however, a slight DC bias was added to the signal as a flux bias for the input SQUID on the Receiver. The Receiver chip consisted of an identical SFQ pseudorandom sequence generator and a data demodulation gate. Demodulating the received data with the code generator produced a replica of the data signal in RZ form. Both time forward and time reversed codes for the spreading/despreading sequence were created.         High-resolution current measurement system using a high-T/sub c/ superconductor sampler    M. Hidaka, N. Ando, T. Satoh and S. Tahara Summary: We are developing a prototype system for measuring high-frequency current flowing through a room-temperature sample without contact. It is based on a high-T/sub c/ superconductor sampler that can measure current waveforms at picosecond and microampere resolution. The sampler chip is housed in a vacuum chamber and is cooled down to its operating temperature by a GM-pulse tube cryocooler. Current flowing through the sample, which is placed just below and outside the vacuum chamber, generates a magnetic field. The sampler can measure this current because a superconducting loop, which includes the comparator junction of the sampler, picks up the magnetic field. Sinusoidal current flowing through a 50-ohm microstrip line was successfully observed up to 7 GHz by the system. Frequency dependence of measurement sensitivity is a problem to overcome for applying it to practical uses.         A hysteretic dc SQUID reading the flux states of an rf SQUID    C. Cosmelli, P. Carelli, M.G. Castellano, F. Chiarello, R. Leoni and G. Torrioli Summary: We have realized a hysteretic dc SQUID to measure the flux states of a rf SQUID inductively coupled to the hysteretic dc SQUID. This type of measurement is required whenever is necessary to make a non invasive measure of the state of the rf SQUID. This is the case of measurements of macroscopic quantum coherence or measurements on q-bits systems. With the proposed set up the hysteretic dc SQUID can switch from the superconducting to the normal state depending on the total applied magnetic flux. On this system we measured at 4.2 K the change on the switching probability of the dc SQUID by varying the flux state of the rf SQUID. The experimental results agree very well with the theoretical predictions showing that this device can be used to perform non invasive measurements of the rf SQUID flux state.         Macroscopic quantum effects in Josephson systems    V. Corato, E. Esposito, C. Granata, A. Monaco, B. Ruggiero, M. Russo, L. Stodolsky and P. Silvestrini Summary: Macroscopic quantum effects in Josephson systems have attracted great interest in the scientific community both for the physics involved and in view of applications. We present data on macroscopic quantum tunneling on Josephson junctions. Actually the most fascinating topic is the observation of macroscopic quantum coherence in rf-SQUID. This effect also has implications for quantum computing, because a quantum two-state system represents a single quantum bit, which is the elementary unit of a quantum computer. In this context, here we present a new method to measure quantum coherence between different fluxoid states of an rf-SQUID by using the procedure of "adiabatic inversion". This method offers the possibility of measuring tunneling and decoherence times in the system.         Design for effective thermalization of junctions for quantum coherence    R.C. Ramos, M.A. Gubrud, A.J. Berkley, J.R. Anderson, C.J. Lobb and F.C. Wellstood Summary: We present a design for effectively isolating low-dissipation superconducting tunnel junctions without causing excessive heating. In order to obtain a long decoherence time in macroscopic quantum coherence experiments, it will be essential to make high impedance connections to the junction. In our design, the connections are made by thin-film resistors. To prevent excessive heating, we divide the resistors into many short sections, each of which is heat-sunk to small metal banks. We rely on electron diffusion to carry the heat out of the resistors and into the banks. We calculate the resulting temperature profile in the resistors and discuss the effect on the decoherence time of the junction.         Sub-gap leakage in Nb/AlO/sub x//Nb and Al/AlO/sub x//Al Josephson junctions    M.A. Gubrud, M. Ejrnaes, A.J. Berkley, R.C. Ramos Jr., I. Jin, J.R. Anderson, A.J. Dragt, C.J. Lobb and F.C. Wellstood Summary: In an effort to determine the suitability of Josephson junctions for applications in quantum computation, we measured low-noise dc current-voltage characteristics of Nb/AlO/sub x//Nb and Al/AlO/sub x//Al junctions in the temperature range from 90 mK to 1 K. Nb-based samples were obtained from several different facilities with critical currents of a few /spl mu/A and critical current densities between 100 and 3000 A/cm/sup 2/. We fabricated the Al-based samples using double-angle evaporation and obtained critical currents of a few /spl mu/A with critical current densities of about 30 A/cm/sup 2/. We found that the sub-gap leakage current in the Nb-based samples does not depend on temperature in the range 90 mK to 1 K, whereas that for the Al-based samples follows the expected BCS behavior to about 150 mK. Our Al-based samples have a lower level of dissipation than Nb-based devices; however, both Al- and Nb-based samples achieved dissipation levels sufficiently low for some quantum computing applications.         Inductance effects in the persistent current qubit    D.S. Crankshaw and T.P. Orlando Summary: A general method is illustrated to show that the Hamiltonian for circuits of Josephson junctions can be expanded in terms of three Hamiltonians: a Hamiltonian representative of the inductance-free circuit, a Hamiltonian in the form of an harmonic oscillator for the inductance effects of the circulating currents, and a small correction term. This method is used to show that the inductive effects are a small correction to the difference in energy levels in the persistent current qubit.         Characterization of macroscopic quantum behavior using RSFQ circuitry    P. Rott and M.J. Feldman Summary: An integrated circuit has been designed to investigate the quantization of energy levels in an rf SQUID. The experiment is very similar to the rapid-sweep technique of Silvestrini et al. (1997, 1999) except that it is accomplished by using superconducting digital electronic circuitry as the experimental apparatus. This allows the system being studied to be very well isolated from its environment.         Design of an RSFQ control circuit to observe MQC on an rf-SQUID    R.C. Rey-de-Castro, M.F. Bocko, A.M. Herr, C.A. Mancini and M.J. Feldman Summary: We believe that the best chance to observe macroscopic quantum coherence (MQC) in an rf-SQUID qubit is to use on-chip RSFQ digital circuits for preparing, evolving and reading out the qubit's quantum state. This approach allows experiments to be conducted on a very short time scale (sub-nanosecond) without the use of large bandwidth control lines that would couple environmental degrees of freedom to the qubit, thus contributing to its decoherence. In this paper we present our design of an RSFQ digital control circuit for demonstrating MQC in an rf-SQUID. We assess some of the key practical issues in the circuit design including the achievement of the necessary flux bias stability. We present an "active" isolation structure to be used to increase coherence times. The structure decouples the SQUID from external degrees of freedom, and then couples it to the output measurement circuitry when required, all under the active control of RSFQ circuits.         A tipping pulse scheme for a rf-SQUID qubit    Xingxiang Zhou, J.L. Habif, A.M. Herr, M.J. Feldman and M.F. Bocko Summary: We present a technique to control the quantum state of a rf-SQUID qubit. We propose to employ a stream of single flux quantum (SFQ) pulses magnetically coupled to the qubit junction to momentarily suppress its critical current. This effectively lowers the barrier in the double-well rf SQUID potential thereby increasing the tunneling oscillation frequency between the wells. By carefully choosing the time interval between SFQ pulses one may accelerate the interwell tunneling rate. Thus it is possible to place the qubit into a chosen superposition of flux states and then effectively to freeze the qubit state. We present both numerical simulations and analytical time-dependent perturbation theory calculations that demonstrate the technique. Using this strategy one may control the quantum state of the rf SQUID in a way analogous to the /spl pi/ pulses in other qubit schemes.         Linear microwave response of a charge-type qubit    W. Krech, D. Born, T. Wagner and H.-G. Meyer Summary: Using Bloch-type equations with phenomenological energy relaxation and dephasing terms, we investigate analytically the linear response of a superconducting charge qubit (single-Cooper-pair box) to a microwave field within a two-band model. Coherence of the macroscopic quantum states of the autonomous device is due to the competition of irradiation and dephasing. An extra qubit impedance arises from this quantum effect which can be expressed in terms of quantum resistance unit, quality and detuning. The theoretical results may support the design of microwave experiments with charge-type qubits. Especially, we present a proposal for determining the dephasing time by means of reflection measurements, anticipating a high quality of the extra (quantum) impedance.         Jim Zimmerman and the SQUID    R.L. Kautz Summary: The career of Jim Zimmerman, beginning with a solid foundation in electronics and cryogenics, reached a turning point in 1965 when he became coinventor of the rf SQUID (Superconducting QUantum Interference Device), while working at the Scientific Laboratory of the Ford Motor Company in Dearborn, Michigan. Recognizing the exquisite sensitivity of the SQUID as an amplifier and magnetometer, Zimmerman devoted the remainder of his career, at Ford and later at the National Bureau of Standards, to the further development of the SQUID and its applications. In 1969, Zimmerman also helped found SHE Corporation, which marketed the first commercially successful SQUID. While at NBS, Zimmerman introduced two variations, the SQUID gradiometer and the fractional-turn SQUID, to enhance the sensitivity of SQUIDs in special situations. He also developed an improved understanding of SQUID dynamics by exploring the pendulum analog using carefully made models, work that has benefited a generation of students. Putting the SQUID to work, Zimmerman investigated applications in metrology, biomagnetism, and geophysics. Notably, he participated in collaborations that recorded the first magnetocardiogram made with a SQUID and the first magnetoencephalogram of an evoked auditory response. Later, Zimmerman explored closed-cycle refrigeration as a means of making SQUIDs more useful outside the laboratory environment, and in 1977 he demonstrated an operating SQUID cooled to 8.5 K by a Stirling-cycle refrigerator made largely of plastic. Zimmerman is remembered for his keen physical insight, the elegance and simplicity of his experiments, and his willingness to question conventional wisdom in all aspects of life.         Defect detection and classification using a SQUID based multiple frequency eddy current NDE system    M.v. Kreutzbruck, K. Allweins, T. Ruhl, M. Muck, C. Heiden, H.-J. Krause and R. Hohmann Summary: The probability of detection (POD) of hidden fatigue defects in riveted multilayer joints, e.g. aircraft fuselage, can be improved by using sophisticated eddy-current systems which provide more information than conventional NDE equipment. In order to collect this information, sensor arrays or multi-frequency excitation schemes can be used. We have performed simulations and measurements with an eddy current NDE system based on a SQUID magnetometer. To distinguish between signals caused by material defects and those caused by structures in the sample, such as bolts or rivets, a high signal-to-noise ratio is required. Our system provides a large analog dynamic range of more than 140 dB//spl radic/Hz in unshielded environment, a digital dynamics of the ADC of more than 25 bit (>150 dB) and multiple frequency excitation. A large number of stacked aluminum samples resembling aircraft fuselage were measured, containing titanium rivets and hidden defects in different depths in order to obtain sufficient statistical information for classification of the defect geometry. We report on flaw reconstruction using adapted feature extraction and neural network techniques.         Evolution of HTS rf SQUIDs    Y. Zhang Summary: I present the evolution of rf-SQUIDs towards modern planar thin film devices. My main objective is to describe our own planar HTS rf washer SQUIDs and their operation with coplanar resonators and multiturn flux transformers. This publication is dedicated to the memory of J.E. Zimmerman, whose ideas have guided us through the development of rf SQUID planar technology.         High performance Nb Josephson devices for petaflops computing    A.W. Kleinsasser Summary: The Hybrid Technology Multi-Threaded (HTMT) approach to petaflops computing includes large numbers of ultra-high performance Nb Rapid Single Flux Quantum (RSFQ) processor and memory chips, making it by far the largest active superconducting electronics project in the United States. In order to achieve petaflops, RSFQ circuits with 10/sup 5/ to 10/sup 6/ junctions per chip will be required to operate at clock speeds of 50 to 100 GHz, far beyond the current state of the art. In this paper, we review the state of the art of Nb circuit fabrication and discuss the requirements for significantly improving circuit density and speed.         Can RSFQ logic circuits be scaled to deep submicron junctions?    A.M. Kadin, C.A. Mancini, M.J. Feldman and D.K. Brock Summary: Scaling of niobium RSFQ integrated circuit technology to deep submicron dimensions (linewidths of 300 nm or less) should permit increased clock rate (up to 250 GHz) and increased areal density of Josephson junctions (up to 1 million junctions/cm/sup 2/), without the need for external shunt resistors. It is shown how existing circuit layouts can be scaled down to these dimensions, while maintaining the precise timing essential for correct operation. Additional issues related to the practical realization of such circuits are discussed, including effects of self-heating and models for the generation and propagation of sub-ps single-flux-quantum pulses.         Physics of high j/sub c/ Nb/AlO/sub x//Nb Josephson junctions and prospects of their applications    Y. Naveh, D.V. Averin and K.K. Likharev Summary: At critical current density of the order of 100 kA/cm/sup 2/, tunnel Josephson junctions become overdamped and may be used in RSFQ circuits without external shunting, dramatically increasing circuit density. However, the physics of electron transport in such high-j/sub c/ junctions differs from the usual direct tunneling and until recently remained unclear. We have found that the observed dc I-V curves of niobium-trilayer junctions with j/sub c/=210 kA/cm/sup 2/ can be explained quantitatively by resonant tunneling through strongly disordered barriers. According to this interpretation, random spread of critical current in high-j/sub c/ junctions may be rather small (below 1% r.m.s.) even in deep-submicron junctions, making VLSI RSFQ circuits, with density above 10 MJJ/cm/sup 2/, feasible.         A high density 4 kA/cm/sup 2/ Nb integrated circuit process    G.L. Kerber, L.A. Abelson, M.L. Leung, Q.P. Herr and M.W. Johnson Summary: We have developed an improved 4 kA/cm/sup 2/ process technology that allows a significant increase in circuit speed and density. Improved photoresist and dry etch processes have reduced critical dimension (CD) variation and improved CD linearity to below 1 /spl mu/m. These improvements have enabled a substantial reduction in feature size and full utilization of existing photolithography and etch tools. We have demonstrated mire pitch of 2.0 /spl mu/m with less than 0.1 /spl mu/m CD loss. Minimum junction diameter and contact are 1.75 /spl mu/m and 1.0 /spl mu/m, respectively. Junctions, fabricated using a new barrier oxidation method with improved pressure control, have excellent I-V characteristics and array I/sub c/ nonuniformity less than 1.6% (1/spl sigma/). We have demonstrated a 200 GHz, 12-stage divider circuit that is the fastest complex digital superconductor integrated circuit fabricated to date. With the present process tools, defects are the limiting factor to further increases in circuit density and yield. In this paper, we discuss process improvements, electrical performance, defect reduction, and circuit performance.         SNS junction on Nb-Ti base for microwave circuits    M. Schubert, L. Fritzsch, G. Wende and H.-G. Meyer Summary: Superconductor-normal metal-superconductor (SNS) junctions are well-suited for large-scale integrated superconducting circuits. Potential applications are programmable voltage standards, digital-to-analog converters and large-scale RSFQ circuits. The application of SNS junctions provides some advantages, e.g. a simplified fabrication technology and reduced parasitic inductances. But it requires a technological process with dimensions down to the submicrometer region to achieve sufficiently high characteristic voltages I/sub C/R/sub N/. In our process the normal metal interlayer is titanium. Therefore the sidewall insulation of the junctions can be made by anodization, as it is known from the Nb-Al technology. Nb-Ti-Nb Josephson junctions and junction arrays were fabricated down to the submicrometer range with I/sub C/R/sub N/ values up to 87 microvolt depending on the titanium thickness. Their measured critical currents have a small spread of about 10 percent. Shapiro steps are observed under the influence of microwave irradiation. For the application of such junctions in a programmable Josephson voltage standard a new type of microwave circuit using coplanar strips is proposed and successfully tested in 10 V SIS circuits.         SINIS process development for integrated circuits with characteristic voltages exceeding 250 /spl mu/V    D. Balashov, M. Khabipov, F.-I. Buchholz and J. Niemeyer Summary: At PTB, the fabrication process in Nb-Al/Al/sub x/O/sub y//Al/Al/sub x/O/sub y//Al-Nb SINIS multilayer technology has been improved to raise the characteristic voltage of SINIS two-tunnel Josephson junctions up to V/sub C/=I/sub C/R/sub n/=245 /spl mu/V. The process has been realized in LTS implementation. Various sets of the test wafers and wafers containing dc/SFQ and SFQ/dc converters, Josephson transmission lines, and T-flipflop circuits were fabricated and measured. The critical current densities of the junctions have been varied in the range from 70 A/cm/sup 2/ to 2.2 kA/cm/sup 2/ with corresponding characteristic voltages of V/sub C/=55 /spl mu/V and 245 /spl mu/V at the temperature of 4.2 K. The junctions show nearly hysteresis-free behaviour (less than 15%), the intra-wafer parameter spread is smaller than /spl plusmn/10%. RSFQ circuits have been realized with operation margins of the bias currents larger than /spl plusmn/20%.         High-frequency performance of RSFQ circuits realized in SINIS technology    M. Khabipov, D. Balashov, F.-I. Buchholz and J. Niemeyer Summary: The paper presents the determination of the high-frequency performance of Rapid Single Flux Quantum (RSFQ) circuits fabricated in superconductor-insulator-normal metal-insulator-superconductor (SINIS) technology. Circuits of different designs have been realized and were experimentally investigated, including specially designed T flip-flop (TFF) structures and circuits consisting of a switch terminated in Josephson transmission lines. For TFF circuits, the operational functionality was investigated in the frequency range from dc up to nearly 200 GHz. Two frequency domains were found. In the first domain, ranging up to frequencies of 80 GHz (f/sub C//spl cong/Y/sub C///spl Phi//sub 0/), correct digital operation of the device was ascertained. Beyond this range a second domain was found, ranging to nearly 200 GHz, for which quasi-analog frequency dividing is assumed. The bias current margins are /spl plusmn/30% at 40 GHz and /spl plusmn/15% between 130 GHz and 200 GHz. For circuits consisting of a switch, the operational functionality was proved in the frequency range from dc up to 50 GHz, with bias current margins of more than /spl plusmn/20%. The critical current density of the circuits is j/sub C//spl cong/750 A/cm/sup 2/. The smallest junction area is about A=12 /spl mu/m/sup 2/, and the characteristic voltage is V/sub C/=170 /spl mu/V.         Improved methods for yield-optimization of digital logic    Q.P. Herr and M.W. Johnson Summary: Yield optimization remains the primary device-level design task in digital superconductor electronics. We discuss yield-optimization in the context of our particular software implementation, Malt2, which interfaces to the circuit simulator Spice. This version contains significant improvements both to the numerical algorithms and in ease of use. Two special algorithms of yield-optimization are extant, both of which map out the multidimensional operating region of the circuit and center parameters within the operating region. We describe modifications to these methods that make them practical. The greatest improvement to usability is a new method of defining correct circuit operation; an envelope is defined around each Spice-generated waveform based on two parameters that describe acceptable time and level uncertainty. The envelope can be applied to arbitrary waveforms and can be represented graphically. The features and algorithms of Malt2 are illustrated with circuit examples. Finally, we describe the role of yield optimization within the larger context of a complete design methodology and tool set.         High frequency operation of JTL ring oscillator with a passive transmission line    H. Suzuki, S. Nagasawa, H. Hasegawa, T. Hashimoto, K. Miyahara and Y. Enomoto Summary: We have designed ring oscillators to test rapid single flux quantum (RSFQ) circuits with passive transmission lines at high frequencies. To reduce the width of the transmission line, design methods for increasing the characteristic impedance of the transmission line have been investigated and then we designed a 5-stage of Josephson transmission line (JTL) receiver which can transform the impedance from 1 to 4 /spl Omega/ by changing the critical current and the inductance. The receiver, driver, and micro-strip line were inserted in a ring oscillator. The ring oscillator fabricated with the Nb/AlOx/Nb junction process was successfully operated at frequencies ranging from 6 to 10 GHz for line lengths of 0.6, 3, 6, and 9 mm. The usefulness of the impedance transformation was then confirmed experimentally. A propagation delay per unit length of 8.4 ps/mm was also obtained.         Measurement of jitter in a long Josephson junction soliton oscillator clock source    J.L. Habif, C.A. Mancini and R.F. Bocko Summary: Stability of Josephson junction clock sources can be a limiting factor in the operation of RSFQ digital and mixed signal circuits. We have developed techniques for the characterization of the short-term stability, i.e., the jitter, of Josephson junction clock sources, and in this paper we present measurements of the jitter for a long Josephson junction soliton oscillator clock. The output frequency of the soliton oscillator was prescaled by using a chain of T flip-flops and using a current bias feedback the oscillator was phase locked to a stable room temperature RP source. Phase noise spectra of the clock signal were measured at the successive stages of the T flip-flop chain and interpreted to infer the cycle-to-cycle jitter of the soliton oscillator. The jitter at the output of the soliton oscillator was measured to be 60 fs at a frequency of 26 GHz, or 0.16% of the period of the clock.         3D-MLSI: software package for inductance calculation in multilayer superconducting integrated circuits    M.M. Khapaev, A.Yu. Kidiyarova-Shevchenko, P. Magnelind and M.Yu. Kupriyanov Summary: A new software package 3D-MLSI was developed for inductance calculation in multilayer superconducting integrated circuits. The key advantages of 3D-MLSI are: a new mathematical model that takes into account the 3D distribution of magnetic field, and a user interface compatible with the Cadence and ACAD design tools. The program is most applicable when both kinetic and magnetic inductances are important. A method of equivalent circuits inductance extraction is suggested.         Bit error rate measurement of a high-speed small-voltage signal using a superconducting transmission line    K. Shimaoka, S. Tokunaga, M. Nemoto and I. Yoshida Summary: We developed a measuring system that has a magnetically shielded wide-band test fixture mounted on a closed-cycle cryo-cooler, and used this system to investigate the feasibility of cryo-packaging technology for high-Tc superconducting digital electronics. In this work, we evaluated the bit-error-rate (BER) performance of a system in which was installed a 50-/spl Omega/ standard microstrip line (MSTL) and a YBa/sub 2/Cu/sub 3/Ox microstrip line to a coplanar waveguide (CPW) transmission line converter (MCC). In the experiment, we used 3-Gbps, 2/sup 15/-1 pseudo-random binary sequence (PRBS) signals. The temperature of the test fixture was 20 K. Results showed that the BER was 3.74/spl times/10/sup -9/ for the 50-/spl Omega/ MSTL when the signal amplitude at the sample was 13.3 mV, and 1.52/spl times/10/sup -9/ for the MCC when the amplitude was 30.8 mV. The effect of the signal loss and impedance mismatch on the BER is also discussed.         Top-down RSFQ logic design based on a binary decision diagram    N. Yoshikawa and J. Koshiyama Summary: We have proposed a top-down design methodology for RSFQ logic circuits using a binary decision diagram (BDD). The BDD is a way to represent a logical function by a directed graph, which consists of binary switches having one input and two outputs. The important features of the BDD RSFQ logic circuits are a small number of primitives, dual rail and non-clocked logic style, and a small gate count. We have constructed a cell library for the BDD RSFQ logic design, which is composed of five square basic cells. Any logic function can be constructed by simply connecting the library cells. CAD tools for the logic level simulation, the circuit simulation and a layout view extraction have been developed to carry out the top-down RSFQ logic design on the Cadence CAD environment. A design flow of the RSFQ full adder is demonstrated to show the potential of the top-down design methodology for the design of large-scale RSFQ integrated circuits.         Analysis of electromagnetic coupling effects in integrated Josephson junction logic devices by the FDTD technique    B. Dimov, H. Toepfer and H.F. Uhlmann Summary: A very important step of the design of circuits and devices in the Josephson junction technology is the complete and correct calculation of their electrical characteristics. Due to the very high clock speed of up to 100 GHz, dynamic effects like the electromagnetic coupling start to play a significant role over the operation of the system. The presented work reports on the implementation of the FDTD technique for the description of the electromagnetic coupling effects in the Josephson devices. Some typical microstrip layouts are considered strictly taking in account the technological specifications. The obtained results are analyzed in respect to the constraints, which the coupling effects impose on the lateral dimensions of the microstrip lines.         Dual bias current operation of 2-SQUID directly coupled magnetometers    A. Tsukamoto, Y. Soutome, T. Fukazawa and K. Takagi Summary: High-T/sub c/ directly coupled magnetometers made from thin films of single layer YBa/sub 2/Cu/sub 3/O/sub y/ deposited on bicrystal substrates were investigated. A series 2-SQUID structure with a common pickup coil was designed to increase voltage modulation depth (/spl Delta/V). A second bias current was introduced to compensate for the disagreement between the two optimal bias currents and the voltage peak positions. The distribution of the second bias current was controlled by selecting the proper electrodes formed on the pickup coil, thus eliminating the difference in the voltage peak positions. The value of /spl Delta/V was doubled. The white noise in the magnetometer decreased by using this 2-SQUID design, but the low-frequency noise increased slightly. In addition, another type of the 2-SQUID magnetometer was proposed. This magnetometer has SQUIDs with different inductances. The overlapped V-/spl Phi/ curve showed the modulation beat caused by the difference in V-/spl Phi/ periodicity, and a high /spl Delta/V was observed at several /spl Phi//sub 0/ intervals.         Effects of modulation schemes on the performance of directly coupled high-T/sub c/ dc SQUID magnetometers    Jau-Han Chen, Kuen-Lin Chen, Hsiao-Wen Yu, Ming-Jye Chen, Chiu-Hsien Wu, Jen-Tzong Jeng, Herng-Er Horng and Hong-Chang Yang Summary: We have designed and fabricated the directly coupled YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// dc SQUID magnetometers with two different modulation schemes to study the crosstalk effect in the on-chip multi-channel magnetometers. In one of the modulation schemes, the modulation current was directly injected into the SQUID body and the pick-up coil. The modulation efficiency was changed by the ratio of the modulation current flowing through the SQUID to the pick-up coil. In the other schemes, the modulation flux is mutually coupled through an external coil, and the modulation efficiency was changed by the mutual inductance of the external coil and the magnetometer. The results show that the modulation efficiency was varied when the value of self-inductance or the mutual inductance of SQUIDs change. Usually, lower modulation efficiency results in a higher crosstalk. The performance of magnetometers was also influenced by different modulation schemes. Their noise spectrum was compared as evidence.         Signal properties of radio frequency SQUID with a finite amplitude of the second harmonic in the current-phase relationship    E. Ilichev, Ya.S. Greenberg, R.P.J. Ijsselsteijn, V. Schultze, H.E. Hoenig and H.-G. Meyer Summary: The signal properties of radio frequency (rf) SQUIDs with a finite amplitude of the second harmonic in the current-phase relationship have been theoretically and experimentally investigated. Both amplitude as well as phase detection has been considered in order to readout the SQUID's output signal. We observed peculiarities of the rf SQUID response of a SQUID with YBCO 45 degree grain boundary Josephson junction. We found that the current-phase relationship contains a finite amplitude of the second harmonic. Comparison of the theoretical and experimental results is given. It is shown that the sign of the amplitude of the second harmonic can be determined from the shape of experimental curves, and the value of this amplitude is defined by the positions of extrema of these curves.         Mutual inductance and noise of high-T/sub c/ SQUIDs with flip-chip and integrated input coils    J. Ramos, V. Zakosarenko, R. Ijsselsteijn, V. Schultze and H.-G. Meyer Summary: We investigated the mutual inductance and the noise of high-T/sub c/ superconducting quantum interference devices (SQUIDS) with flip-chip and integrated input coils. The dc SQUIDs are prepared on bicrystal substrates with misorientation angle of 30/spl deg/. The number of turns of the input coils is varied between 5 and 25 turns. For 19-turn input coils, the mutual inductance is about 0.75 nH and 1 nH for the flip-chip and integrated SQUIDs, respectively. The spread in noise at 1 Hz is less than a factor of 2 for the flip-chip devices and about a factor of 5 for the integrated devices.         Versatile high performance digital SQUID electronics    C. Ludwig, C. Kessler, A.J. Steinforc and W. Ludwig Summary: The digital SQUID Electronics DSE32 has been developed to perform software gradiometry with SQUID magnetometers in multi-channel systems using both High-T/sub c/ and Low-T/sub c/ SQUIDs. A low-noise preamplifier is followed by a fast hybrid feedback-loop, combining the bandwidth of an analog feedback-loop with the accuracy of a digital loop. By resetting and counting of flux quanta in the SQUID, the dynamic range has been substantially increased. All parameters of SQUID and electronics are firmware controlled and allow for auto-setup and tuning. Data are transferred with a rate of 20 Mbit/s by means of noise-minimizing, bi-directional optical fiber. Low power consumption allows the use of a battery, further reducing external noise pick-up. The electronics layout is designed for multi-channel applications, as needed in biomagnetic systems.         Nanoscale SNS junction fabrication in superconductor-normal metal bilayers    R.H. Hadfield, G. Burnell, W.E. Booij, S.J. Lloyd, R.W. Moseley and M.G. Blamire Summary: We have developed a reliable and versatile technique for fabricating SNS junctions in a superconductor-normal metal bilayer using a focused ion beam microscope (FIB) in conjunction with an in-situ resistance measurement technique. This technique offers a simple method for creating multi-junction devices (SQUIDs, 3-terminal devices, arrays) with high integration densities. In this paper we discuss recent results from devices created in Nb-Cu tracks by cutting 50 nm trenches in the top Nb layer to weaken the superconducting coupling. Cuts of depths between 60 and 100% of the Nb thickness yield reproducible junctions with current voltage (I(V)) characteristics in accordance with the resistively-shunted-junction (RSJ) model, characteristic voltage I/sub C/R/sub N//spl sim/50 /spl mu/V at 4.2 K and excellent microwave response. A thorough study has been carried out of the effect on device parameters of varying the Cu layer thickness (0-175 nm). In addition transmission electron microscopy (TEM) studies have been carried out on the device structure. A two-channel model of device operation has been developed and related to the results of I/sup C/R/sub N/(T) measurements (down to 350 mK) on selected devices.         Fabrication and characterization of SNS Josephson junctions with an aluminum barrier    V. Lacquaniti, S. Maggi, A. Polcari, R. Steni and D. Andreone Summary: We report the current status of our SNS technology aimed at the development of programmable voltage standard devices. Using the simple Nb/Al/Nb trilayer process, with an Al barrier thickness of the order of 100 nm, we have fabricated SNS Josephson junctions whose electrical properties can be changed by varying the morphology of the Al film. The major role in determining the electrical behavior of the junctions is played by the roughness of the thick Al barrier. AFM analysis shows that the Al roughness is strongly reduced by increasing its deposition rate. The critical current density varies by two orders of magnitude, from 10/sup 3/ A/cm/sup 2/ up to 10/sup 5/ A/cm/sup 2/, with correspondingly normal resistances from 1 /spl Omega/ down to few m/spl Omega/. The magnetic field dependence of the critical current is also affected by the barrier structure, while all the junctions show regular Shapiro-like rf-induced steps at 70 GHz.         Development of sub-micron SNS ramp-type Josephson junctions    D. Hagedorn, R. Dolata, R. Popel, F.-I. Buchholz and J. Niemeyer Summary: At PTB, a fabrication technology for sub-micron superconductor-normal metal-superconductor (SNS) ramp-type Josephson junctions has been developed which allows these junctions to be used as active elements in highly integrated circuits. Test circuits of series arrays containing up to 10000 junctions with contact areas below 0.4 /spl mu/m/sup 2/ and of single junctions with contact areas reduced down to 0.03 /spl mu/m/sup 2/ have been successfully realized and measured. To achieve high values of the characteristic voltage V/sub c/, different N-layer materials, i.e. Al, PdAu and HfTi with thicknesses down to d=15 nm and different layer sequences have been investigated. Typical parameters of SNS junctions with a thickness of the HfTi N-layer of d=20nm are about j/sub c/=470 kA/cm/sup 2/ and V/sub c/=100 /spl mu/V. The junctions realized allow for application in superconducting circuits.         Investigation of double-barrier Nb-Al-AlO/sub 2/-Al-AlO/sub x/-(Al-)Nb junctions under high-frequency irradiation    I.P. Nevirkovets, J.B. Ketterson and M. Siegel Summary: We have studied experimentally the current-voltage characteristics of double-barrier Nb-Al-AlO/sub x/-Al-AlO/sub x/-(Al-)Nb junctions exposed to microwave radiation at 4.2 K. Both integer and fractional Shapiro steps were observed. A complicated behavior of the step heights was observed as a function of both the microwave power and an applied magnetic field. Reasonable agreement with the RSJ model was obtained only for the steps 0 to 2 observed in current-voltage characteristics of the junctions with a "clean" middle Al layer. A deviation from RSJ-like behavior was found for higher-order integer steps and fractional steps. Devices with a "dirty" middle Al layer displayed more significant deviation from RSJ-like behavior. Step heights vs. magnetic field dependences in some cases were found to be qualitatively different from the field dependence of the dc Josephson current.         Current-phase relation in Nb-Al based SINIS-type Josephson junctions    M. Gotz, V.V. Khanin, H. Schulze, A.B. Zorin, J. Niemeyer, M. Grajcar, E. Il'ichev, H.E. Hoenigm and H.-G. Meyer Summary: The supercurrent-phase relation (CPR) of NbAl based Josephson elements of superconductor/insulator/normal conductor/insulator/superconductor-type is deduced from impedance measurements of the phase-biased junction. The chosen temperature range from 1.9 to 8.0 K covers the superconducting transition of the aluminum interlayer below which a pronounced non-harmonic CPR is found. At temperatures higher than the corresponding critical temperature, the CPR did not deviate significantly from purely harmonic shape. Both results are in agreement with theoretical predictions.         Double-barrier Josephson junctions: theory and experiment    A. Brinkman, D. Cassel, A.A. Golubov, M.Yu. Kupriyanov, M. Siegel and H. Rogalla Summary: New theoretical and experimental results on double-barrier SIS'IS Josephson junctions are presented (I is a tunnel barrier, S' is a thin film with critical temperature lower than that of S). The previously developed microscopic model for the stationary case, which describes the critical currents in Nb/Al/Nb junctions, is extended to the non-equilibrium regime of finite voltage. In particular, an intrinsic shunting resistance is estimated from I-V curves. We formulate the requirements for interface barriers in order to realize non-hysteretic SIS'IS junctions with high critical current density and I/sub c/R/sub N/ products. A comparison with single-barrier SIS junctions with high critical current density is carried out.         Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ heterostructures grown on LaAlO/sub 3/ substrate by pulsed laser deposition for voltage tunable microwave filter applications    P. Woodall, K. Bouzehouane, B. Marcilhac, D.G. Crete, E. Jacquet, J.C. Mage and J.P. Contour Summary: The performance of microwave devices containing electrically tunable layers of strontium titanate has been evaluated for samples produced by pulsed laser ablation over a range of deposition temperatures on [001] LaAlO/sub 3/ substrate. At zero bias the samples which exhibited the highest agility also exhibited the highest loss. It has been observed that the SrTiO/sub 3/ lattice parameter is the relevant parameter in determining both the frequency agility of the sample and its dielectric loss. Furthermore, it was seen that whilst the SrTiO/sub 3/ lattice parameter is dependent on deposition temperature, it has a maximum, and that samples grown at higher/lower temperatures around this maximum exhibit similar electrical properties for similar lattice parameter. A sample was then processed by a high temperature annealing of the SrTiO/sub 3/ layer prior to YBCO deposition and it was found that dielectric loss is reduced over the whole range of agility without deterioration of the frequency agility.         Anisotropy in the transparency of HTS films at millimeter and submillimeter microwave radiation    M.A. Tarasov, E.A. Stepantsov, T. Lindstrom, A.S. Kalabukhov, Hongqi Chen, L.-G. Johansson and Z.G. Ivanov Summary: The propagation of microwave radiation through YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and Tl/sub 2/Ba/sub 2/Cu/sub 1/O/sub 6/ films deposited on Al/sub 2/O/sub 3/, MgO, LaAlO/sub 3/ and LaSrAlTaO single crystal substrates, as well as through the bare substrates, has been studied in the 60-600 GHz frequency range. The angular dependence of the transmitted radiation was found to have a rather complicated structure. The dependence is affected by anisotropy of the substrate due to birefringence, resonance in substrate modes, non-homogeneity and the granular structure of the HTS film. To reduce reflections from the surface of the substrate, quarter-wave matching layers were used at selected frequencies. After correction for stray effects, the common feature is the presence of four maxima with a period of /spl pi//2 with four minima in between that can be due to the energy gap anisotropy in d-wave superconductors.         Ferroelectric characterisation using Josephson junctions    P.F. McBrien, W.E. Booij, G. Burnell, F. Kahlmann, M.G. Blamire, R.J. Romans, C.M. Pegrum and E.J. Tarte Summary: Measurements of the permittivity of a series of strontium titanate films of various thicknesses at frequencies from 100 to 900 GHz are reported. The permittivity was measured using Josephson junctions coupled to external resonators. The permittivity was found to decrease with decreasing film thickness and was frequency independent. On application of a dielectric bias voltage, the permittivity of a 200 nm film was tunable between 245 and 112 at 30 K.         SQUID photoscanning: an imaging technique for NDE of semiconductor wafers and devices based on photomagnetic detection    J. Boyer, D. Drung and T. Schurig Summary: The SQUID Photoscanning technique enables the noninvasive evaluation of semiconductor wafers and photovoltaic devices. The basic idea of the method is to detect photogenerated currents via their magnetic field by means of sensitive SQUID magnetometers. A magnetic imaging with high spatial resolution is performed by scanning the sample with a focused laser beam and synchronously measuring the magnetic field of the net photocurrents. Objects of analysis are semiconductor wafers with doping level fluctuations or electrically active defects, such as grain boundaries. Furthermore, the SQUID Photoscanning allows for the localization of artefacts in photovoltaic devices. The system uses sensitive, low-noise dc-SQUID magnetometers operated in a flux-locked loop (FLL) at 4.2 K or 77 K, respectively. The FLL electronics is adapted to the operation of the SQUID Photoscanning system in the presence of large, low-frequency interferences by implementing a frequency dependent feedback range. A digital signal processor (DSP) based control and data acquisition unit controls the amplitude modulation of the laser illumination, the xy-motion of the sample and the phase sensitive detection of the SQUID signal. The SQUID Photoscanning signal strengths obtained from the samples under investigation cover a range of about 100 fT for slight doping inhomogeneities in high purity silicon wafers up to several nT for photocurrent distributions in solar cells. The results of numerical simulations of SQUID Photoscanning signals are qualitatively and quantitatively in fair agreement with the experimental findings.         Multiplexed SQUID array for non-destructive evaluation of aircraft structures    H. Krause, S. Gartner, N. Wolters, R. Hohmann, W. Wolf, J. Schubert, W. Zander, Yi Zhang, M. v. Kreutzbruck and M. Muck Summary: SQUID sensors offer a significant advantage for eddy-current (EC) testing of aircraft components for material flaws hidden deeply in the tested structure. However, the requirement to take maps of the magnetic field, usually by meander-shaped scans, leads to unacceptably long measurement times. Due to their inductive coupling to a tank circuit, several rf SQUID sensors may be read out sequentially by selectively coupling to their tank circuits, using only one electronics with a multiplexer. The multiplexed operation of three planar HTS rf SQUID gradiometers with one electronics and one cable is shown, demonstrating the advantage of lower liquid nitrogen boil-off. Independent operation and switching is confirmed using local coil excitation of the individual SQUIDs. We report on the implementation of two multiplexed SQUID sensors in conjunction with an EC excitation and lock-in readout at unshielded laboratory environment. Scanning is performed while continuously switching the operating SQUID, thus obtaining two traces simultaneously. The applicability to EC testing of riveted sections of aircraft fuselage is discussed.         Analysis of low-velocity impact damage in reinforced carbon fiber composites by HTS-SQUID magnetometers    A. Ryosi, M. Valentino, G. Peluso and G. Pepe Summary: Composite materials are susceptible to damage which can be induced by service loads and accidental impacts. The detection of any signature produced by damage is critical to maintaining the integrity of aircraft parts during routine maintenance. A high critical temperature SQUID magnetometer has been successfully employed in the evaluation of the behavior of multi-ply carbon fibers reinforced composite panels for aeronautical applications under low-velocity impacts. Measurements of the induced magnetic field have been carried out above specimen damaged with energy impact from 1 to 40 J. A quasi-linear behavior in two different regimes between the SQUID's response and the energy of the impact has been found. This suggests a correspondence to the detection of intrinsically different damage that occurs in the laminates at different energies.         Improvement of spatial and field resolution in NDE systems using superconducting sensors    P. Seidel, S. Wunderlich, F. Schmidl, L. Dorrer, S. Linzen, F. Schmidt, F. Schrey, C. Steigmeier, K. Peiselt, S. Muller, A. Forster, S. Losche and S. Gudochnikov Summary: We present a NDE scanning system for industrial purposes in magnetically and electrically unshielded environment. In this scanning system, planar galvanically coupled dc SQUID gradiometers with a field gradient resolution of 300 fT.(cmHz/sup 1/2 /) in the white noise region are used. The spatial resolution is above 1 mm in this case. On the other hand many applications in NDE do not require the extraordinary sensitivity of SQUID based sensors. For those purposes hybrid sensors, in which Hall sensors are connected with high-T/sub c/ superconducting antennas, are an alternative sensor concept less sensitive than SQUID sensors but exhibiting better performance compared to other commercially available magnetic field sensors.         Determination of magnetic properties using a room-temperature scanning SQUID microscope    E.F. Fleet, S. Chatraphorn, F.C. Wellstood and C. Eylem Summary: We have used a YBCO de SQUID at 77 K to image room-temperature magnetic thin film samples. Samples imaged include Fe/sub 3/O/sub 4/, rare earth magnets such as samarium cobalt, and CMR materials. We typically saturate the magnetization of the sample in fields up to 8.5 Tesla, and then image the remanent (zero applied field) state. To help quickly interpret and quantify the SQUID microscope data, we have developed several analytical techniques. These techniques yield quantifiable results of magnetic properties, including magnetization, total dipole moment, and the demagnetizing field. We will present our results and discuss applications and limits of SQUID microscopy to the characterization of bulk and thin-film magnetic materials.         Two-dimensional Josephson junction arrays coupled through a high-Q cavity    G. Filatrella, N.F. Pedersen and K. Wiesenfeld Summary: The problem of disordered two-dimensional arrays of underdamped Josephson junctions is addressed. Our simulations show that when coupled to a high-Q cavity, the array exhibits synchronized behavior, and the power emitted can be considerably increased once enough junctions are activated to pump the cavity. The highly resonant cavity induces synchronized behavior, which is qualitatively different than what is familiar from other studies on nonlinear oscillator arrays, for example the Kuramoto model. We also address the effects of disorder, as well as the role of detuning between the spontaneous emission frequency of the junctions and the cavity resonant frequency. We show with a simple argument that we can predict the scaling behavior of disorder with the size of the array. The consequences for the design of microwave oscillators in the Gigahertz region are discussed.         Constant-voltage resonant steps in underdamped Josephson-junction arrays and possibilities for optimal millimeter-wave power output    B. Vasilic, P. Barbara, S.V. Shitov and C.J. Lobb Summary: When a parallel external magnetic field is applied to underdamped Josephson-junction arrays, constant-voltage steps appear in their current-voltage characteristics. These steps correspond to different numbers of rows being switched to a new resonant state. If the number of switched rows is larger then a threshold number, the array radiates coherent microwave radiation. When the array is biased on a step, the number of radiating rows stays fixed and we can change the input power, P/sub DC/, by changing the bias current. We measure the output power, P/sub AC/ as a function of P/sub DC/. This dependence is linear at high powers with a slope /spl alpha/, while at low powers P/sub AC/ vanishes nonlinearly with P/sub DC/. For a given array, the slope /spl alpha/ is larger for steps that correspond to a larger number of switched rows. We present a systematic study of the dependence of the slope or on the size of the array and discuss its implications for obtaining optimal DC-to-AC conversion efficiency.         FIR response of intrinsic Josephson junctions    S. Rother, Y. Koval, P. Muller, R. Kleiner, Y. Kasai, K. Nakajima and M. Darula Summary: We present experiments on the far infrared response of intrinsic Josephson junctions in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO). We detected first order Shapiro steps on resistive branches in a frequency range between 584 GHz and 2.5 THz. Due to the very low power coupled into the junctions the suppression of the critical current was only weak. With increasing number of junctions in the resistive state a higher amplitude of the Shapiro steps was measured. As the frequencies are well above the plasma frequency of our junctions, the steps are expected to be stable at any power level. To verify this, step heights were studied at various power levels as a function of frequency. The impedance matching of the system improved considerably when several junctions have switched into the resistive state.         Cryogenic high-Q microwave resonators for stable oscillators    S. Vitusevich, M. Winter and N. Klein Summary: Cryogenic microwave resonators have a strong potential as frequency stabilising elements for oscillators to be used in advanced radar systems and high-bitrate microwave communication links. Depending on frequency, either 2D planar HTS-resonators, HTS-shielded sapphire TE/sub 011/ resonators or cryogenic sapphire whispering-gallery mode resonators represent the best compromise between resonator quality factor and size. We have built and tested an all-cryogenic oscillator based on a WG-resonator at f=23 GHz. Phase noise measurements indicate values superior to quartz stabilized oscillators. A two-step electric frequency tuning consisting of an integrated varactor phase shifter and a dielectric plunger moved by a piezomechanical transducer is introduced to compensate frequency drifting with temperature. For further improvement of long-time frequency stability we have developed rutile-sapphire composite dielectric resonators. Due to the opposite sign of the temperature slope of the dielectric constant of sapphire and rutile a turning point appears in the temperature dependence of the resonance frequency. Employing a moderate temperature stabilization as good as a few millikelvin around the turning point at T=78 K, we have demonstrated a long time frequency stability at least as good as for oven controlled quartz oscillators.         Microwave responses of an insular intrinsic Josephson junction stack fabricated from Bi-Sr-Ca-Cu-O single crystal    H.B. Wang, P.H. Wu and T. Yamashita Summary: The conventional c-axis intrinsic Josephson junction (IJJ) stack is usually fabricated from a piece of single crystal in such a way that it looks like a small mesa sitting on a big pedestal. In some cases the effects of this pedestal should be taken into account in order to explain the experimental observations. To avoid this problem we have developed a novel technique by which we are able to remove a small sample from the single crystal and place it on a substrate with low microwave loss. This enable us to couple it to other microwave devices such as antenna etc. This small sample, or junction stack, measures a few micrometers by a few micrometers in the a-b plane and a few hundred angstroms along the c-axis and is plated with normal metal on both the top and the bottom. To distinguish the structure from the conventional one, we call it an insular intrinsic Josephson junction stack. We carefully study current-voltage characteristics, microwave responses, frequency mixing properties, and discuss the possible applications.         Microwave emission from two-stacked arrays of long Josephson junctions    G. Carapella, G. Costabile, R. Latempa, N.H. Rasmussen and J. Mygind Summary: We have recorded the radiation generated by magnetic flux quanta oscillations and by cavity mode oscillations in two-stacked arrays each consisting of five long Josephson junctions biased in parallel. The two arrays have in common the middle electrode, which is thinner than the London penetration depth, and can be biased independently. Basically, two kind of fluxon states can be generated, one consisting of a row of five fluxons oscillating in one of the arrays, the other consisting of a row of five fluxons in one array and five antifluxons in the other array, bound in a coherent state. It is found from the microwave emission that the latter configuration is less sensitive to low-frequency noise.         Resonant Cherenkov radiation in Josephson flux flow oscillators with integrated meander-shaped transmission line    A.V. Yulin and J. Mygind Summary: A novel Cherenkov flux flow oscillator (CFFO) is considered. The system consists of a long Josephson junction with an overlaying meander-shaped stripline. The traveling wave in the line is exited at each intersection point by the chain of fluxons moving along the junction. At certain resonance frequencies the radiation delivered to the stripline from all intersections points interfere constructively and the generated power reaches its maximum value. To first order the resonance condition is given by the distance between the fluxons, and is independent of the system boundaries. So one can change the resonance frequency by varying the external magnetic field. This is radically different from oscillators relying on conventional internal junction resonances such as the Fiske resonance, and allows for design of a powerful CFFO which can be electronically tuned. The existence of resonant interactions with both forward and backward waves is shown, and the analogy to the Cherenkov synchronism is demonstrated. Numerical simulations confirm the analytical predictions and allow us to investigate the strongly nonlinear case. The proposed CFFO is ideally suited for realization in HTSC technology.         Superfine resonant structure on IV-curves of long Josephson junction and its influence on flux flow oscillator linewidth    V.P. Koshelets, A.B. Ermakov, S.V. Shitov, P.V. Dmitriev, L.V. Filippenko, A.M. Baryshev, W. Luinge, J. Mygind, V.L. Vaks and D.G. Pavel'ev Summary: The Josephson Flux Flow Oscillator (FFO) has proven to be a perfect on-chip local oscillator for integrated submm receivers; a noise temperature (DSB) below 100 K has been achieved at 500 GHz. Recently a FFO linewidth as low as 1 Hz has been measured in the frequency range 270 - 440 GHz. A new technique for both linewidth measurements and phase locking of the FFO is developed; this method employs an offchip harmonic multiplier. By measuring the frequency of the FFO radiation emission, its IV-curve (IVC) can be reconstructed with an accuracy better than 1 nV. A superfine resonant structure with a voltage spacing of about 20 nV and extremely low differential resistance has been observed in the FFO IVCs. This resonant structure modifies the performance of the FFO compared to the one expected from the "averaged IVC". The influence of this resonant structure on phase locking is discussed. Also results of FFO phase noise measurements are presented.         Temperature dependence of the Josephson linewidth of resistively shunted double junction HTS SQUIDs    D.A. Peden, L. Hao, J.C. MacFarlane, R.A.M. Lee and J.C. Gallop Summary: Double Josephson junction HTS resistive SQUIDs have been fabricated using an on-chip shunt Au resistor across a gap in an YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// loop, providing a low shunt resistance of R/sub s/ /spl sim/26 /spl mu//spl Omega/ at T/spl les/77 K. The dependence of the heterodyne oscillation linewidth of the R-SQUID on the thermal noise across the shunt resistor is under investigation with a view to the development of an absolute noise thermometer. Signal powers /spl sim/nW have been measured and the device has been shown to be tunable from 5 to 50 MHz. The measured oscillation linewidth (/spl sim/30 kHz at 17 K) is believed to be the narrowest reported for such an HTS device, however non-thermal broadening of the linewidth is also observed, as has been reported for single junctions at GHz frequencies. We describe measurements on such devices over a range of temperatures and bias conditions.         Some properties of Eck-like steps in 2D underdamped Josephson junctions arrays    C. de Leo and G. Rotoli Summary: Two-dimensional (2D) Josephson Junctions arrays have been studied largely in the overdamped case. Only recently some experimental, numerical and theoretical results have been obtained in the underdamped case. The nature of dynamical states of an array when placed in a magnetic field is again not fully explained and only approximate (linear) models have been proposed. On the other hand, the comprehension of such dynamics is of great importance for understanding the behavior of such arrays. In this work, we study numerically some of the dynamical states in 2D arrays using a full inductance matrix in the array equations. The results show that the response of the array to the magnetic field is governed at large by the parameter /spl beta//sub L/. Moreover we study the underlying dynamics which is dominated by so-called checkerboard solutions. The properties of such arrays are investigated in view of applications.         Magnetic flux controlled Josephson array oscillators    D.S. Crankshaw, E. Trias and T.P. Orlando Summary: One-dimensional parallel arrays of Josephson junctions have the ability to perform as oscillators tunable by magnetic flux. We have designed and tested an array impedance matched to a detector junction load. The amplitude and frequency of the array are controlled by the independent variables of magnetic field and current bias. We report on the array's characteristics and compare them to the results predicted by nonlinear simulations and a linear circuit model. This confirms the accuracy of the circuit model, both for impedance matching and in describing the dynamics of the array, even in a multiple-frequency regime.         Arrays of Josephson junctions coupled by distributed circuits    V.K. Kornev, N.A. Shcherbakov, A.V. Arzumanov, P.B. Mozhaev, A.D. Mashtakov, K.Y. Constantinian and G.A. Ovsyannikov Summary: Both the linewidth reduction and the gain in output power have been analyzed for Josephson-junction arrays with distributed coupling circuits. Different ways of Josephson junction connection to the distributed circuits, as well as both the nonlinear interaction effect and the crucial role of high frequency losses have been studied. It has been found that the contradictory requirements to the junctions as nonlinear active elements on (i) low wave reflection and (ii) high total power produced can be fulfilled by an increase in number of Josephson junctions with a proper impedance value. The first condition is necessary to provide the most reduction in the linewidth, and the second one is needed to compensate for the power output. An array of biased in parallel bicrystal Josephson HTSC junctions coupled by a microstrip circuit has been fabricated and preliminary tested.         Superconducting electronics requirements for single-photon, energy resolving detectors    A.M. Gulian, G.G. Fritz, K.S. Wood and D. Van Vechten Summary: Development of single photon sensors capable of determining the energy ("color") of each photon incident on a pixelated focal plane in real time is a central activity of many groups worldwide developing state-of-the-art hardware for the space astrophysics community. Terrestrial applications in materials analysis are also being targeted. The most successful class of approaches uses "hot-electron" microbolometers in which the energy of the photon elevates the electronic temperature in a metallic absorber and a dedicated thermometer measures this excursion. In a class of devices called thermoelectric microbolometers the temperature sensor utilizes the Seebeck effect. Estimates of theoretical performance for a complete megapixel array are quite positive and the prototype single-pixel devices are under test. Superconducting electronics is a critical part of the signal acquisition chain. Three different types of SQUID-array amplifiers coupled to our detector pixels have been tested. The parameters of optimized SQUID-array preamplifiers are discussed.         Design of a fast digital double relaxation oscillation SQUID    M. Podt, A.J. Mieog, J. Flokstra and H. Rogalla Summary: A fast digital Double Relaxation Oscillation SQUID (DROS) with a relaxation oscillation frequency of 100 MHz has been developed. The digital DROS incorporates a DROS and a superconducting up-down counter that supplies the feedback flux. The major advantage of a DROS is that the relaxation oscillations generate an on-chip clock signal and therefore, no external clock is required. In order to maximize the slew rate without compromising the sensitivity, the quantization unit of the feedback flux was adapted to the flux noise of the DROS. This resulted in a designed flux slew rate of 5/spl middot/10/sup 6/ /spl Phi//sub 0//s. We will discuss the design optimization, numerical simulations, the layout and some experimental results of the digital DROS.         Low-noise S-band DC SQUID based amplifier    G.V. Prokopenko, S.V. Shitov, D.V. Balashov, P.N. Dmitriev, V.P. Koshelets and J. Mygind Summary: A low-noise rf amplifier based on a dc SQUID (SQA) is tested in the frequency range 3.3-4.1 GHz. A new signal launching system for the SQA rf coupling has been developed and successfully implemented. The following parameters have been measured at 3.65 GHz using a band-pass filter at the input of a single-stage SQA: gain (11.0/spl plusmn/1.0) dB, 3 dB bandwidth of 300 MHz and noise temperature (4.0/spl plusmn/1.0)K. This figure corresponds to a flux noise S/sub /spl Phi///sup 1/2 /=0.6 /spl mu//spl Phi//sub 0//Hz/sup 1/2 / and an energy sensitivity /spl epsi//sub i//spl ap/75 h. The input saturation power, P/sub s/, (1 dB gain compression) is measured for different bandwidths of the input band-pass filter, A corresponding input signal saturation temperature (normalized for a 1 GHz bandwidth) T/sub SAT//sup 1GHZ/=P/sub SAT//k/sub B/ is estimated to be 11.5 K GHz at an SQA bias voltage 27 /spl mu/V (condition for minimum noise temperature). The dependencies of the SQA gain, noise temperature and saturation level on the operation point are studied. The reason for the SQA saturation is discussed.         Niobium-copper superconductor-normal metal-superconductor asymmetry modulated SQUIDs    G. Burnell, E.J. Tarte, W.E. Booij and M.G. Blamire Summary: We have developed a fabrication method using a focused ion beam microscope that allows us to produce SNS junctions in which thermally energetic electrons can enter the N region. We report on SQUIDs made with this technique which we are developing as proof of concept devices and prototype high energy resolution spectrometers. We discuss the various design parameters used for our devices and present results from our prototype SQUIDs. We present results for devices with a variety of N-electrode structures and discuss their suitability for our application.         Multi-loop relaxation oscillation SQUID magnetometers with large flux-to-voltage transfer functions    J. Kawai, G. Uehara, M. Higuchi, H. Ogata and H. Kado Summary: A multi-loop Relaxation Oscillation SQUID (ROS) with direct voltage readout is fabricated and characterized. We designed and fabricated four-loop ROSs with the size of 5 mm /spl times/5 mm. A maximum voltage modulation of 100 /spl mu/V and a flux-to-voltage transfer function of more than 10 mV//spl Phi//sub 0/ were obtained. With a direct voltage readout flux locked loop (FLL), a magnetic field resolution of 4 to 10 fT//spl radic/Hz was obtained in the frequency range from 0.3 Hz up to the white region. Using this magnetometer, we demonstrated the measurement of a brain response.         DC SQUID series array amplifiers with 120 MHz bandwidth    M.E. Huber, P.A. Neil, R.G. Benson, D.A. Burns, A.M. Corey, C.S. Flynn, Y. Kitaygorodskaya, O. Massihzadeh, J.M. Martinis and G.C. Hilton Summary: We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 /spl mu/m center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/ Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.         Long baseline thin film SQUID gradiometers    R. Stolz, V.M. Zakosarenko, L. Fritzsch, N. Oukhanski and H.-G. Meyer Summary: We have developed a highly sensitive SQUID gradiometer for unshielded operation in the Earth's magnetic field. It is implemented in an all-refractory Nb-AlO/sub x/-Nb technology, and consists of gradiometer pick-up loops with an inductance of about 250 nH coupled to the SQUID by a flux transformer. The SQUID is designed as a highly balanced second order gradiometer consisting of four pairs of washers. It has an inductance of about 300 pH. The gradiometer chip has a size of 6 cm /spl times/2 cm. The baseline of the gradiometer is 4 cm and the effective volume is about 300 mm/sup 3/. We measured a white noise level of below 10 /spl mu//spl Phi//sub 0//Hz/sup 1/2 /, corresponding to a gradient field resolution smaller than 40 fT/m/spl middot/Hz/sup 1/2 /. The total flux noise in the frequency band from 0.01 Hz to 10 Hz is below 150 /spl mu//spl Phi//sub g/. The balance of the gradiometer was determined by moving the gradiometer in the Earth's magnetic field. Due to the high balance we can operate the gradiometer in field experiments.         Subranging digital SQUID ammeter    D. Gupta and M. Radparvar Summary: A digital SQUID (Superconducting Quantum Interference Device) has an extremely large dynamic range that makes it attractive for measurement of widely varying magnetic field or current. However, if we use a single digital SQUID device to simultaneously measure large and small signals that differ by 4-5 orders of magnitude, either resolution or input bandwidth must be compromised. We are implementing a subranging architecture, where multiple SQUID devices, coupled to a common input coil, are employed for different ranges of signal amplitude, to provide high-resolution digitization of signals with much higher bandwidth. The simplest subranging ammeter will consist of two digital SQUIDs, one with a fine resolution and the other with coarse resolution. The coarse resolution SQUID measures the current in larger steps leaving a smaller current, less than its step size (resolution) to be measured by the fine resolution SQUID with smaller steps. Each digital SQUID consists of an analog SQUID followed by a comparator gate that feeds a quantum of magnetic flux (+/spl Phi//sub 0/ or -/spl Phi//sub 0/ depending on the polarity of the net magnetic flux sensed by the SQUID) back to the SQUID upon clocking. The two SQUIDs are alternately clocked. The digital outputs from the two SQUIDs can be combined off chip.         SQUID operational amplifier    K.D. Irwin and M.E. Huber Summary: The nonlinear response of Superconducting Quantum Interference Devices (SQUIDs) has limited their usefulness. We describe the SQUID Operational Amplifier, which consists of several stages of SQUIDs with high open-loop current gain. When connected in a negative-feedback configuration by passing some of the output current through a feedback coil connected to the first stage, the response is linearized. An analog of the semiconductor op-amp, the SQUID op-amp can be used in superconducting equivalents of op-amp circuits such as current amplifiers, current-to-voltage converters, and differentiators. We present experimental results with a /spl times/10 current amplifier as well as a 750 /spl Omega/ current-to-voltage amplifier which can couple directly to a room-temperature amplifier without a transformer or a feedback line.         Superconducting multiple loop quantum interferometers    J. Oppenlander, T. Trauble, C. Haussler and N. Schopohl Summary: We present experimental results on the magnetic field B dependent voltage response V(B) of a number of N resistively shunted Josephson junctions connected in parallel by a multiple loop network. For an appropriate distribution of the array loop sizes, such networks constitute superconducting quantum interference filters (SQIFs) with voltage response functions V(B) that are not /spl Phi//sub 0/-periodic. The voltage response of SQIFs is a unique function around a global minimum at B=0 that has a high sensitivity and a low noise level. In contrast to conventional superconducting quantum interference devices, SQIFs can be directly employed as highly sensitive magnetometers allowing the absolute measurement of magnetic fields. The experimental results are in very good agreement with the theoretical predictions on which basis the SQIF has been fabricated, All findings suggest that superconducting quantum interference filters may allow the design of novel superconducting devices.         LC-resonant voltage response of superconducting quantum interference filters    C. Haussler, T. Trauble, J. Oppenlander and N. Schopohl Summary: The voltage vs. magnetic field relation V(B) of superconducting interferometers consisting of two or more Josephson junctions is the basic characteristic of their operation as highly sensitive magnetometers and amplifiers. The conversion efficiency /spl part/V//spl part/B of interferometers containing two Josephson junctions, i.e. dc SQUIDs, decreases significantly with increasing loop inductance L. Therefore, the range of SQUID loop sizes for which the SQUID operates properly is very restricted. However, for sufficient coupling between the SQUID and the signal coil a large value of L is desirable. In this work theoretical and experimental results on the voltage response function of quantum interference filters (SQIFs) are presented. A SQIF consists of N Josephson junctions connected in parallel to form a 1D array. The array loop sizes are chosen such that the voltage response becomes a unique function around B=0. It is shown that for McCumber parameters /spl beta//sub C/>0.5 and sufficiently large array inductances the V(B) relation of SQIFs shows LC-resonances that lead to two pronounced minima in the response function. In the LC-resonant operation mode the conversion efficiency of SQIFs is not degraded even for large array inductances. By this, a very strong coupling to signal coils can be achieved. The experimental results agree very well with the theoretical predictions on which basis the SQIF has been fabricated.         Aircraft wheel testing with remote eddy current technique using a HTS SQUID magnetometer    R. Hohmann, D. Lomparski, H.-J. Krause, M. v. Kreutzbruck and W. Becker Summary: An aircraft wheel testing system using a planar HTS SQUID gradiometer with Joule-Thomson machine cooling in conjunction with differential eddy current (EC) excitation has recently been developed. From a routine performance test in the wheel testing facility at the Lufthansa Base, Frankfurt/M. Airport, we learned that quadrupolar flaw signatures complicate signal interpretation considerably. In order to overcome these difficulties, the system was equipped with a HTS rf magnetometer SQUID sensor and an absolute EC excitation coil. The coil was mounted with a lateral displacement with respect to the SQUID. The geometry was chosen similar to the remote EC technique: a given point on the rotating wheel first passes underneath the excitation coil and then underneath the sensor. We analyzed the dependence of the response field of an inside crack on excitation coil displacement, EC frequency and lock-in phase angle and found an optimum rotation velocity for deep lying defects. The depth selectivity of the technique is discussed.         Hybrid double-D sheet-inducer for SQUID-based NDT    J.A. Lobera-Serrano, J.R. Claycomb, J.H. Miller Jr. and K. Salama Summary: We have developed a High Temperature Superconducting Quantum Interference Device (HTS SQUID)-based eddy current probe that incorporates a Hybrid Double-D (KDD) sheet-inducer coil design for the nondestructive evaluation of conducting materials. Cylindrical high-T/sub c/ superconducting shields assist the device's operation in magnetically noisy environments. Experimental results are presented comparing the flaw response, at various depths, obtained with a conventional sheet inducer with that from the HDD sheet-inducer.         Eddy current probe patterned in YBCO    W.N. Podney and J.M. Murduck Summary: Superconductive quantum interference devices (SQUIDs) coupled to arrays of small pickup loops can give images of millimeter fatigue cracks deep inside structures, using eddy currents. Coupling magnetic flux from a pickup loop to a SQUID commonly leads to a thousand fold loss. An eddy current probe, patterned in YBCO, uses 37 parallel turns to couple magnetic flux from a pickup loop 8 mm in diameter to give an expected gain in flux transfer of about six, instead of a loss.         Non-destructive testing using a HTS SQUID    H. Nakane, R. Kabasawa and H. Adachi Summary: We have used a high temperature superconductor (HTS) SQUID in an unshielded environment to perform eddy current nondestructive testing measurement of a multi-layer aluminum structure. The sensor consists of an YBCO dc superconducting quantum interference device (SQUID). As a demonstration of the system's capabilities, subsurface defects in a multi-layer aluminum structure have been located and mapped using eddy current with no magnetic shielding around the specimen.         Detection of deep flaws by using a HTS-SQUID in unshielded environment    J.T. Jeng, S.Y. Yang, H.E. Horng and H.C. Yang Summary: We reported the nondestructive evaluation of flaws in conductive samples with the high-T/sub c/ SQUID operated at 77 K. By nulling the SQUID with an additional compensation, we can sensitively detect the excited magnetic field due to the eddy current around a deep flaw. To investigate the effects of the size and the depth of flaws on the induced magnetic field, the excited magnetic fields as a function of the depth were measured for buried slots with various widths and thickness. Besides, the amplitude and the phase with different excitation frequencies for a fixed slot size are also studied. It was found that for a fixed excitation frequency, the phase of the measured signal linearly responds to the depth of the slot, while the amplitude correlates with the height of the slot. The results are valuable for quantitative evaluation of flaws.         Improving the detection of flaws in steel pipes using SQUID planar gradiometers    E. Andrade Lima and A.C. Bruno Summary: The detection by magnetic techniques of corrosion pits on pipes covered with thermal insulation is critical. Without removing the insulating layer, SQUID technology is the only one available, because the sensor must be placed at a distance from the pipe surface. In this paper we compare the performance of different SQUID gradiometer designs, varying coil area and gradiometer baseline, to determine the best configuration for this task. The gradiometer response was simulated and analyzed by using a spatial frequency model that incorporates the design parameters mentioned before. A three-dimensional finite element model was developed to simulate a typical flaw geometry in small diameter steel pipes due to corrosion pitting. It is shown that planar gradiometers enhance dramatically flaw signal visualization when compared with a typical axial gradiometer design.         Non-destructive evaluation with a linear array of 11 HTS SQUIDs    M.A. Espy, A.N. Matlashov, J.C. Mosher and R.H. Kraus Jr. Summary: A linear array of 11 High Temperature Superconducting (HTS) SQUIDs was used for non-destructive evaluation (NDE) applications. The array consists of 11 SQUID magnetometers arranged linearly along a single substrate with 0.75 mm spacing. The SQUIDs have 105 nT//spl Phi//sub 0/ field sensitivity and <20 /spl mu//spl Phi//sub 0///spl radic/Hz noise values at 1 kHz with DC bias current. We used an eddy current NDE technique. The eddy current induction coils were arranged such that there was a null in the induction field at the SQUIDs. Single Frequency and white-noise (frequency-continuum) induction schemes were used. Both SQUIDs and induction coils were placed at the bottom of a liquid nitrogen dewar with a 4 mm hot-to-cold distance. Flawed and unflawed samples were scanned beneath the array. The phase and amplitude of the SQUID's response relative to the induction signal were acquired. This paper presents experimental results and their interpretation.         Detection of plastic deformation gradients in steel using scanning SQUID microscopy    D.M. Clatterbuck, Tae-Kyu Lee, T.J. Shaw, N.F. Heinig, Hsiao-Mei Cho, J. Clarke and J.W. Morris Jr. Summary: Scanning SQUID microscopy is shown to be capable of detecting deformation gradients when accompanied by significant changes in hardness. Deformation which does not increase the dislocation density (as measured by the increase in hardness) has little effect. The effect can be produced by different techniques including cold rolling and tensile deformation. The effect is shown to occur in at least two different alloys with very different microstructures indicating the possibility of wide applicability.         Development of an NDE method using SQUIDs for the reconstruction of defect shapes    Y. Hatsukade, N. Kasai, H. Takashima, R. Kawai, F. Kojima and A. Ishiyama Summary: The widespread use of the SQUID-NDE requires the visualization of defects. We have developed a method to obtain depth information by monitoring the SQUID output while changing the frequency of the current flowing in a sample. The effectiveness of this method was verified by experiment and simulation.         Optimization of direct-coupled high-T/sub c/ SQUID magnetometers for operation in magnetically unshielded environment    F. Ludwig, A.B.M. Jansman, D. Drung, M.O. Lindstrom, S. Bechstein, J. Beyer, J. Flokstra and T. Schurig Summary: To further improve the design of our direct-coupled SQUID magnetometers, we performed simulations of the current distribution and thus of the effective area and inductance for various distributions of the 16 parallel 50-/spl mu/m-wide loops forming the pickup structure. It is shown that an optimization of the line distribution yields an increase of the effective area of only 2.2% but could be advantageous for the operation in time-varying magnetic fields. Based on the devices which were optimized with regard to their operation in magnetically unshielded environment, we have developed a single-channel second-order gradiometer system that allowed us to record real-time magnetocardiograms in a typical laboratory environment.         HTS dc SQUID behavior in external magnetic fields    V. Schultze, N. Oukhanski, V. Zakosarenko, R. Ijsselsteijn, J. Ramos, A. Chwala and H.-G. Meyer Summary: Several types of HTS dc SQUID magnetometers - directly coupled magnetometers with either a conventionally solid pickup loop or with 17 narrow loops in parallel and flip-chip magnetometers-are tested concerning their behavior in external fields. The stability against flux penetration was measured by the determination of the magnetic hysteresis. This stability is increased by steep structure edges in the SQUID and in the pickup loop. The intrinsic noise of SQUIDs during operation in external fields was determined by simultaneous measurement of the spectra of two SQUIDs. A directly coupled magnetometer with narrow parallel loops showed much smaller intrinsic noise after movement in the Earth's magnetic field than one with a solid pickup loop.         High-Tc SQUID magnetometers for use in moderate magnetically-shielded room    M. Matsuda, S. Ono, K. Kato, T. Matsuura, H. Oyama, A. Hayashi, S. Hirano, S. Kuriki and K. Yokosawa Summary: We have fabricated and characterized high-T/sub c/ planar SQUID magnetometers and first derivative gradiometers with directly-coupled pickup loops. The devices were made from single layer of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film on LSAT bicrystal substrate with 30/spl deg/ or 24/spl deg/ misorientation angle. Magnetic properties were investigated by applying a magnetic field B/sub 0/ for the SQUID magnetometer patterned with holes to reduce the maximum structural width. We found an increasing low frequency noise with cooling fields B/sub 0/ larger than 1.5 /spl mu/T. This value consists with the threshold field estimated from the maximum structural width. A magnetic field noise level of 500 fT/Hz/sup 1/2/ at 10 Hz was observed by using FLL electronics with a bias current reversal in a moderate magnetically-shielded room consisting of only two 1 mm thick layers of permalloy. Measurements of magnetocardiograms demonstrate the suitability of this magnetometer for biomagnetic applications. On the other hand, the gradiometer with two symmetric pickup loops was operated without any shielding. The performance obtained was a field gradient resolution of about 1 pT/cmHz/sup 1/2/ at 1 kHz and 10 pT/cmHz/sup 1/2/ at 1 Hz, with a baseline of 4 mm. The imbalance of this gradiometer was around 0.7%, limited by the sensitivity to homogeneous field of the SQUID itself.         Integrated multilayer high-T/sub c/ SQUID magnetometers with slotted washer    H.J. Lee, W.K. Park, S.-M. Lee, J.D. Park, S.H. Moon and B. Oh Summary: We have fabricated and characterized multilayer high-T/sub c/ SQUID magnetometers designed for a magnetically unshielded environment. The magnetometers consist of YBa/sub 2/Cu/sub 3/O/sub 7-x/(YBCO)/SrTiO/sub 3/(STO)/YBCO trilayers deposited by pulsed laser deposition (PLD) on an STO bi-crystal substrate. We fabricated SQUIDs with slotted washers at the bottom or top YBCO layer. The slots consist of 4 /spl mu/m wide superconducting lines separated by 8 /spl mu/m. A flux transformer with a multi-turn input coil was defined on the top or bottom YBCO layer, and the SQUID washer was used as a crossover pattern to simplify the fabrication process. The pickup loop size was 4 mm/spl times/7 mm, and the magnetometer effective area was found to be 0.67 mm/sup 2/. The SQUID inductance was 85 pH. For the operation of our SQUID in unshielded environments, compact 3 MHz modulation flux locked loop (FLL) electronics with bias-reversal were developed. The system bandwidth was greater than 500 kHz, and maximum slew rate was about 10/sup 6/ /spl Phi//sub 0//sec. The flux noise spectra of the magnetometers were measured and compared with our single layer devices. We also investigated the effect of slots on the coupling strength between the input coil and SQUID.         Effects of flux dam on low-frequency noise in high-T/sub c/ SQUID magnetometers    H. Oyama, S. Kuriki and M. Matsuda Summary: We demonstrated that the low-frequency noise in a high-T/sub c/ superconducting quantum interference device (SQUID) magnetometer when an external magnetic field is changed could be reduced by forming slots in a flux dam. We designed and fabricated directly coupled dc SQUID magnetometers having a mesh structure and flux dams. In order to suppress the vortex motion in the flux dams, we formed 5-/spl mu/m-wide strip lines and slots across the grain boundary of the flux dams. The output of the magnetometer in a flux-locked loop (FLL) operation became stable and low-frequency noise was suppressed up to an applied field of 83 /spl mu/T in field cooling and 40 /spl mu/T for field change after zero field cooling. The importance of the structure of the flux dam in controlling the vortex motion is discussed.         Effect of a static magnetic field on a slotted high-T/sub c/ SQUID magnetometer without a flux dam    K. Yokosawa, H. Oyama, S. Kuriki, D. Suzuki, K. Tsukada and M. Matsuda Summary: A direct-coupling-type high-critical-temperature (high-T/sub c/) SQUID magnetometer with two pickup loops per SQUID on a bicrystal substrate has been fabricated. To avoid flux trapping, the superconducting films of the pickup loops have slits with a separation of 5 /spl mu/m. To suppress flux entry into the pickup loops, there are no weak links on the pickup loops, i.e., no flux dams. In field cooling, noise did not substantially increase in the low frequency region unless the field reached around 100 /spl mu/T. Regardless of whether the magnetometer was previously zero-field cooled or field-cooled, the flux did not enter the pickup loop until the changing field exceeded about 10 /spl mu/T. The magnetometer cooled under geomagnetic- and environmental-field noise could work in an unshielded environment. A gradiometer was made by connecting the feedback coils of two magnetometers in series. The environmental field noise was reduced by the gradiometer by about 35 dB.         Magnetic field behavior of YBCO step-edge Josephson junctions in rf-washer SQUIDs    M. Bick, J. Schubert, M. Fardmanesh, G. Panaitov, M. Banzet, W. Zander, Y. Zhang and H.-J. Krause Summary: The suppression of the critical current in YBCO Josephson junctions by the Earth's magnetic field strongly affects the operation of SQUIDs outside magnetic shielding. Commonly, one observes a modulation of the SQUID flux-voltage transfer function amplitude, V/sub sq-pp/, with a period of /spl Delta/B/sub 0-v/ leading to an increased white flux noise level or unstable SQUID operation. Here, we report on the investigation of /spl Delta/B/sub 0-v/ of rf-SQUID sensors based on step edge junctions (SEJ) operated in a flip chip configuration with coplanar resonators with integrated flux concentrators. To investigate the origin of the suppression of V/sub sq-pp/, we opened the SQUID loop of some samples and measured the magnetic field dependence of the critical current I/sub c/(B) directly and compared it to V/sub sq-pp/(B). It is shown that a junction width in the submicrometer scale is required for operation of the sensors in the Earth's magnetic field.         Balancing of the single-layer second-order high-T/sub c/ SQUID gradiometer    Y. Hwang, Jong Rok Ahn, Soon-Gul Lee, Jin-Tae Kim, In-Seon Kim and Yong Ki Park Summary: We have designed a prototype single-layer second-order high-T/sub c/ SQUID gradiometer that detects the transverse field gradient, and balanced the device by adopting a step-down method. The device consists of symmetrically designed 3 parallel-connected square pickup loops that are directly coupled to the SQUID. The dimensions of side loops are 3 mm outside and 1.8 mm inside. The inner dimension of the center loop is 1 mm. Step-down balancing was achieved by varying the outer dimension of the center loop until a null response was detected under uniform fields. The uniform field was generated by a 250 mm/spl times/25 mm square coil wound on a grooved garolite tube. Deviation of the coil field along the abscissa was calculated to be less than 1/spl times/10/sup -5/ within the sample range. We have investigated response of the device to field gradients along the transverse direction. Details of the design, fabrication, and results will be discussed.         NdBa/sub 2/Cu/sub 3/O/sub 7/ bicrystal Josephson junctions and SQUIDs operating at 77 K    E.J. Romans, A. Eulenburg, C. Carr, A.J. Millar, G.B. Donaldson and C.M. Pegrum Summary: Recently there has been considerable interest in the use of NdBa/sub 2/Cu/sub 3/O/sub 7/ (NBCO) as an alternative thin-film material to YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) for device applications. This is due to the its potentially superior surface and structural properties. However the development of NBCO Josephson junctions and superconducting quantum interference devices (SQUIDs) has been found difficult worldwide due to the degradation in the transition temperature upon patterning. This effect appears to be target dependent. By careful patterning and annealing of samples we have been able to obtain working NBCO Josephson junctions and SQUIDs at 77 K. Here we report on their electrical and noise characteristics.         Step-edge Josephson junctions and their use in HTS single-layer gradiometers    A.J. Millar, E.J. Romans, C. Carr, A. Eulenburg, G.B. Donaldson and C.M. Pegrum Summary: We describe reproducible technology for fabricating YBa/sub 2/Cu/sub 3/O/sub 7/ step edge Josephson junctions on SrTiO/sub 3/ substrates. We report on the electrical characteristics of the junctions at 77 K and the dependence on the ratio of film thickness to step height. Single-layer gradiometers incorporating step-edge junction dc SQUIDs have been fabricated. We compare the performance of identical SQUID gradiometers based on our step-edge junctions and on 24/spl deg/ SrTiO/sub 3/ bicrystal junctions. Gradiometric SQUIDs (G-SQUIDs) incorporating step-edges have also been fabricated. We measured the effective area of several G-SQUIDs to be in the range of 1-2 /spl mu/m/sup 2/, approximately two orders of magnitude lower than for conventional SQUIDs of similar inductance. We demonstrate that when incorporated into a gradiometer the G-SQUID leads to an improved performance in an unshielded environment.         Noise properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ step-edge junction dc SQUID magnetometers prepared on sapphire substrates    Hae-Ryong Lim, In-Seon Kim, Yong Ki Park and Dong Ho Kim Summary: Step-edge YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) dc SQUID magnetometers on sapphire substrates have been fabricated. CeO/sub 2/ buffer layers and YBCO films were deposited in situ on the low angle (/spl sim/35/spl deg/) steps formed on the sapphire substrates with various thickness ratio of YBCO thin film to step height. Noise properties of the magnetometer exhibit quite different behavior according to the thickness ratio. The field noise of the dc SQUID magnetometer was measured to be 100/spl sim/300 fT//spl radic/Hz at 100 Hz and about 1.5 pT//spl radic/Hz at 1 Hz with a dc bias method, and 450 fT//spl radic/Hz at 1 Hz with an ac bias method.         Development of a high-T/sub c/ first-order gradiometer system    In-Seon Kim, Jin-Mok Kim, Hae-Ryong Lim and Yong Ki Park Summary: The high-T/sub c/ superconducting quantum interference device (SQUID) gradiometer system was developed for operation in unshielded environment. The system consists of the first-order gradiometer and the flux-locked loop electronics. YBa/sub 2/Cu/sub 3/O/sub 7/ single-layer first-order SQUID gradiometers were fabricated on 15 mm/spl times/7.5 mm SrTiO/sub 3/ bicrystal substrates with a baseline of 7 mm. The gradient sensitivities at 77 K and 100 Hz were 0.1 pT/(cm/spl radic/Hz) in magnetic shielding and 1.4 pT/(cm/spl radic/Hz) when operated unshielded in our laboratory. The high-T/sub c/ SQUID gradiometer system demonstrated successful measurement of small magnetic fields in a laboratory environment without any shields.         1/f noise characteristics of SEJ Y-Ba-Cu-O rf-SQUIDs on LaAlO/sub 3/ substrate and the step structure, film, and temperature dependence    M. Fardmanesh, J. Schubert, R. Akram, M. Bick, Y. Zhang, M. Banzet, W. Zander, H.-J. Krause, H. Burkhart and M. Schilling Summary: Step edge junction (SEJ) rf-SQUID magnetometers and gradiometers were fabricated using PLD Y-Ba-Cu-O films on LaAlO/sub 3/(100) and SrTiO/sub 3/(100) substrates. Effects of different step structure and the film properties on the yield, optimal operating temperature, and the 1/f noise of the SQUIDs were investigated. The step structure was controlled using various IBE processes. The devices on LaAlO/sub 3/ showed higher sensitivity to the step structure compared to those on SrTiO/sub 3/. This was due to re-deposition of substrate material at the steps prepared using the conventional IBE process resulting in a very low yield of unstable SQUIDs. High yield of low 1/f noise stable SQUIDs was obtained on LaAlO/sub 3/ substrates with sharp steps prepared using an optimized IBE process. A typical 1/f noise corner frequency of about 10 Hz at 77 K with two major temperature dependencies was obtained. The temperature dependencies of the 1/f noise could be correlated to the junction and the film of washer area of the SQUIDs. The white noise of our devices showed a dependency mainly on the amplitude of the flux to voltage transfer function signal. The operating temperature range of the SQUIDs could be controlled by the step structure and narrowed when the optimal operating temperature range was increased. All the measured junctions of our devices on the modified steps showed RSJ type behavior with a moderate decrease of the R/sub N/ versus temperature.         First-order high-T/sub c/ single-layer gradiometers: Parasitic effective area compensation and system balance    C. Carr, E.J. Romans, A.J. Millar, A. Eulenburg, G.B. Donaldson and C.M. Pegrum Summary: We have previously reported an anti-parallel two-SQUID coupling scheme which can significantly improve the balance of first-order HTS single-layer gradiometers, and therefore improve the device performance in unshielded environments. We report on the behaviour of such devices fabricated on 10/spl times/10 mm/sup 2/ and 30/spl times/10 mm/sup 2/ STO bicrystal substrates. We present detailed studies of the balance of such devices, with particular emphasis on the time-dependent behaviour in unshielded environments, and with the device in motion.         Low T/sub c/ SQUID measurement system for magnetic relaxation immunoassays in unshielded environment    A. Haller, H. Matz, S. Hartwig, T. Kerberger, H. Atzpadin and L. Trahms Summary: A novel technique for detecting immunochemical reactions based on a SQUID measurement system has recently been demonstrated. The reaction partners are labeled by magnetic nanoparticles which, after an immunochemical reaction, display changes of their magnetic relaxation behaviour due to a reduction of their mobility. We have developed a SQUID system dedicated to magnetic relaxation immunoassays (MARIAs) operating in unshielded environment. The system consists of 6 SQUID magnetometers electronically combined to a second-order gradiometer. The gradiometer is formed by electronic subtraction of FLL output signals or by the Three SQUID Gradiometer approach. By evaluating the amplitude of relaxation signals (average of 4 magnetization cycles) a minimum amount of (selected) Fe/sub 2/O/sub 3/-particles corresponding to 600 pmol Fe was detected demonstrating the potential of the measurement system for biochemical laboratory diagnostics.         Geophysical exploration using magnetic gradiometry based on HTS SQUIDs    C.P. Foley, D.L. Tilbrook, K.E. Leslie, R.A. Binks, G.B. Donaldson, J. Du, S.K. Lam, P.W. Schmidt and D.A. Clark Summary: Magnetic tensor gradiometry provides gradient components of true potential fields which enables unique depth estimates and improves analytic signal methods as well as providing a number of other advantages. A high temperature SQUID (HTS) gradiometer can provide measurements of the components of the earth's field tensor creating a new tool for mineral exploration. A successful comparison between a HTS SQUID gradiometer and a Cs-vapour gradiometer under survey conditions has been conducted. Both instruments were configured vertically. The HTS gradiometer measured the B/sub zz/ component of the gradient tensor, while the Cs-vapor gradiometer measured the vertical gradient of the total magnetic intensity. The HTS gradient measurement was the difference in output between two coaxial SQUID sensors. Effective noise levels achieved were 0.16-0.3 nT/m RMS, compared with 0.1-0.5 nT/m RMS for the Cs-vapor system. The SQUID noise was dominated by vibration with additional contributions from the multiplexed sampling between the SQUIDs. This paper reports on the system development, design issues, trial results and the implications for geophysical exploration.         Testing Einstein's equivalence principle at Bremen Drop Tower using LTS SQUID technique    W. Vodel, H. Koch, S. Nietzsche, J.V. Zameck Glyscinski, R. Neubert and H. Dittus Summary: Free fall tests to prove the Weak Equivalence Principle (WEP) were rarely be done in history. Although they seem to be the natural experiments to test the equivalence of inertial and gravitational mass, best results for WEP-proofs could be attained with torsion pendulum tests to an accuracy of 10/sup -12/ because these pendulum tests are long term periodic experiments, Otherwise, free fall tests on Earth can be carried out only for seconds causing certain principle limitations. Nevertheless, very precise fall tests in the 10/sup -13/ range are possible and under preparation to be carried out on Drop Tower Bremen during free fall over 109 m. A level of accuracy of 10/sup -18/ will be achieved in the current STEP (Satellite Test of the Equivalence Principle) space mission of NASA/ESA. Both kinds of experiments require position detectors with an extremely high resolution to measure infinitesimal displacements of freely falling test masses. On the basis of the LTS SQUID system of the Jena University an experimental set-up was developed containing a pair of superconducting levitated test masses installed in a vacuum chamber at 4.2 K. The resolution of the SQUID position detector was measured to be as high as 4/spl times/10/sup -14/ m//spl radic/Hz. This whole apparatus was successfully tested and dropped at the Drop Tower Bremen providing a free fall height of 109 m corresponding to a flight time of 4.7 s. Recent results of this measurements are described in this work.         Low noise HTS dc-SQUID flip-chip magnetometers and gradiometers    M.I. Faley, U. Poppe, K. Urban, D.N. Paulson, T.N. Starr and R.L. Fagaly Summary: We have fabricated HTS dc-SQUID flip-chip sensors with a large area multilayer flux transformers. Different layouts of the flux transformers provide a large variety of magnetometers and planar gradiometers. For the magnetometers a resolution /spl sim/6 fT//spl radic/Hz and the planar gradiometers a resolution of about /spl sim/30 fT/cm./spl radic/Hz were routinely obtained at 77 K. The noise was nearly white down to frequencies of few Hz. The sensors were vacuum-tight encapsulated together with a heater and a feedback coil. This makes the handling of the sensors more reproducible and convenient. Production of the magnetometers and gradiometers in small series was proven.         On-wafer measurements of nonlinear effects in high temperature superconductors    J.C. Booth, L.R. Vale and R.H. Ono Summary: We present the results of comprehensive on-wafer microwave probe station measurements of the nonlinear properties of coplanar waveguide devices patterned from high-temperature superconductor (HTS) thin films. We introduce a sequence of measurements and analysis that is designed to describe the nonlinear response of microwave devices in increasingly general terms, and that verifies the resulting description with a number of different nonlinear measurements of different patterned devices. We demonstrate the use of this methodology to analyze the nonlinear response of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films at 76 K, and find that all of our measurements can be satisfactorily explained by a current-dependent penetration depth of the form /spl lambda/=/spl lambda//sub 0/[1+(J/J/sub 0/)/sup 2/]. The parameter J/sub 0/ is a current-density scale that describes the strength of the material nonlinearity, and can be used as a suitable parameter for optimizing film growth techniques.         Vortex pairs and nonlinear inductance of high-T/sub c/ superconducting microwave resonators    T. Dahm and J. Oppenlander Summary: Recently, an unusual power dependence of two-tone intermodulation has been observed in high-T/sub c/ superconducting microwave resonators. In order to address this problem, we study the nonlinear response of a two dimensional Josephson junction array as a coupled grain model for the high-T/sub c/ films. On a microscopic scale the calculated current distributions within the array show a strong tendency to form topological Josephson vortices which organize themselves in vortex-antivortex clusters even in the absence of an external magnetic field. These vortex clusters are stable within an external ac drive and cause a redistribution of the input current. The resulting current distributions possess pronounced transversal components. On the macroscopic scale such current distributions lead to a nonlinear inductance that varies linearly with the magnitude of the input current consistent with the observed power dependence. This result suggests the dynamics of topological Josephson vortices within the coupled grains as a possible explanation for the unusual nonlinear response.         Nonlinear simulation and characterization of devices with HTS transmission lines using harmonic balance algorithms    C. Collado, J. Mateu and J.M. O'Callaghan Summary: This work presents the use of Harmonic Balance to simulate the nonlinear behavior of HTS transmission lines. Good agreement with theoretical cross-checks is found. We also show the use of this algorithm to fit the model of HTS lines from experimental measurements. We illustrate this by fitting several types of experimental data, and discuss how to avoid ambiguity in this fitting.         Electronics Abstracts (2000 - Part 1)    No author information available Summary: Abstracts of papers not included in the conference proceedings. The full papers may appear in a later issue of IEEE Transactions on Applied Superconductivity.         Author Index (2000 - Part 1)    No author information available Summary: Not available

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