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1994 Part 3     Front Cover (1994 - Part 3)    No author information available Summary: Not available         Table of Contents (1994 - Part 3)    No author information available Summary: Not available         Superconducting cueing receiver for space experiment    T.C.L.G. Sollner, W.G. Lyons, D.R. Arsenault, A.C. Anderson, M.M. Seaver, R.R. Boisvert and R.L. Slattery Summary: Exploiting the high-temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO), we have extended chirp-transform processing to instantaneously analyze the spectrum of an incoming signal over greater bandwidth than any competing technology. A compact receiver has been developed that can analyze a 3 GHz bandwidth in 120 ns with 110 MHz resolution. The cryogenic YBCO chirp filter and ambient-temperature semiconductor electronics have been space qualified for flight on the US Navy's High-Temperature Superconductivity Space Experiment, a package to be launched on the US Air Force ARGOS scientific satellite.         Design and performance of low-noise hybrid superconductor/semiconductor 7.4 GHz receiver downconverter    J.B. Barner, J.J. Bautista, J.G. Bowen, W. Chew, M.C. Foote, B.H. Fujiwara, A.J. Guern, B.J. Hunt, H.H.S. Javadi, G.G. Ortiz, D.L. Rascoe, R.P. Vasquez, P.D. Wamhof, K.B. Bhasin, R.F. Leonard, R.R. Romanofsky and C.M. Chorey Summary: Low noise receivers play critical role in space applications. Thin film high-critical-temperature-superconducting (HTS) passive circuits were combined with GaAs microwave devices to achieve ultra low noise and small size receiver downconverter at 77 K. HTS pre-select filter, a cryogenic mixer, and a hybrid oscillator with an HTS resonator were designed, fabricated and interconnected to produce a low-noise hybrid superconductor/semiconductor 7.4 GHz microwave receiver. When cooled to 77 K, the downconverter plus cables inside a cryogenic refrigerator had a noise figure of approximately 0.7 dB with conversion gain of 18 dB. In addition to reduce noise figure, advantages of small size and low power consumption are observed due to the use of HTS circuits in the downconverter.         High-temperature superconducting four-channel filterbanks    S.H. Talisa, M.A. Janocko, D.L. Meier, C. Moskowitz, R.L. Grassel, J. Talvacchio, P. LePage, G. Hira, D.C. Buck, S.J. Pieseski, J.C. Brown and G.R. Wagner Summary: A high-temperature superconducting four-channel filterbank was fabricated and tested. The device was made in microstrip configuration with an architecture that included two branch-line hybrids and two identical parallel-coupled line filters per channel. The filterbank was fully integrated, with microstrip interconnections between channels and thin-film load terminations in the out-of-phase port of the output hybrid.         YBCO/ferrite low-loss microwave phase shifter    G.F. Dionne, D.E. Oates and D.H. Temme Summary: Microstrip-geometry phase shifters have limited use at microwave frequencies because of high insertion losses resulting from resistance in the metal conductors. We report a phase shifter fabricated from a YBa/sub 2/Cu/sub 3/O/sub 7-x/ microstrip line on LaAlO/sub 3/ coupled to a ferrite toroid. The magnetic flux required for gyromagnetic interaction with the microwave signal is contained within the closed magnetic path of the ferrite toroid so that the superconductor encounters a very low external magnetic field. Initial measurements at 77 K using a meanderline structure to provide nonreciprocal operation have demonstrated greater than 700 deg of differential phase shift at 10 GHz in a compact structure 2.5 cm long by 0.5 cm wide. The insertion loss is smaller than 0.7 dB which yields a figure of merit considerably greater than 1000 deg/dB. The best conventional phase shifters have an estimated figure of merit of 300 deg/dB at 77 K. Potential radar system applications and improvements in the figure of merit are discussed.         YBCO step edge junctions on various substrates    C.L. Pettiette-Hall, J.A. Luine, J. Murduck, J.F. Burch, R. Hu, M. Sergant and D. St. John Summary: We have fabricated YBCO 90/spl deg/ grain boundary junctions on step edges in NdGaO/sub 3/ and in deposited dielectric (CeO/sub 2/ on YSZ and SrTiO/sub 3/ on MgO) in order to compare junction performance to our standard, LaAlO/sub 3/. Average I/sub c/R/sub n/ values at 77 K in the 300-400 /spl mu/V range were measured for 2 /spl mu/m step edge junctions on NdGaO/sub 3/, LaAlO/sub 3/, and SrTiO/sub 3//MgO. Junction I/sub c/ is greatly reduced with the CeO/sub 2//YSZ system. I/sub c/R/sub n/ values in the 300-400 /spl mu/V range were measured at 65 K for 4 /spl mu/m junctions.         Proximity effect in edge type junctions with PrBa/sub 2/Cu/sub 3/O/sub 7/ barriers prepared by Br-ethanol etching    M.I. Faley, U. Poppe, C.L. Jia, K. Urban and Y. Xu Summary: Multilayer Josephson edge type junctions were prepared on the edges of c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7/ thin films structured by chemical etching in a Br-ethanol solution. Resistive PrBa/sub 2/Cu/sub 3-x/Ga/sub x/O/sub 7/ (x=0, 0.15, and 0.3) films were deposited by the high oxygen pressure dc-sputtering technique and used for barrier and insulation layers. Basic properties of the junctions such as I/sub c/(T), I/sub c/(d), R/sub n/(T), and basic characteristics of the proximity effect such as /spl xi//sub n/, /spl gamma/ and /spl gamma//sub B/ were obtained and discussed.         Ramp type HTS Josephson junctions with PrBaCuGaO barriers    M.A.J. Verhoeven, G.J. Gerritsma, H. Rogalla and A.A. Golubov Summary: Ramp type Josephson junctions have been fabricated using DyBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// as electrode material and PrBa/sub 2/Cu/sub 3-x/Ga/sub x/O/sub 7-/spl delta// with x=0, 0.10 and 0.40 as junction barriers. Barrier thickness lie between 6-30 nm. Several junctions without barrier were made in order to find ways to minimize the damage of the ramp interface. In total about 40 chips were fabricated each containing several junctions and their I-V characteristics measured for various temperatures down to 4.2 K. Only those junctions showing clear RSJ-like curves were selected to be analyzed. In some cases we also measured I/sub c/ as a function of a small applied field and obtained a clear Fraunhofer pattern, but there is a tendency to flux trapping as evidenced by LTSEM. It was found at 4.2 K that the critical current density J/sub c/ scales with the specific resistance R/sub n/A as J/sub c/=C/sub bar/(R/sub n/A)/sup -m/ (m=1.8/spl plusmn/0.5). The barrier material dependent constant C/sub bar/ increases with x, whereas, for a given d, J/sub c/ is constant and R/sub n/A increases.         Transport properties of YBCO/PBCO/YBCO junctions    Y. Sawada, H. Terai, A. Fujimaki, Y. Takai and H. Hayakawa Summary: We studied on the transport properties of edge-type YBCO/PBCO/YBCO junctions. They showed clear Josephson characteristics with I/sub c/R/sub n/ products of a few mV. The experimental results revealed that normal-state characteristics were dominated by the tunneling via localized states. Besides, taking account of constant I/sub c/R/sub n/ products, we could consider the transport mechanism of supercurrent as the resonant tunneling.         Fabrication and characterization of high temperature superconductor Josephson junctions with a novel device design    Q.X. Jia, X.D. Wu, S.R. Foltyn, D. Reagor, M. Hawley, K.N. Springer, P. Tiwari, C. Mombourquette, R.J. Houlton, I.H. Campbell, H. Kung, T.E. Mitchell and D.E. Peterson Summary: A unique normal-metal (N) layer construction was used to fabricate high temperature superconducting (S) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// SNS Josephson junctions. The normal-metal included a gradient Pr-doped Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// layer which was composed of a light doping (x=0.1) next to both YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N-layer. A gradient of the doping profile of the N-layer instead of an abrupt one provides good thermal, structural, and chemical compatibility between adjacent regions. The multilayer configuration of the gradient Pr-doped N-layers on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// showed good growth structure as confirmed by X-ray diffraction and Rutherford backscattering channeling tests. The SNS junctions fabricated in such a way showed resistively shunted junction current vs voltage characteristics above 77 K. Microwave induced Shapiro steps above 77 K and voltage modulation of dc SQUIDs at 77 K were both demonstrated with this technology.         Properties of YBaCuO thin film single-level dc SQUIDs fabricated using step-edge junctions    J.Z. Sun, L.S. Yu-Jahnes, V. Foglietti, R.H. Koch and W.J. Gallagher Summary: A quantitative comparison study of single-level step-edge junction-based SQUIDs and bicrystal-substrate-based SQUIDs is given. Similar SQUID performance was found in terms of white flux noise level and junction-critical-current-related 1/f noise. Excess current was found in most step-edge devices. Issues related to systems applications, such as magnetic field-induced noise, junction cyclability upon repeated use, and environmental stability of oxide-metal contacts are also discussed.         The PTB 83-SQUID system for biomagnetic applications in a clinic    D. Drung Summary: The PTB 83-SQUID (superconducting quantum interference device) system is described which is operated in a clinical environment. Integrated dc SQUID magnetometers with additional positive feedback (APF) are used in order to realize electronic first- or second-order gradiometer configurations. The dewar for the system has a flat bottom. It allows the detection of vertical (B/sub z/) and horizontal (B/sub x,y/) field components: 49 sensors (plus 14 reference magnetometers) are sensitive for B/sub z/ and 14 sensors (plus 6 reference magnetometers) for B/sub x,y/. The system is installed inside a standard shielded room (Vakuumschmelze type AK3b) in the Klinikum Benjamin Franklin, Steglitz, Berlin. A typical white noise level of 2.5 fT//spl radic/(Hz) has been measured in the first-order gradiometer mode. Due to the very low system noise level it became possible for the first time to detect the extremely weak neuromagnetic fields (5-10 fT peak amplitude) generated by the nerve roots deep in the lower back which are evoked by electrical nerve stimulation at the foot (200 Hz system bandwidth, 8000 responses averaged).         Noise cancellation by a whole-cortex SQUID MEG system    J. Vrba, B. Taylor, T. Cheung, A.A. Fife, G. Haid, P.R. Kubik, S. Lee, J. McCubbin and M.B. Burbank Summary: We report on the noise cancellation performance of several whole-cortex MEG systems operated under diverse noise conditions, ranging from unshielded environments to moderately shielded rooms. The noise cancellation is performed by means of spatial filtering using high order gradiometers (2nd or 3rd), which can be formed optionally either by SQUID electronics firmware or by software. The spatial dependence of the gradiometer responses was measured in an unshielded environment and compared with simulations to yield an estimate of the system common mode magnitudes relative to field, 1st, and 2nd gradients. High order gradiometers were also formed when the system was operated in moderately shielded rooms. The combination of the spatial filtering and room shielding resulted in very high combined noise rejections approaching that of high quality shielded rooms. Examples of noise cancellation under various conditions are shown.         Superconducting magnetic sensors operating from a moving platform    T.R. Clem Summary: Sensors incorporating Superconducting Quantum Interference Devices (SQUIDs) provide the greatest sensitivity for magnetic anomaly detection available with current technology, The Coastal Systems Station (CSS) has pioneered the use of superconducting magnetic sensors in the field operating onboard airborne and undersea moving platforms, where environmental and instrument noises present operational problems which are not encountered under laboratory conditions. Basic conceptual approaches for utilizing these sensors onboard moving platforms, including field deployable sensor configurations, are described. Environmental and instrumental technical issues are also addressed. A historical sketch of sensor development, current sensor capabilities, recent technology advances, and future trends is included. Naval applications and dual use opportunities for this technology are given based on experience developed at CSS.         An experimental digital SQUID with large dynamic range and low noise    Perng-Fei Yuh and S.V. Rylov Summary: A digital SQUID chip designed for large dynamic range and intrinsic sensitivity as good as an analog SQUID was fabricated and tested. It consists of a pickup coil, a SQUID amplifier, edge-triggered latching comparators, and a feedback loop using an integrating single-flux-quantum D/A converter. Proper operation of the chip was demonstrated, with the output one-bit data stream averaged and integrated to reconstruct the input signal. A sampling rate up to 500 MHz was achieved.         Design and performance aspects of pickup loop structures for miniature SQUID magnetometry    M.B. Ketchen and J.R. Kirtley Summary: As miniature SQUID susceptometers and scanning SQUID microscopes come into wider use, it is important to understand in detail the magnetic coupling of objects of interest to small superconducting pickup loops as well as our ability to scale such pickup loop structures to sub-/spl mu/m dimensions. In this paper we address important aspects of both of these issues. First, assuming a perfect circular pickup loop, we examine the coupling to three-dimensional objects and arrive at a number of simple practical results for measurements on small samples with various geometries and positions. Second, we examine the nature of small superconducting pickup loop structures and the impact on scaling of factors such as connecting leads, local groundplanes and the superconducting penetration depth. We conclude that highly localized pickup areas of well under 1 /spl mu/m/sup 2/ are possible with existing technology.         High-frequency magnetic microscopy using a high-T/sub c/ SQUID    R.C. Black, F.C. Wellstood, E. Dantsker, A.H. Miklich, D. Koelle, F. Ludwig and J. Clarke Summary: We have used a liquid-nitrogen-cooled scanning SQUID microscope to obtain magnetic images at frequencies ranging from zero to 200 GHz, that is, from audio frequencies through the radio frequency band and into the millimeter microwave band. We present images of thin film and bulk metallic samples, with a spatial resolution of about 30 /spl mu/m, taken using various readout schemes we have developed.         An integrated digital SQUID magnetometer with high sensitivity input    M. Radparvar and S. Rylov Summary: A single chip SQUID magnetometer is described that integrates a SQUID-based pre-amplifier with a high sensitivity comparator gate and feedback circuitries on the same chip. The comparator gate is an asymmetric SQUID gate driving two SQUID quantizers in series with the feedback coil. The chip's sensitivity and noise level are primarily determined by the pre-amplifier SQUID. The pick up coil is in series with the feedback transformer. Since the current in the feedback coil is maintained close to zero, the dynamic range of the chip can be extremely wide and is independent of the SQUID pre-amplifier or comparator architectures. The chip's slew rate is determined by the bipolar clock biasing the comparator gate. Clocks running in the tens of MHz result in a magnetometer system with slew rate exceeding 10/sup 5/ /spl Phi//sub 0//s (/spl Phi//sub 0/=2.07/spl times/10/sup -7/ Gauss-cm/sup 2/). This chip simplifies room temperature electronics and, due to its digital output, can be easily multiplexed on-chip. A system based on this chip can be operated in a relatively high magnetic field environment without extensive magnetic shielding. The details of the chip as well as preliminary measurement results for the pre-amplifier as well as the digital circuit will be presented.         DC-SQUID electronics based on the noise cancellation scheme    M. Kiviranta and H. Seppa Summary: We have constructed a compact dc SQUID electronics unit, in which the noise of the room-temperature amplifier is measured by the SQUID and cancelled out. This makes it unnecessary to use a transformer and a modulation scheme to achieve noise matching between the SQUID and the amplifier. The electronics unit contains a PI/sup 3/2/-controller and it has demonstrated a bandwidth of 100 kHz, a 1.2 /spl mu//spl Phi//sub 0///spl radic/(Hz) white noise level and a 1/f noise corner of 0.3 Hz in a flux-locked loop mode. The design criteria for the noise-cancelled electronics are discussed, including the problem of excess noise.         Portable DC SQUID based magnetic susceptibility meter    V.V. Khanin, J.N. Sotnikova, V.Y. Slobodchikov and A.N. Matlashov Summary: The device is designed as a top-loading system for operation in a storage helium dewar with a 1 1/4" dia neck. Sample temperature is regulated in the range of 4.2-300 K using gaseous helium fed from a helium bath. The sample diameter is up to 4.0 mm, the maximum magnetizing field 0.18 T, the magnetic moment resolution 5/spl times/10/sup -12/ A/spl times/m/sup 2/. The high sensitivity of the instrument makes it possible to investigate the magnetic susceptibility of 1 mm/spl times/1 mm HTc thin films as a function of temperature in a transverse magnetic field of about 10/sup -3/ T. The provisions for measuring the magnetizing field with the help of a Hall sensor enable samples to be cooled down in the fields below 10/sup -5/ T to measure the Meisner effect.         Application of high performance DC SQUIDs in precision measurement technique    W. Vodel, H. Koch, P. Seidel, K. Bluthner and P. Weber Summary: In this review the performance of a DC SQUID system with Nb-NbO/sub x/-Pb/In/Au window-type Josephson junctions is described. The SQUIDs and the SQUID control units were developed for universal applications in precision measurement technique. Under optimum conditions a flux noise level of 2/spl times/10/sup -6/ /spl Phi//sub 0///spl radic/Hz was achieved corresponding to an energy resolution of 3/spl times/10/sup -31/ J/Hz. The contribution gives the design of the DC SQUID device and summarizes recent results of its application in precision measurement technique. The applications include a cryogenic current comparator for non-destructive measurement of the beam intensity produced in a particle accelerator, a high-sensitive SQUID voltmeter for investigations of the low-field Hall coefficient of high purity metals, the upgrade of a multichannel RF SQUID neuromagnetometer for biomagnetic research, and a planned high-precision experiment in fundamental physics.         3-channel double relaxation oscillation SQUID magnetometer system with simple readout electronics    Y.H. Lee, J.M. Kim, H.C. Kwon, Y.K. Park, J.C. Park, M.J. van Duuren, D.J. Adelerhof, J. Flokstra and H. Rogalla Summary: Recently several approaches have been made to simplify the readout scheme of the standard dc SQUID. A double relaxation oscillation SQUID(DROS) consisting of a hysteretic dc SQUID and a reference junction in series shunted by an inductor and a resistor can provide a very large flux-to-voltage transfer coefficient. Thus, a DROS with direct readout with room temperature dc amplifier can be a good candidate for the next-generation SQUID magnetometer. We report on the development of a 3-channel magnetometer system based on DROS. The DROS is based on Nb/AlO/sub X//Nb Josephson junctions and the main feature of the system is its simple readout electronics.         High sensitivity magnetic flux sensors with direct voltage readout: double relaxation oscillation SQUIDs    D.J. Adelerhof, M.J. van Duuren, J. Flokstra, H. Rogalla, J. Kawai and H. Kado Summary: The experimental sensitivity of double relaxation oscillation SQUIDs (DROSs) has been compared with theory and with the results obtained by numerical simulations. The experimental sensitivity ranges from 60 to 13h, where h is Planck's constant, for relaxation frequencies from 0.4 up to 10 GHz. For low frequencies the DROS characteristics can be explained by thermal noise on the critical currents. For high frequencies, the voltage-flux characteristics and the sensitivity are limited by the plasma frequency. The cross-over frequency is at 2 GHz, which is about 2% of the plasma frequency of the DROSs.         Theoretical analysis of a relaxation oscillation SQUID    M. Morisue, M. Yamadaya, A. Kanasugi and G. Uehara Summary: Describes the theoretical analysis of oscillation modes produced in a relaxation oscillation SQUID (ROS). It is made clear what kind of oscillation modes are produced in ROS in relation to circuit parameters of the SQUID from the viewpoint of relaxation oscillation. Emphasis is placed on mapping of oscillation modes to design the ROS. Furthermore, the effect of mutual inductance between the load impedance and SQUID to the oscillation frequency is analyzed.         Washer designs for SQUIDs with several junctions in a parallel array    M.E. Huber, A.T. Champion and M.W. Gleason Summary: We report on washer designs for superconducting quantum interference devices (SQUIDs) which include more than two Josephson junctions in a parallel array, and on calculations of the operating characteristics of such devices in the resistively-shunted junction model. Coupling of the operating current to the multi-junction device suppresses the voltage biased at constant current. The coupling decreases as the ratio of the mutual inductance between adjacent loops to the self inductance of a single loop approaches 0.5. In various washer designs, however, the practical limit for the ratio is no greater than about 0.4. At this value, the simulations indicate that significant reductions in voltage modulation occur for even a small number of junctions. Also, the flux responsivity increases with the number of junctions only slightly more rapidly than does the total loop area, so the sensitivity to a current in a coupling coil is nearly the same as that of a single-loop device. This trend may ultimately limit the usefulness of these devices.         Optimization of a dc SQUID magnetometer to minimize the field resolution    K. Suzuki and Y. Okabe Summary: The circuit parameters of a dc SQUID magnetometer have been optimized by computer simulations. Our principle of optimization is to minimize the field resolution. We have optimized the circuit parameters of a dc SQUID magnetometer, such as a Ketchen type, Drung type, directly-coupled type, etc. The only noise source was thermal noise from the shunt resistors. For a Ketchen type SQUID, our results show that the inductance of the input coil should be larger than that reported previously. It is also the case for a Drung type SQUID that the inductance of the SQUID washer coil should be slightly increased. By this design method, the optimum field resolution of a Ketchen type SQUID magnetometer is improved by a factor of 2/3. Furthermore, we compared the resolution of 3 types of dc SQUIDs and concluded that the optimum type of SQUID depends on the value of the critical current and the radius of the pick-up coil. Finally, we have proposed a new design method that can optimize the field resolution of dc SQUIDs under constraints on the critical current and the spatial resolution.         Investigation of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions on MgO bicrystal substrates    L. Vonderbeck, C.A. Copetti, A.M. Klushin, G. Kunkel, M. Siegel, E. Sodtke, J. Schubert and W. Zander Summary: We report on the characterization of the dynamic (ac) properties of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions on MgO bicrystal substrates with 24/spl deg/ angle. Shapiro steps have been measured in the frequency range 80-95 GHz. Measured current-voltage characteristics, as well as the dependence of Shapiro step height on microwave power, were compared to numerical simulations within the RSJ model including thermal noise. At 77 K, the junctions showed ideal RSJ behavior. The occurrence of half-integer Shapiro steps at lower temperatures could be explained by an inhomogeneous critical current density of the junctions yielding a dc SQUID-like behavior. A nonsinusoidal current-phase relation could be ruled out because of the periodicity of the half-integer steps.         Fabrication of biepitaxial YBCO Josephson junctions on different substrates    K. Petersen, C. Stolzel, M. Schmitt, C. Krimmer, W. Wilkens, J. Sollner, H.W. Grueninger and H. Adrian Summary: Biepitaxial Josephson junctions were fabricated on MgO and SrTiO/sub 3/ (STO) substrates. Electrical characteristics such as the critical current densities J/sub c/, contact resistivities /spl rho//sub n/ and I/sub c/R/sub n/-products on both substrates are investigated. Junctions on MgO substrates are stable against thermal cycling in contrast to many junctions on STO substrates. The obtained current-voltage characteristics and Shapiro step oscillations are in agreement with the RSJ-model. The resistive transitions are strongly broadened. DC-SQUIDs patterned on both substrates show modulations dV/d/spl Phi/ at 77 K. At 55 K the energy resolution /spl epsi/ in the range of white noise lies within a factor of two of the theoretical limit.         Critical current density distribution and magnetic flux states in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bicrystal grain boundary Josephson junctions    G.M. Fischer, B. Mayer, H. Schulze and R. Gross Summary: We have studied the spatial homogeneity of the critical current density J/sub c/ and static magnetic flux states in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bicrystal grain boundary Josephson junctions (GBJs) using Low Temperature Scanning Electron Microscopy (LTSEM). By LTSEM the J/sub c/ distribution and the static magnetic flux states in the GBJs could be imaged with a resolution of less than 1 /spl mu/m. Varying the applied magnetic field B the different magnetic flux states with up to more than 15 vortices in the GBJ could be observed. The spatial variation of the measured LTSEM voltage signal agrees well with the theoretically expected signal according to the sinusoidal modulation of the maximum Josephson current density by an external magnetic field. The LTSEM analysis clearly demonstrates that the spatial variation of J/sub c/ along the grain boundary is less than about 30% on the length scale of the spatial resolution of the LTSEM technique.         Supercurrent density correlation function of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grain boundary Josephson junctions    O.M. Froehlich, H. Schulze, A. Beck, R. Gerdemann, B. Mayer, R. Gross and R.P. Huebener Summary: We have measured the thermal noise induced slope R/sub p/(B) of the current-voltage characteristics of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Grain Boundary Josephson Junctions (GBJs) for I/spl rarr/0 in magnetic fields up to B=12 T. From the measured R/sub p/(B) dependences the magnetic field dependence of the critical current I/sub c/(B) was derived in the large magnetic field range between 0 and 12 T. Finally, the supercurrent density correlation function was obtained from the I/sub c/(B) dependence using the Wiener-Khinchine relation. By introducing the concept of the bright (BGCF) and dark ground correlation function (DGCF) a spatial filtering of the information on the supercurrent density distribution was obtained. The investigation of the BGCFs and the comparison to DGCFs gives clear evidence that supercurrent density has strong inhomogeneities on small length scales in the nanometer regime.         Fabrication and superconducting transport properties of bicrystal grain boundary Josephson junctions on different substrates    A. Beck, A. Stenzel, O.M. Froehlich, R. Gerber, R. Gerdemann, L. Alff, B. Mayer, R. Gross, A. Marx, J.C. Villegier and H. Moriceau Summary: We have reproducibly fabricated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) grain boundary Josephson junctions (GBJs) on SrTiO/sub 3/ and MgO bicrystals as well as by introducing buffer layers between the c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// film and the SrTiO/sub 3/ bicrystal substrate. For the additional layers non-superconducting Nd/sub 1.85/Ce/sub 0.15/CuO/sub x/ (NCCO) and NdGaO/sub 3/ were used. The effect of the layer structure on the superconducting transport properties of the GBJs was analyzed by measuring the current-voltage characteristics (IVCs), their derivatives, the resistive transition R(T), and the magnetic field dependence of the critical current I/sub c/(B). YBCO-GBJs fabricated on MgO and SrTiO/sub 3/ bicrystal substrates were found to have very similar low frequency characteristics. Fiske resonances were investigated to obtain information on the high-frequency properties. The Swihart velocity was found to be considerably smaller for GBJs fabricated on SrTiO/sub 3/ as compared to MgO due to the large relative dielectric constant of SrTiO/sub 3/ and the related stray capacitance.         Microwave-enhanced superconductivity and transport properties of Y-Ba-Cu-O bicrystal weak-links    C.M. Fu, J.Y. Juang, M.F. Chen, K.H. Wu, T.M. Uen and Y.S. Gou Summary: The effects of the tilt angle on microwave-enhanced transition temperatures and critical currents of YBCO bicrystal weak-links have been investigated. It was found that, with smaller grain boundary tilt angles (e.g. 24/spl deg/), the enhancement was small, displaying essentially the same behavior as that manifested in intragranular regions. By contrast, when the tilt angle was increased from 36.8/spl deg/ to 45/spl deg/, noticeable Tc enhancement was found to occur even at low input microwave powers. The results were compared to the temperature dependent critical current, in order to delineate possible correlations between the two physical parameters.         Parallel plate resonators in YBa/sub 2/Cu/sub 3/O/sub 7/ bicrystal grain boundaries    Y.M. Zhang, D. Winkler, G. Brorsson and T. Claeson Summary: Intrinsic properties, such as the London penetration depth /spl lambda//sub L/, and the surface resistance R/sub s/, can be estimated in high-T/sub c/ films by studying self-induced electromagnetic resonances (Fiske modes) in bicrystal grain boundaries. Grain boundaries, 4-30 /spl mu/m long and 0.2 /spl mu/m thick in YBa/sub 2/Cu/sub 3/O/sub 7/ made on yttria-stabilized zirconia 0-32/spl deg/ [001]-tilt bicrystals were investigated. Typical values obtained for /spl lambda//sub L/ and R/sub s/ (at approximately 200-400 GHz) are 110-170 nm, and 20-710 m /spl Omega/, respectively.         Effect of the misorientation angle on the magnetic properties of YBCO grain boundary Josephson junctions    T. Ogawa and T. Yamashita Summary: We have studied magnetic properties of YBa/sub 2/Cu/sub 3/O/sub x/ grain boundary Josephson junctions (GBJJs) fabricated on SrTiO/sub 3/ bicrystal substrates to investigate whether the Josephson characteristics change or not owing to the variation of the misorientation angle. When the misorientation angle was 36.8/spl deg/, the total current was periodically suppressed by the applied field; the current component was almost Josephson current. On the contrary, for the GBJJs (/spl theta/=24/spl deg/), the n-th minima (n/spl ges/2) in the Ic(B) patterns did not occur at zero; a constant non-Josephson current (bulky supercurrent) contribution to the patterns was present. The results were also identified from the existence of an excess current in the I-V curves (/spl theta/=24/spl deg/) and a residual supercurrent in the strong magnetic field dependence of Ic for the GBJJs with /spl theta/=24/spl deg/ (the field was applied up to 14 T). Next, the junction homogeneity was investigated from the differences between measured Ic(B) patterns and that of an ideal Josephson junction. Contrary to expectation, the deviations of the GBJJs with /spl theta/=24/spl deg/ or /spl theta/=36.8/spl deg/ from an ideal Ic(B) pattern corresponded; the first minima did not occur at zero, then the first maxima occurred at higher values than normalized ideal case (I/sub 1-th minima//Ic/sub MAX//spl ap/0.22). As a result, the current density distribution is considered as an asymmetrical current density profile peaked at the junction edges. Last, we have tried to control Jc on the same tilt angle by changing the laser power in the pulsed laser deposition process. The results showed Jc varied at the range of about two order.         Ba/sub 1-X/K/sub X/BiO/sub 3/ grain boundary junctions prepared on SrTiO/sub 3/ bicrystal substrates    S. Imaeda, M. Inoue, A. Fujimaki and H. Hayakawa Summary: We succeeded in the fabrication of Ba/sub 1-X/K/sub X/BiO/sub 3/ artificial grain boundary junctions prepared on SrTiO/sub 3/ bicrystal substrates. These junctions showed the Josephson current and the energy gap structure in the I-V characteristics. In a magnetic field, the critical current was modulated and the I/sub c/-B curve showed a clear Fraunhofer pattern. Fiske steps were also observed in the I-V characteristics. In the radiation of 10.5 GHz microwaves, Shapiro steps were observed.         Excess low-frequency noise in YBCO thin-film devices    J.C. Macfarlane, Ling Hao, C.M. Pegrum and G.B. Donaldson Summary: Excess low-frequency noise degrades the performance of many of the high T/sub c/ superconducting devices that have been proposed or demonstrated. We report measurements of noise in grain-boundary junctions and flux-flow amplifier devices that have been fabricated in several different laboratories. The system is calibrated in terms of absolute noise temperature, and its voltage noise sensitivity is below 0.1 nVHz/sup -1/2/. Device characteristics and noise have been measured as a function of junction area, critical current, temperature, bias current and magnetic field. Noise levels in a fixed frequency band of 40-60 kHz are reported, as well as the frequency dependence between 0.1 Hz and 60 kHz. Noise temperatures exceeding the device physical temperature at certain levels of bias current are attributed to fluctuations in critical current and normal tunnelling resistance. Noise due to magnetic flux motion is also seen. We compare results with available theory and other relevant data in the literature, and assess the practical effects of noise on the performance of high T/sub c/ devices such as SQUIDs, flux flow amplifiers and bolometers.         Niobium SIS mixers at 490 GHz, 690 GHz and 810 GHz    C.E. Honingh, K. Jacobs, S. Haas, D. Hottgenroth and J. Stutzki Summary: Low noise mixers are developed for a dual channel heterodyne receiver for astronomical applications which will operate alternatingly in two of three the frequency bands 460-490 GHz, 660-690 GHz, and 800-850 GHz. As mixing elements Nb-Al/sub 2/O/sub 3/-Nb (SIS) tunnel junctions are used, fabricated at the University of Cologne with integrated RF and IF circuitry, also made of niobium. The frequency dependent RF-properties of the circuitry are calculated for all bands using Mattis-Bardeen theory in the extreme anomalous limit. The circuits are optimized for a large instantaneous receiver bandwidth to facilitate the use of waveguide type mixer mounts without mechanical tuners. Results on receiver noise, stability and design accuracy will be presented.         Fabrication and mixer performance of Nb/Al double-barrier junctions    T. Lehnert, Sheng-Cai Shi and T. Noguchi Summary: Specific difficulties of the fabrication of Nb/Al double-barrier junctions with high current density (10 kA/cm/sup 2/) and small area (1-3 /spl mu/m/sup 2/) are discussed and possible solutions are presented. The problem of nonuniform areas of the two superposed junctions was circumvented by introducing a loading effect in the etching process. Strong backbending of the I/V-curve was reduced by increasing the thickness of the Nb layer between the two superposed junctions. In a mixer experiment in the 100 GHz frequency band a broad-band response of the double-barrier device was obtained with a minimum receiver noise temperature of 45 K at 115 GHz.         Modulation of self-resonant modes in NbCN/MgO/NbCN junctions by quasiparticle injection    S. Kohjiro, S. Kiryu, A. Shoji, S. Kodaira and S. Takada Summary: In the submillimeter wave region, we have studied the modulation of self-resonant modes in NbCN/MgO/NbCN Josephson junctions (detectors). The tuning mechanism is based on the quasiparticle injection via an overlaid tunnel junction (injector). From the current-voltage characteristics of detectors, the maximum shift of resonant frequencies /spl Delta/f and Q factors due to electrode loss at the injected state Q/sub inj/ have been estimated to be /spl Delta/f/f(0)=0.11 and Q/sub inj/=100 at 470 GHz, where f(0) is the resonant frequency without quasiparticle injection. It is found Q/sub inj/ decreases with increase of the injector bias voltage.         An SIS mixer using two junctions connected in parallel    T. Noguchi, Sheng-Cai Shi and J. Inatani Summary: We have fabricated a superconductor-insulator-superconductor (SIS) mixer using a couple of junctions connected in parallel through a stripline inductor. The junctions have significantly larger area, i.e. larger capacitance, and smaller normal resistance than conventional ones. In order to obtain a good impedance matching between the source and the junctions, an impedance transformer made of a superconducting stripline was integrated with the junctions. The capacitance of the junctions was tuned out by the inductor to obtain a broadband operation without mechanical tuning elements. It was shown that the double sideband noise temperature of the receiver employing this type of mixer device was less than 40 K over the bandwidth of 90-115 GHz. The lowest receiver noise temperature of /spl sim/20 K, which is only 4 times as large as the quantum limited photon noise of hv/k/sub B/, was obtained around 105 GHz.         Hot electron quasioptical NbN superconducting mixer    B.S. Karasik, G.N. Gol'tsman, B.M. Voronov, S.I. Svechnikov, E.M. Gershenzon, H. Ekstrom, S. Jacobsson, E. Kollberg and K.S. Yngvesson Summary: Hot electron superconductor mixer devices made of thin NbN films on SiO/sub 2/-Si/sub 3/N/sub 4/-Si membrane have been fabricated for 300-350 GHz operation. The device consists of 5-10 parallel strips each 5 /spl mu/m long by 1 /spl mu/m wide which are coupled to a tapered slot-line antenna. The I-V characteristics and position of optimum bias point were studied in the temperature range 4.5-8 K. The performance of the mixer at higher temperatures is closer to that predicted by theory for uniform electron heating. The intermediate frequency bandwidth versus bias has also been investigated. At the operating temperature 4.2 K a bandwidth as wide as 0.8 GHz has been measured for a mixer made of 6 nm thick film. The bandwidth tends to increase with operating temperature. The performance of the NbN mixer is expected to be better for higher frequencies where the absorption of radiation should be more uniform.         A heterodyne receiver at 533 GHz using a diffusion-cooled superconducting hot electron bolometer mixer    A. Skalare, W.R. McGrath, B. Bumble, H.G. LeDuc, P.J. Burke, A.A. Verheijen and D.E. Prober Summary: This paper describes heterodyne measurements at 533 GHz using a novel superconducting hot electron bolometer in a waveguide mixer block. The bolometer is a thin (10 nm) and narrow (0.1 /spl mu/m) strip of niobium with a length of less than half a micron and a critical temperature of approximately 5.5 K. The short length ensures that diffusion dominates over electron-phonon interaction as a cooling mechanism for the hot electrons, thus allowing heterodyne detection with intermediate frequencies of several GHz. A Y-factor response of 1.15 dB has been obtained at an intermediate frequency of 1.4 GHz with hot/cold load temperatures of approximately 295/77 K, indicating a receiver noise temperature around 650 K DSB. The IF response extends up to at least 2 GHz and possibly higher.         Signal resolution of RSFQ comparators    T.V. Filippov, Y.A. Polyakov, V.K. Semenov and K.K. Likharev Summary: We have designed and tested a Rapid Single-Flux-Quantum (RSFQ) circuit for experimental measurement of the fluctuation-induced threshold uncertainty of switching of SFQ comparators, which are essential components of RSFQ logic devices, analog-to-digital converters, and digital SQUIDs. Statistical density of the switching events in comparators using externally-overdamped Nb-trilayer Josephson junctions has been found to be in agreement with the distribution which follows from a simple theory based on a time-dependent harmonic-oscillator model of the device. Width of the distribution (i.e, the single-shot current resolution of the comparator) measured as a function of temperature in the range 1.7-4.2 K corresponds to fundamental (thermal/quantum) fluctuations, with no evidence of excess noise sources.         Design and testing of QOS comparators for an RSFQ based analog to digital converter    D.K. Brock, S.S. Martinet, M.F. Bocko and J.X. Przybysz Summary: Successful utilization of the quasi one-junction SQUID (QOS) as a signal comparator for analog-to-digital conversion (ADC) has been demonstrated by several groups, This idea is extended to show how similar comparators can be integrated into an all rapid single flux quantum (RSFQ) digital architecture. Comparators are interrogated by SFQ sampling pulses and in turn give output according to the RSFQ convention. One- and two-bit ADC's have been simulated, fabricated and tested at low speed. Total performance of these devices is estimated within the framework of a multiple bit parallel flash ADC architecture.         Two-loop modulator for sigma-delta analog to digital converter    J.X. Przybysz, D.L. Miller and E.H. Naviasky Summary: A two-loop modulator has been designed for a superconductive sigma-delta analog to digital converter. In contrast to semiconductor modulators, which use high-gain amplifiers in the signal feed forward path, the superconductive modulator used digital gain in the signal feedback path. The use of superconductive electronics to precisely feed back a single flux quantum into the second integrator loop and multiple flux quanta into the first integrator loop is a key to this circuit. In simulations of a 40 GHz sampling rate, the modulator obtained a 98 dB signal to noise ratio on the dc-60 MHz band. The modulator tolerated thermal noise well, obtaining 98 dB SNR on the dc-4 MHz band, while sampling at a rate of 4 GHz. The modulator tolerated clock timing jitter better than Nyquist-rate A/D converters, obtaining equivalent performance with 3 times as much rms jitter. Compared to single-loop sigma-delta and oversampled lobe-counting A/D converters, the two-loop modulator can achieve equivalent performance at a significantly reduced sampling and digital filter rate.         Design of SFQ-counting analog-to-digital converter    J.C. Lin, V.K. Semenov and K.K. Likharev Summary: We describe the design of an oversampling single-flux-counting analog-to-digital converter with the estimated bandwidth of a few tens of MHz, based on Rapid Single-Flux-Quantum (RSFQ) devices. It consists of an input analog circuit, high-speed quantizer with an original analog/digital negative feedback loop, decimation (comb) filter, and supporting subsystems including clock distribution circuits, quantization signal conditioner, and output drivers. We have applied a new approach, the 'symmetrizing' negative feedback, to free the quantizer from the intrinsic hysteresis without dynamic range sacrifice. The 16-bit version of the system comprises about 1,500 Josephson junctions and consumes 1.2 mW of DC power, when implemented using Nb-trilayer technology with 1 kA/cm/sup 2/, 3.5 /spl mu/m Josephson junctions. All subsystems of the converter have been successfully tested and testing of the system as a whole is in progress.         Superconducting high-resolution A/D converter based on phase modulation and multichannel timing arbitration    S.V. Rylov and R.P. Robertazzi Summary: We have developed a flux-quantizing A/D converter (ADC) based on RSFQ elements, employing a novel front end capable of generating high-linearity multibit differential code within a wide dynamic range (up to 16 bits). The front end operates as a phase modulator/demodulator and uses fractional-flux-quantum least significant bit (LSB). It runs at multi-GHz speed, enabling ADCs with large oversampling ratio and effective resolution in excess of 20 bits (after decimation filtering). We have designed, fabricated and tested several versions of a complete ADC using this new architecture and demonstrated its operation with dynamic range of 14 bits. We have also confirmed continuous phase modulation of the flux quantizer with a carrier frequency of 10 GHz.         Design and high-speed testing of a superconducting delta-sigma oversampled converter    P.H. Xiao, D. Hebert, S.R. Whiteley and T. Van Duzer Summary: A delta-sigma modulator with a lowpass filter can achieve the same signal-to-noise ratio (SNR) and dynamic range as a delta-sigma modulator with an integrator by adjusting the cut-off frequency of its lowpass filter. A lowpass filter modulator in superconducting niobium technology was designed and tested up to a 1 GHz sampling rate and was shown to be operating correctly. The bits of a pseudo-random bit stream digital output are acquired individually by a high-speed logic analyzer. The acquired data show 6 bits of modulator dynamic range, which is limited below the simulated value of 11 bits, at least in part, by errors in the test equipment.         Operation of Josephson comparator under Josephson noise from SQUID    E. Takeda, T. Nishino and K. Takagi Summary: Operation of a Josephson comparator for analog-to-digital conversion of signal from a SQUID is studied. In the study, a test circuit consisting of the SQUID and the comparator is used. The measured result shows that the comparator responds to AC noise due to the AC Josephson effect. Numerical simulation shows amplitude, which is determined from the response of the comparator, is smaller than the original AC noise amplitude. The difference comes from low-pass characteristics of the Josephson junction in the comparator due to the turn-on delay. The delay is effective in reducing the AC noise, and provides a means for the accurate conversion.         Microwave properties of voltage-tunable YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ coplanar waveguide transmission lines    D.C. DeGroot, J.A. Beall, R.B. Marks and D.A. Rudman Summary: To explore the electrical characteristics of monolithic microwave circuits with integrated high-temperature superconductor and ferroelectric materials, we fabricated a series of coplanar waveguide transmission lines in laser-deposited YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and SrTiO/sub 3/ thin films. We characterized the voltage-tunable two-port microwave response of the transmission lines at cryogenic temperatures using a calibrated network analyzer system. Total phase shifts and phase tuning in these devices increased for increasing ferroelectric film thickness with only moderate increases in transmission loss.         Optical switching of HTS band reject resonators    E.R. Soares, K.F. Raihn, N.O. Fenzi and G.L. Matthaei Summary: A method for optically switching HTS (High Temperature Superconducting) band reject resonators is presented. Fast low loss switching of HTS filter elements enable digital selecting of arbitrary pass bands and stopbands. Each switch element must preserve the high Q of the HTS filter element in one switch state, and remove the HTS filter element without adding loss in the other state. Patterned pieces of GaAs are used as the switch. Fiber optic cabling is used to bring the optical energy to the cryogenic package. This minimizes the thermal loading of the filter package. Cryogenic switching of a single resonator is discussed, as well as integration of the switching method to entire filters and banks of fibers. Measured and modeled data are compared.         A 4 bit instantaneous frequency meter at 10 GHz with coplanar YBCO delay lines    M. Biehl, A. Vogt, R. Herwig, M. Neuhaus, E. Crocoll, R. Lochschmied, T. Scherer, W. Jutzi, H. Kratz, P. Berberich and H. Kinder Summary: A device on a single 2"-LaAlO/sub 3/ wafer for a four bit instantaneous frequency measurement between 9.5 GHz and 10.5 GHz has been developed with coplanar YB/sub 2/Cu/sub 3/O/sub 7-/spl delta// delay lines and power dividers. Compared to known triplate strip lines, coplanar delay lines are easier to fabricate monolithically and allow for a greater flexibility in the circuit design. Simulated and measured results are in good agreement.         An integrated 11 GHz cryogenic downconverter    W.A. Phillips, D. Jedamzik, K. Lamacraft, S. Zammattio, R.B. Greed, S.J. Hedges, P.R. Whitehead, B.F. Nicholson, T.W. Button, P.A. Smith, N.M. Alford, N. Peters and J. Grier Summary: A cryogenic downconverter has been designed and built to demonstrate the integration of semiconducting and superconducting components in a complete subsystem cooled by a closed cycle Stirling cryocooler. The frequency selective receiver converts 11 GHz (X-band) signals to an IF of 1000 MHz using a high temperature superconducting (HTS) microstrip input filter with a 1% bandwidth, a silicon diode mixer and a local oscillator stabilized by means of a 10 GHz HTS cavity and driven by a GaAs HEMT. The components are packaged into a cryogenic unit cooled to 60 K. Details of the system integration are presented, together with microwave and thermal test results.         A superconducting and integrated microwave transmitter and receiver in microstrip using thick-film YBCO    M.W. Hosking, Y.G. Proykova, A. Hewitt, N.McN. Alford and T.W. Button Summary: Results are presented of the design and performance of a microstrip transmitter/receiver circuit using thick-film yttrium barium copper oxide on a yttria-stabilised zirconia substrate. The resonant circuit is in the form of a ring resonator and the active component is a transferred electron device integrated within the circumference of the ring. In receive mode, the circuit operates as a self-oscillating mixer. Operating frequencies lie in the range 8 to 16 GHz and measurements include: Q-factor by injection phase locking; oscillator output power and conversion loss.         High-temperature superconducting wide band delay lines    S.H. Talisa, M.A. Janocko, D.L. Meier, C. Moskowitz, R.L. Grassel, J. Talvacchio, P. LePage, D.C. Buck, R.S. Nye, S.J. Pieseski and G.R. Wagner Summary: Stripline non-dispersive delay lines with 20 GHz of bandwidth were designed and fabricated using YBCO thin films deposited on both sides of 2-inch-diameter, 10-mil thick LaAlO/sub 3/ wafers. A double-wound spiral configuration was used yielding a line length of approximately 150 cm. Novel approaches were used to minimize the effect of air gaps between the two substrates needed to form the stripline structure, and to realize a wide band transition from the coaxial external connections to stripline. Experimental results showed 5 dB of insertion loss at 20 GHz, with 1 dB amplitude ripple over most of the 0-20 GHz, range for a 22.5 ns delay.         A robust fabrication process for a refractory integrated SQUID gradiometer    D. Hutson, R.G. Weston, R.J.P. Bain, M.J. Lawrenson, C.M. Pegrum, K. Popova and R. Scarfone Summary: We describe a process used successfully to fabricate large second-order planar gradiometers with integrated DC SQUIDs on two-inch silicon wafers. All the refractory materials (Nb, Mo and SiO/sub 2/) are deposited by magnetron sputtering. The Josephson junctions are based on the well-established Nb/AlO/sub x//Nb trilayer technology. All Nb layers are patterned by Reactive Ion Etching using a procedure optimized by experimental design. Since only one gradiometer can fit on a wafer, extra care had to be taken in both the design of the device and the fabrication process to ensure that the yield was high. Excellent process latitude is achieved by sufficient built-in design margins to accommodate any tolerance difficulties during fabrication.         Effects of aluminum over-layer thickness on characteristics of niobium tunnel junctions fabricated by DC magnetron sputtering    A. Nakayama, H. Nagashima, J. Shimada and Y. Okabe Summary: We have fabricated Nb/AlO/sub x//Nb Josephson tunnel junctions using a sputtering apparatus with a load-lock system. The junctions that had 50 /spl mu/m/spl times/50 /spl mu/m area showed a V/sub m/ value (the product of the critical current and the subgap resistance at 2 mV) as high as 50 mV at a current density of 160 A/cm/sup 2/. Moreover, junctions having different thicknesses of the Al overlayer were concurrently fabricated on one wafer to study the dependence of the current-voltage characteristics on this Al over-layer. The I-V characteristics were also calculated by McMillan's tunneling model and were compared with the measured I-V characteristics.         Superconducting integrated circuit fabrication with low temperature ECR-based PECVD SiO/sub 2/ dielectric films    J.E. Sauvageau, C.J. Burroughs, P.A.A. Booi, M.W. Cromar, R.P. Benz and J.A. Koch Summary: A superconducting integrated circuit fabrication process has been developed to encompass a wide range of applications such as Josephson voltage standards, VLSI scale array oscillators, SQUIDs, and kinetic-inductance-based devices. An optimal Josephson junction process requires low temperature processing for all deposition and etching steps. This low temperature process involves an electron cyclotron resonance-based plasma-enhanced chemical vapor deposition of SiO/sub 2/ films for interlayer dielectrics. Experimental design and statistical process control techniques have been used to ensure high quality oxide films. Oxide and niobium etches include endpoint detection and controlled overetch of all films. An overview of the fabrication process is presented.         Fabrication of submicron Nb/AlO/sub x/-Al/Nb tunnel junctions using focused ion beam implanted Nb patterning (FINP) technique    H. Akaike, T. Watanabe, N. Nagai, A. Fujimaki and H. Hayakawa Summary: We have successfully fabricated 0.2 /spl mu/m/sup 2/ Nb/AlO/sub x//Nb tunnel junctions using the focused-ion-beam implanted Nb patterning (FINP) technique for junction definition. The success was due to improvement of the edge profile of the counter electrode. The vertical edge profile was realized with the large etching selectivity of Ga implanted Nb over unimplanted Nb by controlling the reactive neutrals in the plasma. The critical current I/sub c/ and the quality parameter V/sub m/ of 0.2 /spl mu/m/sup 2/ junctions were 10.5 /spl mu/A and 11 mV, respectively. The R/sub sg//R/sub n/ was 12. The maximum to minimum spread in I/sub c/ of 60 series junctions with areas of 0.5 /spl mu/m/sup 2/ was /spl plusmn/10%.         The fabrication and characterization of NbCN/AlN heterostructures    Z.H. Barber, D.M. Tricker and M.G. Blamire Summary: Very high quality niobium nitride based superconductor-insulator-superconductor (SIS) junctions have been prepared using aluminium nitride barrier layers deposited by dc reactive magnetron sputtering. These barriers have been shown to grow epitaxially on high quality epitaxial niobium carbonitride (NbCN) base electrodes. High total gap voltages, equal to the maximum that can be expected theoretically, illustrate that there are no degraded layers at the superconductor/insulator interfaces. We have also demonstrated the first SISIS double barrier devices. Transmission electron microscopy has been used to study the growth of a thick AlN layer sandwiched between NbCN and the microstructure of NbCN/AlN multilayers prepared with several different orientation relationships.         Nb/AlN/Nb Josephson junctions with high critical current density    A.W. Kleinsasser, W.H. Mallison and R.E. Miller Summary: We have produced Nb/AlN/sub x//Nb Josephson tunnel junctions with the aims of improving the control of critical current density J/sub c/ in the high-J/sub c/ range and exploring the possibility of high-J/sub c/ junctions with low subgap quasiparticle currents. Conventional Nb/AlO/sub x//Nb junction barriers are formed by oxidizing a thin Al overlayer on the Nb base electrode, and precise control of the oxidation process is difficult at low levels of oxygen exposure. The reactivity of Al with N/sub 2/ is very low, and AlN/sub x/ barriers are therefore formed using an N/sub 2/ plasma. We report the fabrication of AlN/sub x/ barrier junctions with J/sub c/ as large as 4 mA//spl mu/m/sup 2/ and compare their properties to Nb/AlO/sub x//Nb ones of similar J/sub c/.         NbN/AlN/NbN tunnel junctions fabricated at ambient substrate temperature    Z. Wang, A. Kawakami, Y. Uzawa and B. Komiyama Summary: We have prepared NbN/AlN/NbN tunnel junctions at ambient substrate temperature. The AlN barriers are fabricated by reactive rf magnetron sputtering in the N/sub 2/ sputtering gas. We describe the electric and crystalline properties of the NbN and AlN thin films, and discuss tunneling characteristics and the properties of the junction interface. Even though the NbN/AlN/NbN trilayers were deposited without intentional heating, the junctions had a large gap voltage (V/sub g/=5 mV), sharp quasiparticle current rise (/spl Delta/V/sub g/=0.16 mV), and small subgap leakage current (V/sub m/=25 mV). A high critical current density (J/sub c/=8 KA/cm/sup 2/) is obtained in junctions with 1.5 nm thick AlN barriers. These results show that high-quality NbN/AlN/NbN tunnel junctions can be prepared at ambient substrate temperatures.         Stress and source conditions of DC magnetron sputtered Nb films    R.S. Amos, P.E. Breyer, H.H. Huang and A.W. Lichtenberger Summary: We have studied the quality of Nb films from two different DC magnetron sources in a vein similar to previous work at Fujitsu Laboratories and NIST. In particular we are interested in the effects of target erosion on Nb film quality and on operating conditions of the magnetron sources. We find that the concept of a current-pressure (I-P) stress line of constant voltage (NIST), though giving qualitative guidance on proper source operating conditions, is not a sufficiently accurate model to set either of our magnetron source conditions over the life of the targets. In particular we find that: (1) the shape of our I-P "lines" change with target usage, (2) the stress values attributed to different points on a given I-P line at one "snapshot" in the target life are often different, and (3) the stress attributed to a given point on an I-P line may change over the life of a target. Alternative source operation strategies for maintaining stress free films will be discussed and the influence of other parameters including temperature, substrate material, source distance, substrate motion and target to target repeatability will also be examined.         Effect of growth conditions on the electrical properties of Nb/Al-oxide/Nb tunnel junctions    W.H. Mallison, R.E. Miller and A.W. Kleinsasser Summary: We have investigated the dependence of the critical current density J/sub c/ of Nb/AlO/sub x//Nb Josephson tunnel junctions on substrate temperature T/sub s/ and oxygen exposure E (the product of oxidation time and pressure) during growth. For low O/sub 2/ exposures, J/sub c/ depended sensitively on exposure, J/sub c//spl prop/E/sup -1.6/, independent of temperature for 77 K         An improved etching process used for the fabrication of submicron Nb/AlO/sub x//Nb Josephson junctions    M. Aoyagi, M. Maezawa, H. Nakagawa, I. Kurosawa and S. Takada Summary: It is important to develop a reliable and reproducible fabrication process of submicron Nb/AlO/sub x//Nb Josephson junctions to improve the integration level and the operating speed of the Josephson LSI circuit. For this purpose, we have developed an improved etching process by introducing a dummy etching process and using a scanning electron microscope (SEM) as an etching end-point detector. The dummy etching process improves the anisotropy of a reactive ion etching (RIE) process using CF/sub 4/. The etching residue around a junction is detected easily and correctly by the SEM observation. We have successfully fabricated Nb/AlO/sub x//Nb Josephson junctions with critical current density of 10/sup 4/ A/cm/sup 2/ using the cross-line patterning (CLIP) method and electron beam lithography, where the junction size was varied from 2 /spl mu/m to 0.5 /spl mu/m at 0.1 /spl mu/m intervals. High-quality submicron junctions for integrated circuits with suitable critical current variations were obtained.         Monolithic flux transformer-coupled high-T/sub c/ DC SQUID magnetometers    J.W.M. Hilgenkamp, G.C.S. Brons, S. Hoogeveen, J. Flokstra and H. Rogalla Summary: YBa/sub 2/Cu/sub 3/O/sub 7-x/ based monolithic flux transformer-coupled high-T/sub c/ DC SQUID magnetometers operating up to 73 K have been realized. The devices are characterized by high values of the modulation voltage, up to 32 /spl mu/V at 40 K. A minimal white noise level of 0.10 pT//spl radic/Hz was obtained above 200 Hz, and 0.64 pT//spl radic/Hz at 1 Hz and 55 K. The temperature dependence of the modulation voltage, the effective sensing area and the field sensitivity are discussed. Model-calculations have been performed to investigate high frequency resonances in the washer-input coil structure. Methods for damping are considered.         Integrated YBa/sub 2/Cu/sub 3/O/sub 7/ multi-loop magnetometers at 77 K    D. Reimer, M. Schilling, S. Knappe and D. Drung Summary: We present a multi-loop DC SQUID magnetometer operated at 77 K. In a multi-layer process YBa/sub 2/Cu/sub 3/O/sub 7/, PrBa/sub 2/Cu/sub 3/O/sub 7/, and SrTiO/sub 3/ films are deposited by KrF-excimer laser deposition on SrTiO/sub 3/(100) substrates. The preparation consists of four film deposition and three patterning steps. We employ YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions with artificial barriers of PrBa/sub 2/Cu/sub 3/O/sub 7/ in a ramp-type geometry. The characterization is made by electrical transport and by noise measurements. The measured magnetic field sensitivity of 1.25 nT//spl Phi//sub 0/ of our device fits well with the calculated value of 1.17 nT//spl Phi//sub 0/.         DC-SQUIDs and flux transformers in YBa/sub 2/Cu/sub 3/O/sub 7/ magnetometers at 77 K    M. Schilling, R. Scharnweber and S. Volkl Summary: For biomagnetic applications magnetometer devices are prepared in a multilayer process based on KrF-excimer laser deposition of superconductor and insulator layers as well as semiconducting barriers. For patterning conventional photolithography and argon-ion etching are used. In the DC-SQUIDs we employ Josephson junctions with artificial barriers of PrBa/sub 2/Cu/sub 3/O/sub 7/ in a ramp-type geometry. As insulating layers in the flux transformers we use SrTiO/sub 3/. Both, the DC-SQUIDs and the input-coils operate up to temperatures of 86 K. The characterisation of the devices is made by electrical transport and by noise measurements. For the use as sensitive magnetometers the DC SQUIDs are either used in inductively shunted magnetometers with galvanic coupling to a large pick-up coil or are coupled to flux transformers in a flip-chip arrangement.         SNS-DC-SQUIDs and flux transformers for integrated magnetometers in flip-chip technique    B. Meyer, J. Hollkott, C. Francke, R. Wunderlich and J. Muller Summary: YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///Ag/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson-junctions across steps in MgO substrates were used to fabricate SNS-DC-SQUIDs in the step-and-gap geometry. The necessary break of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-film at the step was confirmed by transmission electron microscopy investigations. The removal of the Ag-layer eliminates the shunt resistance on top of the HTSC which increases the normal resistance R/sub N/ by more than two orders of magnitude with only a slight reduction in I/sub C/. The junctions can be described by the SINS-formalism, which allows high I/sub C/R/sub N/-products with large values of the normal resistances R/sub N/. For thin-film flux transformer epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// trilayers were grown using a co-sputter process. Test coils exhibited a current density in excess of 8/spl times/10/sup 5/ A/cm/sup 2/ and insulation resistivities of 10/sup 8/ /spl Omega/cm at 77 K. By coupling the flux transformers to SQUIDs using a flip-chip technology the magnetic field response were increased by a factor of 9.         High-T/sub c/ superconducting image surface magnetometers    N. Tralshawala, J.H. Miller Jr. and D.R. Jackson Summary: We present an overview of the concepts of image surface magnetometry, and analyze various shapes of superconducting shields in the presence of uniform background noise fields and current sources that simulate biomagnetic sources. We show that, for certain geometries and sizes, these shields can selectively shield background noise fields as opposed to signals of interest. We also show that clever use of these shields can, in some cases, allow an undisturbed measurement of the signals of interest while attenuating noise fields by as much as four orders of magnitude.         Characteristics of a NiO barrier layer for high-T/sub c/ superconducting tunnel junction    M. Moriya, T. Hobayashi and T. Goto Summary: Characteristics of a NiO barrier layer for high-T/sub c/ superconducting tunnel junctions were investigated. Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (BSCCO) films were deposited on a MgO or SrTiO/sub 3/ substrate using a dc hollow cathode sputtering system. In situ superconducting BSCCO films deposited in Ar+20%O/sub 2/ gas at T/sub s/=680/spl deg/C on a MgO substrate were c-axis oriented 2212 phase. A NiO layer was formed by reactive sputtering in Ar+20%O/sub 2/ gas using a NiO hollow cathode, and the layer on the BSCCO film was of [100] and [110] orientation. The current-voltage characteristics of an Ag/NiO/BSCCO junction with a NiO barrier layer 5 nm thick were investigated. In the G-V curves of some junctions, a zero bias conductance peak was observed. It is assumed that this behavior is probably due to the nonuniform thickness of the barrier layer. The junction with a thicker barrier layer (18 nm) showed tunnel current characteristics without anomaly.         YBa/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) a-axis films and planar junctions    R.G. Wichern, E.M.C.M. Reuvekamp, G.J. Gerritsma and H. Rogalla Summary: In order to prepare planar junctions, multilayers were sputtered, using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// as superconductor and PrBa/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) as barrier material. The sandwiches are a-axis oriented. Out of these, single junctions were etched, planarized with CeO/sub 2/. Finally gold contacts were sputtered. The junctions are squares of size 20/spl times/20 to 100/spl times/100 /spl mu/m/sup 2/. A prerequisite for successful preparation of junctions from a-axis oriented multilayers is a study of such films. Films deposited by RF off-axis sputtering were characterized electrically, Their morphology was investigated by XRD, AFM and TEM. The films are very smooth and have a grain size of below 100/spl times/100 nm/sup 2/. To improve T/sub c/ and crystal quality, template layers were used. The T/sub c/ of a single film is about 62 K; by using a template layer up to 78 K can be reached. For a-axis oriented growth not only a reduction of the deposition temperature is important, but also the growth rate must be high enough. Best results were obtained at rates higher than 150 nm/h. The first planar junctions show a supercurrent, but otherwise rounded I-V curves.         Heterostructure applications of in-plane oriented a-axis YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on LaSrGaO/sub 4/    I. Takeuchi, Z. Trajanovic, J.L. Peng, Z.Y. Li, S.N. Mao, P.A. Warburton, C.J. Lobb and T. Venkatesan Summary: We have fabricated various heterostructures using in-plane oriented a-axis YBa/sub 2/Cu/sub 3/O/sub 7/(-x) and PrBa/sub 2/Cu/sub 3/O/sub 7/(-x) on LaSrGaO/sub 4/ substrates. Superconductor-insulator-superconductor multilayers were fabricated with LaSrGaO/sub 4/ and Nd/sub 2/CuO/sub 4/ as dielectric layers. For such structures with approximately 3000 /spl Aring/ of Nd/sub 2/CuO/sub 4/, both top and bottom layers had T/sub c/ (R=0)/spl ges/85 K. YBa/sub 2/Cu/sub 3/O/sub 7-x//PrBa/sub 2/Cu/sub 3/O/sub 7-x//YBa/sub 2/Cu/sub 3/O/sub 7-x/ ramp-edge junctions were fabricated in the b-direction of the a-axis fame, and an I/sub c/R product of 1 mV was obtained at 4.2 K.         Single and stacked Josephson junctions based on c-axis YBCO/PBCO multilayers    M.A. Bari, B. Ghyselen, E.J. Tarte, R.E. Somekh, Y. Yan, J.E. Evetts, M.G. Blamire, N.G. Chew and R.G. Humphreys Summary: Using whole wafer superconducting device technology we have fabricated vertically stacked sandwich junctions with c-axis oriented YBCO/PBCO/YBCO trilayers and double barrier junctions. The resulting devices exhibit supercurrents through 130 nm at 4.2 K. We have observed RSJ-like I-V curves, Shapiro steps and almost Fraunhofer-like dependence of the critical current as a function of magnetic field. The scaling behaviour of devices fabricated on perovskite (SrTiO/sub 3/ and LaAlO/sub 3/) and MgO substrates differ. The results indicate a certain uniformity for the barriers on the scale of the size of the junction. We propose different mechanisms for supercurrent and quasiparticle transport through the PBCO barrier for the two substrate types.         Anomalous temperature dependence of critical current in YBaCuO/PrBaCuO/YBaCuO trilayer Josephson junctions    H. Akoh, H. Sato and S. Takada Summary: We have observed an anomalous temperature dependence of the critical current I/sub c/ in all (103)-oriented YBaCuO/PrBaCuO/YBaCuO trilayer Josephson junctions with barrier thicknesses of 50 nm and an Ar plasma treatment for the barriers. I/sub c/ of the junction increases drastically at around 40 K as temperature is increased, has a maximum value at about 65 K, and decreases towards the critical temperature of the junction. The normal resistance of the junction, on the other hand, decreases exponentially with increasing temperature. The anomalous temperature dependence of I/sub c/ may come from the proximity effect, taking into account the semiconductor-like properties of the PrBaCuO barrier.         YBCO/metallic oxide/YBCO trilayers for high-T/sub c/ superconducting SNS junctions    Xiaofan Meng, O. Takahashi and T. Van Duzer Summary: Some metallic oxides are prospective barrier materials for high-T/sub c/ superconducting SNS junctions. Among them, SrVO/sub 3/ is a metallic oxide with a bulk resistivity of 1-1000 /spl mu//spl Omega/-cm and a cubic perovskite-type crystal structure. The lattice constant of SrVO/sub 3/ is 3.84 /spl Aring/ which is close to that of the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO, a=3.82 /spl Aring/, b=3.89 /spl Aring/). We report the fabrication of metallic SrVO/sub 3/ thin films and YBCO/SrVO/sub 3//YBCO trilayers using pulsed laser ablation. The crystal structure and surface morphology of the films were studied by X-ray diffraction and AFM. The electrical properties of the films were measured by the standard four probe method. The potential application of SrVO/sub 3/ thin films for the barriers of high-T/sub c/ superconducting SNS junctions is discussed.         Properties of tunnel junctions with [103]YBa/sub 2/Cu/sub 3/O/sub y//SrTiO/sub 3//[013]YBa/sub 2/Cu/sub 3/O/sub y/ layered structure    T. Matsui, T. Suzuki, H. Kimura, D. Yamaguchi, A. Ueda and H. Kamijo Summary: Properties of tunnel junctions have been studied in a [103]-oriented YBa/sub 2/Cu/sub 3/O/sub y//SrTiO/sub 3//[013]-oriented YBa/sub 2/Cu/sub 3/O/sub y/ ([103]YBCO/STO/(013)YBCO) layered structures. In the junctions, we observed similar electrical properties to those in [001]-oriented YBCO/barrier/[001]-oriented YBCO junctions, such as broad gap like structure and a conductance peak at zero bias voltage. Cross-sectional observation for the junction revealed that facets were mainly formed by [100]-, [010]- and [001]-planes at the bottom of the top [103]YBCO layer and by [010]- and [001]-planes at the bottom [013]YBCO surface, respectively. The observation also revealed the existence of amorphous-like layers at both the top [103]YBCO/STO and STO/bottom [013]YBCO interfaces.         Fabrication and properties of YBCO tunnel junctions by ion beam sputtering    X.Y. Cai, K. Usami, T. Kobayashi and T. Goto Summary: Au/SrTiO/sub 3//YBCO tunnel junctions were fabricated by ion beam sputtering. The electrodes of YBCO and SrTiO/sub 3/ barrier layer were deposited on MgO [100] substrate at 700/spl deg/C and 550/spl deg/C respectively. The electrodes of YBCO had a T/sub c/ of 70/spl sim/80 K. SrTiO/sub 3//YBCO bilayers have been examined by X-ray diffraction and the results show that both the YBCO and barrier layer were well oriented. The current-voltage (I-V) and dV/dI-V characteristics of the junctions were measured. In a pin hole free junction, the resistance dip, corresponding to the density of states, was obtained at voltage of 22 mV.         The effect of trapped flux upon the magnetic field dependence of the critical current of Josephson junctions    E.J. Tarte, H.W. Lean and J.R. Waldram Summary: Measurements of the magnetic field dependence of the critical current I/sub c/(B) of Josephson junctions, involving high temperature superconductors, often give evidence that the supercurrents are spatially non-uniform. However, flux trapping can complicate the interpretation of I/sub c/(B) curves. A model has been developed for the behaviour of SNS type junctions in a trilayer geometry containing trapped flux. We have investigated, using this model, combined with simulations, how the features of the I/sub c/(B) curve change as the number of trapped fluxlines increases. For a uniform junction, flux-trapping distorts the I/sub c/(B) curve and suppresses the maximum critical current by 1//spl radic/N/sub f/ where N/sub f/ is the number of fluxlines. The effect of trapped flux on current density correlation functions derived using the Wiener-Khinchine theorem from I/sub c/(B) curves has also been investigated and is described. In addition we discuss the relevance of the model to planar geometries.         A microwave technique for characterization of SNS and grain-boundary junctions    J. Wosik, Lei-Ming Xie, M.F. Davis and J.C. Wolfe Summary: We have utilized a magnetic field modulated microwave absorption technique for characterizing SNS and grain-boundary junctions. The technique is based on the measurements of the first derivative microwave absorption P, with respect to an applied magnetic field B at 9.5 GHz, as a function of dc magnetic B/sub dc/. A homodyne detection system is used. Due to flux quantization in a non-uniform junction a series of equally spaced microwave absorption lines can be observed for B/sub dc/ and, in strongly coupled junction cases, the dependence of I/sub c/ on magnetic field and temperature can be extracted. Both the intra-grain boundary in a melt-textured YBa/sub 2/Cu/sub 3/O/sub x/ bulk material and thin film single grain boundary junction (GBJ) YBa/sub 2/Cu/sub 3/O/sub x/ were investigated. The result of the measurements agrees with a model in which the grain boundary consists of several sub-junctions in parallel.         Epitaxial growth of NbN and NbC/sub x/N/sub 1-x/ films on 3C-SiC film-covered Si wafers    A. Shoji, S. Kiryu and S. Kohjiro Summary: Epitaxial NbN and NbC/sub x/N/sub 1-x/ (x<0.3) films were fabricated on 3C-SiC film-covered Si wafers. It is found that epitaxial NbN films fabricated on 3C-SiC/Si substrates have about one degree higher T/sub c/'s than those for epitaxial NbN films fabricated on MgO substrates. T/sub c/ and normal-state resistivity of fabricated epitaxial NbC/sub x/N/sub 1-x/ films depended on the 3C-SiC overlayer thickness of substrates. From results of R-T characteristic measurements, it is deduced that contact resistance of 3C-SiC and NbN strongly depends on the growth orientation of crystals.         Oxygen annealing of ex-situ YBCO/Ag thin-film interfaces    J.W. Ekin, C.C. Clickner, S.E. Russek and S.C. Sanders Summary: The resistivity of YBCO/Ag interfaces has been measured for different oxygen annealing temperatures for a series of ex-situ fabricated thin-film contacts having sizes from 16 /spl mu/m/spl times/10 /spl mu/m down to 4 /spl mu/m/spl times/4 /spl mu/m. The interface resistivity began to decrease after annealing at 10 minutes in one atmosphere oxygen. After annealing at 400/spl deg/C, the contact resistivity decreased by several orders of magnitude to the 10/sup -7/ range. The 500-nm thick Ag layer showed surface diffusion and agglomeration for annealing temperatures above 400/spl deg/C; this temperature thus represents a practical limit for oxygen annealing the YBCO/Ag interface system for more than 10 minutes. Rapid cooling of the chip after annealing led to a severe loss of critical current density in the YBCO layer, which could be restored by reannealing and cooling at a slower rate of 50/spl deg/C/min. The relative shape of the conductance-vs.-voltage characteristics of the YBCO/Ag interface were essentially unaltered by oxygen annealing; the overall parabolic shape, superconducting gap features, and magnetic-scattering zero bias anomaly remained constant, even though the contact conductance increased by several orders of magnitude. These data suggest main reduction in interface resistivity enhancement of the effective contact area, not a change in interface conduction mechanism.         Evidence for tunneling and magnetic scattering at in situ YBCO/noble-metal interfaces    S.C. Sanders, S.E. Russek, C.C. Clickner and J.W. Ekin Summary: We report low-temperature conductance data for in situ YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)/Ag, YBCO/Au, and YBCO/Pt planar c-axis interfaces. Analysis of the conductance data for these interfaces, which have resistivities as low as 1/spl times/10/sup -8/ /spl Omega//spl middot/cm/sup 2/, indicates that tunneling is the predominant transport mechanism. Zero-bias conductance peaks are present for all of the in situ interfaces. These peaks are analyzed in the framework of the Appelbaum model and are attributed to the presence of isolated magnetic spins at the interface. The presence and similarity of the peaks for each noble-metal overlayer supports the hypothesis that the magnetic spins are inherent to the YBCO surface.         Electrical interface structure in YBa/sub 2/Cu/sub 3/O/sub 7-x//metal contact    H. Terai, A. Fujimaki, Y. Takai and H. Hayakawa Summary: We have investigated the electrical contacts between YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) and Au. The dI/dV characteristics of the c-axis-oriented YBCO/Au/Nb junctions reveal the existence of a tunnel barrier at the YBCO/Au interface. The experimental results of the YBCO/LaGaO/sub 3//Au/Nb junction suggest p-type degenerate semiconductor-like behavior of YBCO along the c-axis direction. The anomalously small I/sub c/R/sub n/ of a few /spl mu/V in the c-axis direction are interpreted as the band bending at the YBCO surface. On the other hand, the experimental I/sub c/R/sub n/ value of 120 /spl mu/V in the a-axis-oriented YBCO/Au/Nb junction is understood within the scope of conventional theory.         The YBCO[001]/Ag interface: correlation between specific contact resistance and interfacial microstructure    Z.H. Gong, J.K. Grepstad and R. Fagerberg Summary: The influence of the sample temperature during metallization on the electrical performance of silver contacts to c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films has been investigated. The specific contact resistance, /spl rho//sub c/, was measured for contacts of different lateral dimensions, prepared by in situ Ag deposition at different temperatures and defined by standard photolithography. When corrected for a non-uniform current distribution, this data shows that on average /spl rho//sub c/ is at least a factor 4 lower for contacts prepared by metallization on a heated (T/sub sub//spl ap/600/spl deg/C) YBCO surface than for contacts prepared by metallization at room temperature (RT). The improved electrical performance correlates with a distinct difference in the interfacial microstructure of similar contacts, previously observed with high-resolution transmission electron microscopy.         Combined photodiode and high-T/sub c/ transition edge bolometer function on zirconia buffered silicon membranes    E. Steinbeiss, W. Michalke, H. Neff and B. Schwierzi Summary: We report on a novel photoreceiver on silicon membranes, comprising both, an efficient photodiode or quantum detector and a transition edge bolometer on the same substrate material. The photodiode action of the device originates from the silicon substrate and delivers a fast optical response, with a limited sensitivity range at wavelength <1.1 /spl mu/m. The bolometer response, in contrast, is broadband, but rather slow with response times in the ms regime. The combination of both detectors thus represents a new optical receiver concept, and should be useful for a broad range of optical applications.         Reduced temperature processing of YSZ buffer layers for HTSC transition edge bolometers    M. Burnus, T. Heidenblut, G. Hefle, O.K. Semtchinova, B. Schwierzi, W. Michalke, E. Steinbeiss, H. Neff and J. Laukemper Summary: Using the steep change in the resistance at the superconducting transition edge a sensitive and spectral broadband membrane type bolometric detector prototype was developed. Response S, noise equivalent power NEP and the time constant /spl tau/ were examined. Employing inhibit technology and prefabrication of silicon membranes, the developed process sequence clearly separates the fabrication into silicon processing technology and commonly explored HT/sub c/-superconductor deposition with impact on cost effective future batch fabrication. Buffer layer epitaxy at reduced deposition temperature improves production yield (membranes!) and a recently developed passivation technique saves process steps. Applying the maximum bias current the bolometer prototypes already reveal detectivities in excess of 1/spl times/10/sup 8/ [cm Hz/sup 1/2/ W/sup -1/] and a time constant of the order of milliseconds.         Microfabricated free-standing epitaxial Y-Ba-Cu-O microbolometers on silicon substrates    R. Barth, J. Siewert, B. Spangenberg, C. Jaekel, H. Kurz, B. Utz, W. Prusseit, H. Kinder and H. Wolf Summary: The fabrication sequence of Y-Ba-Cu-O air-bridge microbolometers on silicon substrates is described. A comparison of air-bridge microbolometers and bolometers on bulk silicon is given. The bolometric response of the bolometers is studied with chopped IR illumination at a wavelength of 1.3 /spl mu/m. The influence of the fabrication technique on the bolometer performance is discussed. Measurements of the voltage noise in free-standing Y-Ba-Cu-O microbolometers are presented and compared with the predicted values.         Progress toward a low-noise temperature regulation using a superconductive high-T/sub c/ microbridge    E. Lesquey, C. Gunther, S. Flament, R. Desfeux, J.F. Hamet and D. Robbes Summary: Our results measuring I-V characteristics of YBCO/MgO microbridges show that large current sensitivities (10 mA/K) as a function of temperature can be obtained, roughly independently of the applied voltage V up to a few hundred mV. This offers the possibility of working with high values of the dynamic resistance so that the phonon noise associated to the thermal boundary resistance, located at the YBCO/MgO interface, becomes dominant. A noise equivalent temperature of 10/sup -8/ K//spl radic/Hz (T=85 K, f>1 kHz) has already been obtained in a 0.2/spl times/12/spl times/10 /spl mu/m/sup 3/ microbridge. We describe a process involving the periodical sampling of the I-V characteristics that eliminates 1/f amplifier noise and returns the current value (temperature dependent) at fixed voltage bias (/spl plusmn/1 mV). This output, locked to a reference voltage through a commercial temperature regulator, leads to temperature fluctuations less than 100 /spl mu/K/sub pp/ in a 10 Hz bandwidth. These results are promising to enhance performances of high-T/sub c/ microbolometers as infrared detectors.         Optical mixing in thin YBa/sub 2/Cu/sub 3/O/sub 7-x/ films    M. Zorin, G.N. Gol'tsman, B.S. Karasik, A.I. Elantev, E.M. Gershenzon, M. Lindgren, M. Danerud and D. Winkler Summary: High quality, j/sub c/ (77 K)>10/sup 6/ A/cm/sup 2/, epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ films of 50 nm thickness were patterned into ten parallel 1 /spl mu/m wide strips. The film structure was coupled to a single-mode fiber. Mixer response was obtained at 0.78 /spl mu/m using laser frequency modulation and an optical delay line. Using two semiconductor lasers at 1.55 /spl mu/m wavelength the beating signal was used to measure the photoresponse up to 18 GHz. Nonequilibrium photoresponse in the resistive state of the superconductor was observed. Bolometric response dominates up to 3 GHz, after which the nonequilibrium response is constant up to the frequency limit of our registration system. Using an electron heating model the influence of different thermal processes on the conversion loss has been analyzed. Ways of increasing the sensitivity are also discussed.         Thermal budget simulations and device performance of microstructured high-T/sub c/ transition edge bolometers on silicon    M. Berg, J. Laukemper, H. Neff, E. Steinbeiss, W. Michalke, M. Burnus and T. Heidenblut Summary: Silicon represents the material of choice for fast superconducting high quality transition edge bolometers. The performance of these devices sensitively depends on their thermal properties where the heat flux critically affects time constant, optical response and noise behavior. In this work extensive numerical Finite Element-calculations have been performed for various bolometer configurations, using the ABAQUS-code. A high degree of thermal isolation can be established through microstructuring techniques. The bolometric performance of a prototype device is compared with the simulated data. Values of the detectivity D* as high as 1/spl times/10/sup 10/ cm Hz/sup 1/2/ W/sup -1/ already should be feasible, while a time constant in the regime below 10 ms would be retained.         Silicon ion implantation of YBaCuO films for bolometer application    X. He, J. Musolf, E. Waffenschmidt, K. Heime, H. Wolf and K. Pierz Summary: Silicon ion implantation was used to shift the critical temperature of YBaCuO films continuously to lower temperatures. The variation of T/sub c/ and other superconducting properties with ion fluence was investigated in detail. Based on these results a new bolometer structure was designed, fabricated and characterised. The sensor area of the bolometer consists of a locally implanted area with a lower critical temperature, while the contact pads and connecting lines retain the original T/sub c/. At the operating temperature the bolometer has a exactly defined temperature sensitive area and shows a lower contact resistance. Finally the feasibility of integrated bolometer arrays is discussed.         Mixing and detection in YBaCuO step-edge Josephson junction arrays up to 670 GHz    J. Konopka, I. Wolff, S. Beuven and M. Siegel Summary: Submillimeter wave detectors and mixers based on YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step-edge Josephson junctions incorporated into planar antennas were designed and tested up to 670 GHz at temperatures from 12 to 65 K. A quasi-optic coupling system with a LaAlO/sub 3/ lens was used. In some samples the noise intrinsic in the detection process does not follow the Johnson noise law but has a minimum, which for a given sample may occur in the temperature range between 35 to 50 K. Harmonic mixing recorded at 670 GHz proves that the system equilibrium is established in a time shorter than 500 fs.         A 380 ps, 9.5 mW Josephson 4-Kbit RAM operated at a high bit yield    S. Nagasawa, Y. Hashimoto, H. Numata and S. Tahara Summary: We have developed a Josephson 4-Kbit RAM with improved component circuits and a device structure having two Nb wiring layers. A resistor coupled driver and sense circuit are improved to have wide operating margins. The fabrication process is simplified using bias sputtering, as a result, its reliability is increased. The RAM is composed of approximately 21000 Nb/AlO/sub x//Nb Josephson junctions, Mo resistors, Nb wirings, and SiO/sub 2/ insulators. Experimental results show a minimum access time of 380 ps and power dissipation of 9.5 mW. Maximum bit yield of 84% is obtained in minimum magnetic field of about 20 /spl mu/G. We confirm that most of fail bits are caused by trapped magnetic flux, and the RAM functions properly for 98% of the memory cells after measuring fail bit map several times.         Characterization of a superconductive sigma-delta analog to digital converter    D.L. Miller, J.X. Przybysz, D.L. Meier, Joonhee Kang and A.H. Worsham Summary: Sigma-delta analog to digital converters (ADCs) use a combination of oversampling and feedback to concentrate quantization noise outside the frequency band of interest. Subsequent digital filtering can then be used to suppress the quantization noise and yield a large signal to noise ratio. Sigma-delta ADCs dominate the high performance audio market, where the signal band is limited to frequencies below 50 kHz and 8 octave oversampling requires a sampling rate of only 25.6 MHz. Przybysz et al. have described a superconductive circuit capable of >40 GHz sampling, thereby extending the useful bandwith to tens of MHz. In this paper, we describe the realization of that circuit and present measurements of its performance. Spectral analysis of the modulator performance shows spur-free dynamic range of over 78 dB and third order intermodulation products less than -68 dBc. Quantization noise shaping is also demonstrated.         Design of a 10 K NbN A/D converter for IR focal plane array sensors    L.R. Eaton, D.J. Durand, R. Sandell, J.W. Spargo and T. Krabach Summary: We are implementing a 12 bit SFQ counting ADC with parallel-to-serial readout using our established 10 K NbN capability. This circuit provides a key element of the analog signal processor (ASP) used in large infrared focal plane arrays. The circuit processes the signal data stream from a Si:As BIB detector array. A 10 mega samples per second (MSPS) pixel data stream flows from the chip at a 120 megabit bit rate in a format that is compatible with other superconductive time dependent processor (TDP) circuits being developed. We will discuss our planned ASP demonstration, the circuit design, and test results.         Implementation of a FFT radix 2 butterfly using serial RSFQ multiplier-adders    O.A. Mukhanov and A.F. Kirichenko Summary: We have designed a Decimation-in-Time (DIT) radix 2 butterfly integrated circuit. This circuit will be used to implement the 32-point Fast Fourier Transform (FFT) in a parallel data flow architecture. The radix 2 butterfly circuit uses serial RSFQ math and consists of four single bit-wide serial multipliers and eight carry-save serial adders. The circuit with 16-bit word-length employs only 3400 junctions, occupies an area of 3.8/spl times/2.0 mm/sup 2/, and dissipates less than 1.1 mW power. The multiplier is implemented using the unique RSFQ bit-clock-pipelined schema. We have successfully tested a library of serial multiply-add elements: the 8-bit multiplier at 6.3 GHz and adders with dc bias margin /spl plusmn/20%. Finally, we have demonstrated full operation of the radix 2 butterfly chip with 5-bit word length.         Development of a biomagnetic measurement system for brain research    M. Ueda, A. Kandori, H. Ogata, Y. Takada, T. Komuro, K. Kazami, T. Ito and H. Kado Summary: The tail of the dewar of the authors' system has a special shape that makes it possible to measure the brain activity of anyone lying on a bed regardless of head shape or size. It allows the parietal, one side of the temporal and the occipital regions to be measured simultaneously. In the system, 128 axial first-order gradiometers are mounted at intervals of about 26 mm. The diameter and baseline length of the pickup coil are 14 mm and 50 mm, respectively. The authors use square-shaped double-washer DC-SQUIDs with additional positive feedback to improve the flux resolution. System reliability is improved by hermetically sealing the SQUID in a ceramic package and including a heater resistor to eliminate trapped flux. To decrease the liquid helium evaporation rate, output cables are made with flexible printed circuits. The read-out electronics are based on the Direct Offset Integration Technique, which is a highly simplified feedback method. The white noise level measured in a magnetically shielded room is less than 10 fT//spl radic/Hz above 5 Hz. This system has successfully been applied to measuring auditory evoked fields.         Active noise compensation for multichannel magnetocardiography in an unshielded environment    W.A.M. Aarnink, P.J. Van Den Bosch, T.-M. Roelofs, M. Verbiesen, H.J. Holland, H.J.M. Ter Brake and H. Rogalla Summary: A multichannel high-T/sub c/-SQUID-based heart scanner for unshielded environments is under development, Outside a magnetically shielded room, sensitive SQUID measurements are possible using gradiometers. However, it is difficult to realize large-baseline gradiometers in high-T/sub c/ materials, Therefore, the authors developed two active noise compensation techniques. In the Total Field Compensation technique, a Helmholtz type coil set is placed around the sensors. One magnetometer is used as a zero detector controlling the compensation current through the coil set. For Individual Flux Compensation, the reference signal is sent to the separate SQUIDs (or their flux transformer circuits) to compensate the local environmental noise fluxes, The latter technique was tested on low-T/sub c/ rf-SQUID magnetometers, each sensor set to a field resolution SQUID magnetometers, i.e. 0.1 pT/sub RMS///spl radic/Hz. The authors were able to suppress the environmental disturbances to such an extent that magnetocardiograms could be recorded in an ordinary environment. Here the two suppression techniques are described and experimental results are presented.         Development of semi-portable DC-SQUID magnetometer    A. Kandori, M. Ueda, H. Ogata and H. Kado Summary: A semi-portable DC-SQUID magnetometer with a liquid helium continuous flow cryostat has been developed. The cryostat is 340 mm long and 50 mm in outer diameter. The pick-up coil is a co-axial, first order, differential type, 20 mm in diameter and 30 mm in baseline. The distance between the pick-up coil and the outer surface of the cryostat is 5 mm. It is easy to set this cryostat on the chest wall or on a human head. The cool down time is about 20 minutes, which is much shorter than that for a conventional storage Dewar. The white noise level, measured in a magnetically shielded room, is 8.7 fT//spl radic/Hz at 30 Hz. Noise at 1 Hz is about 30 fT//spl radic/Hz. Noise from temperature fluctuations (<9 mK) and drift (4.22 K /spl sim/ 4.55 K) is negligible. The consumption rate of liquid helium is 10 l/h. Here, the authors show the measurement of a magnetocardiogram in a magnetically shielded room.         Image processing techniques for NDE SQUID systems    C.H. Barbosa, A.C. Bruno, L.F. Scavarda, E.A. Lima, P. Costa Ribeiro and C. Kelber Summary: Image processing techniques were used to enhance magnetic data generated by SQUID nondestructive evaluation of conducting plates. The process consists of low-pass filtering the acquired data with a FIR filter with order depending on the standoff distance and background noise. In addition a high-pass FIR filter is used to enhance the magnetic field disturbance due to the flaw. The technique was tested on magnetic field data generated through a dc current applied to flawed aluminum test samples, and detected by using an RF-SQUID system. It was observed that when the standoff distance exceeds 5 times the size of the flaw, image inspection is difficult. Applying the enhancement algorithm, magnetic field disturbances could be visualized at distances 10 times the size of the flaw.         Measurements of surface-breaking flaws in ferromagnetic plates by means of an imaging SQUID susceptometer    A.C. Bruno, A.P. Ewing and J.P. Wikswo Jr. Summary: We detected sub-millimeter surface-breaking flaws in ferromagnetic plates using an imaging SQUID susceptometer. The normal component of the field was imaged with an axial, first order gradiometer with 3 mm diameter coils and a 4 cm baseline. We mapped the field above mild steel test samples, detecting field distortions due to surface flaws with volumes as small as 0.1 cubic millimeter. A comparison is made with conventional flux leakage methods. Our method of observing distortions in a perpendicularly applied field may be more sensitive for detecting surface-breaking flaws. Image enhancement techniques successfully removed background signals with low spatial frequencies.         Magnetomechanical behavior of steel via SQUID magnetometry    J. Banchet, J. Jouglar, P.-L. Vuillermoz, P. Waltz and H. Weinstock Summary: Steel bars were subjected to stress-strain hysteresis cycles in a horizontal tensile-testing machine while changes in the vertical component of the magnetic field above these bars was recorded by a DC SQUID second-order gradiometer. Magnetic Barkhausen noise was observed after repeated cycling and especially at stress levels for which the magnetic field was at an extremum value. Of greatest practical interest is the fact that the area of the magnetomechanical hysteresis loop (/spl Delta//spl Phi//sub z/-/spl sigma/) increased dramatically-by orders of magnitude-over a large number (up to 10/sup 5/) of fatigue cycles. This may have important implications for the in situ nondestructive evaluation of steel.         Eddy current evaluation of airframes using refrigerated SQUIDs    W.N. Podney Summary: A superconductive quantum interference device, RF SQUID, fixed to the cold pad of a Heliplex HS-4 refrigerator shows a baseline noise of 1.6/spl times/10/sup -4/ flux quanta in a one hertz bandwidth at frequencies above about 25 Hz. The refrigerator adds noise below 25 Hz. Remote pickup loops couple flux to the SQUID through a cryogenic umbilical, 500 mm long, attached to the cold pad. It enables scanning a 100/spl times/100 millimeter section of airframe without moving the expander, which connects to compressors through flexible gas lines 3 m long. Thermal conduction through copper braiding in the umbilical keeps pickup loops at 5.5 K, 3 mm from an airframe at ambient temperature. Drive currents of a few amperes, oscillating at one to three hundred Hertz enable identifying 5 to 10 percent material loss through 10 to 15 mm of aluminium.         Integrated LTS gradiometer SQUID systems for measuring of magnetic field distributions in an unshielded environment    P. Weber, V.M. Zakosarenko, K.-H. Berthel, K. Bluthner, J. Schambach, L. Warzemann, G. Kirsch, T. Dohler and R. Stolz Summary: Planar dc SQUID gradiometers with integrated antenna were designed for measurement of field distributions with gradients much smaller than 1 pT/cmHz/sup 1/2/ in an unshielded environment. Four types of first-order-gradiometer SQUIDs were fabricated in Nb-Pb technology and investigated. Their layouts are highly symmetrical and they can be made also with HTS materials. Further reduction of the effect of disturbances was achieved with a second order gradiometer realized electronically. The stable function of the systems under unshielded conditions is shown.         Study of DyBaCuO DC SQUIDs for low noise and high flux focusing    Y. Higashino and T. Umezawa Summary: We have fabricated DyBaCuO DC SQUIDs by MBE growth on MgO substrates containing 45/spl deg/ step-edge Josephson junctions. They showed RSJ-like current-voltage characteristics and periodic modulation of voltage aroused by an applied magnetic field at 77 K. The flux resolution of the 1.9 mm square washer SQUID was measured to 3/spl times/10/sup -4/ /spl Phi//sub 0//Hz/sup 1/2/ at 1 Hz, which corresponds to a magnetic field sensitivity of 14 pT/Hz/sup 1/2/. Effective flux capture areas were investigated for varying SQUID size of washer and hole.         Microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7-x/ resonators coupled to single-junction SQUIDs    M.A. Hein, S. Schmoe, M. Strupp, H. Piel, Y. Zhang and A.I. Braginski Summary: The effects of microwave current and dc magnetic field on quality factor and resonant frequency at 3 GHz of planar resonators, which were differently coupled to hysteretic microwave SQUIDs, are discussed. The dissipative response is analyzed in terms of a single-junction SQUID, and its coupling to a resonant tank circuit. The temperature dependences and field periodicities of all relevant parameters are discussed, and conditions for optimized operation are deduced. The results indicate potential for further improvement of the performance of microwave SQUID magnetometers.         Reproducible step-edge junction SQUIDs    Y.Q. Shen, Z.J. Sun, R. Kromann, T. Holst, P. Vase and T. Freltoft Summary: High-T/sub c/ superconducting YBCO SQUIDs have been developed based on step-edge junctions. The step-edges were fabricated by using electron-beam lithography and Ar-ion milling on SrTiO/sub 3/ substrates. The V(/spl Phi/) peak-to-peak voltage is around 10 /spl mu/V, and the I/sub c/R/sub n/ product is 150 /spl mu/V at 77 K. The SQUIDs prepared on the same substrate show reproducible parameters within 30%. At 77 K the noise properties of the SQUIDs have been studied. At lower frequencies (1 Hz-100 Hz), we observe a flat noise level just below 10/sup -4//spl Phi//sub 0//Hz/sup 1/2/ probably limited by switching effects. Above 100 Hz the noise is gradually reduced to 10/sup -5//spl Phi//sub 0//Hz/sup 1/2/ at 1 kHz. The geometry of the step-edges has also been investigated by scanning electron microscopy, and the relation between the properties of the SQUID and the step height is reported.         High T/sub c/ SNS step-edge junctions and SQUIDs by using; YBa/sub 2/Cu/sub 3/O/sub 7//CaRuO/sub 3/ double layer    Soon-Gul Lee, Keunseop Park, Hyuk Chan Kwon, Yong Ki Park, Jong-Chul Park and Doo-Sup Hwang Summary: Superconductor-normal-superconductor (SNS) step-edge junction dc SQUIDs were fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films with CaRuO/sub 3/ (CRO) on top as the normal metal. The films were made by pulsed laser deposition (PLD) and patterned by photolithography and ion milling. The junctions and SQUIDs had to be annealed in oxygen environment for a much longer period of time (5-48 hours) compared with standard YBCO film preparation (as deposited or 1 hour), indicating that the top CRO film blocks oxygen in and out of the YBCO film. Before annealing T/sub c/'s of CRO/YBCO double layers and junctions made from them were <70 X and <50 K, respectively, and increased to >88 K and >77 K, respectively after long time annealing. Current-voltage curves of the junctions showed well-behaved resistively-shunted-junction (RSJ) properties and the temperature dependence of the junction critical current was roughly linear. SQUIDs made of those junctions showed voltage modulation in response to applied fields at 77 K.         High T/sub c/ bi-epitaxial junctions and dc SQUIDs structured by focused ion beam etching    R.P.J. Ijsselsteijn, J.W.M. Hilgenkamp, D. Velhhuis, J. Flokstra, H. Rogalla, C. Traeholt and H.W. Zandbergen Summary: Focused ion beam etching has been used to pattern dc SQUIDs into previously characterised template bi-epitaxial grain boundary junctions. Using this technique the screening parameter /spl beta//sub L/ can be optimised for a chosen temperature (in our case 30 K). Electrical characteristics, including noise measurements, are presented. A minimal white noise level of 22 /spl mu//spl phi//sub 0//spl middot/Hz/sup -1/2/ (1.8/spl middot/10/sup -29/ J/spl middot/Hz/sup -1/) has been obtained at 20 K. Using bias current modulation the 1/f noise could almost completely be suppressed down to 1 Hz in the entire temperature range (10-65 K).         Optical diagnostics for fabrication of YBCO thin film DC SQUIDs    A.N. Obraztsov, A.G. Maresov, I.I. Vengrus, O.V. Snigirev and S.I. Krasnosvobodtsev Summary: Optical reflectance spectra of thin YBCO films on SrTiO/sub 3/ bicrystals were measured in a photon energy range of 1-3 eV at room temperature. Raman spectra measurements in the range 200-700 cm/sup -1/ were performed. The best samples were shown to have high reflectance anisotropy and a well-defined Raman peak /spl nu//sub 1/=500+1 cm/sup -1/. YBCO thin films on a bicrystal substrate that successfully passed optical control were used for Josephson junctions and DC SQUID fabrication. The fabricated SQUIDs operated at 77.3 K in the flux locked loop mode and had a typical white noise (1-2)/spl times/10/sup -5/ /spl Phi//sub 0//Hz/sup 1/2/ at frequencies higher than 200-500 Hz. The best magnetic field resolution was 650 fT/Hz/sup 1/2/ at frequencies f>200 Hz.         Normal-state properties and Josephson effects in HTS weak links produced by electron beam    S.K. Tolpygo, S. Shokhor, B. Nadgorny, J.-Y. Lin, M. Gurvitch, S.Y. Hou and J.M. Phillips Summary: A description is given of the fabrication method and Josephson properties of high temperature superconducting junctions produced by focused electron beam writing. The nature of a weak link, I-V characteristics, transition to flux flow, and magnetic field modulation are discussed in some detail. The materials aspects such as the mechanism of e-beam damage to HTS, threshold energy, junction stability, and some technological issues such as reproducibility and uniformity are also addressed.         Current-voltage characteristics of shunted Josephson weak links with excess current    R.G. Seed, C. Vittoria and A. Widom Summary: Many superconducting Josephson weak link junctions are not adequately or accurately modeled by the resistively shunted junction model. For point contact junctions, step edge junctions and grain boundary junctions, a large excess current in the I-V characteristic is often observed. A new model has been proposed, which provides a more accurate technique of describing the behavior. Using this theory of shunted weak link junctions with excess current, calculations are presented here which accurately describe the magnitude and position of microwave induced current steps in the dc current versus voltage characteristics of such devices.         Progress in understanding the physics of HTS Josephson junctions    M.Y. Kupriyanov and J.S. Tsai Summary: The experimental results obtained in high-T/sub c/ Josephson junctions are reviewed with the emphasis on intrinsic Josephson effect and long-range proximity effect junctions (LRPJ). The possibility of the experimental observation of the intrinsic Josephson effect is discussed. A theoretical model based on resonant tunneling via localized states is proposed for the description of normal and supercurrent flow in LRPJ.         Optical response of superconducting Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films    S. Bhattacharya, S.N. Mao, M. Rajeswari, W. Jiang and T. Venkatesan Summary: The normal state and transition edge optical response of epitaxial thin films of n-type superconductor Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ has been measured. In contrast to the optical response of p-type superconductors such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// the normal state optical response of these films were not proportional to the temperature derivative of the resistance. The normal state optical response of films with different transition temperature (and, therefore, different oxygen content) were also remarkably different from each other. We attribute the observation of anomalous optical response to the possible presence of photoconductivity in Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/. We also discuss the feasibility of fabricating bolometers based on superconducting p-n bilayers.         Temperature dependence of the Josephson critical current in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ break junctions    R.S. Gonneli, I. Puttero, G.A. Ummarino and V.A. Stepanov Summary: We measured the I-V characteristics of break junctions obtained at 4.2 K in single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ that exhibited a stable nonhysteretic Josephson effect. The product I/sub c/R/sub N/ at 4.2 K was about 10 mV and the I-V curves followed the Resistively Shunted Junction (RSJ) model up to the T/sub c/ of the crystals. The temperature dependence of the critical current I/sub c/(T) is fitted by a new model that takes into account the effect of an intrinsically depressed order parameter at the surface of a superconductor with a short coherence length and, for comparison, by a model that introduces the effect of a proximity layer and of a finite transparency at the junction interfaces. The results can indicate that the intrinsic lowering of the pair potential at the sample surfaces is the cause of the deviations of our I/sub c/R/sub N/ from ideal BCS value.         Low magnetic field sensitivity of c-axis transport in BSCCO (2212) single crystals    Ji Ung Lee, G. Hohenwarter, R.J. Kelley and J.E. Nordman Summary: We have examined the sensitivity to low magnetic fields of c-axis transport in BSCCO (2212) bulk single crystals. A uniform field is applied along the ab planes of a mesa structure which was formed by etching. Four terminal volt-ampere curves in liquid nitrogen show a field dependent critical current and flux flow region followed by a multiple branch region, suggestive of stacks of hysteretic junctions.         Two-GHz microstrip thin-film resonators of Nb and YBa/sub 2/Cu/sub 3/O/sub 7/    J.D. Goettee, W.J. Skocpol, D.E. Oates and P.M. Mankiewich Summary: Dissipation and phase noise have been measured for 2-GHz linear microstrip resonators on 0.5-mm LaAlO/sub 3/. Fifty-ohm YBCO resonators with Nb ground planes (YBCO/Nb) showed quality factors of approximately 100,000 at 2 GHz and 4.2 K, somewhat less than measured in all-Nb resonators of the same geometry. The corresponding surface resistance of 10 microhms was maintained to average current densities of 1 MA/cm/sup 2/. All-YBCO resonators were measured to higher temperatures, and showed significant excess dissipation above about 60 K. The normalized phase noise of S/sub y/=-20/spl plusmn/2 was maintained to at least 30 K. This resonator was also operated in a resonator-stabilized oscillator configuration. The effect of package interactions on microstrip devices was also investigated.         Passivation of YBaCuO coplanar microwave structures    E. Waffenschmidt, J. Musolf, Xiaoyin He, K. Heime, S. Hofschen and I. Wolff Summary: Thin layers of Al/sub 2/O/sub 3/ and SiO/sub x/ were examined as dielectric passivations for thin films and coplanar microwave structures made of YBaCuO. The efficiency of the 300 nm thick material was shown by measuring the microwave surface resistance R/sub S/ (24.5 GHz, 77 K) of passivated YBaCuO layers before and after heat treatment in inert atmosphere. No significant changes were observed after heating for 1 h at 200/spl deg/C, whereas R/sub S/ of an unprotected sample increased strongly. After 1 h at 300/spl deg/C R/sub S/ of the passivated samples increased from 10 m/spl Omega/ to values between 70 m/spl Omega/ (SiO/sub x/) and 270 m/spl Omega/ (Al/sub 2/O/sub 3/) while the unprotected samples lost their superconductivity, The degradation was mainly caused by loss of oxygen, since the unprotected sample could be recovered by annealing in O/sub 2/ at 650/spl deg/C. The effect on the properties of microwave structures was calculated and measured using 25 /spl mu/m wide coplanar line resonators on LaAlO/sub 3/ at 5 GHz. No significant change of the quality factor was found after coating the structure with 300 nm SiO/sub x/ and Al/sub 2/O/sub 3/. The shift of the resonance frequency was less than 1%. The performance of a higher order filter showed neglectable change.         Temperature dependence of surface impedance of pulsed-laser-deposited YBCO films    J.H. Clark, G.B. Donaldson, J.C. Gallop and R.M. Bowman Summary: One promising application of HTS materials is as the reference resonator element for a stable frequency source. A high Q superconducting resonator operated at low reduced temperature (T/T/sub c//spl Lt/1) should offer excellent frequency stability due to its low temperature coefficient of resonant frequency. HTS planar resonators appear to be particularly promising since a reduced temperature of 0.1 may be readily achieved with a closed-cycle cryocooler. We report here microwave measurements made on YBCO films grown by pulsed laser deposition (PLD), using both a Nb cavity and a parallel-plate resonator configuration, with particular emphasis on the variation of resonant frequeney with temperature. We compare the data with simple theoretical models and find evidence from the low temperature data for a low energy gap parameter /spl Delta/(0)=6 meV. Some predictions of attainable frequency stability of planar resonator structures are also made.         YBCO X-band microstrip linear resonators on (1I02)- and (1I00)-oriented sapphire substrates    C.H. Mueller, F.A. Miranda, S.S. Toncich and K.B. Bhasin Summary: YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films on sapphire substrates have been tested for planar microwave applications such as filters and resonators. We have measured the unloaded quality factors (Q/sub 0/) of X-band microstrip linear resonators patterned into YBCO films on R-plane (1I02-oriented) and M-plane (1I00-oriented) sapphire substrates with CeO/sub 2/, and MgO buffer layers, respectively. For the fW on M-plane sapphire, the T/sub c/ and x-ray FWHM values were 87-88 K and 1.2/spl deg/, respectively, while for those on R-plane sapphire the values were 88-89 K and 0.4/spl deg/. Despite the superior properties of the film on R-plane, the YBCO on M-plane sapphire resonators had Q, values over 2000 at 77 K while those on R-plane sapphire had Q, values of less than 600. This could be correlated with the anisotropy of the R-plane sapphire as evidenced by the observed dependence of the shape of the resonance on the orientation of the resonator relative to the in-plane direction of the substrates. Possible causes for this behavior will be discussed.         Fabrication of YBCO superconducting dual mode resonator for satellite communication    Sang Yeol Lee, Kwang Yong Kang and Dal Ahn Summary: Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films have been grown epitaxially on (100) MgO substrates of laser ablation technique. Superconducting properties of YBCO thin films on MgO substrates have been investigated by X-ray diffraction pattern, scanning electron microscope, transport and magnetized T/sub c/ measurements. Superconducting dual mode disk resonators were designed by microwave design software, EEsof and fabricated by photolithography and wet-etch process using YBa/sub 2/Cu/sub 3/O/sub 7-x/, superconducting thin films with T/sub c/ of 87 K. The unloaded quality factor of the superconducting dual mode disk resonator was measured to be 1312 at 77 K by a HP8510B vector network analyzer. A clear resonant frequency splitting in the frequency range of 7.7-9.7 GHz was observed in a perturbed dual mode disk resonator. This type of dual mode disk resonator could be utilized as a dual mode resonator filter for satellite communication.         Role of perturbations for dual mode superconducting microstrip resonators fabricated by laser ablation    Sang Yeol Lee, Kwang Yong Kang and Dal Ahn Summary: The comparison of frequency response characteristics between various types of superconducting dual mode resonators has been performed. Epitaxial superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films have been have been grown on MgO substrates by laser ablation. Perturbed disk and ring types of superconducting dual mode resonators were patterned by photolithography and a wet-etch process. Unlike the unperturbed case, dual mode resonators have different resonant properties for the perturbed case depending on the position of the perturbation. We observed the same resonant peak splitting properties at the fundamental resonances of the perturbed dual mode disk and ring resonators. Peak properties caused by perturbation in the dual mode resonators could be used in implementing a two pole bandpass filter by itself.         Effects of microstructures on microwave properties in Y-Ba-Cu-O microstrip-resonators    T. Yoshitake, H. Tsuge and T. Inui Summary: We examined the microwave properties of YBa/sub 2/Cu/sub 3/O/sub x/ films with different microstructures at 5.7 GHz using a microstrip resonator technique. The films were prepared with several types of substrate temperature profiles. Films with small grains (/spl sim/100 nm) and larger critical current density show fairly small rf magnetic field dependence of surface resistance and resonance frequency up to about 50 Oe. On the other hand, films with large grains (/spl sim/200 nm) and smaller critical current density show significant changes in these properties. These results suggest that the coupling strength at the grain boundaries mainly dominates the power handling capability, according to a qualitative explanation based on the coupled-grain model.         Ferroelectric thin film characterization using superconducting microstrip resonators    D. Galt, J.C. Price, J.A. Beall and T.E. Harvey Summary: We describe a novel technique for characterizing the dielectric response of ferroelectric thin films at microwave frequencies. The method involves a microstrip resonator which incorporates a ferroelectric capacitor at its center. To demonstrate this method rye have fabricated a superconducting microstrip resonator from a laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) film on a LaAlO/sub 3/ (LAO) substrate with a SrTiO/sub 3/ (STO) capacitor at its center. We report the observed dielectric behavior of the STO laser ablated film as a function of bias at liquid He and N/sub 2/ temperatures and at high and low frequencies. It is observed that the electrically tunable dielectric constant of the STO film is roughly independent of frequency up to 20 GHz (especially at high bias). The loss tangent of the STO/LAO capacitor decreases with increasing bias and is apparently independent of frequency between 6 and 20 GHz.         Nonlinear thermal effects in the HTSC microwave stripline resonator    A.N. Reznik, A.A. Zharov and M.D. Chernobrovtseva Summary: We report a theoretical study of nonlinear electromagnetic phenomena for HTSC stripline resonators. We have considered a thermal nonlinearity resulting from heating of HTSC by electromagnetic field. It was shown that a microwave input power excess of some threshold level leads to formation of a normal-state domain. We have obtained that emergence and disappearance of the domain have a hysteresis character with respect to the input power which provides a hysteresis for the transmission coefficient and frequency response.         Quantum detectors in superconducting YBCO    N. Bluzer and M.G. Forrester Summary: A superconducting quantum detector structure in YBCO is described with a directly coupled SQUID read out circuit. The detector geometry is optimized for maximum photoresponse with the use of a serpentine pattern. The serpentine pattern reduces quasiparticle diffusion effects and maximizes the photoinduced changes in the kinetic inductance. The operation of this sensor is analyzed in terms of geometry and quasiparticle lifetime to obtain expressions for the signal and noise of this detector. The background limited infrared performance of this detector is calculated to be about 5/spl times/10/sup -17/ NEP. The photoresponse is expected to be limited by the superconducting energy gap, about 30-40 /spl mu/m.         Nonbolometric NbN photodetector    M.W. Johnson, A.M. Domino and A.M. Kadin Summary: There have been several recent reports of apparently nonbolometric optical responses in superconducting thin films. The photoresponse of 10 nm thin superconducting NbN meander lines on Si is measured at 670 nm using a diode laser modulated to more than 100 kHz. Several types of photoresponse are identified, some apparently due to the Si substrate. A fast photoresponse due to the NbN film with a responsivity of up to 125 V/W of absorbed power was observed. Results are analyzed in the context of a bolometric model, and the magnitude of the photoresponse is found to be too large for a purely bolometric response. Possible nonbolometric alternatives are discussed.         Nonequilibrium kinetic inductive response of YBCO thin films to low power laser pulses    G. Gol'tsman, P. Kouminov, I. Goghidze and E. Gershenzon Summary: We have discovered a transient nonequilibrium kinetic inductive voltage response of YBCO thin films to 20 ps pulses of YAG:Nd laser radiation with 0.63 /spl mu/m and 1.54 /spl mu/m wavelength. By increasing the sensitivity of the read-out system with 100 ps resolution time and diminishing the light intensity (fluence 0.1-2 /spl mu/J/cm/sup 2/) and transport current (density /spl les/10/sup 5/ A/cm/sup 2/) we were able to observe a peculiar bipolar signal form with nearly equal amplitudes for each sign. The integration of the kinetic inductive response over time gives the result which is qualitatively, of the same form as the response in the resistive and normal states: the nonequilibrium picosecond scale component is followed by the bolometric nanosecond component. The nonequilibrium response is interpreted as suppression of the order parameter by excess quasiparticles followed by a change both in resistance (for the resistive state) and in kinetic inductance (for the superconducting state).         Nonthermal kinetic inductance photoresponse of thin superconducting films    M.A. Heusinger, A.D. Semenov, R.S. Nebosis, Y.P. Gousev and K.F. Renk Summary: We report on the photoresponse of structured superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and NbN films to femtosecond visible light pulses. The photoresponse signals obtained at temperatures below the transition temperature consist of a positive voltage peak of 25 ps width for the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// sample and 40 ps for the NbN sample, each limited by the temporal resolution of the different setups, followed by a longer negative voltage transient. We attribute the photoresponse signals to a nonthermal change of the kinetic inductance of the superconducting films. We also present a model describing the dynamics of nonequilibrium quasiparticles (QP) and phonons, allowing to simulate our results. Our model provides the physical background for optimization of fast detectors based on the kinetic inductance photoresponse of thin superconducting films.         Quantum effects in the hot electron microbolometer    A. Tang and P.L. Richards Summary: The theory of the hot electron microbolometer proposed by Nahum et al. assumed that the photon energy is thermalized in the electrons in the Cu absorber before relaxing to the lattice. Since the photons initially excite individual electrons to /spl planck//spl omega//spl Gt/k/sub B/T, however, direct relaxation of these hot electrons to phonons must also be considered, Theoretical estimates suggest that this extra relaxation channel increases the effective thermal conductance for /spl planck//spl omega//spl Gt/k/sub B/T and influences bolometer noise. Calculations of these effects are presented which predict very useful performance both for ground-based and space-based astronomical photometry at millimeter and submillimeter wavelengths.         The single-electron transistor as an ultrasensitive microwave detector    J.M. Hergenrother, J.G. Lu and M. Tinkham Summary: We have measured single-electron tunneling transistors with superconducting islands and conclude that they may be used as ultrasensitive detectors of microwave radiation for frequencies /spl ges/80 GHz. These devices contain a small superconducting Al island that is weakly coupled to a bias circuit through two small-capacitance tunnel junctions and a capacitive gate. At low bias voltages and temperatures, a single quasiparticle may only be introduced to the island through photon-assisted tunneling. Once this occurs, the quasiparticle is trapped on the island for /spl sim/1 /spl mu/s because it takes a relatively long time for this specific quasiparticle to tunnel off. While it is trapped, charge is transported through the system two electrons at a time. Since the photon-assisted transition merely switches the detector current on, this device is not limited to one electron tunneled through the system per absorbed photon. Measurements indicate that at least 100 electrons can tunnel for every absorbed photon, which corresponds to a noise-equivalent power of 3/spl times/10/sup -20/ W//spl radic/Hz at 80 GHz if the current is measured with a commercial current amplifier.         Application of Josephson edge type junctions with a PrBa/sub 2/Cu/sub 3/O/sub 7/ barrier prepared with Br-ethanol etching or cleaning    M.I. Faley, U. Poppe, C.L. Jia, U. Dahne, Yu. Goncharov, N. Klein, K. Urban, V.N. Glyantsev, G. Kunkel and M. Siegel Summary: The technique of the edge preparation for multilayer Josephson edge type junctions on the basis of c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7/ thin films with the help of etching in Br-ethanol solution was improved. Microwave induced Shapiro steps, Josephson radiation, and characteristics of dc-SQUIDs were investigated. The developed technique prevents the junctions and device properties from degradation due to aging or thermal cycling.         Resonant tunneling transport in YBaCuO/PrBaCuO/YBaCuO edge-type Josephson junctions    T. Satoh, M.Y. Kupriyanov, J.S. Tsai, M. Hidaka and H. Tsuge Summary: YBaCuO/PrBaCuO/YBaCuO edge-type Josephson junctions were fabricated and their transport properties were studied. Josephson effect in these structure was confirmed by the observation of microwave induced Shapiro steps and periodic magnetic field dependence of the critical current. Normal electron transport in the junctions was well explained by Glazman and Matveev's theory for hopping transport via localized states. In addition, the supercurrent transport in PrBaCuO is possibly supported by the resonant tunneling via the localized states. We estimated the density of the localized states to be 10/sup 16/ cm/sup -3/.         Fabrication of field effect devices based on YBaCuO/PrBaCuO/YBaCuO junctions    H. Kimura, Y. Okabe and H. Kamijo Summary: In order to investigate an electric field effect in the junction, the three terminal device was fabricated. When the gate voltage of +2 V (E=7/spl times/10/sup 4/ V/cm) was applied, the drain-source resistance decreased above the temperature of 100 K. However, the electric field effect could not be observed below the temperature of 100 K. Above the temperature of 100 K, it is found that the CuO chain in PBCO behaved itself as a doped semiconductor (acceptor level=26.5 meV).         Properties of multilevel ramp edge junctions and SQUIDs with laser-ablated SrTiO/sub 3/ barriers    R.B. Laibowitz, J.Z. Sun, V. Foglietti, R.H. Koch, R.A. Altman and W.J. Gallagher Summary: We have fabricated junctions and DC SQUIDs using laser ablation for both the YBCO electrodes and the thin SrTiO/sub 3/ (STO) barrier regions in a variety of device configurations. These SQUIDs operate reliably at 77 K and preliminary results on a limited number of devices show that they store reasonably well for periods in excess of one year, and exhibit only small changes with repeated cycles (/spl sim/10) between room temperature and 77 K. Noise measurements made using bias reversing on a SQUID (92 pH) at 77 K give a white noise of about 15 /spl mu//spl Phi//sub 0///spl radic/Hz and a 1/f upturn at about 0.2 Hz.         Fabrication of YBaCuO/nonsuperconductive-YBaCuO/YBaCuO co-planar Josephson junction by focused ion beam    Y. Soutome, Yunn Ghee Gheem and Y. Okabe Summary: A thin film of YBa/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) grown on an MgO substrate damaged by a focused ion beam loses superconductivity due to abnormal growth. We have fabricated a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// co-planar Josephson junction whose coupling region is nonsuperconductive YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grown on an MgO substrate damaged locally by focused ion beam scanning. The I-V characteristic of the junction behaves like a flux flow type. At temperatures from 4.2 K to 60 K, Shapiro steps were observed for the junctions in which the length of the coupling region was from 0.2 /spl mu/m to 1 /spl mu/m. The highest I/sub c/R/sub n/ product of the junction was 5.0 mV. The critical current density decreased exponentially with the junction length. It is considered that nonsuperconductive YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grown on the damaged substrate works as a normal layer in an S-N-S junction. Also the junction responded to the magnetic field and behaved like an asymmetric dc-SQUID.         Modeling of an ADC based on high-T/sub c/ QOJS comparators    T. Harnisch, F.H. Uhlmann, H. Topfer, D.F. Moore, A.J. Pauza and K. Lamacraft Summary: Existing proposals for high temperature superconductor analog to digital converter (ADC) circuits suffer performance penalties because of the difficulty of fabricating devices with small and controlled inductances. The design of a quasi-one junction SQUID (QOJS) comparator for a high-T/sub c/ flash ADC is proposed and discussed. The inductances are calculated with the help of a three-dimensional field calculation program, and simulations on the QOJS-comparator are performed using a SPICE-type simulation program.         A proposal of Josephson binary-to-ternary converter    Fu-Qiang Li, M. Morisue and T. Ogata Summary: This paper presents a novel Josephson converter to perform signal conversion from a binary system to a ternary system. Most converters perform conversion in successive steps from the least significant bit to the most significant bit. Therefore, the circuits become complicated and operation speed becomes low. In order to overcome these shortcomings, a novel converter based on Josephson technology is proposed. The principle of the converter is described in detail and simulation results for an 8-bit converter are illustrated. The advantages of this converter are simple construction with a small number of elements and high speed operation.         Performance of MVTL logic at multi-GHz frequencies    M. Leung, J.W. Spargo, B.J. Dalrymple, D.J. Durand, M.S. Wire and A. Spooner Summary: Demonstrating superconductive logic circuits at high speeds is crucial in gaining acceptance by potential users. We are taking an integrated approach toward demonstrating the potential of such circuits. Issues addressed include the effects that layout have upon a circuit and gate (particularly in scaling down the size of gates to increase density), testing limitations, designing for minimum crosstalk and ground ripple, and fundamental limitations to gate performance. In this paper, we report our progress in resolving and understanding these issues. Circuits such as shift registers were used to understand the influence of layout on performance, circuits such as gate chains and punchthrough detectors to explore fundamental gate limitations. We also report on signal processing circuits of several hundred gates tested at clock frequencies up to several hundred MHz and the relationship between these results and the fundamental gate performances.         CMOS amplifier designs for Josephson-CMOS interface circuits    U. Ghoshal, S.V. Kishore, A.R. Feldman, Luong Huynh and T. Van Duzer Summary: We discuss the design of CMOS amplifiers for Josephson-CMOS interface circuits in three different application scenarios, these circuits form important building-blocks of Josephson-CMOS memories, A/D converters (ADC), and other novel circuits, all these designs have been implemented in the UC Berkeley Josephson-CMOS technology.         CMOS self-calibration of Josephson flash-type A/D circuits    S.V. Kishore, U. Ghoshal, L. Huynh and T. Van Duzer Summary: We present CMOS self-calibration and bias circuits for Josephson circuits. In Josephson technology, process variations in critical circuit parameters such as junction critical current, resistance, and inductance adversely affect the performance. For example, process deviations in junction critical currents leads to low dynamic range and nonuniform quantization steps in flash-type A/D converters. While CMOS technology has a speed disadvantage with respect to Josephson technology, it does make available highly accurate current sources that are relatively process independent and difficult to obtain in Josephson technology. Here, we discuss how the 4 K CMOS self-calibration of a Josephson flash type A/D converter can be used to improve dynamic range.         Hybrid Josephson-CMOS FIFO    A.R. Feldman and T. Van Duzer Summary: We describe the design of a hybrid Josephson-CMOS first-in-first-out memory (FIFO) for communications and signal processing applications. The FIFO takes advantage of high speed Josephson logic and dense CMOS memory. We focus on the low power CMOS ring pointer architecture employing a dual-port CMOS SRAM array and illustrate how a high speed Josephson demultiplexor-multiplexor pair can greatly increase throughput. We describe a novel eight transistor dual-port CMOS SRAM cell with low swing write and current-mode read with an asymmetric SQUID to perform differential current-sensing. Finally, we discuss the peripheral Josephson demultiplexor and multiplexor designed in edge-triggered logic.         High-power high-temperature superconducting microstrip filters for cellular base-station applications    G.-C. Liang, D. Zhang, C.-F. Shih, M.E. Johansson, R.S. Withers, A.C. Anderson and D.E. Oates Summary: We report narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7/(-x) high-temperature superconducting films. One 5-pole filter on a LaAlO/sub 3/ substrate, consisting of backward-coupled and forward-coupled resonators, can handle over 27 W input power at 10 K. It has 1% fractional bandwidth and 10-/spl Omega/ internal impedance. The insertion loss increase in passband at 10 K, as the input power changed from a few mW to 27 W, is less than 0.25 dB. We also report a forward-coupled microstrip filter centered at 2 GHz, with a 1.2% fractional bandwidth, 10-/spl Omega/ internal impedance, and parallel-coupled feed lines. We applied over 10 /spl Omega/ to the filter at 45 K without noticeable degradation of the filter performance. The insertion loss at 45 K is less than 0.2 dB. The return loss is better than 12 dB.         Compact forward-coupled superconducting microstrip filters for cellular communication    Dawei Zhang, G.-C. Liang, C.F. Shih, R.S. Withers, M.E. Johansson and A.D. Cruz Summary: A compact forward-coupled microstrip filter structure is presented for narrow-band applications in cellular communications. The structure consists of a parallel array of fully aligned half-wavelength resonators. Coupling is controlled by the spacing of the adjacent resonators, and is based on the even- and odd-mode phase velocity difference of coupled lines in a microstrip configuration. Two filter designs, based on the forward-coupled structure, were fabricated using YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) high-temperature superconducting (HTS) thin films on LaAlO/sub 3/ substrates. One filter, a 9-pole 2.8% fractional-bandwidth YBCO filter at 900 MHz, has less than 0.27 dB insertion loss and better than 16 dB return loss. The other filter, a 5-pole 1.2% fractional bandwidth YBCO filter with 10-/spl Omega/ internal impedance at 2 GHz, has less than 0.35 dB insertion loss and better than 12 dB return loss. All designs showed excellent measured frequency response.         Applications of high-T/sub c/ superconductors in sub-Gigahertz r.f. cavity resonators    A.E. Centeno and P.S. Excell Summary: The size of cavity resonators below 1 GHz may be reduced by using dielectric or helical loading. With normal conductors, such electrically small resonators suffer problems of losses and inadequate Q-factor. However, by using superconductor in the portions with the highest current density, very good performance may be obtained with very electrically-small cavities. A cylindrical dielectric resonator was used to load a corrugated cavity, having YBaCuO thick-film end plates, and operated at VHF. The results showed a significant improvement over corrugated cavities with copper end plates. Investigations have also been undertaken with high-T/sub c/ superconductor helical loading. The size of the cavities was electrically very small (about 0.02 of free space wavelength), and results with both bulk and thick-film helical loading elements were obtained. The results showed a significant improvement over a similar copper helically-loaded cavity resonator.         YBCO shielded LaAlO/sub 3/ dielectric resonators for stable oscillators    N. Klein, N. Tellmann, T. Dahne, A. Scholen, H. Schulz, G. Hofer and H. Kratz Summary: We have investigated dielectric resonators (SDROs) fabricated from single crystalline LaAlO/sub 3/ shielded by two epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO). At the resonant frequency of the TE/sub 011/-mode of 5.6 GHz unloaded quality factors Q/sub 0/ of 8/spl times/10/sup 5/ at 20 K and 4/spl times/10/sup 5/ at 60 K were obtained. These values were limited by dielectric losses in LaAlO/sub 3/. At 50 K we obtained a a Q/sub 0/ of 2/spl times/10/sup 5/ at a level of dissipated rf power of 2 W corresponding to an average rf magnetic surface field of 150Oe. Moreover, we used one SDRO as a feedback for a HP8349 amplifier to measure oscillator phase noise. At 60 K and helium gas cooling the phase noise was beyond the sensitivity limit of our HP8565 spectrum analyzer of about -90dBc/Hz at an offset frequency of 1 kHz. For operation with Stirling coolers, microphonics dominates the noise properties.         A compact two-pole X-band high-temperature superconducting microstrip filter    B. Oh, H.T. Kim, Y.H. Choi, S.H. Moon, P.H. Hur, M. Kim, S.Y. Lee and A.G. Denisov Summary: In this paper we examine a microstrip line filter with three gaps separated by approximately a quarter wavelength. Two filters, one with gold and the other with YBCO were fabricated. The thickness of top conducting microstrips was 600 nm. The ground plane under the 0.5 mm-thick lanthanum aluminate (LaAlO/sub 3/) substrate was implemented with a 2 micron-thick gold layer for both filters. These filters showed similar frequency responses with 5% 3-dB bandwidth. The insertion loss, however, improved from 2.8 dB to 1.5 dB by using the superconductor. The performance of the filter was also tested by employing the three dimensional microwave FEM software, and the simulation result compared well with the measured data.         Microwave multipole lowpass and bandpass filters fabricated by high-T/sub c/ superconducting thin films    Kwang-Yong Kang, Sang Yeol Lee, Seok Kil Han and Dal Ahn Summary: The design, fabrication, and measurement of 7-pole microstrip lowpass filters and 4-pole parallel coupled-line bandpass filters using superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ epitaxial thin films are presented. The YBa/sub 2/Cu/sub 3/O/sub 7-x/ films were grown in situ at 770/spl deg/C and 200 mTorr oxygen partial pressure in a pulsed laser deposition system. The 7-pole microstrip-line lowpass filter and 4-pole parallel coupled-line bandpass filter patterned on the laser ablated YBCO films with dimension of 20 cm/spl times/10 cm/spl times/0.5 mmt were generated using photolithographic and wet etching processes. The complete devices packaged in a 3-component type brass test-fixture were characterized. The results showed the center frequency of 11.2 GHz with 6% bandwith and less than 1 dB insertion loss(IL) for the case of bandpass filters below 77 K.         Improvements in superconducting linear phase microwave delay line bandpass filters    H.C.H. Cheung, G. Huang, M.J. Lancaster, R.G. Humphreys and N.G. Chew Summary: Microwave delay line filters can be designed to specified amplitude and phase characteristics using a synthesis procedure which takes into account multiple reflections and losses in the delay lines. The time domain synthesis procedure has now been extended so that frequency-dependent loss and delay line dispersion can also be allowed for. Meanwhile experimental results on linear phase microstrip and coplanar filters show significant improvements on stopband attenuation and phase linearity over previously published data on microstrip devices.         Fourier spectroscopy study of Josephson junction own radiation    A.P. Lipatov, V.A. Ilyin and A.A. Verevkin Summary: The frequency characteristics of Josephson own radiation have been studied by means of Fourier spectroscopy. The FIR measurements were performed with the help of Fourier spectrometer coupled with the Nb Josephson junction. The main feature of this technique is that one Josephson junction operates as both generator and detector of own radiation at the same time. The spectrometer operates either in double-beam mode with resolution /spl sim/2 GHz or in multi-beam mode with resolution /spl sim/1 GHz.         Modulation of I-V characteristics of YBCO films and tunnel junctions under microwave irradiation and tunnel current injection    Qian Wang, Kijin Lee and Ienari Iguchi Summary: We present the measurements on the I-V characteristic modulation of YBCO films under microwave irradiation and tunnel current injection. In the case of tunnel current injection through a Pb(or Au)/MgO/YBCO junction, the critical current I/sub c/ of a YBCO film decreases drastically with the increase in tunnel current, and a normal state appears when the injection current reaches a certain value smaller than I/sub c/, leading to a current gain greater than one. The I-V characteristics of a YBCO film under both current injection and external microwave irradiation (fa=11 GHz) show strong modulation behavior. We find that the above modulation is mainly caused by the Cooper-pair breaking effect due to injected quasiparticles with energy greater than 2/spl Delta/ and not by heating.         Quasioptical Hilbert transform spectrometer    M.A. Tarasov, A.Ya. Shul'man, G.V. Prokopenko, V.P. Koshelets, O.Yu. Polyanski, I.L. Lapitskaya, A.N. Vystavkin and E.L. Kosarev Summary: A quasioptical spectrometer using Hilbert transformation of Josephson junction response has been designed, fabricated and experimentally studied. Resistively shunted SIS junctions have been used as the Josephson sensor placed in the centre of a complementary logarithmic spiral antenna. The response was studied in the 75-150 GHz frequency band. A resolution below 1 GHz and noise equivalent power about 10/sup -13/-10/sup -14/ W has been measured for the 0.7 /spl Omega/ junction. The measured spectrum is obtained by means of Hilbert transformation via a novel deconvolution program based on the maximum likelihood approach. This allows one to diminish the measured interval of bias voltage and avoid measurements of the noisy part of the response curve without loss of the spectral resolution.         A self-biasing cryogenic particle detector utilizing electrothermal feedback and a SQUID readout    K.D. Irwin, S.W. Nam, B. Cabrera, B. Chugg, G.S. Park, R.P. Welty and J.M. Martinis Summary: We are developing and testing a new type of superconducting transition edge sensor for phonon mediated particle detection. This sensor consists of a superconducting tungsten thin film deposited on a silicon substrate. The temperature of the film is held constant within the superconducting transition (T/sub c//spl ap/70 mK) by an electrothermal feedback process, while the substrate temperature is well below the film temperature. Phonon energy deposited in the film is removed by a reduction in feedback Joule heating, which is measured using a series array of DC SQUIDs. The resulting signals show improvements in linearity and signal to noise ratio over our previous transition edge sensors.         An analysis of superconducting acoustic sensor with Josephson junction    Shu-Ang Zhou Summary: This article presents a theoretical analysis of the effect of an elastic wave incident upon a deformable Josephson junction, which is a basic component of superconducting acoustic sensors. The model introduced for the analysis is based on the generalized London equations which account for the effect of inertia of superconducting electron pairs in the dynamically deformed superconductors that form the junction. The result indicates possible Josephson pair tunneling current induced by the transverse elastic wave, but not by the longitudinal elastic wave. It is shown that for a transverse elastic wave incident on the Josephson junction, the induced Josephson pair tunneling current may appear theoretically at any non-zero frequency, which is different from the well-known phonon-assisted single electron tunneling phenomenon where a minimum frequency exists. It is also shown that a DC current step structure may appear in the current-voltage characteristics of the deformable Josephson junction biased by a DC voltage and exerted by a transverse elastic wave.         Resonant steps in parallel Josephson junction arrays: parametric instabilities of whirling modes    S. Watanabe, S.H. Strogatz, H.S.J. van der Zant and T.P. Orlando Summary: Circular arrays of underdamped Josephson junctions exhibit a series of resonant steps in the return path of the subgap region in the current-voltage characteristics. We show that the voltage locations of the steps can be predicted by studying the parametric instabilities of whirling periodic solutions, and experimentally verify the prediction in a ring of 8 underdamped junctions. The whirling modes become unstable in certain voltage intervals, and a branch (a resonant step) of more complicated solutions emerges from the endpoint of each interval. We extend the analysis to open-ended arrays and find that for f=0, the onset of a zero-field step has the same underlying mechanism. For f>0, combinations of lattice eigen-frequencies are excited.         Phase locking in two-dimensional arrays of Josephson junctions: effect of critical-current nonuniformity    R.L. Kautz Summary: Numerical simulations are used to study mutual phase locking in two-dimensional arrays of Josephson junctions for parameters typical of successful millimeter-wave oscillators. Such arrays are shown to be very tolerant of random critical-current nonuniformities. However, comparison with an equivalent series array reveals that the locking between rows in a two-dimensional array is principally due to feedback through the external load and not to internal coupling between rows.         Self-field effects in two-dimensional Nb Josephson-junction arrays    E. Trias, J.R. Phillips, H.S.J. van der Zant and T.P. Orlando Summary: We have measured two-dimensional niobium Josephson junction arrays in which self induced fields are important. We find an increase of the depinning current when /spl lambda//sub /spl perp//, the penetration depth in the array, is of the order of one. There is evidence for a destruction of commensurate vortex states in the arrays as the depinning current becomes almost independent of the applied magnetic field. Our data also show that self-field effects change the array flux-flow dynamics and decrease the effective array viscosity.         600 GHz resonant mode in a parallel array of Josephson tunnel junctions connected by superconducting microstrip lines    V.K. Kaplunenko, B.H. Larsen, J. Mygind and N.F. Pedersen Summary: The high frequency properties of the one-dimensional transmission line consisting of a parallel array of resistively shunted Josephson tunnel junctions have been studied in the limit of relatively low damping where this nonlinear system exhibits new and interesting phenomena. Here we report on experimental investigations of a resonant step observed at a voltage corresponding to 600 GHz in the dc current-voltage characteristic of a parallel array of 20 identical small NbAlO/sub x/Nb Josephson junctions interconnected by short sections of superconducting microstrip line. The junctions are mutually phase locked due to collective interaction with the line sections excited close to the half wavelength resonance. The phase locking range can be adjusted by means of an external dc magnetic field and the step size varies periodically with the magnetic field.         Phase locking experiments in distributed arrays of Josephson junctions    R.P. Robertazzi Summary: Arrays of phase locked Josephson junctions are attractive for use as sub-mm wavelength voltage controlled oscillators for heterodyne mixers and free space radiators. We have performed phase locking experiments on 40 junction, parallel biased arrays of Josephson junctions coupled through transmission lines of varying delays. The longest junction to junction delay implemented was 5.4 ps for a design frequency of 90 GHz, while the shortest was 1.45 ps, for a design frequency of 345 GHz. The resonant frequency f/sub 0/ of the arrays was found to be almost independent of the transmission line delay with f/sub 0/, scaling with the plasma frequency for arrays fabricated at critical current densities of 10/sup 3/ and 4.5/spl times/10/sup 3/A/cm/sup 2/. The data indicate that at the resonant frequency, strong phase locking is present among the junctions for junction separations significantly less than one half wavelength even in arrays many wavelengths long.         Phase-locking of stacked all-niobium junction arrays to external rf-irradiation    A.M. Klushin, H. Kohlstedt and J. Niemeyer Summary: We have experimentally investigated the range of locking to external rf-bias current for large 3D arrays. Up to 2000 series connected stacks with two junctions in a stack and 84 series connected stacks with four junctions in a stack were incorporated into a microstripline. Our measurement showed a drastic reduction of the phase locking range with an increasing number of junctions in an individual stack of the array. We investigated the dependence of the attenuation in the microstripline for different numbers of junctions in a stack. In addition, the attenuation of the rf current in the neighboring junctions in a stack was measured.         Direct observation of vortex dynamics in two-dimensional Josephson-junction arrays    T. Doderer, S.G. Lachenmann, R.P. Huebener, P.A.A. Booi and S.P. Benz Summary: Spatially resolved images of the dynamic states of current-biased overdamped two-dimensional arrays of Nb/AlO/sub x//Nb Josephson junctions were obtained using low-temperature scanning electron microscopy. We present two-dimensional imaging results describing various vortex dynamic regimes in zero applied magnetic field. The nucleation of current-induced vortices at the array boundaries and their subsequent motion into the array interior are observed for bias currents slightly above the array critical current. With increasing bias current, vortex-vortex interaction becomes important. Discussions on the coherent microwave radiation emission are presented.         LTS Josephson junction critical current uniformities for LSI applications    L.A. Abelson, K. Daly, N. Martinez and A.D. Smith Summary: Manufacturing yields of large scale superconducting circuits depend strongly on the uniformity of junction critical currents. We report on junction manufacturing tolerances based on extensive measurements of Nb- and NbN-based junction arrays and individual junctions. Transient waveforms induced by switching of a single junction have sufficient amplitude to switch other junctions in a series array. We have measured the effect of sympathetic switching and developed damping structures to dissipate switching transients. Comparisons of critical current distributions measured on individual junctions with critical current distributions determined from series junction arrays are presented. In addition, the validity of using series arrays of large numbers of junctions to assess the critical current uniformity is discussed.         Fabrication of high quality, deep-submicron Nb/AlO/sub x//Nb Josephson junctions using chemical mechanical polishing    Z. Bao, M. Bhushan, Siyuan Ran and J.E. Lukens Summary: A reliable process based on Chemical Mechanical Polishing (CMP) has been developed for the fabrication of high quality, deep-submicron Nb/AlO/sub x//Nb Josephson junctions on 2 inch wafers. The Nb counter electrode is defined using low pressure SF/sub 6/ reactive ion etching (RIE) with a mask of SiO, which is thermally evaporated through a bilayer resist stencil patterned by electron beam lithography. After RIE, the entire wafer is coated with SiO, which is then planarized using CMP (which also removes the etch mask) to expose the counter electrode. This technique has produced high quality (V/sub m//spl sime/60 mV for J/sub c/ of 2 kA/cm/sup 2/) junctions with areas as small as 0.003 /spl mu/m/sup 2/ demonstrating that the process does not degrade the junction quality. Junctions with critical currents of 22 /spl mu/A and areas of 0.006 /spl mu/m/sup 2/ have been fabricated from trilayers with J/sub c/>300 kA/cm/sup 2/.         Electrical characterization of Nb/Al-oxide/Nb Josephson junctions with high critical current densities    A.W. Kleinsasser, W.H. Mallison, R.E. Miller and G.B. Arnold Summary: Transport in Nb/AlO/sub x//Nb junctions involves two parallel channels, barrier defects (pinholes) with sub-nanometer dimensions and nearly-ideal tunneling regions. We fit junction characteristics using only a single parameter, the ratio of the normal state conductances of these current paths. Our barrier model accounts for the excellent Josephson behavior and highly non-ideal quasiparticle characteristics of junctions with critical current densities as high as 4 mA//spl mu/m/sup 2/. It appears to be quite generally applicable to tunnel junctions.         Characteristics of high critical current density Josephson junctions with Nb/AlO/sub x//Nb trilayers    H. Sugiyama, A. Fujimaki and H. Hayakawa Summary: We fabricated high critical current density (high J/sub c/) Josephson junctions, up to 47 kA/cm/sup 2/, consisting of Nb/AlO/sub x//Nb trilayers by use of high vacuum dc magnetron sputtering (less than 10/sup -6/ Pa). The relationship Jc/spl prop/(Pt)/sup -0.5/ can be obtained up to 47 kA/cm/sup 2/, where P and t are pressure and time, respectively, in oxidizing an Al surface. In the high J/sub c/ junctions, microshorts existed in Al surfaces. A property peculiar to most of the high J/sub c/ junctions was a step appearing at 1/3 gap voltage on their I-V curves. Magnetic field dependence of this step was different from that of a Fiske step.         Coherent flux-flow in vertically stacked long Josephson tunnel junctions    A.V. Ustinov, H. Kohlstedt and C. Heiden Summary: Vertical stacks of two Nb/Al-AlO/sub x//Nb long Josephson junctions with nearly identical parameters have been studied experimentally. The magnetic coupling between the junctions was provided by their common electrode of thickness d/spl sime//spl lambda//sub L/. The I-V characteristics displayed flux-flow resonances of the two junctions. Two different mutually phase-locked regimes were found: the lower velocity anti-phase mode, and the high velocity in-phase mode. These modes, while staying locked, could be tuned by the magnetic field in a broad voltage range which corresponds to the Josephson frequencies of 150-600 GHz for the lower mode and 280-400 GHz for the upper mode. Our observations suggest applications of the stacked long Josephson junctions as local oscillators for millimeter and sub-millimeter wave circuits.         A cryogenic scanning laser microscope for investigation of dynamical states in long Josephson junctions    J. Helm and J. Mygind Summary: The first local oscillators based on moving magnetic flux quanta in long Josephson junctions are being developed for superconducting integrated quasi-optical SIS receivers. In order to further refine these oscillators one has to understand the complex dynamics of these devices. Since the local tunnel current is one of the most important internal junction parameters which together with the boundary conditions determine the dynamics, it is of vital importance to experimentally determine the current density throughout the entire junction with high spatial resolution. Here we report on measurements on different oscillator samples, performed with a novel Cryogenic Scanning Laser Microscope (CSLM) having a spatial resolution of less than /spl plusmn/2.5 /spl mu/m over a 500 /spl mu/m/spl times/50 /spl mu/m wide scanning area in the temperature range 2 K-300 K. Even though the dynamical states are extremely sensitive to external noise this microscope enables us to make stable in-situ measurements on operating Josephson junctions. Recent results are presented and discussed.         Multilevel devices of YBa/sub 2/Cu/sub 3/O/sub 7/ with NdGaO/sub 3/ barrier    D. Grundler, J.-P. Krumme, B. David and O. Doessel Summary: We have fabricated YBa/sub 2/Cu/sub 3/O/sub 7/ ramp-type junctions incorporating a barrier layer of NdGaO/sub 3/ with a nominal thickness of 2 nm. The junctions exhibit pronounced Josephson effects and operate up to 82 K. The characteristics are well described within the resistively shunted junction model. We observe large hysteresis parameters /spl beta//sub c/ even at elevated temperatures. The output voltage of a high-T/sub c/ dc SQUID is found to benefit from the intrinsic junction capacitance.         Fabrication and characterization of ramp edge-type junction and SQUIDs    G.A. Alvarez, M. Kuroda, M. Matsuda, K. Miyamoto, N. Kasai, M. Koyanagi and T. Nemoto Summary: We have investigated the properties of high-T/sub c/ ramp-edge geometry Josephson weak links using superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) electrodes and PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(PBCO) normal-metal layers. Unambiguous evidence of Josephson behaviour has been observed. Current-voltage characteristics (CVC) were qualitatively consistent with the resistively-shunted-junction (RSJ) model. Well developed Shapiro steps for 8.9 GHz microwave irradiation have been observed. Furthermore we have fabricated dc-SQUIDs with PBCO barriers that modulate up to a temperature of 80.6 K. At 4.2 K we find a flux-voltage modulation depth of /spl ap/36 /spl mu/V.         First space test of high-T/sub c/ SQUIDs    M. Klinger, J.H. Hinken and S.S. Tinchev Summary: On September 12, 1993, the German satellite ASTROSPAS was launched on board the Space Shuttle Discovery, Flight STS-51. The satellite included the scientific device ORFEUS, as well as the SESAM experiment, developed by Deutsche Forschungsanstalt fur Luft- und Raumfahrt in Braunschweig, Germany, to investigate surface effects. One of the 20 SESAM samples was a chip with 16 high-T/sub c/ RF SQUIDs on a SrTiO/sub 3/ substrate. The SQUIDs were made using YBCO films and local oxygen-ion irradiated weak links, at launch time the sample was 19 months old. No changes were observed in the SQUID operation after this 10 days flight. This is the first space test of electronic devices based on high-T/sub c/ materials.         Method for improving voltage modulation depth of high T/sub c/ DC SQUID with large inductance    K. Enpuku, H. Doi, G. Tokita and T. Maruo Summary: Two methods are proposed in order to improve the voltage modulation depth of high-T/sub c/ DC SQUIDs in the case of large inductances. One is a damping resistance parallel to the inductance, and the other is a new SQUID using three junctions, which we call 3J-SQUID. Numerical simulation shows the usefulness of the present method. Moreover. It is shown that the improvement of the voltage modulation depth results in the improvement of magnetic flux noise in the white noise region. Therefore, the present method will enable the use of large inductances. The usefulness of the present method is also confirmed partly by experimental results.         Inductance calculation for integrated superconducting structures by minimizing free energy    G. Hildebrandt and F.H. Uhlmann Summary: We present a method to calculate the inductance matrix of three dimensional superconducting structures by minimizing the free energy. In the case of high-T/sub c/ superconductors, the kinetic inductance becomes substantial and an accurate calculation of inductances is required. The London penetration depth /spl lambda/ and the kinetic inductance are accurately included by this method. The results of this program agree well with measurements of high-T/sub c/ DC-SQUIDs (superconducting quantum interference devices).         Application of small-signal model to DC SQUID circuit design    W.P. Geren Summary: As the performance of HTS DC SQUIDs continues to improve, their utilization in RF devices (e.g., amplifiers, nuclear magnetic resonance detectors) having complex circuitry becomes more attractive. To fully realize their potential in this application, accurate and efficient analysis techniques are required to assist the circuit designer. Beginning with measured V-phi and I-V data for the device, we have used the small-signal model to optimize the design of a two-stage low-noise amplifier (LNA) comprised of DC SQUIDs. Optimization criteria were maximum gain and minimum noise figure at the upper band edge. We have shown that the small signal model is an invaluable design tool which provides the analytical performance data needed to optimize the SQUID and its attendant RF circuitry.         YBa/sub 2/Cu/sub 3/O/sub 7/(-x) step-edge junctions prepared on sapphire substrates with YSZ buffer layer    R. Adam, S. Benacka, S. Chromik, M. Darula, V. Strbik, S. Gazi, R. Kostic and E. Pincik Summary: Electrical properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/(YBCO) step-edge junctions were investigated. Steps of height approximately 90 nm were prepared on sapphire substrates by Ar milling. Step angles were adjusted by the angle of incidence of Ar ions. After vacuum deposition of the YSZ buffer layer (50 nm thick) an epitaxial YBCO film was grown by magnetron sputtering. Step edge junctions were prepared by wet etching. The current-voltage characteristics were of RSJ type, with I/sub c/R/sub n//spl ap/0.5 mV at 77 and Shapiro steps were observed up to 0.2 mV (at 9.2 GHz in the temperature range 4.2-80 K) and compared with the resistively shunted Josephson junction (RSJ) model including capacitance and noise.         Electron beam lithographed straight and wavy YBa/sub 2/Cu/sub 3/O/sub 7/ step edge junctions    H.R. Yi, D. Winmer, Z.G. Ivanov and T. Claeson Summary: We have developed a process for the fabrication of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step edge junctions. This process greatly improved the uniformity of the step angles, the straightness and sharpness of the step edges on LaAlO/sub 3/ substrates. We used an electron beam lithography defined amorphous carbon film as an ion milling mask. By studying junctions made across straight and wavy step edges, we showed the importance of the straightness on the quality of YBCO junctions. Junctions fabricated across these improved step edges showed less j/sub c/ variations (a factor of 2-3 compared to >10 for standard step edge junctions) and improved current distribution. We increased the McCumber constant /spl beta//sub c/ by varying the step height and the YBCO film thickness (h and t). Hysteresis was observed in the I-V characteristics at 4.2 K for junctions with h=240 nm and t=180 nm. The capacitance per unit area was calculated to be 15 fF//spl mu/m/sup 2/. The magnetic field (H) dependence of the critical current (I/sub c/) showed well-defined periods with a main peak in the center. The I/sub c/ in the first minimum can be suppressed to 20-40% in most cases. For some junctions, I/sub c/ can also be suppressed to zero at higher temperatures. However, we did not observe a perfect Fraunhofer pattern in the I/sub c/ vs. H curve. The field period /spl Delta/H was found to have a w/sup -2/ dependence on the junction width (w).         Fabrication of YBCO step-edge Josephson junctions by inverted cylindrical magnetron sputtering technique    A. Di Chiara, F. Lombardi, F. Miletto Granozio, F. Tafuri, M. Valentino, S. Matarazzo, S. Pagano, B. Ruggiero and M. Russo Summary: The Inverted Cylindrical Magnetron Sputtering (ICMS) technique been used to fabricate YBCO step-edge dc SQUIDs. Steps are obtained by standard ion milling procedure on LaAlO/sub 3/ (100) substrates using Nb-masks patterned by reactive ion etching. Thin films are then deposited under different conditions (both step and deposition angles) and patterned by standard lithography and wet chemical etching. An analysis of junction properties in terms of step height and film thickness has been carried out. Measurements on current vs magnetic field and SQUID voltage response measurements have been performed. Their temperature dependences have been also considered. Operating temperature as high as 77 K has been achieved. At 4.2 K the SQUIDs show a maximum voltage to flux transfer function (/spl part/V//spl part//spl phi/)/sub max/=870 /spl mu/V//spl Phi//sub 0/ and a good periodicity of the V-/spl phi/ modulation up to 20 /spl Phi//sub 0/ without any sign of hysteresis.         YBa/sub 2/Cu/sub 3/O/sub 7/ nano-bridge junctions and dc SQUIDs made by focused ion beam milling    D.H.A. Blank, W. Booij, H. Hilgenkamp, B. Vulink, D. Veldhuis and H. Rogalla Summary: YBa/sub 2/Cu/sub 3/O/sub 7/ nano-bridges with widths ranging from 200 to 800 nm were made using Focused Ion Beam milling. The I-V characteristics of the narrowest nano-bridges show, under microwave irradiation, pronounced Shapiro steps up to the transition temperature. An inductively shunted single layer SQUID, using these nano-bridges, has been realised by a combination of Focused Ion Beam milling and selective epitaxial growth. Flux to voltage modulation up to 82 K was observed, with a maximum modulation depth of 3.7 /spl mu/V at 78 K.         Current phase relation of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) step edge junction    V. Polushkin, S. Uchaikin, S. Knappe, H. Koch, B. David and D. Grundler Summary: The small signal rf impedance of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// step edge junction rf SQUIDs operating in a strongly nonhysteretic mode has been measured. The phase dependent inductance L/sub J/(/spl phi/) and the current phase relation I/sub p/(/spl phi/) of step-edge junctions embedded in SQUIDs are calculated from measurement data following the Vincent-Deaver approach. Two of three junctions investigated revealed a sinusoidal current phase relation. I/sub p/(/spl phi/) of the third junction seemed to be non-sinusoidal and hysteretic. A model explaining the origin of the non-sinusoidality of I/sub p/(/spl phi/) is proposed.         Detection of the Josephson self-radiation from YBCO step-edge junctions in millimeter-wave    K. Lee and I. Iguchi Summary: We have investigated both DC and AC Josephson effects of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film step-edge junctions; single step-edge junction on LaAlO/sub 3/ substrate with the step angle about 50-60/spl deg/ and biepitaxial double step-edge junction made on MgO substrate with a CeO/sub 2/ seed layer. The Josephson self-radiation was directly detected using the total power radiometer receiver systems with receiving frequencies of K band (21-23 GHz) and millimeter-wave (46-48 GHz and 71-73 GHz) range, respectively. For single step-edge junctions, the Josephson self-radiation peaks exhibited at the voltages corresponding to the basic Josephson voltage-frequency relation. The maximum first-harmonic self-radiation power at receiving frequency f/sub REC/=72 GHz and Josephson linewidth were P(I)=2.0/spl times/10/sup -3/W and /spl Delta/f=3.62 GHz at 4.2 K, respectively. For microwave irradiation, the harmonic Shapiro steps and additional half integer steps with their quasi-periodic variation satisfying the Josephson equation V=(n/m)(hf/2e) were clearly observed. For double step-edge junctions, we also observed the steps corresponding to the two junction boundaries on the two steep steps. These behaviors described with different current-phase relations corresponding to the crystal orientation relationship between the two junction boundaries.         High T/sub c/ superconducting step-edge junctions and their properties in millimeter-wave band    Y.J. Feng, L. Kang, X.B. Wang, S.Z. Yang, J.P. Zuo, H.B. Wang, W.W. Xu, Q.H. Cheng, P.H. Wu, S.L. Yan and L. Zhou Summary: Superconducting step-edge junctions were fabricated on step-edges in (100) LaAlO/sub 3/ substrates by sputter-deposited epitaxial YBaCuO and TlBaCaCuO thin films. The substrate steps were patterned by ion beam etching using metal film as a mask. The transport properties of the junctions were characterized by four-probe electrical measurements. The critical current-normal resistance product (I/sub c/R/sub N/) was larger than 0.2 mV (77 K) for most of the junctions. Clear Shapiro steps were observed in the current-voltage characteristics of the junctions with 36 GHz or 95 GHz millimeter-wave irradiation. The high frequency properties of these high T/sub c/ Josephson junctions showed that they were quite suitable for the Josephson harmonic mixer used in the digital phase locked millimeter and sub-millimeter wave sources.         Millimeter and submillimeter wave responses of YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge Josephson junctions    H. Shimakage, Y. Uzawa, Z. Wang, A. Kawakami, W. Chujo and B. Komiyama Summary: We have fabricated YBCO step-edge Josephson junctions and measured the responses to millimeter and submillimeter irradiation. In the substrate milling process for the purpose of fabricating the step, the step angle was controlled using a Nb metal mask. At a step angle of 20 degrees, we obtained Josephson junctions, the characteristics of which are consistent with the RSJ model. We estimated the capacitance to be 4.4 fF using the RSJ model, but such a value for an 8 /spl mu/m wide and 300 nm thick junction seems too small. When the junctions were irradiated by 300 GHz radiation, Shapiro steps up to the 4th were observed. The junctions were used as mixers in the 100 GHz band, and as harmonic mixers in the 100 GHz LO and 700 GHz RF bands. Beat signals were observed in both cases. We also estimated the quasi-optical conversion losses of the step-edge junctions as mixers.         Josephson behaviour and flux penetration effects in YBCO double tilt-angle step-edge junctions    C.P. Foley, G.J. Sloggett, K.-H. Muller, S. Lam, N. Savvides, A. Katsaros and D.N. Matthews Summary: YBCO thin-film step-edge junctions have been prepared whose characteristics show features corresponding to the two tilt-angle grain-boundary junctions formed at the step. The I-V characteristics of these junctions are fitted to high accuracy by a model consisting of two noisy resistively-shunted Josephson junctions. In applied magnetic fields up to a few hundred microtesla, both junction critical currents show reversible flux modulation, in one case indicating excellent uniformity of the critical current distribution along the step. In stronger magnetic fields, the junction critical current modulation shows evidence of flux penetration into the film, i.e. the mixed state. Taking demagnetising effects into account the lower critical field of YBCO at 77 K, /spl mu//sub 0/H/sub e1,e/, is found to be 12 mT.         Design and testing of high-T/sub c/ Josephson pulse driver using selective SEJs    T. Umezawa and Y. Higashino Summary: We have designed a novel Josephson pulse driver based on SFQ circuits using high-T/sub c/ junction parameters, and fabricated it using selective SEJs. Simulation showed that the output pulse can be stepped up to 2.5 mV, which is 13 times larger amplitude than the input pulse. In the fabricated driver using a microstrip line, two dozen SEJs were integrated with Au resistors and inductors. The driver operated at 77 K with a conversion factor of (1-1.5) at best.         Modification of step-edge grain boundary Josephson junctions by electromigration    J.B. Bulman and J.M. Murduck Summary: We report on the effects of large electric currents (>2 MA/cm/sup 2/) applied at /spl sim/300 K to step-edge thin-film microbridges of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. These step-edge Josephson junctions showed an increase in their critical current (I/sub c/) after application of electromigration current, I/sub EM/. This increase of I/sub c/ was a permanent phenomenon. Electromigration was also performed on SNS YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin-film microbridges and an increase in critical current was observed.         Fabrication of Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ thin film grain boundary junctions    K. Ohbayashi, H. Fujii, A. Kuzuhara, T. Ohtsuki, M. Inoue, A. Fujimaki and H. Hayakawa Summary: As-grown high-quality superconducting thin films of the Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ were prepared by RF magnetron sputtering with a regulated shuttering technique. 2223 phase films with a 2201 phase buffer layer were deposited on MgO (100) substrates under rigorous control of the bismuth content and valence. As a source of bismuth, Bi(metal) and Bi/sub 2/Sr/sub 2/CuO/sub x/ targets were used. At the preparation no post-treatment steps were performed. The zero resistivity critical temperature of the as-grown film was 107.3 K. Using these films, Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ step-edge and bicrystal Josephson junctions were prepared. At step-edge junctions, Josephson current was observed up to 41 K, below this temperature I-V curves were RSJ-like. On the other hand, bicrystal junctions were fabricated,on the bicrystal MgO (100) substrate with a misorientation angle of 24/spl deg/. Typical RSJ model I-V curves were observed up to 60 K. The modulation depth goes up to 90%. I/sub c/R/sub n/ values were about 1.0 mV at 4.2 K.         RSFQ pseudo random generator and its possible applications    A.Yu. Kidiyarova-Shevchenko and D.Yu. Zinoviev Summary: We have analyzed theoretically and simulated a set of 4-bit RSFQ-logic-based Pseudo Random Generators (PRG). These circuits have been fabricated using low-T/sub c/ niobium technology. We have also investigated experimentally an XOR cell and a shift register with parallel outputs that have been used as compound parts of the PRGs. Experimentally measured margins for DC power supply voltage for a PRG with a serial output, an XOR cell and shift register were 10%, 15%, and 15% respectively. In this paper we discuss various possible applications of a PRG in testing RSFQ circuits and also as a source of "quasiwhite" digital noise.         RSFQ arithmetic blocks for DSP applications    S.V. Polonsky, Jao Ching Lin and A.V. Rylyakov Summary: We have designed a Rapid Single-Flux-Quantum (RSFQ) bit-serial real-time pipeline multiplier for digital signal processing (DSP) applications. A single-bit module of this multiplier consists of 96 Josephson junctions and uses a B-flip-flop-based carry-save adder (CSA). For HYPRES' standard 1-kA/cm/sup 2/ Nb process with 3.5 /spl mu/m-diameter Josephson junctions the module occupies all area of 350/spl times/600 /spl mu/m/sup 2/. Simulations show that the circuit should dissipate 28 /spl mu/W of power at 2.6 mV dc supply voltage and operate at frequencies of up to 25 GHz. We have successfully tested all cells of the module and verified correct operation of a simplified version of the module at low frequencies. According to numerical simulations, the speed of the multiplier is limited by the CSA. In order to overcome this bottleneck we have developed a concept of a fast carry-save pipeline adder based on XOR gates which uses an RSFQ-specific algorithm for carry bit calculation.         4.6 GHz SFQ shift register and SFQ pseudorandom bit sequence generator    Joonhee Kang, A.H. Worsham and J.X. Przybysz Summary: Superconductive electronics can provide low power, GHz speed spread spectrum satellite communications. The key components to construct the spread spectrum modem are an analog filter and a digital pseudorandom bit sequence generator, Various SFQ logic circuits are required to construct a code generator. These circuits include a shift register, a reset switch, and an XOR or XNOR. To make a 4 bit 15 sequence code generator, a four stage shift register with a fan-out of two on each stage was designed. These circuits, fabricated with eight level Nb/AlO/sub x//Nb Josephson junction integrated circuit process, showed correct operation at low speed digital tests. The low speed digital test was done by using a "catcher", the combination of a read SQUID and a Josephson transmission line (JTL) which were magnetically coupled to each other. High speed testing of the shift register used a latch amplifier, which amplified an SFQ pulse to a latching output voltage of about 2 mV. This test showed correct operation of the shift register at speeds of up to 4.6 GHz.         Operation of a 1-bit quantum flux parametron shift register (latch) by 4-phase 36-GHz clock    M. Hosoya, W. Hioe, K. Takagi and E. Goto Summary: The Quantum Flux Parametron (QFP) is a SFQ-type logic device which uses a single flux quantum (SFQ) to represent 1-bit of information. QFP circuits use a multi-phase external ac power which also acts as the clock for synchronization, hence QFP circuits are highly pipelined. The clock frequency must be increased to improve the throughputs of the circuits, so the control of a high frequency clock is a key technology for the QFP. This paper describes a clock distribution technique which utilizes the characteristics of a standing wave. Using this technique, the operation of a 1-bit QFP shift register by a 4-phase clock up to 36 GHz is shown. In the 4-phase clock operation of QFPs, the input is given in phase 1, the QFP switches in phase 2, the output is held during phase 3, and the QFP resets in phase 4. Therefore, the 4-phase 36-GHz operation means that each QFP switches or resets in less than 7 ps.         A new design approach for High-T/sub c/ based RSFQ logic    V.K. Kaplunenko, Z.G. Ivanov, A. Bogdanov, E.A. Stepantsov, T. Claeson, T. Holst, Z.J. Sun, R. Kromann, Y.Q. Shen, P. Vase, T. Freitoft and E. Wikborg Summary: We suggest a new design of Rapid Single Flux Quantum (RSFQ) logic circuits which is based on a single superconducting layer and does not require a superconducting ground plane. The small inductances of about 10 pH, that are obligatory for the RSFQ applications, are formed as narrow slits with width comparable to the London penetration depth (/spl cong/0.15 /spl mu/m). The design allows us to decrease the geometric size of the RSFQ cell and can be applied to low-T/sub c/ circuits as well. Test circuits have been implemented using YBaCuO grain boundary junctions on assymmetric 32/spl deg/Y-ZrO/sub 2/ bi-crystals to measure the slit inductance per unit length and the mutual inductance of neighboring slits. A typical inductance of a 0.4 pm slit was determined to be 0.7pH//spl mu/m. We present a new design and a computer simulation of a flip-flop circuit based on these inductance measurements. To realize these circuits experimentally one needs at least two grain boundaries, separated by a distance of 10 to l5 /spl mu/m, or to use bi-epitaxial or step-edge junction technology.         Picosecond optoelectronic study of superconducting microstrip transmission lines    J.F. Bulzacchelli, Hae-Seung Lee, K.G. Stawiasz, S. Alexandrou and M.B. Ketchen Summary: The ballistic transport of picosecond digital signals along terminated microstrip lines is a key feature of single flux quantum (SFQ) logic. In this work, we have used fast photoconductors driven by a femtosecond laser to measure directly for the first time the propagation and termination of picosecond pulses along Nb microstrip lines. Electrical pulses as short as 0.8 ps full-width-at-half-maximum (FWHM) have been measured. After propagating distances of 200 /spl mu/m, 1 mm, and 6.5 mm, the pulses broadened to 1.0, 1.2, and 1.8 ps (FWHM), respectively. In the frequency domain, attenuation is found to be negligible up to the gap frequency of Nb(0.7 THz), beyond which attenuation increases rapidly. We have also measured the reflections of the picosecond pulses off different terminations: open circuit, short circuit, and various resistors. The effective suppression of reflections with matched resistive loads is demonstrated up to frequencies approaching 1 THz.         On-chip picosecond delay measurement of RSFQ digital logic gates    D.K. Brock, S.S. Martinet and M.F. Bocko Summary: Because RSFQ circuits are intended to operate at multi-GHz frequencies, a logical requirement for developing the technology is a method of accurately measuring the picosecond delays associated with individual logic circuits. A technique has been developed for on-chip measurements of such RSFQ gate delays. The central element in this scheme is a race between a path of calibrated variable delay and a path of unknown delay. Modification of the canonical RSFQ RS flip-flop circuit yields a multiple state destructive readout cell (MDRO), in which one can configure the number of flux quanta to be stored. This circuit has been experimentally verified for groups of two flux quanta. Used in concert with the confluence buffer, this scheme can provide the RSFQ designer with sub-picosecond pulse arrival delay information crucial for higher order circuit simulation. A detailed experimental process is presented from which this timing information can be extracted using basic low-speed measurement techniques.         An optoelectronic testing system of rapid, single-flux quantum circuits    M. Currie, Chia-Chi Wang, D. Jacobs-Perkins, R. Sobolewski and T.Y. Hsiang Summary: We have generated picosecond voltage pulses on a superconducting microstrip line by using a metal-semiconductor-metal photodiode as an optoelectronic switch. These pulses are fed into a two-Josephson-junction pulse shaper to generate single-flux quantum (SFQ) pulses. Using a reflective electro-optic sampling system, SFQ pulses are directly observed for the first time. This important demonstration of nonintrusively detecting electrical signals from superconducting microstrip lines at the level of rapid, single-flux quantum (RSFQ) circuits opens up a new way to test such circuits, on issues such as design verification, jitter, and failure-mode testing. Further, we propose a variable-rate optoelectronic clock for testing the functional speed of RSFQ logic circuits, with an adjustable clock rate up to 38 Gb/s.         Operation of a superconductive demultiplexer using rapid single flux quantum (RSFQ) technology    S.B. Kaplan and O.A. Mukhanov Summary: A superconductive demultiplexer was designed, simulated, and tested as an interface between ultra-fast superconductive circuits and slower room-temperature electronics. The modular RSFQ shift-and-dump circuit was designed as a register of Non-Destructive Read-Out (NDRO) cells, which are timed by pulses from the system clock. Data is read out from a 1:N demultiplexer every N clock periods by applying a read-out pulse to the register's NDRO input. Circuit simulations and results for the successful experimental test of a 2-stage demultiplexer will be discussed.         4-bit rapid single-flux-quantum decoder    A.F. Kirichenko, V.K. Semenov, Y.K. Kwong and V. Nandakumar Summary: We describe the design of a fast single-flux-quantum decoder which can be used, e.g., in fast RAMs, general-purpose microprocessors, and communication channel switches. The core of the circuit is a tree of the single-bit SFQ demultiplexer with toggle (rather than the reset-set) control. Three new RSFQ cells: the demultiplexer, D flip-flop with complementary outputs, and serial XOR with large parameter tolerances (dc bias margins of /spl plusmn/25%, /spl plusmn/26%, and /spl plusmn/27%, respectively) have been developed for the decoder project. We have designed the first 16-bit prototype of the decoder for 1-kA/cm/sup 2/ niobium-trilayer technology and tested it at low frequencies. The circuit was completely operable except for 3 (of 16) output SFQ/DC converters. Simulations show that the circuit should allow data rate in excess of 60 Gbit/s and channel switching time below 20 ps.         Field effects on the dielectric property of YBCO bicrystal grain boundary junctions    K. Nakajima, K. Yokota, H. Myoren, J. Chen and T. Yamashita Summary: Electric field effects on YBCO grain boundary Josephson junctions combined with inverted MIS (Metal, Insulator, Superconductor) structures were studied. Current steps and hysteresis recognized in current-voltage curves were strongly affected by the field. The current steps were attributed to the self-excited resonances, i.e., Fiske steps. Both the effects were interpreted by the field dependence of the effective dielectric constant of the grain boundary which has a certain contribution from the large dielectric constant of SrTiO/sub 3/ substrates. The effective dielectric constant normalized with barrier thickness of the junction was estimated to be about 40 nm/sup -1/ for the zero gate voltage and was decreased by a factor of 2 with the electric field of /spl plusmn/16 kV/cm. This feature is assumed adequate for tuning the phase velocity in the bicrystal grain boundaries.         The SUPFET, a new photodetector with ultrathin YBaCuO/PrBaCuO multilayer channel    A. Jager and J.-C. Villegier Summary: Several electric field effect devices have been built with YBaCuO/PrBaCuO layers and multilayers; The layers are deposited by an inverted cylindrical magnetron sputtering process (ICM) on MgO substrates. This process has been proved to give very good performances even for thinner and ultra thin films. The films used for the field effect transistor devices consist of one or two bilayers of YBaCuO and PrBaCuO with a nominal thickness of each material of about 4 nm. Small channel geometries of 50/spl times/60 microns are etched by argon ion milling and the channel is covered by a silicon dioxide dielectric layer (50-100 nm). The gate contacts as well as the drain and source contacts are made by sputtered gold pads. These devices are tested in static and dynamic measurements: the silicon dioxide layer inhibits symmetric I-V characteristics of the dielectric layer with high breakdown field strength up to 4 MV/cm. The gate capacity of a few pF allows the test of the device in a kHz frequency range. Tests with sine wave gate voltages show low distortion of the output signal with a voltage gain of about 0.01. Smaller dielectric layers could raise the gain close to one. The results of these field effect experiments are compared with optically induced effects. The optical measurements are performed with a helium-neon laser (633 nm) with a power density of 600 W/cm/sup 2/. The laser pulses with frequencies up to 1 MHz give responses somewhat similar to the observed field effect responses. Combining field effect and optical irradiation, it Is found that the laser pulses seem to create charge carriers, screening the field effect. Based on this principle a new photodetector is proposed.         Modified deposition procedure for high quality YBa/sub 2/Cu/sub 3/O/sub 7-x//SrTiO/sub 3/ bilayers    V. Talyansky, K. Petersen, C. Doughty, X.X. Xi and T. Venkatesan Summary: The degradation of an ultrathin YBCO layer under SrTiO/sub 3/ due to oxygen deficiency poses a fundamental problem in growing a bilayer which may be patterned into a superconducting FET. Annealing between depositions while growing the bilayer can help increase the T/sub c/ of the YBCO while retaining acceptable quality of the SrTiO/sub 3/. This study found T/sub c/ in the range of 60-80 K for a 4 unit-cell thick YBCO film under SrTiO/sub 3/.         Superconducting field effect devices with high transition temperature and critical current density    C. Doughty, V. Talyansky, C. Kwon, A.T. Findikoglu, X.X. Xi and T. Venkatesan Summary: We have investigated buffer layers of Pr/sub 0.55/Y/sub 0.45/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (PY)BCO for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)/SrTiO/sub 3/ field effect devices. The transitions of single unit cell thick YBCO films in (PY)BCO/YBCO/(PY)BCO trilayers depend strongly on the buffer layer thickness, with optimum T/sub c//spl ap/40 K obtained at a buffer layer thickness of 5nm. SuFET devices deposited on such an optimized buffer layer exhibit substantial improvements in channel quality. For a 3.6 nm thick channel, transition temperature >55 K and critical current density /spl sim/10/sup 6/ A/cm/sup 2/ are obtained. The modulations observed in both the normal and superconducting states are consistent with those obtained in earlier work on non-weak-link dominated samples.         Electric field effect of SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-x/ multilayers grown by all-MBE    T. Nakamura, H. Tokuda and M. Iiyama Summary: Epitaxial SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-x/ (STO/YBCO) multilayers for a superconducting field-effect transistor (SuFET) were fabricated by an ozone assisted Molecular Beam Epitaxy (MBE) method. To eliminate interdiffusion at the interface, we deposited high quality STO films at around 500/spl deg/C on YBCO films with clean surfaces. At this temperature, interdiffusion was negligible through in-situ Auger Electron Spectroscopy (AES). The electric field effect in a Ag/STO/YBCO device configuration also indicated the suppression of the interfacial layer between the STO and YBCO film.         Electric field effect in Sm/sub 1-x/Ca/sub x/Ba/sub 2/Cu/sub 3/O/sub y/ bicrystal junctions    Z.W. Dong, V.C. Matijasevic, P. Hadley, S.M. Shao and J.E. Mooij Summary: A three terminal device was fabricated by depositing a thin film of Ca-doped SmBa/sub 2/Cu/sub 3/O/sub y/ on a bicrystal SrTiO/sub 3/ substrate and then structuring a gate over the resulting junction. The channel shows RSJ-like Josephson junction behavior. By applying a voltage to the gate, a large electric field effect was observed. The largest field effect was observed in films where 30% of the Sm was replaced by Ca. The critical current of the junction was modulated 23% by the application of an electric field of 5/spl times/10/sup 5/ V/cm. This electric field is about 100 times smaller than the electric field necessary for the field effects observed in homogeneous films. The sign of the field effect is consistent with that expected for a carrier-depleted grain boundary region.         Transistor performance of high-T/sub c/ three terminal devices based on carrier concentration modulation    K. Joosse, Y.M. Boguslavskij, L. Vargas, G.J. Gerritsma and H. Rogalla Summary: Electric field effect devices and quasiparticle injection effect devices are good candidates for the realization of three terminal devices from high-T/sub c/ materials, since they take explicit advantage of the low carrier concentration in these compounds. We describe the fabrication and operation of both types of devices, and discuss their performance as transistor-like elements.         Superconducting junctions using a 2DEG in a strained InAs quantum well inserted into an InAlAs/InGaAs MD structure    T. Akazaki, J. Nitta, H. Takayanagi and K. Arai Summary: A newly fabricated three-terminal Josephson junction is coupled with a two-dimensional electron gas (2DEG) in a strained InAs quantum well inserted into an InAlAs/InGaAs modulation-doped structure. The 2DEG is confined in the InAs quantum well and has a maximum mobility of 155000 cm/sup 2//Vs at a sheet-carrier density of 1.86/spl times/10/sup 12/ cm/sup -2/ at 10 K. The supercurrent flows through the 2DEG and can be controlled by adjusting the gate voltage. The critical current and normal resistance are measured as a function of the gate voltage, and the sheet-carrier density dependence of the critical current is obtained. We also measure the temperature dependence of the critical current at different gate voltages. The results indicate that, when using this junction, the superconducting characteristics can range between the clean and dirty limits.         Three-terminal field effect superconducting device using SrTiO/sub 3/ channel    A. Yoshida, H. Tamura, H. Takauchi, T. Hato and N. Yokoyama Summary: As a first step toward fabricating transistors to control supercurrent, we fabricated two- and three-terminal devices that have coplanar Nb electrodes coupled with a SrTiO/sub 3/ substrate. In the two-terminal devices, the Nb electrodes were coupled with an Nb-doped SrTiO/sub 3/ substrate with a carrier concentration of 2/spl times/10/sup 19/ cm/sup -3/. Electrode spacing was about 50 nm. The devices showed Josephson effect at 4.2 K. Three-terminal devices were made on a thinly doped surface of a non-doped 0.4-mm-thick SrTiO/sub 3/ substrate with gate electrodes on the non-doped area of the substrate. Resistance of the three-terminal devices was controlled by applying voltages to the gate electrode at 4.2 K.         Microwave radiation from Josephson junctions built in micro-strip line    V.V. Kurin, M.Yu. Levichev, V.A. Markelov, V.D. Gelikonova, P.A. Shisharin, S.I. Borovitsky and A.M. Klushin Summary: In this paper we present the results of investigation of high frequency dynamics of Josephson junction array built in niobium strip line with fin-line antenna. Mutual interaction between junctions and microwave radiation produced by the array is investigated.         Resonances in two-dimensional array oscillator circuits    P.A.A. Booi and S.P. Benz Summary: We present experimental results on the emission from phase-locked two-dimensional arrays of Josephson junctions. We have coupled the emission from 10/spl times/10 arrays to a room-temperature mixer through a fin-line antenna and WR-12 waveguide. A single voltage-tunable peak was detected up to 230 GHz. A stripline resonance in antenna reduced the array's dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data. When the array's emission was coupled to an on-chip detector junction through a dc blocking capacitor, we detected voltage-tunable emission from 75 GHz up to 300 GHz, and in some circuits emission above 400 GHz. Here, the coherent power spectrum depends on internal resonances.         Performance of Josephson array systems related to fabrication techniques and design    F. Muller, J. Kohlmann, F.X. Hebrank, T. Weimann, H. Wolf and J. Niemeyer Summary: Arrays of Nb/Al/sub 2/O/sub 3//Nb Josephson tunnel junctions show dc characteristics of high quality when the trilayer is deposited direct on polished Si wafers. Underlayers such as rf-sputtered SiO/sub 2/, can considerably degrade the junction parameters. These results suggest that voltage standard chips should be produced with a cover instead of a groundplane. First results of attenuation measurements on such circuits are presented and discussed. Furthermore, a new and more simple fabrication process without a window-insulating layer and only two photolithographic steps is presented. Arrays of several thousands of junctions showed no problems of any kind with trapped flux.         Josephson voltage standard microwave circuits operating at 10 GHz    H.-G. Meyer, H.-J. Kohler, G. Wende and A. Chwala Summary: A new type of microwave circuit for the generation of frequency-scaled voltages is investigated. The circuit is designed as a superconducting microstrip line resonator and series arrays of Josephson tunnel junctions located within the rf current antinodes. The circuits are designed to obtain highly accurate voltages at low rf power level and low frequencies of about 10 GHz. For a resonator circuit with 432 junctions driven at about 10 GHz we have observed steps up to 0.25 V, the lifetime of which is about 20 minutes.         Hybrid integration of microwave oscillators with Josephson series arrays for the use as voltage standards    F.X. Hebrank, P. Gutmann, F. Muller, E. Vollmer and J. Niemeyer Summary: We have designed and fabricated a new type of Josephson device to be hybrid integrated with microstripline oscillators. For optimum matching of the Josephson series array to the oscillator the samples make use of a new stripline design. The first circuits were fabricated in a simplified Nb/Al/sub 2/O/sub 3//Nb technology and exhibit excellent dc characteristics and good microwave coupling to the junctions of the array. At 70 GHz constant voltage steps up to 350 mV could be observed. By hybrid integrating different samples with a new 10-GHz oscillator, constant voltage steps were created. For this experiment the Josephson current density had to be low enough to reduce the plasma frequency of the junctions to well below the driving frequency.         Step-edge and stacked-heterostructure high-T/sub c/ Josephson junctions for voltage-standard arrays    S.P. Benz, C.D. Reintsema, R.H. Ono, J.N. Eckstein, I. Bozovic and G.F. Virshup Summary: We have explored two high-transition-temperature Josephson junction technologies for application in voltage standard arrays: step-edge junctions made with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and Au normal-metal bridges, and stacked series arrays of Josephson junctions in selectively doped, epitaxially grown Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ heterostructures. For both kinds of junctions, Shapiro steps induced by a microwave bias were characterized as a function of power. We compare the technologies with respect to critical current and normal resistance uniformity, maximum achievable critical current, critical-current normal-resistance product, and operating temperature.         High-T/sub c/ multilayer magnetometers with improved 1/f noise    F. Ludwig, E. Dantsker, D. Koelle, R. Kleiner, A.H. Miklich, D.T. Nemeth, J. Clarke, D. Drung, S. Knappe and H. Koch Summary: We have fabricated three types of high T/sub c/ magnetometers using a YBa/sub 2/Cu/sub 3/O/sub 7-x/-SrTiO/sub 3/-YBa/sub 2/Cu/sub 3/O/sub 7-x/, multilayer process: multiturn flux transformers coupled to single layer dc SQUIDs in a flip-chip arrangement, multiturn flux transformers integrated with dc SQUIDs, and multiloop magnetometers (fractional turn SQUIDs). The magnetic field noise of the best flip-chip magnetometer was 74 fTHz/sup -1/2/ at 1 Hz and 31 fTHz/sup -1/2/ at 1 kHz. The magnetic field noise of the multiloop magnetometer, measured in a YBCO tube, was 37 fTHz/sup -1/2/ at 1 Hz and 18 fTHz/sup -1/2/ at 1 kHz.         Low noise HTS gradiometers and magnetometers constructed from YBa/sub 2/Cu/sub 3/O/sub 7-x//PrBa/sub 2/Cu/sub 3/O/sub 7-y/ thin films    M.N. Keene, J.S. Satchell, S.W. Goodyear, R.G. Humphreys, J.A. Edwards, N.G. Chew and K. Lander Summary: D.C. SQUID based gradiometers and magnetometers have been fabricated using thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ and PrBa/sub 2/Cu/sub 3/O/sub 7/ on MgO substrates. Flip-chip magnetometers with 1 cm and 6.25 cm/sup 2/ substrates have been constructed. Our device on the larger substrate with a 430 mm/sup 2/ pickup loop had a sensitivity of (42/spl plusmn/3) fT//spl radic/Hz above 3 Hz and (75/spl plusmn/7) fT//spl radic/Hz at 1 Hz. Numerical simulations of d.c. SQUIDs at 77 K have been conducted over an inductance range from 2 to 1000 pH and a critical current range from 3.2 to 322 /spl mu/A. The results emphasise the need to reduce SQUID inductances in order to obtain lower flux noise. Three layer gradiometric SQUIDs with c-axis microbridge junctions and low inductance have been fabricated. First order gradiometric flux transformers were also made with twin 20 turn spiral SQUID input coils and a pair of larger area balanced sensing coils. These were mounted with the gradiometric SQUIDs in a flip chip configuration to complete the highly symmetrical gradiometers. Measurements at 79 K on one gradiometer gave a gradient sensitivity of (49/spl plusmn/3) pT/m//spl radic/Hz at 300 Hz and (103/spl plusmn/7) pT/m//spl radic/Hz at 1 Hz.         Low-noise, single-layer YBa/sub 2/Cu/sub 3/O/sub 7-x/ DC SQUID magnetometers at 77 K    R. Cantor, L.P. Lee, M. Teepe, V. Vinetskiy and J. Longo Summary: We describe a low-noise dc Superconducting QUantum Interference Device (SQUID) magnetometer that is fabricated from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7-x/ on a 2 cm/spl times/2 cm bicrystal substrate. The magnetometer design consists of a single-turn pickup loop that is directly coupled to a low inductance SQUID. Using conventional flux-locked loop electronics with bias current reversal, the white flux noise of several of these magnetometers operated at 77 K is observed to be as low as 2.2 /spl mu//spl Phi//sub 0///spl radic/Hz above 10 kHz, increasing to about 5.7 /spl mu//spl Phi//sub 0///spl radic/Hz at 1 Hz. The field-to-flux conversion efficiency is measured to be 4.6 nT//spl Phi//sub 0/, resulting in a white magnetic field noise of to fT//spl radic/Hz above 10 kHz, increasing to 26 fT//spl radic/Hz at 1 Hz.         Investigation of thin film DC SQUID gradiometer using a single YBCO layer    P. Seidel, V. Zakosarenko, F. Schmidl, L. Dorrer, H. Schneidewind, S. Linzen, E.V. Il'ichev and M. Darula Summary: Thin film DC SQUID gradiometers with a large effective pickup area using only a single YBa/sub 2/Cu/sub 3/O/sub 7-x/ layer and step edge Josephson junctions on SrTiO/sub 3/ substrate have been prepared. The planar gradiometer consist of two loops coupled directly to a small area SQUID in the center of the structure. The main advantage in comparison to magnetometers is the possibility of direct measurements in magnetically unshielded environment. At 77 K without bias reversal technique we obtain a white noise level about 3.6/spl times/10/sup -5/ /spl Phi//sub 0//Hz/sup 1/2/ or 700 fT/cmHz/sup 1/2/. Some peculiarities for a two SQUID arrangement with 4 Josephson junctions are observed and simulated on the base of the RSJ model.         Integrated high-T/sub c/ SQUID magnetometer    B. David, D. Grundler, J.-P. Krumme and O. Doessel Summary: We have fabricated an integrated SQUID magnetometer based on Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ step-edge Josephson junctions. A tight coupling between the input coil and the SQUID washer has been achieved with a coupling coefficient K of 0.9. Noise measurements on our SQUIDs showed a nearly frequency independent flux noise of 50 /spl mu//spl Phi//sub 0///spl radic/Hz at 77 K. 1/f-noise contributions at lower temperatures were always completely suppressed by bias reversal. From our measurements of the field sensitivity and the flux noise we can estimate a field resolution of the magnetometer of 60 fT//spl radic/Hz down to 1 Hz.         Double barrier long Josephson junctions with a contact to the intermediate superconducting layer    H. Kohlstedt, A.V. Ustinov and F. Peter Summary: We demonstrate a double barrier long Josephson tunnel junction device of overlap geometry with an external electric contact to the middle electrode. The junctions were fabricated with a standard Nb/Al-AlO/sub x//Nb process. To exhibit fluxon coupling effects in stacked junctions, the intermediate Nb layer thickness between two barriers has to be of the order of the London penetration depth, i.e. 90 nm for sputtered Nb films. By using a planarization process, we were able to avoid steep steps on the wafer and so to reduce the intermediate layer thickness to 90 nm. Double-junction stacks with areas from 10/spl times/10 /spl mu/m/sup 2/ to 20/spl times/600 /spl mu/m/sup 2/ were fabricated. In the best stacks, the difference in the critical currents of two junctions was less than 3%. Clear voltage locking effects were observed in current-voltage (I-V) characteristics.         Comparison of simulation and experiment for a Josephson fluxonic diode    F. Raissi and J.E. Nordman Summary: With a slight modification to the control line and its bias configuration, a long Josephson junction vortex flow transistor structure can become a so-called fluxonic diode containing fluxon and antifluxon "doped" regions in analogy to a pn junction. Such structures have been made with Nb-Pb tunnel junctions allowing testing of the same device with a number of different doping configurations. This paper compares experimental results with a one dimensional numerical simulation. Different configurations for the diode have been modeled with Stewart-McCumber loss parameters ranging between 50 and 1400. The simulation clarifies the origin of a number of experimental observations, including a peculiar dependence of resonance induced step behavior on loss parameter, and a limit to the value of the gradient of doping in the transition region below which an asymmetric I-V curve representing forward and reverse biases is obtained. In forward bias, the I-V curve above a threshold current is roughly linear and devoid of resonance structure, provided injection of carriers occurs from one region to the other. Injection is a function of loss and the asymmetry of doping.         Internal resonances in periodically modulated long Josephson junctions    B.H. Larsen, J. Mygind and A.V. Ustinov Summary: Current-voltage (I-V) characteristics of long Josephson junctions with a periodic lattice of localized inhomogeneities are studied. The interaction between the moving fluxons and the inhomogeneities causes resonant steps in the IV-curve. Some of these steps are due to a synchronization to resonant Fiske modes in the sub-junctions formed between the inhomogeneities. The voltage positions of the resonant steps oscillate as function of the applied magnetic field with a period corresponding to the inclusion of one magnetic flux quantum, /spl Phi//sub 0/=h/2e, per sub-junction. A qualitative explanation that takes into account the interaction between the resonance in the sub-junction and the magnetic flux density waves excited in the whole junction is given.         Properties of autonomous and injection locked flux flow oscillators    J. Mygind, V.P. Koshelets, A.V. Shchukin, S.V. Shitov and I.L. Lapytskaya Summary: Flux flow oscillators (FFO) have been experimentally investigated at frequencies up to 850 GHz. At 440 GHz the received power in an on-chip integrated SIS mixer is 5 /spl mu/W. The first experimental measurements of the FFO linewidth as a function of applied dc bias current and magnetic field have been performed both for two autonomous FFOs and with one of the FFOs injection-locked to a narrow-band external microwave source. By beating the two autonomous FFOs an integral spectral linewidth as low as 750 kHz is measured at 280 GHz. Mechanisms leading to a broadening of the FFO linewidth are discussed. Experimentally it is shown that the FFO can be used as harmonic generator.         Fabrication of all-NbCN flux-flow oscillators with a tapered slotline antenna and off-chip detection of their radiation power    S. Kiryu, S. Kohjiro, A. Shoji, S. Kodaira, K. Kawaguchi and J. Inatani Summary: All-NbCN flux-flow oscillators (FFO) with tapered slotline antenna (TSA) were fabricated on MgO substrates. A five-step microstrip transformer was used to couple an FFO, which has a low impedance, to a TSA having a high impedance, The microstrip transformer is designed to have a return loss more than 20 dB at the center frequency. We have measured submillimeter wave radiation from the oscillators using an off-chip silicon-composite bolometer. Radiation from a fabricated FFO was detected in a bias voltage range from 1.18 mV to 1.48 mV, which corresponds to a frequency range from 570 GHz to 710 GHz.         Dynamics of triangular and tetrahedral Josephson junction oscillator arrays    S.P. Yukon and N.C.H. Lin Summary: Triangular and tetrahedral arrays of Josephson junctions are considered as rf oscillator sources. Enhanced power production is possible due to a) series rf voltages developing in junctions transverse to the forcing current and b) modular array design. Exact solutions are found for the basic triangular array elements.         Experimental study of fluxon resonances in window-type long Josephson junctions    N. Thyssen, A.V. Ustinov, H. Kohlstedt, S. Pagano, J.G. Caputo and N. Flytzanis Summary: We report first systematic measurements of zero-field steps in I-V characteristics of long Nb/Al-AlO/sub x//Nb Josephson junctions made in a window of a stripline structure. We compared the data for junction series of the same dimensions but with different ratio of the junction width W to the width of the idle window part W' surrounding them. Zero-field steps were found to be stable only in structures with W'/W<3. With increasing the ratio W'/W, the effective fluxon propagation velocity is found to increase and fine structure resonances appear on fluxon resonant steps. Experimental data are compared with numerical simulations using the modified two-dimensional sine-Gordon equation and qualitative agreement is found.         Temperature dependence and magnetic field modulation of critical currents in step-edge SNS YBCO/Au junctions    N. Missert, L.R. Vale, R.H. Ono, C.D. Reintsema, D.A. Rudman, R.E. Thomson and S.J. Berkowitz Summary: We compare the electrical transport properties of superconductor-normal metal-superconductor SNS step-edge YBCO/Au junctions where the Au is deposited at 100/spl deg/C and 600/spl deg/C. For both types of junctions we observe resistively shunted junction current-voltage characteristics. The critical currents I/sub c/ in all cases are similar for a given ratio of YBCO thickness-to-step height, while the normal resistance R/sub n/ for the Au deposited at 600/spl deg/C is consistently 25% lower than for the Au deposited at 100/spl deg/C. The normalized temperature dependence of the I/sub c/R/sub n/ product is nearly identical for all junctions with Au deposited at high temperatures but varies among junctions on a single chip for Au deposited at 100/spl deg/C. Low magnetic field modulation of the critical current can show either the expected Fraunhofer-like pattern or a double-junction modulation for both types of devices. The modulation period is consistently a factor of 3 lower for the high-temperature deposited Au.         Voltage-current characteristics and noise properties of SNS junctions    A. Flett, M.S. Colclough, Y. He, C.M. Muirhead, R.A. Robinson and K. Char Summary: We report measurements of V/I/B characteristics for a number of YBCO/N/YBCO junctions where the N layer is Co doped YBCO. The field dependence of about half the junctions tested showed I/sub c//B characteristics which approached 100% modulation for T>80K far field directions both perpendicular to the plane of the junction and along the width of the junction. Other junctions showed an anomalous field modulation which decreased as the temperature was increased. More detailed measurements are reported for one junction which showed fairly large modulation. The V/I characteristics were found to be in very good agreement with a thermally rounded RSJ model in the temperature range 74-80 K. The voltage noise peaked at I/sub c/, and had a 1/f dependence in the range measured. It had a value of 8 nV Hz/sup -1/2/ at 1 Hz and 75 K.         Comparative study of the stationary properties of high-T/sub c/ proximity-coupled Josephson junctions    K.A. Delin and A.W. Kleinsasser Summary: Much recent research aimed at developing high temperature Josephson junctions for electronics applications is based on superconductor-normal metal-superconductor (SNS) edge junctions which, in some instances, exhibit excellent current-voltage characteristics, high critical current-resistance products, and low noise. We review the data available in the published literature and conclude that, despite the useful performance of these junctions, there is little evidence that the behavior of most reported high-T/sub c/ SNS devices can be described by conventional proximity effect theory.         Co-doped-YBCO SNS junctions for superconductive integrated circuits    A.E. Lee, J.A. Luine and C.L. Pettiette-Hall Summary: We have established a high temperature superconductor SNS junction fabrication process and are reproducibly fabricating junctions whose behavior is rooted in the physics of the proximity effect. SNS edge junctions are being fabricated using YBa/sub 2/Cu/sub 2.8/Co/sub 0.2/O/sub 7-/spl delta// (Co-YBCO) as the normal barrier, and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) as the superconductor. In the small junction regime, the junctions have RSJ characteristics with I/sub c/R/sub n//spl sim/ 50 /spl mu/V at 77 K. Junction normal resistance values are consistent with known values of the barrier bulk resistivity and junction geometry, indicating that the interface resistance between YBCO and Co-YBCO is not significant. We have demonstrated I/sub c/ and R/sub n/ 1-/spl sigma/ spreads of 33% and 17%, respectively, for 6-junction strings. Barrier thickness and/or morphology variations appear to significantly contribute to these spreads.         Novel tri-stable elements for binary RSFQ circuitry    D.Y. Zinoviev and O.A. Mukhanov Summary: A set of tri-stable RSFQ cells has been designed, simulated, fabricated in Hypres, Inc. using 1 kA/cm/sup 2/ low-T/sub c/ Niobium technology and successfully tested. The elements (including a generic X cell, XOR and inverted XOR cells) are fully compatible with binary RSFQ circuits and do not require any input/output conversion. Their use provides an effective way to simplify some complex functional RSFQ blocks. We also describe a novel automated setup for testing of digital superconductive devices which has been used for experimental study of the cells.         Single flux quantum circuits using the residue number system    Qing Ke and M.J. Feldman Summary: We have designed and developed superconducting single flux quantum (SFQ) digital signal processing circuits using the residue number system (RNS). RNS arithmetic is a complete alternative to binary arithmetic for performing digital computations, which appears to have many advantages for SFQ circuits. We present a scheme for performing all RNS arithmetic functions using Josephson shift registers alone, and suggest that this Is advantageous for high-temperature superconductor computational circuits. We have designed a one-decimal-digit adder, realized with Nb-based superconducting circuitry. Its most complex component, the mod5 adder, has been simulated to show perfect functionality and subcell simulated margins are compared with the experimental results.         Design and operation of a Quantum Flux Parametron bit-slice ALU    W. Hioe, M. Hosoya, S. Kominami, H. Yamada, R. Mita and K. Takagi Summary: The design of Quantum Flux Parametron (QFP) majority logic circuits presents a number of unique constraints. For example, interconnects must be kept short and have a common small inductance. The former suggests that the bit-slice architecture is well suited to QFP circuits. In order to test this conjecture, a suitably complex logic circuit was designed and a small part of it was fabricated. A design for a 16-function bit-slice arithmetic-logic unit (ALU) was found that satisfied the constraints. It can compute on n-bit operands in 2n+4 QFP stages. A reduced version of the bit-slice ALU cell, containing 30 QFP's, was fabricated and successfully tested at low speed. The design experience showed that complex combinatorial QFP logic circuits are possible. Larger circuits will be feasible with computer-aided tools.         A Single Flux Quantum cross-bar switch and demultiplexer    A.H. Worsham, J.X. Przybysz, Joonhee Kang and D.L. Miller Summary: A Single Flux Quantum (SFQ) demultiplexer and a cross-bar switch for a high speed data switch are described. Both circuits were error-free in simulation to 15 Gbps. The cross-bar switch was two input, two output (2/spl times/2) and used /spl sim/400 /spl mu/A control signals to set the data path. The switch has been demonstrated at over 15 Gbps/line using average voltage measurements. The correct routing of a bit stream was demonstrated at 2.488 Gbps.         Rapid single flux quantum random access memory    S.V. Polonsky, A.F. Kirichenko, V.K. Semenov and K.K. Likharev Summary: A new design concept for the Josephson-junction random access memory (RAM) has been developed. In contrast to previous RAMs based on single flux quantization (SFQ), in our system READ and WRITE operations employ ballistic transfer of SFQ pulses along bit lines (either Josephson transmission lines, or passive superconducting microstrip lines, or their combination). The basic memory cells are the single-junction SQUIDs, connected serially by the bit lines and inductively coupled to word lines. READ and WRITE operations are performed by sending SFQ pulses in appropriate directions along bit lines, and DC currents of appropriate polarity into word lines. This approach allows design of very dense memories with n/spl les/2 Josephson junctions per bit, memory cell area smaller than 80 /spl lambda//sup 2/ (where /spl lambda/ is the minimum feature size), and the critical parameter margin well above /spl plusmn/20%. In this paper we present the general structure of the RSFQ RAM, as well as design and results of testing of the basic memory cell and decoder circuitry using Hypres' 3.5-/spl mu/m, 1-kA/cm/sup 2/ Nb-trilayer technology.         Adder-accumulator cells in RSFQ logic    S.S. Martinet, D.K. Brock, M.J. Feldman and M.F. Bocko Summary: We are in the process of designing a Finite Impulse Response (FIR) filter for use in a Digital Signal Processing (DSP) system based entirely on Rapid Single Flux Quantum (RSFQ) logic. One aspect of this project involves the development of the arithmetic unit of the filter, in this case an adder-accumulator multiplier. This article describes two cells can perform the function of accumulated addition in the adder-accumulator multiplier. We have fabricated both cells and tested them at low speed.         Implementation of novel "push-forward" RSFQ Carry-Save Serial Adders    A.F. Kirichenko and O.A. Mukhanov Summary: We have developed a novel, so-called "push-forward" design approach in Rapid Single-Flux-Quantum (RSFQ) logic. This approach leads to a more efficient circuit design at the gate level using fewer Josephson junctions combined with reasonable circuit parameter margins. Other advantages include higher operational speed and smaller power dissipation. This novel method is based on a specific type of interaction (pushing forward) between single flux quanta already stored by RSFQ gates and newly arriving data SFQ pulses. It implies a reuse of an internal gate memory as well as realization of multi-quantum storage. Using this push-forward design approach, we have designed, optimized, fabricated, and successfully tested two versions of Carry-Save Serial Adders for digital signal processing applications.         Ta-based tunnel junctions for energy resolving X-ray detection    M.G. Blamire, F.S. Porter, E.C.G. Kirk and K. Van Vechten Summary: We report the results of a programme to develop an energy-resolving superconducting tunnel junction based on a Ta X-ray absorber. The design is based on a vertical heterostructure consisting of a Nb underlayer to act as a quasiparticle reflector, a thick Ta absorber layer and an Al trap layer. The upper surface of this trap layer is oxidised to form the tunnel barrier. The counterelectrode consists of an Al and thin Nb layer with thicknesses controlled to give approximately equal energy gaps in both electrodes and minimal absorption in the Nb counterelectrode. The effect of electro-magnetic barrier resonances on detection performance has been evaluated. Very high quality junctions have been fabricated, tested and evaluated for X-ray energy resolution.         Response of Nb-based tunnel junctions to synchrotron radiation    K. Ishibashi, T. Noda, K. Maehata, H. Nakagawa, H. Akoh, S. Takada, T. Nakashima, H.M. Shimizu, M. Yoshizawa and M. Katagiri Summary: Superconducting tunnel junctions have potential high energy-resolution for X-ray detection. The excellent performance may be suited for experiments making use of X-rays from a synchrotron radiation. The characteristics of the Nb-based junction were studied to know the response of Nb-based junctions to the synchrotron radiation. We obtained the dependence of the detector pulse height on X-ray energies in a range of 4 to 15 keV.         Quasiparticle lifetimes in epitaxial niobium and tantalum films    P.A. Warburton and M.G. Blamire Summary: By using three-terminal double tunnel junction devices at 2.2 K we have injected quasiparticles into epitaxial thin films of niobium and tantalum. The two junctions are coupled by quasiparticle diffusion and the diffusion of recombination phonons through the sapphire substrate. A comparison of our experimental results with a random walk simulation of the quasiparticle diffusion process enabled us to estimate the lifetime of the injected quasiparticles. The quasiparticle lifetime is not recombination limited in epitaxial Nb and Ta films. Furthermore Ta is less susceptible to the (as yet undetermined) loss mechanisms which govern the quasiparticle lifetime. This result indicates that tunnel junction particle spectrometers utilising Ta absorbers may display better energy resolution than those with Nb absorbers.         Suppression of extrinsic resolution limiting factors in epitaxial superconducting tunnel junction detectors    F.S. Porter, D. Van Vechten, M.G. Blamire and E.C.G. Kirk Summary: Superconducting tunnel junctions have been shown to have potential as high resolution X-ray detectors. Recent reductions in the noise environment of our experiment have yielded a substantial increase in the resolution of our Nb/Ta junctions. The junctions used in the experiment are epitaxial base layer devices including a thick Ta absorber and have survived more than 30 cycles to low temperatures. Current experiments with a /sup 55/Fe source have yielded an energy resolution of 68 eV at 5.89 keV with a quantum efficiency of 13%. Additional measurements using a higher energy /sup 109/Cd source are also reported. We discuss how a reduction of extrinsic and quasi-extrinsic noise sources affects the performance of the detectors and why we believe we are still not observing the intrinsic limitations of these junctions.         Modeling the spectra of superconducting tunnel junction x-ray detectors    D. Van Vechten, F.S. Porter, K.S. Wood, M.G. Blamire and E.C.G. Kirk Summary: SIS tunnel junctions (STJD) are predicted to have exceptionally good energy resolution as x-ray detectors. This paper spectra illustrative of the current state of the art. They were obtained when /sup 55/Fe and /sup 109/Cd x-ray sources bombarded an epitaxial base layer Nb/Ta/Al/AlO/sub x//Al/Nb junction having a diamond shape and sides 15 microns long. Our model of energy loss via the escape of photoelectrons early in the energy cascade is demonstrated to lie qualitatively correct. Earlier results based on fine-grained junctions suggested that such small area devices will have a large characteristic "foot" (asymmetric broadening of low energy side) on the peaks in the spectra that correspond to complete capture of the incident energy in the device. Our device is small, yet its full energy peaks lack significant feet. We conclude that this device is in the fast diffusion limit. This result contradicts the suggestion that Andreev reflection should severely restrict lateral diffusion in clean superconducting bilayers.         Low-energy response of superconducting tunnel junction X-ray spectrometers    S.E. Labov, L.H. Hiller, C.A. Mears, M. Frank, H. Netel, F. Azgui and A.T. Barfknecht Summary: Thin film structures incorporating metallic superconducting layers and tunnel junctions can be configured as low-energy X-ray spectrometers. We present results obtained when low-energy X-rays are absorbed in niobium films coupled to aluminum layers that serve as quasiparticle traps in an Nb/Al/Al/sub 2/O/sub 3//Al/Nb tunnel junction X-ray detector. The linearity of the pulse height as a function of energy Is discussed along with the energy dependence of the observed resolution and its relation to the broadening mechanisms. A resolution of 14 eV at 1 keV has been measured with our detector cooled to 0.3 K.         New modes guided by a thin superconducting film    O. Buisson and J. Richard Summary: New modes guided by an aluminum superconducting film deposited on a SrTiO/sub 3/ dielectric have been observed in the 100 MHz-1 GHz frequency range. Such modes have been understood as a propagating plasma modes of the superconducting electrons. We present impedance measurements which indicate plasma modes resonances. An equivalent electrical circuit is proposed in order to simulate the frequency dependent impedance of our sample.         High speed current switching of homogeneous YBaCuO film between superconducting and resistive states    B.S. Karasik, I.I. Milostnaya, M.A. Zorin, A.I. Elantev, G.N. Gol'tsman and E.M. Gershenzon Summary: Transitions of thin structured YBaCuO films from superconducting (S) to normal (N) state and back induced by a supercritical current pulse has been studied. A subnanosecond stage in the film resistance dynamic has been observed. A more gradual (nanosecond) ramp in the time dependence of the resistance follows the fast stage. The fraction of the film resistance which is attained during the fast S-N stage rises with the current amplitude. Subnanosecond N-S switching is more pronounced for smaller amplitudes of driving current and for shorter pulses. The phenomena observed are viewed within the framework of an electron heating model. The expected switching time and repetition rate of an optimized current controlling device are estimated to be 1-2 ps and 80 GHz respectively.         A superconducting microwave switch    G.D. Poulin, F.A. Hegmann, J. Lachapelle, S.H. Moffat and J.S. Preston Summary: We describe a superconducting microwave switch. The switch comprises a tapering microwave transmission line which can he switched from a very low loss ON state to a high impedance OFF state with a DC voltage applied to the transmission line through a bias-tee. Switching is essentially thermal in nature, occurring due to the formation of a 'hot spot' in the transmission line. Thermal runaway is avoided through the use of voltage rather than current biasing. Once switched, the transmission line attenuates the applied microwave signal. An isolation of 20 dB is readily achievable. The intrinsic response time of the hot spot to applied microwave fields was estimated to be approximately 1 /spl mu/s by measuring the frequency dependence of the transmitted signal.         Multilayer ferroelectric-high T/sub c/ structures with poled ferroelectric layers    G.L. Larkins Jr., M.Y. Avello, J.B. Boyce and D.K. Fork Summary: We have observed shifts of from 0.5 to -6/spl deg/K in the T/sub C(ONSET/) of YBa/sub 2/Cu/sub 3/O/sub 7-x/(123) in laser ablated thin film 123-BaTiO/sub 3/ multilayer structures on (100) oriented LaAlO/sub 3/ upon poling of the BaTiO/sub 3/ with a positive potential. Poling was carried out at between 120 and 150/spl deg/C in air with an applied field of about 10/sup 5/ V/cm after which a positive shift in the T/sub C(ONSET/) of the 123 by an amount of approximately 1/spl deg/K was observed. Samples were also poled at room temperature (20/spl deg/C) with an applied field of 10/sup 6/ V/cm (2-6/spl deg/K shift observed depending on T/sub c/ (R=0)). Negative potentials showed no apparent shift in T/sub C(ONSET/). A dc-poling with no applied field at 150/spl deg/C for 10-30 minutes in air was observed to restore the R vs. T curve to its original, unpoled, state. Details of the deposition parameters, structures and the mast recently obtained results will be presented possible explanations for the effect will also be discussed.         Low-noise slot antenna SIS mixers    J. Zmuidzinas, N.G. Ugras, D. Miller, M. Gaidis, H.G. LeDuc and J.A. Stern Summary: We describe quasi-optical SIS mixers operating in the submillimeter band (500-750 GHz) which have very low noise, around 5 h/spl nu//k/sub B/ for the double-sideband receiver noise temperature. The mixers use a twin-slot antenna, Nb/Al-Oxide/Nb tunnel junctions fabricated with optical lithography, a two-junction tuning circuit, and a silicon hyperhemispherical lens with a novel antireflection coating to optimize the optical efficiency. We have flown a submillimeter receiver using these mixers on the Kuiper Airborne Observatory, and have detected a transition of H/sub 2//sup 18/O at 745 GHz. This directly confirms that SIS junctions are capable of low-noise mixing above the gap frequency.         Integrated sub-MM wave receivers    V.P. Koshelets, S.V. Shitov, A.M. Baryshev, I.L. Lapitskaya, L.V. Filippenko, H. van de Stadt, J. Mees, H. Schaeffer and T. de Graauw Summary: The concept of a fully integrated superconducting receiver looks very attractive for sub-mm space astronomy where low weight, power consumption and volume are required. The possibility to integrate on a few chips the different planar components: a SIS mixer, a superconducting local oscillator (LO), an intermediate frequency amplifier followed by superconducting circuits for digitizing and processing of down converted signals, is discussed. A first implementation of a real integrated quasioptical receiver for frequencies up to 500 GHz is described. The one-chip receiver comprises a double dipole antenna, parallel biased SIS array mixer and Josephson Flux Flow Oscillator (FFO) with matching circuits. The results of extensive investigations of the integrated receiver as well as design and investigation of novel superconducting elements are presented.         30 THz mixing experiments on high temperature superconducting Josephson junctions    E.N. Grossman, L.R. Vale, D.A. Rudman, K.M. Evenson and L.R. Zink Summary: We have investigated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductor-normal-superconductor Josephson junctions as mixers of 30 THz radiation. We have directly observed (2nd order) difference frequencies from 10 MHz to 12.8 GHz between two CO/sub 2/ laser lines. Applying a third microwave signal to the junction, we have observed CO/sub 2/ laser difference frequencies up to 27 GHz. The d.c. bias dependence of the difference frequency signal, as well as other evidence, suggests two distinct mixing mechanisms: hot-electron mixing in the junction banks at high d.c. biases, and bolometric Josephson mixing at low d.c. biases. The latter is the first observation of Josephson mixing at CO/sub 2/ laser frequencies in high-T/sub c/ junctions. The Josephson mixing has generated observable mixing products up to 6th order.         NbN hot electron superconducting mixers for 100 GHz operation    G.N. Gol'tsman, B.S. Karasik, O.V. Okunev, A.L. Dzardanov, E.M. Gershenzon, H. Ekstrom, S. Jacobsson and E. Kollberg Summary: NbN is a promising superconducting material for hot-electron superconducting mixers with an IF bandwidth larger than 1 GHz. In the 1OO GHz frequency range, the following parameters were obtained for 50 /spl Aring/ thick NbN films at 4.2 K: receiver noise temperature (DSB) /spl sim/1000 K; conversion loss /spl sim/10 dB; IF bandwidth /spl sim/1 GHz; and local oscillator power /spl sim/1 /spl mu/W. An increase of the critical current of the NbN film, increased working temperature, and a better mixer matching may allow a broader IF bandwidth up to 2 GHz, reduced conversion losses down to 3-5 dB and a receiver noise temperature (DSB) down to 200-300 K.         High-resolution superconducting X-ray spectrometers with aluminum trapping layers of different thicknesses    C.A. Mears, S.E. Labov, L.H. Hiller, M. Frank, H. Netel, F. Azgui and A.T. Barfknecht Summary: Superconducting tunnel junctions coupled to superconducting absorbers may be used as high-resolution, high-efficiency X-ray spectrometers. We have tested devices with niobium X-ray absorbing layers coupled to aluminum layers that serve as quasiparticle traps. We present a study of device performance as a function of thickness of the trapping layers. We measured the best energy resolution using a device with a high-quality barrier and 200 nm-thick trapping layers on both sides of the tunnel barrier. This energy resolution was 36 eV full width at half maximum at 6 keV, about 4 times better than that obtainable using semiconductor ionization detectors.         Subgap characteristics of Nb/AlOx/Nb tunnel junctions with high critical current density    M. Maezawa, M. Aoyagi, H. Nakagawa, I. Kurosawa and S. Takada Summary: We have investigated subgap characteristics of Nb/AlOx/Nb tunnel junctions with high critical current density (high-J/sub c/). A good agreement of the experimental data with the solution of Werthamer's equation clearly shows that steep current steps observed at odd submultiples of the gap voltage, which cannot be explained by multiparticle tunneling and/or multiple Andreev reflection, are mainly caused by Josephson self-coupling. Our experimental results suggest that Josephson self-coupling is important to high-J/sub c/ tunnel junctions.         Characterization of Andreev reflection barriers by low frequency noise spectroscopy in all-thin-film superconducting point contacts    K. Hamasaki, T. Ikuta, A. Tachibana and T. Fukumoto Summary: Low-frequency noise properties of all-thin-film superconducting point contacts have been investigated. Device characterization is also reported here. The quasi particle behavior is well explained by the Andreev reflection. The low-frequency noise spectral density scaled by frequency and normal resistance is studied as a function of junction (contact) resistance.         Effect of temperature on the resonant macroscopic quantum tunneling in small Josephson junctions    B. Ruggiero and P. Silvestrini Summary: The study of the quantum behaviour of Josephson junctions is interesting not only by itself, but also for the technological importance in electronics employing superconducting weak links. Recently great attention has been devoted to the effects of Resonant Macroscopic Quantum Tunneling (RMQT) between levels the same energy in neighbouring wells of the potential shape describing the junction. This can produce voltage spikes along the supercurrent branch of the I-V curves and peaks in the current switching distributions. Schmidt, Clealand, and Clarke have presented a detailed analysis of the resonant tunnel dynamics for the T=0 case. The present paper is based on a different theoretical approach, first proposed by Larkin and Ovchinnikov, which allows one to include explicitly the temperature. We study the phenomenon in its time dependence and this allows us to consider the lifetime of the voltage spikes as well as the effect of the RMQT on the quantum escape rate out of the V=0 state.         Advantages of superconducting Coulomb-blockade electrometers    D. Song, A. Amar, C.J. Lobb and F.C. Wellstood Summary: We have measured the current-voltage gate charge characteristics and noise in superconducting Coulomb-blockade electrometers from 50 mK to 1.05 K. The Al-AlO/sub x/-Al junctions in our devices have capacitances which range from 0.3 fF to 1 fF and tunneling resistances from 20 k/spl Omega/ to 200 k/spl Omega/. We find that our normal and superconducting electrometers have comparable charge noise but that the latter have much larger modulation which persists to significantly higher temperatures. The maximum operating temperature in the superconducting state is close to T/sub c/. This behavior Is consistent with a simple model and makes the superconducting electrometer preferable for many applications.         Electrical field effect in highly resistive NbN microbridge    N. Yoshikawa, N. Miura, Xiao Chen, K. Yokoyama and M. Sugahara Summary: We investigate conduction properties and electrical field effect of highly resistive NbN microbridges. The bridge region consists of NbN thin films which have granular structure with /spl sim/10 nm. The dimension of the microbridge is approximately /spl sim/200 nm in length and /spl sim/50 nm in width. The highly resistive (100 k/spl Omega/) microbridges exhibit nonlinear current-voltage (I-V) characteristics at low temperatures which are similar to those of an array of single electron tunneling (SET) junctions. The offset voltage ranges from 2 mV to 300 mV at 4.2 K depending on the bridge resistance and the bridge width. Periodic modulation of bridge conductance is observed when external gate electric field is applied to the bridges. These results coincide fairly well with the simulation based on the SET array model.         Complex dynamical behavior in RCL-shunted Josephson junctions    C.B. Whan and C.J. Lobb Summary: We present numerical simulation results on the dynamical behavior of resistively, capacitively and inductively shunted Josephson tunnel junctions (RCLSJ). We found Josephson oscillations, chaotic oscillations, subharmonic oscillations and relaxation oscillations dominate the dynamics of the circuit in this order as we increase the inductance of the shunt. Long apparently chaotic transient states were found in the intermediate range values of the shunt inductance. Difficulties in comparing simulation with experiments due to the existence of the long transients are discussed.         Reduction of telegraph noise in superconducting short weak links    H. Ohta, T. Matsui, K. Shinada, Y. Yamada, T. Munaka and Y. Fujiyama Summary: It has been proved that, in the large channel number limit, the Josephson current of short weak links derived with a quantum mechanical scattering theory is analytically equal to the Josephson current derived with a classical transport equation in the dirty limit. It means that the former expression of the Josephson current can explain temperature dependence of the maximum critical current of short weak links in the dirty limit as well as in the clean and tunnel limits. The proved generality of the expression of the Josephson current helped us find a reproducible method to reduce telegraph noise in devices of short weak links and get a 130-channel dc-SQUID system.         Synchronous switching in vertically stacked Josephson junctions    H. Yamamori, A. Fujimaki, Y. Takai and H. Hayakawa Summary: Vertically stacked Josephson junctions with different thickness of 2, 4, 8, 14, 20, 40 nm for the intermediate electrode have been experimentally investigated. In the double junction, the synchronous switching between the lower and upper junctions is observed. Though simultaneous switching is also observed in the series-connected Josephson junction, some differences only in the double junction with thin intermediate Nb layer such as 4 nm or 8 nm are observed. We have also fabricated three stacked junctions and four stacked junctions and have investigated the magnetic field dependence of the critical currents.         Three-terminal Josephson device with direct bias-current controlled phase difference    I.P. Nevirkovets, M.G. Blamire and J.E. Evetts Summary: We have fabricated and characterized the Nb/Al-AlO/sub x/-Nb/Al-AlO/sub x/-Nb three-terminal double junction Josephson device in which the phase difference across the whole device is controlled by the tunnel current flowing through one of the junctions. The device reveals current gain about 10 and has good isolation of the input and output circuits.         Single layer YBaCuO-gradiometer    G.M. Daalmans, L. Bar, M. Kuhnl, D. Uhl, M. Selent and J. Ramos Summary: A single layer YBaCuO-gradiometer galvanically coupled to DC-SQUIDs were prepared on bicrystal substrates. The devices were operated at 77 K without any shielding. The best performance obtained was a field gradient resolution of 0.5 pT/cm/spl radic/(Hz) for a device with a baseline of 7 mm and a pickup-area of 2 cm/sup 2/.         Noise performance of high-T/sub c/ DC SQUID magnetometers    A.A. Fife, G. Anderson, V. Angus, C. Backhouse, K. Betts, M.B. Burbank, R.A. Cragg, K. Ferguson, F. Habib, P.R. Kubik, J. Nomura, M. Smith, P. Spear, W. Westera, H. Zhou, J. Vrba, B. Heinrich, A.E. Curzon, J.C. Irwin, J. Chrzanowski, X.M. Burany, S. Govorkov, P. Brown and W.B. Xing Summary: High-T/sub c/ DC SQUID magnetometers operating at 77 K have been fabricated from epitaxial YBCO and SrTiO/sub 3/ films and characterized. The DC SQUID washers incorporated either bicrystal or step-edge microbridge junctions of widths down to about 3 /spl mu/m. Three types of DC SQUID magnetometer are described-(a) a single layer device with a direct-coupled loop; (b) a DC SQUID plus flip-chip coupled flux transformer; (c) a fractional turn device with a direct-coupled multi-loop. The 1/f noise in the spectra of uncoupled DC SQUIDs and some magnetometers is significantly reduced by using AC bias modulation. Low frequency energy sensitivities of uncoupled SQUIDs at 77 K have been improved by use of AC bias to 7/spl times/10/sup -30/ J/Hz at 1 Hz (45 pH inductance). For flip-chip coupled magnetometers (15-turn input coil, pick-up coil area 13 mm/sup 2/), excess low frequency noise was observed, only partially reduced by AC biasing, with field sensitivities of 1 pT rms//spl radic/(Hz) and 130 fT rms/spl radic/(Hz) above 200 Hz.         DC SQUID magnetometers with the directly coupled pick-up loop    Keunseop Park, Soon-Gul Lee, Hyuk Chan Kwon, Yong Ki Park and Jong-Chul Park Summary: DC SQUID magnetometers with a directly coupled square pick-up loop have been made from single layer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films using step edge junctions or bicrystal grain boundary junctions on SrTiO/sub 3/ substrates. YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films were deposited by off-axis RF sputtering or laser ablation and patterned by photolithography and Ar ion milling to form the SQUID, pick-up loop and modulation coil. The SQUIDs showed RSJ like current vs. voltage characteristics and voltage modulation in response to external fields at 77 K. The SQUID inductance was 55-140 pH, pick-up loop size was 47 mm/sup 2/ and the effective area of magnetometers estimated from the measured modulation period was 0.2-0.4 mm/sup 2/. The magnetic field noise was 7.4/spl times/10/sup -13/ T//spl radic/(Hz) at 10 Hz and 77 K.         Nonlinear response in thin film magnetometer sense loops at 77 K    J.W. Purpura, T.R. Clem and R.F. Wiegert Summary: The onset of nonlinear response to applied magnetic field in GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film magnetometer sense loops was measured in equipment performing at 77 K. As the magnetic field applied to the magnetometers was ramped, the output magnetic flux of the sense loops was monitored with a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// DC superconducting quantum interference device flip-chip coupled to the loop sample's output washer. In experiments devised to minimize circulating current in the magnetometers, nonlinear onset fields ranging from 26 to 120 /spl mu/T were measured for samples having linewidths ranging from 20 to 800 /spl mu/m. The loops also exhibited hysteresis in conjunction with the nonlinear behavior. These results indicate that nonlinear hysteresis is an issue for magnetometer loops operating in the Earth's field.         Electromagnetic nondestructive evaluation with simple HTS SQUIDs: measurements and modelling    L.N. Morgan, C. Carr, A. Cochran, D.McA. McKirdy and G.B. Donaldson Summary: For AC EM NDE research, the field sensitivity of a SQUID should be around 100 pT, in a bandwidth of 5 Hz or less in the frequency range from 1 Hz to 10 kHz or more. Existing HTS SQUIDs and commercial electronics can already satisfy these demands. Moreover, the small size of HTS SQUIDs and the large dynamic range of SQUID systems permit measurements even in some magnetically unshielded environments. Here, we describe non-contacting AC EM NDE with a simple, small, single layer HTS SQUID. We present results demonstrating the detection of a subsurface feature in aircraft-grade aluminium by horizontal field measurement. Although they indicate the potential usefulness of HTS SQUIDs, variation between nominally identical data has been much greater than expected. This is because of fundamental HTS SQUID problems and the fact that experimental constraints on SQUID position, induction coil geometry and stand-off led to a far from optimum system design. We have analysed the problem using FEM; here we present selected results and indicate how they may affect future designs.         Integration of step-edge grain boundary Josephson junctions with YBCO multilayers for electronics applications    K.P. Daly, J.M. Murduck, C.L. Pettiett-Hall and M. Sergant Summary: We discuss our multilayer YBCO process which uses step-edge junctions. Key issues are dielectric defect density, wiring layer critical current over edges of underlying features and junction critical current uniformity. We have demonstrated an average defect density of about 450/cm/sup 2/ over many wafers. Wiring critical current exceeds 1 mA//spl mu/m of line width. We have demonstrated SQUIDs at 77 K using this process.         Process issues and components for HTS digital integrated circuit fabrication    A.P. Marathe, F. Ludwig, T. Van Duzer and L. Lee Summary: An etch-back planarization technique has been developed to planarize SrTiO/sub 3/ insulating layers, which may be used in a YBCO IC process. Films of YBCO have been deposited on the planarized SrTiO/sub 3/ surface. Structural and electrical characterization of these films suggests that the planarized surface can support the growth of epitaxial, c-axis oriented YBCO films. Experiments to evaluate and compare coupling efficiency in YBCO and Nb thin film transformers are also described. Easy flux penetration in YBCO films may reduce the efficiency of transformer coupling below that found for Nb transformers. The current coupling for Nb transformers, as extracted from the SQUID threshold curves, was found to be high (M/L/spl sim/0.93). The coupling in YBCO transformers, as measured from the voltage modulation of bicrystal grain boundary junction SQUIDs, was found to be much lower (M/L/spl sim/0.75).         Properties of passive structures for multilayer HTS digital circuits    J. Talvacchio, M.G. Forrester and J.R. Gavaler Summary: The passive structures required for HTS digital circuits that must be formed at high temperature (650-750/spl deg/C) were evaluated by fabricating crossovers, vias, YBCO/YBCO contacts, and multiple coverage of steps with trilayer structures of YBCO/epitaxial insulator/YBCO. Two insulator materials were used, high-/spl epsiv/ SrTiO/sub 3/ and relatively low-/spl epsiv/ Sr/sub 2/AlTaO/sub 6/ (SAT). The deposition conditions for both insulators had to be optimized to simultaneously obtain smooth surfaces, sufficiently high oxygen diffusion rates to re-oxidize underlying YBCO, and resistivities in planar capacitor structures of >10/sup 9/ /spl Omega/-cm at 77 K. The particular process used to clean film surfaces after photolithography and Ar ion milling was also critical in obtaining smooth surfaces for a subsequently deposited film layer. For the non-planar capacitor structures formed at crossovers, the effective resistivity of insulators decreased as a function of linewidth, particularly for lines less than 10 /spl mu/m wide. However, even for narrow lines patterned in the top YBCO layer, critical current densities, J/sub c/(77 K), exceeded 106 A/cm/sup 2/.         Vertical c-axis microbridge junctions in YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ thin films    S.W. Goodyear, N.G. Chew, R.G. Humphreys, J.S. Satchell and K. Lander Summary: The fabrication and measurement of microbridge junctions in the vertical c-axis direction of YBCO/PBCO/YBCO evaporated thin films is described. Single junctions show critical current modulation with applied magnetic field, the period scaling with junction size. The IV characteristics show Shapiro steps to high order when irradiated with microwaves. Initial measurements of linear arrays suggest that with further optimisation of the processing steps a reproducible junction technology could emerge. Very low inductance (L/spl ap/5-15 pH) SQUIDs have been demonstrated with dV/d/spl Phi/>1 mV//spl Phi//sub 0/ at 50 K. The vertical SQUID loop geometry of these SQUIDs has allowed a direct determination of the penetration depth as a function of temperature.         Multilayer Josephson junction flux quantum devices    S. Lomatch, E.D. Rippert and J.B. Ketterson Summary: We describe the properties of flux quantum circuitry employing the relatively young technology of multilayer Josephson junctions with n superconductor-insulator (SI) layers. Multilayer junctions can be employed as both passive and active devices to increase circuit integration density, allow for new logic/voltage thresholds and higher impedances, and improve thermal noise stability. We present the results from numerical simulations of a conventional RSFQ circuit and two novel circuits with multilayer junction designs. Neural circuitry is a focus of our novel multilayer designs. We also discuss layout and fabrication issues, considering the recent progress in the fabrication of Nb multilayer junctions with AlN tunnel barriers, which exhibit intrinsic overdamping at the level of each SI layer. Included in this discussion is a long term assessment of a multilayer approach in view of deep sub-micron and high T/sub c/ technologies.         Broadband interfacing of superconducting digital systems to room temperature electronics    D.F. Schneider, J.C. Lin, S.V. Polonsky, V.K. Semenov and C.A. Hamilton Summary: We have developed and tested simple and inexpensive electronics for interfacing Rapid Single-Flux-Quantum (RSFQ) Josephson-junction circuits to room temperature digital systems. Voltage-level (Non-Return-to-Zero) bit signals with a swing of /spl sim/150 uV, developed on-chip by standard SFQ/DC converters, and in some cases amplified to 1.5 mV swing by HUFFLE-type circuits, are passed to the 300 K environment using a high density (40 channel) flexible coplanar waveguide assembly. AC-coupled, 2-3 stage microwave Si-bipolar amps, and Emitter-Coupled-Logic (ECL) buffers accomplish voltage level translation to the standard ECL levels, Using this technique, data rates in excess of 1 Gb/s per channel can be achieved at low cost per channel,.         Ultrafast, integrable, optics-based interface between superconducting and room-temperature electronics    Chia-Chi Wang, M. Currie and T.Y. Hsiang Summary: An ultrafast optical interface between superconducting and room-temperature electronics is proposed to take full advantage of high-speed superconducting circuits. We report on the computed and experimental studies of an optical receiving and modulating system that is compatible in processing with the prevailing integrated-superconducting-circuit technology. Planar interdigitated Nb/Si/Nb metal-semiconductor-metal (MSM) photodiodes are demonstrated as optical receivers with resolvable bit-rate as high as 38 Gb/s, and the response of MSM diode was shaped to be a single-flux-quantum pulse to drive Josephson-junction-based circuits. A similar interdigitated structure on a silicon waveguide is proposed to be an ultrafast light-intensity modulator, with its operation based on carrier-density modulation of the optical index of refraction. This field-effect device has insignificant power dissipation, in addition to high speed. A sample modulator with 5-V bias is shown to have a modulation depth of 40% and a bandwidth over 70 GHz.         Multi-chip packaging for high speed superconducting circuits    R.D. Sandell, G. Akerling and A.D. Smith Summary: We report the development of a multi-chip module (MCM) technology using Nb metallization and benzocyclobutene (BCB) polymer dielectric. The Nb/BCB structure displays very low loss, has low processing temperature, and forms a wide range of microstrip transmission line impedances. We are developing flip chip, solder attachment for die mounting. We also report the electrical characterization of Nb/BCB/Nb for both microstrip resonators, delay lines, and bandpass filters.         A superconductive ring-pipelined network system    S. Tahara, S. Yorozu and H. Matsuoka Summary: A superconductive ring-pipelined network system is proposed to improve performance of multi-processor systems, and a prototype chip is designed. A throughput of a data exchange between processor elements limits the effective performance of the multi-processor systems. The features of the superconductive ring-pipelined network system are a high-clock-frequency operation by using high-speed Josephson gates and wide band superconductive transmission lines, and a high-density package because of its low power consumption. These advantages significantly reduce pipeline loss and improve flexibility in data exchange. Therefore, this network system is capable of improving the overall effective performance of multiprocessor systems. The prototype chip consists of three Josephson ring interface circuits and superconductive interconnections positioned in between these interface circuits. There are a total 1,130 gates. The prototype chip is designed to be operated up to a clock frequency of 10 GHz. Therefore, the total system throughput is estimated to be 60 Gbps.         Superconducting neural circuits using SQUIDs    Y. Mizugaki, K. Nakajima, Y. Sawada and T. Yamashita Summary: Superconducting implementation of neural circuits is presented. A neuron element is composed of a coupled-SQUID, which is a combination of a single-junction SQUID and a double-junction SQUID. A synapse element is composed of multiple double-junction SQUIDs. To demonstrate the abilities of these circuits experimentally, a 8-bit neural-based A/D converter, which contains three neurons and three synapses, has been fabricated using a niobium integration technology. This is the first successful implementation of both neuron and active synapse elements into a superconducting neural network.         A Josephson-junction-bridge track-and-hold circuit    K.Y. Tam and J.P. Sage Summary: This paper describes the design and test of a high-speed monolithic track-and-hold circuit (T/H) consisting of a Josephson-junction-bridge current switch and a superconducting storage inductor. The bridge, under the control of a common-mode clock current, switches a balanced, differential input current. The T/H was fabricated using a 5-/spl mu/m, 1000 A/cm/sup 2/ niobium trilayer process. Calculations and simulations of the T/H predict 5-bit dynamic range, 4.6-bit effective dc resolution, 750 MHz analog bandwidth, 725 ps acquisition time, 700 MS/s peak sampling rate, and an unlimited hold time. Measurements on the fabricated T/H verify the proper qualitative behavior of the T/H and show that it has 5-bit dynamic range, 4.5-bit effective dc resolution, 900 MHz analog bandwidth, and a 550 ps acquisition time, commensurate with a 900 MS/s sampling rate.         Operation of SAIL HTS digital circuits near 1 GHz    S.M. Schwarzbek, K.E. Yokoyama, D.J. Durand and R.A. Davidheiser Summary: Using Series Array Interferometer Logic (SAIL) components, we have demonstrated an HTS gate driving an exclusive OR, whose second input is being driven at 1 GHz. This digital technique serves as an output interface: data is placed on an rf carrier as phase information (Phase Shift Keying). Low voltage, baseband, differential data can be amplified by low noise, narrow bandwidth, single-ended amplifiers. A simple demodulator completes the connection to standard semiconductor electronics.         Optimization of NbN MVTL logic gates for 10 K operation    M. Leung, D.J. Durand, L.A. Abelson, L.R. Eaton and J.W. Spargo Summary: We have systematically studies designs for Modified Variable Threshold Logic Gates (MVTL) in NbN within the framework of factorial analysis. Our goal is to attain optimized margin and fanout for 10 K operation. Significant parasitic inductances, associated with current crowding at junction vias, were measured and are found to affect the operating margin. We report the progression of designs, margin measurements and yield data for our 10 K circuits.         Application of superconducting electrodes to resonant-type LiNbO/sub 3/ optical modulator    K. Yoshida, A. Nomura, K. Komura and Y. Kanda Summary: A study has been made of a resonant type LiNbO/sub 3/ optical modulator employing superconducting electrodes. Numerical calculations of the modulation depth of the optical modulator show that the driving power of the optical modulator using superconducting electrodes can be much smaller than that using normal metals. Experiments to demonstrate the operations of the optical modulator with Pb-In electrodes resonant at 14.8 GHz have been successfully made at 4.2 K. An excellent agreement between theory and experiments is obtained. It is shown that the modulation power in the superconducting state was estimated to be as small as 140 mW compared with 400 mW in the normal state. The present results demonstrate the possible application of superconducting electrodes to high performance LMbO/sub 3/ optical modulators.         Microwave losses of interferometers with many Josephson junctions versus DC magnetic field    R. Lochschmied, W. Benzing and W. Jutzi Summary: The average microwave losses of interferometers with two and four strongly damped Josephson junctions biased by a microwave current source at 10 GHz much below the plasma frequency have been simulated as a function of an external magnetic field. Microwave losses appear periodically within distinct ranges of the magnetic field, with microwave amplitudes below and above threshold currents. The main period corresponds to one flux quantum in every interferometer loop. The absorption rate increases with the microwave amplitude in qualitative agreement with measurements.         HTS/ferroelectric thin films for tunable microwave components    F.A. Miranda, C.H. Mueller, C.D. Cubbage, K.B. Bhasin, R.K. Singh and S.D. Harkness Summary: We report on the electrical characterization of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///LaAlO/sub 3/ multilayer structure. This structure was fabricated using a pulsed laser deposition technique yielding film thicknesses of 300 nm and 800 nm for the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) and the Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST) films, respectively, A transition temperature T/sub c/=91.5 K was measured for the YBCO film in this structure after deposition of the BST layer. The structure was patterned into parallel plate capacitors with 400/spl times/400 /spl mu/m gold contacts and YBCO electrodes on top and underneath the BST, respectively. A relative dielectric constant (/spl epsiv//sub r/)/spl sim/425 and a loss tangent (tan/spl delta/)=0.010 were measured at 1.0 MHz at 298 K and zero dc voltage (V/sub dc/=0 volts). At 77 K, the dielectric data showed 320/spl les//spl epsiv//sub r//spl les/360 and tan/spl delta/=0.036 at V/sub dc/=0 volts. For 5.0/spl ges/V/sub dc//spl ges/-3.0 volts /spl epsiv//sub r/ could be varied from 180 to 370. For -5.0/spl les/V/sub dc//spl les/-3.0 volts, /spl epsiv//sub r/ decreased rapidly with little change in tan/spl delta/. The /spl epsiv//sub r/ versus V/sub dc/ data suggest that changes in /spl epsiv//sub r/ were affected by electrode space charge layers.         RF coupling to single crystal BSCCO under c-axis bias    G.K.G. Hohenwarter, A.W. Laundrie, J.U. Lee, J.B. Beyer and J.E. Nordman Summary: We have explored rf coupling to BSCCO single crystals with c-axis bias currents over a wide range of frequencies. A structure was developed that afforded the necessary impedance transformations at several frequencies from dc to 35 GHz. At low frequencies, connections were made to a coaxial cable. At X-band, the sample was placed in front of a short section of waveguide, forming a resonator. Above 12 GHz, the sample mount formed a coplanar resonator. At 35 GHz it was used as the end plate of a cylindrical cavity with degenerate mode spoilers and a loaded Q-factor of 3800 at 38.3 GHz. Fabricated BSCCO samples showed evidence of hysteretic Josephson junction stack behavior at 77 K. Application of low frequency rf signals caused steps to appear in the sample I-V. At frequencies above 6.4 GHz only a reduction of critical current was observed.         A high gain YBCO antenna array with integrated feed and balun    L.P. Ivrissimtzis, M.J. Lancaster and N.McN. Alford Summary: A supergain antenna array of closely spaced printed dipoles made of thick film YBCO was designed and experimentally tested. An optimization of the directive gain with respect to interelement spacing, dipole length, and other circuit parameters, subject to constraints in array size, was performed by combining the spectral domain method of moments and transmission line theory. The design procedure accounts far losses associated with the strip material, both at the feed and the radiating dipoles, and power dissipation in the substrate. A practical design of a sixteen element array is demonstrated, with an integrated feeding network and a balun, also made of high-T/sub c/ superconductors (HTS). Performance is compared against simulated data. The superconducting array has gain significantly higher than that of a similar supercooled silver array albeit at the expense of transmission bandwidth. It is shown that supergain is practically achievable by miniature, printed HTS dipole arrays.         The ARPA high temperature superconductivity program    F.W. Patten and S.A. Wolf Summary: This paper presents an overview of the Advanced Research Projects Agency (ARPA) program on high temperature superconductivity (HTS). This multidisciplinary effort has, since 1987, spent about $220,000,000 on promoting the science and technology of these materials. Support of many aspects of R and D has been provided to universities, national laboratories and an emerging industrial base. The current program is focused on several promising applications: (1) the development of RF and microwave passive components and subsystems for radar, EW, wireless communications and medical instrumentation; (2) developing digital applications of cryogenic technology both utilizing superconductors as well as semiconductors; (3) contributing to the development of a conductor for power applications, and (4) developing a variety of low-cost reliable cryocoolers that will be the enabler for many aforementioned applications.         Cryogenic electronics in advanced sensor systems    M.M. Fitelson Summary: Cryogenic Electronics technologies are discussed from the standpoint of meeting sensor performance requirements. Capabilities that are provided by cryogenic electronics are described. Radar and Electronic Warfare (EW) Systems requirements are based on the need to detect and track targets in the presence of clutter and jamming signals. Radars must transmit high fidelity signals, and receive returns with high fidelity and wide dynamic range for Doppler Processing, to discriminate targets from clutter and jamming. Requirements are translated into radar specifications: transmitter, receiver, antenna array, and other components must produce low phase noise. The receiver and analog to digital converter (ADC) need wide linear dynamic range. HTS technology provides key devices to achieve phase noise supression and large signal dynamic range. Examples include: HTS resonators generate stable reference signals in the radar; switchable preselectors remove out of band jamming; HTS circuits enable digital to analog converters (DACs) and ADCs to provide direct synthesis of complex waveforms and digitization of received signals. EW System requirements are high dynamic range reception, and real-time signal processing; they must be wide-band and recognize a diverse set of waveforms. An HTS switchable preselector and delay line provide the front end for an advanced EW receiver and processor. The application of HTS technology to Radar and EW Systems will be addressed, and progress to date in development of analog and digital HTS devices will be described.         Improved design of an optically switched inductance modulation circuit for noise reduction in SQUID systems    G.S. Park, Sae Woo Nam, B. Cabrera and M.E. Huber Summary: We have modeled and optimized the design of an optically driven inductance modulation circuit, for use as part of a 1/f noise reduction scheme for SQUID magnetometers. We modulate the effective inductance of a photolithographically patterned coil via its mutual inductance with three concentric superconducting washers directly above the coil. The superconducting loops formed by each of these washers can be broken by sending laser light onto a constricted meander section of each of these washers. With the laser off, the superconducting washer loops diamagnetically shield the coil, and the coil has a low effective inductance. With the laser on, the meanders are driven normal and the superconducting washer loops are open, greatly reducing the shielding. The coil then has a high effective inductance. In a series of computational runs, we have optimized the design of this circuit in terms of its inductance modulation depth and its avoidance of flux jumping incidents. The free parameters in this study were the inner diameter of the coil, the number of loops in the coil, the dimensions of the three washers, and the size of the overlaps between washers.         Use of a DC SQUID receiver preamplifier in a low field MRI system    H.C. Seton, D.M. Bussell, J.M.S. Hutchison and D.J. Lurie Summary: We have used tuned receiver coils coupled to a dc SQUID preamplifier in a small scale magnetic resonance imaging (MRI) system operating at 425 kHz (B/sub 0/=0.01 T). The coil and SQUID are cooled to 4.2 K in a modified biomagnetic cryostat. The modifications provide transparency to rf signals originating outside the cryostat while maintaining an acceptably low liquid helium boiloff rate. By applying negative feedback we have damped low loss, high Q-factor SQUID input circuits to achieve a useful imaging bandwidth of over 2 kHz.         High slew rate large bandwidth integrated dc SQUID magnetometer for NMR applications    S.L. Thomasson and C.M. Gould Summary: We have developed an integrated dc SQUID magnetometer, with additional positive feedback (APF) unmodulated SQUID electronics system for low frequency true NMR applications. We constructed our SQUID circuit using an 11-layer Nb/Al/AlO/sub x//Nb process. Our design modifies previous APF approaches by incorporating selectable, high resolution on-chip feedback resistance. The on-chip resistance selection allows us to maximize the SQUID gain, dV/d/spl Phi/, at the operating point. With the use of APF we have achieved a slew rate greater than 10/sup 6/ /spl Phi//sub 0//s, and a bandwidth of approximately 300 kHz, which is suitable for sensitive NMR measurements.         Integrated rf amplifier based on dc SQUID    M.A. Tarasov, G.V. Prokopenko, V.P. Koshelets, I.L. Lapitskaya and L.V. Filippenko Summary: Integrated radio-frequency amplifiers comprising a 4-loop dc SQUID, seriesly connected input coil turns, a resonant capacitor parallel to the input coil, series capacitors at the input and output ports and bias resistors have been designed, fabricated and experimentally studied. A multiloop dc SQUID with parallel loops and seriesly connected single-turn input coils placed inside each loop and integration with the input resonant matching circuit elements and with elements of dc bias circuit allows one to increase signal frequency and reduce the influence of external noise. The amplifiers with three different capacitors have resonant frequencies 560, 656, 758 MHz and bandwidth about 50 MHz. The noise temperature of such amplifiers below 1.5 K has been measured using cold attenuator and room-temperature noise sources. The layout comprising three pairs of such amplifiers placed on the same 15/spl times/24 mm substrate was designed to increase the bandwidth over the bandwidth of the individual amplifiers.         White noise performance of integrated DC SQUID susceptometers in high magnetic fields    K.G. Stawiasz, M.B. Ketchen and L.R. Narasimhan Summary: We have characterized the white noise performance of integrated DC SQUID susceptometers in magnetic fields up to 400 G. The field is applied in the plane of the tunnel junctions and pickup loops. For 1 /spl mu/m diameter junctions, the noise does not increase significantly as the field is increased to 125 G. Further increase of the applied field results in higher noise until approximately 200 G where the critical current of the junctions is at a minimum. The noise then improves to approximately 4 times the zero field value at the maximum of the first lobe of the single junction interference pattern. We have also measured the noise of a SQUID with 0.6 /spl mu/m junctions and found no increase up to 250 G.         Using a scanning SQUID to determine the symmetry of the order parameter in YBCO    A. Mathai, Y. Gim, R.C. Black, A. Amar and F.C. Wellstood Summary: We have determined the time and spatial symmetry of the superconducting order parameter in YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) by using a Scanning SQUID Microscope to perform a time-reversal invariance test. We find the order parameter in YBCO has a time-reversal invariant d(x/sup 2/-y/sup 2/) symmetric component. In addition, we find that the amplitude of any imaginary isotropic s-wave symmetric component must be less than 6% and any real isotropic s-wave component less than 89%.         Multi-loop self-shielded dc-SQUID with meander-shaped input coil    V.V. Masalov, A.N. Samoos, A.N. Matlashov, V.Y. Slobodchikov and Y.V. Maslennikov Summary: A multi-loop design insensitive to external uniform magnetic fields is suggested for a dc SQUID. The SQUID has a meander-shaped coupling coil, which show promise both for LTc and HTc biomagnetic measuring systems. The 16- and 32-loop versions of the SQUID were manufactured using niobium technology and were tested experimentally. On the basis of the experimental data it was shown that the use of LTc multi-loop SQUIDs makes it possible to develop biomagnetic measuring gradiometers with a resolution of the order of 3-4 fT/spl radic/Hz. A multiloop SQUID may be used with a flux transformer in the form of a first-order gradiometer free from conductor crossings. Such a gradiometer has a single-layer design and can be easily fabricated from HTc materials.         A double dc SQUID based magnetometer    Yu.V. Maslennikov, A.V. Baljaev, O.V. Snigirev, O.V. Kaplunenko and R. Mezzena Summary: We have developed a double dc SQUID based magnetometer with a direct read-out circuit and measured its signal and noise characteristics. The inductances of the input SQUID and SQUID-preamplifier were 120 and 250 pH. Thin-film flux transformers on the separate substrates had an inductance of the order of 1 /spl mu/H each and a current sensitivity of 0.54 and 0.32 /spl mu/A//spl Phi//sub 0/ for the first and the second SQUIDs, respectively. The intrinsic energy resolution of the fabricated magnetometer for an optimal gain of 58 for the first stage was close to 1.6/spl times/10/sup -32/ J/Hz. The dynamic range and the slew rate were about 126 dB and 4/spl times/10/sup 4/ /spl Phi//sub 0//s.         Thin-film resistive SQUIDS    G.S. Krivoy and H. Koch Summary: Different all thin-film partly resistive superconducting quantum interference devices (RSQUIDs) for noise thermometry in the liquid helium temperature range were designed and investigated. Three different types of RSQUID were realised: (i) dc RSQUID, (ii) rf RSQUID, and (iii) RSQUID with two quantization loops (double RSQUID). Shunted tunnel junctions were used as weak links. The resistive parts have been made as a Cu thin film combined with Nb thin films either as a sandwich or a planar element. The devices using a rf pump have integrated rf coupling coils. Resistances of the resistive parts in the range from 2.69 /spl mu//spl Omega/ to 246 /spl mu//spl Omega/ were obtained. The output signal was /spl ap/50 /spl mu/V for the dc RSQUIDs, up to 80 /spl mu/V for the rf RSQUIDs, and up to 1.2 mV for the double RSQUIDs. The linear dependences of the output signal frequency versus a dc current passed through the resistive part were observed up to 40 MHz. The double RSQUIDS described have a clear advantage in the output signal compared to the other RSQUIDs.         Dc SQUID based on unshunted Josephson junctions: experimental results    H. Seppa, M. Kiviranta and L. Gronberg Summary: It has been proposed that a new SQUID type be constructed by using unshunted Josephson junctions instead of resistively shunted junctions. Using this approach we are able to present a SQUID having a high output dynamic resistance and a device characterized by a negative output resistance and an extremely low noise. The first mentioned is called a high-gain SQUID, the latter an unshunted SQUID. This article describes preliminary experiments obtained from the SQUIDs based on this concept. The iv characteristics are shown to resemble the theoretically predicted characteristics but the noise performance was higher than expected. Most likely the reason for the high noise was the imperfect damping of the SQUID in the frequencies near 1 GHz.         Effects of high energy proton bombardment (50-280 MeV) on dc SQUIDS    B. Muhlfelder, G.M. Gutt, J.M. Lockhart, P. Carelli, A. Zehnder, F. Mattenberger, W. Hajdas, P. Lerch and R. Henneck Summary: Three thin film dc SQUIDs of varied construction were bombarded with energetic protons in the energy range of 50 to 280 MeV. Measurements of the voltage output of the dc SQUIDs were taken in open loop, as well as flux locked mode, in an environment of proton flux that was varied from 10/sup 4/ to 10/sup 7/ protons/cm/sup 2//s. Discrete voltage jumps corresponding to 0.01 to 0.001 flux quanta were observed in two of the three SQUIDs in the flux locked mode; discrete changes in the open loop SQUID output voltage were also observed. Some data appear to be consistent with proton-induced flux motion in the body of the SQUID loop.         Measurement and simulation of the voltage-flux transfer function of SQUID arrays    Kin Li and S.P. Hubbell Summary: We measured the V-/spl Phi/ of 100-element SQUID arrays and compared them to simulations. Two SQUID inductances, 13 pH and 5 pH were studied. The change of voltage modulation depth per /spl Phi//sub 0/ in a 5 pH SQUID array was faster than that in a 13 pH SQUID array due to larger effective area variations. The effect of magnetic field uniformity on the SQUID arrays output was also studied. We found that a non-uniform magnetic field had the effect of reducing the output voltage and periodicity in V-/spl Phi/ for a SQUID array with high flux bias.         A novel method of realizing two-dimensional array systems of high-T/sub c/ step-edge Josephson junctions    C.D. Reintsema Summary: We have developed a unique substrate terracing process to achieve two-dimensional arrays of high-T/sub c/ step-edge superconductor-normal metal-superconductor Josephson junctions. This process has been used to realize 3/spl times/3 and 3/spl times/6 antenna coupled arrays for direct detection of emission. An enhancement to this process incorporating a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// base layer and a Nb/PdAu ground plane is described. This modification enabled the fabrication of arrays capacitively coupled to detector junctions for detection of emission at frequencies beyond 300 GHz. This report details the motivation, design, fabrication process, and preliminary results of several array experiments.         Properties of YBaCuO step-edge Josephson junction series arrays    J. Konopka, I. Wolff, S. Beuven, M. Siegel and A.I. Braginski Summary: YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) structures composed of 10 and 100 step-edge Josephson junction series arrays incorporated into two-arm logarithmic spiral or bow-tie type were designed, fabricated by pulsed-laser deposition on structured LaAlO/sub 3/ substrates and measured in the temperature range 12 to 70 K at frequencies up to 150 GHz. At 18 K the I/sub c/R/sub N/ product of 10 junction arrays was up to 0.8 mV. Wide Shapiro steps at voltages corresponding to the multiple frequency of irradiation of 100 and 150 GHz were measured, as well as the emitted power and the linewidth at 12 GHz. In some arrays, 30 to 40% of the junctions were phase locked. This indicated that the spread of critical parameters of that fraction of the total junction population did not exceed 10%.         Microwave response of intrinsic Josephson junctions in BSCCO single crystals    A. Irie and G. Oya Summary: We have studied the microwave response of an array of intrinsic Josephson junctions in the c-axis direction in large Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 7/ (BSCCO) single crystals indicating multiple resistive branches on the I-V characteristics. Under the 8-10 GHz microwave irradiation, they showed three types of responses depending on its power P. For relatively low P, the Shapiro steps were observed, whose voltage separations were two order magnitude larger than that calculated from /spl Delta/V=hf/2e, indicating that about one hundred intrinsic junctions in the crystal are phase-locked. For high P, two types of RF-induced steps were observed. In the case of resonance mode, the I-V curve showed the pronounced constant voltage step together with subharmonic ones. On the other hand, for off-resonance mode the broad step was observed. The voltages of these steps increased lineally with p/sup 1/2/. These results suggest that the fluxon motions in intrinsic Josephson junctions interact with external RF field.         Intrinsic Josephson junctions in high-T/sub c/ superconductors as high frequency sources    K. Schlenga, G. Hechtfischer, W. Walkenhorst, P. Muller, F.X. Regi, H. Savary, J. Schneck, M. Veith, W. Brodkorb and E. Steinbeiss Summary: We report on microwave emission experiments of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/-single crystals at frequencies between 12 GHz and 95 GHz. Due to the intrinsic Josephson effect these samples form series connections of typically 2000 contacts. For the first time we observed phase-locking of more than 1000 junctions at 93.7 GHz in Bi/sub 1.8/Pb/sub 0.2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/ single crystals. Concerning the development of high frequency sources we report on first experiments on vertically structured thin films of Tl/sub 2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/.         Integrated High-T/sub c/ oscillator array and high resistance detector junction    J. Edstam, G. Brorsson, E.A. Stepantsov and H.K. Olsson Summary: We have integrated an array of five High-T/sub c/ Josephson junction oscillators with a Josephson detector junction of high resistance, e.g. 25 /spl Omega/. High impedance detectors are suitable in integrated superconducting receivers. We find the output power to be sufficient to modulate the detector junction with large Shapiro steps in the frequency range 200-700 GHz. The oscillator junctions were dc-biased in parallel and integrated in an inductive high frequency coupling circuit to oscillate coherently in-phase. The high frequency coupling circuit is evaluated through its influence on the current-voltage characteristic of the Josephson junctions.         Broadband detection properties of EuBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// array junctions    K. Tsuru, M. Suzuki and O. Michikami Summary: We have fabricated EuBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junction arrays of two different sizes to improve detection output and microwave coupling between junctions and an rf source. The arrays contain three weak link grain boundary junctions made on an MgO bicrystal substrate. It is demonstrated that both the junction array configuration and smaller junction size are effective in improving microwave coupling and hence in increasing the responsivity. The best responsivity obtained is 1085 V/W for broadband detection at 11.9 GHz.         Stacked series arrays of high-T/sub c/ trilayer Josephson junctions    J.N. Eckstein, I. Bozovic, G.F. Virshup, R.H. Ono and S.P. Benz Summary: We report on the properties of stacked series arrays of trilayer Josephson junctions grown by atomic layer-by-layer molecular beam epitaxy. Trilayer Josephson junctions oriented so that the current travels in the c-axis direction have been described previously. Series arrays are made by placing more than one barrier layer in the Ba/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/-based, (2212), epitaxial structure. Single molecular layers of 2212 doped with Dy to reduce the local carrier concentration are used as barriers, and are placed very close to each other, e.g., separated by only a few molecular layers of the superconducting phase. Phase locking of a.c. Josephson currents has been observed. The critical current density of such junctions has been observed to be very uniform on wafers that are free of second phase defects, and operation up to 60 K has been obtained.         Phase locking of HTS Josephson junctions closed into a superconducting loop    S. Beuven, M. Darula, J. Schubert, W. Zander, M. Siegel and P. Seidel Summary: We investigated the mutual interaction of four high-T/sub c/ Josephson junctions which were closed into a superconducting loop. Phase locking of all four junctions was demonstrated in the temperature range from 4.2 K to 48 K. Locking intervals of 18% of the critical current were obtained up to voltages corresponding to a frequency of 180 GHz, according to the second Josephson relation. By comparing our data with numerical simulations, we could show that the junctions were locked in the in-phase state and that the circuit can act as a source of coherent radiation which can deliver power to a load.         Josephson vortex-flow transistors based on parallel arrays of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bicrystal grain boundary junctions    R. Gerdemann, L. Alff, A. Beck, O.M. Froehlich, B. Mayer and R. Gross Summary: Three-terminal electronic devices based on flux-flow phenomena have attracted considerable interest due to their potential application in the interface between superconducting and semiconducting electronics. We have fabricated Josephson vortex flow transistors based on parallel arrays of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) bicrystal Grain Boundary Junctions (GBJs). The array critical current I/sub c/ has been measured as a function of an external magnetic field B or the magnetic field of the current I/sub ctrl/ that is fed through the control line coupled inductively to the array. By varying the device geometry we have studied the influence of the coupling of the magnetic control and the array parameters such as the number N of discrete Josephson elements and the screening parameter /spl beta//sub L/ on the I/sub c/(B) dependences of the arrays. Going from /spl beta//sub L//spl Lt/1 to /spl beta//sub L//spl Gt/1 the measured I/sub c/(B) curves changed from a dependence similar to the diffraction pattern of a grid to a dependence dominated by the parameters of a single array cell. The impact on the available current gain is discussed.         Applications of mm-wave SIS mixers to middle atmosphere monitoring systems    H. Suzuki, T. Imamura, N. Yokoyama, M. Suzuki, H. Ogawa, K. Kawabata and Y. Fukui Summary: We have already developed a low-noise 100 GHz band (98-115 GHz) SIS mixer using Nb/AlOx/Nb junction technology. The mixer has a noise temperature of 17 K when used as a double sideband (DSB) heterodyne receiver. The SIS receiver has been in use in the 4 m radio telescope at Nagoya University for five years. As a further application of the SIS mixer, we developed middle-atmosphere ozone monitoring system using an SIS mixer for the first time. The system can measure ozone mixing ratio every 5 minutes. The integration time is less than 1/10 of the time needed in a conventional system using Schottky barrier diode (SBD) mixers. We have also begun developing developing a 200 GHz band (210-280 GHz) SIS mixer for radio astronomy and for monitoring other minor constituents such as ClO. The preliminary experiment showed that the mixer has a rather low noise temperature of 60 K (DSB).         Mixer of short weak link using a resonance effect due to multiple Andreev reflections at subgap voltages    T. Matsui and H. Ohta Summary: Short metallic weak links of Nb are used for millimeter-wave mixer experiments at 100-110 GHz. When the weak links are connected to a voltage bias circuit with zero output impedance, subharmonic gap structures are observed as a large dynamic resistance region or a negative differential resistance region at voltages V/sub u/=2/spl Delta//ne on the I-V curve, where n=1, 2, 3, ... . These strong structures are caused by a resonance effect between the energy gap and the multiple Andreev reflections that are present whenever there is a spatial inhomogeneity of the pair potential. Enhancement of IF signal peaks is observed at the subgap voltages. These experimental results suggest the appearance of the density of states predicted theoretically by R. Kummel et al. The subharmonic gap structure and details of the SNS mixer experiment will be described.         Four photons sensitivity heterodyne detection of submillimeter radiation with superconducting tunnel junctions    A. Karpov, J. Blondel, M. Voss and K.H. Gundlach Summary: An ultra low noise SIS receiver has been prepared for radio astronomy. The minimum double sideband receiver noise temperature is about 30 K which corresponds to 2 /spl planck//spl omega//k or an equivalent number of 4 photons of noise. The minimum measured double sideband mixer noise temperature is about 10 K which corresponds to 0.6 /spl planck//spl omega//k or approximately to 1 photon of noise. The fixed tuned SIS mixer operates in the 290-370 GHz frequency range. The submicron niobium junctions mere fabricated using photoresist lines for junction definition. The receiver has been used at the 30 m IRAM radio telescope in Spain in winter 1994. Telescope system noise temperature of 500 K single sideband has been achieved when the sky opacity was about 0.17.         Shot noise and photon-induced correlations in 500 GHz SIS detectors    N.B. Dubash, M.J. Wengler and J. Zmuidzinas Summary: Photon-induced current correlations in SIS detectors can result in an output noise that is greater or less than shot noise. Evidence of these correlations had been observed for 100 GHz rf by accurate noise measurements as reported in our previous work. We now present a detailed analysis of these current correlations for frequencies between 100 and 500 GHz. We also report new measurements of photon-induced noise in a 490 GHz SIS mixer, and discuss the Gaussian beam techniques used to eliminate the thermal background radiation. For small 490 GHz rf power, the output noise is equal to shot noise. The results of the 100 and 490 GHz photon noise measurement are summarized in context to shot noise and the effect of the current correlations predicted by the theoretical model.         Measurement of the noise contributions to SIS heterodyne receivers    D.P. Woody Summary: The development of quantum limited heterodyne receivers requires that you understand and are able to measure the major sources of noise in the receiver system. The major sources of noise in millimeter- and submillimeter-wave SIS heterodyne receivers are the optical front end losses, vacuum fluctuation noise associated with the RF coupling efficiency to the SIS tunnel junction and IF amplifier noise. Although there are several methods for estimating the optical losses and IF amplifier noise, the RF coupling efficiency or quantum efficiency has been much more difficult to ascertain. This paper describes in situ techniques for measuring all three noise contributions in a standard receiver used for astronomical observations. Results are presented for the receivers operating in the Owens Valley Millimeter Interferometer Array.         Superconducting packet switch    M. Hosoya, T. Nishino, W. Hioe, S. Kominami and K. Takagi Summary: Very broad band throughputs greater than 1T bit/sec are desired in heavily loaded communication systems. Using the merits of superconducting devices, a superconducting network system is expected to improve the throughputs of such communication bottleneck systems. The paper describes a superconducting packet switch which is indispensable to a proposed superconducting network system. Considering the characteristics of various switch architectures, the space-division Banyan type architecture is adopted for a superconducting packet switch proto-type. The complete design of the proto-type is performed and the total operation is numerically simulated and confirmed. A 2/spl times/2 switching element which controls the paths of two packets is a key component of the proto-type. The basic switching element with one-bit data width is fabricated and the correct operation is completely confirmed.         A clock distribution scheme for large RSFQ circuits    K. Gaj, E.G. Friedman, M.J. Feldman and A. Krasniewski Summary: A primary issue in maximizing the performance of large scale synchronous digital systems is the clock distribution scheme. We present novel clocking scheme, developed specifically for RSFQ logic, which is based on the concurrent flow of the clock and data signals. The scheme permits the circuit throughput to be independent of inter-cell connection delays and significantly reduces the dependence of the throughput on the clock-to-output delay of the cells. Concurrent flow clocking is particularly well for structured architectures. The simulated maximum clock frequency of an RSFQ decimation digital filter currently under development at the University of Rochester can be as much as seven times higher using concurrent-flow clocking rather than conventional (counterflow) clocking. This advantage, however, is reduced to a factor of two due to fabrication parameter variations in present day superconductive technologies.         Design of an RSFQ microprocessor    P. Bunyk and V.K. Semenov Summary: We are discussing a general-purpose microprocessor architecture that is suitable for implementation using the Rapid Single-Flux-Quantum (RSFQ) family of logic-memory circuits. While the microprocessor provides a functionally complete RISC instruction set with 16-bit words, a bit-serial self-timed approach makes it simple enough to be fabricated using the current Josephson junction technology. Our plans are to design, fabricate and test a completely operational prototype of this system.         A novel Josephson cellular array    M. Morisue and Fu-Qiang Li Summary: This paper describes a novel Josephson combinational logic cellular array which can perform any function of n-variable. The basic logic functions such as AND, OR, NOT and Exclusive-OR can be easily achieved by the proposed cellular array. In this paper the principle to construct the cellular array by using SQUID gate is described in detail. In order to verify the operation of the cellular array, simulations have been made for basic logic circuits and a full adder with a satisfactory reliability and high speed operation.         One-dimensional parallel Josephson-junction arrays as a tool for circuit diagnostics    H.S.J. van der Zant, T.P. Orlando and A.W. Kleinsasser Summary: We propose and demonstrate the use of underdamped, one-dimensional parallel arrays of Josephson junctions as a tool for circuit diagnostics. By measuring the Fiske modes and the critical current in a magnetic field, we determined the self and nearest neighbor inductances as well as the capacitances of single junctions. We have used this technique to find the capacitance of Nb-Al/sub 2/O/sub x/-Nb junctions for critical current densities of 0.3-20 kA/cm/sup 2/. We find that the specific capacitance increases by about a factor of 2 over this range. This increase has important consequences for the design of single-flux-quantum circuits and SQUIDs. Measurement of the junction capacitance for critical current densities of 100 kA/cm/sup 2/ is possible, but requires submicron junctions with dimensions of the order of 0.3 /spl mu/m.         Multiparameter optimization of RSFQ circuits using the method of inscribed hyperspheres    Q.P. Kerr and M.J. Feldman Summary: Rapid Single Flux Quantum (RSFQ) circuits must be designed with large operating margins because of variations in the fabrication process. We describe a routine to optimize the yield, rather than the critical margin, of RSFQ circuits, based on the method of inscribed hyperspheres. The operating region is mapped out with a minimum of circuit simulations taking into account the relative size of the process variations. The method is effective for as many as nine parameters. We show that the standard optimization of critical margin will often give a seriously wrong result for multidimensional parameter space.         A computer-aided design framework for superconductor circuits    M. Khalaf, S. Whiteley and T. Van Duzer Summary: This report describes a Computer-Aided Design (CAD) framework for superconducting digital circuits that will automatically transform a high-level combinational circuit description to a gate-level netlist. The framework involves enhancing the current semiconductor logic synthesis CAD tools developed at UC Berkeley (SIS) for application to superconductor digital circuits. The issues specific to superconducting circuits at the synthesis level include the use of multi-phase ac clocking for combinational logic, latching behavior with resetting time constraints, and dual-rail noninverting logic.         Design tools for parameter determination and simulation of integrated Josephson structures    H. Topfer, H. Uhlmann, M. Knoll, H. Thiele and M. Selent Summary: The recent development of integrated Josephson circuits with increased complexity-e.g. RSFQ devices-invokes the need of a comprehensive computer-aided design support. The derivation of circuit parameters from layout data as well as an efficient and versatile simulation technique are essential means in the design and dimensioning of complex integrated structures. We present a comprehensive solution for calculating circuit parameters and simulating the device dynamics. The calculation of inductances and capacitances is performed by three-dimensional field computation using special developed programs which have been proven in high-T/sub c/ SQUID design. They can process layout information in standard graphic interchange formats (e.g. DXF). The netlists for device simulation can be generated automatically from the equivalent circuit schematic. Additionally, a technique for distributed simulation, which allows performing margins-and-yields-analyses in an efficient manner, was elaborated. The performance of the whole design tool set is demonstrated using basic RSFQ circuits.         Series Josephson junction arrays as a high output voltage amplifier    E. Terzioglu and M.R. Beasley Summary: We are investigating the potential of series arrays of nonhysteretic Josephson Junctions as high output voltage amplifiers. Such amplifiers may be useful in Josephson Junction-to-CMOS drivers in Superconductor/Semiconductor hybrid systems. The I-V curves of these arrays are sensitive to the nature and degree of coupling between the junctions in the array. The coupling is determined by the type and the value of the load as well as the junction capacitance (i.e. /spl beta//sub c/) Depending on the nature of the load, the junctions may lock in phase ("in-phase state") or couple such that the fundamental of the Josephson oscillations cancel ("anti-phase state"), suppressing the high frequency Josephson oscillations in the load. Using numerical simulations, we studied the stability of such states to various loads of interest and under static and dynamic drive conditions.         Circuit design for a high-T/sub c/ Josephson sampler    M. Hidaka and J.S. Tsai Summary: We propose a high-speed and high-sensitivity sampler circuit using high T/sub c/ superconducting (HTS) Josephson junctions. This circuit consists of five non-latching junctions, superconducting lines and a superconducting ground-plane. A main feature of this circuit is a non-latching comparator junction whose switching generates a circulating current in a superconducting loop. Computer simulation and prototype layout were performed to study its ability and feasibility.         Discrete underdamped vortex flow devices    A.E. Duwel, H.S.J. van der Zant and T.P. Orlando Summary: Vortex flow devices consisting of discrete arrays of underdamped Josephson junctions have been fabricated and measured. These devices and their long, continuous junction counterparts are based on the ability to magnetically control the Eck voltage in an underdamped system. We find that both transistor and oscillator parameters are improved by placing the arrays above a superconducting ground plane and by connecting two arrays in series. We developed models for the device behavior which numerically account for the measured parameters. Our models also suggest that junctions with smaller capacitances will further improve the device parameters.         Generation of single vortices and local detection by integrated dc SQUIDs    F. Peter, M. Grimm, M. Muck and C. Heiden Summary: A test circuit for the local generation and detection of single vortices has been fabricated, based on a multilayer structure with low-pinning e-beam evaporated Nb and high-pinning reactively sputtered NbN films. The generation of vortices is performed by a current through a control line perpendicular to a low-pinning channel. For the detection and determination of the position of generated vortices, several dc SQUIDs were located around the low-pinning channel and the control line. The presence of single vortices in the channel lead to a shift in the dc SQUID flux-to-voltage transfer function. By computer simulations of the flux that a single vortex generates at the position of the SQUIDs, the number and location of generated vortices could be determined. The spatial resolution of this procedure was determined to be about /spl plusmn/1 /spl mu/m normal to and /spl plusmn/2 /spl mu/m along the channel.         Gain limitations in narrow width Josephson junction vortex flow transistors    M.A. Ketkar, J.B. Beyer and J.E. Nordman Summary: The number of devices required to achieve a practical gain from a Josephson junction vortex flow transistor (JVFT) distributed amplifier is inversely proportional to the gain or the transresistance, r/sub m/ of each active device. A large number of devices means longer transmission line lengths associated with increased loss and size. Reducing the junction width results in increased r/sub m/, however there is a fundamental limit for achievable r/sub m/. This is basically due to two reasons, increased fringing field effects and edge penetration at smaller aspect ratios. Field analyses made on devices with various dimensions show this limitation in the magnitude of r/sub m/ for narrower junctions. The analysis also provides valuable information on parasitic elements in the circuit model for a JVFT. Results of the analyses on devices having different geometries suitable for high frequency operation are presented.         Mechanisms for conduction via low-frequency noise measurements of high-T/sub c/ thin-film microbridges    T. Nguyen, J.M. O'Callaghan, B.A. Davidson, R.D. Redwing, G.K.G. Hohenwarter, J.E. Nordman and J.B. Beyer Summary: We have investigated possible mechanisms for conduction in high-T/sub c/ thin-film microbridges biased into the voltage state via the low-frequency noise properties. Measurements on thinned YBCO microbridges indicate that the voltage noise power spectral density S/sub V/(f) is proportional to the DC voltage .         Discrete models of Abrikosov vortex flow transistors    A. Davidson and N.F. Pedersen Summary: Electronic devices based on flux flow phenomena in oxide superconductors have been under development, and are potentially important for applications, particularly in the interface between RSFQ circuits and silicon based room temperature electronics. Models for these flux flow transistors (FFTs) usually have been based on discrete Josephson elements, ignoring the physics of fluxoid nucleation. We have explored a numerical simulation of flux flow also using discrete Josephson elements, but at the level of the Abrikosov vortex, so that nucleation at the film edge becomes part of the model. Our results imply that the inhomogeneous coupling of the magnetic control is important for a saturated transfer function, rather than a periodic one, and that there is no advantage in putting flux flow strips in parallel, separated by open gaps. Furthermore, gain may be increased by arranging the bias to separately optimize nucleation and transfer to the load.         Computer simulations of dynamics of vortex lines in superconducting flux flow transistors    H. Andoh, M. Kusunoki, A. Fujimaki and H. Hayakawa Summary: We study the dynamics of vortex lines in superconducting flux flow transistors (SFFTs) made of High T/sub c/ superconductors, YBa/sub 2/Cu/sub 3/O/sub x/. By computer simulations we have found that the density of vortex lines in SFFTs has close relation to device I-V characteristics rather than the velocity of vortex lines and that we have to increase the density of vortex lines to get ones with available gain. To be more concrete, in order to increase the density of vortex lines we have to lower surface barriers at the edge of weak-links and heighten the magnetic field near the edge of weak links. Especially, it is very important to heighten the magnetic field at the both sides of a link in a SFFT. Under the control of the control current, vortex lines in a SFFT are driven by the transport current (the bias current) mainly, but it is important to think of the other forces such as the force by screening current, the force induced by the other vortices and the force induced by the image vortices. Based on the local stochastic equation of motion for vortex lines, computer simulations for some conditions are performed to discuss the dynamic behavior of vortex lines in a SFFT. We report the effect of the external magnetic field induced by the control current on the motion of vortex lines in SFFTs.         Characteristics of high-T/sub c/ superconducting flux flow transistors with submicron channels    K. Miyahara, K. Tsuru, S. Kubo and M. Suzuki Summary: High-T/sub c/ superconducting flux flow transistors were fabricated by focused ion-beam irradiation with thin films of co-evaporated YBaCuO. The line-shaped vortex flow channels (0.8 /spl mu/m in width) were constructed by scanning a focused Ga ion-beam (500 nm in diameter) to reduce the critical super-current of the film. The three terminal characteristics of the device were successfully measured. The flux flow characteristics and the transresistance of the submicron channel were measured and compared with those of an ordinary device with a channel wider than 2 /spl mu/m. The measured flow voltage, transresistance and current gain are discussed in relation to the parallel flow of the vortices in the wide channel.         RF characterization of Josephson flux-flow transistors: design, modeling, and on-wafer measurement    Y.M. Zhang, E. Carlsson, D. Winkler, G. Brorsson, H. Zirath and E. Wikborg Summary: Josephson flux-flow transistors based on 0-32/spl deg/ [001]-tilt YBa/sub 2/Cu/sub 3/O/sub 7/ bicrystal junctions have been fabricated with Au loops as the control current lines. In order to measure the S-parameters of the transistors, no matching elements are implemented and 50 Omega coplanar lines are used as the input and output ends of the transistors. The rf properties of the transistors have been modeled on an HP microwave CAD design system, with the junction parameters taken from our dc measurements. Simulations indicate that the transistors can have a maximum stable gain of 20 dB at 7 GHz and 6 dB around 35 GHz under matched conditions. An 'on-wafer' transmission-reflection-load (TRL) method is used for calibrating the S-parameters of the transistor. A low temperature microwave probe station has been built: a pair of microwave probes inside a cryostat are moveable in the xyz-directions. Together with a Wiltron 360B vector network analyzer, this setup provides a convenient way for doing on-wafer characterization of the transistors in the frequency range from 40 MHz to 60 GHz, and in the temperature range from 20 to 80 K.         Superconducting flux flow transistors with submicrometer structures    M. Kusunoki, H. Akaike, A. Fujimaki and H. Hayakawa Summary: A miniaturization of high critical temperature (T/sub c/) superconducting flux flow transistor (SFFT) was studied. The weak link width in the direction of the vortex flow was varied from 5 /spl mu/m to 10 /spl mu/m. The weak link length in the direction of bias current flow was fixed to 5 /spl mu/m. An increase in the gain was observed as the weak link width decreased. A control line was placed close to the weak link at a distance of 0.5 /spl mu/m to compensate for a decrease of magnetic sensitivity due to the miniaturization. We also improved the characteristics of the SFFT by forming a corrugated structure, which is named corrugation flux flow transistor (CFFT). A submicron patterning of YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film was performed using focused ion beam lithography. Furthermore, we demonstrated a micro flux flow transistor (MFFT) consisting of a single bridge. The MFFT also operated as well as the CFFT.         Superconducting flux-flow transistors based upon YBa/sub 2/Cu/sub 3/O/sub 7/ nanobridges    J. Schneider, A. v.d. Hart and R. Wordenweber Summary: Superconducting flux-flow transistors were fabricated from thin (50 nm) high temperature superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ films. In order to determine whether the suppression of the critical current by an applied control current is caused by the magnetic induction or thermal heating due to dissipation in the control line, two different device geometries were developed. The first structure consists of a parallel array of short nanobridges and one parallel control line. In the second structure, a single 10 /spl mu/m long nanobridge is arranged with two parallel long control lines placed on both sides of the signal line. Our measurements demonstrate that in both geometries the magnetic induction of the control lines suppresses the transport properties of the nanobridges. However, for control currents larger than the critical current the transport properties of the bridge are additionally strongly suppressed by thermal effects, which are caused by heating of the current-biased control lines. Furthermore, transistor structures with one long nanobridge and two control lines react more sensitively to small control currents than the device with a single and short control line. They can operate at currents far below the critical current, which leads testable transistor devices.         HTS flux-flow channels on silicon wafers    D.B. Fenner, J.I. Budnick, D.M. Potrepka, Q. Li, P.A. Rosenthal, J. Luo and W.D. Hamblen Summary: New process/structure designs for the channel in the vortex flux-flow transistor (VFFT) have been explored utilizing thin YBCO films on silicon wafers. Two designs are reported: first, films on micromachined Si(100) surfaces, and second, films ex-situ annealed in bromine. Shallow trenches are anisotropically etched into Si(100) wafers forming (111) facets, and films are grown by pulsed laser deposition. Bromination processing of YBCO is preceded by mild de-oxidation and followed by a re-oxidation. Broad-area characterizations by R(T), dc magnetometry, and ac susceptibility are given. On Si(100), epitaxial YBCO films have sharp R(T) transitions and high J/sub c/. Films on Si(111) and brominated films have a toe in R(T) at T/sub co/, and lower J/sub c/ more easily reduced by H. YBCO falling across the trenched surfaces or small brominated regions have R(T), I-V, and I/sub c/ promising for use as flux-flow channels in VFFT.         A single flux quantum shift register operating at 65 K    M.G. Forrester, J.X. Przybysz, J. Talvacchio, J. Kang, A. Davidson and J.R. Gavaler Summary: We report the fabrication and quasi-static testing of a two-stage, high-temperature superconducting, Single Flux Quantum shift register. The five-junction circuit was fabricated using a single YBCO film, with step-edge grain boundary junctions. Storage of flux, and its motion in response to LOAD and SHIFT signals, was demonstrated at 65 K.         The critical current and normal resistance of high-T/sub c/ step-edge SNS junctions    C.D. Reintsema, R.H. Ono, G. Barnes, L. Borcherdt, T.E. Harvey, G. Kunkel, D.A. Rudman, L.R. Vale, N. Missert and P.A. Rosenthal Summary: We have fabricated high-T/sub c/ superconductor-normal-superconductor Josephson junctions with a variety of controlled geometries and measured the resulting dependences of critical current and normal resistance. These studies show that we can adjust our junction parameters over orders of magnitude, thus allowing us to tailor the junctions for a variety of applications.         Electron beam damaged high-T/sub c/ junctions-stability, reproducibility and scaling laws    A.J. Pauza, D.F. Moore, A.M. Campbell, A.N. Broerst and K. Char Summary: The problems of stability and reproducibility of the electron beam irradiated high-T/sub c/ junctions have been studied. It is found that with a overdamage-anneal protocol that stable junctions can be obtained. While on chip uniformity can be very good (1%), the chip to chip reproducibility is not better than 20%. The annealing process allows us to vary T/sub c/ of the junctions over a wide range, making it possible to study the scaling behaviour of a single junction. We find that in these junctions I/sub c/R/sub n//spl prop/J/sub c//sup n/, with n=0.75-0.8 or, since the quasiparticle and Cooper-pair cross sections appear to be equivalent, I/sub c/R/sub n//spl prop//spl sigma//sub N//sup p/ where p=3.0-3.7.         Electromagnetic properties of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin-film grain-boundary weak links    B.H. Moeckly and R.A. Buhrman Summary: The I-V characteristics of thin film microbridges containing 900 basal-plane-faced tilt boundaries (TBs) exhibit pronounced resonant structure. This structure is attributable to the presence of "beating modes" previously studied in high Q DC SQUID structures having substantial shunt capacitance and large inductance. Less pronounced but clear resonant structure is also observable in in-plane c-axis TBs. We discuss a model which accounts for this behavior.         Author Index (1994 - Part 3)    No author information available Summary: Not available

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