Home Welcome Getting Started Conferences Authors

1992 Part 3     Front Cover (1992 - Part 3)    No author information available Summary: Not available         Table of Contents (1992 - Part 3)    No author information available Summary: Not available         Octagonal washer DC SQUIDs and integrated susceptometers fabricated in a planarized sub- mu m Nb-AlO/sub x/-Nb technology    M. Ketchen, D.J. Pearson, K. Stawiasz, C.-K. Hu, A.W. Kleinsasser, T. Brunner, C. Cabral, V. Chandrashekhar, M. Jaso, M. Manny, K. Stein and M. Bhushan Summary: The authors have designed, fabricated, and measured a number of Nb-AlO/sub x/-Nb octagonal washer DC superconducting quantum interference devices (SQUIDs) and miniature DC SQUID susceptometers having minimum feature size down to 0.5 mu m. With SQUID inductance values on the order of 100 pH, typical noise performance is better than 1 mu Phi /sub 0// square root Hz. The small minimum feature size of input coils and pickup loop structures will facilitate tight coupling to a wide variety of systems ranging from submicron particles and structures to conventional approximately mu H input circuits. A single-washer SQUID with an 80-turn 0.5- mu m-linewidth, 630-nH input coil has user-friendly V- Phi (voltage-flux) curves and a coupled energy sensitivity of 20 h at 4.2 K. Susceptometers with pickup loops ranging from 20- mu m to 0.8- mu m across have very user-friendly V- Phi curves and a resolution of order 100 mu /sub B// square root Hz at 4.2 K for devices with the smallest loops.         A high performance integrated DC SQUID magnetometer    R. Cantor, K. Enpuku, T. Ryhanen and H. Seppa Summary: The authors have carried out extensive mappings of the DC characteristics and flux noise of an integrated, DC superconducting quantum interference device (SQUID) magnetometer as functions of bias current and applied flux. The open-loop white flux noise at 1 kHz measured without flux modulation is Phi /sub n/<7*10/sup -7/ Phi /sub 0// square root Hz throughout a broad region of operation where the current-voltage and voltage-flux characteristics are smooth. The corresponding flux density noise B/sub n/<4 fT/ square root Hz. In addition, a recent model of the coupled DC SQUID was used to calculate the frequency-dependent impedance Z(f) seen by the Josephson junctions. The peaks observed in Z(f) are shown to be consistent with features in the current-voltage characteristics at high bias currents.         Detection of magnetic flux with superconducting quantum interference gratings    J.H. Miller Jr., G.H. Gunaratne and Z. Zou Summary: The authors have carried out finite-inductance calculations of the critical current vs. flux (I/sub c/- Phi ) and voltage vs. flux (V- Phi ) characteristics of superconducting interferometers with many Josephson junctions in parallel. At least two features of the calculations suggest that many junction interferometers, called superconducting quantum interference gratings, might be advantageous for the detection of magnetic flux. First, the voltage noise can be reduced significantly for a given flux-to-voltage transfer coefficient, a feature which is likely to improve the magnetic flux sensitivity of both low- and high-T/sub c/ superconducting devices. In addition, nonuniformity of the junction critical currents appears to have little adverse effect on the predicted diffraction grating such as enhancement and narrowing of the peaks in the I/sub c/- Phi characteristic. Specific schemes for efficiently coupling flux into the device are proposed.         Noise measurements of series SQUID arrays    K.G. Stawiasz and M.B. Ketchen Summary: Series arrays of 50 gradiometer superconducting quantum interference devices (SQUIDS) and 100 magnetometer SQUIDs have been fabricated using Nb/AlO/sub x//Nb junctions with a planarized all-refractory technology for superconductivity (PARTS), the white noise of these arrays has been measured. The individual devices are 50-pH, 2-hole and 100-pH, 1-hole SQUIDs with integrated single turn input coils, 1- mu m/sup 2/ and 0.5- mu m/sup 2/ junctions, and PtRh shunt resistors. The input coil inductance of 10 nH will effectively match with a wide bandwidth to miniature pick-up loop structures for various experiments. Ideally, the coupled energy sensitivity should remain constant as devices are added in series, while the output impedance rises to a level practical for direct coupling to room-temperature electronics. The output impedance of the arrays is 250-1000 Omega . The white noise was measured directly with an ultra low noise preamplifier at room temperature. The best result was Phi /sub N/=0.12 mu Phi /sub 0// square root Hz with a corresponding coupled energy sensitivity of 56 h.         Even harmonic Josephson magnetometry    Q. Geng and E. Goto Summary: A novel Josephson junction magnetometry scheme is proposed in which magnetic flux is applied to Josephson junctions with a modulation flux +or-z( Phi /sub 0//2 pi ) cos omega t. Two Josephson junctions are used in a push-pull mode to perform amplification through two mechanisms: negative inductance amplification of DC (low frequency) components and parametric amplification of the second harmonic. The second harmonic component of the Josephson currents, which is directly proportional to the strength of the input flux, is then selected and amplified by a phase-sensitive detector. Computer simulations show that the device behaves very well as a magnetic flux sensor with a DC offset free feature. The device's parameters and noise problems are also discussed. A preliminary analysis indicates that it is likely to have a better sensitivity than superconducting quantum interference devices.         A coupled DC SQUID with low 1/f noise    H. Seppa, M. Kiviranta, A. Satrapinski, L. Gronberg, J. Salmi and I. Suni Summary: A low-noise coupled DC superconducting quantum interference device (SQUID) especially optimized for low frequency is discussed. Using large Josephson junctions and a low loop inductance the contribution of the critical current fluctuation to 1/f noise can be minimized. To minimize the inductance the Josephson junctions are placed in the center of the washer close to the SQUID loop. A scaled-up copper model of the SQUID and the signal coil is used to analyze the impedance of the SQUID loop affected by the signal coil. An equivalent circuit model describing the effective inductance of the SQUID loop as a function of the frequency is used to design appropriate damping of the resonances. The DC SQUID characteristics are smooth and the noise performance of the SQUID does not markedly suffer from resonances. The contribution of the 1/f noise at 1 Hz is found to be about 5*10/sup -7/ Phi /sub 0// square root Hz.         Improved sensitivity of planar microwave based RF-SQUIDs using a cryogenic HEMT preamplifier    G. Fontana, R. Mezzena, S. Vitale, M. Cerdonio, M. Muck, G. Hallmanns and C. Heiden Summary: The design and performance of a planar microwave RF-SQUID (superconducting quantum interference device) read out by a cryogenic high-electron-mobility-transistor (HEMT) preamplifier are described. The SQUID sensor consists of a planar half-wavelength microstrip resonator, into which the SQUID loop is integrated. The SQUID is operated at a pump frequency of 1.7 GHz. The cryogenic preamplifier uses a microwave HEMT, located close to the SQUID sensor. Measurements of the flux noise and the fractional step rise parameter were carried out in the temperature range between 4.2 K and 1.5 K. In an open loop, a flux noise of 2*10/sup -6/ Phi /sub 0// square root Hz was measured at 4.2 K, resulting in an energy resolution of about 100 h. The design of a 3-GHz magnetometer is also described, and the preliminary results of the measurements are reported.         Magnetic field sensors with digital feedback read-out    W. Eschner, U. Fath, G. Hofer, R. Hundhausen, H. Kratz, W. Ludwig, W. Rothmund and M. Wulker Summary: Magnetic field sensors consisting of a DC superconducting quantum interference device (SQUID) and a close-by superconducting digitizer, both realized in NbN-MgO-NbN technology, are presented. The superconducting circuits have been specifically designed to suppress the influence of external fields on the operation of the sensor and to assure good balancing for gradiometer input coils. It is shown how the different parts of the sensor can be adapted for different modes of operation. The superconducting sensors are operated with digital feedback electronics mounted in the dewar. The operation of digital circuitry in the vicinity of the sensors affects their operation slightly. Most functions, particularly the adjustment and optimization of bias points, can be controlled from a remotely positioned data acquisition system. In view of multisensor applications several precautions have been taken to decouple the data acquisition from the electronics units.         Performance of DC SQUIDs fabricated on 4-inch silicon wafer    N. Shimizu, N. Chiba, S. Yabe, T. Ishikawa, K. Chinone and S. Kiryu Summary: A Nb/AlO/sub x//Nb Josephson process has been developed to fabricate DC superconducting quantum interference devices (SQUIDs) for biomagnetic measurements on 4-in silicon wafers. The purpose of the process is to fabricate high-quality junctions and to keep the quality uniform over a silicon wafer. All the films were deposited using magnetron sputtering. The components of the SQUID, except the junctions, were formed by taper etching to improve the step coverage. The uniformity of the SQUID characteristics (critical current, modulation depth, and mutual inductance between SQUID and modulation coil) was measured, and an excellent value of less than +or-5% was obtained. Three different configurations of SQUIDs, single washer (SW), double washer series (DWS), double washer parallel (DWP) have been fabricated with the same characteristics. The SW (single washer) had a white noise level of 6.3*10/sup -6/ Phi /sub 0// square root Hz, lower than those of DWS and DWP. 1/f crossover frequencies were below 1 Hz.         High slew rate 'channel equalized' DC SQUID flux-locked loop: concept and simulation    M. Gershenson and R.J. McDonald Summary: The concept of improving conventional DC superconducting quantum interference device (SQUID) flux-locked loop (FLL) performance by applying a channel equalization circuit after the pre-amp, but prior to the demodulation process in order to compensate for bandwidth limitations imposed by conventional DC SQUID impedance matching networks is discussed. The equalization circuit is a bandlimited inverse filter which corrects for the phase and amplitude distortion caused primarily by the DC SQUID impedance matching network. Improvements in the FLL performance were verified with analog circuit simulations in both the time and frequency domains. Using an analog circuit simulator the various subcircuits of the FLL were modeled, and a comparison between a conventional FLL and an equalized one was performed. Computer simulations for the open and closed loop cases were used to quantify the increase in slew rate for the equalized FLL system.         A method for simulating a flux-locked DC SQUID    G.M. Gutt, N.J. Kasdin, M.R. Condron II, B. Muhlfelder, J.M. Lockhart and M.W. Cromar Summary: The authors describe a computationally efficient and accurate method for simulating a DC superconducting quantum interference device's (SQUID's) V- phi (voltage-flux) and I-V characteristics which has proven valuable in evaluating and improving various SQUID readout methods. The simulation of the SQUID is based on fitting of previously acquired data from either a real or a modeled device using the Fourier transform of the V- Phi curve. This method does not predict SQUID behavior, but rather is a way of replicating a known behavior efficiently with portability into various simulation programs such as SPICE. The authors discuss the methods used to simulate the SQUID and the flux-locking control electronics, and present specific examples of this approach. Results include an estimate of the slew rate and linearity of a simple flux-locked loop using a characterized DC SQUID.         Analysis of the 4-junction SQUID    K. Suzuki and Y. Okabe Summary: The circuit of the 4-junction superconducting quantum interference device (SQUID), which has two series of Josephson junctions at each side of the SQUID coil, is analyzed. The 4-junction SQUID is considered to have the advantage of a larger voltage modulation depth than that of the normal DC SQUID. The authors have tried to make its behavior clear by computer simulations. It has been found that the 4-junction SQUID has a different mode from that of the normal DC SQUID in its dynamic behavior, which causes hysteresis in the I-V characteristics. It has also been found that a large voltage modulation depth can be realized in spite of large SQUID coil inductance, so that the area of the primary coil can be more than 10 times larger. The noise performance of the 4-junction SQUID is also analyzed, and it is possible that this SQUID has higher sensitivity by virtue of circuit-parameter optimization.         Interactive graphics simulation program for the RF-SQUID    A.C. Bruno and J.E. Zimmerman Summary: An interactive graphics simulation program for the RF-SQUID (superconducting quantum interference device) has been developed. The program allows the user to graphically observe fluxoid quantization, the amplitude-limiting effect of the tank circuit voltage due to the SQUID coupling, the periodic voltage response due to an external DC flux, the tank circuit and SQUID voltage versus time, and the tank circuit voltage versus current. Having a graphical user interface, the program also provides a means for changing circuit and SQUID parameters, namely, RF drive, DC bias, coupling, tuning, Q, and critical current.         Nonlinear response of low temperature superconducting thin film gradiometer sense loops    T.R. Clem, J.W. Purpura, R.F. Wiegert and W.L. Goodman Summary: Experimental measurements of the nonlinear response of superconducting thin-film gradiometer sense loops to changes in magnetic field at 4.2 K are described. The sense loops were fabricated from niobium and niobium nitride. The basic experiment involved the ramp of a uniform magnetic field from zero up to a predetermined value. The performance of the loops was measured by means of a superconducting-quantum-interference-device (SQUID)-based readout system inductively coupled to the samples. Threshold values of external field were observed to characterize the onset of nonlinear behavior for all samples measured. The performance of the loops as measured by this onset of nonlinearity is correlated with important parameters including material, aspect ratio, edge quality, and the effect of crossovers. The empirical results are compared with predictions from an ideal diagmagnet model to describe demagnetization effects.         Study of current peaks in DC SQUID with integrated coupling coil    S. Kohjiro, N. Simizu, S. Kiryu, N. Chiba and M. Koyanagi Summary: The mechanism and the damping condition are investigated for the resonant peak in the current-voltage characteristics of a DC superconducting quantum interference device (SQUID) coupled to an integrated multiturn input coil. It is experimentally confirmed that the resonant voltage, V/sub r/, depends on parameters of the coupling structure. The V/sub r/ and peak height are calculated based on an RF admittance and a balance equation for incident and dissipated powers in them SQUID. The analytical results agree qualitatively with experimental ones. A simple analytical formula for the damping condition is derived.         Resonant properties of a DC SQUID coupled to a multiturn input coil    K. Enpuku, R. Cantor and H. Koch Summary: In order to investigate the characteristics of a DC superconducting quantum interference device (SQUID) coupled to a multiturn input coil, resonances occurring in this configuration, such as input coil resonances and washer resonances, are studied using an expanded model of the coupled SQUID. These resonances are shown to be suppressed well using proper damping resistors. The expressions for the optimum damping resistors have been obtained as a function of SQUID parameters. It is also shown that the optimum values of the damping resistors depend on the configuration of the SQUID washer. Based on the results obtained for the resonant properties, the authors discuss the design of highly sensitive DC SQUIDs coupled to the multiturn input coil.         Relaxation oscillation SQUIDs with high delta V/ delta Phi    D.J. Adelerhof, H. Nijstad, J. Flokstra and H. Rogalla Summary: Relaxation oscillation SQUIDs (ROSs) based on Nb/Al, AlO/sub x//Al/Nb Josephson tunnel junctions have been designed and fabricated. The hysteretic SQUIDs (superconducting quantum interference devices) have a maximum critical current of about 130 mu A and an inductance of 20 pH. A voltage modulation of 40 mu V and a flux to voltage transfer delta V/ delta Phi of 4 MV/ Phi /sub 0/ have been measured in these SQUIDs. Double relaxation oscillation SQUIDs (DROSs), which are based on two hysteretic SQUIDs, showed transfer coefficients up to 77 mV/ Phi /sub 0/. The intrinsic white flux noise of the DROSs is smaller than 3-5 mu Phi /sub 0// square root Hz. It is noted that the results are very promising for a next generation of SQUID systems with simplified read-out.         Characteristics of the relaxation oscillating SQUID with tunnel junctions    G. Uehara, T. Morooka, J. Kawai, N. Mizutani and H. Kado Summary: The authors describe a relaxation oscillating superconducting quantum interference device (SQUID) fabricated using the Nb/AlO/sub x//Nb Josephson tunnel junction technique. It is demonstrated that this SQUID transfers flux changes into frequency changes. The relative linewidth of the frequency spectrum is on the order of 10/sup -5/. The spectral density of frequency fluctuations is 2*10/sup 4/ Hz/sup 2//Hz at both 10 kHz and 100 kHz. A method to evaluate the flux resolution of relaxation oscillating SQUIDs without a flux-locked loop is also proposed; the result is S/sub phi /(f)=2.1*10/sup -14/ phi /sub 0//sup 2//Hz at both 10 kHz and 100 kHz. The advantage of the relaxation oscillating SQUID is that it does not suffer from amplifier noise as long as the signal is treated in the frequency domain.         Josephson voltage standard at low drive frequencies    H.-G. Meyer, H.-J. Kohler, F. Muller, K. Bluthner, P. Weber and A. Chwala Summary: The authors report on the design and operation of a superconducting microstrip resonator containing four series-connected highly hysteretic Josephson junctions in the top layer. This arrangement generates constant-voltage steps at X-band drive frequencies useful for a Josephson voltage standard. At 12 GHz, steps up to 5 mV have been obtained with step amplitudes of about 100 mu A. The resonator principle can be used to save microwave power and to simplify the microwave circuit. To obtain sufficiently large and stable steps the critical current density and the junction length must be matched carefully with the order of maximum step used for the operation of the Josephson voltage standard. The X-band microwave drive frequencies offer substantial advantages in terms of costs and handling of microwave equipment.         Accuracy comparisons of Josephson array systems (voltage standards)    R.L. Steiner, A.F. Clark, C. Kiser, T.J. Witt and D. Reymann Summary: Five Josephson-array voltage standard systems were compared using several different methods. All of the tests were performed on a site at a 1.018-V level, either by direct connection or through successive measurements of independent voltage sources. The resulting agreement between different systems measuring the same source was generally better than 10.0 parts in 10/sup -9/, limited by source noise and detector resolution. Direct array-to-array comparisons for independent systems achieved agreement to within random uncertainties of 0.2 parts in 10/sup -9/. The basic conclusion is that Josephson-array voltage standard systems can be readily transported and tested to assure one-site equivalence. Also, these tests can be done quickly and with high precision, limited by the detector noise if directly compared, or by the transfer reference noise if done indirectly.         Whole cortex, 64 channel SQUID biomagnetometer system    J. Vrba, K. Betts, M. Burbank, T. Cheung, A.A. Fife, G. Haid, P.R. Kubik, S. Lee, J. McCubbin, J. McKay, D. McKenzie, P. Spear, B. Taylor, M. Tillotson, D. Cheyne and H. Weinberg Summary: The authors report on the development and testing of a novel, whole cortex, 64-channel superconducting quantum interference device (SQUID) biomagnetometer system operating in an unshielded environment. The essential features of this instrument, including the cryogenics system, the room-temperature digital electronics, and signal processing capabilities, are described. A noise cancellation scheme is incorporated which allows extraction of biomagnetic signals over the surface of the cortex while operating in the presence of large background magnetic interference. A system description and the results of preliminary magneto-encephalographic measurements are presented. Measurements of noise performance and human auditory evoked response in an unshielded industrial environment have largely validated the noise cancellation methods incorporated in the instrument.         A modular 31-channel SQUID system for biomagnetic measurements    O. Dossel, B. David, M. Fuchs, J. Kruger, K.-M. Ludeke and H.-A. Wischmann Summary: A modular multichannel superconducting quantum interference device (SQUID) system, in which every channel can be optimized or replaced individually, was further improved. The number of channels was increased to 31. The noise level is better than 10 fT/ square root Hz. A novel way of RF shielding using conductive paint avoids degradation of the SQUID characteristics due to RF interference without introducing significant extra noise, so that the system works without any Faraday cage. A simplified way of coupling the modulation and feedback signal directly to the SQUID was developed and tested successfully. The SQUID module with superconducting connections to the gradiometer and its superconducting shield was miniaturized to an outer diameter of 5 mm, so that it can be placed near the gradiometer without introducing significant unbalance. Tests have demonstrated that the accuracy of the system with respect to the localization of a single current dipole is better than 2 mm.         Design and fabrication of multichannel DC SQUIDs for biomagnetic applications    S. Yamasaki, T. Morooka, N. Matsuda, J. Kawai, N. Mizutani, K. Tsukada, G. Uehara and H. Kado Summary: A hybrid DC superconducting quantum interference device (SQUID) system is developed for biomagnetic applications. It consists of a high-performance square-shaped double-washer DC SQUID and a highly accurate planar pick-up coil. The DC SQUID device and the pick-up coil are designed and fabricated separately. Coupling this device and the separately fabricated pick-up coil allows flexibility in the construction of multichannel systems as well as sensitivity and stability.         Operation of a hybrid 28-channel neuromagnetometer    V. Foglietti, A. Pasquarelli, V. Pizzella, G. Torrioli, G.L. Romani, S. Casciardi, W.J. Gallagher, M.B. Ketchen, A.W. Kleinsasser and R.L. Sandstrom Summary: A 28-channel system for neuromagnetic measurements operative at CNR-IESS (Instituto di Elettronica dello Stato Solido) is described. The instrument uses 28 Nb/PbAuIn DC-SQUID (superconducting quantum interference device) sensors coupled with a flux transformer configuration. The detection coils are arranged on concentric circumferences. Sixteen axial first-order gradiometers are arranged in the internal circles, while the external circle consists of 12 first-order planar gradiometers. The vertical gradiometers show a white noise level of approximately=5 fT/ square root Hz, while the planar ones have a noise approximately=6 fT/cm square root Hz, with a 1/f corner at a few hertz. The evoked potentials of normal subjects and patients affected by various kinds of vascular disturbances have been studied. The system has succeeded at one-shot localization of some cortical activity. The instrument has also been used to record the spontaneous brain activity in patients affected by focal epilepsy.         11 channel magnetometer for biomagnetic measurements in unshielded environments    S. Casciardi, C. Del Gratta, S. Di Luzio, G.L. Romani, V. Foglietti, A. Pasquarelli, V. Pizzella and G. Torrioli Summary: The authors describe a novel 11-channel magnetometer designed for operation in unshielded environments. The planar geometry of the system is particularly suitable for recording biomagnetic signals over a flat surface, as required for cardiac and gastrointestinal applications. The specific configuration of the sensor array also makes it possible to use the system for reliable and fast cardiac clinical measurements. Ambient noise rejection was achieved by the use of second-order gradiometers, optimized by means of additional fine balancing, whereas a sensitivity of less than 10 fT/Hz/sup 1/2/ was obtained by low-noise DC-SQUIDs (superconducting quantum interference devices), using Nb/Nb/sub 2/O/sub 5//PbAuIn technology for the Josephson junctions. The system is presently utilized for a systematic investigation of the localization properties of cardiac sources from data obtained during single-shot measurements, which are believed to be suitable for clinical studies. The results of localization are compared with anatomical information from magnetic resonance imaging data.         DC-SQUID system with flexible pickup coil connected by a novel superconducting technique    K. Chinone, N. Chiba, S. Nakayama, N. Shimizu, S. Kiryu and N. Kasai Summary: A reliable and compact bonding method for superconductively connecting input coils to pickup coils has been developed using a low-temperature flip-chip bonding technique which does not cause the deterioration of Josephson junctions. Axial first-order gradient pickup coils made of a flexible sheet were fabricated and tested to investigate their mass producibility. The system noise of a single-channel system with a flexible pickup coil, with 17-mm coil diameter and 60-mm baseline, connected by a superconductive flip-chip bonding technique, was about 20 fT/ square root Hz using a large beta L DC-SQUID (superconducting quantum interference device).         Inversion calculation of two dimensional current distributions from their magnetic field    W. Benzing, T. Scherer and W. Jutzi Summary: For nondestructive evaluation and geophysical explorations, e.g., with superconducting quantum interference devices, efficient inversion calculations are needed. A program has been developed to compute the current distribution in a plane from the magnetic field sampled in a parallel plane. The process uses an iterative matrix inversion for the relation between current and magnetic field (the Biot-Savart law). Examples of the determination of up to 100*100 current dipoles out of magnetic field components with different signal-to-noise ratios as a function of distance are presented. The efficient indirect inversion procedure for calculating currents of up to 100*100 dipoles requires about 1 h on a VAX 3100 workstation, even if all three components of the magnetic field are disturbed by noise and the distance between the field and current plane is large, corresponding to a normalized distance g=10.         An automatic measurement system of DC SQUID characteristics using a computer control    N. Shimizu, A. Odawara, S. Nakayama and K. Chinone Summary: The authors have measured the characteristics of DC superconducting quantum interference devices (SQUIDs) using a computer-controlled, automatic measurement system. The system can obtain data from four SQUIDs at a time. The following sequences of measurements were conducted: (1) the basic characteristics, current-voltage and flux-voltage, were measured and (2) the noise performance was measured using the flux locked loop (FLL) mode. This system is composed of three parts: a control computer, commonly used instruments (DC source and monitor, lock-in amplifier, function generator, fast-Fourier-transform analyzer, and switch control unit), and electronics, (i.e. low-noise preamplifier and feedback unit). The computer drives these instruments with a GP-IB interface and acquires the data. The SQUID characteristics measured by this system as well as manual measurement data have been obtained by using battery-operated low-noise FLL electronics. This system is very useful for estimating DC SQUID performance in a short period of time, and for developing FLL electronics.         Effect of RF interference on characteristics of DC SQUID system    N. Ishikawa, K. Nagata, H. Sato, N. Kasai and S. Kiryu Summary: The effects of RF interference on the characteristics of DC superconducting quantum interference devices (SQUIDs) are investigated. The noise of a DC SQUID gradiometer radiating an RF field with a frequency between 100 kHz and 80 MHz was measured. As the RF field strength intensified, the white noise level increased and the cut-off frequency was lowered. The flux-voltage transfer function (dV/d Phi ) of the DC SQUID was influenced strongly by the RF field. dV/d Phi decreased as the RF field intensified. Based on these results, the level of the electromagnetic environment at which the operation of the SQUID system would not be affected was found. The effect of high-frequency magnetic field on the flux to voltage transfer function was investigated by computer simulation using a simple resistively shunted junction (RSJ) model.         Performance measurements of a superconductive microprobe for eddy current evaluation of subsurface flaws    W.N. Podney Summary: First measurements of the performance of the superconductive microprobe show that its depth of field and resolution are far superior to those of conventional eddy-current probes. It is shown that the superconductive microprobe can detect millimeter-size flaws to depths of 5 mm in 2024 aluminum. It also easily detects a 1.4% loss in material owing to corrosion at the bond line of two 2.29-mm-thick, 7075 aluminum plates. The corrosion patch is 15.9 mm in diameter. The prototype shows three main limitations: standoff distance, electronic noise in the feedback circuitry, and interference from fluctuations in tilt while scanning a test surface. Decreasing the size of the pickup loops and source coil can decrease both the standoff distance and interference from tilt. Using digital circuitry can suppress the noise of feedback circuitry.         Design and implementation of a scanning SQUID microscope    L.N. Vu and D.J. Van Harlingen Summary: A cryogenic two-dimensional magnetic imaging system that incorporates a sensitive DC superconducting quantum interference device (SQUID) detector is described. In this instrument, which is called the scanning SQUID microscope, a flux transformer coupled to the SQUID is scanned over the surface of a planar sample by a room-temperature, stepping-motor-controlled manipulator with a positional resolution of about 2 mu m. With the present input coil, spatial resolution of 20 mu m and a flux sensitivity at the sample of 10/sup -5/ Phi /sub 0//Hz/sup 1/2/ is attainable. This system has been designed specifically to image the vortex structure and dynamics of weakly coupled superconductor arrays.         Passive nondestructive evaluation of ferromagnetic materials during deformation using SQUID gradiometers    R.B. Mignogna, V. Browning, D.U. Gubser, R.S. Schechter, K.E. Simmonds and H. Weinstock Summary: An experimental system is described for in situ passive measurement of changes in the magnetic field of ferromagnetic materials subject to tensile deformation. Changes in magnetic field during deformation are monitored using a three-axes first-order superconducting quantum interference device (SQUID) gradiometer. The gradiometer is held in a fixed position while a horizontal load frame has been constructed from nonferromagnetic materials. Results are presented for cold-rolled steel specimens. The magnetic field gradient was measured by scanning the specimen in the x-y plane while at a constant stress at a fixed distance from the tail of the SQUID dewar.         SQUID systems for non-destructive testing by AC field mapping    A. Cochran, L.N.C. Morgan, R.M. Bowman, K.J. Kirk and G.B. Donaldson Summary: The authors describe a low-temperature liquid-helium superconducting quantum interference device (SQUID) system with high spatial resolution and a wider bandwidth than usual for an all-metal cryostat and which also provides access for a mechanism to balance the pick-up coils. They discuss the effects of these properties on AC field measurement and present experimental results from small slits which mimic growing fatigue cracks. Related work on high-temperature superconducting devices indicates that they will offer important advantages over low-temperature SQUIDs, particularly in terms of cryogenic design which has been so restrictive in low-temperature systems. The authors suggest that even relatively poor high-temperature-superconductor SQUID performance will be acceptable if these advantages can be exploited.         Theoretical and experimental verification of the properties of superconductor surface imaging    W.C. Overton Jr., D.B. van Hulsteyn and E.R. Flynn Summary: Electric currents in the vicinity of a superconductor induce surface currents which contribute to the complete expression for the magnetic field. The solution can be written in terms of a magnetic scalar potential that satisfies the Neumann condition at the superconducting boundary. A sensing coil whose axis is normal to the surface detects a field component which is the sum of these direct and induced current contributions. As a result of this imaging effect, a single coil acts like a first order gradiometer. Furthermore, it can be shown that the surface deflects noise from distant sources. An experimental verification of the properties of the superconductor surface imaging discussed here is presented. The primary application of the principles considered here will be the sensing of extremely weak magnetic fields, such as those encountered in magnetoencephalography, nondestructive evaluation, and corrosion analysis.         High-resolution SQUID imaging of octupolar currents in anisotropic cardiac tissue    D.J. Staton, R.N. Friedman and J.P. Wikswo Jr. Summary: A monopolar stimulus electrode triggered depolarization in a 1-mm-thick slice of canine ventricular myocardium, maintained in a thermally regulated, oxygenated chamber. Five hundred milliseconds of data at 2 kHz were recorded with a MicroSQUID (superconducting quantum interference device) magnetometer at 1-mm intervals over a 23-mm*23-mm area, centered on the stimulus site. Without averaging, a signal-to-noise ratio of better than 100:1 was achieved, and the field maps provided evidence of a propagating wavefront of activity. Application of an inverse Fourier filter yielded current density images that consisted of four expanding circular current paths, in agreement with predictions of the bidomain model. The ability to image action currents in a DC to 2-kHz bandwidth should prove useful for understanding the complex anisotropy of cardiac tissue and how it is altered by pharmacological interventions.         Spatial resolution and sensitivity of magnetic susceptibility imaging    I.M. Thomas, Y.P. Ma, S. Tan and J.P. Wikswo Jr. Summary: The use of a scanning susceptometer to image the 2-D distribution of magnetic susceptibility in thin samples is discussed. High-resolution magnetic field data recorded above complex shapes of plexiglass, scanned in a uniform applied field, are presented. Deconvolution of these data yielded magnetization distributions that were accurate images of the samples. It was found that the susceptibility of plexiglass is -9.0*10/sup -6/ (SI) and it was demonstrated that the present system is sensitive to susceptibility contrasts as small as 5*10/sup -7/ (SI), with a spatial resolution better than 1 mm. This performance is limited by the strength of the applied field, by the size and distance from the sample of the sensing coils, and by superconducting quantum interference device (SQUID) noise. It is estimated that one could increase spatial resolution by a factor of two, and sensitivity to susceptibility contrast by at least one order of magnitude by using an imaging susceptometer whose SQUIDs are integrally mounted within a superconducting magnet.         A high resolution imaging susceptometer    Y.P. Ma, I.M. Thomas, A. Lauder and J.P. Wikswo Jr. Summary: A high-resolution, MicroSQUID (superconducting quantum interference device)-based susceptometer has been constructed for imaging the susceptibility distribution in diamagnetic and paramagnetic objects. The maximum available applied field, produced by the Helmholtz pair, is 300 mu T, which provides an adequate signal-to-noise ratio for common susceptible materials. The calculated variation in the applied field within 20 mm of the center is less than 0.1% of the field at the center. In a 100-Hz bandwidth, the minimum detectable susceptibility-induced field change, (limited by SQUID noise) is 3*10/sup -9/ of the applied field. The sensitivity of the system may be improved by increasing the applied field, for instance by incorporating a superconducting magnet into the magnetometer dewar, and by using lower-noise SQUIDs.         High resolution SQUID imaging of current and magnetization distributions    S. Tan, Y.P. Ma, I.M. Thomas and J.P. Wikswo Jr. Summary: Interpretation of high-resolution SQUID (superconducting quantum interference device) magnetometer data is facilitated by inverting them into current or magnetization images. Different deconvolution algorithms utilizing the finite element method (FEM), spatial filtering (SF) and lead field analysis (LFA) are compared. The authors applied an appropriate algorithm to magnetic field data produced by current distributions in high-T/sub c/ superconducting thin films (TlBaCaCuO), by the diamagnetic magnetization of plexiglass and by planar and cylindrical current-carrying conductors with flaws. They demonstrate and compare the performances of the algorithms and conclude that, with all of the approaches, the deconvolved images are easier to interpret than the original field maps. The FEM and SF can both solve for discontinuous sources. The FEM allows the solution to be constrained with boundary conditions but it is much slower than SF, which cannot constrain the solution. LFA is numerically simple for complex geometries but it is slow and cannot deal with discontinuous sources.         SQUID NDE: detection of surface flaws by magnetic decoration    I.M. Thomas, Y.P. Ma and J.P. Wikswo Jr. Summary: A nondestructive evaluation (NDE) surface-flaw detection technique involving decoration of the samples with a ferromagnetic or paramagnetic tracer and subsequent scanning with a high-resolution magnetometer or susceptometer is considered. The authors present the results of a preliminary study demonstrating that this technique is sensitive enough to detect and image defects at least as small as 254 mu m*51 mu m*76 mu m deep in a nickel-alloy test block. Applied field strength and superconducting quantum interference device (SQUID) noise limit sensitivity, and sensing coil characteristics limit spatial resolution.         Neuromagnetic SQUID measurements in a helmet-type superconducting magnetic shield of BSCCO    H. Ohta, A. Koike, K. Hoshino, H. Kotaka, E. Sudoh, K. Kato, H. Takahara, Y. Uchikawa, K. Shinada, M. Takahata, Y. Yamada and T. Matsui Summary: A superconducting quantum interference device (SQUID) magnetometer has successfully detected magnetic fields emitted from a human brain in a helmet-size superconducting magnetic shield of the high-T/sub c/ superconductor Bi-Sr-Ca-Cu-O/sub x /(BSCCO). The sensitivities of the RF-SQUID and the DC-SQUID of quasi-planar Josephson junctions-superconducting weak links are 20 fT/ square root Hz and 4 fT/ square root Hz, respectively. The magnetic shield can reduce a magnetic field to -120 dB or 10/sup -6/ even at as low a frequency as 0.2 Hz. The authors have detected somatosensory evoked magnetic fields stimulating the tibial nerves of the patient by current pulses.         Fabrication and characterization of HTS/semiconductor three terminal device    Q. Huang, N. Yoshikawa and M. Sugahara Summary: The authors present preliminary experimental results of a high-T/sub c/ superconductor/semiconductor three-terminal device with a SUBSIT (superconducting base, semiconducting isolated transistor) structure, where Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (BSCCO) and Te are used as superconducting base and semiconducting collector, respectively. The device with a Au/Te/BSCCO/BSCO/BSCCO structure is fabricated on a MgO (100) substrate by RF magnetron sputtering and vacuum deposition. When the temperature is lower than the critical temperature T/sub c/ of the superconducting base, the collector-base current is modulated by current injection in the emitter-base junction. The current gain coefficient ( alpha ) in the common-base configuration increases with the increase of emitter current (I/sub E/) and collector-base voltage (V/sub CB/). The maximum of alpha is about 0.18 when I/sub E/=1.4 mA, V/sub CB/=150 mV, and temperature T=15 K.         Superconducting contacts to a two-dimensional electron gas in GaAs/AlGaAs-heterostructures    K.-M.H. Lenssen, M. Matters, C.J.P.M. Harmans, J.E. Mooij, M.R. Leys, W. van der Vleuten and J.H. Wolter Summary: The process of Sn/Ti-diffusion is shown to provide low-resistance (highly transmissive) contacts to the two-dimensional electron gas (2DEG) in GaAs/AlGaAs-heterostructures. At temperatures down to 80 mK the resistance stays very low. The temperature and gate-voltage dependence of the dV/dl-V-curves shows that Andreev reflection must take place in the sample. The measurements suggest that Ti is the relevant superconductor and not Sn. The fact that the bottom of the low-resistance region is very flat and does not show a peak near V=0 V means that the transmission of the NS (normal metal-superconductor) interface is very close to 1. Therefore these superconducting contacts seem to be very suitable for studying SNS (superconductor-normal metal-superconductor) junctions in the clean limit.         A three-terminal semiconductor-superconductor transimpedance amplifier    T. Pham, M. Leung, B. Dalrymple, L. Abelson, J. Spargo, S. Ou, H. Chan and A. Silver Summary: The authors report an improved hybrid three-terminal transimpedance amplifier (TIA) with significant current gain. The TIA consists of a semiconductor diode configured for injection of electrons into a thin base electrode (<25 nm) superconductor-insulator-superconductor junction, whose response is read out by low-impedance superconductive electronics. An input dynamic impedance greater than 10/sup 11/ Omega , an output dynamic impedance of approximately 10/sup -3/ Omega a current gain of 20, and an effective input noise current less than 10/sup -14/ A/ square root Hz were achieved. The TIA was operated in a sensor test bed with an extrinsic silicon infrared (IR) detector and superconductive analog-to-digital (A/D) converter. This device permits matching state-of-the-art semiconductor IR detectors with superconductive A/D converters, enabling a fully digital cryogenic focal plane array sensor with high sensitivity and speed but reduced power consumption.         Transistors based on proximity effect control of the critical current of a superconductor    A.W. Kleinsasser Summary: The critical current of a bilayer consisting of a thin superconductor in contact with a normal conductor depends on the thickness of the normal layer due to the proximity effect. Using one electrode of a semiconductor pn junction as the normal material, it is possible to vary the normal layer thickness by applying a voltage to the pn junction. The author discusses the feasibility of transistors based on such structures. He concludes that there is no fundamental impediment to operating a transistor based on proximity effect control of a superconductor. However, the proposed device requires that both superconductor and semiconductor layers be no thicker than roughly a coherence length. The large mismatch at the superconductor-semiconductor interface reduces the size of the proximity effect, possibly making the desired effect too small to be useful. It is difficult to construct a nonlatching device, or one with voltage gain. Thus, the proposed device has major drawbacks which prevent it from being considered as more than a scientific curiosity.         Single-electron tunneling transistors incorporating Cooper pair processes    M.T. Tuominen, J.M. Hergenrother, T.S. Tighe and M. Tinkham Summary: A superconducting single-electron tunneling transistor composed of two ultrasmall capacitance Al/Al/sub 2/O/sub 3//Al tunnel junctions and a capacitively coupled gate electrode has been fabricated. Transistor operation is based on single electron and Cooper pair charging effects. This three-terminal device exhibits novel I-V characteristics not seen in either conventional superconducting tunnel junctions or normal metal Coulomb blockage devices. Current peaks appear above V approximately 2 Delta /e which originate from combined Cooper pair/quasi-particle tunneling processes. These peaks show e-periodic modulation with respect to the gate-induced charge. At lower voltages, the I-V curve shows features which are 2e-periodic. In a magnetic field, it is found that the 2e-periodicity changes into e-periodicity above a crossover line, T*(H). The data strongly suggest the existence of a free energy difference between states with an even versus an odd number of electrons on the metal island between the two junctions.         Tunneling studies of mesoscopic all-NbN junctions    M.D. Reeve, O.G. Symko and R. Li Summary: A scanning tunneling microscope was used to position a NbN tip near a NbN thin film sputtered on a Si substrate. Measurements at 4.2 K clearly show an energy gap of 5.0 mV. The Coulomb blockade of tunneling and the Coulomb staircase, formed by single-electron charging of the central electrode of a double capacitor system consisting of a substrate, a particle lodged in the oxide, and a tip, were observed at a number of points on the film. Experiments were repeated at room temperature. Fitting I-V and dI/dV-V curves to theory yields capacitances on the order of 5*10/sup 19/ to 2*10/sup -18/ F. The granular nature of the sputtered NbN greatly facilitates formation of the requisite double junction structure.         Fabrication and characterization of single-electron tunneling transistors in the superconducting state    J.M. Hergenrother, M.T. Tuominen, T.S. Tighe and M. Tinkham Summary: Electron-beam lithography was used to fabricate single electron charging effect devices with ultrasmall capacitance Al/Al/sub 2/O/sub 3//Al tunnel junctions. The single electron transistor is a three-terminal device composed of two series tunnel junctions and a gate electrode capacitively coupled to the island between them. Typical junctions are of area 60 nm*60 nm with a capacitance of 190 aF. The authors outline the fabrication procedures, discuss operational properties, and give sample handling considerations. These devices exhibit a highly nonlinear I-V characteristic which is modulated by the gate voltage, as expected for the Coulomb blockage. In the superconducting state, the superconducting gap in the quasiparticle density of states leads to transistor action above 1.3 K, a temperature easily reached with pumped liquid /sup 4/He refrigeration. The authors also discuss the observation of an intermittent intrinsic switching noise in the offset charge of the central island.         Experimental evidence for the autonomous Bloch oscillations in single Josephson junctions    L.S. Kuzmin Summary: The charging effects in single ultrasmall Josephson junctions with area S approximately=0.01 mu m/sup 2/ have been studied at low temperatures, T approximately=50 mK. The junctions were isolated from the electromagnetic environment by high-ohmic metallic resistors with R approximately=500 k Omega inserted into the current and voltage leads. For improvement of the isolation by a factor of two, additional tunnel junctions of the same area were inserted into the current leads. Existence of Bloch oscillations was demonstrated by observation of the self-selective videoresponse of the junction under irradiation by a small amplitude-modulated RF signal. The amplitude of the signal was 2-3 orders smaller than in previous experiments. The amplitude of the response had a linear dependence on the power of the signal, and the DC current position of its peak was proportional to the frequency of the signal with the relation I=+or-2 ef. All these observations can be explained as an interaction of the small external signal with the narrowband Bloch oscillations generated by the junction.         Sub-micron field-effect transistor using granular NbN thin films    L. Zhang, N. Yoshikawa and M. Sugahara Summary: The conductance modulation induced by an electrostatic field is observed in highly resistive NbN granular thin films at low temperatures. The measurement is performed using a three-terminal device with FET structure, whose channel is made of NbN thin films. The field effect is interpreted based on the single electron charging effect of small intergrain junctions. The submicron-size channel (0.5 mu m) is fabricated by using the electron-beam lithography technique. The conductance modulation is found to be enhanced by the reduction of the channel size. In order to assess the feasibility of the FET using FET phenomena, the gate voltage dependence of the I-V curve and of the conductance of the channel part is examined. The charging effect is discussed on the basis of a one-dimensional array model of the small tunnel junctions.         Measurement of conduction properties of highly resistive superconducting microbridges    X. Chen, N. Yoshikawa and M. Sugahara Summary: The authors present experimental results on the properties of very small microbridges with high junction resistance. The authors fabricated NbN microbridges with very narrow width (<100 nm) and length ( approximately 100 nm) by electron beam lithography, and measured the junction properties, such as I-V characteristics and temperature dependence. The junctions with very high resistance (>>k Omega ) exhibit unusual nonlinearity in the I-V relation, which is dual to the Josephson characteristics. The electric field effect in a two-junction array is also examined, where a gate electric field is applied to a center electrode. Experimental results agree fairly well with numerical calculations, assuming that the bridge consists of a one-dimensional array of the single-electron-tunnel junction.         Magnetic susceptibility imaging for nondestructive evaluation (using SQUID magnetometer)    J.P. Wikswo Jr., Y.P. Ma, N.G. Sepulveda, S. Tan, I.M. Thomas and A. Lauder Summary: High-resolution superconducting magnetometers such as MicroSQUID (superconducting quantum interference device) have been shown to be effective for nondestructive evaluation. MicroSQUID can also be used with a room-temperature magnet to image the magnetic susceptibility of materials. A diamagnetic or paramagnetic sample is scanned in the applied field, and the local perturbations are measured. For thin samples, such as plates, sheets, or thin sections of rock, the data are deconvolved to generate two-dimensional susceptibility images. Three-dimensional structures can be imaged with magnetic susceptibility tomography: deconvolution of a large data set obtained by applying the field and scanning in multiple orientations. Extremely small surface defects on nonmagnetic or weakly magnetic samples are imaged by decorating the sample with paramagnetic microspheres prior to scanning. Magnetic susceptibility imaging demonstrates the feasibility of SQUID nondestructive evaluation on materials that could previously be examined only with X-rays or ultrasound.         Progress in RF-SQUIDs    M. Muck Summary: The author reviews recent developments towards practical RF-SQUIDs (superconducting quantum interference devices) made of high-T/sub c/ as well as conventional superconductors. It is noted that progress has been made in RF-SQUIDs towards practical low-noise sensors. The flux noise values obtained from planar thin-film devices made of both conventional and high-temperature superconductors are comparable to what is currently obtainable with DC-SQUIDs. RF-SQUIDs seem to offer somewhat lower values of low-frequency excess noise than DC-SQUIDs at frequencies below 1 Hz. To obtain optimum sensitivity, it seems advisable for RF-SQUIDs to use a cooled preamplifier. The losses in cooling liquid due to dissipation in the amplifier are negligible in the case of liquid nitrogen, and lead to an increased evaporation of liquid helium on the order of 100 ml/day. Starting from bulk material devices with relatively high flux noise levels, at present the best high-T/sub c/ RF-SQUIDs offer a field sensitivity of less than 200 fT/ square root Hz (at 1Hz). This is already sufficient for a number of biomedical applications.         Low-noise high-T/sub c/ DC SQUIDs at 77 K    M.S. Dilorio, S. Yoshizumi, K.-Y. Yang, M. Maung, J. Zhang and B. Power Summary: Low-noise DC superconducting quantum interference devices (SQUIDs) have been fabricated using a reproducible superconductor-normal metal-superconductor (SNS) step-edge technique. The superconductor is YBa/sub 2/Cu/sub 3/O/sub 7-x/ and the normal metal is either Ag or an Ag-Au alloy. At 77 K, the energy sensitivity for the SQUIDs with the smallest inductance, L=12 pH, is below 9*10/sup -30/ J/Hz at 1 Hz. The energy sensitivity of SQUIDs with L=70 pH is 5*10/sup -29/ J/Hz at 1 Hz. These measured noise values are sufficient for many practical applications. The larger SQUID inductance is also adequate to permit coupling to multiturn input coils. Thin-film input coils with as many as 30 turns have been developed. Critical current densities for the multiturn coils routinely exceed 10/sup 6/ A/cm/sup 2/ at 77 K.         Noise properties of YBaCuO step edge DC-SQUIDs with different inductance    G. Friedl, G. Daalmans, M. Vildic, D. Uhl, F. Bommel, B. Roas, B. Hillenbrand, B. Stritzker and H.E. Hoenig Summary: Autonomous step edge DC-SQUIDs (superconducting quantum interference devices) with inductances between 20 pH and 140 pH have been prepared on one chip. The noise properties of these devices have been determined by operating them in the flux locked loop. The best energy sensitivity of 6*10/sup -31/ J/Hz was obtained for a 20 pH SQUID and frequencies above 100 Hz. The frequency-dependent noise for the best devices was about 2*10/sup -29/ J/Hz at 1 Hz and could be reduced by applying an AC bias.         Nonlinear hysteresis in thin film SQUID magnetometers    J.Z. Sun, W.J. Gallagher and R.H. Koch Summary: Measurements on both YBaCuO- and Nb-based thin-film DC superconducting quantum interference device (SQUID) magnetometers reveal a nonlinear hysteresis at fields above 0.1 G. The nonlinear hysteresis is sensitive to sample temperature but insensitive to the time scale of the field sweep in the millisecond region. Such hysteresis can be accounted for by the nucleation and subsequent displacement of vortices at the edges of the SQUID input washer. A model has been developed that relates hysteresis to film current density. The model predicts an asymptotic quadratic field dependence, quantitatively consistent with the present data, and also predicts a threshold field which is suggested by the data.         YBa/sub 2/Cu/sub 3/O/sub 7/ thin film Josephson junctions    R.G. Humphreys, J.S. Satchell, J.A. Edwards, N.G. Chew, S.W. Goodyear, M.N. Keene and S.F. Morgan Summary: YBa/sub 2/Cu/sub 3/O/sub 7/ thin film step edge junctions have been studied using a magnetic field applied perpendicular to the substrate. The authors outline a theory to describe the magnetic field dependence of the critical current in the step edge junction geometry, and show that it is in broad agreement with the results of experiments.         Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7//MgO/Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ edge Josephson junctions    R.P. Robertazzi, R.H. Koch, R.B. Laibowitz and W.J. Gallagher Summary: Josephson edge junctions have been fabricated using thin sputtered films of MgO (8-32 AA) to produce a weak connection between high-T/sub c/ electrodes. The current-voltage characteristics of these junctions can be well modeled by the resistively shunted junction (RSJ) equation, and they possess excellent Josephson properties, exhibiting strong magnetic field modulation and microwave response at 10 and 100 GHz up to 85 K. The best high temperature (T>70 K) operation has been obtained with devices which have critical current densities in excess of 10/sup 5/ A/cm/sup 2/ at 4.2 K, and junction critical current resistance products I/sub c/R/sub n/ equivalent to 0.10 mV at 83 K. Experiments indicate that improvements in device quality are expected as the base electrode junction surface is improved. Preliminary results indicate that the cyclability of these junctions is good.         Transport processes and reduction of I/sub c/R/sub n/ product in YBa/sub 2/Cu/sub 3/O/sub x//PrBa/sub 2/Cu/sub 3/O/sub x//YBa/sub 2/Cu/sub 3/O/sub x/ ramp-type Josephson junctions    Y.M. Boguslavskij, J. Gao, A.J.H.M. Rijnders, D. Terpstra, G.J. Gerritsma and H. Rogalla Summary: The mechanisms of current passage and the causes of I/sub c/R/sub n/ (critical-current normal-resistance) product reduction of YBCO/PBCO/YBCO ramp-type junctions are analyzed. At PBCO (PrBa/sub 2/Cu/sub 3/O/sub x/) barrier thicknesses L=8-20 nm the junction characteristics are determined by the thickness of the PBCO barrier and its nature. The boundary resistance and depression of the YBCO (YBa/sub 2/Cu/sub 3/O/sub x/) superconducting parameters near the interface do not strongly affect the junction parameters. The behaviour of the YBCO/PBCO/YBCO junctions cannot be described by simple SNS (superconductor-normal metal-superconductor) weak-link or SIS (superconductor-insulator-superconductor) tunnel models. A strong pair-breaking effect and a one-center inelastic tunneling process are taken into account to explain the Josephson and normal state characteristics of these junctions.         Electromigration studies of the role of oxygen defects in YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary weak links    B.H. Moeckly and R.A. Buhrman Summary: Electromigration experiments were used to help establish the role of local basal-plane oxygen disorder in determining the properties of grain-boundary (GB) weak links in YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films. The response to electromigration currents allows an estimate of the atomic force required to promote chain oxygen disorder in this material. In addition, it was determined that a lesser force is sufficient to promote long-range motion (1-2 mu m) of oxygen defects once they have been created. The activation energy for this process is approximately 0.8 eV. The creation of localized regions of disorder by electromigration in microbridges without GBs shows that these regions have superconductive properties indicative of a filamentary superconductive system shunted by nonsuperconductive ohmic paths. Parallels are drawn between the bulk thin film behavior and the effects due to the presence of GBs. These boundaries can be viewed as limiting the degree of connection between two disordered regions created by the elastic strain gradients caused by the GB.         A superconductive integrated circuit foundry    L.A. Abelson, S.L. Thomasson, J.M. Murduck, R. Elmadjian, G. Akerling, R. Kono and H.W. Chan Summary: A foundry has been established for production of superconductive integrated circuits, modeled after semiconductor application-specific integrated circuit (IC) production. The foundry supports and improves standardized Nb-based IC processing, and develops advanced processes such as a novel NbN-based process. The authors discuss the operation of the foundry, standardized process technologies, design rules, process flows, in-line product tracking, statistical process control, and automated parametric testing. The advantages of fine-line lithography and a class 10/100 environment are presented. Internal and external customer support with standard layout and circuit design tools enables reliable, quick turnaround production of a wide range of circuits. Finally, the authors present examples of concurrent device and process development towards improved, denser circuits, while maintaining a disciplined foundry environment.         All niobium nitride Josephson tunnel junctions with thermally oxidized magnesium barrier    M. Radparvar, L.S. Yu-Jahnes and R.T. Hunt Summary: A process suitable for producing Josephson tunnel junction circuits using all-niobium nitride (NbN) refractory electrodes is described. In this process, an in-situ-deposited trilayer film of NbN/MgO-Mg/NbN is used to fabricate the Josephson junctions. The barrier is formed by thermal oxidation of a thin Mg film sputtered from an Mg target. This process has produced NbN-based Josephson junctions with good tunneling characteristics for devices as small as 3 mu m/sup 2/. High-quality tunnel junction devices have been achieved using this process, with energy gap voltages of nearly 5 mV. These devices exhibit characteristics similar to those of junctions fabricated with barriers deposited from a ceramic MgO target. Thermally oxidized Mg barriers offer a higher degree of control over the tunnel barrier thickness, which results in a significant improvement over processes where the tunnel barrier is directly deposited from an MgO target. The application of this process to all-NbN-based circuits is also discussed.         Fabrication and characterization of all-refractory NbCN/Al/AlO/sub x//Al/Nb junctions    Z.H. Barber, M.G. Blamire, R.E. Somekh and J.E. Evetts Summary: High-quality AlO/sub x/ tunnel barriers have been fabricated on epitaxial niobium carbonitride (NbCN) base layers by the deposition of an Al layer followed by thermal oxidation. By careful control of its uniformity, the thickness of the Al layer has been reduced to less than 3 nm, which results in an average gap voltage, V/sub g/(NbCN), of up to 2.65 mV. Using a self-aligned whole-wafer processing route, high-quality NbCN/Al/AlO/sub x//Al/Nb junctions as small as 0.6 mu m/sup 2/ have been made. These junctions offer considerable advantages over directly deposited barriers in terms of minimal subgap leakage, good control of the barrier conductance, and simple processing procedures. It was shown that submicron junctions can be fabricated with no gap smearing or reduction in quality. Using only Nb counterelectrodes total gap voltages up to 4.0 mV, with widths of 0.6 mV, have been demonstrated in high-quality junctions.         All refractory NbN integrated circuit process    S.L. Thomasson, A.W. Moopenn, R. Elmadjian, J.M. Murduck, J.W. Spargo, L.A. Abelson and H.W. Chan Summary: The authors describe the fabrication and electrical performance of an eight mask step, 2.5- mu m*2.5- mu m minimum junction size, all refractory NbN integrated circuit process. NbN/MgO/NbN trilayers sputtered in situ are patterned by reactive ion etching to form Josephson tunnel junctions. A two-level dielectric process has been developed to ensure low defect densities. Sputtered molybdenum films form a resistor layer. NbN wire J/sub c/ enhancement and improved step coverage have been achieved. This process has been used to successfully fabricate SQUID amplifier circuits, digital modified variable threshold logic circuits, arrays of 256 SQUIDs, SFQ counters, and 4000 junction strings. NbN logic circuit operation above 10 K was demonstrated.         Calorimetric particle detectors with superconducting transition edge thermometers    D. Dummer Summary: The author discusses the development of calorimetric detectors utilizing large absorber crystals coupled to superconducting transition edge thermometers. At low temperature, high energy resolution results from the low detector heat capacity and the strong temperature dependence of the resistance of the thermometer at the normal/superconducting phase transition. The transition edge thermometer is a thin film at very low T/sub c/ superconductor deposited directly on the absorber. Results from two detectors yielding excellent energy resolution are presented. One of these detectors was fabricated with an Ir strip thermometer, and the other with an Ir/Au proximity effect bilayer. Detailed studies have resulted in a model which will be used to optimize future detectors.         Quasiparticle trapping in distributed three-terminal double tunnel devices (particle detectors)    P.A. Warburton and M.G. Blamire Summary: Devices of the structure S/sub 1/IS/sub 2/S/sub 1/S/sub 2/IS/sub 1/ have been fabricated in which the common S/sub 1/ layer is an epitaxially grown Nb base electrode and S/sub 2/ is Ta. By strongly biasing one junction a nonequilibrium distribution of quasi-particles is established in the Nb base. These quasi-particles may be detected by the other junction which is biased in the subgap region. Quasi-particle multiplication in the Nb and Ta layers has been observed. Quasi-particle trapping, in which quasi-particles are confined to the Ta layer adjacent to the barrier, has been shown to be an effective method of increasing the detected current.         Superconductive tunnel junctions for X-ray spectroscopy    J.B. le Grand, M.L. van den Berg, M.P. Bruijn, M. Frericks, P.A.J. de Korte, J.G. Gijsbertsen, E.P. Houwman and J. Flokstra Summary: In order to investigate the influence of quasi-particle trapping on the performance of superconductive tunnel junctions as X-ray detectors, a series of Nb/Al/Al/sub 2/O/sub 3//Al/Nb junctions have been produced with different Al-layer thicknesses in the bottom electrode. The proximity effect between the Nb absorber and the Al trapping layer plays a dominant role, because it greatly influences the trapping time of excess quasi-particles from the Nb electrode to the Al trapping layer. A study of the influence of Al layer thickness on the operation of tunnel junctions as X-ray detectors is presented. Quasi-particle trapping is shown to be quite an efficient process in Nb junctions with Al-layers of 10 nm and thicker. The proximity model of A.A. Golubov and E.P. Houwman can explain the present data quite well. Nb junctions suffer from the bandgap reduction at oxidized and anodized surfaces. Without any special attention, extremely fast loss processes, about 30 ns, are present.         A prototype dark matter detector using a series array of aluminum superconducting tunnel junctions    K.E. Laws, W.C. Barber, R.W. Bland, J.W. Carpenter, R.T. Johnson, J. Lockhart, J.S. Lee, R.M. Watson, S.E. Labov, C.A. Mears and B. Ellman Summary: The authors have fabricated an array of series-connected superconducting aluminum tunnel junctions on the surface of a large sapphire crystal, as a prototype of a detector for massive, weakly interacting elementary particles. Such particles might constitute the missing matter of our galaxy. Tests on a 14-g crystal with 6-MeV alpha particles gave an energy resolution of 450 keV full width at half maximum (300 keV due to electronics and microphonics alone). The ultimate energy resolution to be obtained from this type of detector is discussed.         Highly collimated photon detection using strongly coupled superconducting tunnel junctions    N. Rando, C.L. Foden, A. Peacock, A. van Dordrecht, J. Lumley and C. Pereira Summary: Preliminary results on the X-ray performance of Nb-based superconducting tunnel junctions (STJs) with a highly transmissive barrier are reported. The results show that the energy resolution of these detectors can be improved by collimating the X-ray photons onto the junction barrier area, thus reducing illumination of the surrounding substrate and leads. A charge output of about 50% of the theoretical maximum has been recorded for these STJs, with full width at half maximum resolution of about 200 eV at 6 keV. Several mechanisms which are believed to degrade the energy resolution are also discussed. X-ray events are also detected by other junctions on the same chip which are not illuminated. This may indicate the presence of a marked phonon transmission along the sapphire substrate which acts as a phonon waveguide analogous to the light transmission mechanism in fiber optics.         Spatial and temporal dynamics of superconducting Nb/AlO/sub x//Nb tunnel junction detectors    F. Hebrank, S. Lemke, M. Breunig, R. Gross, T. Doderer and R.P. Huebener Summary: Nb/AlO/sub x//Nb tunnel junction detectors have been irradiated locally with electrons having energies in the range between 6 and 35 keV. By the measurement of the temporal and spatial dynamics of the detector response the characteristic time and length scales of the radiation-induced nonequilibrium state were obtained. The spatially resolved measurements show the importance of the coupled diffusion of the quasi-particles and phonons in the junction electrodes and the wiring and of the phonon propagation in the substrate material. The observed temporal and spatial detector response gives constraints for the development of superconducting-tunnel-junction particle detectors with improved efficiency and energy resolution.         Superconducting Al-trilayer tunnel junctions for use as X-ray detectors    M.C. Gaidis, S. Friedrich, D.E. Prober, S.H. Moseley and A.E. Szymkowiak Summary: Photolithographic techniques have been developed to fabricate high-quality Al-Al oxide-Al superconducting tunnel junctions for use in X-ray detectors. These devices are designed to incorporate approximately=1- mu m-thick superconducting X-ray absorbers for the detection of <10-keV single photons. In an effort to increase energy resolution, superconductor bandgap engineering with lateral and vertical trapping has been used to shorten quasi-particle tunneling times and diffusion lengths and to prevent quasi-particle diffusion away from the tunnel junction. Methods that have been developed for overcoming materials incompatibility and device degradation upon thermal cycling are reported. The authors also report on the use of a nonrectangular tunnel junction geometry which reduces the magnetic field needed to suppress the Josephson current for stable biasing. Work in progress to measure the energy resolution of these X-ray detectors at 0.35 K is also discussed.         Energy resolving X-ray detectors using niobium absorbers and multiple quasiparticle tunneling between two aluminum traps    C.A. Mears, S.E. Labov, G.W. Morris, C.E. Cunningham, M.A. Le Gros, E.H. Silver, A.T. Barfknecht, N.W. Madden, D.A. Landis, F.S. Goulding, R.W. Bland, K.E. Laws and R.C. Dynes Summary: Superconducting tunnel junction devices are being developed for use as high-resolution, high-efficiency X-ray spectrometers. A device with niobium X-ray absorbing layers coupled to two aluminum layers on either side of the tunneling barrier which serve as quasi-particle traps has been tested. These devices were fabricated photolithographically using a modified niobium/aluminum/niobium trilayer fabrication process. The first devices have a very thin barrier with specific normal state resistance of 1.5*10/sup -6/ Omega -cm/sup 2/, and also exhibit very low leakage current (<15 nA below 200 mK). The energy resolution at 6 keV was 120 eV full width at half maximum. It is estimated that each quasi-particle tunnels an average of eight times before recombining, increasing the total charge transferred and decreasing the effects of electronic noise.         Escape of photoelectrons: a major energy resolution degrading mechanism in thin superconducting tunnel junction X-ray detectors    D. Van Vechten and K.S. Wood Summary: The authors consider the consequences of fabricating integral X-ray detectors with thin electrodes, 0.17 mu m for Nb and 0.25 mu m for Sn, with 6-keV photons incident. A simple geometric argument demonstrates that energetic electron loss during the first 1 ps of each event will cause less than the full energy of the incident photon to be captured in a large fraction of the events. This reduces the ultimate energy resolution the devices can achieve. Use of thicker absorbers (electrodes) is thus highly desirable, both from this point of view and to increase the quantum efficiencies of the devices. Nb electrodes should be about 0.8- mu m thick to reduce the escape probability of photoelectrons of energy >or=5 eV during the first 1 ps of an event.         Field dependence of Fiske resonances in Nb-AlO/sub x/ based Josephson junctions    J.G. Gijsbertsen, E.P. Houwman, J. Flokstra, H. Rogalla, J.B. le Grand and P.A.J. de Korte Summary: Fiske resonances have been measured in a rectangular Nb-Al, AlO/sub x/, Al-Nb Josephson junction as a function of the magnetic field applied parallel to a junction side. Due to the high quality factor of the junction, many resonant modes could be measured, using a special measuring technique. Each mode shows more lobes than reported before. The measured curves are in very good agreement with the high Q theory of I.O. Kulik (1967), and Q-values ranging from 40 to 450 have been obtained. The surface resistance of the Al/Nb barrier probably dominates the microwave losses in the junction barrier at 4.2 K. Losses due to the quasi-particle tunneling current can be neglected. Fiske resonances in a square junction at a field angle of pi /4 rad were also measured. Two-dimensional resonant modes have been found. The field dependence of the (1,1) mixed mode agrees well with the theory of M.A.H. Nerenberg et al. (1976).         Optical and thermal performance advantages for silicon substrates in YBCO bolometer devices    D.B. Fenner, Q. Li, W.D. Hamblen, M.E. Johansson, D.G. Hamblen, L. Lynds and J.I. Budnick Summary: The authors review recent progress they have made in the fabrication of epitaxial YBCO thin-film bolometers (photothermal infrared detectors) on Si wafers. Infrared (IR) transmission of the Si substrates, yttria-stabilized zirconia (YSZ) buffer layers on Si, and YBCO/YSZ/Si has ben measured from the near to the far IR at low temperatures. Si is shown to be much superior to other available choices of substrate for epitaxial-YBCO film bolometers. It is also shown, by various wafer fabrications, that the high strength and thermal conductivity of Si can be exploited to considerably reduce the device thermal-equilibration time, when irradiated with weak IR pulses, and concomitantly increase the device sensitivity. Further, the authors have fabricated monolithic quad arrays of bolometers, and found excellent element-to-element uniformity in their transitions and in their function as detectors for Fourier-transform IR spectroscopy. They have also fabricated an epitaxial YBCO-film bolometer on a submicron-thick window in a Si wafer. The rise and fall times (10-90%) were less than 500 mu s, under chopped IR illumination.         Enhanced optical detection in a Josephson junction    M.S. Wire, L.O. Heflinger, B.J. Dalrymple, M. Leung, T. Pham, L.R. Eaton and A.H. Silver Summary: Shifting of the energy gap of a Nb Josephson junction under direct optical illumination was measured. The response is linear with optical input power over more than five orders of magnitude and is nearly independent of temperature from 4 to 8 K. The rise time of this signal is faster than the 2- mu s rise time of the chopped light signal. These direct signals are 500 to 1500 times larger than those obtained when the same optical power is focused elsewhere on the substrate. This enhanced direct response is interpreted as resulting from thermal isolation of the Josephson junction from the substrate due to thermal boundary resistance.         Influence of substrate and biasing current on response of YBCO microbolometers    K. Li and J.E. Johnson Summary: The authors fabricated YBCO thin films by RF magnetron sputter deposition onto ZrO/sub 2/, SrTiO/sub 3/, LaAlO/sub 3/, and MgO substrates and patterned these films into microbolometers. The influence of substrate type and device biasing current on the response of the microbolometers was measured. The responsivity and the speed of the devices were found to depend on the thermal conductivity of the substrates used. The fastest YBCO device was found on MgO, whereas the largest bolometric response was found on ZrO/sub 2/. It was found that the responsivity of a microbolometer increased with biasing current, but there was an optimal biasing current beyond which device performance deteriorated due to self heating. The results indicate that the most sensitive microbolometer requires a sharp YBCO resistivity transition, a low thermal conductivity substrate, and an optimal biasing current.         Design of high-T/sub c/ superconducting bolometers for a far infrared imaging array    S. Verghese, P.L. Richards, D.K. Fork, K. Char and T.H. Geballe Summary: The design of high-T/sub c/ superconducting bolometers for use in a far-infrared imaging array for 30-100- mu m wavelengths is discussed. Measurements of the voltage noise in thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / on yttria-stabilized zirconia buffer layers on silicon substrates are used to make performance estimates. It is noted that useful opportunities exist for imaging and spectroscopy with bolometer arrays made on micromachined silicon membranes. A circuit on each pixel which performs some signal integration can improve the sensitivity of large two-dimensional arrays of bolometers which use multiplexed readout amplifiers.         YBCO microbolometer operating below T/sub c/: a modelization based on critical current-temperature dependence    D. Robbes, P. Langlois, C. Dolabdjian, D. Bloyet, J.F. Hamet and H. Murray Summary: Using careful measurements of the I-V curve of a YBCO thin-film microbridge under light irradiation at 780 nm and temperature close to 77 K, it is shown that the critical current versus temperature dependence is a good thermometer for estimating bolometric effects in the film. A novel dynamic voltage bias is introduced which directly gives the device current responsitivity and greatly reduces risks of thermal runaway. Detectivity is very low but it is predicted that a noise equivalent temperature of less than 10/sup -7/ K/ square root Hz would be achievable in a wide temperature range (10-80 K), which is an improvement over thermometry at the resistive transition.         Design analysis of a novel hot-electron microbolometer    M. Nahum, P.L. Richards and C.A. Mears Summary: The authors propose a novel antenna coupled microbolometer which makes use of the weak coupling between electrons and phonons in a metal at low temperatures. The radiation is collected by a planar lithographed antenna and thermalized in a thin metal strip. The resulting temperature rise of the electrons is detected by a tunnel junction, where part of the metal strip forms the normal electrode. The active area of the bolometer is thermally coupled by its small volume, by the thermal resistance between the electrons and phonons in the strip, and by the reflection of quasi-particles at the interface between the strip and the superconducting antenna. Design calculations based on a metal volume of 2 mu m*6 mu m*0.05 mu m at an operating temperature of 100 mK give an NEP of about 3*10/sup -19/ WHz/sup -1/2/, a time constant of about 10 mu s, and a responsivity of about 10/sup 9/ V/W. The calculated sensitivity is almost two orders of magnitude higher than that of the best available direct detectors of millimeter and submillimeter radiation operated at the same temperature.         A comparison of the nonbolometric microwave response with the bolometric optical response of Tl- and Bi-oxide superconductors    J.D. Chern, H.C. Lai, A. Guldeste, S. Aslam, D.H.T. Wu, D. Dew-Hughes, C.R.M. Grovenor, M.J. Goringe and B. Minakovic Summary: The distinction between the bolometric and nonbolometric responses of high-T/sub c/ Tl- and Bi-oxide superconducting thin films is presented by comparison of the characteristics of the responses at different temperatures and chopping frequencies. The bolometric optical response of the films is proportional to the dR/dT of the films; experimentally, the peak optical response decreases as the chopping frequency of the radiation is increased. The nonbolometric response is not proportional to the dR/dT of the films, and the peak microwave response was found to be almost independent of the chopping frequency. It is found that both components can be observed in the microwave response of a superconducting epitaxial film. The optical response of a continuous-wave (CW) He-Ne laser is mainly due to the bolometric effect, whereas the microwave response using a 34.5-GHz Gunn diode microwave generator is predominantly nonbolometric.         Non-equilibrium quasiparticle response to radiation and bolometric effect in YBaCuO films    A.D. Semenov, I.G. Goghidze, G.N. Gol'tsman, A.V. Sergeev, E.E. Aksaev and E.M. Gershenzon Summary: The voltage photoresponse of structured current biased YBCO films on different substrates to 20-ps laser pulses of 0.63- mu m and 1.54- mu m wavelengths and to continuously modulated radiation of 2-mm wavelength is measured to temperatures around T/sub c/. Fast picosecond decay of the response to pulsed radiation is followed by slow exponential relaxation with a nanosecond characteristic time depending on the substrate material and film dimensions. The slow component does not depend on wavelength and is attributed to the bolometric effect, while the magnitude of the fast component associated with nonequilibrium response rises with wavelength. More than an order-of-magnitude increase of the nonequilibrium response is seen from near-infrared to millimeter-wave range. This dependence plausibly reflects the low efficiency of multiplication of photoexcited electrons in YBaCuO compared to conventional superconductors.         Ultrafast nonbolometric photoresponse of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films    A. Ghis, S. Pfister, J.C. Villegier, M. Nail and J.P. Maneval Summary: Ultrafast transient voltage (<12-ps risetime, 30-ps width) has been measured on a current-biased, very thin (30-nm) YBa/sub 2/Cu/sub 3/O/sub 7-x/ epitaxial film, illuminated by a picosecond laser pulse ( lambda =1.06 mu m) at approximately 50 K. The experimental set-up and the measuring apparatus used allowed precise time measurements. The narrow and high electric pulse obtained is faster than any previously reported. It is attributed to a nonequilibrium Cooper pair breaking process. This first response pulse is followed by a longer bolometric decay interpreted using parameters obtained from measurements taken at smaller fluence and lower temperature as the combination of a phonon escape time and an electron-phonon energy relaxation time.         Concept for a high-resolution thermometer utilizing the temperature dependence of the magnetic penetration depth    P.J. Shirron and M.J. DiPirro Summary: A thermometer using the temperature dependence of the magnetic penetration depth in superconductors is described which has the potential for temperature resolution, when using a DC superconducting quantum interference device (SQUID) readout, on the order of 1 pK. One such device has been fabricated and characterized to demonstrate proof of concept. It consists of primary and secondary coils of NbTi wire wound on a copper toroidal core on which a thin ( approximately 15-nm) layer of In (T/sub c/=3.4 K) has been deposited. The temperature dependence of the mutual inductance, M(T), or self-inductance, is used to detect changes in temperature. Measurements of M(T) have been made with an AC excitation of the primary for various frequencies and peak magnetic field strengths. Estimates of ultimate temperature resolution are given.         Observation of the London moment and trapped flux in precision gyroscopes    Y.M. Xiao, W. Felson, C.H. Wu, G.M. Keiser and J.P. Turneaure Summary: The London-moment readout has been observed in flight quality gyroscopes and it has been demonstrated that it is possible to reduce magnetic field trapped in these gyroscopes to levels as low as 1.5*10/sup -11/ T. A preliminary analysis shows that the horizontal component of the London-moment signal is 60% of the total expected London-moment signal and is proportional to the gyro spin speed. Experiments were carried out in a unique ground test facility which was designed to provide the conditions necessary to observe the London moment of the spinning gyroscope.         High-T/sub c/ transition-edge bolometer for detecting guided millimeter waves    D. Janik, D. May, H. Wolf and R. Schneider Summary: Long meanders of the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ were investigated for their suitability as transition-edge bolometers for determining the absolute power of guided millimeter waves. The devices were made of 200-300-nm-thick YBaCuO films sputtered by an inverted cylinder magnetron onto yttria-stabilized zirconia (YSZ) substrates. These films were structured by photolithographic methods to meanders 30 mm in length and 30- mu m wide. The devices structured in this way show resistances of around 30 k Omega at the midpoint of the transition to superconductivity. Measurements were performed at frequencies of 35, 70, and 94 GHz. The working temperature was at the midpoint of the transition to superconductivity, about 90 K. The responsitivity of the device measured in waveguides is 4000 V/W at 35 GHz and 2600 V/W at 70 and 94 GHz. It exceeds the value of 1000 V/W typical of semiconductor diodes in the range below 100 GHz.         Proposed high-accuracy superconducting power meter for millimeter waves    R.L. Kautz, D.G. McDonald, D.K. Walker and D. Williams Summary: A prototype bolometer is described which offers potential as a nearly ideal power meter by absorbing and measuring nearly all of the incident power. The load developed for this bolometer is shown to reflect no more than 0.01% of the incident power. Assuming that the losses in niobium are no greater than those in lead, the power absorbed by the bolometer but not measured is less than 0.02% over a significant fraction of the WR-22 band (33-50 GHz). If the DC substitution error can be reduced to a comparable level, the proposed bolometer offers a possibility of improving the accuracy of millimeter-wave power measurement by an order of magnitude.         A practical microwave detection system using a high-impedance microbridge and a miniature refrigerator    M. Takai, K. Niki, T. Ikemachi, S. Yoshikawa, Y. Yoshisato and S. Nakano Summary: The authors have developed a high-impedance Josephson-type microwave detector and a practical microwave video detection system using a small Stirling refrigerator. The detector was fabricated from a newly developed YBCO-BiO composite superconductor prepared by doping YBCO with Bi/sub 2/O/sub 3/. The I-V response of the detector showed enhanced mode detection under microwave irradiation. A measured responsivity of more than 180 V/W was obtained at 58 K.         Ultrafast photoresponse of a structured YBa/sub 2/Cu/sub 3/O/sub 7- delta/ thin film to ultrashort FIR laser pulses    R.S. Nebosis, M.A. Heusinger, W. Schatz, K.F. Renk, G.N. Gol'tsman, B.S. Karasik, A.D. Semenov and G.M. Gershenzon Summary: The authors have investigated the photoinduced voltage response of a current-carrying structured YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin film to ultrashort far-infrared (FIR) laser pulses in the frequency range from 0.7 THz to 7 THz. The detector has shown an almost constant sensitivity of 1 mV/W and a noise equivalent power of less than 5*10/sup -7/ W/ square root Hz. The temperature dependence of the decay time of the detector signal was studied for temperatures around the transition temperature of the film ( approximately 80 K). For a detector temperature where dR/dT had its maximum, the authors observed bolometric signals with decay times of about 2 ns, and for lower temperatures they observed nonbolometric signals with decay times of approximately 120 ps; the duration of the nonbolometric signals was limited by the time resolution of the electronic registration equipment.         Improved performance of a superconductive optical detector with planar antennas    M. Leung, M. Wire, L. Heflinger, T. Pham, L. Eaton and D. Rutledge Summary: A significant improvement in performance of an ultrathin-film NbN superconductive infrared detector was demonstrated by using a planar antenna concept. The output signal voltage is increased through improved optical coupling and the detector noise is decreased by reducing the total area of the NbN detector element. An enhancement in the signal-to-noise ratio by 32 dB was observed when comparing antenna-coupled detectors to area detectors (e.g., meandering lines). In addition, the authors observed a polarization selectivity of about 13 dB to linearly polarized light, which can provide additional discrimination. The primary noise mechanism in these films is confirmed to be voltage shot noise due to fluctuations in the motion of flux quanta in the film. This is a precise dual to current shot noise.         Responsivity calculation and measurement of YBaCuO optical detector    J.H. Hao, F.Q. Zhou, X.R. Zhao, H.D. Sun, X.J. Yi and Z.G. Li Summary: The optical response of granular YBa/sub 2/Cu/sub 3/O/sub 7- delta / films using microbridge structure was investigated. Considering the self-heating effect of the detector from the bias current, a bolometric model was proposed to calculate the temperature rise and responsivity of the bolometer. The responsivity of a nonequilibrium detector on the basis of grain boundary Josephson junctions in granular films has also been demonstrated. Optical detectors with responsivities of more than 10/sup 3/ v/w at liquid nitrogen temperature have been fabricated. Experimental evidence for the coexistence of bolometric and nonbolometric effect is given. Calculations based on the proposed model are in agreement with the experimental results.         Proximity effect in Nb/Al, AlOoxide, Al/Nb Josephson tunnel junctions    E.P. Houwman, J.G. Gijsbertsen, J. Flokstra, H. Rogalla, J.B. le Grand, P.A.J. de Korte and A.A. Golubov Summary: Regions with reduced energy gap induced by the proximity effect give rise to quasi-particle loss in Josephson-junction X-ray detectors, but may also be used advantageously for quasi-particle collection. The influence of the thickness of the Al proximity layers in Nb/Al/sub 1/, AlO/sub x/, Al/sub 2//Nb Josephson tunnel junctions on the electrical characteristics has been investigated theoretically and experimentally. Theoretically it is found that the strength of the proximity effect is mainly determined by the proximity effect is mainly determined by the proximity parameters gamma /sub M1/ ( gamma /sub M2/) of the electrodes. Good fits of the measured I-V curves with theory were obtained for junctions with thicknesses d/sub A11/ ranging from 4 to 25 nm and d/sub A12/=3 nm, with gamma /sub M2/ approximately=0.12 and gamma /sub M1// gamma /sub M2/=d/sub A11//d/sub A12/. For all junctions the proximity knee remains more pronounced than predicted.         Reproducibility of niobium junction critical currents: statistical analysis and data    A.D. Smith, S.L. Thomasson and C. Dang Summary: The authors present a statistical model to account for Josephson-junction critical current variability produced in integrated circuit processing. On the basis of data gathered from over a thousand junctions from the TRW superconducting integrated-circuit foundry line, it is shown that present niobium technology can produce junctions with critical currents identical to within a few percent, depending on junction size. Less than 2% (1 sigma ) spread critical currents were measured for 10 mu m junctions.         The influence of Al morphology on quality in Nb/Al/AlO/sub x//Al/Nb epitaxial base layer junctions    E.C.G. Kirk, M.G. Blamire, R.E. Somekh and J.E. Evetts Summary: Nb/Al/AlO/sub x//Al/Nb devices with single-crystal base electrodes and low subgap current leakage have applications for particle detectors. To increase the quality and reproducibility in these devices, the authors sought to characterize and improve the microstructure of the first Al layer, from which a better-quality AlO/sub x/ barrier can then be formed. Using a liquid-nitrogen-cooled stage, they have established a temperature range over which it is possible to grow ultra-high-purity Al epitaxially on single-crystal Nb layers. They compared the effect of epitaxial and nonepitaxial layers on device quality, and the effect of varying the Al deposition temperature and therefore the nucleation rate at the start of Al layer growth. The main factor in improving V/sub m/ was the lower Al deposition temperature. The authors have seen an improvement of 20-30% in V/sub m/ values at 4.2 K, using single-crystal Nb base electrodes, across a range of J/sub c/ (critical current) from 50 to 9000 A cm/sup -2/.         Effects of underlayer roughness on Nb/AlO/sub x//Nb junction characteristics    S. Kominami, H. Yamada, N. Miyamoto and K. Takagi Summary: The effects of underlayer roughness on Nb/AlO/sub x//Nb Josephson junction characteristics are clarified. MoN/sub x/ and SiO films with 0.1-2.7-nm surface roughness are used as underlayers for the junctions. MoN/sub x/ films with varying levels of roughness are prepared by sputter-etching. SiO films retain a smooth surface after sputtering etching. The existence of grain boundaries in the MoN/sub x/ films causes surface roughness. Subgap leakage current of junctions on MoN/sub x/ underlayers is higher than that of junctions on SiO underlayers, and it increases with the roughness of the underlayers. The roughness of the underlayer's surface is reflected in the Nb base electrode's surface; however, the roughness of the Nb surface is not directly reflected in the AlO/sub x/ surface. The AlO/sub x/ surface is smoother than the Nb surface. The cause of the leakage increase in the junctions on rough underlayers may be dispersion in the deposited-Al thickness.         Fabrication of Nb/AlO/sub x//Nb tunnel junctions using focused ion beam implanted Nb patterning (FINP) technique    H. Akaike, A. Fujimaki, Y. Takai and H. Hayakawa Summary: The focused ion beam implanted Nb patterning (FINP) technique was applied to the fabrication process of Nb/AlO/sub x//Nb tunnel junctions. The essence of this technique is that Ga-ion-implanted layers in Nb films serve as a masking layer during reactive ion etching in CF/sub 4/ plasma. Uniform and reproducible patterns of 0.3*0.3 mu m/sup 2/ have been formed by this technique. The tunnel junction fabricated with a 60-keV ion beam had the quality parameter Vm of 48 mV, which indicates no degradation of junction characteristics by focused ion beam irradiation. The authors also investigated the CF/sub 4/ plasma etching characteristics of Ga-ion-implanted Nb films and found that an improvement in the characteristics is achieved by lowering beam energy and raising CF/sub 4/ gas pressure.         Investigation of etching techniques for superconductive Nb/Al-Al/sub 2/O/sub 3//Nb fabrication processes    A.W. Lichtenberger, D.M. Lea and F.L. Lloyd Summary: Wet etching, CF/sub 4/ and SF/sub 6/ reactive ion etching (RIE), RIE/wet hybrid etching, Cl-based RIE, ion milling and liftoff techniques have been investigated for use in superconductive Nb/Al-Al/sub 2/O/sub 3//Nb fabrication processes. High-quality superconductor-insulator junctions have been fabricated using a variety of these etching methods; however, each technique offers distinct tradeoffs for a given process an wafer design. In particular, it was shown that SF/sub 6/ provides an excellent RIE chemistry for low-voltage anisotropic etching of Nb with high selectivity to Al. The SF/sub 6/ tool has greatly improved the trilevel resist junction insulation process. Excellent repeatability, selectivity with respect to quartz, and submicron resolution make Cl/sub 2/+BCl/sub 3/+CHCl/sub 3/ RIE a very attractive process for trilayer patterning.         Preparation and properties of Nb/Al-AlO/sub x//Nb multilayers    H. Kohlstedt, G. Hallmanns, I.P. Nevirkovets, D. Guggi and C. Heiden Summary: The authors have deposited Nb/Al-AlO/sub x//Nb multilayers on Si substrates by DC and RF magnetron sputtering. To assist the fabrication of stacked tunnel junctions they investigated the layers by transmission electron microscopy and anodization spectroscopy. The accumulated internal mechanical stress in the niobium films depends on the argon sputtering pressure and was analyzed by the X-ray stress evaluation method. Up to ten junctions in one stack were prepared. Performance of the junctions is discussed on basis of I-V characteristics and Fraunhofer patterns.         Josephson junction integrated circuit process with planarized PECVD SiO/sub 2/ dielectric    A.T. Barfknecht, R.C. Ruby, H.L. Ko and G.S. Lee Summary: As part of the authors' efforts to reach very-large-scale integration for Nb Josephson junction circuits, they have developed a process technology that includes plasma-enhanced chemical-vapor-deposited (PECVD) SiO/sub 2/ for all interlayer dielectrics, as well as sacrificial resist etch-back planarization to smooth the surface topology under the trilayer. The simple etch-back planarization process is shown to produce quite smooth surfaces. Since the process includes a redeposition step after the planarization etch, the interlayer dielectric integrity is excellent, and no interlayer shorts were observed for these levels. Several products, including DC superconducting quantum interference devices (SQUIDs), have been manufactured using this process technology, with good results and high yield.         The critical current-field dependence of a Josephson superlattice    H. Amin, M.G. Blamire and J.E. Evetts Summary: The set of coupled nonlinear equations that describes the phase in the Josephson superlattice is presented. Numerical solutions for the simplest of the stacked junction systems, the two-junction system, are investigated in the stationary state for a number of cases of differing critical current densities and junction spacings as a function of parallel applied magnetic field. The results show that the behavior of the system is determined to a great extent by the higher J/sub c/ junction. The numerical solutions are compared with experimental results obtained from SISIS (superconductor-insulator-superconductor-insulator-superconductor) devices (where the superconductor is Nb and the insulator is Al/sub 2/O/sub 3/) and their significance for the Fraunhofer response of high-T/sub c/ bijunction structures is discussed.         NbN-MgO-NbN Josephson junctions prepared by window isolation process    W. Rothmund, H. Downar, P. Meisterjahn, W. Scherber and M. Wulker Summary: NbN-MgO-NbN Josephson junctions prepared by the window isolation process are investigated with the aim of setting up a reliable fabrication process for integrated thin-film superconducting quantum interference device (SQUID) applications. Compared to the SNAP, SNIP, and other related processes, the trilayer is built up in two separate steps, which has the advantage that the base- and the counter-electrode can be formed without affecting the junction edges, and therefore leakage currents at the edges can easily be prevented. The critical current density can be varied between 0.1 and 4.0 kA/cm/sup 2/ with values of V/sub M/ on the order of 40 mV. For the integration of the junctions into a multilayer SQUID system, the authors developed for each relevant material (Nb, NbN, SiO) a specific reactive ion etching process to produce oblique edges of the structures. This facilitates the crossing of narrow current leads of moderate film thickness without any reduction in cross section or even interruptions.         Niobium nitride Josephson junction process development    J.M. Murduck, J. DiMond, C. Dang and H. Chan Summary: NbN/MgO/NbN tunnel junction fabrication has been developed using statistical experimental design for insertion into a Josephson LSI (large-scale integration) fabrication technology. Junction deposition conditions have been studied and correlated with structural characterization and junction I-V measurements. Josephson junctions with sum gaps as large as 5.0 mV and junction quality factor of 47 mV have been produced. Current density uniformity, a critical parameter in circuit design, has also been investigated. I/sub c/(O) uniformity at 4.2 K of a 4000 junction array was within sigma =3.1% and was +or-10% across 1 in/sup 2/. The utility of this junction process has been demonstrated by insertion into a standard circuit fabrication process that has produced logic circuit operation above 10 K.         Andreev reflection current in clean and one-dimensional Nb short weak links    K. Hamasaki and H. Abe Summary: Nb-(fine Nb wires)-NbN short weak links (SWLs) have been reproducibly fabricated by the field evaporation technique. By this method, one could continuously vary the I-V curve from insulator type to tunnel-type to metallic-contact type. The quasiparticle characteristics are qualitatively very similar to the prediction of Klapwijk, Blonder, and Tinkham (KBT) theory for the simple case of two independent normal metal-superconductor interfaces in the clean contact limit.         Hysteretic Josephson junctions from high T/sub c/ superconducting thin films    R.L. Fink, M. Thompson, C. Hilbert and H. Kroger Summary: Hysteretic superconductor-insulator-superconductor (SIS) and superconductor-normal metal-superconductor (SNS) Josephson junction devices have been fabricated from epitaxial thin-film structures. The SIS tunnel junctions were made of BKBO (Ba/sub 1-x/K/sub x/BiO/sub 3/) thin-film electrodes and a KNbO/sub 3/ barrier. Tunnel structures with gap voltages as high as 8 mV and switching voltages as high as 5 mV have been demonstrated. Nearly ideal SIS tunnel characteristics for high-temperature superconductive thin-film trilayer structures are reported. Zero bias currents are modulated by small magnetic fields and Shapiro steps are observed under RF-irradiation. SNS devices made from a YBCO (YBa/sub 2/Cu/sub 3/O/sub 7-y/) bottom thin-film electrode, a SrTiO/sub 3/ barrier, and a top BKBO film possessed McCumber parameters in excess of 100 and displayed I/sub c/R (critical-current resistance) products of up to 1 mV at 4.2 K.         Fabrication and properties of Nb/MgO/Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ tunnel junctions using crystalline and amorphous MgO films grown by the MBE method    K. Yamano, K. Shimaoka, K. Takahashi, T. Usuki, Y. Yoshisato and S. Nakano Summary: The properties of tunnel-type junctions have been improved by using the Nb/MgO/Au/BSCCO structure. Tunneling spectroscopy was examined in junctions such as Nb/MgO/BSCCO and Nb/MgO/Au/BSCCO. MgO films for tunnel barriers were grown by molecular-beam epitaxy (MBE). In a Nb/MgO/BSCCO junction with no Au layer, the superconducting gap parameters, Delta , of BSCCO single crystals with crystalline and amorphous MgO barriers were estimated to be 25 meV and 38 meV, respectively. Nb/MgO/Au/BSCCO junctions with a 20-nm-thick Au layer indicated a clear gap structure induced by the proximity effect at 30 meV. These junction characteristics were confirmed to be closely related to the existence of interdiffusion between BSCCO and other materials.         Experimental implications of intrinsic quasiparticle mechanisms of dissipation in the switching dynamics of Josephson devices    B. Ruggiero and P. Silvestrini Summary: The decay of the zero-voltage state is studied, including quasi-particle tunneling and the interference cos phi term in the equivalent circuit model. As a result of the approach used, the effective resistance for describing the junction dissipation, which was an arbitrary parameter in the resistively shunted junction (RSJ) model, can now be obtained in terms of the measurable junction parameters and bias conditions. This allows a direct comparison of data with theory. The very good agreement between data and theory confirms the essential correctness of the authors' assumptions. The data also provide an excellent experimental test of the thermal activation theory in underdamped physical systems.         Experimental verification of the photodiode theory of SIS mixers    D.P. Woody and M.J. Wengler Summary: The authors describe the characterization and interpretation of the performance of superconductor-insulator-superconductor (SIS) receivers within the framework of the photodiode theory of mixing. The quantum efficiency plays a dominant role in the theory, and a simple method of accurately measuring this parameter is presented. It is demonstrated that the quantum efficiency measurements can be conveniently made on a standard radio astronomy receiver and combined with the usual hot and cold load characterization to improve the understanding of the receiver's performance. The measurements verify that the photodiode theory of mixing accurately describes the receiver noise even at local-oscillator power levels well above the linear response range. The results for receivers operating at 100 and 240 GHz verify the utility of this approach. These methods should also prove useful in evaluating submillimeter receivers.         Measurements of the Riedel peak in superconducting aluminum tunnel junctions (mixers)    D. Winkler Summary: The Riedel singularity in thin-film aluminum tunnel junctions was measured from temperature behavior of the zero voltage step and the RF-induced Josephson steps at around the gap frequency. From these experiments the author derived a value of the imaginary gap parameter to be about 1% of the gap parameter value at the gap edge when the temperature was 0.7 of the transition temperature. The author believes that, using magnetic field for tuned superconductor-insulator-superconductor (SIS) mixers with relatively large area, the Riedel singularity should not play an important role for frequencies around the gap frequency at finite temperatures.         Detection of 110 GHz millimeter-wave signal using DyBaCuO step-edge junction    Y. Fukumoto, I. Shigaki, H. Kajikawa, R. Ogawa and Y. Kawate Summary: Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction (SEJJ) fabricated by a sputter-deposited DyBaCuO thin film. The SEJJ exhibited a clear response to 110-GHz millimeter-wave irradiation, and Shapiro steps could be observed up to the seventh step. Harmonic mixing detection was successfully achieved using microwaves of 6 approximately 22 GHz as a local oscillation signal. The dependence of conversion efficiency ( eta ) on the harmonic number was expressed as eta varies as N/sup -3.3/. The detector was operative at temperatures up to 65 K, although the efficiency rapidly decreased above 50 K.         Fully quantum analysis of radiation detection in an SIS    M.W. Johnson and M.J. Wengler Summary: The authors calculate the current response of a superconductor-insulator-superconductor (SIS) to second order in photon operators and shows that, under certain conditions, an ideal SIS junction can be operated as a photon detector. The theory presented is a quantum generalization of the semiclassical diode theory developed by Werthamer (1966) and Tucker (1979). The dependence of the DC tunneling current on the number of photons present on the transmission line is shown. It is found that one electron tunnels for each photon absorbed by the junction.         Constant output noise temperature of the superconducting quasiparticle mixer    Q. Ke and M.J. Feldman Summary: The output noise temperature, rather than the standard input noise temperature, is shown to be the fundamental measure of the shot noise of the superconducting (SIS) quasiparticle mixer. This conclusion is based on extensive numerical computations of the properties of optimized SIS (superconductor-insulator-superconductor) receivers and also on analytic calculations with separate consideration of correlated and uncorrelated noise sources. The quantum theory of mixing is used to derive a simple analytic expression for the mixer output noise which is independent of frequency, and qualitatively explains the dependence of the output temperature on each of the receiver's operating parameters. The derivation leads to a novel understanding of the SIS mixer which, distinguishes between its correlated and uncorrelated noise sources. The authors predict T(receiver)=2*T(mixer) for many SIS receivers. Numerous experiments substantiate the analysis.         A 100 GHz Josephson mixer using resistively-shunted Nb tunnel junctions    R.J. Schoelkopf, T.G. Phillips and J. Zmuidzinas Summary: The authors describe preliminary mixer results using resistively shunted Nb/AlO/sub x//Nb tunnel junctions in a 100-GHz waveguide mixer mount. The mixer utilizes robust, lithographically defined devices which have nonhysteretic I-V curves. A receiver temperature of 390 K (D5B) has been obtained with a conversion loss of -6.5 dB. The receiver's behavior agrees qualitatively with the behavior predicted by the resistively shunted junction model. Substantial improvements in performance are expected with the use of better-optimized shunted junctions and numerical simulations suggest that, if devices with higher I/sub C/R/sub N/ (critical-current normal-resistance) products can be obtained. Josephson effect mixers could be competitive with superconductor-insulator-superconductor (SIS) mixers at high frequencies.         Integrated receiving structure comprising complementary spiral antenna and tuned parallel biased SIS array    M.A. Tarasov, S.V. Shitov, V.P. Koshelets and G.V. Prokopenko Summary: A type of superconducting receiving element comprising a complementary spiral antenna and a series-parallel superconductor-insulator-superconductor (SIS) array with individual tuning of each SIS junction has been designed, fabricated, and experimentally studied. The array was designed for the 80-160 GHz waveband and consists of five SIS junctions, each with a 1.5- mu /sup 2/ area, six inductive short-ended slotlines, and two decoupling capacitances. The effective direct detector bandwidth of this structure with a quantum efficiency equalling unity has been estimated to be as wide as 70 GHz. The noise temperature of the heterodyne mixer has been measured in a three-lens Gaussian beam guide by means of the hot/cold load method, yielding a receiver DSB noise temperature of 80 K. The intermediate-frequency (IF) mixer port load bandwidth and the effect of thermal background radiation on the I-V curve and the saturation of the SIS mixer have been studied.         Direct detection at FIR frequencies with niobium tunnel junctions    J.D. Prince, B.S. Deaver Jr. and S. Withington Summary: Measurements have been made on an array of six niobium/aluminum-aluminum oxide/niobium junctions with an integrated bow-tie antenna at 584 GHz. These measurements include examining the response of current-voltage curves at different incident radiation powers, both with and without an applied magnetic field. The measurements also include the responsivity and the noise of the devices as direct detectors. A planar superconducting quantum interference device (SQUID) was used as the low-frequency amplifier, and a chopped far infrared (FIR) laser generated the radiation. Comparisons with theoretical predictions show good fits to the current-voltage curves, except at the highest powers where there is evidence of heating and possibly nonequilibrium processes. Current responsivities of greater than one-half of the quantum limit and a noise equivalent power of 2*10/sup 1-4/ W/ square root Hz have been obtained.         Perfectly matched SIS arrays for mm wave receivers    S.V. Shitov, V.P. Koshelets, S.A. Kovtonyuk and A.M. Baryshev Summary: A novel conception of improved matching for both input and output mixer ports has been developed and confirmed successfully with experimental receivers in the 40-180-GHz frequency range. Parallel and parallel-series combinations integrated up to 11 Nb-AlO/sub x/-Nb type superconductor-insulator-superconductor (SIS) junctions have been tested in full-height waveguide mixers. Receivers' noise temperatures T/sub r/(DSB)         Quasioptical SIS mixer with broadband integrated tuning elements    G. Pance, N. Dubash and M.J. Wengler Summary: The authors have designed and tested a quasioptical superconducting tunnel junction (superconductor-insulator-superconductor, or SIS) mixer with integrated tuning elements. The designs consists of a self-complementary log-periodic antenna, the SIS tunnel junction, and the broadband superconducting tuning circuit. The tuning circuit is placed between the SIS junction and the center of the antenna. Tuning circuits are designed for 98 GHz and 492 GHz. Self-induced resonant steps are observed in I-V curves. Results of noise temperature measurements performed between 89 GHz and 104.4 GHz are reported. Results from the Touchstone simulation program, when run with the actual fabrication process parameters, show agreement with the experiment. Three types of measurements are presented: DC I-V curve measurement, heterodyne detection measurement, and direct detection measurement. All measurements show consistent results and they all agree with the theoretical predictions.         Conversion gain and noise of YBa/sub 2/Cu/sub 3/O/sub 7/ weak-link mixers    D.P. Butler, J. Wang, A. Bhandari and Z. Celik-Butler Summary: Microwave mixing and parametric conversion in YBa/sub 2/Cu/sub 3/O/sub 7/ microbridges were investigated. The devices have been operated as down-converters, converting a 20-GHz radio frequency to a 1.5-GHz intermediate frequency under the action of an 18.5-GHz local oscillator. The microbridges were fabricated both as granular films on MgO substrates possessing grain boundary weak links and as epitaxial films deposited over substrate steps in LaAlO/sub 3/ substrates. The authors have measured conversion gains as high as -8+or-4 dB when mixing on the nonlinear resistive (superconducting-normal) transition and as high as -30 to -40 dB when parametrically converting via the nonlinear inductance of the bridge at bias currents less than the critical current. Output referred noise powers as low as -206 dB/Hz (3*10/sup -21/ W/Hz) have been measured. In some samples, noise switching events were observed.         Arrays of high temperature superconductor Josephson junctions    J.S. Satchell, R.G. Humphreys, J.A. Edwards and N.G. Chew Summary: The authors present results on parallel, series, and two-dimensional arrays of high-temperature superconductor junctions. The parallel arrays show the expected field dependence of critical current and can function as vortex flow transistors. The series arrays give data about the spread in junction critical currents for the present process. The two-dimensional arrays show many of the phenomena previously observed in low-T/sub c/ technology, such as field frustration of the phase transition, some evidence for superlattice states, and the tentative indications of giant Shapiro steps, showing large-scale cooperative behavior in the device.         Fabrication and tunneling characteristics of low-leakage All-YBa/sub 2/Cu/sub 3/O/sub 7-x/ edge junctions    Q.-Y. Ying, C. Hilbert and H. Kroger Summary: All-YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) superconductor-insulator superconductor tunnel edge junctions have been fabricated. Y/sub 2/O/sub 3/ is used as the barrier material. YBCO and Y/sub 2/O/sub 3/ are deposited by electron-beam evaporation under the same deposition conditions. Special attention is paid to creating a smooth base-electrode edge by ion-mill etching. The junction width is reduced to submicron size in order to avoid defects in the junction region. The YBCO superconductive gap structure observed in dynamic conductance, measurements is very pronounced. Quasi-particle tunneling is observed with very low leakage in the subgap region. No zero-bias anomalies are present. The edge junction fabrication and the junction tunneling characteristics are discussed.         Intrinsic Josephson effects in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ single crystals    B. Aigner, B. Avenhaus, R. Kleiner, C. Kreuzer, G. Kunkel, P. Pospischil, F. Steinmeyer, P. Muller and K. Andres Summary: The authors report on microwave emission of Bi/sub 2/Sr/sub 2/Ca/sub 2/O/sub 8+x/ single crystals with current flow along the c-axis. The results show that a small Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ single crystal behaves like a series array of several thousand Josephson junctions which can exhibit mutual phase-locking. At least at low temperatures there is evidence for mutual phase locking between several tens of junctions. It is noted that improving the crystal quality should increase the number of phase-locked junctions and therefore provide the possibility of using such crystals as naturally grown high-frequency oscillators.         Fabrication of heteroepitaxial Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub x//Bi/sub 2/Sr/sub 2/CuO/sub y//Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub x/ Josephson junctions    T. Satoh, J. Fujita, T. Yoshitake and H. Tsuge Summary: Josephson junctions using c-axis oriented heteroepitaxial Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub x//Bi/sub 2/Sr/sub 2/CuO/sub y//Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub x/ trilayer films have been fabricated. The junctions showed the resistively shunted junction-like characteristic up to 50 K. The highest value of the product of the critical current and the normal state resistance of the junctions was about 0.2 mV. Clear Shapiro steps at the expected voltages were observed up to 50 K in the presence of external microwave irradiation. The microwave power dependence of the height of these steps was qualitatively in agreement with the resistively shunted junction model behavior. Moreover, the Fraunhofer-like diffraction pattern in an applied magnetic field was clearly observed. These results indicate that nearly uniform Josephson junctions had been fabricated.         Multi-fluxon effects in long Josephson junctions    A.V. Ustinov, T. Doderer, R.P. Huebener, J. Mygind, V.A. Oboznov and N.F. Pedersen Summary: Experiments with fluxons moving in long Josephson junctions of different geometries are reviewed. A controllable way of introducing fluxons one by one into annular Josephson junctions has been realized. This allows a comparison with existing fluxon chain perturbation theory. Several new millimeter-wave stimulated regimes found in linear junctions are discussed. Large asymmetric zero-crossing steps of constant voltage have been observed in the I-V curves. These steps may have a potential application in Josephson voltage standards. Large narrowband radiation emitted from the flux-flow oscillator in the 62-77-GHz frequency range has been detected.         Flux flow microelectronics    J.S. Martens, V.M. Hietala, T.A. Plut, D.S. Ginley, G.A. Vawter, C.P. Tigges, M.P. Siegal, J.M. Phillips and S.Y. Kou Summary: Flux-flow-based devices such as the superconducting flux flow transistor and magnetically controlled long junctions have been made from thin films of TlCaBaCuO and YBaCuO. The devices are based on the magnetic control of flux flow in their respective structures: a long junction or an array of weak links. The equivalent circuits of the two devices are similar: a low-impedance input control line, an output impedance of 3-20 Omega , and an active current-controlled element. The long junctions have tended to be slower, to have lower gain, and to be somewhat less noisy than their counterparts. Circuits such as narrowband and distributed amplifiers (50-GHz bandwidths, noise figures <3 dB), phase shifters (continuous with <2-dB loss, 4-40 GHz), logic gates (2-3-ps gate delays). and memories made using these devices are compared and analyzed in terms of performance.         Distributed Josephson junction arrays as local oscillators    B. Bi, S. Han, J.E. Lukens and K. Wan Summary: The power and linewidth of the radiation, near 250 GHz, of small distributed Josephson junction array sources have been measured using a single-chip integrated source and receiver. The intermediate frequency (IF), coupled off the chip to a room-temperature spectrum analyzer, permitted a direct measurement of the oscillator linewidth. The one-dimensional arrays were of a novel design with junctions placed in 1/4 wavelength lumps separated by one half wavelength. The measured power ( approximately=2 mu W) and linewidth ( approximately=10 MHz) for the 10 junction sources were in reasonable agreement with those obtained from computer simulations.         Can superconductive digital systems compete with semiconductor systems?    H. Kroger and U. Ghoshal Summary: The authors review the current status of silicon microprocessors and memories, and briefly contrast this with the current status of superconducting processors and memories. Possible applications for conventional Josephson computers are mentioned, and the difficulties in supplanting silicon technology by any new technology are discussed. An alternate strategy of hybridizing superconductor and semiconductor circuits is proposed. These hybrid circuits will be able to outperform either technology separately. The hybrid circuits combine the virtues of semiconductor circuits which have high density and excellent manufacturability with the virtues of superconductor circuits which are extremely sensitive in detecting currents and have the capability to drive currents in low impedance lines. The authors examine how hybrid circuits can improve two deficiencies of conventional silicon technology, high power dissipation in interconnection circuits and long memory access times, without requiring the use of many superconductive devices.         Superconductor-semiconductor memories    U. Ghoshal, H. Kroger and T. Van Duzer Summary: The authors describe new types of hybrid superconductor-semiconductor RAMs which utilize the current switches in superconductive electronics to remove important constraints on the design of semiconductor memories and achieve performances attainable by the individual technologies separately. They focus on a voltage word line RAM architecture and illustrate the basic designs in terms of a low-T/sub c/ Josephson-CMOS technology. They discuss the design of interface circuits, word-line drivers, memory cells, and fluxoelectronic current sensing of bit lines. Current projections for 4 K operation indicate that sub-nanosecond 64-kb RAMs using a 0.8- mu m CMOS technology are possible. Extensions of this design to high-T/sub c/ superconductor-CMOS circuits operating at 77 K are briefly discussed.         Noise properties of biepitaxial HTS junctions    S.G. Hammond, Y. He, C.M. Muirhead, P. Wu, M.S. Colclough and K. Char Summary: The authors have measured the voltage noise across a biepitaxial junction at both low current, where the noise is dominated by critical current fluctuations, and at high current, where the noise is dominated by resistance fluctuations. They have used a phase-sensitive technique to show that the noise from these two regions is not correlated. This gives support to the suggestion that the normal and supercurrent components are carried through the junction in different channels. The result suggests that the normal and supercurrent components are carried through a series of parallel tracks.         Multilayer studies and applications in template bi-epitaxial DC SQUIDS    R.P.J. Ijsselsteijn, J.W.M. Hilgenkamp, M. Eisenberg, D. Terpstra, J. Flokstra and H. Rogalla Summary: Multilayer deposition for the creation of a well-defined grain boundary, based on different in-plane orientations of c-axis oriented thin YBa/sub 2/O/sub 2/Cu/sub 3/O/sub 7- delta / layers on a single substrate, has been performed on three different kinds of substrates: (1102)-oriented Al/sub 2/O/sub 3/, (100) SrTiO/sub 3/, and (100) MgO. The multilayers consist of combinations of SrTiO/sub 3/, MgO, CeO/sub 2/, and YBa/sub 2/O/sub 2/Cu/sub 3/O/sub 7- delta /. The YBa/sub 2/O/sub 2/Cu/sub 3/O/sub 7- delta / top layers on (1102) Al/sub 2/O/sub 3/ and (100) SrTiO/sub 3/ were polycrystalline. Josephson junctions and DC superconducting quantum interference devices (SQUIDs) have been structured in the layers on MgO. Shapiro steps were observed. The J/sub c/ rho /sub n/-product of the junctions at 4.2 K is on the order of 1 mV. The critical current decreases in good approximation linearly with increasing temperature, whereas the normal state resistance is nearly temperature independent. Voltage modulation was observed at temperatures up to 77 K.         Artificial grain boundaries of YBa/sub 2/Cu/sub 3/O/sub 7-x/ on MgO bicrystals    H.B. Lu, T.W. Huang, J.J. Wang, J. Lin, S.L. Tu, S.J. Yang and S.E. Hsu Summary: The weak-link properties of laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films on MgO-bicrystals with different misorientation angle ( theta ) along the (001) tilt boundary have been investigated. The critical current density across the grain boundary is exponentially dependent on theta . DC superconducting quantum interference devices (SQUIDs) made on theta =30/sup 0/ misoriented grain boundary exhibited resistively shunted junction (RSJ) behavior in I-V characteristics and showed periodic modulation of voltage-flux characteristics. The modulated voltages were 40 mu V and 4 mu V at 4.4 K and 60 K, respectively.         Magnetic field dependence of critical currents of single grain boundary junctions in Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / superconductor    E. Sarnelli, P. Chaudhari, M. Daumling and J.A. Lacey Summary: The authors present data on the magnetic field dependence of critical currents in epitaxial films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / containing a single boundary. The data are obtained as a function of temperature, the orientation of the grain boundary, and magnetic fields of up to 5 T. A significant residual critical current is observed which increases with decreasing angle of misorientation at a given field and temperature. The data are in qualitative accord with a model in which the grain boundary comprises a large number of microbridges in parallel.         YBCO artificial grain boundary junctions on Si    J. Chen, T. Yamashita, H. Suzuki, H. Myoren, K. Nakajima and Y. Osaka Summary: Si bicrystal substrates with different misorientation angles were fabricated using the hot-press method and their qualities were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) epitaxial thin films were grown on such substrates by RF magnetron sputtering, with yttria and yttria-stabilized zirconia as the buffer layers. The properties of bridge-type junctions patterned on the film by an excimer laser were studied from 4.2 K to 77 K. It was found that the critical current density of the artificial grain boundary (AGB) junction (J/sub c//sup A/) was always less than that of the junction made on Si single-crystal grains (J/sub c//sup G/). The (J/sub c//sup A/)/(J/sub c//sup G/) ratio decreased exponentially as the misorientation angle ( theta ) was increased. The effect of temperature and microwave irradiation showed that the properties of AGB junctions with theta <5 degrees were limited by flux creep. In contrast, AGB junctions with theta >or=10 degrees showed the Josephson effect.         Linewidth of Josephson oscillations in YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions    Y.Y. Divin, J. Mygind, N.F. Pedersen and P. Chaudhari Summary: The AC Josephson effect in YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary junctions (GBJs) was studied in the temperature range from 4 K to 90 K. The temperature dependence of the linewidth of millimeter-wave Josephson oscillations was measured, and it is shown that the derived effective noise temperature of GBJ might be as low as the physical temperature in the temperature range investigated. This makes it possible to use the resistively shunted junction (RSJ) model with thermal fluctuations to get a limiting performance of high-T/sub c/ devices utilizing the AC Josephson effect. The lowest value of the linewidth of 72 GHz Josephson oscillations observed at 77 K was equal to 380 MHz, which demonstrates the applicability of GBJ, particularly in the field of radiation spectroscopy, even at liquid nitrogen temperatures.         High temperature performance of HTS step-edge DC SQUIDs    J. Luine, J. Burch, K. Daly, R. Davidhesier, R. Hu, A. Lee, C. Pettiette-Hall and S. Schwarzbek Summary: YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step edge DC superconducting quantum interference devices (SQUIDs) have been developed which exhibit characteristics suitable for near-term incorporation into high-temperature superconductive (HTS) circuitry. Step-edge junction DC SQUIDs for series array interferometer logic (SAIL) digital applications exhibit resistively shunted junction (RSJ) properties, 65 K I/sub c/ values of approximately 150 mu A, 65 K I/sub c/R/sub n/ values up to approximately 300 mu V, and large I/sub c/ modulation (>50%) in accordance with a standard DC SQUID model. 65 K SQUID switching voltages of approximately 100 mu V have been demonstrated and are sufficient for near-term applications of SAIL digital circuitry operating on a cryocooler platform.         Capacitively shunted, hysteretic YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions    K.P. Daly, J.F. Burch, R. Hu, A.E. Lee, J. Luine and C. Pettiette-Hall Summary: Hysteretic YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions on LaAlO/sub 3/ substrates have been fabricated by shunting intrinsically overdamped junctions with a monolithic capacitor. By comparing the I-V curves of junctions fabricated on the same substrate with and without capacitor counterelectrodes, the authors are confident that the observed hysteresis is due to the shunting capacitor. The capacitor consists of a dielectric layer (SrTiO/sub 3/ or LaAlO/sub 3/), deposited on the YBa/sub 2/Cu/sub 3/O/sub 7/ directly over the step-edge junction and an Ag counterelectrode. Capacitor counterelectrodes ranging in area from 10 mu m*30 mu m to 200 mu m*220 mu m have been investigated. Dielectric layers several tens of nanometers thick have been used. The inferred beta /sub c/ values are as large as 10 at 4 K and decrease with increasing temperature. At 65 K, beta /sub c/ of 1.3 was observed. The measured beta /sub c/ values are smaller than one would naively calculate. These differences are attributed to the usual limitations of lumped-element circuit analysis and resistive losses.         Superconducting transport properties of step-edge Josephson junctions    F. Schmidl, L. Alff, R. Gross, K.-D. Husemann, H. Schneidewind and P. Seidel Summary: The electrical transport properties of YBa/sub 2/Cu/sub 3/O/sub 7- delta / step-edge junctions (SEJs) fabricated on step edges in (100) SrTiO/sub 3/ substrates have been investigated. In particular, the influence of the step angle and the ratio of the step height and the film thickness on the superconducting properties of the junctions were studied. Steps of different height and angle were patterned into (100) SrTiO/sub 3/ substrates by ion beam etching (IBE). Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7- delta / films were grown on these substrates by sputtering and patterned by IBE. The samples were characterized by four-probe electrical measurements. The critical current density of the SEJs was found to depend strongly on the ratio of the step height to the film thickness. The critical current density distribution of the SEJs was imaged by low-temperature scanning electron microscopy and was found to be strongly inhomogeneous.         High-T/sub c/ Josephson junctions and DC SQUIDs    P. Seidel, E. Heinz, F. Schmidl, K. Zach, H.-J. Kohler, H. Schneidewind, J. Borck, L. Dorrer, S. Linzen, T. Kohler, W. Michalke, M. Manzel, E. Steinbeiss, H. Bruchlos, E.-B. Kley and H.-J. Fuchs Summary: Step edge Josephson junctions and DC superconducting quantum interference devices (SQUIDs) made of laser ablated and sputtered YBaCuO (YBCO) films and grain boundary junctions in polycrystalline TlBaCaCuO (TBCCO) films have been investigated. Bridges on the micrometer scale have been structured by laser or ion beam etching as well as by the inhibit-layer technique. The Josephson junctions are characterized comparing I-V measurements under microwave irradiation to calculations within the resistively shunted junction (RSJ) model with finite capacitance and white noise. The dependence of the I/sub C/R/sub N/ product on temperature can be fitted to the microscopic theory of superconductor-normal insulator-normal superconductor (SNINS) or superconductor-normal conductor-superconductor (SNS) junctions with additional temperature-independent pair breaking. Flux modulation and noise properties of the DC SQUIDs at 77 K are shown.         Transport properties of YBaCuO step edge Josephson junctions    M. Vildic, G. Friedl, D. Uhl, G. Dallmans, H. Kohler, H. Meyer, F. Bommel and G. Saemann-Ischenko Summary: Step edge Josephson junctions have been prepared on (100)-oriented SrTiO/sub 3/ substrates. The width of the junctions varied between 3 mu m and 10 mu m. The current-voltage characteristics were measured at 77 K and 4 K, and showed either a superconductor-normal conductor-superconductor (SNS)-like or a flux flow character. The I/sub C/*R/sub N/ product was measured as a function of the critical current density and compared with data for grain boundary junctions on bicrystalline substrates. The critical current was measured as a function of an applied magnetic field. The interference pattern suggested at least one short circuit in the barrier. The critical current was also influenced by irradiating the junctions with microwaves of 35 GHz, and Shapiro steps could be induced. I/sub C/(B) measurements and induced microwave current step measurements indicate that the typical junctions contain microshorts. It was demonstrated on one sample that it is possible to prepare step edge junctions without microshorts.         New techniques for fabricating step-edge junctions for high-T/sub c/ SQUIDs on MgO substrates    C.P. Foley, D.L. Dart, A. Katsaros, N. Savvides, M. James, J.C. Macfarlane, N. Scheepers and G.J. Sloggett Summary: The authors describe two methods used to produce step-edge junctions on MgO substrates suitable for superconducting quantum interference devices (SQUIDs). In both processes a titanium mask has been used to produce a straight, well-defined step which assists in minimizing the occurrence of multiple junctions. They describe two ion-milling processes which produce differently connected step-edge junctions as indicated by scanning electron microscope (SEM) micrographs, and I-V and I/sub C/-B characteristics. Predictable relationships between the ratio of the film thickness to step height and the junction critical-current density are demonstrated; these enable the creation of step-edge junctions with appropriate values of I/sub C/ for particular SQUID designs.         Step-edge junction of YBCO thin films on MgO substrates    S. Tanaka, H. Kado, T. Matsuura and H. Itozaki Summary: The authors have studied the microstructure of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) thin films epitaxially grown on MgO (100) and SrTiO/sub 3/ (100) substrates with step-edges using transmission electron microscopy (TEM). The YBCO thin films were grown on the substrates with step-edges by means of laser deposition. Samples with steps of 200 and 300 nm were prepared for the TEM cross section observation. The direction of a-b planes of YBCO thin films at the slope of the step was not parallel to the (100) plane of the MgO substrates but parallel to the ion-milled local surface of the MgO. Some grain boundaries were observed. The a-b planes of YBCO on the step-edge SrTiO/sub 3/ substrate were parallel to the (100) plane of the SrTiO/sub 3/ substrate and were tilted at a right angle at the edges. The microstructure of the YBCO on SrTiO/sub 3/ was different from that on MgO. It seems that this difference is due to the difference in the lattice matching. DC superconducting quantum interference devices (SQUIDs) with step edge junctions were fabricated and showed good modulation at 77 K.         Investigation of YBCO step-edge Josephson junctions    M. Siegel, K. Herrmann, C. Copetti, C.L. Jia, B. Kabius, J. Schubert, W. Zander, A.I. Braginski and P. Seidel Summary: The authors report on the superconducting transport properties of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) Josephson junctions fabricated by pulsed laser deposition on steep steps in epitaxial substrates. The steps were prepared by Ar-ion milling. The YBCO thin films were patterned either by Ar-ion milling or an inhibit process. The current-voltage characteristics of step-edge junctions (SEJs) fit approximately the resistively shunted-junction (Stewart-McCumber) model up to temperatures of 85 K. The temperature dependence of the characteristic voltage can be explained by a superconductor-normal-superconductor (SNS)type model. Simulations of Shapiro steps were performed. The simulations, the form of the I(V) curves, the I/sub c/(H) curves. and the DC superconducting quantum interference device (SQUID) quantization properties all suggest that a SEJ consists of two weak links in series formed by the grain boundaries at the lower and upper edges of the steps. This conclusion is in good agreement with HREM results, which show that the upper and lower grain boundaries at the step edge are different. Each of these weak links is a parallel array of Josephson junctions with different current densities.         Planarization techniques for multilevel HTS integrated circuit process    A.P. Marathe, X. Meng, D.F. Hebert, Y. Nagai and T. Van Duzer Summary: Various approaches to achieve planarization for a multilevel Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) circuit process are discussed and compared. Results on ion beam planarization (IBP) and etch-back planarization (EBP) techniques are reported, and their application to a potential high-temperature superconductive (HTS) circuit process is demonstrated. Since IBP is based on the mechanical action of etching, its advantage is that, in principle, it can be used to planarize any dielectric film. But it does not have much selectivity; hence, it is very difficult to control etching in a multilayer process. The success of this technique also depends, to some extent, on the pattern to be planarized. As seen from the experimental results, the degree of planarization (DOP) varies inversely, with the linewidth of the pattern. The DOP for 1- mu m line was found to be more than 70% after 45 min of ion milling. In the EBP technique using dry etching, a DOP of around 60% was obtained. This can be improved with thicker resist layers. In wet etching selectivity can be put to an advantage so that etching can be stopped at a desired point.         In-situ fabrication of SNS junction consisting of YBaCuO/PrBaCuO/YBaCuO structure    H. Sato, H. Akoh and S. Takada Summary: All high-T/sub C/ superconductor-normal conductor-superconductor (SNS) junctions have been fabricated using in-situ deposition of YBaCuO/PrBaCuO/YBaCuO trilayer films. The trilayer films of YBaCuO(200 nm)/PrBaCuO(50 nm)/YBaCuO(100 nm) with c-axis orientation were fabricated on the (100)MgO single crystal substrate. The trilayer films were deposited by oxygen reactive coevaporation without breaking vacuum. In order to avoid the influence of moisture and/or photoresist developer, a 70-nm-thick Au layer was deposited as a passivation layer on the top YBaCuO film. The trilayer films were etched using a liquid-nitrogen-cooled dry etching process to ensure less etching damage. The junctions had dimensions ranging from 10 mu m*10 mu m to 300 mu m*300 mu m. By this fabrication method, the self-aligned SNS junction process was successfully performed. Preliminary experiments showed that the junction with 30 mu m * 30 mu m had a supercurrent with a small resistance connected in series to the junction, but had Shapiro steps under microwave radiation.         DC-SQUIDs of YBa/sub 2/Cu/sub 3/O/sub 7/ with artificial PrBa/sub 2/Cu/sub 3/O/sub x/ barriers    M. Schilling, T. Bade and U. Merkt Summary: For the preparation of Josephson junctions and DC-SQUIDs (superconducting quantum interference devices), epitaxial, c-axis-oriented YBa/sub 2/Cu/sub 3/O/sub 7/ films are deposited in-situ on SrTiO/sub 3/ substrates by laser deposition with a KrF excimer laser in a multilayer process. As insulator between subsequent superconductor layers, laser-deposited MgO films are used. The patterning is done with conventional photolithography and argon ion beam etching. The DC-SQUIDs are characterized by electrical transport measurements with and without magnetic fields. Flux modulation up to 72 K is observed. The critical current depends exponentially on the artificial barrier thickness and yields a coherence length across the junction of about 3 nm.         Magnetic field effect on YBCO/PBCO/YBCO Josephson junctions    T. Hashimoto, M. Sagoi, Y. Mizutani, J. Yoshida and K. Mizushima Summary: Using magnetic field effects, the barrier-layer thickness dependence of the critical-current normal-resistance product (I/sub c/R/sub n/) of a-axis-oriented YBa/sub 2/Cu/sub 3/O/sub 7- delta //PrBa/sub 2/Cu/sub 3/ O/sub 7- delta //YBa/sub 2/Cu/sub 3/O/sub 7- delta / Josephson junctions exhibiting a clear magnetic field dependence has been experimentally obtained. Since the magnetic penetration depth of an a-axis-oriented thin film is large, the Josephson penetration depth of the junction easily becomes less than the junction-length, and the observed I/sub c/ is no longer equal to the product of the critical current density j/sub c/ and the junction area A when j/sub c/ approaches 1 kA/cm/sup 2/. The authors studied the magnetic field effects on the junction to evaluate the intrinsic I/sub c/ defined by j/sub c/A under such a condition, and evaluated the I/sub c/R/sub n/-values as j/sub c/AR/sub n/ by using the results. The maximum values of j/sub c/ and I/sub n/R/sub n/ were 310 A/cm/sup 2/ and 170 mu V, respectively, at 4 K for a junction with a 25-nm-thick PrBa/sub 2/Cu/sub 3/O/sub 7- delta /, barrier-layer. The intrinsic I/sub c/R/sub n/-value was found to increase exponentially with decrease in the barrier layer thickness.         High-T/sub c/ SNS junctions for multilevel integrated circuits    R.H. Ono, L.R. Vale, K.R. Kimminau, J.A. Beall, M.W. Cromar, C.D. Reintsema, T.E. Harvey, P.A. Rosenthal and D.A. Rudman Summary: High-quality superconductor-normal metal-superconductor (SNS) Josephson microbridges have been fabricated in a variety of configurations across the edge of steps in a manner that is consistent with a multilevel integrated circuit process. The best junctions have critical current-resistance products of 1-3 mV at 4 K and 100-500 mu V at 77 K, useful values for many analog and digital applications not requiring hysteretic junctions. The DC transport characteristics of the junctions and issues of reproducibility and uniformity are discussed. In particular, a simple theoretically based analysis of junction parameter spread is presented.         Hysteretic YBa/sub 2/Cu/sub 3/O/sub 7- delta /-Au- YBa/sub 2/Cu/sub 3/O/sub 7-/ delta proximity effect Josephson junctions    K.J. Kirk, G.B. Donaldson, R.M. Bowman, A. Cochran, J.A. Edwards, N.G. Chew and J.S. Satchell Summary: The superconducting proximity effect can be used to produce Josephson junctions in high-temperature superconducting structures with a normal conducting carrier. The authors describe work on edge-microbridge junctions made by defining 10-30- mu m-wide Au bridges to link the upper and lower layers of a YBa/sub 2/Cu/sub 3/O/sub 7- delta /Y/sub 2/O/sub 3/-YBa/sub 2/Cu/sub 3/O/sub 7- delta / trilayer. The structures are patterned by photolithography and ion milling from multilayers grown in situ by electron-beam evaporation. The best junctions operate up to around 20 K, exhibit hysteresis in their current-voltage characteristics, and have an I/sub c/R/sub N/ (critical-current normal-resistance product) greater than 200 mu V at 4.2 K. With a 400-nm-long microbridge, the maximum junction T/sub c/ observed was 25 K, and the largest I/sub c/R/sub N/ product at 4.2 K was 400 mu V.         YBaCuO-insulator-normal metal tunnel junctions    B. Ghyselen, R. Cabanel, G. Garry, D. Dubreuil, F. Mayca, P. Hartemann and A. Schuhl Summary: YBaCuO-insulator-normal metal tunnel junctions were fabricated and characterized. The thin insulating barrier was formed using a CHF/sub 3/ treatment in a reactive ion etching system. X-ray photoelectron spectroscopy (XPS) measurements and Auger depth profiling confirmed the formation of a fluorinated surface layer. First electrical results are similar to those generally obtained for natural barriers: no well-defined gap but small gaplike structures; existence of a conductance at zero bias; and an increasing conductance, often linear versus voltage, at high biases.         Fabrication and tunneling measurements of YBa/sub 2/Cu/sub 3/O/sub x//CaF/sub 2//Nb thin film tunnel junctions    H. Tsuge and N. Matsukura Summary: The heteroepitaxial growth of YBa/sub 2/Cu/sub 3/O/sub x/(YBCO)/CaF/sub 2/ has been studied and this structure has been applied to tunnel junctions. The CaF/sub 2/ thin film were epitaxially grown with [111] orientation on YBCO[110] films. The tunneling measurements of YBCO[110]/CaF/sub 2//Nb junctions exhibited that the differential conductance curves have pronounced gap-like structures with sharp peaks at the energy gap edge. The temperature dependence of the energy gap was well fitted to the scaled BCS curve. The 2 Delta /kTc of about eight was derived from the energy gap of 15 meV and T/sub c/ of 45 K obtained by the fitting. This 2 Delta /kTc value was consistent with the infrared reflectivity data reported for the direction parallel to the Cu-O planes.         High-T/sub c/ Josephson junctions by electron beam irradiation    A.J. Pauza, A.M. Campbell, D.F. Moore, R.E. Somekh and A.N. Broers Summary: Josephson junctions were produced by electron beam irradiation of patterned YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin film tracks on MgO substrates. Single weak links show Fraunhofer-type critical current behavior as a function of field (I/sub c/(H)), indicating reasonable current uniformity across the junction. Simple low inductance superconducting quantum interference devices (SQUIDs) have also been made with greater than 70% critical current modulation at 25 K. The relatively high critical current density of these weak links means that it is possible to observe a crossover from small to large junction behavior at a temperature only a few degrees below the T/sub c/ of the junction. In the small junction regime the current-voltage (I-V) curve can be fitted by the resistively shunted junction (RSJ) model, whereas in the large junction regime the I-V curves change to be non-RSJ-like. The I/sub c/R/sub n/ (critical-current normal-resistance) product is typically around 0.05-0.2 mV at temperatures a few degrees below the T/sub c/ of the junction and, for a junction with high T/sub c/, can reach 1 mV at 4.2 K.         Millimeter wave responses of YBCO variable-thickness bridges    C.H. Park, T. Kobayashi and T. Goto Summary: YBCO films were prepared on a MgO (100) substrate by DC hollow cathode sputtering using a stoichiometric YBa/sub 2/Cu/sub 3/O/sub y/ target. Variable-thickness bridges (VTBs) were fabricated by Al slant evaporation and low-energy ion beam etching techniques using the YBCO epitaxial films. The voltage-current characteristics and microwave and millimeter-wave response of the VTBs were investigated. The responses of microwave radiation (f=9.67 GHz) and millimeter-wave radiation (f=94 GHz) to VTBs show well-defined constant voltage steps of 20 mu V and 194 mu V intervals, respectively. A periodic modulation of the magnetic flux-voltage characteristics due to superconducting quantum interference effects was observed for a YBCO DC-SQUID (superconducting quantum interference device) with VTB.         Characteristics of Josephson junctions using the crack in YBCO thin films    H. Kimura, M. Miyazaki, K. Tsuda and Y. Okabe Summary: The authors studied (013)-oriented YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) thin films on SrTiO/sub 3/ (110) substrates. Although the surfaces of the films were smooth enough, there were parallel and straight cracks in the films more than 150-nm thick. These cracks were caused by the c-axis shrinkage associated with the tetragonal-to-orthorhombic phase transition during the cooling process. An attempt was made to fabricate Josephson devices using these cracks. In order to control the electrical properties of the crack junctions, the thickness of the films was studied. The electric resistance of the film increased with thickness. The crack formed a weak link since Shapiro steps were observed. The fabricated devices are considered to be typical microbridges.         Fabrication and measurement of submicron planar YBa/sub 2/Cu/sub 3/O/sub 7/ microbridge Josephson junctions    Z. Bao, L. Ji, K.Y. Lin, B. Bi, S. Han and J.E. Lukens Summary: Deep-submicron planar YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) microbridge Josephson junctions (about 0.1- mu m to 0.5- mu m long and wide) were fabricated using two different approaches: (1) using electron beam lithography and argon-ion milling to make the designed bridge pattern; and (2) depositing YBCO on a substrate with a prepatterned MgO/sapphire bilayer structure. Both approaches have yielded microbridges showing constant voltage steps in the current-voltage characteristics under applied microwave fields. The step width is also found to show oscillatory microwave power dependence. The possible mechanism for the Josephson-like behavior observed and the physical significance of these deep submicron bridges are discussed. The observed phenomena might be explained by the vortex motion model.         The AC Josephson effect and submillimeter wave mixing with a weak-link array of grain boundaries formed in YBCO film    T. Matsui and H. Ohta Summary: The authors present a model for a series-parallel array of small metallic (nontunneling) Josephson junctions. The transmission and configuration of pair electrons between small superconducting regions are considered assuming the presence of a strong interaction between the electrostatic energy (2e)/sup 2//2C and the Josephson effect in a network of metallic weak links. The model predicts that the same behavior as that of a single junction is obtained with a superconducting weak-link device comprising multiple small superconducting regions joined by conductive bridges. In an experiment in the 100- and 320-GHz frequency ranges, the constriction of a YBCO film formed with a network of grain-boundary Josephson weak links showed that the AC Josephson effect is the same as for a single Josephson element. It is confirmed that the constriction works as a harmonic mixer at 318 GHz and that a network of high-T/sub c/ superconducting weak links can be used for a practical device operating at submillimeter-wave frequencies.         DC-SQUIDs with low noise and large beta /sub L/-values on (Y)ZrO/sub 2/ bicrystal substrate    H.K. Olsson, R.H. Koch, P.-A. Nilsson and E.A. Stepantsov Summary: High-quality YBa/sub 2/Cu/sub 3/O/sub 7/ DC-SQUIDs (superconducting quantum interference devices) fabricated on bicrystal (Y)ZrO/sub 2/ substrates have been operated at temperatures from 10 K to the critical temperature at 89 K. Stable operation with low white noise levels is found even for beta /sub L/-values as large as 60 for these nonhysteretic junctions ( beta /sub c/<<1). In addition, two noise sources were identified in the 1/f noise: (1) a junction critical current dependent noise S/sub v/ approximately I/sub 0/(T)/sup 2.7/ and (2) a narrow peak in S/sub v/(T) centered at 87 K with its origin in vortex motion within the superconductor. Optimum low-noise operation was obtained in a minimum at 85 K with a flux noise S/sub Phi /(10 Hz)=1.5*10/sup -9/ Phi /sub 0//sup 2//Hz.         Thin film HTc SQUID construction and characterisation    M.N. Keene, S.W. Goodyear, J.S. Satchell, J.A. Edwards, N.G. Chew and R.G. Humphreys Summary: The authors describe the process for manufacturing DC superconducting quantum interference devices (SQUIDs) using both step junctions and 45 degrees -rotated grain boundaries. An assessment of the noise performance and flux-to-voltage ratio for fourteen devices of various inductances, operating temperatures, and junction technologies is given. Systematic experiments on the technology steps required to construct fully integrated magnetometers and gradiometers are described. These include crossovers, superconducting interconnects, and film growth on undulating surfaces. For each of these, test structures have been constructed, and their properties have been measured. A simplified three-layer fully integrated DC SQUID magnetometer design is described. The authors highlight the need for improved reproducibility and demonstrate that, for a number of devices, there is no obvious relation between the temperature and the magnetic flux noise. The process for constructing interlayer superconducting contacts is shown to work, and the insulator has sufficient resistance for flux transformer applications.         Bicrystal YBCO DC SQUIDs with low noise    A.H. Miklich, D. Koelle, E. Dantsker, D.T. Nemeth, J.J. Kingston, R.F. Kromann and J. Clarke Summary: The authors have fabricated 12 DC superconducting quantum interference devices (SQUIDs) by laser-depositing YBa/sub 2/Cu/sub 3/O/sub 7-x/ on a SrTiO/sub 3/ bicrystal substrate with a misorientation angle of 24 degrees . At 77 K all 12 devices had acceptable values of critical current, resistance, and voltage modulation produced by an external magnetic field. The white noise energy of one device with an estimated inductance of 41 pH was 1.8*10/sup -30/ JHz/sup -1/. The noise power scaled as 1/f at frequencies below about 1 kHz; by using a bias current reversal scheme it was possible to reduce this noise by two orders of magnitude at 1 Hz, to a value of about 1.5*10/sup -29/ JHz/sup -1/. A magnetometer was made by coupling the SQUID to a flux transformer with a 5-turn input coil. The measured magnetic field gain was 60, and the white noise was 36 fT/ square root Hz. However, the transformer produced relatively large levels of 1/f flux noise, not reduced by the bias reversal scheme, that limited the noise at 1 Hz to 1.7 fT/ square root Hz. A single-layer magnetometer with a single-turn pick-up loop is described.         YBCO DC SQUID on MgO bicrystal substrate with flux transformer    J. Lin, T.W. Huang, J.J. Wang, H.B. Lu, S.L. Tu, S.J. Yang and S.E. Hsu Summary: A superconducting quantum interference device (SQUID) was fabricated from a YBCO thin film on MgO (100) bicrystal substrates. The resulting device contained a pancake-shaped SQUID with a 25- mu m*25- mu m hole at the center. A pair of microbridges was attached to the side of the SQUID in which a 5- mu m slot was located at the center and extended to the hole. phi -V measurement showed that dV/d phi was about 40 and 4 mu V/ phi /sub 0/ at 4.4 K and 60 K, respectively. The flux transformer contained a 3-mm*3-mm pickup loop and a 75- mu m*75- mu m coupling coil in which the center of the square hole of the SQUID was carefully aligned. The flux transformer has been found to enhance the sensitivity of the SQUID. The coupling constant of the SQUID and flux transformer was about 0.28.         Preparation and characterization of planar YBa/sub 2/Cu/sub 3/O/sub x/ flux transformers    B. Roas, G. Friedl, L. Bar, F. Bommel, G. Daalmans and L. Schultz Summary: Planar magnetometer and gradiometer flux transformers, which can be used for high-temperature superconductor superconducting quantum interference devices (SQUIDs), were fabricated from epitaxial, excimer-laser-deposited YBa/sub 2/Cu/sub 3/O/sub x/ three-layer stacks. The first YBa/sub 2/Cu/sub 3/O/sub x/ layer and the SrTiO/sub 3/ insulator layer were deposited through silicon shadow masks. As the edges of these layers are very smooth, a second YBa/sub 2/Cu/sub 3/O/sub x/ film can grow epitaxially onto the device without forming grain boundaries. It was subsequently patterned by argon ion milling to magnetomer and gradiometer flux transformers with up to 12 turns and 25- mu m linewidth. The flux transformers were characterized by resistance and persistent current measurements, using a conventional SQUID magnetometer. At 77 K a persistent current of about 1 mA was measured in the flux transformer with 50- mu m linewidth.         Nonlinear response in thin film high temperature superconducting magnetometer sense loops    J.W. Purpura, T.R. Clem and R.F. Wiegert Summary: Measurements of nonlinear response in Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8+y/ and YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin-film magnetometer sense loops were performed at 4.2 K. The thallium-based films were deposited by laser ablation onto lanthanum aluminate substrates and the yttrium-based films were prepared by sputtering onto strontium titanate substrates. Both types of superconducting films were patterned using photolithography into sense loops, each consisting of a magnetometer input loop connected to a magnetometer output loop by a pair of closely spaced parallel strip lines. The thin-film output loop of a given sample was coupled inductively to a sensitive measurement system using a superconducting quantum interference device to measure magnetic flux. A uniform DC magnetic field applied to the sample input loop was slowly ramped to plus and minus a predetermined value and then ramped back to zero. The sample output was monitored to determine the value of applied field corresponding to the threshold of nonlinear response of the film loop. Film loops having various thicknesses and line widths were studied to correlate aspect ratio to nonlinear effects. Possible mechanisms for the observed nonlinear behavior are discussed.         Thin-film HTS probe coils for magnetic-resonance imaging    R.S. Withers, G.-C. Liang, B.F. Cole and M. Johansson Summary: Several planar coil designs, with integral resonating capacitors, are reported using large-area sputtered YBCO films. One design utilizes a distributed interdigital capacitor, while a second exploits capacitive coupling of two films on opposite sides of a dielectric. Devices of the first design made on LaAlO/sub 3/ have achieved Q>10/sup 4/ at 18.5 MHz, possibly limited by the loss tangent of this substrate. Identical coils made with silver films have Q=10. With the second design, Q>10/sup 4/ was achieved at the even lower frequency of 5.7 MHz.         Novel design and operation of thin film high T/sub c/ magnetometer    M. Gershenson and R. Williams Summary: The concept of a magnetometer based on the nonlinear magnetic properties of a high-T/sub c/ superconductor thin film was developed and tested. A novel detection method which allows microwave operation was tested. The superconductor, driven into the nonlinear regions by applying an amplitude-modulated magnetic field, generates a low-frequency field at the modulation frequency commensurate with the externally applied fields. The particular advantage of this system versus the superconducting quantum interference device (SQUID) alternative is the minimal processing of the superconducting material necessary to construct such a device. An electronic system which allows operation up to 2.4 GHz was tested with a YBCO thin film sample in a magnetometer configuration. A noise density of 15 nT/sup 1/2/ was measured.         YBCO DC SQUIDs utilizing sapphire step edge junctions    A.B. Berezin, C.W. Yuan and A.L. de Lozanne Summary: A number of superconducting quantum interference devices (SQUIDs) which utilize a step edge grain-boundary junction process on sapphire substrates have been measured. White noise levels of about 7 mu Phi /sub 0// square root Hz at 1 Hz in a 16-pH device at 77 K were measured. By modulating the bias current, only about a factor of 3 to 4 reduction in the amplitude of low-frequency noise is achieved. Excess flux noise is believed to constitute the remainder. A square washer configuration yields flux noise at 100 Hz at about 140 mu Phi /sub 0// square root Hz, giving a field sensitivity of 11 pT/ square root Hz. Measured hysteresis is about -1 to -5*10/sup -3/ in a low ambient field.         Characteristics of YBCO step-edge weak links and SQUIDs    S. Kuriki, T. Kamiyama, D. Suzuki and M. Matsuda Summary: The authors have fabricated step-junction and bicrystal-junction superconducting quantum interference devices (SQUIDs) using YBCO films that were deposited respectively on etched step on (100) MgO substrates and (100) SrTiO/sub 3/ bicrystal substrates of 38.4 degrees tilt angle. Distinct differences in I-V and noise characteristics between the two types of SQUIDs were observed. The I-V characteristics for the step SQUID have finite excess current, while those for the bicrystal SQUID are of resistively shunted-junction type. The 1/f noise is much lower in the step SQUID than in the bicrystal SQUID. A white noise level of 1*10/sup -5/ Phi /sub 0//Hz/sup -1/2/ at about 60 K was obtained in both SQUIDs.         Sensitive RF-SQUIDs and magnetometers operating at 77 K    Y. Zhang, M. Muck, K. Herrmann, J. Schubert, W. Zander, A.I. Braginski and C. Heiden Summary: Large 6-mm*6-mm and 8-mm*8-mm flux-focusing washer structures with inductances L/sub S/ between 25 pH and 500 pH were fabricated from epitaxial, c-axis YBa/sub 2/Cu/sub 3/O/sub 7/ films. Double step-edge junctions having a low 1/f noise were incorporated in these washers to form RF-SQUIDs (superconducting quantum interference devices). A high tank circuit frequency near 150 MHz was chosen to reduce noise and improve the sensitivity of the SQUIDs. At 77 K, a transfer function exceeding 100 mu V/ Phi /sub 0/ and a white flux noise of 3*10/sup -5/ Phi /sub 0// square root Hz down to below 0.3 Hz were attained with L/sub S/=25 pH. A magnetometer with L/sub S/=190 pH was demonstrated. The best magnetic field and energy resolutions were 170 fT/ square root Hz and 5*10/sup -29/ J/Hz respectively, over a signal frequency range to below 1 Hz. The magnetometer was used to record human magnetocardiograms and auditory evoked human brain responses.         High-T/sub c/ RF SQUID magnetometer system for high-resolution magnetic imaging    S.S. Tinchev, J.H. Hinken, M. Stiller, A. Baranyak and D. Hartmann Summary: A high-T/sub c/ RF superconducting quantum interference device (SQUID) magnetometer system has been developed. The SQUID sensor is made from YBCO thin films using local oxygen-ion-irradiated microbridges. The SQUID is cooled by liquid nitrogen in an open cryostat. For the scanning process the sample is placed on a nonmagnetic stage inside a magnetic shield. The instrument has a spatial resolution of about one millimeter, which can be further improved. The system is used for nondestructive testing and for detecting the magnetic fields generated by corrosion currents.         Noise properties of SQUIDs with step-edge Josephson junctions    V.N. Glyantsev, M. Siegel, J. Schubert, W. Zander, U. Poppe, H. Soltner, A.I. Braginski and C. Heiden Summary: The authors investigated low-frequency noise in RF and DC superconducting quantum interference devices (SQUIDs) with step-edge Josephson junctions (SEJs). The noise properties have been measured as a function of frequency, temperature, bias current, and magnetic field. The low-frequency noise has a telegraph-like character in certain conditions and depends quasi-periodically on flux and temperature. This telegraph noise was also observed in single step-edge junctions. The experimental results were explained by a model of such a junction in which an array of parallel and series connected weak links acts like a two-level fluctuator. This fluctuator arises from the quantum states of a multijunction SQUID with spatially inhomogeneous SEJs resembling a multijunction array.         A YBa/sub 2/Cu/sub 3/O/sub 7/ thin film SQUID gradiometer for measurements in unshielded space    Y. Tavrin, Y. Zhang, M. Muck, A.I. Braginski and C. Heiden Summary: Low-noise RF superconducting quantum interference device (SQUID) washers fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/ epitaxial thin films have been used to construct a first-order electronic gradiometer operating at 77 K and suitable for biomagnetic measurements. Mechanical adjustment of one SQUID's plane in a gradiometric setup, which consisted of two SQUIDs separated by a vertical 6-cm base, made it possible to attenuate signals due to far DC magnetic field sources by three orders of magnitude. A magnetic field resolution of 280 fT/ square root Hz above 2 Hz was attained through the use of large thin-film and bulk flux focusers. The fine structure of human-heart magnetocardiograms could be recorded in unshielded space. In a shielded room, magnetoencephalograms were obtained. The system was used to obtain new data on the acoustically evoked cortical response.         Dynamics of quasioptical Josephson junction arrays for submillimeter coherent sources    A. Pance and M.J. Wengler Summary: The dynamics of the quasi-optical two-dimensional Josephson junction arrays for oscillators is investigated. Numerical time-domain simulations of small-scale parallel arrays were performed. It is found that the DC biasing circuit determines the states of these arrays. It is also found that other states exist in which parts of the array operate in phase. The authors investigate the sensitivity of in-phase states to variations in junction critical currents and to nonvanishing fluctuations. It is found that the DC self-field effects do not provide a stable phase-locking mechanism and that RF interactions are necessary for locking the array in phase.         Quasi-optical Josephson-junction oscillator arrays    J.A. Stern, H.G. LeDuc and J. Zmuidzinas Summary: Josephson junctions are natural voltage-controlled oscillators capable of generating submillimeter-wave-length radiation, but a single junction usually can produce only 100 nW of power and often has a broad spectral linewidth. The authors are investigating 2-D quasi-optical power combining arrays of 10/sup 3/ and 10/sup 4/ NbN/MgO/NbN and Nb/Al-AlO/sub x//Nb junctions to overcome these limitations. The junctions are DC biased in parallel and are distributed along interdigitated lines. The arrays couple to a resonant mode of a Fabry-Perot cavity to achieve mutual phase-locking. The array configuration has a relatively low impedance, which should allow the capacitance of the junctions to be tuned out at the oscillation frequency.         Complete phase-locking in a one-dimensional series biased Josephson-junction array    S. Han, A.H. Worsham and J.E. Lukens Summary: The RF power at approximately 300 GHz coupled to a 52- Omega load by a one-dimensional DC series biased Josephson junction array has been measured using an on-chip Josephson detector. The array was fabricated using the planarized all-refractory technology for low-T/sub c/ superconductivity (PARTS). From the measured RF power and DC voltage levels, it is concluded that the 100 junctions in this array were locked in-phase. The effects of the finite inductance, associated with the junction's shunt resistor, on the array output power and detector's current-voltage characteristics are also discussed.         Frequency dependence of the emission from 2D array Josephson oscillators    P.A.A. Booi, S.P. Benz, T. Doderer, D. Hoffmann, J. Schmidt, S. Lachenmann and R.P. Huebener Summary: Coherent emission from 2-D arrays of Josephson junctions, coupled to a detector junction through a DC blocking stripline capacitor, was detected over a frequency range from 50 to 210 GHz. A power of 0.26 mu W, which is larger than the 0.1 mu W expected from the resistively shunted-junction model, was detected in a range from 140 to 150 GHz. Frequencies where no emission was detected correspond to standing waves in the capacitor when multiples of the half-wavelength match the capacitor length. Low-temperature scanning electron microscopy confirmed the presence of standing waves at these frequencies, but also revealed standing waves at other frequencies, indicating an impedance mismatch and a possible extension of the standing waves into the array.         Design of a lumped array of Josephson junction oscillators    J. Edstam and H.K. Olsson Summary: It is shown that inductively resistively shunted junctions are good candidates for Josephson-junction oscillator arrays. The shunt resonates out the junction intrinsic capacitance, allowing a much higher effective impedance at the resonance frequence, but still with a small shunt resistance giving a narrow linewidth. Compared to resistively shunted junctions they are advantageous for frequencies greater than about 100 GHz, when fewer junctions and lumped arrays can be used, giving larger bandwidths. Design rules that avoid chaotic solutions and optimize output power are given. A design example of an integrated circuit consisting of an SIS-mixer pumped by an array of as few as four junctions at 350 GHz is given. A bandwidth of 160 GHz and a linewidth of 400 kHz should be feasible in a practical situation.         Coupling of long Josephson junction oscillators at millimeter-wave frequencies    M. Cirillo, F. Santucci, P. Carelli, M.G. Castellano and R. Leoni Summary: The authors report on results of phase-locking experiments in a system composed of two long Josephson junctions oscillating at millimeter-wave frequencies. The effects of the coherent behavior of the two junctions are visible on the current-voltage characteristic of the long junctions and in the power enhancement effects observed on the current-voltage characteristic of a detector junction. It is shown that is possible to couple two long junctions in such a way that the enhanced radiation can be transmitted to other devices. Results from another mode of operation of the long Josephson junction as an oscillator are also presented. This mode is based on magnetic-field-induced singularities in long junctions (Fiske steps) generated by the interaction of the cavity modes of the junction seen as an open-ended transmission line and the Josephson oscillations. This mode has given very promising results above 200 GHz, where a power of 20 nW was coupled in a 30- Omega normal state resistance tunnel junction.         Josephson soliton oscillators in a superconducting thin film resonator    J. Holm, J. Mygind, N.F. Pedersen, P. Barbara, G. Filatrella and A. Davidson Summary: Josephson soliton oscillators integrated in a resonator consisting of two closely spaced coplanar superconducting microstrips have been investigated experimentally. Pairs of long 1-D Josephson junctions with a current density of about 1000 A/cm/sup 2/ were made using the Nb-AlO/sub x/-Nb trilayer technique. Different modes of half-wave resonances in the thin-film structure impose different magnetic field configurations at the boundaries of the junctions. The DC I-V characteristic shows zero-field steps with a number of resonator-induced steps. These structures are compared to RF-induced steps generated by phase-locking of the soliton motion to an external microwave source. The two different resonant configurations identified may be interpreted as a coupling to the microwave field at the end boundary and as a more homogeneous coupling distributed over the junction length.         Interaction of fluxons with Abrikosov vortices in long Josephson junctions    A.V. Ustinov, T. Doderer, A.A. Golubov, R.P. Huebener, B. Mayer and V.A. Oboznov Summary: Low-temperature scanning electron microscopy was used to investigate the interaction of fluxons (Josephson vortices) with a superconducting (Abrikosov) vortex trapped in one of the electrodes of a long quasi-one-dimensional Josephson junction. The Abrikosov vortex penetrated a top superconducting film and spread out in the tunnel barrier area between the films. It was possible to move the Abrikosov vortex across the junction by the electron beam and to measure at the same time the value of the critical current of the junction. The bound states of a fluxon trapped by the Abrikosov vortex in the Josephson junction were also observed.         Vortex motion and Josephson effect in superconducting microbridges in    M.J.M.E. de Nivelle, W.A.M. Aarnink, M.V. Pedyash, E.M.C.M. Reuvekamp, D. Terpstra, M.A.J. Verhoeven, G.J. Gerritsma and H. Rogalla Summary: Microbridges with dimensions smaller than the effective penetration depth have been prepared in epitaxially grown (001)- and (105)-oriented YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films. The current-voltage characteristics of these bridges show specific kinks and steps which can be attributed to discrete coherent vortex motion along single or multiple paths across the microbridges. The critical current of a configuration with two very small microbridges in parallel shows periodic superconducting quantum interference device (SQUID) modulation at 4.2 K.         Pinning of fluxons by structure of Abrikosov vortices in long Josephson tunnel junction    V.N. Gubankov, M.P. Lisitskii, I.L. Serpuchenko and M.V. Fistul Summary: The influence of Abrikosov vortices (A-vortices) on the dynamics of fluxons (Josephson vortices) in Nb-AlO/sub x/Nb long Josephson tunnel junctions (LJTJs) has been investigated experimentally. Trapping of Abrikosov vortices was obtained by cooling of the junction through the superconducting transition temperature in magnetic fields applied perpendicularly to the plane of the junction (H/sub perpendicular to /). The dependences of the Josephson critical current on an external magnetic field applied parallel to the plane of the junction were measured after cooling at different values of H/sub perpendicular to /. Changes of both the maximum Josephson critical current and the critical magnetic field of LJTJ H/sub c1/ have been observed for an LJTJ with an irregular structure of A-vortices trapped in the electrodes of the junction. The effects are explained by the pinning of Josephson vortices at the effective misaligned A-vortices.         Detection of mm and submm wave radiation from soliton and flux-flow modes in a long Josephson junction    Y.M. Zhang, D. Winkler and T. Claeson Summary: The authors report on the coupling of millimeter and submillimeter waves from a long (3- mu m*350- mu m) Josephson junction to a small (2- mu m*2- mu m) superconductor-insulator-superconductor (SIS) junction by using a center-fed interdigital capacitor. Coupled power at around 100 GHz and 261 GHz was observed. Experiments confirm that the critical current density j/sub c/ of a long junction determines the fluxon motion. Coupled irradiation (>3nW) at around 100 GHz, which corresponds to resonant soliton oscillations in low j/sub c/ samples (250 A/cm/sup 2/ to 1000 A/cm/sup 2/), is detected by the SIS junction. The incident power to the SIS detector junction could be tuned with only little frequency pulling by adjusting the current bias of the oscillator. For j/sub c/>1000 A/cm/sup 2/, coupled radiation at around 100 GHz (about 3 nW) and 261 GHz (4.6 nW), from flux-flow oscillations, is also clearly seen. Flux-flow radiation at 350 GHz is also observed. It is concluded that a large j/sub c/ value is preferable for high-frequency flux-flow oscillators.         Superconducting millimeter wave oscillators and SIS mixers integrated on a chip    V.P. Koshelets, A.V. Shchukin, S.V. Shitov and L.V. Filippenko Summary: All-refractory material superconducting millimeter-wave oscillators have been designed and investigated experimentally with different superconductor-insulator-superconductor (SIS) mixers integrated on the same chip. Tested structures include a flux-flow oscillator (FFO) based on a long Josephson junction, a coupling section, and an SIS detector with tuned out junction capacitance. Coupling sections were designed as multistep microstrip quarter-wave impedance transformers. All junctions have been fabricated on the basis of a high-quality trilayer Nb-AlO/sub x/-Nb process. Microwave oscillations in the frequency range 75-500 GHz have been detected experimentally. The level of delivered power was estimated from the pumped I-V curve of the strongly coupled single junction detector. Coupled power levels higher than 0.1 mu W at 256 GHz were achieved. A spectral linewidth of the FFO of less than 1 MHz has been estimated experimentally. The first attempt to create an integrated receiver based on an FFO and an SIS array mixer integrated on the same chip was made in the 2-mm wavelength band.         Flux-flow-type Josephson oscillator consisting of epitaxial NbCN/MgO/NbCN junction    S. Kiryu, S. Kohjiro, A. Shoji, S. Kodaira, J. Inatani and S. Sato Summary: Flux-flow-type Josephson oscillators consisting of epitaxial NbCN/MgO/NbCN junctions were fabricated and their current-voltage (I-V) characteristics were measured in various magnetic fields to evaluate their oscillation characteristics. On the I-V curve for a fabricated oscillator, clear current steps were observed up to 3 mV, indicating that oscillation occurs up to 1.4 THz. Using a theoretical model, available output power for the oscillator was calculated to be in the range from 20 mu W to 40 mu W in the frequency range from 500 GHz to 1.2 THz.         Kink excitations and fluxon oscillators in coupled long Josephson junctions    S.P. Yukon and N.C.H. Lin Summary: The properties of a system of N=3 maximally coupled Josephson junctions for which symmetry is broken by having the physical parameters of one junction (the shunt junction) different from those of the other two are examined. It is found that the family of integer fluxon excitations of the symmetric case becomes distorted in a way that is best described in terms of two independent fractional fluxon subkinks theta and psi . The subkinks retain some of the qualities of quarks in that they may not be liberated from the integer-valued fluxons in which they reside, but may be created and destroyed in subkink-antisubkink pairs and exchanged in collisions. The authors have investigated forming resonant fluxon oscillators in shunt coupled Josephson-junction (JJ) systems using both bound K-K ( theta - theta ) pairs of fluxons accelerated by parallel forcing currents and bound K-K pairs ( psi - psi ) of fluxons accelerated by series forcing currents. These systems are able to accommodate larger pair breaking forces induced by forcing currents than those of similar coupled JJ systems where the pairs are bound only by mutual inductance coupling.         Design of superconducting thin film microwave oscillators with weak variable thickness bridges    J.P. Burke, G.K.G. Hohenwarter, J.B. Beyer and E. Track Summary: Oscillator designs based on superconducting variable-thickness bridge devices have been developed. Design considerations and constraints in the layout and fabrication of the circuits are discussed, and a test fixture suitable for circuit testing is described. Circuits fabricated with YBCO films were tested, but do not yet show the desired operating properties. Preliminary tests indicated poor film quality as the cause. Multiple oscillator designs operating at 40 GHz have been designed and simulated and are currently being tested using YBCO on LaAlO/sub 3/. Simulations were limited by the availability of specific simulation models for individual components.         Elimination of output voltage quantization in the vortex flow transistor    J.H. Thompson, M.A. Ketkar, J.B. Beyer and J.E. Nordman Summary: The authors discuss, in theory, the problems associated with quantization in the output voltage of the vortex-flow transistor (VFT) and investigate practical solutions. Removing the quantization from the junction flux flow steps is shown to be a nontrivial problem. Termination of one boundary of the junction seems to be the most elegant solution. Numerical solutions to the sine-Gordon equation show that a linear RC termination can remove the staircase structure from a junction's flux flow branch by eliminating boundary reflections of fluxon energy. This simple solution is hard to effect because thin-film components of the proper dimensions and values are difficult to realize in the laboratory. The addition of shunting loss to the junction is an alternate solution. It involves adding a distributed loss across the length of the junction to reduce the Q of the cavity resonator produced by the junction electrodes. A decrease in Q increases the voltage width of the individual resonances which make up the flux flow branch at low voltages. If the voltage width of each resonant mode is as large as the voltage separation of each mode, the quantization is removed.         Large steps in long Josephson junctions    L. Baselgia-Stahel, O.G. Symko and D.J. Zheng Summary: Large constant voltage-current steps were observed in the I-V characteristics of long NbN-MgO-NbN Josephson junctions in the presence of external magnetic fields of a few Gauss. The steps are separated by a voltage corresponding roughly to three to five times the voltage spacing expected between adjacent Fiske steps. Models addressing the origin of such steps are presented. Simultaneous nucleation of fluxons at several sites along the junction with thin electrodes, favored by the large London penetration depth of NbN, would introduce a large amount of magnetic flux into the junction at once, leading to large steps. A model which involves pinning of fluxons in the junction is given. Due to the granularity of NbN and its very small coherence length, there will be pinning sites in the junction preventing single fluxons from moving at low bias currents. At particular junction parameter values the steps become very regular and sharp. The sharp steps can be used as a voltage standard without external RF bias or as a high-power oscillator when the device is suitably biased.         A 6-bit Josephson flash A/D converter with GHz input bandwidth    P. Bradley Summary: Edge-triggered periodic comparators based on low-inductance superconducting quantum interference devices (SQUIDs) have been combined with a 5-mV step generator used as a clocked power supply to produce an analog-to-digital (A/D) converter with the widest input bandwidth of which the author is aware. The noise and linearity have been measured to be more than adequate for 6 b. Asynchronous beat frequency tests indicate that the current design is capable of about four effective bits resolution at 5-GHz input bandwidth and 3 b at 10 GHz. The aperture jitter at 6-GHz clock rates has been measured to be 100 fs rms indicating that the intrinsic noise is low enough to permit subpicosecond aperture times in faster designs. Further advantages include tolerance of large critical current variations and a sinewave clock as the only high-speed waveform necessary to drive the circuit. The amplitude and spectral purity of the sinewave are not critical as long as it reaches a threshold value, since it is regulated by the step generator.         Measurements of dynamic range and linearity of flux-quantizing A/D converters    S.V. Rylov Summary: High-precision measurements of the linearity of a flux-quantizing analog-to-digital converter (ADC) using a pair of 6-b rapid single-flux-quantum (RSFQ) counters have been made. The sensitivity and dynamic range of the ADC were 13.3 mu A/least significant bit (LSB) and +or-30 mA, respectively (12 b). The conversion curve was measured with an accuracy of +or-7.5% of LSB within a dynamic range of 9 b and exhibited no evidence of nonlinearity. In addition, tests have been made on stand-alone flux quantizers with dynamic range up to 16 b, and a unidirectional 12-b ADC which directly demonstrated a correct divide-by-2/sup 12/ operation with a 10-GHz, 4 LSBs sinewave input signal (peak counting frequency in excess of 80 GHz).         Design, fabrication, and testing of a high-speed analog sampler    J.P. Sage, J.B. Green and A. Davidson Summary: The authors describe the design, fabrication, and first successful operation in the gigahertz frequency range of a Josephson-junction-based sampling circuit designed to provide 6 b of resolution ( approximately 35 dB) and 10 GHz or more of bandwidth. The first experimental demonstration of a prototype circuit sampling a sine wave at up to 1 GHz is reported. This sampler has properties that make it amenable to incorporation into complex, mixed-analog/digital integrated circuits. Such a circuit can be used in the implementation of such signal processing subsystem components as a transient waveform data recorder, a programmable analog-binary correlator, and a flash analog-to-digital converter.         New RSFQ circuits (Josephson junction digital devices)    S.V. Polonsky, V.K. Semenov, P.I. Bunyk, A.F. Kirichenko, A.Yu. Kidiyarova-Shevchenko, O.A. Mukhanov, P.N. Shevchenko, D.F. Schneider, D.Y. Zinoviev and K.K. Likharev Summary: Several novel circuits of the rapid single-flux-quantum (RSFQ) family of Josephson-junction digital devices have been designed, fabricated using a 2.5- mu m 1000-A/cm/sup 2/ Nb trilayer technology, and tested at low frequencies. Numerical simulation and measurements have shown that these circuits have considerably wider parameter margins, due to application of several novel design methods. The authors have also carried out an experiment to measure the rate of errors in a simple RSFQ circuit including an inverter, confluence buffer, and Josephson transmission line. Near the middle of the parameter window at 4.2 K, the error probability was definitely lower than 3*10/sup -15/ per logic operation, despite experimentation with rudimentary shielding and filtering.         Rapid single flux quantum (RSFQ) shift register family    O.A. Mukhanov Summary: The author presents the design and test results for a novel, buffered RSFQ shift register. The register design makes it possible to build a circular 64-b shift register which is insensitive to the clock pulse direction within the experimentally measured DC bias margin of +or-15%. The implementation of a large variety of unidirectional shift registers using either a buffered or a two-Josephson-junction cell design confirms an expected wide DC bias margin of +or-30% (for a 32-b) and high speed, up to 60 GHz (for a 4-b register). Among these circuits is a 256-b shift register. To the author's knowledge, this is the largest RSFQ circuit (533 junctions) reported to date. This shift register was tested to have a DC bias margin of +or-6% and proper high-speed operation up to 12 GHz.         Experimental results on single flux quantum logic    S.P. Benz, C.J. Burroughs and C.A. Hamilton Summary: The authors have optimized the design and calculated the margins for a number of single flux quantum (SFQ) logic elements, including AND, OR, XOR, splitter, DC-to-SFQ converter, and SFQ-to-DC converter. These are the fundamental building blocks necessary to construct more complex logic functions such as the half adder and full adder. Experimental tests of the primary gates, the AND, OR, XOR, and splitter, tests were made by imbedding each test gate between DC-to-SFQ converters at the inputs and SFQ-to-DC converters at the outputs. Automated testing of each circuit was used to determine functionality, optimum bias levels, and margins. The experimental bias current margins for each gate are consistent with the simulations.         Deep sub- mu m low-T/sub c/ Josephson technology: the opportunities and the challenges    M.B. Ketchen Summary: It is suggested that the possibility now exists of highly leveraging existing semiconductor technology to explore submicron Josephson technology. Some of the opportunities and challenges of such an undertaking are discussed in the context of superconducting quantum interference devices (SQUIDs) and digital applications. In the area of digital Josephson technology, a 50-100-ps cycle-time 64-b RISC (reduced instruction set computer) microprocessor is proposed as a long-term goal. While it is unlikely that one will see a sub-100-ps system like this in the near term, research results supporting its feasibility may ultimately help build the case for the resources needed to produce it. Fabrication has been and will probably continue to be an impediment to the exploration of submicron and deep submicron Josephson technology. Coupling to existing semiconductor fabrication capability should help considerably in this area and should help to lay the groundwork for eventual manufacturing of submicron Josephson products.         An electronic second-order gradiometer for biomagnetic applications in clinical shielded rooms    D. Drung and H. Koch Summary: A modular 55-channel magnetometer for biomagnetic studies in clinical shielded rooms is described. Seventy-six superconducting quantum interference device (SQUID) magnetometers in three levels are used to electronically form first-order or second-order gradiometer configurations. The magnetometers are completely integrated on 7.2-mm*7.2-mm chips. Additional positive feedback is used to increase the gradient of the V- Phi (voltage-flux) characteristics to dV/d Phi approximately=1 mV/ Phi /sub 0/, and a novel scheme called bias current feedback reduces the bias current sensitivity to theta Phi / theta I/sub b/ approximately=0.02 Phi /sub 0// mu A. This allows one to couple the SQUIDs directly to simplified feedback electronics without helium-temperature impedance-matching circuits or flux modulation techniques. The magnetometer noise level is typically 1.4 fT/ square root Hz at 1 kHz and 3.2 fT/ square root Hz at 1 Hz, measured inside a Pb/Cryopern shield. A seven-channel prototype module has been tested successfully inside a clinical shielded room. A typical first-order gradiometer noise level of 2.2 fT/ square root THz at 1 kHz and 7 fT/ square root Hz at 2 Hz has been achieved.         Transmission of single-flux-quantum pulses along superconducting microstrip lines    S.V. Polonsky, V.K. Semenov and D.F. Schneider Summary: The authors analyzed, designed, and tested drivers and receivers which make it possible to connect distant circuits of the rapid single-flux-quantum (RSFQ) logic/memory family by passive superconducting microstrip lines. Using these circuits implemented with a niobium trilayer fabrication technology, reliable transmission and reception of the SFQ pulses over distances up to 1 cm, with margins of bias currents as wide as +or-30%, have been demonstrated. The pulses can be passed along wide lines (20 mu m for 3.5 mu Nb-Al/sub 2/O/sub 3/-Nb Josephson junction technology) over such distances and can be picked up by the RSFQ receiver.         8-channel array of single-chip SQUIDs connection to Josephson multiplexer    K. Gotoh, N. Fujimaki, T. Imamura and S. Hasuo Summary: A single-chip superconducting quantum interference device (SQUID) array interfaced to a Josephson multiplexer has been developed. A single-chip SQUID consists of a SQUID sensor and a superconducting feedback circuit. Its output is digital and can be processed with a Josephson digital circuit. The parallel output signal from the SQUID array was time-division multiplexed and summed at a single output cable by a Josephson multiplexer in a cryogenic environment. This method reduces the number of cables required for connection between the SQUID chips and room-temperature electronics. The eight-channel SQUID was tested with a 160-gate Josephson multiplexer. The authors verified the operation of the SQUID array at bias frequencies up to 5 MHz, while the multiplexer was operated at 120 MHz. The measured sensitivity was 1.13*10/sup -5/ Phi /sub 0//(Hz)/sup 1/2/ and the cut-off frequency was 350 Hz.         Two-stage integrated SQUID amplifier with series array output    R.P. Welty and J.M. Martinis Summary: A two-stage integrated DC superconducting quantum interference device (SQUID) amplifier has been fabricated which uses a compact series array of 100 DC SQUIDs as the readout device for a low-noise single SQUID. The output noise is dominated by the amplified noise of the input SQUID and substantially exceeds the input noise of a good room-temperature preamp. The input stage is a low-inductance double-loop SQUID with energy sensitivity of approximately 30-h (equivalent flux noise phi /sub n/ approximately=0.3 mu phi /sub 0// square root Hz), with an input transformer having input inductance L/sub in/ approximately=0.25 mu H and net coupling to the SQUID of k/sup 2/ approximately=0.1. The bandwidth extends from DC to about 390 kHz. The series array has an output voltage swing of 3-4 mV, providing a dynamic range of over 50 dB at full bandwidth. The results suggest the general utility of series SQUID arrays as readout devices for SQUIDs.         High resolution magnetic microscopy using a DC SQUID    A. Mathai, D. Song, Y. Gim and F.C. Wellstood Summary: Using a 4.2 K Nb-PbIn DC superconducting quantum interference device (SQUID) with a 60- mu m inner hole side length, the authors have constructed a novel 1-D magnetic flux microscope with an unprecedented combination of spatial and magnetic field resolutions. During imaging, the sample is moved past the SQUID at a separation of about 38 mu m, and the output from the SQUID is recorded as a function of the sample position. The system achieves a spatial resolution of about 66 mu m and a magnetic field resolution of about 5.2 pTHz/sup -1/2/ at a frequency of 6 kHz. The microscope has been used to obtain susceptibility images of patterned superconducting samples in low fields, and a simple method for measuring static magnetic fields has been devised.         A low noise 410-495 GHz Nb/Al/sub 2/O/sub 3//Nb SIS waveguide mixer    G. de Lange, C.E. Honingh, M.M.T.M. Dierichs, H.H.A. Schaeffer, R.A. Panhuyzen, T.M. Klapwijk, H. van de Stadt and M.W.M. de Graauw Summary: The noise and gain of a heterodyne waveguide mixer using Nb/Al/sub 2/O/sub 3//Nb superconducting tunnel junctions were measured in the 400-500-GHz frequency range. Three different arrays of two junctions in series are analyzed. The minimum receiver noise temperature is 120 K DSB at 480 GHz, measured with an array having integrated tuning stubs. The authors compare data of the pumped I-V curves with the Werthammer-Tucker theory and demonstrate an excellent agreement at frequencies up to 500 GHz. For an array without integrated tuning stubs. a mixer noise temperature of 90+or-30 K and a DSB mixer gain of -12.5+or-0.6 dB were measured. A comparison of the measured gain versus bias voltage with the quantum theory of mixing shows good qualitative agreement, indicating the applicability of this theory to Nb tunnel junctions up to 500 GHz. The noise temperature of an array with a lower gap voltage is 220 K at 495 GHz. This frequency is 85% of the reduced gap frequency, indicating that Nb superconductor insulator-superconductor (SIS) mixers can be used up at least the gap frequency of 680 GHz.         Pb/Bi/In and Nb/Al junctions for a 345 GHz open structure astronomical receiver    K.H. Gundlach, C. Grassl, D. Billon-Pierron and H. Rothermel Summary: The authors report on the preparation and properties of Pb/Bi/In-oxide-Pb/Bi and Nb-Al oxide-Nb junctions prepared for a 345-GHz open-structure heterodyne receiver. The lowest receiver noise temperature with the Pb/Bi/In junctions is 215 K DSB. In this case, no matching network is integrated to tune out the junction capacitance. For the Nb/Al junctions, a microwave transmission line compensates the capacitance around 345 GHz. With the Nb-Al oxide-Nb two-junction array at 4.2 K, the lowest receiver noise temperature is 80 K at 330 GHz. The receiver is in use at the IRAM (Institut de Radio Astronomie Millimetrique) 30-m radio telescope in Spain.         Design and fabrication of a HTC quasi-one junction SQUID based comparator for a 4-bit superconductive flash A/D converter    E.M.C.M. Reuvekamp, P.A.A. Booi, M.A.J. Verhoeven, G.J. Gerritsma and H. Rogalla Summary: The design of a quasi-one-junction superconducting quantum interference device (SQUID)-based comparator for an all HTC superconductive 4-b flash analog-to-digital (A/D) converter is proposed and discussed. Ramp-type junctions of YBCO/PBCO/YBCO are used. The inductance can be realized by a stripline between the junctions. Simulations by the PSCAN package show correct behavior of the quasi-one-junction SQUID (QOS) up to frequencies of approximately 1 GHz. The output voltage pulses are periodic with the input current, as expected. In the dynamic simulations, output voltage pulses are observed at an applied flux of around (2m-1) Phi /sub 0//2. Tile junctions in the QOS are structured on two ramp-edges. The operating frequencies will be below 1 MHz in this first design. A first realization uses the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconductor and PrBa/sub 2/Cu/sub 3/O/sub 7-x /(PBCO) as junction barrier and electrode interlayer material. On a 10-mm*10-mm SrTiO/sub 3/         Superconducting delta-sigma oversampling A/D converter    P.H. Xiao and T. Van Duzer Summary: A superconducting delta-sigma analog-to-digital (A/D) converter is presented. The converter uses a low-pass filter instead of the integrator found in the usual delta-sigma architecture. The converter is analyzed by a behavior-level simulation package as well as the circuit simulator JSIM. Its performance is compared to that of the standard first-order delta-sigma converter. The simulation shows that this converter can achieve a 70-dB signal-to-noise ratio (S/(N+D)) with an oversampling ratio of 128. This corresponds to an 11-b resolution. The signal bandwidth is 4 MHz if the sampling rate is 1 GHz.         INDEX: an inductance extractor for superconducting circuits    P.M. Xiao, E. Charbon, A. Sangiovanni-Vincentelli, T. Van Duzer and S.R. Whiteley Summary: The authors present an extractor, INDEX, designed to extract superconducting circuits from layout. The inductances of the superconducting lines are calculated by a set of analytical models. These self- and mutual-inductance models are generated from a series of numerical simulations and a linear programming curve-fitting. INDEX is based on the MAGIC layout system. INDEX has been tested on a number of cases with good results. A two-junction superconducting quantum interference device (SQUID) was used as one test case.         Fully parallel superconducting analog-to-digital converter    H. Luong, D. Hebert and T. Van Duzer Summary: The authors present measurements that follow up on a design of a 3-b wideband analog-to-digital converter (ADC) given by E. Fang et al. (IEEE Trans. Magn., vol.27, no.3, p.2891-4, 1991). The original design has been modified, and some circuit parameters have been changed to optimize the margins. Based on this modified design, the authors have fabricated and were able to demonstrate the functionality not only of simple logic gates, including inverters, AND, OR, NAND, NOR, and XOR, but also of much more complicated combinations, including a complete 2-b ADC and a complete 3-b binary encoder. After a brief description of the design and modifications, low-speed tests of these circuits are presented and discussed. Simulations have shown that the complete 3-b ADC can work up to 5 GHz.         Digital to analog conversion based on processing of the SFQ pulses    V.K. Semenov Summary: Two novel circuits of DC voltage multipliers have been designed, fabricated using a 3.5 mu m 1000 A/cm/sup 2/ niobium trilayer technology, and successfully tested at low frequencies. A novel primary digital-to-analog (D/A) converter based on the processing of single-flux-quantum (SFQ) pulses has been suggested. The performance of analog-to-digital (A/D) converters combined from such primary D/A converters and voltage multipliers is discussed.         Direct determination of the ultimate performance of the RSFQ digital devices and single flux quantum voltage amplifiers    E.B. Goldobin, V.M. Golomidov, V.K. Kaplunenko, M.I. Khabipov, D.Yu. Khokhlov and A.Yu. Kidiyarova-Shevchenko Summary: The fault-free switching of single-flux-quantum (SFQ) elements was studied by investigating SFQ pulse propagation in a ring Josephson transmission line closed with an SFQ inverter. A lifetime of more than a few hours was obtained that corresponds to at least 10/sup 15/ fault-free switching. The completely DC-powered rapid SFQ (RSFQ) sampler was used to directly measure the repetition rate stability of a Josephson generator loaded by a uniformly shunted transmission line. A stable repetition rate up to 7 GHz was obtained. The authors also report experimental results for two-stage serial and five-stage parallel quasi-digital amplifiers. The precision calculation of the input SFQ pulses is the main idea of these circuits.         Sub-picosecond measurement of time intervals using single flux quantum electronics    P.A. Rosenthal Summary: A single-flux-quantum (SFQ) pulse coincidence detector based on resistively shunted nonhysteretic Josephson junctions was designed and simulated. The coincidence detector generates an SFQ pulse when the delay between the arrival of SFQ pulses at its two inputs is less than the coincidence threshold. Simulations indicate that the minimum coincidence threshold time can be as short as 400+or-200 fs, assuming Josephson junction characteristic voltages of 1 mV, overdamped dynamics, and 4.2 K operating temperatures. Circuit architectures exploiting this gate are suggested. Estimates of the effects of thermal noise on resolution are presented, indicating the potential for various time-domain measurements with subpicosecond resolution.         A three-phase single flux quantum shift register with serial biasing    S.R. Whiteley and A.T. Barfknecht Summary: A three-phase single-flux-quantum (SFQ) shift register has been designed and tested in niobium technology. Serial biasing provides ultralow power dissipation, while allowing operating rates simulated at tens of gigabits per second. This circuit should be compatible with a YBCO weak-link junction process. The authors describe the circuit and its advantages and disadvantages relative to other shift register circuits. They also describe the design constraints, which serve to illustrate some of the issues in general SFQ logic design. Preliminary experimental results from the niobium version are presented. Although the authors are confident that the design works as predicted by simulations they were not able to demonstrate a level of functionality of the pseudorandom generator commensurate with expectations. They believe that this is due to a combination of the usual factors attendant in SFQ circuit testing, i.e. susceptibility to noise and trapped flux, and to correctable conditions related to the treatment of input/output lines on-chip.         Dynamic effects in pulse-driven Josephson junctions    H.A. Kratz Summary: The dynamic threshold characteristics of Josephson-junction circuits operated as fast signal detectors have been simulated for a wide range of load conditions, pulse widths, and pulse amplitudes. The simulations have been carried out using the familiar resistively and capacitively shunted junction model and a modified version of an approximate Werthamer model for the Josephson junctions. Approximation formulas for the dynamic threshold characteristics are given, and a readout circuitry for inductively shunted sampling gates is presented.         Vortex dynamics in one-dimensional parallel arrays of underdamped Josephson junctions    H.S.J. van der Zant, E.H. Visscher, D.R. Curd, T.P. Orlando and K.A. Delin Summary: The dynamics of discrete-one-dimensional parallel arrays of Josephson junctions has been studied experimentally and numerically. The energy barriers for vortex motion from cell to cell have been calculated as a function of the discreteness parameter, the ratio of the Josephson inductance to the self-inductance of the cell. The experimental data show resonances in the current-voltage characteristic, analogous to Fiske steps in a single long Josephson junction. These steps provide a novel experimental method for measuring the self-inductance of 1D parallel arrays.         Experimental implementation of SFQ NDRO cells and 8-bit ADC    V.K. Kaplunenko, M.I. Khabipov, D.Yu. Khokhlov, A.F. Kirichenko, V.P. Koshelets and S.A. Kovtonyuk Summary: Two single-flux quantum (SFQ) logic elements have been designed, fabricated, and successfully tested: an 8 b analog-to-digital converter (ADC) and nondestructive readout (NDRO) cells. The converter consists of an input coil, a comparator, and a reversible ripple counter. The ADC shows a good linearity (+or-12 mA) and a quite high calculated frequency range (up to 2.5 GHz). Two types of input coils differing in inductance and two types of NDRO units also have been investigated: with direct and magnetic coupling between interferometers. The integrated circuits are fabricated using 4 mu m Nb-AlO/sub x/-Nb trilayer technology with a critical current density of about 1000 A/cm. This techniques makes it possible to produce NDRO cells operating up to 10 GHz frequency.         Experimental evaluation of some rapid single flux quantum cells    Y.K. Kwong and V. Nandakumar Summary: Some basic cells in the rapid single-flux quantum (RSFQ) family of superconductive logic circuits were studied. An input stage, a buffer, and an OR gate were simulated and laid out for a standard niobium-based fabrication process. The resulting circuits perform properly for clock speeds up to 1 GHz. For the simpler circuits tested, the measured margins are wide, consistent with simulations, and not very dependent on clock speed. However, margin decreases with increased circuit complexity. The input stage converts a rising edge into an SFQ pulse, which has a small amplitude and narrow width in time. On the present circuits, these pulses are about 200 mu V in amplitude and 10 ps in width. To facilitate measurement, the authors have chosen as the output an asymmetrical superconducting quantum interference device (SQUID) consisting of two Josephson junctions. It converts SFQ pulses into 2.5 mV latching output levels on chip. By inductively coupling SFQ pulses into the SQUID loop, DC current isolation between the RSFQ circuit-under-test and the output stage is provided. The SQUID was optimized for 2 GHz operations.         A 5-32 bit decoder for application in a crossbar switch    D.A. Feld, D.F. Hebert and T. Van Duzer Summary: A novel voltage state multiple input NOR gate has been designed and tested for use as the basic gate in a 5-32 b parallel-input decoder. Two versions of this NOR gate are presented, one with a single output and one with a selectable output. The combination of the two types of NOR gate makes it possible to construct a 5-32 b decoder with considerably less gate current than would be required if it were constructed in other logic families. Since only a single gate current is required by each NOR gate and because only 12 NOR gates are needed to build the full decoder, a clock with a peak current level of only 6 mA is sufficient to power all of the decoder's 72 constituent superconducting quantum interference devices (SQUIDs). The decoder also occupies a small area compared with other designs. The authors review critical design issues of the NOR gates, and present low-speed and high-speed results of subblocks of the full 5-32 b decoder.         Design of a 16 kbit variable threshold Josephson RAM    I. Kurosawa, K. Takashima, H. Nakagawa, M. Aoyagi and S. Takada Summary: A 16 kb Josephson RAM (random access memory) has been designed using a miniaturized variable threshold memory cell based on a 2 mu m Nb/Al-oxide/Nb junction technology. By using a novel strip-line structure for the inductance of the superconducting quantum interference device (SQUID) type selection gate, the miniaturized cell occupies 14 mm 28 mu m, just 20% of the area of a previous cell designed with a 3 mu m rule. OR-INVERT type address decoders are constructed with a new 4JL (four-junction logic) gate with a fan-out of four. The whole circuit occupies a 3.1 mm*5.0 mm area. The access time is evaluated to be 475 ps, with a total power dissipation of 7.3 mW/chip. Based on these performance data and data from a previous 1 kb RAM experiment, the prospects for Josephson VLSIs are discussed.         A speedup method of a high-speed direct-coupled Josephson logic gate    M. Aoyagi, H. Nakagawa, I. Kurosawa, H. Akoh and S. Takada Summary: The switching mechanism of a direct-coupled Josephson logic gate, a four-junction logic gate, has been investigated. It was found that a high-speed input signal current is wasted in an input-output separation resistance (R/sub i/). A speedup method has been developed in which an inductance is connected to (R/sub i/) in series. The value of the inductance was found to be five times larger than the effective inductance of the input junction. A speedup of 40% in the gate switching was demonstrated by a logic delay experiment using submicron NbN-MgO-NbN junction technology. The minimum logic delay of 3.0 ps/gate was obtained with fan-out 1.         A novel Josephson adder without carry propagation delay    F. Li and M. Morisue Summary: The authors describe a novel Josephson adder based on the radix-2 signed-digit number representation. In the proposed adder, the addition operation can be carried out in a constant time independent of word length owing to the elimination of the carry propagation chain. A critical path for generating the sum signal can be completed through only three series gates. A carry signal and an intermediate sum signal for all digits in the adder are simultaneously generated in the first step, and the final sum signal is obtained in the second step. Features of the proposed adder are a simple construction, ultra-high speed, and low power consumption. The principle of constructing the adder with an 8 b word length using superconducting quantum interference devices (SQUIDs) is described in detail, and simulation results are presented. Results show that reliable operation can be achieved for the longest delay time of 120 ps for the 8 b adder.         Automated Josephson integrated circuit test system    C.J. Burroughs and C.A. Hamilton Summary: An automated test system for complex superconductive integrated circuits has been developed. Its low-speed capability consists of 96 identical input/output (I/O) channels controlled by a PC-486 computer. Each channel is capable of driving currents and reading voltages at frequencies up to 40 kHz. Integrating this low-speed I/O capability with high-speed test equipment controlled over the IEEE bus allows measurements at frequencies up to the limits of the test equipment. The system can automatically set biases, display I-V curves, measure parameter margins, plot threshold curves, extract experimental circuit values, and collect statistical data on parameter spreads and error rates. Issues of noise suppression, ground loop handling, and autocalibration are discussed.         Design of a modular, mixed-speed, general-purpose test probe    R.C. Ruby and J. Kral Summary: The authors describe a modular, mixed-speed, general-purpose probe designed and used for the testing of integrated circuits and devices at cryogenic temperature. Modularity is emphasized for flexibility, ease of repair, and construction. The key feature of this probe is the use of a microstrip flex circuit with plated-thru-holes and plated-up copper/gold bumps at the chip-pad locations, both of which help reduce inductive discontinuities between chip and second-level packaging. The chip is mounted face down onto the bumps and held in place by an alignment plate and spring assembly. Little or no soldering occurs between any of the modules: flex circuit, coax cables, coax-to-microstrip launch, twisted-pair wiring harness, and alignment/spring assembly. Swept frequency response measurements and time domain reflectometry were carried out on three different flex circuit designs and two different coax-to-microstrip launch designs. Magnetic contamination, if any, was below the resolution of superconducting quantum interference device (SQUID) and junction arrays placed on the chip.         Switching probability of QFP comparators as a function of exciter slew-rate    R. Ruby, G. Lee, H. Ko and A. Barfknecht Summary: The current noise (inferred from switching probabilities) of quantum flux parametron (QFP) comparators has been measured as a function of exciter slew rates. It was found that at high slew rates the switching probability follows an error-function distribution quite closely. However, at low slew rates, the distribution resembles a Fermi-Dirac distribution. Good agreement with Monte-Carlo simulations for high slew-rates is seen with a current noise proportional to the Johnson noise of the damping resistors. The current noise decreases with decreasing slew rate and is in good agreement with thermal activation calculations in the limit of slow slew rates.         Bit-serial multiplier based on Josephson latching logic    A. Moopenn, E.R. Arambula, M.J. Lewis and H.W. Chan Summary: The authors have designed, fabricated, and tested a Josephson bit serial multiplier based on voltage latching logic. The bit serial implementation takes advantage of high-speed characteristics of Josephson circuits to achieve higher circuit functionality per gate by reducing gate complexity. To facilitate the multiplier design, logic simulation was performed using transistor-transistor-logic (TTL) equivalent gate models of voltage latching modified-variable-threshold-logic (MVTL) gates. A 4-b serial-parallel multiplier based on MVTL gates has been designed and fabricated in niobium. The basic timed-XOR and full adder circuits used in the multiplier were successfully tested. Preliminary testing of the multiplier indicated inadequate operating margin for a full functional test.         Nondestructive readout architecture for a kinetic inductance memory cell    G.J. Chen, M.R. Beasley, M. Horowitz, P. Rosenthal and S. Whiteley Summary: A kinetic inductance memory cell is examined. Such a memory cell can be made small and is more tolerant of the effects of nearby trapped flux than the conventional method of storing data. However, magnetic control of the cell is lost and current injection methods are required to read and write the data. The authors describe a conceptual kinetic inductance nondestructive-read-out memory cell along with a current injection access architecture. A potential fabrication technology that will minimize the size of the memory cells is discussed.         Operation of a 64-bit superconducting shift register at 8 GHz    P.-F. Yuh Summary: A 64 b superconducting shift register based on edge-triggered gates has been tested up to 8.45 GHz with two-phase sine wave clocks. The edge-triggered gates are made by serial connection of a Josephson junction and a modified variable threshold gate, fabricated by an Nb-AlO/sub x/-Nb process. Wide operating margins and simple two-phase clocks make this shift register relatively easy to test. Power dissipation is 10 mu W/b.         'Sail' high temperature superconductor digital logic: improvements and analysis    S.M. Schwarzbek, G.J. Chen, J.A. Luine, N.J. Schneier, G.R. Fischer and R.A. Davidheiser Summary: High-temperature superconductor step-edge junctions have been incorporated into a series array interferometer logic (SAIL) design, resulting in improvements in voltage and temperature performance. The junctions provide an I/sub c/R/sub n/ (critical-current normal-resistance) product of 300 mu V at 65 K, which makes it possible to have 100 mu V switching of gates at cryocooler temperatures. With improvements in I/sub c/ uniformity, the architecture should allow use in gate arrays. The present analysis indicates that the current I/sub c/R/sub n/ is sufficient to run up to 10 GHz; while this is slow compared to other superconducting logic families, it is competitive with bipolar semiconductors, with good prospects for improvement. DC design models have been compared to JSIM simulations, and a sketch of the theoretical margins is presented in this context.         Negative resistance switch using a SNS junction    A.M. Luiz and R. Nicolsky Summary: The authors show the feasibility of a new type of superconducting switch using the negative differential resistance of the current-voltage characteristic curve of a superconductor-normal metal-superconductor (SNS) junction (a nontunneling Josephson junction). With the proper choice of load resistor, astable, monostable, or bistable circuits can be designed. The most relevant characteristic features of the proposed superconducting switch are analyzed. The power consumption and the switching speed of the proposed device are described. It is shown that the maximum switching speed of a single SNS multivibrator is on the order of 0.33 ps.         Computer architecture issues in superconductive microprocessors    J. Fleischman and T. Van Duzer Summary: Results on instruction use in general-purpose computers and some techniques used in conventional high-performance computer architectures are described. Synchronous and asynchronous computer architectures are discussed, and three representative superconductor circuit technologies and the architecture proposed for each of them are described. The architectures are the quantum flux parametron, modified variable threshold logic, and rapid single-flux-quantum logic. Superconductive digital systems are also examined.         Simulation and optimization of binary full-adder cells in rapid single flux quantum logic    S.S. Martinet and M.F. Bocko Summary: The authors consider the design of a binary carry full-adder cell using the logic gates and buffers belonging to the rapid single-flux-quantum (RSFQ) logic family. They have taken advantage of the unique properties of RSFQ pulse logic to realize two designs: one using two logic gates and a toggle flip-flop in two stages of logic, the other using two logic gates in one stage of logic. They have determined the parameter margins of the two full-adder cells and optimized them to obtain critical margins approaching +or-30%. Simulations of the full-adder cells have revealed critical delays and maximum clock frequencies of 58 ps and 17 GHz and 33 ps and 30 GHz, respectively.         SUSAN (Superconducting Systems Analysis) by Low Temperature Scanning Electron Microscopy (LTSEM)    T. Doderer, D. Hoffmann, R.P. Huebener, N. Kirchmann, C.A. Krulle, S. Lachenmann, D. Quenter, J. Schmidt, S. Stehle, J. Niemeyer, R. Popel, S.P. Benz and P.A.A. Booi Summary: Low-temperature scanning electron microscopy was used for spatially resolved investigations of both Josephson junctions and superconducting integrated circuits during their operation with a spatial resolution of about 1 mu m. Using single Josephson tunnel junctions of various geometries, the authors studied different dynamic states such as fluxon oscillations or unidirectional flux flow. With an integrated circuit consisting of a two-dimensional array of tunnel junctions and an RF detection circuit they investigated the RF properties of the coupling circuit and confirmed the existence of an impedance mismatch and a geometrical standing wave in the blocking capacitor. The studies of the dynamics of single Josephson tunnel junctions of various geometries showed a linear behavior (excitation of single cavity modes) if the boundary conditions dominate, and otherwise a nonlinear behavior (excitation of solutions).         Margins and yields of SFQ circuits in HTS materials    D.L. Miller, J.X. Przybysz and J.H. Kang Summary: An analytical model has been developed to project the yield of superconductive integrated circuit chips as a function of circuit operating margins, fabrication process control, and component count. For Gaussian distributed deviations of critical component values from design specifications, chip yield was a highly nonlinear (threshold) function of the ratio of circuit margin to process standard deviation. Computer simulations of single-flux-quantum (SFQ) logic gates with model high-temperature superconductor (HTS) superconductor-normal-metal-superconductor (SNS) junctions operating at GHz clock rates showed at least 50-70% of the margins of similar Nb-Al/sub 2/O/sub 3/-Nb based circuits. Margins and maximum clock rate improved as I/sub c/R/sub n/ (critical-current-normal-resistance product) was increased from 200 to 500 mV.         Josephson sigma-delta modulator for high dynamic range A/D conversion    J.X. Przybysz, D.L. Miller, E.N. Naviasky and J.H. Kang Summary: A Josephson sigma-delta modulator suitable for use in high dynamic range conversion of MHz bandwidth signals was designed and simulated. Input signal voltages were integrated as current in a superconducting inductor. A single junction quantizer provided analog-to-digital (AID) conversion at 40 GHz and fed back single-flux-quantum (SFQ) voltage pulses to balance the input. A JSIM calculation for a 13,110,000-ps interval indicated ideal first-order noise shaping of a 2.44-MHz voltage-source signal. Spur free dynamic range was 102 dB and signal-to-noise-and-distortion was 98 dB on the DC 10-MHz signal band, equivalent to a 16-b, 20-MSample/s, Nyquist-rate A/D. The modulator transfer function was derived for a current-source signal applied to an input resistor. First-order quantization noise suppression was still observed for signal bands wider than the 2 pi R/L modulator cutoff frequency. The superconductive sigma-delta modulator combines the speed of Josephson junctions for GHz sampling and digital filtering with the quantum mechanical accuracy of SFQ feedback to obtain superior A/D performance.         Performance of MVTL OR-AND gates when data precedes bias    D.L. Meier and J.X. Przybysz Summary: A six-stage shift register based on modified-variable-threshold-logic (MVTL) OR-AND gates using 90 Nb/Al-Al/sub 2/O/sub 3//Nb Josephson junctions has been fabricated and tested up to 3.0 GHz. Bias current margins of the shift register were measured to be +or-26% at 200 MHz and below, +or-11% at 2.2 GHz, and +or-1.2% at 3.0 GHz. Calculation of the lobe plots for the OR gate shows that the expected margin is +or-26% when the control current (data) precedes the bias current (clock), and when no appreciable control current is injected into the superconducting quantum interference device (SQUID) loop via the injector junction. Special taps were included in the circuit so that the switching action of each of the 18 gates could be monitored in detail without disturbing the high-speed operation of the circuit.         Large RF-controlled voltage steps in DC SQUIDs applicable to voltage standards and sources    G.S. Lee, H.L. Ho, R.C. Ruby and A.T. Barfknecht Summary: The current height of RF-induced voltage steps in nonhysteretic single Josephson junctions is usually a small fraction of the critical current. It is demonstrated that when a resistively shunted DC superconducting quantum interference device (SQUID) is subjected to an RF magnetic flux, a voltage step with a large current height is obtained. In contrast to weak selection rules for single Josephson junctions, strong selection of the step harmonic number occurs in a shunted DC SQUID for appropriate choice of RF amplitude and DC flux offset, with odd harmonic numbers selected by half-integer flux quantum offsets and even harmonic numbers by integer flux quantum offsets. This pronounced effect has immediate implications for voltage standards and fast, high-precision digital-to-analog converters.         A novel method for correcting device parameter mismatches in Josephson junction circuits    H.L. Ho, G.S. Lee and A.T. Barfknecht Summary: A method for on-chip adjustment of Josephson-junction comparator thresholds is presented. Experimental results confirming the proper function of this circuit are discussed. The use of this circuit in an A/D converter allows individual thresholds to be programmed and compensates all circuit processing variations.         Josephson compensating junction logic    C.J. Anderson Summary: A Josephson superconducting quantum interference device (SQUID) digital logic family was developed that uses the R/sub nn/ region of a Josephson junction (JJ) to compensate for variations in where R/sub nn/ is the effective resistance of a JJ in the linear I-V region beyond the gap. The basic compensating junction logic (CJL) circuit is two 2-input-OR 1-2-1 interferometer isolators that, when switched, inject current into a 2-input-AND 1-2-1 interferometer. The R/sub nn/ region of several JJs is used in series with a resistor to set the current from the power supply to the 2-input-OR interferometers. The 2-input-AND interferometer is implemented with both current injection and magnetic coupling. The latch circuit uses both current injection and magnetic coupling design techniques to increase the range of I/sub O/, inductance, and resistance variation over which the latch will function correctly. Experimental measurements of CJL circuits are described.         Performance issues in single flux quantum shift registers    J.H. Hang and J.X. Przybysz Summary: Testing on a single-flux-quantum (SFQ) shift register fabricated with a SFQ Nb-AlO/sub x/Nb Josephson junction process indicates that a stable flux quantum can be stored in a rapid SFQ (RSFQ) shift register stage and be shifted by SFQ pulses. Design simulations showed that logic errors can occur in SFQ shift registers even though the circuit passes the average voltage test. Three-junction-per-stage shift registers had an advantage over the two-junction-per-stage shift register in handling data with successive 1's and in incorporating resistors to increase tolerance of trapped magnetic flux. Input and output buffers for data and clock pulses were added to get an RSFQ shift register to obtain correct performance. The highest error-free operation speed for the data with successive 1's is about half of the speed for propagation of a lone data 1. Error-free operation of SFQ shift registers with three junctions per stage could be obtained up to speeds of 30-60 GHz with Josephson junctions having I/sub c/R/sub n/ (critical-current-normal-resistance product) values of 600 mu V.         A single QFP timing discriminator    H.L. Ho, G.S. Lee, R.C. Ruby and A.T. Barfknecht Summary: A root-mean-square (RMS) time jitter of 380 fs has been demonstrated in a single quantum flux parametron (QFP) race arbiter circuit with approximately 60-ps-risetime signal inputs. Because of the simple relationship between the QFP current comparator and the race arbiter, it is possible to make direct comparison of the time jitter and current noise results. The measured current noise in a QFP current comparator implies that, for a signal risetime of 10 ps, a time jitter of approximately 200 fs is expected for this race arbiter circuit. Circuit modeling suggests that an optimized design can achieve approximately 100-fs time jitter.         Thermal noise in digital Josephson devices    J.D. Feder, M. Klein and C.J. Anderson Summary: A method of accurately estimating the I/sub 0/ (critical current) of a Josephson junction (JJ) with thermal noise was developed by measuring the effective thermal noise temperature of a JJ. The effective thermal noise temperature of various JJ devices was measured and calculated. The JJ devices evaluated included inductively and resistively coupled logic devices and JJ devices in the presence of various noise sources. The noise sources included room-temperature resistors, switched JJ devices, and JJ devices in the linear I-V region beyond the gap. The R/sub NN/ compensator is shown to result in a noise temperature of about 6 K at an interferometer. The addition of a shunt junction lessens the noise penalty introduced by the compensator. A switched isolation interferometer in a two-input AND gate contributes negligible noise at the injection device. It is also shown that bandwidth connections to room-temperature equipment result in very large excess noise and require special input and output circuits on the chip.         Superconducting implementation of neural networks using fluxon pulses    Y. Mizugaki, H. Nakajima, Y. Sawada and T. Yamashita Summary: The authors fabricated neural-based superconducting integrated circuits by using Nb/AlO/sub x//Nb Josephson junctions, and demonstrated the operation of a 2-b neural-based A/D converter. Fluxon pulses were used as neural impulses, and a Josephson junction was used as a threshold element. The conductance values of resistors by which Josephson transmission lines are connected represent fixed synaptic strengths. The preliminary experimental result suggests that variable critical currents of DC-SQUIDs (superconducting quantum interference devices) may provide synapses with variable strength.         Josephson look-back analog to digital converter    C.J. Anderson Summary: A Josephson analog-to-digital (A/D) converter which uses a look-back algorithm to increase accuracy was designed and experimentally verified. The look-back A/D algorithm and its implementation in a Josephson 6-b A/D converter are described. High-speed measurements verified that the 3-b look-back A/D converter functions at 534 Msamples/s. The look-back algorithm increases the margins of an A/D converter that uses the lobes of a superconducting quantum interference device's (SQUID's) threshold curve. The self-gating AND circuits (SGAs) give the A/D converter a short aperture time. The SGAs sample the analog signal in parallel and then the look-back logic decodes the two's complement outputs in series with only one stage of logic per bit. With a stable process the look-back A/D converter can be generated on chip.         DC magnetic field dependence of the surface impedance in superconducting parallel plate transmission line resonators    M.S. Pambianchi, D.H. Wu, L. Ganapathi and S.M. Anlage Summary: The authors have measured the real and imaginary parts of the surface impedance of cuprate superconducting films in the parallel plate resonator geometry at 11 GHz as a function of perpendicular DC magnetic field. Above a temperature-dependent crossover field, a linear increase of the surface resistance and reactance with field, up to 4 kG, is found. The authors extract the microscopic vortex dynamical parameters-the viscosity and the pinning-potential restoring force constant-along with their temperature dependences, using the low-temperature and low-field limit of the unified model of M.W. Coffey and J.R. Clem (1991). It is found that the pinning frequency is above 40 GHz for temperatures below 60 K. Consequently, a complete understanding of the field dependence of the microwave surface impedance of the cuprates must include both vortex pinning and viscosity. The vortex viscosity is temperature dependent and, in the context of the Bardeen-Stephen model, is consistent with a temperature-dependent normal-state resistivity below T/sub c/.         A superconducting microwave linear phase delay line filter    F. Huang, H.C.H. Cheung, M.J. Lancaster, R.G. Humphreys, N.G. Chew and S.W. Goodyear Summary: A numerical synthesis procedure for low-loss surface acoustic wave devices has been adapted to microwave filters. Multiple reflections and energy depletion are allowed for, permitting relatively large amounts of energy to be drawn by the taps. Using the synthesis procedure, quasi-transversal filter design has been demonstrated for linear phase microwave filters. A copper filter has been produced with performance close to design and a YBCO superconducting filter has shown encouraging results.         Analysis of superconducting transmission-line structures for passive microwave device applications    L.H. Lee, S.M. Ali, W.G. Lyons, D.E. Oates and J.D. Goettee Summary: A full-wave spectral-domain volume-integral-equation technique is used to calculate the complex propagation constant, the complex characteristic impedance, and the current distribution for Nb and YBa/sub 2/Cu/sub 3/O/sub 7-x/ microstrip lines and coplanar waveguides with superconducting ground planes. Measurements of resonant frequency and quality factor are performed on Nb microstrip and coplanar waveguide resonators, and the results are compared with numerical calculations. The power-handling capability of various superconducting transmission-line structures is calculated. Results of phase noise measurements on Nb microstrip resonators suggest that phase noise may be related to the current distribution in the structure.         Microwave filter application of inductively coupled superconducting striplines    K. Yoshida, K. Kudo, M.S. Hossain, K. Watanabe, K. Enpuku and K. Yamafuji Summary: A design theory is presented to apply inductively coupled superconducting striplines to microwave filters, in which the coupled stripline system is considered as four-port circuitry. By obtaining eigenvalues for impedance, admittance, and scattering matrices, the authors obtained general formulas for designing bandpass filters. The microwave filters using this coupling scheme are simple in design and have advantages of external-modulation capability. Experiments to demonstrate the validity of this coupling scheme have been performed in the frequency range between DC and 300 GHz by investigating the coupling between a Josephson oscillator and an external stripline.         Application of superconducting striplines to traveling-wave type LiNbO/sub 3/ optical modulator    K. Yoshida, K. Ikeda, K. Saito and Y. Kanda Summary: The performance of a traveling-wave-type LiNbO/sub 3/ optical modulator with superconducting electrodes has been studied theoretically and experimentally. In the case of velocity matching between signal and optical waves using a shielding plane on top of the coplanar stripline, numerical calculations of the attenuation constants of both superconducting and normal-conducting striplines indicate that the performance of the optical modulator is expected to be much superior to that using normal metals with respect to the figure of merit of bandwidth/driving power. Low-temperature operation of the optical modulator with superconductor electrodes has been demonstrated in the temperature range between 4.2 K and 300 K for DC signals as well as microwave signals at frequencies from 8 GHz to 12 GHz. It was shown that the modulation voltage was not very sensitive to temperature variation.         Cross talk studies for superconducting transmission lines    M. Morisue, W. Lin, S. Furusawa, H. Yasutake and I. Isiguro Summary: The authors describe the analysis of crosstalk on high-T/sub c/ superconducting transmission lines from the viewpoint of interconnection technology. They fabricated YBCO microstrip transmission lines on MgO substrate by sputtering and then measured the crosstalk by applying a high-speed pulse to the one line. They also calculated the current distributions in the YBCO superconductors and ground plane to evaluate the mutual inductance of the lines. After determining the circuit parameters of superconducting transmission lines based on the two-fluid model, they investigated by simulation how an induced pulse on the neighboring line propagates on the line. These simulation results show that the crosstalk on the superconducting transmission lines is smaller than that on the normal-conductor transmission lines owing to smaller mutual inductance of superconducting lines. These simulation results agree well with the experimental results.         High temperature superconductor coplanar delay lines    G.J. Hofer, H.A. Kratz, G. Schultz, J. Sollner and V. Windte Summary: Coplanar delay lines of different geometries for YBaCuO films on LaAlO/sub 3/ substrate have been designed and characterized in the time domain. The lines are of the double spiral type with lengths of 257 mm and 434 mm on 10-mm * 10-mm and 20-mm * 20-mm substrates with a measured pulse dispersion of 0.8 ps/cm and 1.8 ps/cm, respectively. A preparation process which meets the requirements for high aspect ratios was used. The measured results have been compared with the corresponding predictions of specially developed electromagnetic simulators which include both the London and the Mattis-Bardeen theory. The agreement between measured and simulated values was sufficient for design purposes.         Forty five nanoseconds superconducting delay lines    G.K.G. Hohenwarter, E.K. Track, R.E. Drake and R. Patt Summary: The authors report on the design, simulation, fabrication, and measurement of very long superconducting coplanar waveguide delay lines on 3-in-diameter LaAlO/sub 3/ substrates. Variations of the design involving the addition of a ground plane on the backside of the substrate and for the use of gold wire-bond bridges to electrically connect the in-plane ground planes were investigated. A delay of 45 ns was measured for a line length of 4.3 m. The best response was obtained with wire-bond connections and no backside ground plane. A resonance-free insertion loss of less than 0.01 dB/ns was obtained with a 1.7-GHz bandwidth for NbN at 4.2 K. This is to be compared with a loss of 0.1 dB/ns for a 50-ns 0.141-in OD. (outer diameter) copper coaxial delay line that weighs 1.5 lb and 0.02 dB/ns for a 60-ns 1-in OD copper coaxial delay line that weighs 45 lb.         Microwave losses in kinetic-inductance devices fabricated from NbCN/MgO/NbCN trilayers    K.R. Carroll, J.M. Pond and E.J. Cukauskas Summary: The microwave losses in kinetic-inductance devices fabricated from NbCN/MgO/NbCN trilayers are being investigated. The loss tangent of an amorphous MgO thin film has been measured for frequencies near 10 GHz with a kinetic-inductance stub filter. The value of 0.0031 represents a factor of approximately 3 improvement over Si:H films found for a similar kinetic-inductance structure operating in a similar frequency range. Further improvement in the dielectric is also discussed. Other properties of the superconducting trilayer structure are consistent with previous results.         High speed normal and superconducting coplanar transmission lines    U.D. Keil, D.R. Dykaar, A.F.J. Levi, R.F. Kopf, L.N. Pfeiffer, S.B. Darack and K.W. West Summary: The authors present measurements of picosecond pulse propagation on coplanar strip transmission lines for which speed (i.e., group velocity) as well as phase and amplitude information is measured. Electrode effects are studied using transmission line loops 1 mm in diameter with cumulative propagation distances as long as 10 cm. The intrinsically low dielectric constant of coplanar-air transmission lines is shown to result in high signal speed and low attenuation. The results are compared to the case of superconducting electrodes. For superconducting electrodes one sees an apparent negligible loss for frequencies well below the gap and propagation distances up to 10 cm. For higher frequencies almost complete attenuation is found, even for very short propagation distances. The effects of substrate removal are shown to influence not only the speed of a given transmission line, but also the attenuation, due to strong reduction of radiation losses and through lowering of the surface impedance. The results obtained suggest that digital, intrachip communication on length scales of order 1 cm with pulses as short as one picosecond and velocities as high as 0.9c is readily achievable using electrical signals.         Power transmission behaviour of coplanar superconducting waveguides    U. Salz, S. Hofschen and R. Schneider Summary: The authors describe the complex behavior of superconducting coplanar waveguides of varying geometries under the influence of temperature and transmitted power. For this reason high power levels up to 35 dBm have been applied to characterize the saturation behavior of the waveguides at 18 GHz. At low temperatures the transmitted power is shown to drop drastically (about 30 dB) when the waveguide leaves the superconducting state. At higher temperatures a kind of saturation state can be observed. The transmitted power coefficient first remains high and then drops slowly with increasing incident power. The superconducting waveguide recovered reversibly from the state of saturation during the entire measurement. It is shown that it is possible to calculate the current-carrying capacity by using the ratio of the area of the current flow to the complete cross section.         Integral FMCW radar incorporating an HTSC delay line with user-transparent cryogenic cooling and packaging    D.J. Kapolnek, D.L. Aidnik, G. Hey-Shipton, T.W. James, N.O. Fenzi, D.L. Skoglund and B.J.L. Nilsson Summary: A self-contained frequency-modulation continuous-wave (FMCW) radar incorporating a compact 2.2-ns broadband superconducting delay line operating at 80 K has been developed. The authors note that this is the first demonstration of an integral microwave system utilizing high-temperature superconductor (HTSC) circuitry incorporating a closed-cycle cooler and a long-life permanently sealed dewar. They discuss development efforts focused on high-frequency packaging techniques compatible with the stringent thermal and electrical performance requirements of HTSC microwave circuitry. They also review the prospects for development of low-cost and reliable closed-cycle cryogenic coolers in the 2-10-W size range.         HTS-based switched filter banks and delay lines    J.S. Martens, V.M. Hietala, D.S. Ginley, C.P. Tigges, T.A. Plut, J.K. Truman, E.K. Track, K.H. Young and R.T. Young Summary: A thermal switch has been developed that provides good isolation and insertion loss with adequate switching times to allow a monolithic approach to the switched lines and filter banks. Filter banks in the 8-11-GHz range have been demonstrated with insertion losses of < 1 dB and out-of-band rejection greater than a package-limited 50 dB. Switched delay lines have been fabricated with insertion losses less than 0.3 dB/b and peak phase deviations from linearity of less than 5 degrees over 30-GHz bandwidths. The materials and substrate dependencies of the performance are analyzed, and there generally is a trade-off between RF power handling and switching speed/control power requirements. Devices made with TlCaBaCuO tend to switch faster and consume less power than YBaCuO devices because of the effects of flux dissipation. For the same reason, the RF power handling ability of the TlCaBaCuO devices is worse. YBaCuO devices grown on sapphire switch faster than do those on LaAlO/sub 3/ because of substrate properties but do require additional DC power.         Characterisation of a GaAs MESFET oscillator at 4.2 K    E. Vollmer, P. Gutmann and J. Niemeyer Summary: A stripline X-band oscillator for use in Josephson voltage standards and potentiometers has been designed and constructed. The oscillator, comprising a packaged GaAs MESFET, has been tested at temperatures of 300 K and 4.2 K. The conversion efficiency, the power leveling capability, the frequency tuning, and the phase noise have been investigated. The power level can be varied over a range of 35 dB by tuning the drain-source voltage. A hysteretic behavior in the frequency versus the drain-source voltage characteristic has been observed when the drain-source voltage exceeds a device-dependent level. This effect is attributed to the trapping of hot electrons in the drain region. By varying the gate-source voltage, the frequency can be only tuned over a range of 0.8 MHz at 4.2 K. At a gate-source voltage of 0 V, higher harmonics are generated. A phase noise reduction of 22 dB at a frequency offset of 50 kHz from the carrier can be obtained by cooling to 4.2 K and a feedback network consisting of copper layers.         High T/sub c/ superconductor and III-V solid state microwave hybrid circuits    Z.Y. Shen, P. Pang, C. Wilker, D.B. Laubacher, W.L. Holstein, C.F. Carter III and M. Adlerstein Summary: Several high-temperature superconductor (HTS)/III-V solid-state hybrid microwave circuits were designed, fabricated, and tested. The I-V curves, S-parameters, and noise behavior for several solid-state devices at cryogenic temperatures were measured. Several high-electron-mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) C-band low-noise amplifiers were fabricated and tested at cryogenic temperatures with an additional gain of 3 dB when compared to their room-temperature gain. These amplifiers were also used in low-phase-noise oscillators stabilized by a HTS lambda /2 microstrip line resonator with a loaded Q-value of 3*10/sup 3/ or a sapphire-HTS resonator with a loaded Q-value of 1.2*10/sup 6/, both measured at 80 K. Preliminary measurement at 70 K indicates that the phase noise of an oscillator stabilized with a sapphire-HTS resonator was below -125 dBc/Hz at 10-kHz offset and limited by the test setup.         High-T/sub c/ superconducting small antennas    K. Itoh, O. Ishii, Y. Nagai, N. Suzuki, Y. Kimachi and O. Michikami Summary: The authors describe the designs of and report experimental results for one- and two-element high-T/sub c/ superconducting small antennas composed of self-resonant helical radiators and quarter-wave matching circuits. A 500-MHz-band antenna using a lambda /40 ( lambda is the free-space wavelength) radiator fabricated with Bi(Pb)SrCaCuO bulk realized a gain of -1.2 dBi, which indicates that this antenna achieves a high frequency of 70%. A 900-MHz-band two-element array antenna using lambda /20 radiator with a lambda /11 element spacing was designed to obtain a superdirective radiation pattern. The array antenna thus fabricated with YBaCuO bulk realized both a higher efficiency than a Cu antenna and a unidirectional radiation pattern. Furthermore, by adopting EuBaCuO thin-film meander lines as the matching circuit, the total length could be reduced to about 1/4 that of an antenna using a linear circuit.         Experimental results on a scanned beam microstrip antenna array with a proximity coupled YBCO feed network    J.S. Herd, D. Hayes, J.P. Kenney, L.D. Poles, K.G. Herd and W.G. Lyons Summary: The design, fabrication, and measurement of a scanned beam microstrip antenna array with a high-temperature superconducting YBCO feed network are described. A novel geometry is introduced which integrates the antenna array into a window on the vacuum enclosure of the cryocooler for maximum thermal and RF efficiency. The model considered includes surface wave and mutual coupling effects, which are of importance in large array applications. Experimental results demonstrate broadband radiation with expected gain values for broadside and 45-degree scan angles.         Performance of TlCaBaCuO 30 GHz 64 element antenna array    L.L. Lewis, G. Koepf, K.B. Bhasin and M.A. Richard Summary: A 64-element, 30-GHz microstrip antenna array with corporate feed network was designed and built on a 0.254-mm (10-mil) thick lanthanum aluminate substrate. One antenna pattern was fabricated from gold film, and a second pattern used TlCaBaCuO high-temperature superconductor. Both antennas used gold ground planes deposited on the reverse side of the substrate. Gain and radiation patterns were measured for both antennas at room temperature and at cyrogenic temperatures. Observations agree well with simple models for loss and microwave beam width, with a gain on boresight of 20.3 dB and beam width of 15 degrees for the superconducting antenna. The antenna loss is only 1.9 dB.         Picosecond superconductor opening switches    W. Cao, Y.-Q. Liu, C.H. Lee, S.N. Mao, S. Bhattacharya, X.X. Xi, T. Venkatesan, Z.-Y. Shen, P. Pang, D.J. Kountz and W.L. Holstein Summary: Picosecond opening switches using high-T/sub c/ superconductor devices made of TlPbSrCaCuO, TlBaCaCuO, and YBCO films have been successfully demonstrated. The switches were controlled by picosecond laser pulses. A switching risetime of 78 picoseconds and a switching efficiency of 80% have been achieved. The switches were used in an inductive energy storage pulsed power system. Nanosecond electrical pulses with a peak power gain of 22 were obtained.         Optimized design of far-infrared Fabry-Perot resonators fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/    C.G. Malone, Z.M. Zhang, M.I. Flik and E.G. Cravalho Summary: The transmittance of a carefully designed YBa/sub 2/Cu/sub 3/O/sub 7/ Fabry-Perot resonator is predicted analytically. The substrate thickness is shown to strongly influence the transmittance of the YBa/sub 2/Cu/sub 3/O/sub 7/-on-MgO Fabry-Perot resonator. The peak transmittance and finesse of YBa/sub 2/Cu/sub 3/O/sub 7/-on-MgO Fabry-Perot resonators fabricated from the best YBa/sub 2/Cu/sub 3/O/sub 7/ material available are comparable with those of the best metal mesh resonators in the far-infrared spectral region. It is noted that a reduction of the fraction of residual normal-state electrons in YBa/sub 2/Cu/sub 3/O/sub 7/ films will permit the construction of far-infrared Fabry-Perot resonators superior to any existing device.         YBa/sub 2/Cu/sub 3/O/sub 7/ superconductor microbolometer arrays fabricated by silicon micromachining    B.R. Johnson, T. Ohnstein, C.J. Han, R. Higashi, P.W. Kruse, R.A. Wood, H. Marsh and S.B. Dunham Summary: Linear arrays of YBa/sub 2/Cu/sub 3/O/sub 7/ transition edge microbolometers have been fabricated on silicon substrates using silicon micromachining to produce microbolometer structures with good thermal isolation. These bolometers, which are 85 mu m*115 mu m*1 mu m, have a noise equivalent power (NEP) of 9*10/sup -13/ W/Hz/sup 1/2/. (neglecting contact noise) and a thermal time constant of 24 ms. With contact noise, the NEP is 9*10/sup -12/ W/Hz/sup 1/2/. This performance indicates that a 2-D staring focal plane array of superconductor microbolometers could have a performance comparable to that of HgCdTe staring arrays without further improvements in the sharpness of the superconducting transition or reductions in the YBa/sub 2/Cu/sub 3/O/sub 7/ electrical noise. The use of silicon processing technology to fabricate the superconductor microbolometers results in a significant cost advantage over HgCdTe, and there is no long wavelength cutoff dependence in the sensitivity of a superconductor microbolometer.         Superconducting niobium infrared thermal detectors and circuits on back-etched substrates    D.P. Osterman, R. Patt and R. Madhavrao Summary: The authors report on highly sensitive thermal infrared detectors, the result of combining the two technologies of superconducting low-T/sub c/ thin-film electronics and back-etched or 'micromachined' substrates. Functioning detectors have been fabricated consisting of a thin-film niobium Josephson junction thermometer and infrared-absorbing panel, integrated together with a DC superconducting quantum interference device, (SQUID) amplifier on a single back-etched silicon substrate. A detector made with one of two fabricated back-etched geometries has a calculated thermal conductance of 1*10/sup -7/ W/K at 4.2 K. On another device, a measured value of 9* was obtained for the amplification of the thermometer responsitivity by the integrated DC SQUID. Prospects are discussed for operating similar arrays at higher and lower temperatures than 4.2 K.         High-speed optical detectors in YBCO films with non-granular and fine-grain morphologies    Q. Tang, A. Driessen, L.H. Hilderink, R.P.J. Ijsselsteijn, J. Folkstra and T.J.A. Popma Summary: Optical detectors based on YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films have been fabricated, which show a response time of a few ns. Typical dimensions of the active area are 10 mu m*10 mu m. No preamplifier is needed during operation. The authors report on the optical response of detectors having nongranular and fine-grain morphologies to different sources of pulsed laser radiation (e.g., mode-locked Nd:YLF laser at 1.3 mu m and a GaAs diode laser at 0.9 mu m). Emphasis in the study is placed on detection sensitivity for measuring short optical pulses. It is found that the best noise obtained with a fine-grain detector is on the order of 10/sup -10/ W/Hz/sup 1/2/, when irradiated by the 65-ns-pulsewidth diode laser.         Biexponential decay and delay artifact in the photoresponse of superconductors    N. Bluzer Summary: The photoresponse of superconductor exposed to narrow and wide laser pulses is examined in terms of the superconductor's impedance. The impedance helps to identify the causes and the origins of the fast and slow photoresponse decay in YBCO and Nb. The source of the asymmetrical photoresponse signals in Pb is explained in terms of impedance nonlinearities with temperature. Finally, the impedance model is used to explain what has been previously identified incorrectly as delayed photoresponse signals in In and Pb. All these temporal manifestations are produced by the impedance and are not indicative of a delayed response or of intrinsic or sudden changes in the recombination-generation lifetimes in the superconductor.         Semiconductor-coupled Josephson junctions    T.M. Klapwijk, W.M. van Huffelen and D.R. Heslinga Summary: Superconductor-semiconductor-superconductor junctions have been studied using 50-nm-thick silicon membranes sandwiched between niobium electrodes. The normal state resistance is determined by barriers at the interfaces. The supercurrent is well described by the Kupriyanov-Lukichev theory for the proximity effect in SINIS (superconductor-insulator-normal metal-insulator-superconductor) structures, whereas the voltage-carrying state is understood as resulting from a nonthermal distribution of electrons in the semiconductor. The details of the distribution depend on elastic and Andreev scattering at the interfaces. By analogy to semiconductor heterostructures, the authors propose that these structures be called superconducting quantum wells, a concept which is applicable to other double-barrier tunnel devices as well.         Optical data communication between Josephson-junction circuits and room-temperature electronics    B. Van Zeghbroeck Summary: The feasibility of optical data transmission to and from Josephson junction circuits, using metal-semiconductor-metal (MSM) photodiodes and GaAs/AlGaAs semiconductor laser diodes with sub-mA threshold current, is demonstrated. Standard devices can be used with the exception of a cooled GaAs detector. It is shown that silicon MSM detectors compatible with Josephson junction circuits can be fabricated. While these detectors show large photoconductive effects at room temperature they behave as good-quality photodiodes at low temperatures. Power dissipation in the laser diode scales with temperature while maintaining the modulation frequency. It is also shown that the combination of a laser diode and a photodiode provides the voltage gain needed to interface Josephson-junction circuits with room-temperature electronics. Experimental results on MSM detectors and laser diodes are presented. Expected power dissipation is below 1 mW per input/output (I/O) at a data rate of 1 Gb/s.         The High Temperature Superconductivity Space Experiment: HTSSE I-Components and HTSSE II-Subsystems and advanced devices    M. Nisenoff, J.C. Ritter, G. Price and S.A. Wolf Summary: The goals and objectives of the High Temperature Superconductivity Space Experimental (HTSSE) program are described, and a description of the first launch package and plans for future experiments (HTSSE-II) are presented. The objective of the program is to prove that HTS technology is sufficiently robust to survive the space environment and that it has the potential to significantly improve space communications systems. The devices for the initial launch (HTSSE-I) have been delivered to US Naval Research Laboratory, their electrical characteristics have been verified, and their packages have been space-qualified. These devices will be integrated with a cryogenic refrigeration system and a data acquisition system, all space-qualified. Once placed in earth orbit, the experimental package will be cooled to cryogenic temperatures and the characteristics of the HTS devices monitored periodically. The HTSSE-I mission, scheduled to start in 1993, will last for at least six months.         Implementation of a YBa/sub 2/Cu/sub 3/O/sub 7-x/ wideband real-time spectrum-analysis receiver    W.G. Lyons, D.R. Arsenault, M.M. Seaver, R.R. Boisvert, T.C.L.G. Sollner and R.S. Withers Summary: The implementation of a wideband real-time spectrum-analysis receiver based on YBa/sub 2/Cu/sub 3/O/sub 7-x/ chirp filters and a chirp-transform algorithm is presented. The integration of the high-T/sub c/ spectrum-analysis subsystem with high-speed semiconductor output circuits is demonstrated. A compressed pulse is obtained using a voltage-controlled oscillator to generate a flat-weighted chirp signal, and a Hamming-weighted YBa/sub 2/Cu/sub 3/O/sub 7-x/ chirp filter is used to compress the chirp signal into a pulse. The error sidelobe level of the compressed pulse response is -18 dB. Semiconductor circuits are included in the system for envelope detection of compressed pulses and video to emitter coupled logic (ECL) logic-level conversion.         Optically triggered switching of optically thick YBCO films    D. Gupta, W.R. Donaldson, K. Kortkamp and A.M. Kadin Summary: Thin films of high-T/sub c/ superconducting material were used to construct two different types of opening switches: the photoresistive switch and the inductively coupled switch. The former show two distinct switching components in 8000-AA films consisting of a slow bolometric response and a faster nonbolometric response. The fast nonbolometric component had risetimes of approximately 4 ns and falltimes of approximately 6 ns. The slower component was identified to be thermal in origin and was in good agreement with the one-dimensional heat flow model used to simulate the thermal photoresponse. The inductively coupled switch is a contactless switch where the superconducting film screens the flux coupling between two coils of a transformer. The optically induced switching was achieved with risetimes of approximately 50 ns. with a multiturn output coil. Short (150-ps) laser pulses containing energies of up to 3 mJ are used in both cases to perform the switching.         Optically modulated superconducting delay lines    E.K. Track, R.E. Drake and G.K.G. Hohenwarter Summary: Optical modulation is investigated for superconducting microstrip delay lines on 2-in-diameter, 10-mil-thick LaAlO/sub 3/ substrates. The linewidth of 80 mu m yields a characteristic impedance of 50 Omega . The linepitch of 100 mil is chosen to minimize the coupling between adjacent lines. The total meander line length is 64 cm. The measured delay is 8 ns with operation from DC to 20 GHz. The design was implemented using niobium, niobium nitride, and YBCO. The measurements were performed in a dewar and in a closed-cycle refrigerator, with both RF and optical access. Optical illumination of the lines resulted in a phase shift of the transmitted signal. Using a 10-mW He-Ne laser, phase shifts of up to 360 degrees at 20 GHz were measured with NbN and YBCO. The phase shifts increased linearly with frequency and with optically intensity. The effect can be attributed to a small, bolometric modulation of the line inductance.         YBCO thick film loop antenna and matching network    M.J. Lancaster, T.S.M. Maclean, J. Niblett, N.M. Alford and T.W. Button Summary: The authors report the performance of a YBCO planar thick-film small loop antenna with an integral superconducting matching network. The antenna is shown to outperform a similar silver antenna at a temperature of 77 K. The design of the antenna and matching network is such that they both fit onto a 2" square zirconia substrate, almost 1/20th of a free space wavelength at the operating frequency of 300 MHz.         Characteristics of Au/Ba/sub 1-x/K/sub x/BiO/sub 3//SrTiO/sub 3/(Nb) superconducting-base transistor    H. Suzuki, S. Suzuki, M. Iyori, T. Yamamoto, K. Takahashi, T. Usuki, Y. Yoshisato and S. Nakano Summary: An Au/natural-barrier Ba/sub 1-x/K/sub x/BiO/sub 3/ (BKBO)/niobium-doped SrTiO/sub 3/ superconducting-base three-terminal device has been fabricated and tested. BKBO thin film was sputtered to create a base layer on the (110) surface of 0.1 wt.% niobium-doped SrTiO/sub 3/ (an n-type collector). The BKBO/SrTiO/sub 3/(Nb-doped) junction showed Schottky-junction-like current-voltage characteristics. The Au/natural-barrier/BKBO junction showed good tunneling characteristics, reflecting the superconductivity of BKBO. The transfer efficiency for injected low-energy electrons, through a 100 nm-thick BKBO base layer was measured and found to be 0.02 at 4.5 K. A drastic increment in transfer efficiency up to 0.9 for quasi-particles with energy above 0.28 eV was observed.         YBa/sub 2/Cu/sub 3/O/sub 7-x//SrTiO/sub 3/ bilayers for superconducting field effect devices by pulsed laser deposition    C. Doughty, A. Walkenhorst, X.X. Xi, C. Kwon, Q. Li, S. Bhattacharya, A.T. Findikoglu, S.N. Mao, T. Venkatesan, N.G. Spencer and W.R. Grace Summary: Materials issues relevant to the growth of high-quality YBa/sub 2/Cu/sub 3/O/sub 7-x//SrTiO/sub 3/ (YBCO/STO) bilayers for use in superconducting field-effect devices were studied. Different substrate materials and growth conditions were investigated. NdGaO/sub 3/ was determined to be the most promising substrate material due to its low surface roughness and good lattice match to YBCO. The electrical properties of ultrathin YBCO and YBCO/STO bilayers grown by pulsed laser deposition were also investigated as a function of substrate temperature. The optimized deposition temperature for 10-nm-thick YBCO was found to be 60 degrees C below that of thick (100-nm) films. STO overlayers with a dielectric constant of approximately=700 and a breakdown field of approximately=625 kV/cm were fabricated. The STO/YBCO interface was also studied.         YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on nanocrystalline diamond films for HTSC bolometer    G. Cui, C.P. Beetz Jr., R. Boerstler and J. Steinbeck Summary: Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on nanocrystalline diamond thin films have been fabricated. A composite buffer layer system consisting of diamond/Si/sub 3/N/sub 4//YSZ/YBCO was explored for this purpose. The as-deposited YBCO films were superconducting with T/sub c/ of approximately 84 K and a relatively narrow transition width of approximately 8 K. Scanning electron microscope cross sections of the films showed very sharp interfaces between diamond/Si/sub 3/N/sub 4/ and between Si/sub 3/N/sub 4//YSZ. The deposited YBCO film has a surface roughness of approximately 1000 AA, which is suitable for high-temperature superconductive (HTSC) bolometer fabrication. It was also found that preannealing of the nanocrystalline diamond thin films at high temperature was very important for obtaining high-quality YBCO films.         The electric field effect in a BSCCO thin film    X. Han, J.-F. Jiang and M. Sugahara Summary: The electric field effect in a Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ (BSCCO) thin film was studied using a FET structure, the channel of which was made of a BSCCO thin film sputtered on a (100) MgO single-crystal substrate. SrTiO/sub 3/ is used as the insulating layer between gate and channel. Appreciable channel conductance variation caused by the application of the gate field is observed near T/sub c/. Using Hall-effect measurements, the conductance variation is verified to be caused by the carrier density modulation, in the channel part by the gate electric field. The maximum modulation ratio of the channel carrier density reaches is as high as 95%.         Field effect devices based on metal-insulator-YBa/sub 2/Cu/sub 3/O/sub 7-x/ films    G. Brorsson, Yu. Boikov, Z.G. Ivanov and T. Claeson Summary: A comparative study of the electric field effect in both ultrathin (4.5-nm) and comparatively thick (200-nm) polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ films was performed. In the first case SrTiO/sub 3/ was used as gate insulator, and in the second case (Pb,Zr)TiO/sub 3/ was used as the gate insulator. In the ultrathin film the critical current, was increased and decreased up to 2.4%, by applying negative and positive voltages of 80 V. In the polycrystalline film (T/sub c/=84.5 K) an increase of the normal resistance of 7% was measured when applying a gate voltage of +1.78 V. This film consisted of superconducting grains with high T/sub c/, connected by grain boundaries with deteriorated superconducting properties. It is concluded that the electric field influenced the grain boundaries.         Field effect transistor based on a bi-crystal grain boundary Josephson junction    Z.G. Ivanov, E.A. Stepantsov, A.Ya. Tzalenchuk, R.I. Shekhter and T. Claeson Summary: The authors have developed a planar field effect device consisting of an artificial grain boundary junction in an Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ (YBCO) microbridge which was covered by a 300-nm amorphous SrTiO/sub 3/ layer and a 4- mu m-wide gate electrode. The layers were grown on Y-ZrO/sub 2/ bicrystal. The current transport through the weak link, connecting the superconducting drain and source electrodes, was regulated by the voltage of the insulated gate. Devices with different misorientation angles, theta , between the two halves of the bicrystal were studied. For 45 degrees nonsymmetric tilt grain boundaries, the authors observed a strong (more than 50%) enhancement of the supercurrent at positive gate voltage and almost no change, or a slight decrease, at negative voltage. A theoretical model of the device is discussed. At positive gate voltages of 0.5 V and 8 V about 40% and 70% enchancement of the device critical current, respectively, was obtained.         Large modulation of critical currents in high T/sub c/ superconducting field-effect (SUFET) devices    A. Walkenhorst, C. Doughty, S.N. Mao, X.X. Xi, Q. Li and T. Venkatesan Summary: Various properties of ultrathin YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films used in superconducting field effect devices have been shown to vary as a function of the applied gate voltage, i.e., by variation of the areal charge carrier density N. In the present work, the authors have investigated the behavior of the critical current density, J/sub c/, in these devices. In 5-8-nm-thick YBCO films in such devices, J/sub c/ (T=4 K, B=0 T, 1 mu V/mm criterion) of up to 4*10/sup 5/ A/cm/sup 2/ has been observed. By applying moderate gate voltages(<30 V), J/sub c/ can be suppressed by up to 90%. An empirical description of the functional dependence J/sub c/(T,B,N) is given. Examination of the I-V characteristics yields V=a*I/sup alpha /, with alpha dependent on the gate voltage. The data are discussed in terms of the relative importance of field-induced depinning, thermal fluctuations, and pure geometrical effects.         Field effect in multilayered YBaCuO/PrBaCuO devices    A. Jager, J.C. Villegier, P. Bernstein, J. Bok and L. Force Summary: A MOSFET-like device with a thin superconducting PrBaCuO/YBaCuO multilayer channel and SiO/sub 2/ gate oxide was built. The effect of electric field applied on the gate was investigated as a function of temperature and drain-source current for different multilayers. It was shown that the critical temperature, as well as the density of the critical current could be enhanced or suppressed depending on the polarity of the gate voltage. The use of a SiO/sub 2/ layer as a gate insulator gives symmetrical characteristics and low losses in the MHz range. A new slow charge transfer effect has been observed at higher temperatures. Field effects on the resistance and on the critical current have been observed for monolayer channels as well as for multilayer structures with up to three (YBaCuO/PrBaCuO) periods. The field effect decreases with an increasing number of periods because of the semiconducting PrBaCuO layers. In these multilayer structures, the observed charge transfer effects could be an electrical way to definitively tune the charge carrier concentration and the transition temperature of very thin films.         Preparation and characterization of high-T/sub c/ superconducting cross-overs and coils    T. Freltoft, Y.Q. Shen and P. Vase Summary: Superconducting ten-turn pickup coils have been fabricated of YBCO using a shadow mask technique. The three-layer vacuum deposition, including sublayer patterning, was carried out in situ, i.e., without breaching the deposition vacuum. The current status for the coil development is J/sub c/=0.2*10/sup 6/ A/cm/sup 2/ at T=80 K for the bottom strip and for the windings, respectively.         Electronic noise properties of barium potassium bismuth oxide (BKBO) thin films    R.C. Lacoe, D.A. Gutierrez, J.P. Wendt, R. Hu, J.F. Burch and A.E. Lee Summary: The low-frequency electrical noise fluctuations in superconducting barium potassium bismuth oxide (BKBO) thin films deposited by magnetron sputtering and by laser ablation have been measured. The excess noise in the presence of a bias current was 1/f noise. The magnitudes of the room temperature 1/f noise were somewhat higher than observed in the best cuprate high-temperature superconducting thin films. The noise magnitude did not scale as expected with film geometry, and the noisier BKBO film also had the highest superconducting transition temperature. It is suggested that etch pits observed on the patterned films contributed to the total 1/f noise measured. Both films exhibit a peak in the noise voltage at the foot of the superconducting transition which cannot be explained from a model of 1/f noise resulting from temperature fluctuations.         Relationship of Nb surface morphology and Al coverage to the intrinsic stress of magnetron-sputtered Nb films    K. Tsukada, J. Kawai, G. Uehara and H. Kado Summary: To optimize Nb/Al-AlO/sub x//Nb Josephson junctions, atomic force microscopy is used to study the morphology of DC magnetron-sputtered Nb and Al. The Nb film stress was sensitive to Ar pressure, and changed from compressive to tensile as the Ar pressure increased. The roughness of DC magnetron-sputtered Nb films was related to their internal stress. Stress-free Nb films have a smooth surface, without depressions, and a roughness of 14.6 AA. The roughness of the Al surface on Nb film was shown to reflect the roughness of the underlying Nb film, and was least for the stress-free Nb film. Coverage of Al was continuous for Al thicker than 40 AA. To make a fine Nb/Al-AlO/sub x//Nb Josephson junction, one should use a stress-free Nb film and deposit an Al layer at least 40 AA thick on the Nb films.         Measurements of transport properties and noise power spectral densities for Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ single crystals    K.H. Han, M.K. Joo, H.J. Shin, S.-I. Lee and S.-H.S. Salk Summary: The authors measured the current-voltage characteristics of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ single crystals along the a-b plane and observed the behavior of the Kosterlitz-Thouless (K-T) transition. The noise power spectral density, S/sub v/(f), near the K-T transition temperature was studied in detail by changing the temperature, magnetic field, and current S/sub v/(f) at temperatures above the K-T transition temperature T/sub KT/ shows a 1/f behavior, regardless of the external magnetic field. However, near T/sub KT/, the S/sub v/(f) deviates markedly from the 1/f behavior for the experimental frequency range. It is believed that the anomalous variation of frequency dependence near T/sub KT/ originates from the fluctuation effect of the vortex-antivortex pairs, i.e., their annihilation-creating fluctuations.         Etching and annealing of substrates for superconducting multilayers and devices    S.J. Berkowitz, E. De Obaldia, M.L. Galloway, G. Morales, K.F. Ludwig, P.M. Mankiewich, W.J. Skocpol, R.H. Ono, J.A. Beall, L.R. Vale and D.A. Rudman Summary: The structural and electrical quality of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grown on ion-etched substrates by a variety of techniques was investigated. Co-evaporated YBa/sub 2/Cu/sub 3/O/sub 7- delta / films deposited and postannealed on etched LaAlO/sub 3/ substrates have substantially higher room-temperature resistivities and wider c-axis rocking curve widths than films on unetched substrates. Annealing of the etched substrate prior to evaporation narrows the c-axis rocking curve width and restores resistivity and critical current densities to values comparable to those of the unetched controls. Laser-ablated films on etched substrates show a smaller absolute magnitude of rocking curve broadening and no change in DC electrical properties. An increase of the inhomogeneous strain was also observed in coevaporated postannealed and laser-ablated films on etched substrates.         Reactively sputtered niobium nitride thin films for Josephson integrated circuit application    S.Y. Lee, M. Bruns and R.D. Glenn Summary: The properties of sputter-deposited NbN thin films were studied under changes in various deposition conditions including nitrogen flow, substrate heating, the addition of carbon impurities, and the use of an Nb underlayer. Without the underlayer, a semiconductorlike resistive behavior above the superconducting transition temperature and a wide superconducting transition were observed in the niobium nitride films, including those with transition temperatures above 15 K. With the underlayer, metallic behavior and a sharp superconducting transition temperature depended strongly on nitrogen flow and substrate heating but weakly on carbon impurities. The authors present details on the preparation and analysis of niobium nitride thin films with and without a niobium underlayer as well as the measured film characteristics.         Crossovers and vias in YBa/sub 2/Cu/sub 3/O/sub 7//PrGaO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ trilayers    P.A. Nilsson, G. Brorsson, E. Olsson, Z.G. Ivanov and T. Claeson Summary: Key elements have been made for superconducting electronics, crossovers and vias with the microwave compatible insulating material PrGaO/sub 3/. The critical temperatures of the top and bottom layers of YBa/sub 2/Cu/sub 3/O/sub 7/ for a crossover were 88 K and 85 K, respectively. The resistivity between the layers was 100 Omega -cm at 77 K for a 300-nm-thick insulator layer. This insulation was improved by growing 10-nm-thick layers of SiTiO/sub 3/ on both sides of the PrGaO/sub 3/ layer. In this case, the resistivity was 25 k Omega -cm at 77 K.         Magnetic penetration depth and critical current in YBaCuO thin films    T. Kisu, T. Iinuma, K. Enpuku, K. Yoshida, K. Yamafuji and M. Takeo Summary: The ab-plane magnetic penetration depth lambda in c-axis-oriented YBaCuO thin films was estimated from inductance measurements. The temperature dependence of lambda was shown to be consistent with the Bardeen-Cooper-Schrieffer (BCS) theory under the local limit condition. It was also shown that the experimentally obtained relationship among lambda (T=0), the resistivity p, and the critical temperature T/sub c/ was consistent with the theoretical one obtained from the local limit BCS theory. From that relationship, the value of lambda (T=0) could be deduced from p and T/sub c/. Moreover, the critical current was studied on the basis of the bias current dependence of lambda .         Proximity effects in superconducting wire bonding    K. Tsukada, S. Yamasaki, N. Mizutani, G. Uehara, H. Kado, H. Akimoto and T. Ogashiwa Summary: To investigate the superconducting characteristics of a superconducting wire bonding connection, a series of Nb electrodes consisting of an Au pad formed on a Si chip were made, and the pads were connected in series with a superconducting wire (Pb/sub 76/In/sub 20/Au/sub 4/). The I-V characteristics of the superconducting connection reflect the typical characteristics of a superconductor-normal-metal-superconductor (SNS) sandwich structure, with normal resistance on the order of mu Omega when a critical current (I/sub c/) level is exceeded. The dependence of I/sub c/ on the thickness of Au is an exponential decrement, and I/sub c/ is over a hundred mA when the Au thickness is between 20 nm and 230 nm. Auger analysis is applied to obtain the depth profile of the bonded part, revealing mutual Au and In atomic diffusion at the interface between the Au intermediate layer and the PbInAu wire.         Highly textured niobium films for applications in vortex-electronics    F. Peter, M. Muck and C. Heiden Summary: Highly textured Nb-films were grown by electron-beam evaporation on sapphire substrates. The crystalline quality was examined by Rutherford-backscattering-channeling and X-ray diffraction methods. The channeling minimum yield is 2%. On c-plane sapphire the evaluation of rocking curve measurements yielded 99.98% [111] Nb // (0001) sapphire and 0.02% [110] Nb // (0001) sapphire. Measurements on microbridges with widths ranging from 2 mu m to 100 mu m (film thickness 500 nm) showed a residual resistivity ratio (R/sub 295K//R/sub 10K/) of up to 90 and critical current densities at 4.2 K and 0.2 T as low as 1.7*10/sup 4/ A/cm/sup 2/. These Nb-films form the basis for devices for local generation and detection of vortices. The writing and erasure of vortices and their detection by means of an integrated superconducting quantum interference device (SQUID) are demonstrated.         Application of selective leaching in fabrication of thin film YBCO devices    P.M. James, J.M. O'Callaghan and A.B. Ellis Summary: Ethylenediamine solutions have been shown to turn bulk YBCO into insulating materials. The effect of these solutions on thin YBCO films is studied. In both unpatterned and patterned films, a smooth decrease in critical currents, a transition to normal state, and a subsequent gradual increase in resistance are observed as a function of exposure time to the solution. It is noted that these characteristics might make this process desirable for weak-link and on-film resistor fabrication.         High-T/sub c/ superconducting EuBa/sub 2/Cu/sub 3/O/sub y/ thin films and MgO and YAlO/sub 3/ for coplanar devices    H. Asano, M. Satoh and T. Konaka Summary: The authors have studied the microwave properties of high-T/sub c/ superconducting EuBa/sub 2/Cu/sub 3/O/sub y/ (EBCO) films on MgO and YAlO/sub 3/ substrates with low dielectric constants ( in =10 and 16, respectively), and a low loss tangent (tan delta <10/sup -5/). Measurements of surface resistance R/sub s/ at 50 GHz in a cavity show that EBCO films exhibit low R/sub s/ values (77 K) of 2-10 m Omega . A microstructural study using transmission electron microscopy showed that crystal defects related to the in-plane misorientation are observed for films with higher R/sub s/ values. The R/sub s/ values of the patterned films were measured in a coplanar transmission line resonator. A typical value for patterned films was 28 mu Omega at 4 GHz and 28 K.         Deposition of noble metal contacts on YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films    R. Hahn, T. Schaffter, J. Klockau and G. Fotheringham Summary: Ohmic contacts with low specific contact resistivities between YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films and noble metals have been fabricated using ion beam sputter etching and RF-plasma contact preparation. The influence of deposition parameters has been investigated. Specific contact resistivities in the 10/sup -8/ Omega -cm/sup 2/ range at 77 K have been achieved and were evaluated using cross bridge Kelvin test structures with sizes varying between 5 and 50 mu m. The failure rate of wires bonded onto high-temperature superconductor (HTSC)-Au/Ag pads was unacceptable in most cases. Substantial improvements have been achieved with Cr/Ti adhesion sublayers. Deposition parameters for optimum pull test results on MgO and LaAlO/sub 3/ substrates are presented.         Critical currents in submicron YBa/sub 2/Cu/sub 3/O/sub 7/ lines    H. Assink, A.J.M. Harg, C.M. Schep, N.Y. Chen, D. Marel, P. Hadley, E.W.J.M. Drift and J.E. Mooij Summary: Lines in YBa/sub 2/Cu/sub 3/O/sub 7/ with widths down to 200 nm and properties comparable with the original film have been defined using electron beam lithography and plasma etching. One predicted property of lines smaller than the magnetic penetration depth is an increase in the critical current density due to pinning of the vortices at the edge of the sample. There have been several reports of experimental observation of edge pinning in narrow YBa/sub 2/Cu/sub 3/O/sub 7/ lines. The authors present systematic measurements of narrow lines that should be far into the edge pinning regime, but no increase of critical current density is observed in the smallest lines.         Patterning of thin-film high-T/sub c/ circuits by the laser-writing method    R. Sobolewski, W. Xiong and W. Kula Summary: The authors report studies on a laser-based 2-D patterning technique that implements a focused beam from a continuous-wave (CW) Ar-ion laser to locally heat up an epitaxial Y-Ba-Cu-O film in a controlled (oxygen-rich or oxygen-poor) atmosphere. It is shown that the laser-writing method enables a reproducible fabrication in the same film of oxygen-depleted (semiconducting) regions next to enriched ones (superconducting), in a manner similar to n- and p-type diffusion regions in semiconductors. A number of test structures, laser-written in initially oxygen-rich or oxygen-poor films deposited on MgO, SrTiO/sub 3/, and LaAlO/sub 3/ single crystals, have been measured. The best, very homogeneous superconducting (oxygen-rich) circuits were patterned in oxygen-depleted YBCO deposited in the LaAlO/sub 3/ substrates. The structures exhibited a 0.5-K-wide superconducting transition, T/sub c0/=89.5 K, and J/sub c/ above 10/sup 5/ A/cm/sup 2/.         Damage-less dry etching of YBaCuO films under liquid nitrogen cooling (striplines)    H. Akoh, H. Sato and S. Takada Summary: A novel dry etching process has been developed to reduce etching damage for striplines of YBaCuO thin films in which samples are cooled by liquid nitrogen. The patterned striplines have widths ranging from 2 to 100 mu m and a length of 1 mm. The critical current density J/sub c/ at 77 K for striplines of (001) oriented YBaCuO films etched under liquid nitrogen cooling is approximately 2*10/sup 5/ A/cm/sup 2/, which is more than 10 times higher than that for striplines etched at 5 degrees C. This finding suggest that the liquid nitrogen cooling during the dry etching reduces the damage due to the oxygen deficiency of films. Striplines of (103) oriented YBaCuO films fabricated using this dry etching method exhibit an intrinsic anisotropy of J/sub c/.         Author Index (1992 - Part 3)    No author information available Summary: Not available

© Copyright 2009 All Rights Reserved. Developed for IEEE Applied Superconductivity Conference by InControl Productions, Inc..