Home Welcome Getting Started Conferences Authors

1990 Part 3     Front Cover (1990 - Part 3)    No author information available Summary: Not available         Table of Contents (1990 - Part 3)     Summary: Not available         High temperature superconductivity space experiment (HTSSE)    J.C. Ritter, M. Nisenoff, G. Price and S.A. Wolf Summary: An experiment dealing with high-temperature superconducting (HTS) devices and components in space is discussed. A variety of devices (primarily passive microwave and millimeter-wave components) has been procured and will be integrated with a cryogenic refrigerating and data acquisition system to form the space package, which will be launched in late 1992. This space experiment is expected to demonstrate that this technology is sufficiently robust to survive the space environment and that the technology has the potential to improve the operation of space systems significantly. The devices for the initial launch have been evaluated electrically, thermally, and mechanically, and will be integrated into the final space package early in 1991. The performance of the devices is summarized, and some potential applications of HTS technology in space systems are outlined.         High-T/sub c/ superconductive microwave filters    W.G. Lyons, R.R. Bonetti, A.E. Williams, P.M. Mankiewich, M.L. O'Malley, J.M. Hamm, A.C. Anderson, R.S. Withers, A. Meulenberg and R.E. Howard Summary: Four-pole microstrip bandpass filters have been fabricated using both postannealed and in-situ-grown thin films of Y-Ba-Cu-O. The 4-GHz, 3% bandwidth filters exhibit, at 77 K, a passband insertion loss as low as 0.3 dB, compared with the 2.8-dB loss of similar gold metallic filters at the same temperature. These results demonstrate that complex passive microwave devices can be designed and implemented using high-temperature superconducting (HTS) material. More aggressive filter designs utilizing many more poles will result in much greater performance advantages for an HTS filter technology over a normal metal technology. Ultimately, ultrasharp-skirt filters can be produced, which would allow for more closely spaced communication channels and more efficient use of microwave communication bands than is currently possible with conventional filters.         Microwave devices using YBa/sub 2/Cu/sub 3/O/sub 7- delta/ films made by pulsed laser deposition    H.S. Newman, D.B. Chrisey, J.S. Horwitz, B.D. Weaver and M.E. Reeves Summary: High-quality oriented thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / with transition temperatures >88 K and critical current densities (at 77 K, zero magnetic field) >10/sup 6/ A/cm/sup 2/ have been produced by pulsed laser deposition on (100) MgO and LaAlO/sub 3/ substrates. The microwave surface resistance (R/sub s/) was measured between 20 K and 120 K at 36 GHz by a copper cavity end-wall-replacement technique. R/sub s/ measurements show consistently sharp transitions having high critical temperature onsets with low residual surface resistances (<10 m Omega at 36 GHz and 77 K). Microwave devices fabricated from films on MgO have included an X-band modified five-pole Chebyshev filter with an insertion loss of approximately 0.8 dB at 77 K. Irradiation of unpatterned films on LaAlO/sub 3/ with 2-MeV H/sup +/ ions at a fluence increment of 10/sup 16//cm/sup 2/ resulted in only a small shift ( approximately 2 K) in the 36-GHz microwave transition temperature. No accompanying degradation in the residual surface resistance was observed within the sensitivity of the measurement.         Microwave superconducting filters    S.H. Talisa, M.A. Janocko, C.K. Jones, B.R. McAvoy, J. Talvacchio, G.R. Wagner, C. Moskowitz, D.C. Buck, J. Billing and R. Brown Summary: Four-pole, parallel-coupled microstrip line filters were fabricated using epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films deposited by off-axis sputtering on LaAlO/sub 3/ substrates. Filters were made with and without superconducting ground planes. Because it is not yet possible to grow in-situ epitaxial films on both sides of a substrate, two separate substrates were used, one for the filter and one for the ground-plane. The devices were packaged so that the microstrip-to-ground-plane distance was the thickness of one of the substrates (0.43 mm). Passband characteristics, input power, and temperature dependence were measured, as well as the thermal cycling stability.         Microstrip resonators and filters using high-T/sub c/ superconducting thin films on LaAlO/sub 3/    J.H. Takemoto, C.M. Jackson, R. Hu, J.F. Burch, K.P. Daly and R.W. Simon Summary: Very low microwave losses have been measured in YBa/sub 2/Cu/sub 3/O/sub 7/ linear resonators, ring resonators, and bandpass filters. The stoichiometric 1-2-3 compound was deposited on LaAlO/sub 3/ substrates, patterned microwave circuits, and overcoated with a passivating LaAlO/sub 3/ layer. HTS (high T/sub c/ superconductor) linear microstrip resonators demonstrated Q values greater than 1200 at 10 GHz, corresponding to surface resistances less than 300 mu Omega . Identical silver resonators showed Q values of 60 and surface resistance of 15 m Omega . The high-frequency transition temperature for these HTS films was greater than 83 K. Q values of 240 were measured in ring resonators at 15 GHz. Finally, the authors designed, fabricated, and tested a two-pole, Chebyshev narrow-bandwidth bandpass filter. The HTS filter was designed to be a 1% bandwidth with 0.2-dB ripple. Insertion loss was 2 dB at 4 K, rising to 3 dB at 77 K. The authors observed a temperature dependence in the filter center frequency which they attribute to kinetic inductance effects. The proposed HTS filters outperform similar cryogenic silver filters, indicating that practical levels of HTS performance have been achieved.         Fabrication and characterization of high-T/sub c/ superconducting X-band resonators and bandpass filters    D.B. Rensch, J.Y. Josefowicz, P. Macdonald, C.W. Nieh, W. Hoefer and F. Krajenbrink Summary: Microstrip passband filters with 3, 6, and 11 poles, as well as microstrip resonators, have been fabricated using postannealed Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ (YBCO) films deposited on LaAlO/sub 3/ substrates using three-target simultaneous co-sputtering. The insertion loss in the passband for the filters with center frequencies between 9.5 and 13.4 GHz was         Focused ion beam high T/sub c/ superconducting SQUIDs    M.Z. Zani, J.A. Luine, G.S. Lee, J.M. Murduck, R. Hu, R.J.M.J. Lewis, R.A. Davidheiser and L.R. Eaton Summary: The behavior of HTS thin films patterned into microbridge DC and RF SQUID structures and irradiated with a rastered high-energy focused ion beam 70 mm in diameter is discussed. DC SQUIDs have demonstrated 51% modulation of the critical current with an applied magnetic field at 46 K. All devices with appropriate critical currents exhibited Shapiro steps when exposed to microwave irradiation. Multiple interference patterns, probably from weak links within each microbridge segment, are seen at 4 K and disappear at temperatures above liquid helium. The I/sub c/R/sub n/ product of the microbridges is typically a few millivolts, and the temperature dependence of the device resistance is consistent with electrical conduction through metallic filaments. The process demonstrates an acceptable yield and reliability for a variety of microelectronics applications.         Fabrication and characterization of hybrid Nb-YBCO DC SQUIDs    E.K. Track, R.E. Drake, R. Patt and M. Radparvar Summary: Hybrid low T/sub c//high T/sub c/ DC SQUIDs of two types were fabricated. The first utilizes niobium tunnel junctions and a YBCO (Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/) film strip as the most inductive portion of the SQUID loop. This configuration allows a direct measurement of the inductance of the YBCO microstrip from which the effective penetration depth can be calculated. The successful fabrication of these SQUIDs has required superconducting Nb-to-YBCO contacts, deposition and patterning of an SiO/sub 2/ insulation layer over YBCO, and selective patterning of niobium and SiO/sub 2/ relative to YBCO. All These process steps are pertinent to the eventual use of YBCO thin films in electronic devices. The large effective YBCO film penetration depth inferred ( approximately 1.2 mu m) is consistent with the polycrystalline structure of these films. The second squid utilizes grain boundary YBCO junctions engineered by the use of bare sapphire substrate. A single-turn niobium drive coil is then deposited on-chip, separated from the YBCO SQUID by an SiO/sub 2/ insulation layer. Good isolation was obtained, and the observed periodicity of the SQUID response corresponds to the calculated flux from the niobium drive coil penetrating the YBCO SQUID loop. These results and the circuit design and fabrication are presented and discussed.         Characteristics of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary junction DC-SQUIDs    R. Gross, P. Chaudhari, M. Kawasaki, M.B. Ketchen and A. Gupta Summary: The characteristics of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary junction (GBJ) DC-SQUIDs with a square washer geometry design are discussed. The current-voltage characteristics of these SQUIDs are close to those predicted by the resistively shunted junction (RSJ) model. Their flux-voltage characteristics are perfectly periodic from 4.2 to 87 K. The noise characteristics have been measured as a function of frequency, temperature, bias current, and applied magnetic flux. At frequencies above about 1 kHz the magnetic flux noise energy of GBJ-SQUIDs is frequency independent and close to the theoretical value estimated from the Nyquist noise in the junction normal resistance. At lower frequencies the noise scales approximately as 1/f. Above 82-5 K the 1/f noise is dominated by flux noise, presumably caused by thermally assisted flux motion in the film. Below this temperature it is dominated by voltage noise across the junctions.         Thin-film flux transformers of YBa/sub 2/Cu/sub 3/O/sub 7-x/    F.C. Wellstood, J.J. Kingston, M.J. Ferrari and J. Clarke Summary: A three-layer in situ laser deposition process was used to construct superconducting thin-film flux transformers of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO). The transformers are designed for efficient coupling to a planar thin-film DC SQUID, have 0.7-cm/sup 2/ magnetic field pickup areas, and have ten-turn input coils. When coupled to low transition temperature (T/sub c/) SQUID, the resulting hybrid magnetometer exhibits excess low-frequency flux noise which arises in the transformer. This noise depends on the geometry of the flux transformer, and the observed behavior agrees with model calculations of the expected contribution from flux motion in the YBCO. The hybrid magnetometer attains a magnetic field sensitivity of about 0.9 pTHz/sup -1/2/ at 1 Hz with the transformer at 60 K; the RMS noise decreases as 1/f/sup 1/2/ at 1 Hz up to a frequency f approximately=1 kHz. It is believed that the sensitivity is high enough for use, for example, in magnetocardiography.         SQUID magnetometer noise measurements on YBa/sub 2/Cu/sub 3/O/sub 7/ thin films and input coils    M.S. DiIorio, K. Yang, J. Zhang, S. Yoshizumi and M. Maung Summary: A SQUID magnetometer system incorporating a NB-based conventional SQUID operating at 4.8 K was used to measure the magnetic field noise from high-T/sub c/ input coils and unpatterned films at 77 K. The system allows for the rapid measurement of relatively large regions of high-T/sub c/ material. The results on numerous coils and films show the noise decreasing as a function of increasing film critical current density at 77 K. High-T/sub c/ films with J/sub c/(77 K)=3*10/sup 6/ A/cm/sup 2/ appear suitable for use as input coils in SQUID magnetometer applications requiring low noise at frequencies down to 1 Hz.         Controlled transfer of single charge carriers    C. Urbina, H. Pothier, P. Lafarge, P.F. Orfila, D. Esteve, M. Devoret, L.J. Geerligs, V.F. Anderegg, P.A.M. Holweg and J.E. Mooij Summary: Two devices that allow the coherent transfer of single electrons are described. They are based on the electrostatic control of tunnel processes across ultrasmall normal tunnel junctions. When appropriate AC signals are applied to gates a current I=e*f is forced to flow through the devices. There are, however, fundamental differences in their principles which make the pump the only suitable candidate for the controlled transfer of cooper pairs. Although in these experiments the I=e*f relation was verified with only a 1% accuracy, more elaborate versions of these devices could be promising candidates for a current standard.         1-D array implementation of the resistively-coupled single-electron transistor    P. Delsing, T. Claeson, G.S. Kazacha, L.S. Kuzmin and K.K. Likharev Summary: The authors fabricated and tested the first version of the resistively coupled single-electron transistor (R-SET) based on the correlated transfer of single electrons in ultrasmall junctions. In this version, a one-dimensional array of 80*80 nm/sup 2/ Al/Al/sub x/O/sub y//Al junctions served as a resistor for transmission of the signal to the middle electrode of a pair of similar junctions. Of three tested R-SETs, all exhibited a real power gain, and one device showed a DC voltage gain of 0.85. The data are found to be in reasonable agreement with numerical simulations based on the orthodox theory of correlated tunneling taking into account the superconductivity of aluminum electrodes.         Comparison of Si and InSb as the normal layer of S-N-S junctions    T. Hato, H. Akaike, A. Fujimaki, Y. Takai and H. Hayakawa Summary: Superconductor-semiconductor-superconductor (S-N-S) weak-link junctions with a normal layer of Si or InSb thin films were prepared by using focused ion beam (FIB) methods. The electrical properties were measured. Whereas InSb thin films on single crystals did not have an intrinsic mobility, S-N-S junctions with InSb show the characteristics of a Josephson S-N-S junction. A 200-nm-thick film of InSb deposited on MgO has a mobility of 83 cm/sup 2//V-s and a carrier density of 6.5*10/sup 17/ cm/sup -3/ at 4.2 K. The coherence length xi /sub n/ was computed to be 17 nm. A critical superconducting current I/sub c/ of 100 mu A was obtained for the S-N-S junction which had a line width of 10 mu m and a channel length of 20 nm.         Critical currents of semiconductor-coupled Josephson weak links    A.W. Kleinsasser Summary: Critical currents of semiconductor-coupled Josephson weak links, including Josephson field effect transistors, are discussed with emphasis on experimental results. Phenomenological expressions are used illuminate outstanding issues. Recent experiments are described which could lead to improved understanding of the superconductor-semiconductor interfaces of key importance in these devices.         A superconducting resonant tunneling transistor with insulating base layer    H. Tamura, A. Yoshida, K. Gotoh, S. Hasuo and T. Van Duzer Summary: A superconducting transistor that uses resonant tunneling as the carrier transport mechanism is proposed. Carriers travel between two superconducting electrodes by resonant tunneling via impurity levels in a barrier. The barrier is a high-dielectric-constant insulator layer sandwiched between low-dielectric-constant layers. The high-dielectric-constant layer conducts an electric field, and the electric potential in the barrier is controlled by voltage applied to the base electrode connected to the edge of the high-dielectric-constant layer. The coupling coefficient between the base and levels may be more than 90% on the average when the emitter stripe width is about 0.1 mu m and the relative dielectric constant of the high-dielectric-constant layer is on the order of 10/sup 4/. The current-versus-voltage characteristics of the transistor were calculated using a tunnel Hamiltonian approximation. The transistor's calculated transconductance was 6*10/sup 6/ S/cm/sup 2/ at a current density of 3*10/sup 4/ A/cm/sup 2/ when the lifetime broadening of resonant levels was 4 meV and the level density was 10/sup 11/ cm/sup -2/.         Hysteresis effects and bistable switching in SIS'IS tunnel junctions    M.G. Blamire, E.C.G. Kirk, R.E. Somekh and J.E. Evetts Summary: Experimental results that show that gap enhancement can result in a novel double hysteretic structure in the subgap region which arises from a transition from finite to zero voltage across one barrier are presented. Within this hysteretic voltage state, it is possible to switch between two stable voltage levels by the application of an appropriate current pulse. The voltage swings possible in such a device are shown to be on the order of the gap voltage, and the holding currents required to maintain the bistable states are less than 20% of the current rise at the sum of the gaps. The device appears to have potential as a low-dissipation latch.         High-speed Josephson processor technology    S. Hasuo, S. Kotani, A. Inoue and N. Fujimaki Summary: High-speed operation of Josephson processors is demonstrated. They are a 4-b microprocessor, a 4-b processor, and an 8-b digital signal processor. Key technologies to realize these circuits are described from the viewpoint of circuit design. The technologies are a high-speed logic gate, named MVTL (modified variable threshold logic), and a three-phase sinusoidal power supply system. The MVTL gate has a large operating margin and high sensitivity. The MVTL gate family consists of OR, AND, 2/3 majority (MJ), and timed inverter (TI). Using these gates a variety of processors have been designed. These processors operate with three-phase power. The waveform is sinusoidal with DC-offset. This power supply system needs no latch and regulator circuit. This makes the processor very simple, and thus results in high-speed operation. To fabricate these processors, niobium junctions are very important, because they are reliable, uniform, controllable, and reproducible. High-speed gates, three-phase power supplies, and niobium junctions are indispensable for high-speed Josephson processors.         A multichip superconducting microcomputer ETL-JC1    S. Takada, H. Nakagawa, I. Kurosawa, M. Aoyagi, S. Kosaka, Y. Okada and Y. Hamazaki Summary: A multichip 4-b superconducting microcomputer named ETL-JC1 has been designed based on Josephson LSI technology in order to demonstrate the feasibility of a Josephson computer system. The ETL-JC1 is the first Josephson computer than can execute a computer program stored in the ROM chip. In order to make the ETL-JC1, the following key technologies were developed: an Nb tunnel junction integration process, an LSI logic circuit, memory chips of 1-kb ROM and 1-kb RAM a CAD (computer-aided design) system to develop Josephson LSIs, and a multiphase power supply system. The computer consists of four Josephson LSI chips essential to execute the computer functions of arithmetic-logic, sequence control, program memory, and data memory. The whole computer system was based on a RISC (reduced-instruction-set computer) architecture. The four chips were fabricated using a 3- mu m Nb/Al-oxide/Nb junction integration process. Photomasks for the logic circuits were made by using the CAD system, in which the layout of logic gates on the chip and wiring among them were carried out using a standard-cell method. The 128-step program was executed fully in the ETL-JC1 to test a full set of 27 kinds of basic RISC instructions, memory access, subroutine call/return, and so forth, which are sufficient to make any computer program. The total power dissipation was 6.2 mW in all circuits of the ETL-JC1 consisting of more than 22000 junctions. An operation speed of 1 GIPS (giga-instruction per second) can be expected with single CPU in this system by computer logic simulation.         A 1-GHz-clock Josephson microcomputer system    S. Yano, Y. Hatano, H. Mori, H. Yamada, K. Nakahara, M. Hirano and U. Kawabe Summary: A 1-GHz-clock Josephson microcomputer system was developed to demonstrate the possibility of a high-speed superconducting computer system. It consists of a 4-b data processor chip and a 1-kb RAM chip. For the fabrication of these Josephson integrated circuits, a cross-shaped Nb-AlO/sub x/-Nb Josephson junction process was developed in order to realize small junction size and improve critical current uniformity, and has made fabrication of LSIs with several thousand gates possible. A latchup-free DC flip-flop is an important element in the high-speed Josephson logic and memory circuits, having been applied to an all-DC-powered Josephson RAM with asynchronous access capability. A low-inductance chip-to-chip carrier is an architectural and design concept for the Josephson computer's 1-GHz-clock operation, suppressing the crosstalk between the AC power and the output signals. Each chip is 7 mm square and is fabricated using a 2.5- mu m-rule Nb-AlO/sub x/-Nb junction process. The chips are connected on a superconducting carrier by solder bumps in a die size of 15 mm by 25 mm. The system is constructed from 8123 Josephson interferometer devices and is operable in a 1-ns cycle with 50-mW power dissipation.         A 4-kbit Josephson nondestructive read-out RAM operated at 580 psec and 6.7 mW    S. Tahara, I. Ishida, S. Nagasawa, M. Hidaka, H. Tsuge and Y. Wada Summary: A fully decoded 4-kb Josephson nondestructive readout high-speed RAM with vortex transitional memory cells was designed and operated successfully. The 4-kb Josephson RAM is composed of 64-b*64-b cells, polarity-convertible drivers, address decoders using resistor coupled Josephson logic (RCJL) gates, and a resistively loaded sense circuit. The memory cells use vortex transitions in their superconducting loops for writing and reading data. The cells are activated by two control signals without timing control, while all peripheral circuits are activated by an AC power supply. This memory configuration eliminates the timing sequence needed for memory operations, resulting in a decrease in the memory operation time for an actual memory chip. The 4-kb Josephson high-speed RAM was fabricated using niobium planarization technique with a 1.5- mu m design rule. The RAM circuit size is 4.8*4.8 mm/sup 2/ and the memory cell is 55*55 mu m/sup 2/. More than 25000 Nb-AlO/sub x/-Nb Josephson junctions with approximately 1200 A/cm/sup 2/ critical current density are contained in the RAM chip. An access time of 580 ps and a power consumption of 6.7 mW are obtained for the nondestructive memory operation.         A full-band waveguide SIS receiver with integrated tuning for 75-110 GHz    D. Winkler, N.G. Ugras, A.H. Worsham, D.E. Prober, N.R. Erickson and P.F. Goldsmith Summary: The performance of a broadband SIS (superconductor-insulator-superconductor) receiver with no mechanical tuning elements was modeled and tested. The mixer mount had a broadband-waveguide-to-microstripline transition consisting of a four-step Chebyshev single-ridge transformer. The last step of the ridge connected the waveguide to a microstripline circuit. The on-chip circuit consisted of a microstripline that transmitted the RF and the local oscillator signals to the SIS mixer. Both the SIS element and the inductor had RF grounds provided by 90 degrees radial stubs. The inductor tuned out the junction capacitance to allow operation over the full frequency band. The SIS element can be a single junction or series array using Nb-AlO/sub x/-Nb trilayer tunnel junctions with areas as small as 0.5 mu m/sup 2/ and V/sub m/(2 mV)=39 mV. Preliminary results indicated a DSB receiver noise temperature of 65-80 K across the band measured at 4.4 K with an internal cryogenic RF hot/cold source and with T/sub if/=21 K. With another device, a mixer noise temperature of 35 K at 100 GHz was achieved, increasing to 45 K at 79.5 and 110 GHz. Coupled mixer gain of up to +3 dB and negative dynamic resistance on the first photon step were observed. The lowest noise temperature was obtained for an untuned single-junction mixer at 80 GHz: T/sub R/=41 K and T/sub M/=20 K were measured.         SIS junction reactance complete compensation    V.Y. Belitsky and M.A. Tarasov Summary: Superconductor-insulator-superconductor (SIS) junction geometrical capacitance with out of phase current I/sub kk/ impedance component forms sufficient junction reactance X/sub SIS/=( omega C+B/sub Q/)/sup -1/. It is suggested that the way to resonate out both omega C and B/sub Q/ is by using an additional identical SIS junction connected to the first through a long line impedance inverter and RF+DC biased symmetrically to the first. Pumped I-V curves without quantum reactance and frequency impedance patterns of the system are calculated. Calculations demonstrated the presence of high and even negative induced dynamic resistance regions at high-order quasiparticle steps for the case of SIS junction reactance complete compensation. The suggested method may be used in SIS mixers and detectors for a better RF matching.         Parallel biased SIS-arrays for mm wave mixers: main ideas and experimental verification    A.B. Ermakov, V.P. Koshelets, S.A. Kovtonyuk and S.V. Shitov Summary: The possibility of overcoming the main drawbacks of the traditional series arrays by parallel connection of the SIS (superconductor-insulator-superconductor) junctions for DC and IF are demonstrated experimentally. The proposed mixing elements avoid the influence of the junction nonuniformity in the array, provide the optimal matching on both RF input and IF output, and tune out junction capacitance. Experimentally tested arrays contained up to eight high-quality Nb-AlO/sub x/-Nb junctions with R/sub n/=20-70 Omega at junction area 8/14 mu m/sup 2/. The best values of T/sub r/ (SSB) were measured to as low as 5 K on the mixer cold input flange in the 45-55-GHz bandwidth at an ambient temperature of 4.2 K. A mixer gain of up to 10 dB was obtained. The gain values were limited by bias stability at very high or even negative array output impedance. An experimental receiver noise temperature (SSB) of less than 20 K has been achieved.         An analytic investigation of the superconductor quasiparticle mixer in the low power limit    M.J. Feldman Summary: The properties of an SIS (Superconductor-insulator-superconductor) mixer using a slightly nonideal junction, with finite local oscillator (LO) power, are determined by analytic expansion of the equations of the quantum theory of mixing. The result is that the conversion gain using any reasonably good quality SIS junction is essentially equal to that using a perfect junction. Quite to the contrary, the minimum noise temperature is controlled by the leakage current of the junction: the increase in the minimum added-noise temperature over the quantum limit T/sub Q/=h omega /2k is given by delta T/sub Q/=(h omega /k) square root I/sub 0/I/sub 2//I/sub 1/; this minimum requires that the LO voltage across the junction is V/sub LO/=(64I/sub 0//I/sub 2/) /sup 1/4/h omega /e. (I/sub n/ is the current measured on the unpumped I-V curve of the junction at voltage V/sub 0/+nh omega /e). Therefore, although an SIS mixer using an ideal junction can reach the quantum noise limit only in the limit of zero LO power, even the most nearly ideal junctions require a considerable LO for best sensitivity.         Performance of NbN superconductive tunnel junctions as SIS mixers at 205 GHz    W.R. McGrath, J.A. Stern, H.H.S. Javadi, S.R. Cypher, B.D. Hunt and H.G. LeDuc Summary: Small area (         100 GHz SIS mixer with improved RF matching    J.A. Carpenter, A.D. Smith, E.R. Arambula, L.P.S. Lee, T. Nelson and L. Yujiri Summary: A novel superconductor-insulator-superconductor (SIS) mixer coupling scheme with an integrated millimeter-wave transformer has been designed and tested. The impedance transformation allows larger junction sizes and easier fabrication than is possible with single junction or array mixers. Experiments with the front-end transformer mixers demonstrated mixer gains up to 10 dB and instantaneous bandwidths of 700 MHz at W-band. In addition to heterodyne mixing, direct detection measurements were made to measure instantaneous signal bandwidth. Current responsivities of 1000 A/W were measured with a 3-dB bandwidth of 8 GHz. The direct detection performance falls to within experimental uncertainty at the quantum limit of one-electron-per-photon.         Vacuum noise squeezing at microwave frequencies using a Josephson parametric amplifier    R. Movshovich, B. Yurke, P.G. Kaminsky, A.D. Smith, A.H. Silver and R.W. Simon Summary: Experiments on generating squeezed microwave radiation at 19.16 GHz using a Josephson parametric amplifier were performed. The source of the radiation was cooled by a dilution refrigerator down to the lowest temperature of 0.030 K. At this temperature, noise at the input port of the parametric amplifier consists almost entirely of the vacuum fluctuations with a noise temperature h nu /2k of 0.46 K. The authors observed the squeezing of the microwave noise by 47+or-8% as referred to the input of the Josephson parametric amplifier. The measured double-sideband noise temperature of the amplifier is 0.446 K, which is comparable to the vacuum noise level.         Output signal from Nb-based tunnel junctions by irradiation of 6 keV X-rays    K. Ishibashi, K. Mori, K. Takeno, T. Nagae, Y. Matsumoto, S. Takada, H. Nakagawa and H. Akoh Summary: Large-size tunnel junctions with a Nb-Al-AlO/sub x/-Nb structure have been fabricated in order to study their performance in X-ray detection. The junction detected 5.9-keV X-rays with an energy resolution of 1 keV. The output signal was analyzed by the use of coupled Boltzmann equations. The method based on these equations clarifies the basic behavior of the quasiparticles and phonons, and the average energy for producing a single electron is 3.2 Delta .         Superconducting tunnel junctions for use as energy resolving X-ray detectors    D. Van Vechten, C. Boyer, G.G. Fritz, S. King, M.P. Kowaski, M.N. Lovellette, M.G. Blamire, E. Kirk and R.E. Somekh Summary: The response of Nb-Al-Al/sub 2/O/sub 3/-Al-Nb superconductor-insulator-superconductor (SIS) tunnel junctions to pulsed 650-nm radiation was measured. The rise in the voltage developed across the junction increases linearly for the duration of the applied pulse. The decay time of 300 mu s is an intrinsic property of the junction. The response of the junction varies linearly with incident energy over the range 35 to 200 eV/ mu m/sup 2/. Comparison with the junction response caused by higher energy particles should give insight into the microscopic details of the extremely nonequilibrium pair breaking.         Particle pulses from superconducting aluminum tunnel junction detectors    D.A. Stricker, D.D. Bing, R.W. Bland, S.C. Dickson, T.D. Dignan, R.T. Johnson, J.M. Lockhart, K. Laws, M.W. Simon and R. Watson Summary: Superconducting aluminum tunnel junctions have been developed for use as particle detectors. Results on the static characteristics of these devices and from tests of these detectors with 6-keV X-rays are presented. An extrapolation of the properties of these detectors to one suitable for dark-matter detectors is discussed.         Modeling quasiparticle production and propagation in tunnel junction based X-ray detectors    K.S. Wood, M.N. Lovellette and D. Van Vechten Summary: Optimization of the energy resolution of Josephson tunnel junction X-ray detectors requires the minimization of event-to-event variation in the number of nonequilibrium quasiparticles that tunnel and are thereby detected for monochromatic input. This requires a detailed understanding of the determinants of the time scales for the degradation of the energy and expansion of the disturbed volume, of possible quasiparticle (QP) self-trapping and phonon bottlenecking, and of the impact of materials parameters such as grain size. Moreover, the signals of distributed detectors cannot be interpreted without a detailed model of the evolution of the spatial variation in QP density. These matters, and the extent to which the details of the QP tunneling pulse probes the energy degradation and expansion, are discussed. The expansion is modeled in two dimensions with Monte Carlo simulations of ballistic quasiparticle propagation between randomizing collisions and compared with published data for a distributed junction detector. Alternative explanations of the high quasiparticle loss rate and curvature seen in the published plots of the relative fraction of the QP detected by the two sensing junctions are offered.         Far-infrared kinetic-inductance detectors    E.N. Grossman, D.G. McDonald and J.E. Sauvageau Summary: Extremely sensitive far-infrared detectors suitable for both direct detection and heterodyne applications, based on mu m-sized thin films with thickness less than a superconducting penetration depth are possible. The penetration depth of such a film, and therefore its inductance, varies with temperature and with quasiparticle population (described by an effective temperature T*), resulting in both bolometric and nonequilibrium photoinductive responses. Incident radiation is coupled into the small-area kinetic inductor by a lithographic antenna, and the resulting inductance changes are amplified and converted to a voltage signal by an integrated microstrip DC SQUID. The device is sensitive because, unlike junction-based devices with large capacitive reactances, the kinetic inductor is naturally well matched to the antenna impedance at the far-IR frequency ( nu >2 Delta /h) and to the preamplifier (SQUID) impedance at microwave or video frequencies ( nu <<2 Delta /h). The best kinetic inductor materials are those with low electronic mean free path, large penetration depth, and high critical current density. Thus, common magnet alloys such as NbTi are the natural choice for liquid-He temperature operation. A detailed analysis predicts a (phonon-limited) NEP of 4*10/sup -17/ W/ square root Hz for a bolometer with an iridium kinetic inductor operated at 0.1 K. A heterodyne noise temperature of 2250 K (single-sideband) at 3 THz, with a 200-MHz bandwidth, is predicted for a Nb-Ti mixer operated at 4 K.         Superconducting infrared detector arrays with integrated processing circuitry    D.P. Osterman, P. Marr, H. Dang, C.-T. Yao and M. Radparvar Summary: Thin-film Josephson junctions may be used as infrared detectors that function by a thermal sensing mechanism. In addition to the potential for high sensitivity to a broad range of optical wavelengths, they are ideally suited for integration with superconducting electronics on a single wafer. To develop these arrays, work was directed along two avenues: (1) maximizing the sensitivity of individual Josephson junction detector/SQUID amplifier units, and (2) development of superconducting on-chip processing circuitry-multiplexers and analog-to-digital converters. Superconducting detector/amplifier circuits were designed for low-noise performance. Amplification in these chips has been successfully demonstrated. Square 8*8 arrays integrated with various elements of superconducting processing circuitry have also been fabricated and tested. These use niobium Josephson junctions and 65 mu m*85 mu m absorber areas, and have been tested at 4.2 K. One such array includes circuitry for multiplexing all detectors, and was used successfully to form an image that was presented in real time on a computer terminal display. The output of a single detector was also used to drive a superconducting analog-to-digital converter.         Synchronous switching of a large number of Josephson junctions    J. Niemeyer, R. Popel, R. Fromknecht and W. Meier Summary: A circuit that allows at least 400 junctions connected in series to be synchronously switched is described. Instead of a few millivolts for a single junction, an array of 400 junctions switches directly to one volt. The junctions, integrated into a stripline circuit similar to that described for series array voltage standards, are commonly biased by a DC current source. When the DC bias is increased the junction with the smallest critical current first switches to the normal state. This causes a pulse to propagate along the stripline, forcing the rest of the junctions to be switched to the normal state. The maximum number of junctions to be switched is proportional to the average critical current of the circuit. The switching time is mainly determined by the signal speed of the pulse in the stripline. Relatively large junctions were used in this experiment. As a result, the length of the stripline containing, for instance, 400 junctions is 16.8 mm. If the junction with the smallest critical current is located in the center of the stripline the switching pulse takes 70 ps to completely pass the line. This time interval can certainly be reduced by a factor of five when smaller junctions are used.         Microwave detector response of the Josephson junction arrays    G.A. Ovsyannikov, G.E. Babayan, V.N. Laptev and V.I. Makhov Summary: Microwave detector response ( eta ) for three types of superconducting structures-single edge-type Josephson junctions, arrays of series-connected junctions, and arrays of RF-series and DC parallel-connected junctions-were investigated in the frequency range 35-120 GHz. Experimental dependence of eta versus biasing voltage is mainly determined by the interaction of junctions in the array. The selective response, which means a narrow linewidth of Josephson radiation, is observed for the third type of superconducting structure in a small magnetic field changing the phase shift between closely-spaced junctions. These arrays have the advantage in coupling with the external microwave system.         Kinetic-inductance coupling scheme for superconducting stripline system and its device applications    K. Yoshida, K. Kudo, M.S. Hossain and K. Enpuku Summary: The properties and applications of the inductive coupling of a superconducting stripline system, which takes advantage of kinetic inductance of thin superconducting films, are studied. The system, composed of two striplines inductively coupled through a common electrode as a four-port circuit, was formulated by obtaining its scattering coefficients in a general form. The system is characterized with the coupled-mode theory. Based on the analysis, it is proposed that a novel type of kinetic inductance devices for microwave analog components, such as directional couplers, microwave switches, variable filters, and efficient coupling elements for striplines. Experiments on stripline coupling with this scheme are also discussed.         Ultra-compact microwave filters using kinetic inductance microstrip    J.M. Pond, K.R. Carroll and E.J. Cukauskas Summary: Multipole microwave filters were designed and fabricated using microstrip transmission line sections that consisted of two very thin films of sputtered NbN separated by another very thin film of sputtered Si. Since the thicknesses of all three films were much less than the superconducting penetration depth, the kinetic inductance was significantly greater than the magnetic inductance. As a result, the phase velocity of a microstrip transmission line is much less than the free-space speed of light. Since resonant structures are reduced in size proportionately, the size and weight of microstrip circuit can be greatly reduced. Prototype filters consisting of four open-circuited half-wavelength microstrip stubs separated by full-wavelength microstrip sections were measured. The circuits were connected to 34-mil-diameter coaxial cable via an intermediate coplanar waveguide section. Passbands of 4 GHz, separated by 3 GHz reject bands, were measured in a structure which occupied less than 0.5 cm/sup 2/, including the coplanar waveguide transitions. Higher-order passbands, although possessing an increased insertion loss, maintain filter passband characteristics through 20.0 GHz.         Investigation of an electronically tuned 100 GHz superconducting phase shifter    E.K. Track, Z.-Y. Shen, H. Dang, M. Radparvar and S.M. Faris Summary: Turnable superconducting millimeter-wave phase shifters are discussed. The tuning mechanism is based on inductance modulation of NbN microstrips by excess quasiparticle injection. When measured by a DC method, using the interference patterns and resonances of specially designed DC SQUIDs, the inductance of NbN microstrips can be varied by up to 300%. Based on these results, superconducting microstrip interferometers to operate as low-power 100 GHz phase shifters were designed and fabricated. The 100 GHz signal is coupled into and out of the interferometers by finline antennas. Amplitude modulation of the output is used as the criterion for phase shift in one of the interferometer branches. Thin superconducting films (thinner than the penetration depth) and dielectric layers are needed to achieve tunability of the inductance. The conflicting requirements of tunability and efficient signal coupling are quantified in the interferometer testing, and the range of parameter optimization is bracketed. The elements of this required optimization are presented.         Phase-locked Josephson soliton oscillators    T. Holst, J.B. Hansen, N. Gronbech-Jensen and J.A. Blackburn Summary: Detailed experimental characterization of the phase-locking at both DC and at microwave frequencies is presented for two closely spaced Josephson soliton (fluxon) oscillators. In the phase-locked state, the radiated microwave power exhibited an effective gain. With one common bias source, a frequency tunability of the phase-locked oscillators up to 7% at 10 GHz was observed. The interacting soliton oscillators were modeled by two inductively coupled nonlinear transmission lines.         Quasioptical Josephson oscillator    M.J. Wengler, A. Pance, B. Liu and R.E. Miller Summary: Work with large two-dimensional arrays of Josephson junctions for submillimeter power generation is discussed. The basic design of the quasioptical Josephson oscillator (QJO) is presented. The reasons for each design decision are discussed. Superconducting devices have not yet been fabricated, but scale models and computer simulations have been done. A novel method for characterizing array RF coupling structures is described, and initial results with this model are presented. Microwave scale models of the radiation structure were built, and a series of measurements was made with a network analyzer. These measurements were summed in a computer to find properties of the structure when all elements in it are operating in phase. The goal of these measurements was to develop structures for oscillators which are tunable over a very broad band. Computer programs simulating a Josephson junction in any frequency-dependent coupling structure have been developed. An iterative harmonic balance technique finds the time-domain current and voltage waveforms across the junction for an arbitrary frequency-dependent RF load impedance. DC bias, and therefore oscillator frequency, can be held fixed in this technique, in contrast to time-domain techniques where the oscillation frequency is found after the waveform is found. With these programs design goals for maximum oscillator power and design limits to achieve tolerable harmonic distortion were found.         Radiofrequency generation using a SNS microbridge    A.M. Luiz and R. Nicolsky Summary: The feasibility of a sinusoidal oscillator is demonstrated using a SNS microbridge linked with a series RLC tank circuit, supplied by a constant DC current, and operated at the negative differential resistance range of its I-V characteristic curve. The frequency of this sinusoidal generator is equal to the resonant frequency of the tank RLC circuit. This type of generator can be operated for a wide range of frequencies, from audio frequencies up to the limit of microwaves. Other possible electronic applications based on the appropriate use of the negative resistance region of the I-V characteristic curve of the SNS microbridge are suggested.         Magnetic field dependence of the critical current in long 'quasi-overlap' Josephson junctions    E. Sarnelli, S. Pagano, B. Ruggiero and M. Russo Summary: The effect of the magnetic field on the current distribution in one-dimensional long Josephson tunnel junctions is investigated. Overlap and mixed overlap/in-line configurations are considered. The latter geometry corresponds to an experimental situation, since it takes into account nonuniformities of the bias current. A simple method to investigate the dependence of the Josephson critical current on the external magnetic field for any junction length is developed. The predictions, based on the phase space analysis, are compared with experimental results obtained on long junctions of different lengths. The possibility of using this method to evaluate relevant junction parameters from the experimental measurements is discussed.         Millimeter-wave response in NbN(g)/Al nanobridges    Z. Wang, K. Hamasaki, M. Kinoshita, T. Yamashita, T. Matsui and B. Komiyama Summary: The testing of NbN(g) nanobridges with Al direct shunt resistors for use as millimeter-wave Josephson mixers is discussed. The NbN(g)/Al nanobridges have a nearly sinusoidal current-phase relation, high resistance, well-defined gap structure at approximately 4 mV, large I/sub J/ R/sub N/ products of approximately 3 mV, and nonhysteresis I-V curves. By means of the Al direct shunt, the effective noise temperature T/sub N//sup eff/ of the NbN(g) nanobridges, which was calculated by transition-state theory, was reduced to 4.2 K as a result of reducing the self-heating and noise rounding effects. The NbN(g)/Al nanobridges show almost ideal Josephson response to millimeter-wave radiation at 106 GHz. The well-pronounced Josephson steps were observed up to approximately 4 mV. The observed systematic decreasing of the step heights with increasing the RF current can be accounted for by the effect of the thermal noise if an effective noise temperature of T/sub N/=15 K (at i/sub RF/=3) is assumed. The IF peaks in the Josephson mixing were obtained up to the bias voltage of approximately 1.2 mV. The NEP was about 3*10/sup -20/ W/Hz at 4.2 K.         Self-radiation phenomena in LTSC and HTSC bridges    L.E. Amatuni, K.Y. Constantinian, R.B. Hayrapetian, G.A. Ovsyannikov, V.N. Laptev and V.I. Makhov Summary: The nonlinear properties of Nb-Si-Nb high-quality edge-junctions and Y-Ba-Cu-O thin-film bridges were examined at several frequencies: f approximately=1.7, 21, and 39 GHz at T=4.2 K by means of the highly sensitive radiometric probe method. The results of self-pumping mixing regime in a single edge-junction and phase-locking processes in an array of 21 junctions are presented. The HTSC (high-temperature superconducting) bridge has exhibited strong generation intensity, more than 300 times higher than single edge-junctions, and stimulation of self-radiation under external microwave affection.         Dynamics of pulse driven Josephson junctions    B. Christiansen and M.T. Levinsen Summary: It is demonstrated that the pulse-driven Josephson junction for high frequencies reacts in a similar way to the sinusoidally driven junction. At frequencies below the RC cutoff frequency, two distinct kinds of steps arise. The first is the usual series of Josephson steps. The second is a series of steps where the junction spends some time caught in the zero voltage basin of attraction, where a relaxation oscillation takes place. These steps are situated as substeps to the Josephson steps. Regions with seemingly chaotic motion are also observed.         Nonlinear oscillation modes in the 3rd order Josephson junction circuits    K. Araki and K. Akiyama Summary: Autonomous third-order Josephson junction (JJ) circuits containing an angular variable are analyzed. Using piecewise linearizing approximation, the Poincare map, bifurcation diagram, attractor dimension, and Lyapunov spectrum have been efficiently obtained, especially for the chaos in this system. The authors have also obtained the almost one-dimensional feature of the chaos orbit and the fine structure of the chaos oscillation. This chaos has a low attractor dimension nearly equal to that of the quasi-periodic oscillation in nonautonomous second-order JJ circuits. The conditions for the generation and extinction of chaos are provided, since they can be useful in designing a Josephson heterodyne detector, Josephson parametric amplifiers, etc. All the unstable periodic oscillation modes are found to be embedded into the chaos orbit, and these expanding directions are tangential to the chaos orbit. Lyapunov exponents of the chaos orbit are equal to those of unstable periodic oscillation modes. The C/N of the JJ oscillators falls below -20 dB when the chaos occurs.         Coupled long-Josephson junctions and the N sine-Gordon equation    S.P. Yukon and N.C.H. Lin Summary: The Lagrangians and equations of motion are derived for the junction phase differences for a family of coupled Josephson junction devices. These can be considered as the long junction versions and generalizations of the three-coupled Josephson device firs introduced by K.K. Likharev (1986). The possible two-field kink solutions for the long three-coupled Josephson junction device and three-field kinks for the long six-coupled junction device are derived. The two-field and three-field kinks are found to exist in equal mass families with SU(3) and SU(4) symmetries, respectively. With an external magnetic flux of the magnitude Phi = Phi /sub 0//2 present, where Phi /sub 0/=h/2e is the flux quantum, the kinks of the three junction system have 1/3 and 2/3 fluxon subkinks that behave like quarks, e.g. exhibiting permanent confinement. A collective coordinate description and time-dependent one-dimensional numerical solutions for various kink collision, conversion, decay, and internal excitation processes are presented.         RF-induced steps in mutually coupled, two-dimensional distributed Josephson tunnel junctions    U. Klein, P. Dammschneider and J.H. Hinken Summary: The amplitudes of the current steps in the I-V characteristics of mutually coupled two-dimensional distributed Josephson tunnel junctions driven by microwaves are investigated. For this purpose a numerical computation algorithm that is based on a planar resonator model for the individual Josephson tunnel junctions is used to calculate the DC current density distribution. In addition to the fundamental microwave frequency, harmonic contents of the tunneling current are also considered. The lateral dimensions of the individual junctions are small compared to the microwave wavelength and the Josephson penetration depth, giving an almost constant current density distribution. Therefore, the coupled junctions can give much greater step amplitudes than a single junction with an equal tunneling area, because of their nonuniform current density distribution. The calculation show a strong dependence of the Shapiro step amplitudes with respect to the coupling of the tunnel junctions. These studies imply that the choice of proper coupling conditions is important to achieve maximum step amplitudes. These results are helpful in designing tunnel junctions with optimized step amplitudes.         Investigation of the 'wall' effect in the long Josephson junctions    I.P. Nevirkovets and E.M. Rudenko Summary: Long Josephson junctions with edge current injection and shortened control lines are studied experimentally. It is found that the wall effect is connected with the blockage of vortices entry into the junction by control current, as well as with the existence of the energy barrier for the vortices at the boundary between a projection region and the remaining portion of the junction. Significant enhancement of supercurrent due to the blockade was found.         Phonon-mediated particle detection utilizing titanium superconducting transition edge sensors on silicon crystal surfaces    A.T. Lee, B. Cabrera and B.A. Young Summary: Alpha particle interactions with crystalline silicon at approximately 400 mK, which produce phonons, were observed with titanium transition edge sensors on the crystal surface. A calculation of the expected mean free path suggest that the phonons should arrive diffusively, but a significant component of ballistic phonons which experience few or no scattering are observed. There are two sources of evidence for this. First, timing differences between sensors on opposite faces of the crystal are consistent with ballistic propagation. Second, the phonon pattern on one face of the crystal shows lobing indicative of phonon focusing, anisotropic propagation of phonons due to direction-dependent elasticity in the crystal. This pattern would be unobservable if the propagation was truly diffusive. A comparison is made between Monte Carlo simulations of phonon propagation and experimental results. The sensors consist of a 400-A-thick line of titanium patterned into a meander. The width of the lines is 2 mu m, and the pitch is 5 mu m. The line is held just below the superconducting transition temperature and biased with a current. Phonons from a particle interaction in the crystal drive sections of the line normal, resulting in a resistance. Potential methods of increasing the sensitivity of the sensors include reducing the line width and using a superconductor with a lower T/sub c/.         Superconducting kinetic inductance radiometer    J.E. Sauvageau, D.G. McDonald and E.N. Grossman Summary: A bolometer that is based on a differential thermometer that senses temperature changes through changes in the kinetic inductance of a superconducting thin film is being developed. The temperature transducer is an inductance bridge patterned as an integrated circuit on a 1-cm/sup 2/ Si substrate. Two inductors from opposite arms of the bridge are patterned on a 2-mm/sup 2/ thermally isolated Si island which is supported by a 9- mu m thick Si:B membrane. The bridge is excited with audio-frequency current, and the bridge imbalance is detected with a commercial DC SQUID amplifier. The bridge is balanced by applying power to the thermally isolated island. This thermometer is the sensor for a prototype radiometer that will provide an absolute measure of IR power. The radiometer, which is designed for a NEP of about 10/sup -11/ W/ square root Hz, is intended to measure the spectrally dispersed power of a 300-K black body. This absolute radiometer is being developed for use at the Low Background Infrared (LBIR) Facility at NIST, Gaithersburg, MD. The noise floor of the temperature transducer for the radiometer has been measured to be 0.7 pW for a 100-s integration time. This is approximately 150 times lower noise than that of the commercial absolute radiometer currently used at the LBIR facility.         Josephson counting analog-to-digital converter    D.L. Miller, J.X. Przybysz, J. Kang, C.A. Hamilton and D.M. Burnell Summary: A superconductive analog-to-digital converter which uses a DC SQUID as a quantizer and a flip-flop counter as a digitizer has been designed, fabricated, and tested. The circuit was fabricated using a ten-level niobium process. Tests at 4.2 K demonstrated counting to the full 12-b accuracy of the design, monotonic A/D conversion with linearity to less than 1 LSB over the more than 9-b range of conversion, read-on-the-fly operation with counter overflow, and counter operation with a gate current bus.         A new quantum flux parametron logic gate with large input margin    W. Hioe, M. Hosoya and E. Goto Summary: The quantum flux parametron (QFP) is a flux-transfer, flux-activated Josephson logic device which realizes much lower power dissipation than other Josephson logic devices. Being a two-terminal device, its correct operation may be affected by coupling to other QFPs. The problems include backcoupling form active QFPs through inactive QFPs (relay noise), coupling between QFPs activated at different times because of clock skew (homophase noise), and interaction between active QFPs (reaction hazard). Previous QFP circuits worked by wired-majority, which is a linear input logic and has low input margin. A logic gate (D-gate) using a QFP to perform logic operations has been analyzed and tested by computer simulation. Relay noise, homophase noise, and reaction hazard are substantially reduced. Moreover, the inputs have little interaction, and hence input margin is greatly improved. Using only D-gates it is possible to realize any combinational logic function. Important logic functions can be realized using one gate, such as a two-input multiplexer, majority, and parity. Since the QFP has a latching effect, D-gates can realize fully pipelined circuits without additional registers.         Evaluation of flux-based logic schemes for high-T/sub c/ applications    J. Fleischman, D. Feld, P. Xiao and T. Van Duzer Summary: Three digital logic families that can be made using nonhysteretic Josephson junctions (potentially the only kind of Josephson device realizable with superconductors having high transition temperatures) are analyzed. These logic families utilize magnetic flux-transfer, and are characterized by very low power dissipation. Rapid single flux quantum (RSFQ) and phase-mode logic are both based on pulse propagation. The quantum flux parametron (QFP) logic family is based on current latching. Simulations of RSFQ, Phase-Mode, and QFP logic families using high-T/sub c/ junction parameters are presented to demonstrate the compatibility of these logic families with the perovskite superconductors. The operation of these logic families is analyzed, and the advantages and disadvantages of each are discussed.         Shift register performance at 4 GHz    J.X. Przybysz, D.L. Meier and J. Kang Summary: Two mask layouts were designed to give Josephson shift register operation above 2 GHz. Custom instrumentation was assembled for tests up to 4 GHz. Shift registers using coplanar waveguide structures for on-chip power distribution operated properly up to 3.3 GHz. Better performance was obtained when power was distributed through microstrip transmission lines. At the tester limit of 4 GHz, microstrip circuits operated properly with bias margins of +or-15%.         Multichannel DC SQUID sensor array for biomagnetic applications    H.E. Hoenig, G.M. Daalmans, L. Bar, F.R. Bommel, A. Paulus, D. Uhl, H.J. Weisse, S. Schneider, H. Seifert, H. Reichenberger and K. Abraham-Fuchs Summary: A biomagnetic multichannel system for medical diagnosis of the brain and heart has been developed. 37 axial first order gradiometers (manufactured as flexible superconducting printed circuits) are arranged in a circular flat array of 19 cm in diameter. Additionally, three orthogonal magnetometers are provided. The DC SQUIDs are fabricated in all-Nb technology, ten on a chip. The sensor system is operated in a shielded room with two layers of soft magnetic material and one layer of Al. The everyday noise level is 10 fT/Hz/sup 1/2/ at frequencies above 10 Hz. Within two years of operation in a normal urban surrounding, useful clinical applications have been demonstrated (e.g., for epilepsy and heart arrhythmias). For the first time current sources of sporadic events causing epilepsy or ventricular extrasystoles have been localized from coherent recordings of complete biomagnetic field distributions with spatial resolution of millimeters and temporal resolution of 1 ms.         Multichannel SQUID systems for brain research    A.I. Ahonen, M.S. Hamalainen, M.J. Kajola, J.E.T. Knuutila, O.V. Lounasmaa, J.T. Simola, C.D. Tesche and V.A. Vilkman Summary: Basic principles of magnetoencephalography (MEG) and neuromagnetic instrumentation are briefly reviewed. A 24-channel system based on planar gradiometer coils and DC-SQUIDs is described. Finally, MEG-experiments of human somatotopy and focal epilepsy are presented.         A 37 channel DC SQUID magnetometer system    H. Koch, R. Cantor, D. Drung, S.N. Erne, K.P. Matthies, M. Peters, T. Ryhanen, H.J. Scheer and H.D. Hahlbohm Summary: A 37-channel DC SQUID magnetometer system has been built for biomagnetic studies. The SQUID loop of each magnetometer serves as the active sensing element, thereby eliminating the need for flux coupling circuits. The magnetometers are located approximately=3 cm above the outer dewar bottom. The SQUIDs are directly coupled to a highly simplified readout electronics using only five wires per channel; no helium temperature impedance matching circuits are required. Each channel can be independently inserted into or removed from the dewar. Using a novel compensation technique, the system white and 1-Hz flux density noise values are typically 5 fT/ square root Hz and 10 fT/ square root Hz, respectively, including the noise contribution of the in-house fabricated dewar (about 2 fT/ square root Hz at 100 Hz) and the magnetically shielded room (about 1 fT/ square root Hz at 100 Hz). In addition, it is shown that due to the large dynamic range and high slew rate of the sensors it is possible to electronically form a gradiometric configuration that can be exploited in order to improve the signal-to-noise ratio.         A modular low noise 7-channel SQUID-magnetometer    O. Dossel, B. David, M. Fuchs, W.H. Kullmann and K. Ludeke Summary: A modular low-noise seven-channel SQUID-magnetometer for biomagnetic measurements was developed. The DC-SQUIDs are prepared by thin film technology based on the materials NbN-MgO-NbN, and show a flux noise below 10 mu Phi /sub 0// square root Hz. The signal is picked up with first-order wire-wound gradiometers of 2-cm diameter and coupled to the SQUIDs by integrated coupling coils. Individual channels can be replaced from the system, and various gradiometers can be used giving a flexible modular system. The electronics are based on the flux-locked-loop method extended by a bias modulation technique to reduce 1/f noise. The overall system noise is below 20 fT/ square root Hz. Biomagnetic measurements on auditory evoked fields have been carried out.         Fabrication of microstrip transmission line by high-T/sub c/ superconducting materials    M. Morisue, J. Asahina, W. Lin, K. Yo and N. Komine Summary: High-T/sub c/ ceramic (YBCO) superconduction microstrip transmission lines have been fabricated on MgO and SrTiO/sub 3/ substrates by a sputtering technique and a screen printing method. Sputtering conditions for preparation of microstrip lines are described, and properties of the sputter-deposited films are discussed. The characteristic impedance of the microstrip line was measured by a digitizing oscilloscope to compare it with the specifications. A satisfactory agreement is obtained with theoretical results at both room and low temperatures. In order to investigate the properties of the fabricated microstrip transmission line, the propagation constants, mainly the attenuation and the phase constant, were measured for a sinusoidal wave with the frequencies from 10 MHz to 26.5 GHz, in comparison with those of Al microstrip line fabricated on the MgO substrate. The results show that the attenuation of YBCO transmission line at 4.2 K was about the order of 10/sup -2/ dB/cm, a limit of the experimental equipment, for the frequency up to 10 GHz.         Analysis of pulse propagation on high-T/sub c/ superconducting transmission lines    M. Morisue, S. Furusawa, J. Asahina and A. Kanasugi Summary: The propagation characteristics of high-T/sub c/ superconducting microstrip transmission lines are calculated from the viewpoint of interconnection technology. A detailed analysis was made to examine the attenuation and phase velocity of a pulse on a YBCO transmission line, taking into consideration of dielectric loss of the MgO substrate. The results of this analysis are compared with the measured propagation constants of YBCO strip line fabricated on a MgO substrate. It is shown that the effect of dielectric loss of a substrate to the attenuation of a microstrip line is dominant and cannot be neglected as long as a MgO substrate is used. How a pulse propagates on the superconducting transmission line and how the circuit parameters of transmission line affect the propagation characteristics of the line were investigated. Simulation results show that the high-T/sub c/ superconducting transmission lines are more promising for interconnections than the conventional transmission lines by virtue of their lower attenuation and less dispersion, even if a dielectric loss of a MgO substrate is taken into consideration.         HTSC inverted and conventional geometry microstrip resonator for UHF frequencies    M. Kuhn, M. Klinger, A. Baranyak and J.H. Hinken Summary: HTSC (high-temperature superconductor) planar resonators may be used to replace voluminous normal conductivity high-Q resonators by miniaturized ones at UHF frequencies (0.3-3 GHz). Therefore an inverted microstrip resonator has been investigated. Both electrodes of the resonator are made of epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, and one of them is structured into a meander-type stripline. The distance between stripline and ground plane is held by a 50- mu m-thick spacer foil which also carries the resonator feeding lines in conventional microstrip design. The small distance between both electrodes ensures that only a small amount of electrical energy is located in the LaAlO/sub 3/ substrates and that the effective dielectric loss factor is low. At 77 K and at a resonant frequency of 700 MHz the measured unloaded Q was 2800. During improving the structuring process and reoptimizing the resonator design, the unloaded Q of the conventional geometry microstrip resonator has been increased to Q/sub 0/=25000. The use of the inverted microstrip resonator design will improve the Q values beyond that.         Parallel plate resonator for accurate RF surface loss measurements    S.A. Reible and C.W. Wilker Summary: An unique resonator structure for measuring RF surface losses in superconductive materials has been developed, and an absolute accuracy of 20% verified by measurements on copper films. The test structure utilizes two unpatterned, rectangular substrates which are pressed together by a spring-pressure arrangement, providing for short measurement turnaround times and rapid assessment of the microwave quality of high-temperature superconducting films. The unbalanced, parallel-plate transmission line structure is capacitively coupled to a pair of input/output leads. With 1-in-long MgO substrates the fundamental resonance is at about 2 GHz. An rms accuracy of several percent has been confirmed by a series of measurement results obtained with this structure on high-quality, superconducting films.         Parametric mixing in a nonlinear TlCaBaCuO thin film resonator at microwave frequencies    J.H. Thompson, J.B. Beyer and J.E. Nordman Summary: The RF nonlinear behavior of a TlCaBaCuO thin film at 77 K is investigated. The film is patterned to form a disk with small annular perforations along the outer edge, and a dielectric resonator is used to couple to the structure. Thinning of the film with a bromine etch greatly enhances the reactive nonlinearity of the resonator structure. Scalar network analyzer measurements revealed sufficient nonlinearity to achieve parametric amplification at 7.2 GHz. The nonlinearity is tentatively attributed to RF-induced flux in the superconducting film.         Integration of semiconductor and ceramic superconductor devices for microwave applications    B.B.G. Klopman, H.W. Weijers, J. Gao, G.J. Gerritsma and H. Rogalla Summary: Due to the very-low-loss properties of ceramic superconductors, high-performance microwave resonators and filters can be realized. The fact that these devices may be operated at liquid nitrogen temperature facilitates integration with semiconductor devices. Examples are bandpass amplifiers, microwave-operated SQUIDs combined with GaAs preamplifiers, detectors, and MOSFET low-frequency amplifiers. The design of such circuits on a single 1-in alumina substrate using surface mount techniques is discussed. Data on circuits are presented.         Characteristics of the electrical response of YBCO films with different morphologies to optical irradiation    E.K. Track, L. Madhavrao, R. Patt, R.E. Drake and M. Radparvar Summary: YBCO films of varying thicknesses (200-3000 AA) and morphologies, have been fabricated, and their electrical response to optical radiation has been measured. A report on these measurements, emphasizing the dependence on temperature, light chopping frequency, and cryogenic environment is presented. The temperature dependence of the film resistance is determined in part by the film morphology. This morphology may be represented by a simple model consisting of a two-dimensional array of coupled grains. The magnitude of the bolometric response correlates with the sharpness of the superconducting transition. These measurements and observations lead to a proposed optimization scheme to maximize the low-temperature response and fully explore the potential for fast nonequilibrium detectors.         Optical response of highly oriented YBCO thin films    W. Eidelloth Summary: A thin-film transition edge bolometer was fabricated from laser ablated YBCO. The response to chopped 633-nm radiation was measured as a function of temperature, optical intensity, bias current, and signal frequency. At a chopping frequency of 1 Hz and a bias current of 100 mu A, the responsivity was 10 V/W and the noise power was 39 nW/ square root Hz. At low frequencies the device showed all the characteristics of a bolometer. At higher frequencies, however, an additional component of the photo response was found. The magnitude of this component scales roughly like f/sup -0.5/. This additional response is thought to be caused by optically induced depinning of vortices.         Low frequency 1/f noise measurements in YBa/sub 2/Cu/sub 3/O/sub 7/ thin films and the implications for HTS IR detectors    R.C. Lacoe, J.P. Hurrell, K. Springer, I.D. Raistrick, R. Hu, J.F. Burch and R.S. Simon Summary: The low-frequency noise voltage fluctuations were measured on c-axis textured films of YBa/sub 2/Cu/sub 3/O/sub 7/ on (100) SrTiO/sub 3/ and on mixed a- and c-axis textured thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ on (100) LaAlO/sub 3/. In all cases, the power spectral density S/sub v/(f) approximately V/sup 2//f/sup alpha /, where V is the average DC voltage across the film. Measurements on structures of different surface areas indicates S/sub v/(f) is inversely proportional to the film surface area. From room temperature to above the superconducting transition temperature, S/sub v/(f)/V/sup 2/ approximately T/sup 2/, while near the transition S/sub v/(f)/V/sup 2/ levels off before increasing sharply as the resistance goes to zero. The linear dependence of S/sub v//sup 1/2/(f) on the bias current suggests that the noise arises from resistance fluctuations. The resistance fluctuations are interpreted as arising from two different mechanisms; a weakly temperature-dependent contribution which is dominant above the superconducting transition, and a strongly temperature-dependent contribution which dominates at the transition. The implications of these measurements on the potential utility of high-temperature superconductor IR detectors is discussed.         Wide-band highspeed Nb and YBaCuO detectors    E.M. Gershenzon, M.E. Gershenzon, G.N. Gol'tsman, A.D. Semenov and A.V. Sergeev Summary: The physical limitations on the response time and the nature of nonequilibrium detection of radiation were investigated for Nb and YBCO film in a wide spectral range from millimeter to near-infrared wavelengths. In the case of ideal heat removal from the film, the detection mechanism is connected with an electron heating effect which is not selective over a wide spectral interval. For Nb, the dependence of the response time on the electron mean free path l and temperature T is tau varies as T/sup -2/l/sup -1/. The values of detectivity D* and tau are 3*10/sup 11/ W/sup -1/ Hz/sup 1/2/ cm and 5*10/sup -9/ s at T=1.6 K, respectively. For YBCO film the tau value of 1-2 ps at T=77 K was obtained; the NEP value of 3*10/sup -11/ W-Hz/sup -1/2/ can be obtained at T=77 K in the case of the optimal film matching to the radiation.         AC Josephson effect in high-T/sub c/ polycrystalline thin-film bridges    V.N. Gubankov, Y.Y. Divin, I.M. Kotelyanskii and V.B. Kravchenko Summary: The effect of millimeter-wave electromagnetic radiation on the I-V curves of superconducting bridges made from polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ films with a grain size of approximately 1 mu m and a critical current density of j/sub c/(4.2 K) approximately 10/sup 4/ A/cm/sup 2/ was investigated. When the bridge dimensions w*1 were decreased from 200*200 mu m/sup 2/ to 5*5 mu m/sup 2/, the effect of radiation at T<or=100 mu m) to vortex synchronization (20 mu m         Ultrafast superconductive switch    E.M. Gershenzon, G.N. Gol'tsman, A.L. Dzardanov and M.A. Zorin Summary: The transition from superconductive to resistive state caused by infrared radiation and bias current pulses was investigated in order to minimize switching time tau and driving power W. Experimental results for Nb microstrips confirm the correctness of calculations based on the model of electron heating. For Nb switches, tau measured directly is 0.3-0.8 ns for radiation pulses and 1-3 ns for bias current pulses at T=4.2 K, while for YBaCuO switches at T=77 K it is expected to be several picoseconds. For an YBaCuO sample with the dimensions of 5*2*0.15 mu m/sup 2/, W was 10 mW, and it can be further reduced to the order of several microwatts by decreasing the volume of the sample.         Experimental study of a dual-input-multiplexor gate    M. Hosoya, W. Hioe, E. Goto, R. Kamikawai, Y. Wada, N. Miyamoto and H. Nakane Summary: In order to solve the problems of old QFP (quantum flux parametron) logic and to improve the operating margin, a QFP logic uses various circuits including a flux regulator, activation/signal amplifiers, a variable activated QFP (VAQ), and a dual-input-multiplexer gate (D-gate). The detailed designs and experimental results of these circuits are discussed. New QFP logic adopts a novel QFP, which can transfer I/O signals between two stacked chips directly by its I/O transformer. The prototype model of three-dimensional circuits by this kind of QFP is described.         Subharmonic generators and error detection by using the quantum flux parametron (QFP)    J. Casas, R. Kamikawai, Y. Harada, N. Miyamoto, H. Nakane and E. Goto Summary: Several subharmonic generators are presented, the larger of which consists of four shift registers connected serially around a loop. Low-frequency operation was demonstrated for four different devices using one, two, three, and four shift registers, respectively. The circuits presented use a standing wave for powering the QFPs, guaranteeing that all the QFPs are perfectly synchronized and that no power is consumed in the clock lines. If all the QFPs along a clock line are to be power within 20% margin, the maximum operating frequency is limited by the clock lines' length. Concerning the high-speed operation, a frequency divide-by-two circuit was able to work at a clock frequency of 8 GHz. For checking that no error occurs during the operation of the QFPs, a four-bit shift register was used. The latter device was able to work at frequencies up to 3.1 GHz, and all of the four-bit patterns were stored during experimental times of the order of one hour without observing the occurrence of an error. Thus, about 10/sup 14/ error free operations per QFP were demonstrated.         A Josephson systolic array processor for multiplication/addition operations    M. Morisue, F.-q. Li, M. Tobita and S. Kaneko Summary: A novel Josephson systolic array processor to perform multiplication/addition operations is proposed. The proposed systolic array processor consists of a set of three kinds of interconnected cells in which the main circuits are made by using SQUID gates. A multiplication of 2 b*2 b is performed in the single cell at a time, and an addition of three data with two bits is simultaneously performed in an another type of cell. Furthermore, information in this system flows between cells in a pipeline fashion so that a high performance can be achieved. The principle of Josephson systolic array processor is described in detail, and the simulation results are illustrated for the multiplication/addition of (4 b*4 b+8 b). The results show that these operations can be executed in 330 ps.         A fuzzy processor using Josephson junctions    M. Morisue, N. Ishii and A. Kanasugi Summary: A novel Josephson fuzzy processor using SQUID gates is proposed, and the simulation results are illustrated to show how a high-performance fuzzy processor can be realized by taking into consideration of advantages of Josephson devices. The features of the proposed processor are very simple construction, very high-speed operation, and ultra-low power dissipation. The principles of constructing a fuzzy processor using SQUIDs are described in detail, and the simulation results for the essential circuit of the fuzzy processor (which is composed of more than one hundred SQUIDs) are illustrated. These results show that Josephson fuzzy processor with four rules and sixteen input levels can perform the function in less than 1.3 ns, and can perform the fuzzy inferences 0.79*10/sup 9/ times per second.         Artificial neural network circuits with Josephson devices    Y. Harada and E. Goto Summary: A novel approach to Josephson devices for computer applications is described. With an artificial neural network scheme, Josephson devices will be expected to develop a new paradigm for future computer systems. Circuit configurations for a neuron with Josephson devices are described. A combination of a variable bias source and Josephson devices is proposed for a synapse circuit. The bias source signal is steered by the Josephson device input signal and becomes the synapse output signal. These output signals are summed up at the specific resistor or inductor to produce the weighted sum of Josephson devices input signals. According to the error signal, the bias source value is corrected. This corresponds to the learning procedure. Because Josephson devices are threshold logic circuits themselves, they are used as soma circuits. The cell structure of the artificial neural network is discussed.         Design of fast Josephson arithmetic circuits    A. de Lustrac, P. Crozat and R. Adde Summary: A Josephson 2-b full adder and a 4-b parallel multiplier are designed using an advanced design with speed optimization of functional direct coupled logic. Wide margins EXOR, majority 2/3, and delay gates implemented with picosecond junctions (R/sub C/C=2 ps) are presented and their performances are analyzed. The adder consists of 10 gates with 90 Josephson junctions and dissipates 30 mu W. The propagation time along the critical path is 10 ps/b near threshold bias. It rises only at 20 ps/b in the adder at 80% of the maximum bias. The multiplier consists of 60 gates and dissipates 180 mu W. The propagation times along the critical path near threshold bias, and at 80% of maximum bias are respectively 60 ps/b and 100 ps/b.         Design and simulation of a fast Josephson junction on-chip gated clock for frequency and time analysis    R.C. Ruby Summary: As the sophistication and speed of digital communication systems increase, there is a corresponding demand for more sophisticated and faster measurement instruments. One such instrument on the market is the HP 5371A frequency and time interval analyzer (FTIA). This instrument is analogous to a conventional oscilloscope. Whereas the oscilloscope measures waveform amplitudes as a function of time, the FTIA measures phase, frequency, or timing events as function of time. These applications are useful in such areas as spread-spectrum radar, chirp filter designs, disk-head evaluation, and timing jitter analysis. The on-chip clock designed for this application uses a single Josephson junction as the clock and a resonator circuit to fix the frequency. A zero-crossing detector is used to start and stop the clock. A SFQ counter is used to count the pulses generated by the clock and a reset circuit is used to reset the clock. Extensive simulations and modeling have been done based on measured values obtained from an Nb-Al/sub 2/O/sub 3/-Al-Nb process.         A buffered nondestructive-readout Josephson memory cell with three gates    P.-F. Yuh Summary: The design and testing of a nondestructive readout memory cell with buffer gates to eliminate the half-select problem and to increase the operating margins are described. A 50 mu m*52 mu m cell has been fabricated using a Nb-AlO/sub x/-Nb process with 2.5 mu m line width and 3.75 mu m junction size. The measured margins for data, read-enable, and sense lines are +or-27%, +or-17%, and +or-48%, respectively. Variations of this buffer-gate memory design are also discussed.         Computer simulations of a 20 gigasample/second, 500 MHz eight-bit, analog-to-digital converter    G.T. Mallick Jr. Summary: The computer simulation of a realistic, manufacturable superconducting flash analog-to-digital converter which is predicted to operate with an effective accuracy of 7.36 b on a 500-MHz sine wave at a 20-GHz sampling rate is described. At 1 GHz the accuracy degrades to 6.48-b. This circuit is an attractive way to approach a fast, superconducting 8-b flash analog-to-digital converter, as it is simpler and offers better performance than competitive designs.         Superconducting A/D converters based on Josephson binary counters    F. Kuo Summary: A/D converters (ADC) based on Josephson binary counters are demonstrated in all-Nb technology. These A/D converters use a single SQUID as the flux quantizer front-end with a minimum quantization level equivalent to 2 mu A of input current. A 10-b unidirectional ADC and a 5-b tracking ADC are reported. Both circuits have been tested at 1 MS/s sampling rate with very low power consumption. They also exhibit good linearity within the full dynamic range tested.         A high performance Josephson binary counter implemented in Nb and NbN technology    S.R. Whiteley and F. Kuo Summary: A Josephson binary counter with nondestructive readout has been implemented and tested in both niobium and niobium nitride technology. Successful operation of the Nb version has been observed. The design incorporates an additional tapered-edge SiO/sub 2/ level in the Nb processing sequence, which increases interferometer inductance, decreases capacitance, and ensures that geometric resonances are as high in frequency as possible. This level has the added advantage of providing mask compatibility with the NbN process, as this level is skipped in the NbN flow, thereby compensating in part for the larger penetration depth of NbN. The counter cell is designed to be as compact as possible to minimize stray inductance and maximize top count rate and high count rate bias margins. A novel readout SQUID coupling layout that allows low read SQUID inductance and requires no holes in the groundplane is used. Coupling to the adjacent count SQUID is provided by a common control line level metallization, which directs count SQUID flux through the read SQUID loop. Nb versions of the circuit functioned as expected, but low device yield limited the longest chain of functioning stages to five. The NbN circuits did not function due to higher than predicted inductance values.         A multi-gigahertz, Josephson flash A/D converter with a pipelined encoder using large-dynamic-range current-latch comparators    E.S. Fang, D. Hebert and T. Van Duzer Summary: The design of a multigigahertz 4-b A/D converter with a pipelined encoder is presented. A wideband and large dynamic range comparator serves as basic building block for both the quantizer and the encoder, which simplifies the design. The design of the comparator and the building of the quantizer and the encoder with the comparator circuits are discussed. Simulation and initial test results are presented, and the possibility of adapting the design to high-T/sub c/ circuit is discussed.         Quasi-one junction SQUIDs as comparators for analog-to-digital conversion    P. Bradley Summary: Comparators based on single junction superconducting quantum interference devices (SQUIDs) have been fabricated and tested. These comparators demonstrate the periodic behavior of multiple junction SQUIDs without the disturbances due to flux mode boundary crossings, promising higher speed. The proper functioning of all components of a full analog-to-digital converter, including the quasi-one-junction-SQUID (QOJS) and the sampling circuit to measure its output, is demonstrated. The only problem observed is that the magnitude of the pulse in the Josephson sampler is too small to measure the full output of the QOJS. This has recently been corrected. Simulations indicate that 4 b of resolution at 10 GHz input bandwidth, or higher resolution at lower bandwidths, should be achievable.         Josephson 32-bit shift register    P.-F. Yuh, C.-T. Yao and P. Bradley Summary: A 32-b shift register designed by edge-triggered gates was tested with +or-25% bias margin and +or-81% input margin for the full array. Simulations showed +or-55% bias margin at 3.3 GHz and worked up to a maximum frequency of 30 GHz with a junction current density of 2000 A/cm/sup 2/, although the shift register has only been tested up to 500 MHz, limited by instrumentation. This edge-triggered gate, consisting of a pair of conventional Josephson logic gates in series, has the advantages of wide margins, short reset time, and insensitivity to global parameter variations.         Josephson junctions in SPICE3    S.R. Whiteley Summary: SPICE3 is the most recent version of the circuit simulator SPICE from the University of California, Berkeley. Unlike its predecessors, SPICE3 is written in the C programming language, and is designed for interactive use under a modern multitasking operating system. The Berkeley distribution of SPICE3 lacks support for Josephson junctions. As a consequence, the author has developed a customized version of SPICE3b.1 which incorporates a Josephson junction model. The model supports control current modulation, as well as fifth-order polynomial description of the quasiparticle current suitable for NbN junctions. In addition, a margin analysis command has been added, allowing operating ranges to be determined for an arbitrary circuit with a minimum of simulation. Further enhancements include the addition of a second graphics post-processor with new features and display, as well as debugging and streamlining of the original code. The program is currently configured to run on an IBM/Intel 386 compatible computer with Weitek coprocessor, under DOS extender software. The modifications to SPICE3 are described, and some of the issues involved in simulating Josephson circuits are also addressed. The features and philosophy of the SPICE3 program are discussed, and sample results presented.         A new simulator for Josephson circuits with lossy transmission lines    M. Morisue, S. Hayashi, A. Kanasugi and T. Van Duzer Summary: A network simulator for Josephson circuits is described, and its performance is compared with SPICE. The proposed simulator can simulate large-scale networks containing either lossy or lossless transmission lines and nonlinear lumped elements such as Josephson junctions. The transmission line treatment is completely general, but with constant distributed parameters, and all lumped elements may be nonlinear. Attention is focused on the simulation of the transmission lines; the technique for this simulation is based on the linearity of the elements of the transmission line. The propagating waves are divided into short pulses represented by the sum of two step functions delayed with respect to each other. The equations for the treatment of the transmission lines are given, and some example simulations are presented. Emphasis is placed on evaluation of the simulator in comparison with SPICE. It is shown that for circuits with long lossy transmission lines the simulator can be appreciably faster than SPICE, in which the lines would have to be represented by a cascade of lumped elements.         Design of a hysteretic SQUID as the readout for a DC SQUID    M. Gershenson Summary: A novel design is presented for all optimal hysteretic SQUID readout circuit for a DC SQUID, thus eliminating the need for bulky output transformers or resonance matching circuits. The hysteretic readout system, which is based in part on standard sampling theory, is compared to another similar system and shown to be superior in terms of slew rate and immunity to electromagnetic interference. The circuit should be useful in optimizing the performance of biomagnetic systems.         Abrikosov vortex memory based on a single vortex    Q. Li and D.K. Finnemore Summary: An Abrikosov vortex memory device based on a cross strip superconducting-insulating-normal-superconducting (SINS) Josephson junction was developed to investigate the feasibility of using the motion of a single vortex to store information and perform logic. The write operation is performed by moving a single vortex from one pinning site to another using a current in one leg of the cross strip junction. The read operation is performed by measuring the Josephson voltage at a fixed bias Josephson current. For these PbBi-Al/sub 2/O/sub 3/-Al-Pb SINS junctions, the Josephson voltage depends on the vortex position because the vortex distorts the Fraunhofer diffraction pattern in a predictable way. The device is superior to earlier superconductor-normal-superconductor (SNS) devices in that the junction voltages are millivolts and can be read with rather simple electronics.         Design considerations for DC SQUIDs fabricated in deep sub-micron technology    M.B. Ketchen Summary: Practical SQUIDs with well-coupled input coils of usable inductance have generally been fabricated at the 2-5 mu m level of lithography. Other technologies, silicon in particular, are now routinely practised at the 0.5 mu m level of lithography with impressive demonstrations at the 0.1-0.25 mu m level not uncommon. The implications of applying such a fabrication capability to advance DC SQUID technology are explored. In particular, the issues of scaling practical DC SQUIDs down to the 0.1-0.25 mu m regime are examined, using as a prototype design the basic washer SQUID with a spiral input coil. A technical path is mapped out that leads to a practical SQUID less than 0.05 mm/sup 2/ in area with a tightly coupled 2- mu H input coil, user-friendly voltage-flux characteristics, minimal flux creep related hysteresis, and coupled energy sensitivity approaching the quantum limit at 4.2 K.         Systematic studies of the effect of a bandpass filter on a Josephson-junction noise thermometer    R.J. Soulen Jr., W.E. Fogle and J.H. Colwell Summary: Measurements of the effect of a bandpass filter on the noise of an R-SQUID were made. Comparison of the data with a model for the effect indicates good agreement to within the measurement imprecision, although the fitted parameters show some discrepancies. The observed discrepancies influence the temperatures derived from the data by less than 0.1%. Additional studies indicate that the observed noise spectrum is white and uncontaminated to the level of 0.1% by extraneous noise. Finally, the reproducibility of repeated measurements of the noise within an experimental run is at least 0.1%, while the reproducibility between runs, as judged by superconducting fixed points and a /sup 3/He melting curve thermometer, are no worse than 0.3%. It is concluded that an R-SQUID noise thermometer is capable of producing a temperature scale from 6.3 mK to 520 mK which is accurate to 0.1%.         A series array of DC SQUIDs    R.P. Welty and J.M. Martinis Summary: A series array of 100 DC SQUIDs has been fabricated using trilayer Nb-AlO/sub x/-Nb junctions. The SQUIDs are modulated with a common flux bias line and produce an output voltage swing of several millivolts across the array. The large output voltage will allow direct connection to room temperature electronics without the transformer coupling and resulting frequency limitations commonly associated with DC SQUID amplifiers. A bandwidth of DC to at least 175 MHz for a 100-SQUID array has been measured. The series array will be used as the output stage for a multistage integrated SQUID amplifier.         Design and optimization of DC SQUIDs fabricated using a simplified four-level process    R. Cantor, T. Ryhanen, D. Drung, H. Koch and H. Seppa Summary: An optimization procedure is presented which is used to design two types of ultralow-noise DC superconducting quantum interference devices (SQUIDs) with integrated flux coupling circuits, a magnetometer, and a gradiometer. Essential to this design approach is the reduction of the parasitic capacitance, the choice of a layout which moves the input coil resonances well away from the desired operating frequency of the SQUID, and the proper damping of these resonances. It is shown that both the microwave and LC resonances can be damped in a nearly noise-free manner by placing all RC shunt in parallel with the input coil. This leads to smooth voltage-flux modulation characteristics and significantly improved noise performance. A simple, four-level Nb-Si/sub x/N/sub y/-Nb Josephson junction technology for device fabrication is described. White flux noise levels of 5*10/sup -7/ Phi /sub 0// square root Hz for the magnetometer and 7.9*10/sup -7/ Phi /sub 0// square root Hz for the gradiometer were measured. The corresponding uncoupled energy resolutions are 100 h and 130 h, respectively. The 1/f noise of the magnetometer at 1 Hz is less than 4*10/sup -6/ Phi /sub 0// square root Hz.         High-T/sub c/ superconductive delay line structures, and signal conditioning networks    W.G. Lyons, R.S. Withers, J.M. Hamm, A.C. Anderson, P.M. Mankiewich, M.L. O'Malley and R.E. Howard Summary: The design and fabrication of high-T/sub c/ chirp-response tapped delay line filters are discussed. The key components in this development were long delay lines with more than 10 ns of delay, impedance transformers, and backward-wave couplers. All of the typical transmission line geometries were examined, including microstrip, coplanar and stripline. Designs were developed using microwave CAD routines and superconducting niobium delay line prototypes. Tapped delay line chirp filters with up to 12 ns of total delay have been successfully fabricated in YBaCuO.         Fabrication and characterization of YBCO microstrip delay lines    E.K. Track, G.K.G. Hohenwarter, L.R. Madhavrao, R. Patt, R.E. Drake and M. Radparvar Summary: Microstrip delay lines with YBCO films as the material for the strip and polished bulk copper for the ground plane have been fabricated and characterized. The film-carrying LaAlO/sub 3/ substrate is flipped over the copper ground plane and separated from it by a polyimide laminate that acts as the microstrip dielectric. Linewidths are varied from 100 to 600 mu m, total length from 10 to 65 cm. Two winding shapes, concentric circular and serpentine, are evaluated. For a total geometric length of 60 cm, time domain reflectometry measured delay of 5 ns is obtained with a line impedance of 50 Omega . These delay lines require an area of high-quality YBCO films of 1 in/sup 2/. The directly measured transmission loss (S/sub 21/) up to 10 GHz is ten times lower at 77 K than for identical lines made with gold films and comparable at 4.2 K to the loss of identical lines made with niobium films. The design constraints, fabrication, and properties of these lines and the issues involved in obtaining longer delays are discussed.         An experimental study of high T/sub c/ superconducting microstrip transmission lines at 35 GHz and the effect of film morphology    C.M. Chorey, K.B. Bhasin, J.D. Warner, J.Y. Josefowicz, D.B. Rensch and C.W. Nieh Summary: Microstrip transmission lines in the form of ring resonators have been fabricated from a number of in-situ grown laser-ablated films and postannealed cosputtered YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films. The properties of these resonators have been measured at 35 GHz, and the observed performance is examined in light of the critical temperature (T/sub c/), film thickness, and the film morphology, which is different for the two deposition techniques. It is found that T/sub c/ is a major indicator of the film performance for each growth type, with film thickness becoming important as it decreases towards 1000 AA. It is also found that the films with a mixed grain orientation (both a-axis and c-axis oriented grains) have poorer microwave properties as compared with the primarily c axis oriented material. It is speculated that this is due to the significant number of grain boundaries between the different crystallites, which may act as superconducting weak links and contribute to the surface resistance.         A superconducting hydrogen maser resonator made from electrophoretic YBa/sub 2/Cu/sub 3/O/sub 7- delta /    D. Opie, H. Schone, M. Hein, G. Muller, H. Piel, D. Wehler, V. Folen and S. Wolf Summary: The construction and test of three loop-gap resonators which are being prepared for the high-temperature superconductor space experiment (HTSSE) are discussed. The loop-gap electrodes are the lossiest parts of such a resonator. In a first step these electrodes, with a surface of 150 cm/sup 2/, were covered with YBCO. The Q values of the resonators at 77 K ranged between 2.3*10/sup 4/ and 3.1*10/sup 4/ and exceed the minimum requirement for a later maser application. They correspond to a surface resistance between 0.7 and 1.4 m Omega , which is a factor of three to five below the equivalent value of copper. The cavities can be excited in a higher-order mode (HOM) at 4.3 GHz with a field distribution that is still sensitive to the superconducting electrodes. Thus, the experimental requirements for the HTSSE project can be fulfilled.         Microwave resonators incorporating ceramic YBaCuO helices    A. Porch, M.J. Lancaster, T.S.M. Maclean, C.E. Gough and N.M. Alford Summary: Measurements of the unloaded Q-factors of resonators incorporating YBaCuO helices are presented as a function of temperature. All of the bulk helices give unloaded Qs higher at 77 K for frequencies less than 1 GHz than equivalent wholly Cu structures. Approximate microwave modeling of the resonator gives surface resistances around 1 m Omega at 77 K and 500 MHz. Initial measurements on thick-film YBaCuO helices give Q values significantly lower than the bulk, probably due to dielectric loss in the zirconia substrate. The enhancement in Q over similar Cu resonators make these devices useful for demonstration purposes. For practical applications, however, it is unlikely that the improvement observed will affect the status of low-noise microwave oscillators and filters.         Thick film YBCO microstrip resonators    R. Mossavati, J.C. Gallop, T. Button and N.M. Alford Summary: It is concluded from preliminary experiments that thick-film YBCO resonant circuits have superior characteristics to identical copper circuits operated at 77 K up to at least 12 GHz, and therefore appear to have useful potential for microwave applications. Further, the simplicity of the stripline resonator technique presents possibilities for use in material characterization. The method complements the microwave cavity perturbation technique in that the high-temperature superconducting (HTS) surface which is sampled is primarily the one in contact with the substrate.         DC-SQUID sensor system for multichannel neuromagnetometry    E.P. Houwman, D. Veldhuis, J. Flokstra, H.J.M. Ter Brake, W. Jaszczuk, A. Martinez and H. Rogalla Summary: Various DC SQUID sensor configurations were developed for use in a 19-channel neuromagnetometer. Apart from the standard type, resistively and inductively shunted SQUIDs were made, allowing for a large screening factor beta (>1). In this way, signal coupling from the pickup coil to the SQUID is facilitated and can be decreased. The number of turns of the input coil is decreased further by allowing for an inductance mismatch in the input circuit. Although theoretically both measures give rise to an increased field noise of the sensor, they may lead to a reduction of the excess noise and the noise balance may become positive.         28-channel hybrid system for neuromagnetic measurements    V. Foglietti, C. Del Gratta, A. Pasquarelli, V. Pizzella, G. Torrioli, G.L. Romani, W.J. Gallagher, M.B. Ketchen, A.W. Kleinsasser and R.L. Sandstrom Summary: Progress toward the development of a 28-multichannel system for neuromagnetic measurements is described. A novel hybrid design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimize the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the center of the array and features a localization power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnitude measurements over a circular scalp region of 16-cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low-cost electronic system has been designed and fabricated for the DC SQUID sensors, consisting of a compact head mounted on top of the cryogenic probe and a control unit where all the DC remote controls are performed. The dynamic range of 10/sup 7/ square root Hz and the bandwidth of 50 kHz are specifically designed to work in multichannel DC SQUID instrumentation.         High sensitive magnetometers and gradiometers based on DC SQUIDs with flux focuser    A.N. Matlashov, V.P. Koshelets, P.V. Kalashnikov, Y.E. Zhuravlev, V.Y. Slobodchikov, S.A. Kovtonyuk and L.V. Filippenko Summary: Highly sensitive DC SQUID magnetometers and gradiometers with flux focusers instead of traditional coupling coils were designed and experimentally tested. All refractory material DC SQUIDs with shunted Nb-AlO/sub x/-Nb tunnel junctions were used. The outer dimension of the square washer electrode was 2.5 mm and the inner 70 mu m. A wide superconducting washer concentrates the magnetic flux by twenty times, and a flux sensitivity of about 20 nT/ Phi /sub 0/ can be realized without any input coil. The application of the additional 14-mm diameter flux focuser has increased the flux concentration by four times. As a result, a magnetic field resolution of 10 fT/ square root Hz has been achieved; this figure corresponds to the flux resolution about 2*10/sup -6/ Phi /sub 0// square root Hz. Connecting the additional flux focuser to the compensation coils, one can create gradiometers of both the first and higher orders. The flux concentration coefficients were calculated for the several possible mutual positions of the SQUID washer and the focuser. The influence of the two focusers on each other was calculated. The experimental test makes it possible to get the correct relation between the effective area of the SQUID with a focuser and the outer sizes of the focuser. The first-order gradiometer, consisting of the rectangular focuser and compensation coil connected to it, has been experimentally verified. The results demonstrate that sensitivity of the magnetometers and gradiometers with flux focuses are very attractive for multichannel biomagnetic systems and for high-temperature SQUID magnetometers.         High-gain DC SQUID magnetometers with NbN nanobridges    A. Irie, K. Hamasaki, T. Yamashita, T. Matsui and B. Komiyama Summary: High-gain DC SQUIDs using NbN nanobridges have been fabricated for magnetometers with high sensitivity, and their device parameters and intrinsic energy sensitivity have been evaluated. The slit inductance of the square washer SQUID was reduced by using the coplanar edge structure of the low inductance. The junction capacitance is typically 15 approximately 40 fF. The maximum voltage modulation is about 110 mu V for the NbN nanobridge SQUID with an inductance of 0.18 nH. The maximum value of the transfer function mod delta V/ delta Phi mod was approximately 1 mV/ Phi /sub 0/, without matching circuit. The minimum intrinsic energy sensitivity is about 20 h at 50 kHz. The SQUID was operated in a usual flux-locked loop. The flux noise spectrum for a DC SQUID at 4.2 K in a superconducting Nb shield was 4*10/sup -5/ Phi /sub 0/ mod square root Hz at 3 kHz and one order larger than the intrinsic flux noise. The critical current and mod delta V/ delta Phi mod of these SQUIDs show no change after repeated thermal recycling and storage over 250 days.         Pulsed operation of a superconductive electromagnetic gradiometer    P.V. Czipott and W.N. Podney Summary: An electromagnetic gradiometer (EMG) combines a superconducting quantum interference device (SQUID) gradiometer with an active magnetic source for use as an ultrasensitive metal detector. A report on performance tests of an EMG configuration using a pulsed source is presented. Eddy currents persist in metallic targets between pulses and thus make them visible to the receiver. Because the receiver only looks between pulses, when the source is off, it is immune to noise from source interference. Performance tests validate an analytical model that predicts a detection range of 20 m to a target 25 cm in radius for a prototype pulsed EMG producing pulses 10-ms long separated by 10-ms intervals, with a peak moment of 2*10/sup 4/ A-m/sup 2/.         Performance of a double DC SQUID magnetometer    J. Casas, N. Miyamoto, H. Nakane and E. Goto Summary: A magnetic flux sensing device that is made by using two DC SQUIDs is presented. The DC SQUIDs are of familiar characteristics, magnetically coupled by a common coil, and are turned into the voltage state by a single DC current source. As the DC SQUIDs are magnetically coupled, the magnetic flux noise generated by one of the DC SQUIDs is sensed by the other and vice versa. By making a differential measurement across both DC SQUIDs, the magnetic flux noise detected by the DC SQUIDs can be added either constructively or destructively. This means that magnetic flux noise cancellation is possible, as demonstrated experimentally. The double DC SQUID configuration can also be used in the add flux noise mode, in which there is no loss of performance when compared with what is possible to obtain with a single DC SQUID. Another advantage of the two DC SQUID configuration is that the output impedance is twice as large as that of the DC SQUID with Josephson junctions of the same critical current and shunting resistance. In the former configuration, the matching to room temperature electronics is simplified.         Integrated magnetometer with a digital output    H. Matz, D. Drung, E. Crocoll, R. Herwig, E. Kramer, M. Neuhaus and W. Jutzi Summary: A magnetometer with a 50-mm/sup 2/ pickup coil, a sensor SQUID, a flux transformer, and a 1-b A/D converter were integrated on a single 6*12 mm/sup 2/ silicon chip in the Nb-Nb/sub x/O/sub y/-PbInAu technology. The pickup coil has a single turn with a 25- mu m-wide Nb strip. Operated in a flux-locked loop and at a clock frequency of 18.4 MHz, the achieved flux noise and magnetic field sensitivity are 3.5 mu Phi /sub 0// square root Hz and 8.5 fT/ square root Hz at 1.5 Hz. With a digital feedback of constant step size a maximum slew rate of 11500 Phi /sub 0//s was measured. Below the maximum slew rate the linearity between input and output was investigated.         A planar gradiometer based on a microwave RF-SQUID    M. Muck, D. Diehl and C. Heiden Summary: A type of gradiometer, working on the basis of a planar microwave RF SQUID, is described. In this type of RF SQUID, a superconducting half-wavelength stripline resonator serves as tank circuit, into which the SQUID is integrated. If a gradiometer configuration is used for the SQUID (i.e. two loops), a certain asymmetry of the stripline resonator should be provided to ensure sufficient coupling between gradiometer and resonator. Gradiometers were prepared from thin niobium films on sapphire substrates, having either microbridges or tunnel junctions as Josephson elements. When operated in hysteretic mode, modulation voltages of about 100 mu V were measured for both microbridge and tunnel junction SQUIDs.         A three channel SQUID-system using a multiplexed readout    M. Muck Summary: Conventional multichannel SQUID systems require a number of wires connecting the individual SQUIDs and feedback coils to room-temperature electronics. In order to reduce the heat transport by these wires and avoid the accompanied increased helium losses, the possibility of using a multiplexed readout requiring only a fraction of feed lines than needed by conventional systems was studied. RF SQUIDs were used in the experiments to avoid additional wires for DC bias currents. A bias frequency of 100 MHz was chosen to achieve a sufficiently low flux noise. The influence of modulation frequency and multiplexing frequency on the stability of the flux-locked loop and on the slew rate of the system was studied. Careful optimization of these parameters can lead to a multichannel system which requires only one coaxial cable between room-temperature electronics and all SQUIDs.         A double DC-SQUID device for flux locked loop operation    V. Foglietti, M.E. Giannini and G. Petrocco Summary: A novel double DC SQUID device has been developed. It consists of two SQUIDs in a cascade configuration with the same electrical parameters but with a different geometry. This structure makes the device particularly suitable for flux-locked-loop operation without need for modulation flux. Consequently the readout electronic scheme is greatly simplified without degrading the noise performance of the first stage. The first DC SQUID has a gradiometer configuration with extra damping resistors shunting the inductance. The technology used is similar to the seven-layer IBM process with planar Nb-Nb/sub 2/O/sub 5/-PbAuIn junctions and 2.5- mu m minimum size lithography.         Design of a flux buffer based on the flux shuttle    M. Gershenson Summary: The design considerations for a flux buffer based on the flux shuttle concept are discussed. Particular attention is given to the issues of flux popping, stability of operation, and saturation levels for a large input. Modulation techniques used in order to minimize 1/f noise, in addition to offsets, are analyzed. Advantages over conventional approaches using a SQUID for a flux buffer are discussed. Results of computer simulations are presented.         Ultra low noise all niobium DC-SQUIDs    G.M. Daalmans, L. Bar, F.R. Bommel, R. Kress and D. Uhl Summary: The noise and signal properties of SQUIDs with amorphous silicon barriers and Al/sub 2/O/sub 3/ barriers are studied. The barrier material is found to be of great importance for the value of the 1/f noise component. The best results were obtained for SQUIDs with Al/sub 2/O/sub 3/ barriers and a 1/f noise level at 1 Hz of about 1*10/sup -6/ Phi / square root Hz was found. After integration of coupling coils onto the SQUIDs, a signal limitation and a dramatic increase of the noise were found. Implementation of a damping circuitry over the coupling coil results in optimized signals ( Delta V( Phi /sub 0//2) approximately=I/sub c/R) and a white noise level comparable to the white noise level without a coupling coil. The 1/f noise component for SQUIDs with a damped coupling coil is higher than for 1/f noise component of SQUIDs without a coupling coil. For SQUIDs with Al/sub 2/O/sub 3/ barriers, the 1/f noise level keeps below 3*10/sup -6/ Phi /sub 0// square root Hz at 1 Hz. For SQUIDs with an amorphous silicon barrier the 1/f noise component changes per cooling cycle in an irregular way. The stability for thermal cycling and room-temperature storage is very good for all the devices.         Integrated DC SQUID magnetometer with high dV/dB    D. Drung, R. Cantor, M. Peters, T. Ryhanen and H. Koch Summary: A directly coupled DC SQUID magnetometer with very simple feedback electronics is presented. The magnetometer has been integrated on a 7.2*7.2 mm/sup 2/ chip and fabricated using a four-level Nb/Si/sub x/N/sub y//Nb process. Eight pickup loops are connected in parallel to directly form the SQUID inductance of about 0.4 nH which leads to a high sensitivity B/ Phi =0.47 nT/ Phi /sub 0/. An additional positive feedback (APF) circuit on the magnetometer chip has been used to increase the gradient of the V- Phi characteristic to dV/d Phi approximately=300 mu V/ Phi /sub 0/ at the SQUID operating point. The resulting gradient of the transfer function dV/dB approximately=640 mu V/nT makes it possible to directly readout the SQUID without helium-temperature impedance matching circuits or flux modulation techniques. Using a highly simplified feedback electronics consisting of an ultra-low-noise bipolar preamplifier and an integrator on a 10-cm/sup 2/ PC board, a white noise level below 3 fT/ square root Hz with a 1/f corner frequency around 3 Hz, a 3-dB bandwidth of about 40 kHz, and a maximum feedback range of +or-32 nT for frequencies up to 300 Hz have been measured.         Low noise DC SQUIDs fabricated in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology    M.B. Ketchen, M. Bhushan, S.B. Kaplan and W.J. Gallagher Summary: The authors have designed, fabricated and tested all-refractory DC SQUIDs in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology that have noise performance comparable to the best previously reported for any technology. A variety of SQUID designs were incorporated as part of a trilayer process development test vehicle. SQUID inductance, junction area, and resistive shunt geometry were varied in matrix fashion to give SQUIDs with near-optimum parameter values for a factor of five range in Josephson current density and shunt sheet resistance. The devices were fabricated using a selective niobium anodization with a minimum feature size of 2 mu m. The base electrode and Nb wiring were patterned with dry etching, and the junction areas were defined by anodization: the Ti resistors were patterned with a lift-off process. Current density on different wafers was varied from 400 to 1000 A/cm/sup 2/ with typical junction V/sub m/'s of 60 mV. The shunt sheet resistance was varied in the 1-5- Omega / Square Operator range. The noise was measured with an RF SQUID direct small-signal readout scheme. A 50-pH SQUID with 3- mu m/sup 2/, 16- mu A junctions and 14- Omega shunt resistors was shown to have an ideally low white noise of 1*10/sup -13/ Phi /sub 0//sup 2//Hz, a white to 1/f crossover frequency at 7 Hz, and a noise level less than 6*10/sup -12/ Phi /sub 0//sup 2//Hz at 0.1 Hz.         Detection of trapped flux quanta in superconductors by a hydrodynamically controlled SQUID pick-up coil    H. Minami, Q. Geng, K. Chihara, J. Yuyama, H. Nakane, N. Miyamoto and E. Goto Summary: The detection of the flux quanta trapped in a large area superconductor by scanning a SQUID pickup coil is discussed. For this purpose a gas floating technique has been developed. In this technique, the supplied gas flow supports the coil while the coil scans the superconductor surface in liquid helium. The applicability of the gas floating technique is examined, and it is shown that this technique can be utilized even in liquid nitrogen or liquid helium. Measurements of magnetic field distribution over several superconductors in liquid helium are reported. By scanning the pickup coil over the superconductor, changes in the magnetic field, which come from the flux trapped in the superconductor, are observed. Furthermore, the background variation during sample rotation and displacement is reduced to about 2.4 Phi /sub 0/. The minimum detectable flux is shown to be less than Phi /sub 0/. These results show the possibility of using this technique in the detection of trapped flux quanta in superconductors.         Effect of parasitic capacitance on DC SQUID performance    T. Ryhanen, R. Cantor, D. Drung, H. Koch and H. Seppa Summary: The effect of parasitic capacitance C/sub p/ on DC SQUID characteristics and noise performance has been studied using a test structure consisting of 11 identical SQUID washers with Nb films of various widths covering the slit. The measured I-V characteristics are in good agreement with simulations based on a simple lumped circuit model. The energy resolution in seems to scale roughly according to in approximately= gamma /sub k/B/sup T/ square root L(C=2C/sub p/), where gamma is a dimensionless constant, k/sub B/ is the Boltzmann constant, T is the temperature, C is the junction capacitance, and L is the inductance.         DC SQUID small signal analysis    K.R. Carroll Summary: A small signal analysis for the DC SQUID (superconducting quantum interference device) is presented. This analysis involves the linearization of the SQUID equations for a given flux and current bias. Considering the SQUID to be a two-port device, an impedance matrix can be determined for a SQUID coupled to a general input circuit. The two intrinsic noise sources referred to the input are computed. One advantage of this analysis over other models of the DC SQUID is that an analytic expression can be determined for the cross-correlation power spectral density of the noise sources. These results should be useful in determining the signal-to-noise ratio of low-noise SQUIDs for a given application. Other differences and similarities of the small signal analysis to other DC SQUID models are discussed.         Trapped vortices in a superconducting microbridge    G.S. Park, C.E. Cunningham, B. Cabrera and M.E. Huber Summary: Laser light pulsed onto a Nb microbridge drives it momentarily normal and changes the quantum flux state of a superconducting inductive loop. The flux state is measured by a SQUID coupled to the loop. With a Nd:YAG laser, vortices are never trapped in the microbridge; with a diode laser, vortices are sometimes trapped. The spatial distribution of the trapped flux was studied. The effect of the optical pulse fall time on the frequency of flux trapping was found to be unimportant from 200 ns to 8 ms. Noise spectrum analysis indicates that the laser diode is 5 to 25 times noisier than the Nd:YAG laser at the characteristic frequency of the loop. This noise is believed to be responsible for flux trapping in the microbridge.         SQUID magnetometry applied as a non-invasive electroanalytic chemical technique    B.D. Jette and M.L.A. MacVicar Summary: A SQUID magnetometer, used as a highly sensitive ammeter, has been used to perform standard electroanalytic chemical measurements noninvasively. Specifically, the magnetic fields generated by the net ionic movement in the solution of a driven electrochemical system are detected by the gradiometer coils. The SQUID signal can then be compared to conventional current measurements. One such standard measurement investigated is cyclic voltammetry (CV) which determines the I-V characteristics of an electrochemical system yielding critical kinetic parameters. This investigation shows nearly identical results of measurements by the SQUID to those obtained by conventional techniques. A particularly attractive advantage of SQUID magnetometry is that noninvasive magnetic detection of ionic currents in solution may permit spatial resolution of ionic currents, unattainable by conventional techniques.         Fabrication and performance of high T/sub c/ two hole bulk and single hole thick film RF SQUIDs at 77 K    N. Khare, A.K. Gupta, S. Chaudhry, S.K. Arora, V.S. Tomar and V.N. Ojha Summary: Two-hole YBCO bulk and one-hole YBCO, BSCCO thick-film RF SQUIDs have been fabricated and operated at 77 K. RF SQUID behavior has been studied using commercial RF SQUID electronics with external RF and AF sources. Flux noise density of these SQUIDs depends on the quality of the microbridge. Flux noise present in various reported high-T/sub c/ film RF SQUIDs is compared.         High temperature operation of YBa/sub 2/Cu/sub 3/O/sub 7-x/ DC SQUID    A. Irie, H. Sasahara, T. Yamashita, H. Kurosawa, H. Yamane and T. Hirai Summary: Using a YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film deposited by MOCVD, a DC SQUID which is operated at 77 K has been fabricated. The SQUIDs with microbridges are patterned by chemical and laser etching processes. The SQUIDs operate stably without hysteresis in quite a wide range of temperature, within several periods of Phi /sub 0/. At 4.2 K, the voltage modulation of 80 mu V and the intrinsic energy sensibility of 4.0*10/sup -31/J/Hz were obtained for the SQUID with an inductance of 70 pH. The flux noise of the SQUID operating at 77 K in FLL mode was 1.8*10/sup -4/ Phi /sub 0// square root Hz at 10 Hz.         Comparison of YBCO thin films and SQUIDs prepared by ion beam deposition and RF and DC unbalanced magnetron sputtering    C.P. Foley, S.W. Filipczuk, N. Savvides, D.L. Dart, K. Muller and J.C. Macfarlane Summary: Results obtained with DC SQUIDs prepared by ion beam deposited films of YBa/sub 2/Cu/sub 3/O/sub x/ on substrates of (100) yttria stabilized zirconia (YSZ) have been previously reported. Superconducting films have subsequently been deposited by DC and RF unbalanced magnetron sputtering on various substrates including oriented and unoriented YSZ and lithium niobate. Details of films prepared by a different method are presented. Also reported are preliminary results on polycrystalline DC SQUIDs and an attempt to relate the SQUID properties with the morphology and film structure in each case. The implications of off-stoichiometry on film properties are discussed. It is shown that there is little difference between ion beam, RF, and DC unbalanced magnetron sputtering for the production of superconducting YBCO films providing the film is stoichiometric to better than 5%. Films with barium deficiencies over 7% are insulating. The advantage of one deposition method over the other is that RF unbalanced magnetron sputtering does not deplete the target of barium as rapidly as the other techniques. Targets can last up to three times longer.         Noise measurements in a composite niobium/YBCO SQUID and determination of the magnetic noise by direct measurement    S.P. Harrop, M.N. Keene, C.M. Muirhead and C.E. Gough Summary: The noise performance of a composite niobium/YBCO point contact two-hole SQUID was measured at 4.2 K in both RF and DC bias modes. The noise was measured by a technique which allowed the flux noise component to be measured. The flux noise was found to be the same in both bias modes. A direct measurement of the noise in a single hole in the same sample was made as a function of temperature and was found to display two peaks. Possible causes are discussed.         Directly-coupled DC-SQUID magnetometers made of Bi-Sr-Ca-Cu oxide films    M. Matsuda, Y. Murayama, S. Kiryu, N. Kasai, S. Kashiwaya, M. Koyanagi, T. Endo and S. Kuriki Summary: High-T/sub c/ DC-SQUID magnetometers made of Bi-Sr-Ca-Cu oxide films were designed and fabricated. A directly coupled scheme where a SQUID loop and a pick-up loop are connected directly in parallel was chosen to avoid fabricating the multilayered structure. The flux noise, which was measured in FLL (flux locked loop) operation at 4.2 K, increased in a form of 1/f as the frequency decreased below 20 Hz. The level of white noise at the frequency range above 20 Hz was about 1*10/sup -4/ Phi /sub 0// square root Hz, corresponding to the field resolution of 1.5 pT/ square root Hz at the pickup loop.         Anisotropic effect of the magnetic sensor formed from metal/high-T/sub c/ superconductor contact    S. Miyake, T. Aoyama, Y. Suzuki, T. Kusaka, T. Yotsuya and S. Ogawa Summary: The magnetic sensor formed via a metal/high-T/sub c/ superconductor small contact shows anisotropic properties below the lower critical field (H/sub cl/). An Ag wire was connected directly to the superconductor by an ultrasonic bonding method. It is shown that the resistance was changed by the field parallel to the superconductor surface, while it was not affected by the vertical field. The change is estimated to be 5*10/sup -5/ Omega /G. No hysteresis is observed. Magnetic field direction can be detected by using these properties and a deferential measuring method of the resistance.         Use of a bulk high T/sub c/ magnetometer for non-destructive evaluation    J.R. Buckley, N. Khare, G.B. Donaldson, A. Cochran and Z. Hui Summary: A novel use of high-temperature superconductors for detecting defects in ferromagnetic and nonferromagnetic materials is reported. The magnetometer uses the even harmonics generated in a sample of YBaCuO when it is driven by an audio-frequency magnetic field. These harmonics arise from the nonlinear modulation of the critical flux state as vortices are swept through the intergranular spaces of the superconductor, and their amplitude is strongly dependent on DC magnetic field. Two samples of YBaCuO of identical geometry are used and placed in coaxial coils in the form of a gradiometer and driven at 10 kHz. However, a defect (large change in mu /sub r/) in a nearby piece of ferromagnetic material produces a distortion in the local magnetic field (either the earth's field or 30-Hz modulation field) which can be detected in the second harmonic output. For nonferromagnetic conductors, defects become observable through the field distortions caused by eddy currents.         High temperature superconductive flux gate magnetometer    M. Gershenson Summary: A different type of HTS superconducting magnetometer based on the nonlinear magnetic behavior of bulk HTS materials is proposed and investigated. The device design is based on the generation of second harmonics which arise as a result of nonlinear magnetization observed in Type-II superconductors. Even harmonics are generated from the nonlinear interaction of an AC excitation signal with an external DC magnetic field which acts as a bias signal. It is shown that an increase in sensitivity of about one or two orders of magnitude is expected by use of more favorable geometries. An increase in frequency from 100 kHz to 100 MHz is expected to improve sensitivity by 30 dB.         Relaxation oscillator using hysteretic current-voltage characteristics of YBaCuO thin strips    K. Enpuku, T. Kisu and K. Yoshida Summary: It is shown that thin strips of YBaCuO with high critical current densities j/sub c/(4.2 K)>10/sup 6/ A/cm/sup 2/ exhibit hysteresis in their current-voltage (I-V) characteristics, typically in the normalized temperature region T/T/sub c/         Preparation and properties of all high T/sub c/ SNS-type edge DC SQUIDs    J. Gao, W.A.M. Aarnink, G.J. Gerritsma, D. Veldhuis and H. Rogalla Summary: High-T/sub c/ SNS-type Josephson junctions and DC SQUIDs were successfully fabricated using hetero-epitaxially grown multilayers of YBa/sub 2/Cu/sub 3/O/sub x/ and PrBa/sub 2/Cu/sub 3/O. These layers are c-axis oriented, and hence edges of the multilayers give rise to a current flow in the ab-plane between the electrodes of a Josephson junction. The necessary structuring was done by Ar ion beam etching. The individual junctions exhibit a supercurrent up to 80 K. The I/sub c/R/sub n/ product of these junctions usually has a lower limit of 8 mV at 4.2 K. Voltage modulation of the first DC SQUIDs can be observed up to 66 K. The voltage modulation for various bias currents investigated at 4.2 K noise measurements were performed. Details on the fabrication and measurements are presented.         YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge RF SQUID biased at 10 GHz    K.P. Daly, J.F. Burch, S. Coons and R. Hu Summary: The measurement of a YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step-edge RF SQUID is discussed. The step-edge technique permits high-yield fabrication of high-temperature superconducting (HTS) SQUIDs in high-quality epitaxial YBCO films. A comparison is made of measurements made at bias frequencies of 27 MHz and 10 GHz, the latter using a TE/sub 011/ copper cavity. Observed differences in the operation of the SQUID at these two frequencies are largely attributable to differences in the measurement configurations. The 10 GHz bias frequency may exceed the r/2 pi L characteristic frequency of the SQUID loop.         Mixing in TlCaBaCuO superconducting films at 61 GHz    S.T. Ruggiero, A. Cardona and H.R. Fetterman Summary: The results of mixing at 61 GHz using weak-link, grain-boundary junctions in Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8/ thin films are discussed. Films were prepared using laser deposition of precursor material on MgO substrates followed by high-temperature postprocessing. Mixing experiments were conducted at 75 K, at an IF frequency of 1 GHz, using a bow-tie antenna configuration. The signal-to-noise ratio for the system at the IF frequency was approximately 10/sup 4/.         Mixing characteristics of a microwave detector using a granular YBCO superconductor    Y. Yoshisato, M. Takai, K. Niki, S. Yoshikawa, T. Hirano and S. Nakano Summary: Microbridge-type Josephson junctions made of granular bulk YBCO superconductors were experimentally studied at microwave frequencies. Although the bridge included many grain boundaries, clear Shapiro steps were induced at every hf/2e voltage for microwave frequencies, and step height dependence for microwave power similar to that of a single weak link bridge was observed. A heterodyne mixing experiment of microwaves at about 20 GHz was also performed using the detector. The IF signal showed peak amplitudes corresponding to the peak dynamic resistance due to nonlinearity resulting from the Josephson effect. It was confirmed that the detector operates stably for the Josephson-effect heterodyne mixer at 60 K or below. The detector has potential for high sensitivity and good impedance matching due to its large dynamic resistance and high normal state resistance, respectively.         Fabrication of an infrared bolometer with a high T/sub c/ superconducting thermometer    S. Verghese, P.L. Richards, K. Char and S.A. Sachtjen Summary: A sensitive high-T/sub c/ superconducting bolometer has been fabricated on a 20- mu m-thick sapphire substrate with a YBCO thin-film transition edge thermometer. Optical measurements with a He-Ne laser gave a noise equivalent power of 2.4*10/sup -11/ W/Hz/sup 1/2/ at 10 Hz, and a responsivity of 17 V/W in good agreement with electrical bolometer measurements. Gold black smoke was then deposited on the backside of the assembled bolometer as an absorber. Spectral measurements on a Fourier transform spectrometer show that the bolometer has useful sensitivity from visible wavelengths to beyond approximately 100 mu m. This performance is superior to that of a commercial room-temperature pyroelectric detector. Some improvement appears possible.         Fabrication and measurement of high T/sub c/ superconducting microbolometers    M. Nahum, Q. Hu, P.L. Richards, S.A. Sachtjen, N. Newman and B.F. Cole Summary: The authors fabricated and measured the performance of antenna-coupled microbolometers based on the resistive transition of a high-T/sub c/ superconducting film for use as detectors of far-infrared and millimeter waves. A planar lithographed antenna (log-periodic or log-spiral) is used to couple the radiation to a thin YBCO film with dimensions ( approximately=6*13 mu m/sup 2/) which are smaller than the wavelength to be measured. This film acts both as the resistor to thermalize the RF currents and as a transition edge thermometer to measure the resulting temperature rise. Because of its small size, both the thermal conductance from the film into the bulk of the substrate and the heat capacity of the thermally active region are small. Consequently, the microbolometer has low noise, fast response, and a high voltage responsivity. A phonon-limited electrical NEP of 4.5*10/sup -12/ WHz/sup -1/2/ at a 10-kHz modulation frequency and a responsivity of 478 V/W at a bias of 550 mu A were measured. Measurements of the optical efficiency are discussed.         Electron tunneling into 1-2-3 HTSC thin films    J. Geerk, R.-L. Wang, H.-C. Li, G. Linker, O. Meyer, F. Ratzel, R. Smithey and H. Keschtkar Summary: Detailed tunneling measurements on thin-film planar tunnel junctions of the type RE/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7//native oxide/Pb (RE=Y, Eu, or Gd) are reported. The films were sputter deposited and chemically etched prior to the growth of the native oxide. The structural content of the gaplike structure in the I-V characteristic was investigated by taking dI/dV and d/sup 3/I/dV/sup 3/ traces. By analysis of the temperature dependence and temperature smearing, strong arguments could be provided for the fact that all the structures between +or-50 mV measured at low temperature are due to density of states effects. On junctions prepared on 1-2-3 films with T/sub c/ depressed either by partial oxygen depletion or by alloying, it is found that the gaplike structure was weakened, but did not shift on the energy scale.         Barrier technology for DyBa/sub 2/Cu/sub 3/O/sub 7-x/ junctions and related structures    K.M. Beauchamp, Y.-J. Zhang, B.R. Johnson, R.K. Schultz, G.C. Spalding, M. Tsen, T. Wang, J.F. Evans, M.L. Mecartney and A.M. Goldman Summary: Layered structures which include the high-temperature superconductor DyBa/sub 2/Cu/sub 3/O/sub 7-x/ have been fabricated using molecular beam epitaxy with ozone as the activated oxygen source. A c-axis-oriented DyBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film with a T/sub c/ of 74 K has been grown on a layer of the rare earth sesquioxide Dy/sub 2/O/sub 3/ on a (100) oriented SrTiO/sub 3/ substance. Dy/sub 2/O/sub 3/ has also been incorporated as a barrier between two layers of DyBa/sub 2/Cu/sub 3/O/sub 7-x/, where the T/sub c/ of the top layer is 89 K. X-ray diffraction reveals oriented growth of both the DyBa/sub 2/Cu/sub 3/O/sub 7-x/ and the Dy/sub 2/O/sub 3/ layers. Cross-sectional transmission electron microscopy shows the detailed matching of the layers, demonstrating that the interfaces are abrupt, with (100) Dy/sub 2/O/sub 3/ planes parallel to (001) DyBa/sub 2/Cu/sub 3/O/sub 7-x/ planes. These results are an indication that high-quality, all-high-T/sub c/ superconductor tunneling junctions can be fabricated in this system.         Fabrication of monolithic lateral SNS junction structure for Bi-oxide systems    T. Usuki, Y. Yoshisato, I. Yasui, K. Yamano and S. Nakano Summary: A novel monolithic lateral SNS structure of Bi-oxide systems has been developed in which the compositions of films were locally controlled in the lateral direction. Lateral SNS (BiSrCaCuO/BiSrCuO/BiSrCaCuO) structures which were made from a Ca-F/BSCO layer on MgO substrates have been developed. The BiSrCaCuO area, with a thickness of 150 nm, is composed of a 2212 phase with high crystallinity of the c-axis preferred orientation, and shows zero resistance at 85 K. The BiSrCuO indicates sufficiently low resistivity to be used as a normal barrier for SNS Josephson junctions. BSCO formation using Ca-diffusion into the surfaces of 2201 single crystals was successfully carried out.         Fabrication and characterization of YBa/sub 2/Cu/sub 3/O/sub 7//Au/YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions    M.G. Forrester, J. Talvacchio, J.R. Gavaler, M. Rooks and J. Lindquist Summary: All-high-T/sub c/ Josephson junctions have been fabricated in a planar SNS geometry by bridging narrow gaps ( approximately=0.1-0.2 mu m) in epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films with Au. The resulting devices exhibit a variety of nonhysteretic I-V characteristics, with I/sub c/R/sub N/ on the order of 0.1 to 10 mV, and exhibit Shapiro steps under microwave irradiation, and weak periodic modulation of the critical current with applied magnetic field. The transport properties of the junctions appear to be dominated by the Au/YBCO interfaces rather than by the Au itself.         In situ fabrication of reproducible YBCO epitaxial planar Josephson tunnel junctions    I. Iguchi and Z. Wen Summary: The fabrication of YBCO/Pb planar Josephson tunnel junctions using all in-situ processes in the vacuum system is reported. Both artificial and native barriers are used. The reproducible quasiparticle and Josephson tunneling characteristics are observed and discussed.         Proximity-coupled weak links in YBCO films    M.S. Wire, R.W. Simon, J.A. Luine, K.P. Daly, S.B. Coons, A.E. Lee, R. Hu, J.F. Burch and C.E. Platt Summary: Measurements of SNS planar microbridges made from high-quality in situ sputtered YBCO films were made. The devices were fabricated using single superconducting films with a patterned gap bridged by sputter-deposited silver. A number of devices exhibit supercurrents and microwave-induced steps in the current-voltage characteristics. In the best devices the normal state resistance is consistent with expected values. The consequences of the anisotropy of YBCO and the effects of various fabrication techniques on device performance and yield are discussed.         Fabrication process for Josephson computer ETL-JC1 using Nb tunnel junctions    H. Nakagawa, I. Kurosawa, M. Aoyagi and S. Takada Summary: The fabrication process that was used to develop a multichip Josephson computer named ETL-JC1 is described. The ETL-JC1 consists of four Josephson LSI chips: a register arithmetic logic unit chip (RALU), a sequence control unit chip (SQCU), a 1280-b read-only memory chip (IROU), and a 1-kb random access memory chip (DRAU). The fabrication process, based on a 3- mu m Nb/AlO/sub x//Nb junction technology, has been developed to make a complete set of the Josephson LSI chips. The present fabrication process includes a trilayer tunnel junction formation, a Nb underlayer method, a self-aligned insulation method, a reactive ion etching (RIE) process, an etching stopper layer formation, and a superconducting contact formation. The Josephson critical current density was controlled by the oxidation time within the fluctuation of +or-20% in the LSI fabrication runs. The resistors were made of palladium metal film on the LSI chips. The sheet resistance was controlled within the fluctuation between -12.5% and +19% in the LSI runs. It was found that the Josephson LSI chips fabricated by this process showed a high reliability for a long-term storage at room temperature and thermal cyclings between 4.2 K and room temperature without any passivation layers on the LSI surface.         A fabrication process for a 580 ps 4 kbit Josephson non-destructive read-out RAM    I. Ishida, S. Tahara, M. Hidaka, S. Nagasawa, S. Tuschida and Y. Wada Summary: A 4-kb Josephson nondestructive readout (NDRO) random access memory (RAM) has been developed. A process for fabricating the 580-ps 4-kb Josephson NDRO RAM is described that is based primarily on the use of Nb/AlO/sub x//Nb technology and state-of-the-art planarization. The process has evolved from a 1-kb Josephson NDRO RAM previously reported, with changes in memory cell structure, multilevel construction, layer planarization, and minimum design rules. Advanced memory cells with two stacked superconducting loops on which control lines are prepared are formed on ground plane insulation layers. Eight-stacked layers are formed from 200 approximately 300-nm-thick Nb films and 200-nm-thick SiO/sub 2/ films for planarized four-level interconnections including resistors. Planarization is achieved mainly by means of an undercut etching-mask-use lift-off planarization (ULOP) process. A 6-mm-square chip containing more than 25000 junctions whose minimum size is 3 mu m square and top level lines as small as 1.5 mu m in width and space have been successfully fabricated.         Fabrication of a 12-bit A/D converter using Nb/AlO/sub x//Nb Josephson junctions    J.H. Kang, D.L. Miller, J.X. Przybysz and M.A. Janocko Summary: For reliable fabrication of Nb/AlO/sub x//Nb Josephson integrated circuits, a combination of anodization and reactive ion etching techniques was used to make various sizes of high-quality Nb/AlO/sub x//Nb Josephson tunnel junctions with J/sub c/ as high as 5000 A/cm/sup 2/ and V/sub m/(2 mV) as large as 60 mV at 4.2 K. A ten-level process on Nb/AlO/sub x//Nb trilayers with J/sub c/ of 1500 A/cm/sup 2/ was used to fabricate a functional 12-b A/D converter. This circuit included 2.7- mu m-diameter junctions defined by anodization and 5- mu m-diameter junctions defined by reactive ion etching using Nb/sub 2/O/sub 5/ and Al as etch stops. A lift-off process with image-reversal photoresist was used to define SiO/sub 2/ insulators, Mo resistors, and Au resistors. Mo resistor values were adjusted by reactive ion etching. Measurements of the completed circuit show that all circuit components had correct values to well within design tolerance.         Fabrication of an all-refractory circuit using lift-off with image-reversal photoresist    D.L. Meier, J.X. Przybysz and J.H. Kang Summary: A four-stage shift register was fabricated using Nb/Al-Al/sub 2/O/sub 3//Nb Josephson junctions, Mo resistors, Nb transmission lines, and SiO/sub 2/ insulating layers. The circuit has 36 junctions (5 mu m, 1000 A/cm/sup 2/) and 61 resistors (1.2 Omega /square), with a minimum feature size of 2 mu m. An eight-mask process was used in the fabrication. All material layers were deposited by sputtering. Patterning for all but one of the masking levels was done by lift-off using image-reversal lithography in most cases. Lift-off avoided many of the problems common to reactive ion etching (RIE), including the need for etch stops, nonuniformity in etching, and the formation of organic residue (polymer) on the wafer. RIE was used only in the patterning of the Nb counterelectrode, where a natural Al etch stop from the barrier layer is present. The simplicity associated with the lift-off of all other layers, including the trilayer, is thought to be a major factor in the successful fabrication of the circuit which operated properly up to 4.0 Gbit/s.         A simple and robust niobium Josephson junction integrated circuit process    A.T. Barfknecht, R.C. Ruby and H.L. Ko Summary: A simple and robust process for fabricating low-T/sub c/ Josephson junction integrated circuits has been developed. The process is designed around the Nb/Al/sub 2/O/sub 3/-Al/Nb trilayer, and utilized nine masking steps to form two separate levels of trilayer Josephson junctions, as well as resistors, capacitors, and transmission lines. Materials used for interlayer dielectrics and passivation layers are silicon dioxide and silicon nitride formed by plasma-enhanced chemical vapor deposition (PECVD). The PECVD equipment yields a high deposition rate at moderate substrate temperatures. No degradation of the junction characteristics due to these depositions is seen. The measured loss tangent of this dielectric at 10 GHz using a parallel plate technique is 4.44*10/sup -4/. The dielectric constant of this material is 5.1 in the range of 50 to 400 GHz, measured using an on-chip resonator capacitively coupled to a single shunted Josephson junction. The physical quality of the oxide has been investigated using a variety of tests and has proven to be excellent. A variety of simple circuits using this process technology have been fabricated and tested. More complex circuits are currently under development.         PECVD SiO/sub 2/ dielectric for niobium Josephson IC process    S.Y. Lee, V. Nandakumar, B. Murdock and D. Hebert Summary: The authors have produced high-quality SiO/sub 2/ dielectric films by plasma-enhanced chemical vapor deposition (PECVD) applicable to a Nb-based, all-refractory Josephson integrated circuit process. PECVD SiO/sub 2/ was used for two insulating layers, ground plane isolation, and resistor isolation. Evaporated SiO was retained as the last insulating layer because the relatively high temperature needed for PECVD can degrade the already fabricated Josephson junctions. A thin SiO barrier layer had to be used in order to prevent the deterioration of the critical temperature of the ground plane. A successful application has been demonstrated by the fabrication and testing of a Josephson sampler circuit which shows acceptable Josephson junction current-voltage characteristic and a time resolution of 4.9 ps measured in liquid helium.         RHEA (resist-hardened etch and anodization) process for fine-geometry Josephson junction fabrication    L.P.S. Lee, E.R. Arambula, G. Hanaya, C. Dang, R. Sandell and H. Chan Summary: An advanced Josephson junction fabrication process has been developed for making high-quality junctions for Nb or NbCN integrated circuits. The RHEA (resist-hardened etch and anodization) process uses a successive plasma hardening of photoresist, reactive-ion-etch, and anodization process sequence to pattern and fabricate fine-geometry junction devices to below 1- mu m feature size. It is a simple, low-defect process that minimizes critical dimension bias, reduces critical dimension bias dependence on junction geometry, and allows the design flexibility of making either overlap or inside contact from interconnect layer to the junction devices. Key features of the process and experimental results are presented. This process is compared with other existing Josephson junction patterning processes, and the extendibility of the process to VLSI Josephson junction technology is discussed.         Ultra-high quality Nb/AlO/sub x//Nb tunnel junctions with epitaxial base layers    E.C.G. Kirk, M.G. Blamire, R.E. Somekh, J.E. Evetts, D. VanVechten and M.N. Lovellette Summary: Using an ultra-high-vacuum DC sputtering system, Nb/AlO/sub x//Nb tunnel junction devices with epitaxial Nb base layers have been fabricated. Improvements in device quality that can be achieved by heating the substrates during the growth of the tunnel barrier are investigated. By measuring the subgap characteristic under magnetic field at temperatures down to 0.4 K, it is shown that for V< Delta /sub Nb/ the currents in devices with critical current densities in the range of 10/sup 5/-10/sup 6/ AM/sup -2/ follow closely the BCS prediction and show no extrinsic leakage current. The divergence of the curve for higher current densities and at higher voltages is discussed.         High quality Nb-AlO/sub x/-Nb junctions for microwave receivers and SFQ logic device    V.P. Koshelets, S.A. Kovtonyuk, I.L. Serpuchenko, L.V. Filippenko and A.V. Shchukin Summary: The specific capacitance of high-quality (V/sub m/>50 mV) Nb-AlO/sub x/-Nb tunnel junctions is determined by the following methods: the measurement of zero field step resonances in specially prepared long Josephson junctions, and the definition of the resonant voltages in two-junction interferometers based on Nb-AlO/sub x/-Nb junctions. The results obtained by these methods were compared with each other and with the figures calculated from the measurements of tunnel barrier parameters. The application of the procedure for the fabrication of single flux quantum (SFQ) logic devices is discussed.         Fabrication of three terminal devices via a whole-wafer processing route    H. Amin, M.G. Blamire, K. Page and J.E. Evetts Summary: Using a whole-wafer route, the authors have fabricated high-quality three-terminal Nb(AlO/sub x/)Nb(AlO/sub x/)Nb devices with lead connections to each of the Nb layers, the middle Nb layer being on the order of 10 nm thick. A detailed description is presented of the adopted processing route, and recent results showing the junctions, independently biased, behaving as strongly coupled oscillators are discussed. The characteristics of the individual junctions show that the additional processing required to make the middle connection does not reduce the quality of the junctions. Preliminary results also show that the close proximity of the junctions possible with this route ensures strong inductive coupling (calculations for the present wafer dimensions give a coupling coefficient of 0.6) indicating its potential application in millimeter-wave coupling.         Investigation of the tunnel barrier in Nb-based junctions prepared by sputtering and electron beam evaporation    H. Kohlstedt, K.H. Gundlach and A. Schneider Summary: Nb-based tunnel junctions prepared by DC magnetron sputtering and electron beam evaporation are compared. Tunnel barriers consisting of Nb oxide, Al oxide and Si oxide are analyzed by anodization, Auger electron, and inelastic electron tunneling spectroscopy. Results obtained from Nb/sub 2/-Si oxide/Si-Nb/sub 1/ and Pb/Bi-Si oxide/Si-Nb/sub 1/ structures are presented. Nb and Si were deposited by electron beam evaporation and Pb/Bi from tantalum boats. Silicium oxide has a relatively low dielectric constant ( in SiO/sub 2/ approximately=4, in SiO approximately=6) and is thus of interest for tunnel barriers. The anodization profile of Nb/sub 2/-Si oxide Si-Nb/sub 1/ layers for Si thickness up to 10 nm are discussed. Pb/Bi-Si oxide/Si-Nb/sub 1/ junctions showed reasonably good quality Si thickness between 0.5 and 1 nm. The presence of Si in the barrier is confirmed by the inelastic electron tunnel spectrum (d/sup 2/I/dV/sup 2/ as a function of junction bias voltage V) which shows the longitudinal and transversal acoustic phonons of Si.         Characterization of different types of Nb-AlO/sub x/ based Josephson tunnel junctions    D.J. Adelerhof, E.P. Houwman, P.B.M. Fransen, D. Veldhuis, J. Flokstra and H. Rogalla Summary: Three types of Josephson tunnel junctions, standard Nb/Al,AlO/sub x//Nb, symmetric Nb/Al,AlO/sub x//Al/Nb, and Nb/Al,AlO/sub x//AlO/sub x//Nb containing a double-oxide layer were investigated by means of temperature-dependent I-V measurements, conductance-voltage measurements, noise analysis, and Auger electron spectroscopy scanning across the edge of a sputtered crater profile. In standard junctions, frequently small leakage currents have been observed as well as resistance fluctuations, leading to telegraph noise. Both effects can be related to the direct contact between the AlO/sub x/ and the Nb counter electrode. Leakage currents larger than 0.01% of the theoretical maximum critical current have not been observed in any of the symmetric junctions. The sub-gap current of these junctions is dominated by single- and two-particle tunneling. The SNAP process that was used to define the junction areas affects the tunnelling mechanisms below the sum-gap voltage, probably by the introduction of barrier inhomogeneities at the edges of the junctions. The AlO/sub x/ barrier in symmetric and asymmetric junctions cannot completely be represented by a trapezoidal barrier shape. The metal-insulator interface between Al and AlO/sub x/ in both junction types is probably not very sharp, which might be due to oxygen diffusion. The metal-insulator interface between AlO/sub x/ and Nb in standard junctions can be represented by a step-wise increase of the potential barrier, indicating that this interface is very distinct. The AlO/sub x/ barrier in double-oxide layer junctions is not homogeneous and probably contains low barrier channels.         A process for fabricating submicron all-refractory Josephson tunnel junction circuits    H. Dang and M. Radparvar Summary: A process for fabricating submicron Josephson junctions suitable for integration in small- and medium-scale integrated circuits is described. This junction process utilizes a double-layer SiO/sub 2/ lift-off process in a cross-type geometry to define Josephson junctions. A photoresist strip with an arbitrary length and a fixed width defines the length of the junction. Its width is defined simultaneously with the metallization strip that crosses the first strip. The double-layer SiO/sub 2/ insures a pinhole-free oxide and yields excellent insulating properties suitable for medium-scale circuit applications. This process is used to fabricate Nb/AlO/sub x//Nb and NbN/MgO/NbN tunnel junctions as small as 0.5 mu m/sup 2/ with figures of merit (V/sub m/) larger than 30 mV. The repeatability of this process and its utility in high-current-density Josephson junction circuits are discussed.         Fabrication of sub-micron whole-wafer SIS tunnel junctions for millimeter wave mixers    S.E. Huq, M.G. Blamire, J.E. Evetts, D.G. Hasko and H. Ahmed Summary: As part of a program for the development of a space-qualified submillimeter-wave mixer operating in the region of one terahertz, the authors have developed processes for the fabrication of submicron whole-wafer tunnel junctions. Using the self-aligned whole-wafer process (SAWW) with electron beam lithography they have been able to reliably fabricate high-quality (V/sub m/>20 mV) submicron tunnel junctions from whole-wafer Nb/AlO/sub x//Nb structures. In particular, it is shown that the junction quality is independent of size down to 0.3 mu m/sup 2/ junction area. The problems of film stress, anodization, registration for electron beam lithography, and lift-off, which limit the yield of good quality submicron-scale junctions are addressed.         High-quality sub-micron Nb trilayer tunnel junctions for a 100 GHz SIS receiver    A.H. Worsham, D.E. Prober, J.H. Kang, J.X. Przybysz and M.J. Rooks Summary: A modified SNIP process was used to fabricate high-quality 0.5, 2, and 4 mu m/sup 2/ small-area Nb/AlO/sub x//Nb trilayer tunnel junctions with current densities as large as 5000 A/cm/sup 2/. The average junction quality factors for the junctions at 4.4 K were V/sub m/(2 mV)=39 mV for J/sub c/=3000 A/cm/sup 2/ and V/sub m/ (2 mV)=27 mV for J/sub c/=5000 A/cm/sup 2/. The best values of V/sub m/ obtained were 50 mV for J/sub c/=3000 A/cm/sup 2/ and 41 mV for J/sub c/=5000 A/cm/sup 2/. These devices were designed and fabricated for use in a W-band mixer receiver. The substrate was 50- mu m-thick fused or crystal quartz. Special methods were developed for handling such thin insulating substrates and patterning films. The fabrication process was self-aligned and used SiO/sub 2/ instead of anodized Nb as the thick insulator. SiO/sub 2/ isolated the junction area and defined the opening for contact to the Nb wiring layer. The authors have fabricated series arrays of up to 12 junctions, with individual junction areas of 0.5 mu m/sup 2/. The array I-V quality was not degraded compared to that of an individual junction.         Fabrication of micron size Nb/Al-Al/sub 2/O/sub 3//Nb junctions with a trilevel resist liftoff process    A.W. Lichtenberger, D.M. Lea, C. Li, F.L. Lloyd, M.J. Feldman, R.J. Mattauch, S.-K. Pan and A.R. Kerr Summary: A trilevel resist, consisting of polyimide planarization, SiO/sub 2/ barrier, and photoresist, was used to pattern junction areas in Nb/Al-Al/sub 2/O/sub 3//Nb trilayer films. After reactive ion etching to define the junction areas, the perimeter of the junction was revealed, and excellent liftoff structures were defined with an oxygen plasma shrink of the exposed polyimide sidewalls. A subsequently deposited insulation layer seals the sides and the top surface along the perimeter of the Nb counter electrode button. High-quality superconductor-insulator-superconductor (SIS) junctions with diameters as small as 1.2 mu m and V/sub m/ as large as 1500 mV at 2.0 K have been fabricated. An SIS receiver using these junctions with integrated tuning elements has a DSB noise temperature of 58 K at 230 GHz. This is believed to be the lowest receiver noise temperature ever reported at this frequency.         Cross-sectional TEM observation of Nb/AlO/sub x/-Al/Nb junction structures    T. Imamura and S. Hasuo Summary: A study of the microstructure of Nb/AlO/sub x/-Al/Nb Josephson junctions by cross-sectional transmission electron microscopy (TEM) yielded information regarded the junction barrier region. Both thick Nb and several-nanometer Al form polycrystalline films with columnar structures. Nb is oriented to the [110] plane, and Al to the [111] plane. The 200-nm lower Nb has a wavy surface with -5-nm smoothness, but its surface is planarized by several-nanometer Al deposited on it. Thus, AlO/sub x/ with a smoothness under 1 nm can be formed on Al. The upper Nb has a good crystalline structure, even just above the AlO/sub x/ barrier.         Bias-sputtered Nb for reliable wirings in Josephson circuits    T. Imamura, S. Ohara and S. Hasuo Summary: Bias-sputtered Nb films were applied to wirings in Josephson circuits. Applying bias voltage during sputtering improved Nb step coverage and stability against annealing. Deteriorated superconducting characteristics in films were negligible for bias voltage less than -150 V. The characteristics of contacts formed between two Nb wirings were studied. By using bias-sputtered Nb as the upper wiring, the I/sub c/ of the contacts increased 2-10 times. Reduction in contact I/sub c/ after annealing was markedly suppressed. The authors verified that the bias-sputtered Nb was feasible in Josephson circuits as reliable wirings, with no compromise of junction characteristics.         Josephson LSI fabrication technology using NbN/MgO/NbN tunnel junctions    M. Aoyagi, H. Nakagawa, I. Kurosawa and S. Takada Summary: Josephson LSI fabrication technology using NbN/MgO/NbN tunnel junctions has been developed. The deposition process of the NbN electrode was investigated to obtain high uniformity of the electrical properties. The deposition process of the MgO tunnel barrier was investigated to obtain high reproducibility of the Josephson critical current density. The NbN film with high T/sub c/ of 15 K was obtained. The reproducibility of the MgO deposition rate was improved. The 10-b instruction 128-word ROM unit chip was successfully fabricated using the NbN/MgO/NbN junction LSI technology with the 3- mu m design rule. The READ operation test was performed for a few 10-b words. The total access time was measured to be 710 ps. The uniformity and reproducibility of the critical current density in the LSI chip were improved.         Fabrication of all-NbN Josephson tunnel junctions using single crystal NbN films for the base electrodes    A. Shoji Summary: All-NbN Josephson tunnel junctions with sputter-deposited magnesium oxide barriers have been fabricated using single-crystal NbN films for the base electrodes. Fabricated Josephson junctions have shown good tunneling characteristics with large gap voltages (5.6-5.8 mV), narrow gap widths (0.1-0.2 mV, from 30 to 70%), and small subgap leakage currents (V/sub m/=20-30 mV, measured at 3 mV). The results of a measurement of a subgap structure for a fabricated junction suggest that the excess leakage currents of fabricated junctions are due to multiparticle tunneling through locally thin areas in the MgO barriers.         NbCN Josephson junctions with AlN barriers    S.L. Thomasson, J.M. Murduck and H. Chan Summary: Niobium carbonitride (NbCN) Josephson circuits can operate over a wider temperature range than either niobium or niobium nitride circuits. Higher operating temperature places NbCN technology more comfortably within the range of closed-cycle refrigerators, a key factor in aerospace applications. Tunnel junctions have been fabricated from NbCN films with transition temperatures up to 18 K. High-quality NbCN tunnel junction fabrication generally requires low stress films with roughness less than the barrier thickness ( approximately=20 AA). Scanning tunneling microscopy was developed as a tool for measuring and optimizing film smoothness. Junctions formed in situ with AlN tunneling barriers show reproducible I-V characteristics. Unlike NbN, NbCN oxidizes readily, enabling junction definition by a modified SNAP process. This SNAP lithography technique successfully produced NbCn/AlN/NbCN junctions with V/sub m/ values (at 3 mV) up to 27 mV.         Submicron area NbN/MgO/NbN tunnel junctions for SIS mixer applications    H.G. LeDuc, A. Judas, S.R. Cypher, B. Bumble, B.D. Hunt and J.A. Stern Summary: The development of submicron area mixer elements for operation in the submillimeter wave range is discussed. High-current-density NbN/MgO/NbN tunnel junctions with areas down to 0.1 mu m/sup 2/ have been fabricated in both planar and edge geometries. The planar junctions were fabricated from in situ deposited trilayers using electron-beam lithography to pattern submicron area mesas. Modifications of fabrication techniques used in larger-area NbN tunnel junctions are required and are discussed. The NbN/MgO/NbN edge junction process using sapphire substrates has been transferred to technologically important quartz substrates using MgO buffer layers to minimize substrate interactions. The two junction geometries are compared and contrasted in the context of submillimeter wave mixer applications.         Characterization of NbN films and tunnel junctions    J.A. Stern and H.G. LeDuc Summary: Properties of NbN films and NbN/MgO/NbN tunnel junctions are discussed. NbN junctions are being developed for use in high-frequency, superconductor-insulator-superconductor (SIS) quasiparticle mixers. To properly design mixer circuits, junction and film properties need to be characterized. The specific capacitance of NbN/MgO/NbN junctions has been measured as a function of the product of the normal-state resistance and the junction area (R/sub n/A), and it is found to vary by more than a factor of two (35-85 fF/ mu m/sup 2/) over the range of R/sub n/A measured (1000-50 Omega mu m/sup 2/). This variation is important because the specific capacitance determines the RC speed of the tunnel junction at a given R/sub n/A value. The magnetic penetration depth of NbN films deposited under different conditions is also measured. The magnetic penetration depth affects the design of microstrip line used in RF tuning circuits. Control of the magnetic penetration depth is necessary to fabricate reproducible tuning circuits. Additionally, the critical current uniformity for arrays of 100 junctions has been measured. Junction uniformity will affect the design of focal-plane arrays of SIS mixers. Finally, the relevance of these measurements to the design of Josephson electronics is discussed.         Fabrication of NbCN/PbBi edge junctions with extremely low leakage currents    R.S. Amos, A.W. Lichtenberger, M.J. Feldman, R.J. Mattauch and E.J. Cukauskas Summary: High-quality submicron NbCN edge junctions were fabricated using two separate plasma processes. A bilayer NbCN/SiO/sub 2/ edge is cut with an ion gun, using a photoresist mask for each process. The first plasma technique involves lightly cleaning the bilayer surface with a low-energy argon plasma which does not completely remove the thermally oxidized barrier formed after cutting the edge. The second technique involves a CF/sub 4//Ar plasma cleaning; the existing barrier is apparently beneficially modified by the plasma. These two methods have resulted in extremely high-quality junctions with V/sub m/ (3 mV)>150 mV and 250 mV, respectively at 4.2 K. These V/sub m/ (3 mV) figures are much higher than other reports for edge junctions. It was also found that the junction quality was not dependent on the ion beam voltage used to cut the bilayer edges for these thermally oxidized barriers, in strong contrast to previous results with ion beam oxidation.         Josephson-like properties of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film weak links    D.K. Lathrop, S.E. Russek, B.H. Moeckly, D. Chamberlain, L. Pesenson, R.A. Buhrman, D.H. Shin and J. Silcox Summary: Thin-film YBa/sub 2/Cu/sub 3/O/sub 7/ microbridges have been fabricated by photo- and e-beam lithography in polycrystalline thin films grown on MgO substrates and containing a controlled density of large-angle tilt boundaries, thereby isolating individual tilt-boundary weak links. Depending on the growth parameters of the film, such weak links have critical current densities J/sub c/ ranging from <10/sup 4/ A mod cm/sup 2/ to >10/sup 6/ A mod cm/sup 2/. The higher J/sub c/ microbridges exhibit behavior indicative of one-dimensional flux flow and flux creep in the weak links, while the lower J/sub c/ microbridges have RSJ-like properties. Detailed comparisons have been made between the predictions of the resistively shunted junction (RSJ) model including the calculated effects of thermal noise rounding and the measured DC and microwave response of these weak links. Measurements have also been made of magnetic field effects on the critical current density. An unexpected scaling behavior has been observed in the I-V characteristics of certain types of these microbridges containing 45 degrees tilt boundaries that indicates that in those cases I/sub C/R/sub N//sup 2/ is a constant for the tilt-boundary weak link. The implications of these results for developing a successful description of the superconductive properties of YBa/sub 2/Cu/sub 3/O/sub 7/ grain boundary weak links, which electron microscopy reveals to be clean, stoichiometric, and abrupt, are discussed.         Engineered HTS microbridges    R.W. Simon, J.B. Bulman, J.F. Burch, S.B. Coons, K.P. Daly, W.D. Dozier, R. Hu, A.E. Lee, J.A. Luine, C.E. Platt, S.M. Schwarzbek, M.S. Wire and M.J. Zani Summary: A variety of techniques to reproducibly engineer microbridges in high-quality epitaxial YBCO films exist. A report is presented on two such techniques that have resulted in high-yield processes for fabricating both DC and RF SQUIDs operating at temperatures as high as 82 K. The results of these devices (step-edge microbridges) and focused-ion-beam microbridges) are compared with those of several other structures under investigation by other researchers.         Resonant impedance matching of Abrikosov vortex-flow transistors    G.K.G. Hohenwarter, J.S. Martens, J.B. Beyer and J.E. Nordman Summary: Impedance matching to low input impedance flux-flow devices with transmission line resonators has been achieved. A gain of 15 dB in a 50 Omega system was predicted by simulations of the amplifier. The design, layout, and fabrication of an amplifier and an oscillator circuit are presented. Circuit layout and fabrication of YBCO- and Tl-based circuits are briefly described. Measurements performed on fabricated circuits show a gain of 10 dB at 4 GHz for an amplifier circuit and an output power of -73 dBm at 7.1 GHz for an oscillator circuit.         High-T/sub c/ thin-film magnetometer    A.H. Miklich, F.C. Wellstood, J.J. Kingston, J. Clarke, M.S. Colclough, A.H. Cardona, L.C. Bourne, W.L. Olson and M.M. Eddy Summary: The authors have constructed and tested high-T/sub c/ magnetometers by coupling a high-T/sub c/ thin-film superconducting quantum interference device (SQUID) to two different high-T/sub c/ thin-film flux transformers. The SQUID was made from Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8+y/ films grown on MgO, with junctions consisting of native grain boundaries. The flux transformers were made from YBa/sub 2/Cu/sub 3/O/sub 7-x/, and each had ten-turn input coils and a single-turn pickup loop. The first transformer, which was patterned with a combination of shadow masks and photolithography, yielded a magnetic field gain of about -7.5, functioned up to 79 K, and gave a magnetic field sensitivity B/sub N/ (10 Hz) approximately= 3.1 pT Hz/sup -1/2/ at 38 K. The second transformer, which was patterned entirely by photolithography, yielded a gain of about -8.7 functioned up to 25 K, and had a sensitivity B/sub N/ (10 Hz) approximately=3.5 pT Hz/sup -1/2/ at 4.2 K. In both cases, the limiting noise arose in the SQUID.         Fabrication of high-T/sub c/ Josephson effect devices by natural lithography    W.D. Dozier, K.P. Daly, R. Hu, C.E. Platt and M.S. Wire Summary: Thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) have been deposited on LaAlO/sub 3/ substrates previously textured with submicron features by the use of natural lithography (the use of monolayers of polystyrene microspheres as lithographic masks). This weakens the superconducting properties, due to reduced connectivity in the film. Devices fabricated using localized textured regions have shown Josephson coupling. Weak links have shown Shapiro steps at the expected voltage intervals. Magnetic-field-induced modulation in the detected RF voltage with the geometrically correct periodicity has been observed in RF SQUIDs over a limited temperature range.         Superconducting transport characteristics of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary junctions    R. Gross, P. Chaudhari, M. Kawasaki and A. Gupta Summary: The superconducting transport of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grain boundary junctions (GBJs) fabricated by laser ablation deposition on SrTiO/sub 3/ bicrystals is discussed. For narrow GBJs with a width smaller than about four times their Josephson penetration depth, the current-voltage characteristics can be modeled closely by the resistively shunted junction (RSJ) model and the magnetic field dependence of the critical current is Fraunhofer-pattern-like. The temperature dependence of the critical current is proportional to (1-T/T/sub c/)/sup 2/ close to T/sub c/. The characteristic voltages V/sub c/=J/sup gb//sub c/ rho /sub N/, where J/sup gb//sub c/ is the critical current density and rho /sub N/ the normal resistance times unit area of the GBJs, range between 0.2 and 8 mV at 4.2 K and scale proportional to (1/ rho /sub N/)/sup 1.5/. The transport characteristics of the GBJs are in agreement with a SNINS-type junction model.         A review of SQUID magnetometry applied to nondestructive evaluation    H. Weinstock Summary: The development of the SQUID as the most sensitive instrument known for the measurement of changes in magnetic flux has presented new opportunities for its use for nondestructive evaluation (NDE) of electrically conducting and ferromagnetic structures. The preliminary studies of this application within the past few years are reviewed in order to serve as an introduction to those that follow. It includes early work by the author that explored the ability of a SQUID to detect defects in a buried pipe and to detect fatigue in steel structures. Studies designed to find defects in North Sea oil platforms and corrosion currents are covered, as well as more recent work in mapping the magnetic field above a current-carrying circuit board. The future of SQUID-based NDE is discussed.         High-resolution magnetic mapping using a SQUID magnetometer array    D.J. Staton, Y.P. Ma, N.G. Sepulveda and J.P. Wikswo Jr. Summary: A four-channel, high-resolution superconducting quantum interference device (SQUID) magnetometer array was used to map magnetic fields from various samples. Each SQUID has a 3-mm-diameter pickup coil located 4.4 mm from the adjacent channel. The spacing between the cryogenic array and the room-temperature sample is adjustable from 1.5 mm to 4.0 mm. The authors mapped the field from a 350- mu m-diameter hole in an 11 cm*15 cm*60 mu m copper sheet that was carrying a current of 100 mA. Field shape and strength were compared with predictions from analytical and finite-element models, which indicate that this technique should be able to detect an order of magnitude smaller flaws in flat plates. The ability is demonstrated to detect magnetic contamination in a 230- mu m-deep by 1.1-mm-long slot that was electric-discharge-machined into a nonmagnetic tube, and to determine the orientation of the slot with respect to the tube axis. Slices of pyroclastic rock of thickness as low as 30- mu m-thick have also been mapped.         An electromagnetic microscope for eddy current evaluation of materials    W.N. Podney and P.V. Czipott Summary: The concept for a novel instrument to be used in nondestructive evaluation (NDE) is presented. It is called an electromagnetic microscope, formed by superconductive microprobes arrayed in parallel rows. When moved over a test piece, the array generates a scanned image of flaws, stress variations, or changes in composition. Each microprobe comprises drive coils a few millimeters in radius that encircle pickup loops forming a concentric superconducting quantum interference device (SQUID). Drive coils transmit an oscillating magnetic field that induces eddy or magnetization currents in conductive or ferromagnetic materials, respectively. The gradiometer senses distortions in paths of induced currents. The extreme sensitivity of SQUIDS increases sensitivity, penetration depth, and spatial resolution over existing eddy current and magnetic NDE systems. Estimates of performance predict that a current of 1 A oscillating at 1 kHz in the drive coils allows detection of a flaw 0.1-mm in diameter to a depth of several millimeters in aluminum, with a horizontal resolution of about 1 mm and a vertical resolution of 0.3 mm or so.         NDE applications of SQUID magnetometry to electrochemical systems    M. Misra, S. Lordi and M.L.A. MacVicar Summary: A technique utilizing state-of-the-art SQUID magnetometers for noninvasive evaluation of the electrochemical reactivity of materials has been extended to practical systems. For example, sensitization of type-304 stainless steel has been identified. Magnetic signals produced by sensitized and unsensitized samples in acid demonstrate clear differences between the two types of samples. As a second example, electrodeposition of zinc, simulating recharging of Zn/Ni and Zn/Ag batteries, has been noninvasively monitored via magnetic signals. Disturbances in the current distribution over time, caused by nonuniform deposition, have been detected and compared to simulations of dendritic growth. Further investigations will be enhanced by increased flexibility, sensitivity, and spatial resolution available in a prototype SQUID instrument being developed.         Biomagnetic susceptometer with SQUID instrumentation    D.N. Paulson, R.L. Fagaly, R.M. Toussaint and R. Fischer Summary: A novel SQUID magnetometer for noninvasive measurements of hepatic (liver) iron stores is discussed. Placement of the SQUID, detection coil, and magnet in the dewar vacuum region significantly reduced system noise. In addition, the system incorporates multiple magnets and detection coils which may allow the discrimination of the surface skin layer from the deeper (weaker signal) true liver iron concentration. Measurements indicate an instrumental noise level that is <20 mu g/g of equivalent iron concentration.         A superconducting six-axis accelerometer    E.R. Canavan, H.J. Paik and J.W. Parke Summary: A superconducting device that is capable of measuring acceleration in all six degrees of freedom with great sensitivity is discussed. The device makes use of the fact that a superconducting mass levitated over a set of superconducting coils by a persistent current behaves as if it were supported by spring with a very stable spring constant. The displacement of the levitated mass modulates the inductance of spiral coils in close proximity to it. By forming inductance bridges from sets of such coils and reading the bridge misbalance signal with a SQUID, it is possible to sense very small displacements and rotations of the proof mass. In the first full tests of the device, its scale factor for acceleration (angular acceleration) was found to be approximately 2*10/sup 5/ Phi /sub 0//g (10/sup 3/ Phi /sub 0//rad/s/sup 2/) at the SQUID, in good agreement with values obtained from an analytical model. The inherent acceleration (angular acceleration) noise was found to be approximately 5*10/sup -10/ g/ square root Hz (10/sup -7/ rad/s/sup 2// square root Hz) which corresponds to the expected input noise for the commercial RF SQUID used. A substantial augmentation of the scale factors is possible by increasing the area of the sensing coils and improving the resolution with which the proof mass can be positioned. Such improvements, along with the use of lower noise DC SQUIDs, should allow the inherent acceleration (angular acceleration) noise to be reduced to a value close to the Brownian noise limit, approximately 10/sup -13/ g/ square root Hz (7*10/sup -11/ rad/s/sup 2// square root Hz).         Multi-fluxon steps in long Josephson junctions and their application to oscillators    L. Baselgia, O.G. Symko and W.J. Yeh Summary: Studies of long NbN Josephson junctions of the overlap type in the presence of an external magnetic field show constant voltage steps of the Fiske type, and large voltage steps. The latter are attributed to multifluxon resonances within the cavity of the junction. The multifluxon steps correspond to bunches of fluxons introduced in the junction because the junction electrode thicknesses are comparable to the penetration depth. These steps are very sharp, and they have large current amplitudes. When biased at such constant voltage steps, the device can be a resonant mode oscillator. The power and frequency are determined by the mode of fluxon motion inside the junction.         Aspects of dissipation effects on the supercurrent decay of Josephson systems    P. Silvestrini Summary: The effect of the voltage-dependent junction resistance R/sub j/ on the critical current decay of Josephson junctions was studied. In the thermal regime, the author has obtained a simple expression for the lifetime of the zero-voltage state which takes into account the nonlinear dependence of R/sub j/ on the voltage, removing an assumption of the resistivity shunted junction model (RSJ), which assumes an ohmic shunt resistance to describe the junction dissipation. These results are confirmed by experimental data which also show the relevance of the intrinsic dissipation due to the presence of quasiparticles. This latter aspect is relevant, because it allows extremely underdamped systems to be obtained at low temperatures. These conditions are particularly interesting to study a macroscopic quantum aspect, namely the effects of the presence of quantized energy levels on the supercurrent decay. The dependence of this latter effect on the junction resistance is also briefly discussed.         Electron transport in niobium-silicon-niobium structures    D.R. Heslinga, W.M. van Huffelen and T.M. Klapwijk Summary: A model for the voltage-carrying state of semiconductor coupled superconducting weak links is presented. Characteristic elements are the Schottky barrier at the interface and a nonequilibrium population of states in the semiconductor. Experimental results of several Nb-Si-Nb structures are shown to be partial agreement with the model. Deviations are thought to be caused by neglect of multiple Andreev reflections.         Experimental study of a field-effect transistor using granular thin films    N. Yoshikawa, L. Zhang and M. Sugahara Summary: An experimental study of the electrostatic field effect in granular thin films is described. This effect is thought to be grounded on the intergrain junction property which is dual to the Josephson effect. In order to assess the feasibility of a field effect transistor using this phenomena, the authors attempted to enhance the amplitude of the conductance modulation induced by the electric field. The dependence of the field effect on the channel sheet resistance and on the channel dimension is examined. The effect of trapped charge on the grains is also investigated. The prospect of the granular thin-film FETs is discussed.         Parameter limit of the Josephson effect in small superconducting microbridges    M. Sugahara, N. Yoshikawa and S. Furuoya Summary: An experimental study of small superconducting microbridges in order to examine parameter conditions (i.e., junction resistance and junction inductance) necessary for these junctions to exhibit the Josephson effect is described. Nb variable thickness junctions with very narrow width (<50 nm) and short length (<100 nm) were fabricated using electron beam lithography. The junctions which showed the Josephson effect were thinned by ion beam etching, and consequent changes of junction characteristics were measured. The experimental results indicate that the Josephson effect disappears at some critical resistance. These parameter limits of the Josephson junction are compared with theory.         Fabrication and electrical characterization of NbN-interfacial layer-Si contact diodes    S. Wu and D.P. Butler Summary: Nb and NbN-SiO/sub 2/-Si Schottky contact diodes were fabricated on chemically cleaned Si substrates by RF magnetron sputtering in Ar and Ar-N/sub 2/ ambients, respectively. The electrical behavior of the contact diodes was investigated by current-voltage and capacitance-voltage measurements over the temperature range of 10 to 300 K. The Nb contact diodes fabricated on p-type Si substrates have good Schottky barrier diode behavior. The NbN Schottky diodes on both n-type and p-type substrates exhibited lower quality behavior than their Nb counterparts. The electrical measurements have determined the barrier height of both the Nb-Si and NbN-Si systems. The low-temperature characterization yielded lower diffusion potentials than predicted by the theory of F.A. Padovani and R. Stratton (1966).         Properties of Josephson tunnel junction with trapped Abrikosov vortices: physical aspects and application for registration of alpha-particles    V.N. Gubankov, M.P. Lisitskii, I.L. Serpuchenko and F.N. Sklokin Summary: Properties of the Nb/AlO/sub x//Nb Josephson tunnel junction (JTJ) with Abrikosov vortices (AVs) trapped in electrodes were investigated. The trapping of AVs is performed by a field-cooling process when the JTJ is cooled through the critical temperature T/sub c/ either in applied perpendicular magnetic field (B/sub perpendicular to /) (mode 1) or by application of the perpendicular magnetic field B/sub perpendicular to / when the JTJ is at the temperature below T/sub c/ (mode 2). The effect of AVs on dependences of Josephson critical supercurrent I/sub c/ in the parallel magnetic field B/sub /// is studied. It is found that distortion in I/sub c/-versus-B/sub /// curves in the case of mode 1 differ qualitatively from that in the case of mode 2. These differences can be trapped in electrodes of the JTJ. The influence of alpha -particles on AVs trapped in electrodes of the JTJ is investigated. The results can be explained by the single AV motion caused by alpha -particles. It is believed that the JTJ with trapped AVs could be used as a new type of detector of nuclear particles.         A Josephson junction to FET high speed line driver made of TlCaBaCuO    J.S. Martens, D.S. Ginley, J.B. Beyer, J.E. Nordman and G.K.G. Hohenwarter Summary: A Tl-Ca-Ba-Cu-O superconducting flux flow transistor (SFFT) was used as an active impedance converter between Josephson and FET circuitry. The input of the flux flow device is a control line of low impedance that can be driven by a tunnel junction. The output is the signal across the SFFT which is made of a parallel array of weak links. The output impedance is typically greater than 5 Omega , with a maximum voltage swing of over 100 mV into a 50- Omega system. The switching of an all-Nb junction induced a 90-mV voltage swing at the FET input and over 200 mV at the FET output. The line driver can operate anywhere between 4.2 K and 85 K with minor changes in speed (+or-5 ps) and output level (+or-10 mV). The switching time measured was about 100 ps and was fixture limited.         Microwave noise parameter measurements of a high temperature superconducting flux flows transistor    J.M. O'Callaghan, J.S. Martens, J.H. Thompson, J.B. Beyer and J.E. Nordman Summary: The noise parameters of a high-temperature superconducting (HTS) flux flow transistor made of TlBaCaCuO operating at 77 K and 3-5 GHz were experimentally determined. It is assumed that the dominant noise mechanism of the device, which is based on an array of weak links with a magnetic control line, is due to the statistical nature of flux nucleation and motion in the links. The noise parameters dictate the dependence of the noise figure on the source impedance, and are calculated by measuring source impedances. Sensitivity analysis is used to estimate the accuracy of the measurements. The measurements indicate a minimum noise figure of less than 1 dB at 3 GHz.         Elimination of the feed-through effect in vortex flow transistors    M.A. Ketkar, J.B. Beyer, J.E. Nordman and G.K.G. Hohenwarter Summary: The capacitive feed-through effect in a VFT (vortex flow transistor) has been identified as a major limiting factor for high-frequency distributed amplifier applications. Two techniques to eliminate this effect are proposed and discussed. They are the use of a balanced controlled VFT and the use of a modified super current injection transistor. The balanced controlled configuration consists of a pair of Josephson junctions driven by control lines excited by push-pull. The simulations show more than 100-dB improvement in S12 over a single-ended device up to 175 GHz. The modified superconducting current injection transistor is a current controlled current source allowing the output line to be fed against ground. Hence, capacitive feed-through effects are greatly reduced. Device layouts and fabrication techniques are discussed.         Characteristics of superconducting flux-flow transistors    G.K.G. Hohenwarter, J.S. Martens, J.H. Thompson, J.B. Beyer, J.E. Nordman and D.S. Ginley Summary: The operational characteristics and physics of three superconducting thin-film-based transistor structures are compared. The devices are based on the motion of quantized vortices, either Josephson fluxons in a long tunnel junction of Abrikosov fluxons in a superconducting film. The transistor amplification mechanism is accomplished by controlling magnetic field at the boundaries of the structures. An overview of the present understanding of device mechanisms and measured characteristics, including voltampere relations and small and large signal circuit parameters is provided. Demonstrated applications and anticipated limitations are discussed.         Interlocked pair-tunneling phenomenon in a series array of small S-S'-S Josephson junctions    T. Matsui and H. Ohta Summary: A novel macroscopic quantum phenomenon in a series array of small S-S'-S Josephson junctions was found by examination of high-frequency responses and mixing characteristics at 100-115 GHz. The experiments reveal that the M multiphoton process is exclusively enhanced in the M stage array driven by a DC voltage bias source and that pair tunneling at each stage occurs simultaneously. Each Josephson element is a quasiplanar-type Josephson weak-link made of niobium films with small capacitance and bridge length shorter than 3.49 xi , where the ideal Josephson effect can be expected. Current is a natural common variable in a series array. It is therefore reasonable that fluctuation of the Josephson phase phi /sub k/ is effectively reduced in the series array, and that phi /sub k/ is locked on a common value, where k means the kth junction (k=1,2,3. . .N).         YBaCuO superconducting microbridges on Si substrates made by a novel method    X.F. Meng, R.S. Amos, F.S. Pierce, K.M. Wong, C.H. Xu, B.S. Deaver Jr. and S.J. Poon Summary: High-T/sub c/ superconducting microbridges of YBaCuO films were prepared on Si substrates in-situ using a novel method. By means of that method, high-T/sub c/ YBaCuO film microbridges were grown on Si substrates with Y-stabilized ZrO/sub 2/ directly, without the need of etching processes which usually degrade the superconducting properties of the films. The DC Josephson effect, and the microwave and optical response of the microbridges were investigated. The potential applications are discussed.         High frequency properties of YBCO bridges fabricated by MOCVD    J. Chen, T. Yamashita, H. Suzuki, H. Kurosawa, H. Yamane and T. Hirai Summary: The high-frequency properties of YBCO (YBa/sub 2/Cu/sub 3/O/sub 7- delta /) bridges at 4.2 K and 77 K are discussed. The YBCO films were prepared by MOCVD. For small bridges with a width (w) of about 1 mu m and thickness (t) of less than 0.5 mu m, the constant voltage steps at integral multiples of Phi /sub 0/fr-20 mu V were observed up to 1 mV, which is much higher than the I/sub c/R/sub N/ (<0.13 mV) product of these bridges at 77 K. The magnitudes of the current steps as functions of the RF current at 4.2 K and 77 K were in quantitative agreement with the theoretical results based on the RSJ (resistively shunted junction) model. The DC SQUIDs with these small bridges had a good response to external magnetic flux, resulting in a sinusoidal current-phase relation. On the other hand, for large bridges of w>5 mu m and t=1 mu m, the chaotic I-V characteristic was observed, and the shape of chaotic I-V curve was in qualitative agreement with the simulating results based on an RSCJ model.         Size effects in electrical behavior of high-T/sub c/ thin-film bridges    A.S. Afanasyev, V.N. Gubankov and Y.Y. Divin Summary: The size effects in electrical characteristics of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin-film bridges were studied in the temperature range 4-300 K. It is shown that at T>T/sub c/ the decrease of bridge widths w from 200 to 10 mu m leads to an increase of resistance R/sub Square Operator / of several times and to a change in R/sub Square Operator / (T) behavior from a metallic type to an activation type. At T         Evaluation of high-frequency performances of a superconducting base transistor using high-T/sub c/ materials    Y. Tazoh Summary: The high-frequency performances-cutoff frequency f/sub T/, maximum oscillation frequency f/sub max/, and so on-for a superconducting base transistor using high-T/sub c/ materials are evaluated. Calculations are based on a number of key assumptions, summarized as follows: (1) The quasiparticle density of state in high-T/sub c/ oxide superconductors and tunneling between the emitter and base superconductors can be expressed in terms of conventional theories, (2) The barrier height of the Schottky junction between the base superconductor and the collector semiconductor is equal to the gap energy Delta (T) of the base superconductor, (3) Critical temperature T/sub c/=90 K, superconductor energy gap at zero kelvin Delta (0)=30 meV, carrier concentration n=10/sup 21/ cm/sup -3/, resistivity rho =100 mu Omega cm, magnetic penetration depth lambda =0.1 mu m, and effective mass m=5 m/sub 0/ in the emitter and base superconductors. Calculated results reveal that high-T/sub c/ superconducting base transistors have a potential for much higher high-frequency performance values than conventional devices. For example, typical f/sub T/, f/sub max/, and switching energy values are estimated to be 1 THz, 1 THz, and 10/sup -20/ J/gate, respectively.         Josephson effect and small-angle grain boundary in YBCO thin film bridge    H. Suzuki, H. Kurosawa, K. Miyagawa, Y. Hirotsu, M. Era, T. Yamashita, H. Yamane and T. Hirai Summary: Clear AC and DC Josephson effects have been observed only by using the YBCO (YBa/sub 2/Cu/sub 3/O/sub 7-x/) thin films made by MO-CVD on (100) MgO substrates. TEM observation and X-ray analysis of YBCO on MgO were made and these results were compared with those for YBCO on the SrTiO/sub 3/ substrate. It was found that the YBCO films on the MgO substrate consisted of (001) oriented polycrystalline grains with the size of about 0.5 mu m. There were two types of angular misorientation between two adjacent grains: one is a misorientation within several degrees and the other with about 45 degrees, which may be due to lattice mismatching between YBCO and (100) MgO substrate. The small-angle grain boundaries were clearly observed by TEM observation. On the other hand, there was a relatively small misorientation at the grain boundary of YBCO on SrTiO/sub 3/ substrate. J/sub c/ of the YBCO on MgO is from 10/sup 4/ to 10/sup 5/ A/cm/sup 2/ at 77 K, which is lower than that for YBCO on SrTiO/sub 3/ by one order of magnitude, possibly related to the difference of the grain boundary structures. For YBCO on (100) MgO, only a few grains with the small-angle grain boundary exist at the bridge region of the device, and the grain boundaries work as effective barriers for Josephson junctions.         Fabrication and properties of HTS diffusion type weak links    Z.G. Ivanov, G. Brorsson and T. Claeson Summary: Intentionally weakened links were produced by diffusing Al or Cu into the grain boundaries of microbridges of high-T/sub c/ superconductors. Thin and narrow (70-130 mm) strips of Al or Cu were deposited across previously patterned microbridges and diffused into them for a short time at 300-450 degrees C. DC and RF Josephson properties were registered. I/sub c/R/sub n/ products of up to 3 mV were measured at 4.2 K for a laser-ablated Bi-Pb-Ca-Sr-Cu-O film (T/sub c/=64 K) and 0.9 mV at 77 K for a Y-Ba-Cu-O film (T/sub c/=87 K). Problems with electron resist residues could be circumvented by depositing a thin layer of Ag on the high-T/sub c/ superconductor before further processing.         Fluxon electronic devices    N.F. Pedersen Summary: The basic theory and properties of fluxons on Josephson transmission lines (JTL) are outlined. Basic experimental properties are illustrated by examples from the literature. RF applications and analog amplifier applications based on fluxons are discussed.         Experiments on tunable Josephson millimeter-wave oscillators    M. Cirillo, I. Modena, P. Carelli, G. Schirripa Spagnolo, R. Leoni and M. Pullano Summary: The coupling of millimeter-wave radiation from a long Josephson junction to a small-area junction is discussed. The coupling is obtained by means of thin-film technology and the design parameters allowing radiation coupling are discussed. Since the frequency of the oscillator radiation is smaller than the plasma frequency of the detector junction, the latter shows evidence of chaotic dynamics in the current-voltage characteristic. However, very stable zero-crossing bias steps appear for high values of the applied radiation power. The tunability of the oscillator power allows measuring the dependence of the detector critical current on the external radiation to be measured; from this measured dependence and from the observed amplitude of the photon-assisted tunneling steps it is estimated that maximum coupled power is the range of tens of nanowatts.         Refractory submillimeter Josephson effect sources    K. Wan, B. Bi, A.K. Jain, L.A. Fetter, S. Han, W.H. Mallison and J.E. Lukens Summary: Niobium Josephson effect array oscillators have been fabricated and tested. These devices deliver about 1 mu W of power in the submillimeter-wave range to 20-60 Omega load resistors. The present upper frequency limit of about 500 GHz appears to be set by losses in the superconducting microstrip. Data on the submillimeter-wave surface impedance of the niobium microstrip and details of the trilayer junction processing, which gives value of V/sub m/ at 2 K up to 800 mV, are presented.         Low frequency noise in resonant Josephson soliton oscillators    J.B. Hansen, T. Holst, F.C. Wellstood and J. Clarke Summary: The noise in the resonant soliton mode of long and narrow Josephson tunnel junctions (Josephson transmission lines or JTLs) have been measured in the frequency range from 0.1 Hz to 25 kHz by means of a DC SQUID. The measured white noise was found, to within a factor of two, to be equal to the Nyquist voltage noise in a resistance equal to the dynamic resistance R/sub D/ of the current-voltage characteristic of the bias point. In contrast, measurements of the linewidth of the microwave radiation from the same JTL showed that the spectral density of the underlying noise voltage scaled as R/sub D//sup 2//R/sub S/ where R/sub S/ is the static resistance. The origin of the different behavior is not known.         Josephson soliton oscillator arrays for SIS mixers    A. Davidson, N. Gronbech-Jensen and N.F. Pedersen Summary: Experiments on Josephson soliton oscillators phase locked to cavity modes of a coplanar waveguide resonator are discussed. The junctions were made using a trilayer Nb/AlO/sub x//Nb structure with a current density of about 1000 A/cm/sup 2/. Strong coupling between the junctions and the cavity was observed at 34 and 100 GHz. Subharmonic structure on the current-voltage characteristics indicate weaker coupling up to 300 GHz. These results are important for designing integrated soliton local oscillators for superconductor-insulator-superconductor (SIS) mixers in the millimeter band.         Design and performance of flux-flow type Josephson oscillator coupled to a stripline    K. Yoshida, K. Kudo and K. Enpuku Summary: In order to realize efficient coupling between a flux-flow type Josephson oscillator (FFO) and an external stripline, the authors carried out experiments to investigate the inductive coupling scheme in a strong coupling regime. By adopting NbN films with large penetration depths as electrodes for strong coupling, they were able to realize coupling sections with a coupling coefficient alpha =M/ square root L/sub 1/L/sub 2/ as large as 0.7, with M, L/sub 1/, and L/sub 2/ being mutual inductance, self-inductances of, the FFO, and the stripline, respectively. Using this design for the coupling, the authors succeeded in detecting AC fields at frequencies around 150 GHz, which were emitted from FFO to the stripline via the coupling section.         Resonator coupled Josephson junctions; parametric excitations and mutual locking    H. Dalsgaard Jensen, A. Larsen and J. Mygind Summary: Self-pumped parametric excitations and mutual locking in systems of Josephson tunnel junctions coupled to multimode resonators are reported. For the very large values of the coupling parameter, obtained with small Nb-Al/sub 2/O/sub 3/-Nb junctions integrated in superconducting microstrip resonators, the DC I-V characteristic shows an equidistant series of current steps generated by subharmonic pumping of the fundamental resonator mode. This is confirmed by measurement of frequency and linewidth of the emitted Josephson radiation.         Microchip design for a low-frequency Josephson-array voltage standard    W.F. Avrin, M.B. Simmonds and C.A. Hamilton Summary: The complexity of the Josephson array voltage standard can be reduced by using lower-frequency microwaves to excite the junction array. For operation at reduced frequencies, the design of the array must take the large size of the junctions, and the perturbing effect of the junction reactance on the distribution of microwave power into account. Such issues are especially important when durable, but low-capacitance, trilayer junctions are used in the array. These problems are minimized by a design in which the junction array is wound into a continuous spiral.         Quantum limited quasiparticle mixers at 100 GHz    C.A. Mears, Q. Hu, P.L. Richards, A.H. Worsham, D.E. Prober and A.V. Raisanen Summary: Accurate measurements of the noise and gain of superconducting-insulating-superconducting (SIS) mixers using small-area (1 mu m/sup 2/) Ta/Ta/sub 2/O/sub 5//Pb/sub 0.9/Bi/sub 0.1/ tunnel junctions were made. The authors measured an added mixer noise of 0.61+or-0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta. Detailed comparison between theoretical predictions of the quantum theory of mixing has been carried out, and noise and gain have been experimentally measured. The shapes of the I-V curves pumped at the upper and lower sideband frequencies were used to deduce values of the embedding admittances at these frequencies. Using these admittances, the mixer noise and gain predicted by quantum theory are in excellent agreement with experiment.         On-chip diagnostic equipment for 100 GHz superconducting circuits    A.D. Smith, J.A. Carpenter, D.J. Durand and L. Lee Summary: A set of on-chip tools was developed for evaluating superconducting millimeter-wave circuits including: (1) a voltage-standing-wave-ratio (VSWR) reflectometer, (2) a phase meter, (3) a transmission line velocity meter, (4) a transmission line inductance meter, and (5) a double balanced mixer. The circuits consist of pure Nb conductors and Nb/AlO/sub x//Nb superconductor-insulator-superconductor junctions. A report is presented on the design and use of the VSWR probe, which has not appeared in the literature, and the use of the velocity meter, the design for which has previously been reported.         Behavior of noise in a nondegenerate Josephson-parametric amplifier    B. Yurke, R. Movshovich, P.G. Kaminsky, P. Bryant, A.D. Smith, A.H. Silver and R.W. Simon Summary: A systematic study of noise in a nondegenerate Josephson-parametric amplifier as it passes through the threshold for oscillation was performed. Below the threshold all the noise is accounted for by equilibrium fluctuations of the losses. Well above the threshold the noise is 3 dB larger than the below-threshold value and is again accounted for by noise from the losses. In the region near the threshold, the noise can become quite large. The behavior of the noise is in qualitative agreement with that expected for a generic system undergoing a Hopf bifurcation.         Analog signal correlator design and operation    J.B. Green and M. Bhushan Summary: A superconductive tapped delay line, circuits comprising superconductor-insulator-superconductor (SIS) mixers, an L-C integrator, and a tunnel junction comparator, and superconductive digital address encoders have been integrated into a 14-channel analog signal correlator. This 25*38 mm circuit was fabricated using a Nb/Nb/sub 2/O/sub 3//Pb tunnel junction process. Preliminary testing of this device indicates the ability to process long duration, wideband waveforms with time-bandwidth products equal to 6000.         The effect of the quantum susceptance on the gain of superconducting quasiparticle mixers    C.A. Mears, Q. Hu and P.L. Richards Summary: A detailed analysis of the effects of the quantum susceptance on the performance of superconductor-insulator-superconductor (SIS) mixers is performed. It is found that the principal effects of the quantum susceptance are to change the DC bias at which optimum coupling of the signal to the mixer occurs, and to change the output admittance at the IF frequency, thus changing the available gain. It is shown that at the signal port the principal effect is to change the bias voltage at which optimum coupling to the mixer occurs. A more dramatic effect occurs at the IF port, where the quantum susceptance leads to negative values of the output conductance, which causes the available gain to be infinite.         Optimizing double-sideband SIS quasiparticle mixers    D.P. Woody and M.J. Wengler Summary: Calculations based on the quantum theory of mixing in single-particle tunnel junctions show that there is a fairly simple strategy for optimizing the performance of double-sideband superconductor-insulator-superconductor (SIS) quasiparticle mixers. The best mixer noise temperature is obtained when the signal source is matched to the local oscillator (LO) admittance of the junction. This applies over a very wide range of LO and DC bias conditions. These calculations support the contention that it is the energy dissipation in the device which is important in determining the noise performance, not the small signal admittance or the power gain. This appears to be another demonstration of the Callen and Welton fluctuation-dissipation theorem. which states that it is the dissipation of energy which is responsible for the noise generation in a wide range of devices, and it is this energy dissipation mechanism to which the signal should be coupled to minimize the noise.         A phase sensitive SIS mixer to circumvent the quantum limit    M.F. Bocko, Z.-n. Zhang, S. Martinet and M.W. Cromar Summary: A conventional superconductor-insulator-superconductor (SIS) mixer, that is pumped by a single-frequency local oscillator (LO) functions as a phase-insensitive linear amplifier and may achieve a noise level near the quantum limit of one-half photon added noise per unit bandwidth. A phase-sensitive linear amplifier may have less noise than this quantum limit. To overcome the quantum noise limit with an SIS mixer, a two-LO technique which makes the mixer's gain dependent upon the phase of the incoming signal was used. The phase sensitive gain of this two-LO mixer is experimentally demonstrated. The gain variation from maximum to minimum is more than 20 dB. Theoretical predictions of the noise of the two-LO mixer are presented.         Author Index (1990 - Part 3)    No author information available Summary: Not available

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