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We have studied electrical properties of YBCO/Y/sub 0.7/Ca/sub 0.3/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (Ca-YBCO)/YBCO trilayer junctions using c-axis oriented films. The Ca-YBCO films used here are the overdoped version of YBCO and show transition temperatures around 55 K. All of the junctions show RSJ-like current-voltage characteristics in a certain temperature range, though the range decreases with the Ca-YBCO interlayer thickness. For an applied magnetic field, the junctions show Fraunhofer pattern, indicating a Josephson coupling through the interlayers. The normal resistance of the junctions is proportional to the thickness of the interlayer, suggesting little interface resistance. The exponential dependence of the critical current on temperature and that on the interlayer thickness mean that the junctions behave as SNS junctions. These experimental results imply the proximity effect along c-axis in high temperature superconductors. [ABSTRACT FROM PUBLISHER]

The origin of the decoherence in superconducting nanowire single-photon detectors, the so-called dark count, was investigated. We measured the direct-current characteristics and bias-current dependencies of the dark count rate in a wide range of temperatures from 0.5 K to 4.0 K, and analyzed the results by theoretical models of thermal fluctuations of vortices. Our results indicate that the current-assisted unbinding of vortex-antivortex pairs is the dominant origin of the dark count. [ABSTRACT FROM AUTHOR]

Proposes and demonstrates a high-temperature superconductor multilayer structure. Details on the isolation resistance between the ground plane and other layers of the YBCO; Effects of the high temperature process during ground plane formation; Information on the measured voltage modulations of the super-conducting quantum interference device.

To expand designable circuit scale, we have developed a new cell-based circuit design for single flux quantum (SFQ) circuit. We call it CONNECT cell library. The CONNECT cell library has over 100 cells at present. Each CONNECT cell consists of a Verilog digital behavior model, circuit information, and a physical layout. All circuit parameter values have been optimized for obtaining the widest margins and minimizing interactions between cells. At the layout level, we have defined a minimum standard cell size and made cell height and width a multiple of the size. Using this cell library, we can easily expand circuit scale without the time-consuming dynamic simulations of whole circuits. For estimation of the reliability of the library, we designed and fabricated test circuits using CONNECT cells. We demonstrated experimentally correct operations, which means the CONNECT cell library is sufficiently reliable. [Copyright &y& Elsevier]

Abstract: We have calculated a bit-error-rate (BER) of Josephson latching drivers using the Monte-Carlo simulations taking into account the thermal noise at the Josephson junctions. The latching driver under investigation is composed of parallel 8-junction stacks and a SQUID input gate. We have optimized the structure of the SQUID input gate based on the BER simulation to get larger bias margins with acceptable BER. We have shown that the bias margins of the latching driver with a 3-junction SQUID input gate are better than that using a 2-junction SQUID input gate. The high-speed measurement of the Josephson latching driver confirms the validity of the BER based optimization. We have obtained the BER lower than 10−12 at 5GHz and 10−5 at 10GHz in the Josephson latching driver with the 3-junction SQUID input gate by the high-speed test. [Copyright &y& Elsevier]

We have developed essential components for most of microarchitectures based on the single-flux-quantum (SFQ) logic. The circuit under test is composed of two registers, an ALU and a control unit, and made up of about 540 cells, 1600 Josephson junctions on 1.5 × 2.4 mm area. We have obtained the correct results by a sequence of several instructions, in which two integers are written into the registers with the LOAD and COPY operations, and then execute the ADD operation. Some of their functions were tested at both low and high frequencies. As a result, we found that the designed components could work at 15 GHz for the designed bias current and up to 18 GHz for higher bias currents. [Copyright &y& Elsevier]