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IEICE Transactions on Electronics

HTS Quasi-Particle Injection Devices for Interfaces between SFQ and CMOS Circuits.

H. Shiga, Yoichi Okabe

Published Mar 1, 2002• 0 citations
OpenAlex

Abstract

We have fabricated a prototype of interface devices between SFQ and CMOS circuits using HTS quasi-particle injection devices. By the injection of quasi-particles, the bridge area becomes resistive and high voltage appears at the drain electrode. As a test of device operation, we applied the signal of a function generator to the gate electrode and observed that the device successfully repeated on/off operation. We also succeeded in explaining the device characteristics by considering the thermal effects.

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We have fabricated a prototype of interface devices between SFQ and CMOS circuits using HTS quasi-particle injection devices. By the injection of quasi-particles, the bridge area becomes resistive and high voltage appears at the drain electrode. As a test of device operation, we applied the signal of a function generator to the gate electrode and observed that the device successfully repeated on/off operation. We also succeeded in explaining the device characteristics by considering the thermal effects.
Latching-type driver circuits integrated with high-temperature superconductivity (HTS) junctions and two types of resistor were fabricated. These circuits could successfully perform latching operation by means of a single-flux-quantum (SFQ) signal input. Ramp-edge-type HTS junctions were fabricated by interface engineering and showed a hysteretic current-voltage characteristics under a temperature of 50 K. The critical current (I/sub c/) of these 5-micron-wide junctions was about 0.2 mA and the I/sub c/R/sub n/ product was about 1.7 mV at 4.2 K. The circuits included two types of resistors, which were made of RF-magnetron-sputtered indium-tin-oxide (ITO) and Au films. A driver with a parallel 2-junction-stack could convert an SFQ pulse, which was transformed through several Josephson transmission lines (JTL's) from a DC/SFQ circuit, to a 2.3-mV level signal.
We developed a latching-type driver using capacitively shunted high-temperature superconductivity (HTS) junctions for Single-Flux-Quantum (SFQ)-semiconductor output interfaces and fabricated it using ramp-edge-type HTS junctions. Assuming a junction IcRn product of 2 mV, a circuit simulation shows that the driver can produce an output of about 8 mV from an SFQ input pulse with a sufficiently short rise time for an interface clock operation of several gigahertz. HTS junctions were fabricated using the interface engineering method, and capacitors were made from an Indium oxide insulator (the dielectric constant was about 23 at 20 K) sandwiched by YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) electrodes. The hysteresis of the I-V characteristics of the junctions increased by increasing the area of capacitance. The latching operation of the driver was observed with an output voltage of up to 3 mV.
RSFQ circuit elements were fabricated based on the YBa/sub 2/Cu/sub 3/O/sub 7-x/ ramp-edge junctions and their characteristics were investigated. In particular, two types of interface circuits were designed, fabricated and their amplification functions were evaluated. The interface circuits comprised series array of SQUID's that shared a common inductor each other. Each SQUID was switched between zero voltage state and voltage state by current injection. Input signal was AC Josephson current for the type-one interface circuit. The input signal was an SFQ for the type-two interface circuit. Both interface circuits could successfully be operated. In particular, an output voltage more than 1 mV was obtained for the type-one interface circuit that comprised the stack of five SQUID's.
Superconducting devices have intrinsically superior characteristics to those of semiconductor devices. Presently, we can fabricate more than twenty thousand junctions on one chip using niobium technology. We have demonstrated the operation of a network system with a superconducting interconnection chip using voltage-state logic. Single flux quantum devices are promising for future superconducting applications because the clock frequency of SFQ logic is higher than that of voltage-state. We have proposed a high-end switch based on hybrid architecture using optical devices, semiconductors and SFQ devices. To demonstrate the high-speed operation of SFQ circuits, we developed an arbiter circuit that uses SFQ components and the arbiter circuit operates at 60 GHz. We also have developed a high Tc superconducting (HTS) SFQ sampler system for observing ultra-fast signal waveforms. In addition, we will discuss the prospects of future superconducting devices based on the fabrication technologies we developed.
A high-Tcsuperconducting (HTS) single-flux-quantum (SFQ) logic family including an and gate, an or gate, and an inverter was designed. The circuit parameters were optimized for a Josephson junction's critical current density, which may change due to a temperature change or insufficient run-to-run reproducibility of the fabrication process. New circuit design layout rules were implemented to improve Icx uniformity. As a result, all circuits were successfully tested and show at least plusmn40% critical current density operational margins. An effect of the parasitic capacitance formed by a junction electrode and a ground plane on the operating margins of the and gate was investigated by numerical simulation. Test circuits were fabricated using YBa2Cu3O7-deltaramp-edge junction technology and were operated at temperatures higher than 30 K. Bias current margins were also measured, and they found to be close to the simulated ones.
The characteristics of a simple logic gate which consists of an rf-Superconducting QUantum Interference Device (SQUID) and dc-SQUID has been investigated in connection with the Single-Flux-Quantum (SFQ) logic operation and Josephson junction characteristics. The Josephson junctions were made of Neodymium Barium Copper Oxide thin film employing Focused Ion Beam technology. We confirmed the generating SFQ in the rf-SQUID and simultaneous read-out by the dc-SQUID up to 50 K. It has been found that the temperature dependence of output voltage level decreased more rapid than that of critical current normal resistance product. The origin of the discrepancy was studied using a phenomenological model of the Josephson junction and numerical simulation.