The present status and the future prospect of superconducting electronics are briefly overviewed. The progress in Josephson technologies based on refractory superconductors such as Nb and NbN has made it possible to fabricate reliable and high performance in curcuits with LSI complexities. These innovations make superconducting devices in both digital and analog applications more realistic than they used to be. High temperature oxide superconducting devices are now intensively researched and it is needed to solve problems, i.e., single crystal thin films with multilayered structures and well defined interfaces between layers, before realizing useful device structures.

A multi-chip superconducting computer named ETL-JC1 has been constructed based on Josephson computer technology developed in the Electrotechnical Laboratory through 1980s. The technology covers various fields such as material and fabrication technology, logic and memory circuit design, and computer archtecture. Some key technologies for making the ETL-JC1 have been developed; niobium (Nb) tunnel junction integration process, LSI logic circuits, memory chips of a 1-kbit ROM and a 1-kbit RAM, the CAD system for Josephson LSI design, and a multi-phase power supply system. The computer system was totally designed by the RISC (reduced instruction set computer) architecture. It consists of four Josephson LSI chips of an arithmetic/logic unit, a sequence control unit, a program memory unit, and a data memory unit, which are essential to execute computer functions. The four chips were fabricated with a 3-µm Nb/Al-oxide/Nb junction integration technology. The ETL-JC1 was constructed by connecting four Josephson LSI chips on a non-magnetic printed circuit board. Test programs were executed on the ETL-JC1 and the correct execution of all the 27 kinds of instruction including memory access, subroutine call/return, and so on, which are sufficient to make and computer program, was confirmed. A total power dissipation was 6.2 mW in whole circuits of the ETL-JC1 consisting of more than 22,000 Josephson junctions. Operation speed of 1 GIPS (Giga-instruction per second) can be expected with a single CPU in this system according to computer logic simulations.

Josephson integrated circuit technology has progressed remarkably since niobium junctions were introduced in 1983. At present, it is feasible to make LSI level circuits, such as a few thousand gate microprocessor and a few kilobit memory. It has been demonstrated that these circuits are operated with much faster speed and lower power consumption than semiconductor circuits. This paper describes the performance of these circuits.

As an application of superconducting devices to electronic engineering, a novel Josephson fuzzy processor is proposed. Since the integrated circuit technologies of superconducting device were successfully developed by using a hard material such as niobium, several kinds of prototype Josephson processor for a general purpose computer have been constructed. Although a Josephson fuzzy processor is a special purpose computer, it is one of the most promising processors suitable for digital application of Josephson elements. The key function of the fuzzy processor is achieved by Mini-Max circuits. In this paper the principle of construction of the Mini-Max circuit using SQUIDs is mainly described in detail and simulation results are illustrated to show how high performance processor can be realized with a reliable operation. Main advantages of the processor are the very simple construction by use of SQUIDs, very high speed operation and ultra low power dissipation.

For communication relays, the contact reliability in the low electrical load circuit has been of great importance for the purpose of control of highly reliable electronic devices. With reference to the study of contact failure mechanism, the fact that the formation of black powder on the contact surface caused to increase contact resistance of relays in the organic gas atmosphere was well known. In this study, the electrical characteristics of black powder formed on the relay contacts was investigated in comparison with a sulfide. Cosequently, the interesting relationship between contact resistance and electrical breakdown was obtained. The inflection point was observed in voltage-current (V-I) characteristics for the black powder deposit which was more than 200 mΩ in contact resistance. And when the current increased, there occurred not only a decrease but also an increase in contact resistance. These results indicated that the accurate contact resistance should be evaluated using V-I characteristics. In addition to that, it was proposed that the allowable level of contact resistance for the contact failure was about 150 mΩ for the black powder deposit.