Progress in Nb-based low-temperature superconductive electronics for high-speed digital applications in Japan

Recent progress in Nb Josephson junction LSI technology in Japan is described. Improvements in fabrication processes of the Nb/AlOx/Nb junction have brought high junction-current densities and sub-micrometre junction sizes. Research efforts on logic LSIs have mainly focused on applications to high-speed switches for broad-band communication and high-performance parallel computing. The highest achieved clock frequency of the logic LSIs is beyond 3 GHz. Josephson memory technology has also progressed realizing an access time of 380 ps for a 4 kbit LSI. In a new approach toward logic circuits for future information systems, basic research on a hybrid circuit technology, composed of superconductive and semiconductor devices, has also been started in Japan. The present status of these research efforts in Japan is reviewed.