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

Abstract

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.

Millimetre and sub-mm wavelength radiation sources based on discrete Josephson junction arrays

“…It is important, however, to recognize the difference between making a good single junction and making a good array of junctions consisting of as many as hundreds or even thousands of R5 junctions. Today, the production of cryoelectronic circuits made from Nb consisting of some 10 000 Josephson tunnel junctions is successfully performed by several groups around the world owing to enormous efforts aimed at the production of rather complex cryoelectronic circuits [43][44][45][46][47][48]. There are even companies successfully selling circuits which can be custom designed by the customer.…”

Future heat transfer concerns in Josephson junction computers

“…Such low power dissipation allows high integrations and thus even higher speeds. Research in producing high quality sub-m Nb JJ's [21]- [23] continues in order to allow the highest integrations possible. Realization of sub-m JJ's can lead to greater integration by not only reducing junction area, but by reducing area enough that the junctions become innately overdamped [20] and thus eliminate the need for shunt resistors.…”