Superconducting Technology for Digital Applications Using Niobium Josephson Junctions

Shuichi TAHARA
Hideaki NUMATA
Shinichi YOROZU

IEICE TRANSACTIONS on Electronics   Vol.E83-C    No.1    pp.60-68
Publication Date: 2000/01/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section INVITED PAPER (Special Issue on Superconductive Devices and Systems)
Category: Digital Applications
Josephson junctions,  planarization,  moat structure,  memory,  network,  

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In this paper, we describe our superconducting digital technology that uses Nb/AlOx/Nb Josephson junctions. Superconducting devices have intrinsically superior characteristics than those of semiconductor devices, and Nb/AlOx/Nb junctions have ideal current-voltage characteristics for digital applications. Superconducting devices that use Nb/AlOx/Nb junctions have being actively developed because of their high speed and low power characteristics. Presently, we can fabricate more than twenty thousand junctions on one chip. Using niobium technology, a superconducting 4-kbit RAM has been already successfully developed. We have demonstrated the operation of a network system with a superconducting network chip. Some problems, such as difficulty in high-speed testing, disturbance from trapped magnetic flux and so on, have been overcome by techniques such as a clock-driven testing method, moat structures and so on. The developed technologies, such as the fabrication technology, the design technology for moat structures and so on, must become the basic keys for the development of digital applications based on a single flux quantum device, which will be a promising component for ultra-high speed systems in the twenty-first century.