Double-barrier Josephson structures as the novel elements for superconducting large-scale integrated circuits

An overview of the current status of different types of non-hysteretic Jose phson junctions is given with emphasis on double-barrier structures. The re sults of theoretical work on double-barrier SIS'IS Josephson junctions (I i s a tunnel barrier, S' is a thin film with T-C' < T-C) are presented. The m icroscopic model for the supercurrent is developed for two cases: the S' in terlayer in the clean and in the dirty Limit. The model describes the cross -over from direct Josephson coupling of the external S electrodes to the re gime of two serially connected SIS' junctions. We calculate the ICRN produc t as a function of the T-C'/T-C ratio, the interlayer thickness and the bar rier strengths and compare the theory with experimental data for Nb/AlOx/Al /AlOx/Nb junctions. We argue that these junctions are very promising in rap id single flux quantum (RSFQ) and programmable voltage standard application s, since they are intrinsically shunted and have controllable interfaces. W e formulate the requirements for materials and interface barriers in order to increase critical current densities and ICRN products in double-barrier junctions. (C) 1999 Elsevier Science B.V. All rights reserved.