Barrier layers for oxide superconductor devices and circuits

Abstract

A conductor suitable for use in oxide-based electronic devices and circuits is disclosed. Metallic oxides having the general composition AMO.sub.3, where A is a rare or alkaline earth or an alloy of rare or alkaline earth elements, and M is a transition metal, exhibit metallic behavior and are compatible with high temperature ceramic processing. Other useful metallic oxides have compositions (A.sub.1-x A'.sub.x)A'.sub.2 (M.sub.1-y M'.sub.y).sub.3 O.sub.7-.delta. or (A.sub.1-x A'.sub.x).sub.m (M.sub.1-y M'.sub.y).sub.n O.sub.2m+n, where 0.ltoreq.x, y.ltoreq.1 and 0.5.ltoreq.m, n.ltoreq.3, A and A' are rare or alkaline earths, or alloys of rare or alkaline earths, A' and A' are alkaline earth elements, alloys of alkaline earth elements, rare earth elements, alloys of rare earth elements, or alloys of alkaline earth and rare earth elements, and M and M' are transition metal elements or alloys of transition metal elements. The metallic oxides grow epitaxially on oxide superconductors as well as on substrates and buffer layers commonly used for growth of oxide superconductors. The oxide superconductors can also be grown epitaxially on these metallic oxides. Vastly improved performance of superconductor-normal-superconductor (SNS) junctions in high temperature superconductor materials are obtained when the normal material is a metallic oxide of the type disclosed. In the preferred embodiment, the conducting oxide CaRuO.sub.3 is used as the normal material in an SNS junelion with YBa.sub.2 Cu.sub.3 O.sub.7-.delta. as superconductor. A dc superconducting quantum interference device (SQUID) functioning at 77K fabricated with this type of junction exhibits large modulation and low noise.