Prospects for Electronic Applications of Rare-Earth-Free Superconducting Thin Films

Abstract

Thin films of the high-T _c superconductors Bi-Ca-Sr-Cu-O (BCSCO) and Tl-Ca-Ba-Cu-O (TCBCO) were prepared and characterized. A zero resistance state was achieved at 116 K in the TCBCO films. The crystal structures of these films are pseudo-tetragonal, so that the surface morphologies are essentially twin free. Using a SQUID magnetization measurement in a parallel field, a randomly oriented polycrystalline TCBCO thin film showed a critical current density (J _c ) in excess of 1.2×10⁶ A/cm² at 50 K. This large J _c indicates the presence of surface pinning, which is much stronger than any bulk pinning observed by a measurement in a perpendicular field. Anisotropy of J _c is not only dependent on the degree of preferred orientation of the films, but also the presence of surface effects caused by a relatively large penetration depth. Microbridge dc SQUID’s have been fabricated from the BCSCO and TCBCO thin films patterned by maskless etching using focused ion beam (FIB) processes. The SQUID operation observed up to 95 K in TCBCO shows promise for early applications of the films provided that 1/f noise can be reduced.