Growth of High-Temperature Superconductor Thin Films on Lanthanum Aluminate Substrates

Abstract

We report on the use of the pseudo-perovskite crystalline compound LaA1O₃ as a substrate for thin-film growth of high-temperature superconductors. Lanthanum aluminate provides a good lattice match to the basal plane of the superconducting cuprates with its lattice constant of 3.792Å. In contrast with strontium titanate, LaA1O₃ also serves as a useful substrate for high-frequency applications with its low dielectric constant (~16) and low microwave losses (5 × 10^-6 loss tangent at 4.2 K). In this paper we compare the properties of a number of crystalline substrates for use with high-temperature superconducting films.

We have tested the use of LaAlO₃ with thin films of erbium-barium-copper-oxide and yttrium-barium-copper-oxide made by a variety of techniques including multisource sputtering, single-target sputtering, electron-beam evaporation, and pulsed laser deposition. High-quality epitaxial films have been produced using both single-step (in situ) and multi-step (post-anneal) processing. Films on LaAlO₃ exhibit sharp resistive transitions, high current density, strong c-axis orientation, and bulk superconducting properties as evidenced by magnetic susceptibility measurements. Substrate-film interaction effects appear to be minimal for the LaAlO₃/1-2-3 system and the thermal expansion properties of LaAlO₃ substrates are very compatible with 1-2-3 films.