BiSrCaCuO superconducting films by plasma sputtering of nanocrystalline compound targets

Abstract

Bismuth-system thin films on sapphire and alumina substrates were deposited by D-C magnetron sputtering. This is the first report of superconducting bismuth-system films on alumina without buffer layers. The films were formed using dc magnetron sputtering in an argon oxygen environment from a single Bi 4Sr 3Ca 3Cu 6O x conducting target, thermomechanically processed to develop nanoscale size grains of 10–100 nm. Sputtering conditions, such as target power, gas pressure, and substrate bias were found to strongly affect the morphology of the sputtered films. Post-deposition anneals were optimized to yeild superconducting onset temperatures as high as 100°K for films sputtered on sapphire substrates. Superconducting onset temperatures of 85°K were achieved with films sputtered directly on fired alumina substrates, using no buffer layers. Longer anneals on sapphire yielded high Tc onset but also a wider transition.