BiSrCaCuO superconducting films by plasma sputtering of nanocrystalline compound targets

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 Bi₄Sr₃Ca₃Cu₆O_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.