Sputtering Techniques for Controlling Composition of Thin Films of High-Tc Superconducting Compounds

Abstract

Presently known, high transition temperature (≳15 K) superconducting materials have either the β-W (A-15) or rocksalt (B-l) crystal structure. Although these compounds retain the desired crystal structure over a wide composition range, optimum Tc’s are obtained only when the compounds are nearly stoichiometric. Films of some of these materials, including compounds in the Nb–Al, Nb–Sn, and Nb–Al–Ge systems, have been prepared by sputtering. To control composition, various targets have been employed, including ingots made by arc melting, hot-pressed powder mixtures, and multiple targets. Compound formation was achieved in most cases (as verified by x-ray diffraction analysis) regardless of target material used, however, the Tc’s of the films varied from < 10 K to over 16 K. The influence of target material on stoichiometry and on Tc is discussed, and some of the high-field superconducting properties of the deposited films are reported.