Sequential Ar-O2 sputtering of Y2O3, BaF2, and CuO targets for preparation of Y-Ba-Cu-O superconducting films without wet-O2 annealing

Superconducting Y-Ba-Cu-O (YBCO) films have been prepared by ex situ O2 annealing of multilayer films deposited on yttria-stabilized zirconia substrates by sequential rf diode sputtering of Y2O3, BaF2, and CuO targets, all of which are chemically stable. If sputtering is performed in an Ar ambient, the as-deposited films contain sufficient F to require its removal by annealing in wet O2 at about 800 °C or above before the superconducting YBCO phase can be formed by annealing in dry O2. However, sputtering in an Ar-O2 ambient greatly reduces the F content, making it possible to obtain the superconducting phase by annealing in dry O2 only. If the ambient contains about 20% O2, films with Tc (R=0)>85 K can be prepared without wet-O2 annealing. The Ar-O2 process therefore has the potential for in situ preparation of superconducting YBCO films.