Thin films of Y-Ba-Cu-O by RF sputtering

Thin films of Y-Ba-Cu-O have been prepared by RF diode sputtering from a single mixed-oxide powder target. The films were deposited on sapphire and cubic zirconia substrates, with the substrates either cooled, heated, or left to establish thermal equilibrium. The Cu content in the films decreased with increasing substrate temperature. Films having a composition close to the desired 1-2-3 stoichiometry were fabricated either by enriching the target with CuO or by cooling the substrate. Using the latter approach, a single target was used for over 20 depositions yielding films that were uniform in composition (although slightly Cu-rich), and consistent from run to run. These films had as-deposited room temperature sheet resistances on the order of 100 k ohms. Subsequent annealing at temperatures up to 850 C resulted in films that were superconducting with an onset around 90 K and zero resistance at 50 K. The critical current was found to exceed 2000 A/sq cm at 4.2 K.