Effects of processing on electrical properties of YBa₂Cu₃O₇ films. I. Postdeposition anneal process

The effects of several patterning process steps on the critical current density J_c and microwave surface resistance R_s of a‐axis oriented films of YBa₂Cu₃O₇ on LaAlO₃ are described. The films were prepared by cosputtering from Y, BaF₂, and Cu targets, followed by annealing in water‐saturated O₂. J_c and R_s parameters were measured by mutual inductance and parallel plate resonator techniques, respectively, so that the films did not require patterning for the measurement. Application of a polymer film followed by stripping in acetone caused modest degradation, while stripping with an O₂ plasma resulted in no change in the parameters. Brief ion milling, as well as baking at 185 °C with polymer film present, caused severe degradation; other treatments had intermediate effects. The degree of degradation suggests that the surface damage results in secondary effects that penetrate well into the film. A formula is derived for the change in R_s due to a surface layer, providing a quantitative comparison to experiment.