MICROWAVE PROPERTIES OF YBCO THIN-FILMS

We have measured the microwave properties of high quality YBCO thin fi lms using a copper cavity (87GHz) and a dielectric resonator (19GHz) f or unpatterned films as well as a coplanar resonator (5, 8, 10, 15 and 16GHz) for patterned films. For the patterned films the surface resis tance (R(s)) and non-linear effects were studied as a function of temp erature below T-c. For practical applications, the assessment of non-l inear effects in the surface resistance are of great importance. The b est films showed R(s) approximately constant up to microwave peak curr ent densities of the order of the dc critical current density. The mea surements were performed on samples fabricated by a number of differen t techniques.