MICROWAVE PROPERTIES OF YBA2CU3O7-X THIN-FILMS STUDIED WITH COPLANAR TRANSMISSION-LINE RESONATORS

The microwave properties of epitaxial YBa2Cu3O7-x thin films with critical temperatures T(c) up to 91.5 K and critical current densities J(c) up to 6 x 10(6) A/cm2 at 77 K have been in between 5 and 20 GHz using coplanar transmission line resonators. Information about the surface resistance R(s) and the magnetic penetration depth lambda(L) has been obtained from temperature- and power-dependent measurements of the quality factors and resonance frequencies of the resonators. The lowest surface resistance was 105 muOMEGA at 77 K and 38 muOMEGA at 9 K measured at 6.2 GHz, respectively. The dependence of R(s) on the surface magnetic field B(rf) showed that with decreasing film quality the films exhibit a granular behavior. At high critical current densities J(c) > 4 x 10(6) A/cm2, the intrinsic properties of the material show up. The magnetic penetration depth was in the range between 160 and 270 nm. Both R(s) and lambda(L) turned out to be sensitive to the film quality represented by the transition width DELTAT(c) and the critical current density J(c) at 77 K.