ADVANCES IN HTS FILMS FOR HIGH-POWER MICROWAVE APPLICATIONS

This paper describes recent work at DuPont to extend the high power mi crowave performance of YBa2Cu3O7 and Tl2Ba2CaCu2O8 high-T-c supercondu cting (HTS) films. The YBa2Cu3O7 films are produced by in-situ off-axi s sputtering with radiant substrate heating. The Tl2Ba2CaCu2O8 films a re produced by off-axis sputtering followed by annealing in oxygen and Tl2O vapor. The microwave surface resistance and power handling of th ese films has been measured over a wide range of temperature (20 K to 100 K) using a HTS-sapphire resonator technique. At 70 K, the surface resistance of YBa2Cu3O7 films remains below 65 mu Omega (@ 5.56 GHz) w ith microwave surface current densities up to 5 x 10(6) A/cm(2). At 70 K, the surface resistance of Tl2Ba2CaCu2O8 films remains below 200 mu Omega (@ 8.1 GHz) with microwave current densities up to 2 x 10(6) A/ cm(2).