Advances in HTS films for high power microwave applications

This paper describes recent work at DuPont to extend the high power microwave performance of YBa2Cu3O7 and Tl2Ba2CaCu2O8 high-T-c superconducting (HTS) films. The YBa2Cu3O7 films are produced by in-situ off-axis sputtering with radiant substrate heating. The Tl2Ba2CaCu2O8 films are produced by off-axis sputtering followed by annealing in oxygen and Tl2O vapor. The microwave surface resistance and power handling of these 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) with 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).