Advances in HTS films for high power microwave applications

This paper describes recent work at DuPont to extend the high power microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ high-T/sub c/ superconducting (HTS) films. The YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by in-situ off-axis magnetron sputtering using are produced by in-situ off-axis sputtering with radiant substrate heating. The Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films are produced by off-axis sputtering followed by annealing in oxygen and Tl/sub 2/O 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 YBa/sub 2/Cu/sub 3/O/sub 7/ films remains below 65 /spl mu//spl Omega/ (@5.56 GHz) with microwave surface current densities up to 5/spl times/10/sup 6/ A/cm/sup 2/. At 70 K, the surface resistance of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films remains below 200 /spl mu//spl Omega/ (@8.1 GHz) with microwave current densities up to 2/spl times/10/sup 6/ A/cm/sup 2/.