COMPARISONS OF HIGH-TEMPERATURE SUPERCONDUCTOR THIN-FILMS ON VARIOUS SUBSTRATES FOR MICROWAVE APPLICATIONS

Microwave loss tangents of various perovskite-related substrates have been measured at 77 K by inserting them in a 5 GHz microstrip resonator structure. Results include LaAl03 (1 x 10(-5)), NdGaO3 (3 x 10(-4)), and CaNdAlO4 (1 X 10(-4)). High quality single-crystal Tl2Ba2CaCu2O8 (TBCCO) and YBa2Cu3O7-delta (YBCO) thin films have been grown on these substrates by a two-step process for the former and in situ laser ablation for the latter. T(c) values were measured by a.c. susceptibility transition. The near-surface and average film crystallinity were examined by electron channeling pattern and X-ray rocking curve. Both TBCCO and YBCO films on these substrates have been patterned into 2.3 GHz resonators. Low-power Q values of 16 000-20 000 have been obtained for both TBCCO and YBCO on LaAlO3 substrates. Performance of superconductors on NdGaO3 and CaNdAlO4 was inferior because of increased losses from the substrates.