Comparisons of high temperature superconductor thin films on various substrates for microwave applications

Abstract 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 LaAlO 3 (1 × 10 −5 , NdGaO 3 (3 × 10 −4 ), and CaNdAlO 4 (1 × −4 ). High quality single-crystal Tl 2 Ba 2 CaCu 2 O 8 (TBCCO) and YBa 2 Cu 3 O 7t-δ (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 LaAlO 3 substrates. Performance of superconductors on NdGaO 3 and CaNdAlO 4 was inferior because of increased losses from the substrates.