Surface resistance of YBa2Cu3O7 superconducting films on LaAlO3, NdGaO3 and Al2O3 substrates at varying microwave power levels

Nonlinear performance of High Temperature Superconductors at high RF power levels is still one of major constrains in mass market applications of HTS films in cellular and PCS communication systems. We have measured surface resistance of YBa₂Cu₃O₇ films on several substrates and compared their microwave power-handling capabilities. We have found that for high-quality YBCO films the losses of films on LaAlO₃ substrate are the smallest followed by films on NdGaO₃ and then on Al₂ O₃. Also the best quality films exhibited linear behaviour up to very high RF fields. Power-handling properties of YBCO on Al₂O₃ are improved by very good thermal conduction of sapphire. Best films deposited with the thermal co-evaporation and the off-axis sputtering techniques have been found to be of comparable quality