EFFECTS OF GRAIN-BOUNDARIES ON TEMPERATURE-DEPENDENCE OF MICROWAVE SURFACE-RESISTANCE OF YBA2CU3O7-X THIN-FILMS

This paper investigates the temperature dependence of microwave surfac e resistance (R-S) of YBa2Cu3O7-x (YBCO) thin films with different mic rostructures at 10GHz, using a coplanar resonator technique. YBCO thin films with different grain sizes were obtained as a result of changin g the quenching procedure after film deposition by de sputtering. The value of Rs was found to vary with varying surface morphology and fan be explained by the coupled grain model (CGM) when a temperature-depen dent grain boundary resistance (R) is used. The temperature (T) depend ence of R is given by R = R-0 + C(T/T-C)T-2, where T-C is the supercon ducting critical temperature, and R-0 and C are the fitting parameters , depending on the properties of each sample.