THE COPLANAR RESONATOR TECHNIQUE FOR DETERMINING THE SURFACE IMPEDANCE OF YBA2CU3O7-DELTA THIN-FILMS

We describe how coplanar microwave resonators fabricated from patterne d thin films of YBa2Cu3O7-delta (YBCO) can be used to measure the ab-p lane microwave surface impedance Z(s) = R(s) + jX(s) of the films, in particular the absolute value and temperature dependence of the magnet ic penetration depth lambda. The current distribution of the resonator is calculated by modelling the resonator as a network of coupled tran smission lines of rectangular cross-sections; this is then used to est imate the ab-plane lambda(T) from the measurements of resonators of di fferent geometries patterned onto the same him, We obtain values of la mbda(0) in the range 150-220 nm, The unloaded quality factors of the l inear resonators at 7.95 GHz are around 45000 at 15 K and around 6500 at 77 K, We estimate the corresponding values of the intrinsic R(s) at 7.95 GHz to be 23 mu Omega and 110 mu Omega at 15 K and 77 K, respect ively, These values are comparable with those of other high quality un patterned YBCO films reported in the literature, Z(s) for the best opt imised films appears to be insensitive to the effects of patterning.