Surface impedance measurements of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films using coplanar resonators

The microwave response of linear and meander coplanar resonators fabricated from patterned thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) on MgO substrates was studied. Unloaded quality factors in excess of 45000 at 2.36 GHz and 12 K were measured. From the calculated microwave current distribution in the resonator, upper limits of the intrinsic surface resistance of the best film at 15.9 GHz of 150 mu Omega and 690 mu Omega at 12 K and 77 K, respectively, were obtained. Values of the magnetic penetration depth lambda (0) in the films were estimated to be in the range 165-220 nm. It is possible to accurately fit 1/ lambda (T)/sup 2/ to the function 1-(T/T/sub c/)/sup 2/ over the whole of the available temperature range. This behavior is unlike that predicted by BCS theory, but it is probably extrinsic and can be explained by the enhanced field penetration at the film edges due to superconducting weak links. >