THE EDGE EFFECT OF A MICROSTRIP RESONATOR ON THE FIELD-DEPENDENCE OF THE SURFACE-RESISTANCE OF A HIGH-T-C SUPERCONDUCTING THIN-FILM

A new behavior of the field dependence of microwave surface resistance (R-s), which was observed on a microstrip resonator and may be caused by the edge of the center strip, is reported in this paper for epitax ial high-T-c superconducting (HTSC) thin films. The exhibited behavior is that R-s remains almost unchanged below a certain rf magnetic fiel d H-rf, and then increases abruptly at this held, after which it incre ases in proportion to H-rf. To explain the behavior, the morphology of the microstrip resonator was examined by atomic force microscopy (AFM ), which showed that the edge of the resonator was damaged in some reg ions because of the acid etching. If the damaged edge is considered as a weakened granular superconductor, the observed R-s behavior could b e explained well in terms of the high-frequency critical state model. This implies that the edge condition should be considered in studying the field dependence of R-s when the planar resonator technique is use d.