Effects of microstructures on microwave properties in Y-Ba-Cu-O microstrip-resonators
We examined the microwave properties of YBa/sub 2/Cu/sub 3/O/sub x/ films with different microstructures at 5.7 GHz using a microstrip resonator technique. The films were prepared with several types of substrate temperature profiles. Films with small grains (/spl sim/100 nm) and larger critical current density show fairly small rf magnetic field dependence of surface resistance and resonance frequency up to about 50 Oe. On the other hand, films with large grains (/spl sim/200 nm) and smaller critical current density show significant changes in these properties. These results suggest that the coupling strength at the grain boundaries mainly dominates the power handling capability, according to a qualitative explanation based on the coupled-grain model.<<ETX>>