Coplanar resonators fabricated from thin film high-Tc superconductors

The discovery of superconductors with transition temperatures T_c above the boiling point of liquid nitrogen (77.4 K) has opened up the real possibility of practical superconducting microwave applications, utilising the very low surface resistance R _s of the superconductor. As part of a broad research effort on novel superconducting microwave devices, the authors have used the coplanar resonator geometry to assess the microwave properties of thin films of YBa₂Cu₃O₇ (`YBCO´, with T_c≃90 K), in particular the microwave dissipation of the material at patterned film edges which dominates the performance of any planar device. The coplanar resonator is an ideal test structure since only one film surface is required before patterning (thus removing the need for double-sided deposition) in addition, microwave current densities are very high at the film edges, allowing one to study nonlinear dissipation due to high microwave power levels