Microwave characterization of high-T/sub c/ superconducting thin films and devices

Summary form only given. The high-frequency surface resistance R/sub S/ of high-T/sub c/ thin films is typically determined by measuring loss (or quality factor Q) in a resonator and then accounting for the current distribution in the film so that an equivalent surface resistance for a semi-infinite-thick slab can be calculated. A stripline resonator has been the characterization tool of choice at Lincoln Laboratory. The best R/sub S/ values obtained for YBCO at a frequency of 1.5 GHz were 2.6*10/sup -6/ Omega at 4 K and 8.3*10/sup -6/ Omega at 77 K. The surface resistance depends on power, not only because of the nature and quality of the superconducting film, but also because the design of the device will affect current distribution. In particular, current crowding at the edge of transmission lines produces a nonlinearly increasing R/sub S/ with increasing power, and this leads to the generation of harmonics, intermodulation products, and reduction of Q. In linear device applications, power levels must be selected to avoid such nonlinear effects.<>