Surface impedance measurements of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films in stripline resonators

The microwave surface impedance of thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ is measured as a function of temperature, frequency, and RF magnetic field, H/sub RF/, using a stripline-resonator technique. The films were deposited in situ by single-target off-axis magnetron sputtering. The frequency range was from 0.4 to 20 GHz, the temperature range from 4.2 K to T/sub c/, and the RF magnetic field range from 0 to 30 Oe. The surface resistance R/sub S/ at 4.2 K and 1.5 GHz is 4*10/sup -6/ Omega . The penetration depth is determined to be 0.167 mu m in the best film, In some films, R/sub S/ shows a linear dependence on H/sub RF/ and rises rapidly at large fields, showing no evidence of saturation. In others, R/sub S/ shows weak dependence on H/sub RF/ before rising rapidly. These behaviors differ from those observed in bulk ceramic YBa/sub 2/Cu/sub 3/O/sub 7-x/ and in unpatterned films measured in microwave cavities. However, the shape of R/sub S/(H/sub RF/) for the YBa/sub 2/Cu/sub 3/O/sub 7-x/ films is similar to that of Nb and NbN films measured in the same stripline geometry. The authors also present measurements of the intermodulation products in the resonators and discuss the implications of the R/sub S/ and intermodulation measurements for microwave device applications.