Superconducting thin-film YBa2Cu3O7-x resonators

Measurement of surface resistance R_S in thin films of YBa₂Cu₃O_7-x produced by magnetron sputtering have been carried out using a stripline resonator. Four-pole microstrip bandpass filters have been fabricated using these thin films on 1.3×2.3-cm LaAlO₃ substrates. Such filters with a center frequency of 4.8 GHz and a bandwidth of 1% have exhibited a passband insertion loss as low as 0.5 dB at 77 K. The R _S of YBa₂Cu₃O_7-x films has been found to increase with input power at power levels that depend on film quality, an effect that can be related to the RF magnetic field at the conductor surface. The power dependence of R_S leads to nonlinear effects, such as generation of harmonics and intermodulation products, which must be avoided in linear device applications. Measurements of intermodulation products in the filters are presented, as well as measurements of phase noise in filters and resonators