A sapphire resonator for microwave characterization of superconducting thin films

A simple technique has been developed for the high-frequency characterization of superconducting thin films. A microwave resonator is formed by sandwiching a high-purity c-axis-oriented sapphire rod between a pair of superconducting thin films. For the TE/sub 011/ resonant mode, the theoretical treatment allows for the surface resistance and the RF current density to be calculated from the unloaded Q-value and the dissipated power. This technique is especially useful since it has: no sample preparation; no calibration; great sensitivity; great accuracy; great repeatability; great dynamic range; high internal power levels with only moderate input power levels; and broad temperature coverage (4.2 to over 120 K). A round robin experiment using HTS thin films was performed to deconvolute the films´ surface resistance and also to provide a statistical analysis of the method´s reproducibility. The standard error for a single measurement is better than 2%. A Nb thin film was measured to verify the technique.<>