Demonstration of surface resistance mapping of large-area HTS films using the dielectric resonator method

A scanning mapping technique of surface resistance (R_s) using the sapphire dielectric resonator was developed and demonstrated for a 3-inch-diameter YBa₂Cu₃O_y film. The area of the 3-inch film was divided by 5 × 5 mm grid for scan, resulting in 101 measurement points. Values of R_s in the film varied from 2.9 to 3.8 mΩ at 22 GHz and 77 K. The distribution of R_s corresponded to that of the critical current density. Sampling of quality factors at each point was performed using non-contact measurement between film and sapphire. Since the airtight chamber was filled with dry N₂ gas to avoid film degradation by frost and water during the warming process, perfect non-destructive measurement is realized. Fluctuation of distance between the surface of film and dielectric rod was monitored by resonance frequency. Errors in R_s caused by the fluctuation were calculated within ±0.01 mΩ. Furthermore, the system could detect a small (0.3 mm × 0.5 mm) scratch defect as well as the gradient of film thickness on Ag film. This technique is effective for inspection of large-area high temperature superconducting films for microwave applications.