Microwave Properties of Sapphire Resonators with a Gap and Their Applicability for Measurements of the Intrinsic Surface Impedance of Thin Superconductor Films(<Special Section> Superconducting High-frequency Devices)

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A dielectric resonator with a gap between the top plate and the rest has been useful for measuring the penetration depth (λ) of super-conductor films, a parameter essential for obtaining the intrinsic microwave surface resistance (R_s) of thin superconductor films. We investigated effects of a gap on the microwave properties of TE_<0ml>-mode sapphire resonators with a gap between the top plate and the rest of the resonator. Regardless of a 10μm-gap in TE_<0ml>-mode sapphire resonators, variations of the TE_<0ml>-mode resonant frequency on temperature (Δf_0) as well as TE_<0ml>-mode unloaded Q remained almost the same due to lack of axial currents inside the resonator and negligible radiation effects. The λ of YBa_2Cu_3O_<7_δ> (YBCO) films obtained from a fit to the temperature-dependent Δf_0 appeared to be 195nm at 0K and 19.3GHz, which was well compared with the corresponding value of 193nm at 10kHz measured by the mutual inductance method. The intrinsic R_s of YBCO films on the order of 1mΩ, and the tan δ of sapphire on the order of 10^<-8> at 15K and 40GHz could be measured simultaneously using sapphire resonators with a 10μm-gap.
社団法人電子情報通信学会の論文
2006-02-01