Microwave Response of MgB₂/Al₂O₃ Superconducting Thin Films by Microstrip Resonator Technique

Double-sided superconducting MgB₂ thin films are deposited onto c-Al₂O₃ substrates by the hybrid physical chemical vapour deposition method. The microwave response of MgB₂/Al₂O₃ is investigated by microstrip resonator
technique. A grain-size model is introduced to the theory of microstrip resonators to analyse microwave properties of the films. We obtain effective penetration depth of the films at 0K (λ_e0=463nm) and surface resistance (R_s=1.52mΩ at 11K and 8.73GHz) by analysing the resonant frequency and unload quality factor of the microstrip resonator, which suggests that the impurities and disorders of grain boundaries of MgB₂/Al₂O₃ result in increasing penetration depth and surface resistance of the films.