Microwave characterization of as-grown MgB2 thin films prepared by molecular beam epitaxy

The MgB₂ superconductor with T_C of 39 K has great potential to replace some LTS materials in superconducting electronics. Thin films with low surface resistance, (R_S) and negligible nonlinear effects are necessary to realize MgB₂ circuits for microwave applications. The R_S of MgB₂ thin films varies significantly depending on the method of deposition and deposition conditions. We have investigated microwave properties of MgB₂ thin films grown on MgO substrate by the Molecular Beam Epitaxy method with novel co-evaporation conditions at low deposition rate in ultra-high vacuum. The R_S of as-grown MgB₂ thin films have been measured using the Hakki-Coleman Sapphire dielectric resonator technique. High measurement accuracy was accomplished by using multifrequency measurements of S-parameters and the Transmission Mode Q-Factor technique for data processing to obtain the unloaded Q_o-factor and resonant frequency of the dielectric resonator. Measured R_s of the MgB₂ films of 400 μΩ was obtained at frequency of 24.6 GHz and temperature of 13 K. Microwave power characteristics of R_s indicates stable operation of MgB₂ devices for the input power up to 10 dBm.