Nonlinear microwave properties of superconducting YBaCuO and dielectric MgO

We have investigated the nonlinear properties of high-temperature superconducting films on MgO substrates for microwave applications in the UHF-range. Surface impedance and two-tone frequency intermodulation are different sources of nonlinear microwave response, which are subtly related. We have found correlations between the microwave response of the superconducting films and their electronic and structural properties, which are essential to optimise the device performance. Furthermore, for the first time, we have observed a nonlinear dielectric loss tangent of MgO at temperatures up to 70 K. The dielectric losses contribute significantly to intermodulation distortion. Our findings are relevant for conventional and superconducting microwave components involving usual dielectric materials like MgO. The results may also prove helpful for the development of novel RF dielectrics.