High-frequency characterization and modeling of paraelectric∕superconductor resonators for high power-handling microwave passive devices

Abstract

The theoretical conditions required to observe reduced nonlinearities in passive microwave devices made of a paraelectric (PE) thin layer and a high-temperature superconductor (HTS) thin film are presented. In a transmission line (TL) combining both materials, the nonlinear permittivity εr(Vrf) of the PE generates a nonlinear capacitive contribution Cd(Vrf), whereas the nonlinear penetration depth λ(Irf) of the HTS produces a nonlinear inductive contribution Ld(Irf). These contributions act in opposite ways. Under determined conditions that will be defined, they may fully compensate or at least lead to the reduction of the spurious signal level. The HTS nonlinearities may be lowered by employing very thin layers of PE. In this case, the high dielectric loss tangent (tanδ) of PE should not be such an issue. Based on experimental results obtained with superconducting YBa2Cu3O7−δ resonators integrating different thicknesses of paraelectric SrTiO3 (STO) deposited on LaAlO3 substrates, the loss level could then be considered in the simulation of the proposed compensation effect. The results show that the reduction of the unloaded quality factor (Q0) as the thickness of STO increases also impacts the level of spurious signals. Then, an analytic expression for the Q0 of a resonant TL that integrates a PE and a HTS thin layer is proposed. It specifies the conditions for reducing the total nonlinear response. These results could then be applied to realize high power handling HTS passive microwave devices.