Measurement of the Microwave Nonlinear Response of Combined Ferroelectric-Superconductor Transmission Lines

We fabricated nonlinear transmission lines and resonators that incorporate both distributed nonlinear capacitance and distributed nonlinear inductance in order to explore how such nonlinear elements interact in a combined nonlinear device. This work is motivated by the desire to reduce the nonlinearity associated with high temperature superconductor (HTS) microwave circuits by active cancellation through the use of nonlinear dielectrics. We characterized the nonlinear response of composite HTS-ferroelectric devices by combining intermodulation distortion (IMD) measurements vs. incident power with detailed linear measurements to extract the nonlinear circuit impedance. By directly comparing a resonator whose nonlinear response is dominated by the HTS nonlinear response with the nonlinear response of the composite HTS-ferroelectric device at different temperatures, we were able to differentiate between HTS and ferroelectric contributions to the overall nonlinear response. Although we observe no direct evidence for the cancellation or compensation of inductive HTS nonlinear effects due to the capacitive nonlinearity of integrated ferroelectric materials, we do observe a cross-over as a function of temperature from capacitive-dominated nonlinearity to inductive-dominated nonlinearity.