Large signal circuit model of parallel-plate ferroelectric varactors

Abstract

A simple one port reflection method is proposed to measure the large signal permittivity and loss tangent of ferroelectric films. The microwave power levels are changed in the range from −10to17dBm at 0V dc bias. Microwave power causes two effects: (i) generation of higher order harmonics due to the dielectric nonlinearities and (ii) heating of the ferroelectric film. The harmonic generation is measured as loss since the instruments (network analyzer and LCR meter) do not detect the higher order harmonics. The heating, on the contrary, is found to cause a reduction of observed microwave losses and at higher microwave power becomes dominant, partly compensating for the loss increase caused by harmonic generation. The heating effect is substantially reduced if the applied microwave signal is pulsed. The results are used to extract parameters for a simplified large signal circuit model of the thin film parallel-plate ferroelectric varactors in the frequency range of 10–45GHz. Only a limited number of measurements are used in modeling. The model is useful for zero bias mixer (up and down converter) and harmonic generator applications of ferroelectric varactors.