dc-electric-field-induced microwave loss in ferroelectrics and intrinsic limitation for the quality factor of a tunable component

An effect of dc electric field on the intrinsic microwave loss in incipient ferroelectrics is theoretically studied. The contribution of the so-called field-induced quasi-Debye mechanism, which is related to the relaxation of phonon distribution function, is evaluated. It is found that the dc-field-induced loss is controlled by the relaxation of the acoustic-phonon distribution function rather that the distribution function of the soft-mode phonons, as was earlier assumed. The theory gives qualitative explanation for a dramatic field-induced increase of the loss factor recently reported for KTaO3 and SrTiO3 bulk resonators with superconductive electrodes. Numerical estimates performed for KTaO3 are in a good agreement with the experimental data. The field and frequency dependence of the figure of merit of a ferroelectric-based tunable microwave component is evaluated. (C) 2000 American Institute of Physics. [S0003-6951(00)02109-4].