Effect of the incident power on permittivity, losses and tunability of BaSrTiO3 thin films in the microwave frequency range

Abstract

Domain wall motions in ferroelectrics participate to the material's complex permittivity and are responsible for their sensitivity of the dielectric properties to the driving electric field and thus to the incident power at microwave frequencies. In the present study, the dependence of the permittivity, the dielectric losses, and the tunability of Ba2∕3Sr1∕3TiO3 (BST) thin films on the incident power and on the bias fields is examined at a frequency of 500 MHz. While the domain wall motion participates only slightly to the permittivity (<5%), it strongly influences the losses due to its very dissipative behavior. As a consequence, the Figure of Merit (FoM, the ratio between tunability and dielectric losses) of the material depends on the applied microwave power. In the present study, a decrease in the FoM from 29 to 21 is observed for an incident power varying from –20 dBm to 5 dBm. When characterizing ferroelectric materials, the incident power has to be considered; moreover, domain wall motion effects should be limited in order to achieve a high FoM and less power sensitivity.