Characterization of the field-dependent permittivity of Ba_0.5Sr_0.5TiO₃ thin films up to 110 GHz

Abstract

Perovskite Ba_0.5Sr_0.5TiO₃ (BST) thin films with a thickness of 300 nm are deposited on high resistivity silicon through pulsed laser deposition. The permittivity of BST is changed by applying an external electrostatic field. Coplanar waveguides (CPWs) are designed to extract the field-dependent permittivity of the film in the frequency range from 1 GHz to 110 GHz. A Subregional Match 3-Dimensional finite element method (SM 3D FEM) is proposed to implement the permittivity extraction. We analysis the electric field distribution in BST film, and thus divide the BST film in a reasonable way in order to achieve the permittivity of each small region in BST film by S-parameters-phase matching. The relative difference between measured and simulated S-parameters-phase is defined to describe the precision of the result. Experimental results show that the relative difference is less than 1.3%. We also found that the permittivity tunability is almost unchanged in a wide frequency domain, the variation of the tunability less than 0.16. The relative dielectric permittivity ξ_BST at 0 V equals 1148.9 at 1 GHz and reduces to 311.7 at 110 GHz, and ξ_BST at 100 GHz equals 315.8 at 0 V and declines to 193.4 at 30 V. The tunability of BST film is about 38.7% at 100 GHz.