Effect of large strain on dielectric and ferroelectric properties of Ba0.5Sr0.5TiO3 thin films

Abstract

Ba x Sr 1 − x TiO 3 is ideally suited as a tunable medium for radio frequency passive component. In this context we have studied the effect of biaxial strain on the dielectric and ferroelectric properties of Ba0.5Sr0.5TiO3 thin films grown epitaxially on SrTiO3 (001) substrates. The lattice parameters of the films determined by high-resolution x-ray diffraction with the thickness varying from 160 to 1000 nm indicated large biaxial compressive strain which decreased from 2.54% to 1.14% with increasing film thickness. Temperature-dependent measurements of the dielectric constant in our strained Ba0.5Sr0.5TiO3 thin films revealed a significant increase in the Curie temperature as the film thickness is below 500 nm. Enhanced ferroelectric behavior was observed for highly strained films with a remanent polarization of 15 μC/cm2 in the 160-nm-thick layer. However, the thick films (≥500 nm) exhibited weak temperature dependence of the dielectric constant without any pronounced peak corresponding to the Curie temperature, which may suggest inhomogeneous strain distribution in the thick films.