Ferroelectric properties of compressively strained epitaxial SrTiO 3 films on sapphire

Abstract

Magnetron sputtered and laser deposited SrTiO 3 thin films are deposited on CeO 2 buffered sapphire substrates. Their structural and ferroelectric properties are analyzed and possible (mutual) correlations between these properties are investigated. It is shown, that the biaxial compressive strain imposed by the substrate on the ferroelectric films leads to a considerable increase of the Curie temperature, as well as the dielectric constant and the tenability of these films in technically relevant temperature regimes. Generally, the dielectric constant and the tuning decreases with increasing strain. However, the ferroelectric phase transition of the SrTiO 3 films is shifted to higher temperatures compared to that of single crystalline SrTiO 3. As a consequence, the dielectric constant of the films is larger than that of undistorted SrTiO 3 single crystals for small strain (Δ a/ a < 0.005) and temperatures above the Curie temperature. Furthermore, a linear dependence of the loss tangent and the tunability on the dielectric constant is observed, which indicates, that all three properties are affected by the same mechanism that itself is affected by the lattice strain.