Mechanical strain engineering of dielectric tunability in polycrystalline SrTiO3 thin films

Abstract

Optimizing performance using low cost scalable processing and substrates is critical if functional oxide thin films are to achieve commercialisation. Here, we present a comprehensive investigation of the role of low cost Al₂O₃, SrTiO₃, and MgO substrates in the structure, microstructure and electrical properties of SrTiO₃ (ST) thin films, deposited by sol–gel processing. We demonstrate that the dielectric properties of polycrystalline ST films depend on the strain/stress induced by the substrates. ST films deposited on Al₂O₃/Pt substrates under a high tensile stress possess the smallest grain size and present the lowest value of the relative permittivity, ε_r, with the lowest dielectric tunability. In contrast, ST films deposited on MgO/Pt substrates, under the highest compressive stress, have the highest value of ε_r, tunability and polarization. It is thus demonstrated that for polycrystalline ST films the relative permittivity and dielectric tunability may be optimised through an induced compressive stress state.