Effect of misfit strains on fourth and sixth order permittivity in (Ba _0.60, Sr _0.40) TiO ₃ films on orthorhombic substrates

The in-plane dielectric response of [110] oriented Ba0.60 Sr0.40 Ti O3 epitaxial films grown on [100] NdGa O3 is used to determine the field induced polarization at 10 GHz. The nonlinear polarization curve is used to determine the linear and nonlinear permittivity terms for the in-plane principal directions, [001] and [1- 10]. Studied films are in the thickness range of 75-1200 nm, and clearly show the influences that drive tunability down with increasing residual strain. The variation of the tunability, along the [001] direction, proves to be less sensitive to residual strain then the [1- 10] direction, although [1- 10] is capable of greater tunability at low residual strains.