Improved low frequency and microwave dielectric response in strontium titanate thin films grown by pulsed laser ablation

We have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured as a function of temperature and electric field bias using a microwave ring resonator and a flip-chip technique. The films having the highest dielectric constant were grown with an oxygen pressure of 600 mTorr and showed large grains in the plane of the film. The small-signal dielectric constant of these films could be changed by a factor of 4 by applying an electric field. The films with the highest dielectric constant showed increased losses, but an improved figure of merit for application to tunable circuits.