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. (C) 1998 American Institute of Physics.