Sputter deposition of SrTiO3 thin films for voltage tunable capacitors

The electric field dependence of the dielectric constant of ferroelectric and related materials can be used to fabricate voltage tunable filters for microwave applications. In this study, the growth, structure, and dielectric properties of sputter deposited thin films will be discussed. In particular, SrTiO 3 thin films were deposited onto (100) pc LaAlO 3 and r-cut sapphire substrates using RF magnetron sputtering at elevated temperatures. The films deposited on LaAlO 3 were highly (00ι) oriented possessing a cube-on-cube heteroepitaxial structure, while the films deposited directly on sapphire were polycrystalline. We have studied the influence of deposition conditions and post deposition annealing on the crystal quality, microstructure, and electrical properties. We find that post deposition annealing can significantly improve the tunability of heteroepitaxial films. The magnitude and tunability of the dielectric constant will be correlated with film crystalline quality and microstructure.