Sputter deposition of SrTiO₃ thin films for voltage tunable capacitors

Abstract

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, SrTiO₃ thin films were deposited onto (100)_pc LaAlO₃ and r-cut sapphire substrates using RF magnetron sputtering at elevated temperatures. The films deposited on LaAlO₃ 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.

Key Words:

• tunable capacitors
• interdigital electrodes
• SrTiO₃ thin films
• sputter deposition
• dielectric loss