ZnO thin films for high frequency SAW devices

Sezawa wave on a ZnO/sapphire substrate is applied to low insertion loss surface acoustic wave (SAW) filters in microwave band of 1.5 GHz to 2.5 GHz range. RF planar magnetron sputtering (RF-Mg) is used for the fabrication of epitaxial ZnO film. Sputtering conditions and the dopant are decided to realize a stable and reproducible process. Details of ZnO epitaxial growth and practical application results are reviewed. To improve the piezoelectric properties of ZnO film, electron cyclotron resonance (ECR) sputtering is investigated. The ZnO/quartz substrate has small temperature coefficient of frequency (TCF) and medium electromechanical coupling coefficient (k s ) comparable to ST cut quartz and Li 2 B 4 O 7 respectively. Theoretical and experimental results are also discussed.