Theoretical studies on a TeO_2/ZnO/diamond-layered structure for zero TCD SAW devices

摘要

High-frequency surface acoustic wave (SAW) devices based on diamond substrate are useful because of their very high SAW velocity. In the present work, SAW propagation characteristics, such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of a TeO_2/ZnO/diamond-layered structure, are examined using theoretical calculations. The ZnO/diamond bi-layer structure is found to exhibit a high positive TCD value. A zero TCD device structure is obtained after integration with a TeO_2 over layer having a negative TCD value. Introduction of a non-piezoelectric TeO_2 over layer on the bi-layer structure (ZnO/diamond) increases the coupling coefficient. A relatively low thickness of TeO_2 thin film (～(1.6-3.1) × 10~(-3)λ) is required to achieve temperature-stable SAW devices based on diamond.