Surface Acoustic Wave Characteristics with a Layered Structure of IDT/θ° YX-LiTaO3/SiO2/AlN/diamond

Abstract

A new layered surface acoustic wave (SAW) structure was proposed by Murata Co., Ltd recently. It was reported that such structure could achieve an incredible high performance including a higher quality factor Q and electromechanical coupling coefficient K². For deeply understanding propagating characteristics and optimizing the performance of the SAWs in such structure, a layered structure of IDT/θ° YX-LiTaO₃/SiO₂/AlN/Diamond with different structural parameters were theoretically investigated by FEM method. The calculated admittance shows that four eigenmodes simultaneously exist in such layered structure including the main mode SH SAW. And compared with the Traditional SAW structure, the main mode could achieve a higher value of K² with sacrificing its velocity a little. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With Au employed, the K² of the main mode is a little larger resulting from better suppression of the spurious modes. The optimum thickness of electrode and piezoelectric layer are 0.2 and 0.02λ, respectively. In this case, the K² for the SH SAW achieves its maximum value of 12.20% with a large phase velocity of 3608 m/s. Furthermore, the pure SH SAW can be obtained with the Y-cut Euler angle θ from 0° to 60°, where its K² has a wide range of 8.70 to 13.69%. Consequently, the work provides a theoretical guide for designing SAW devices of different bandwidth and operation frequency with such structure.