Enhanced Performance of ZnO/SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> Surface Acoustic Wave Devices with Embedded Electrodes
Rongxuan Su, Sulei Fu, Junyao Shen, Zhenglin Chen, Zengtian Lu, Mingliang Yang, Rui Wang, Fei Zeng, Weibiao Wang, Cheng Song, Feng Pan
Abstract
With the advent of the 5G era, surface acoustic wave (SAW) devices with a larger bandwidth and better temperature stability are strongly required, meanwhile the dimensions of devices are continuously scaling down. In this work, a new layout of ZnO/SiO2/Al2O3 SAW devices with embedded electrodes was developed, and with the help of the finite element method (FEM), the propagation characteristics were simulated. Through adopting embedded electrodes, a large electromechanical coupling coefficient (K2) of 6.6% for the Rayleigh mode can be achieved (5 times larger than that of the conventional ZnO/Al2O3 structure), feasible for wideband SAW devices, and a low acoustic velocity (Vp) of 2960 m/s is exhibited simultaneously, which benefits the miniaturization of SAW devices. The dramatic enhancement of K2 is mainly attributed to the more efficient excitation of SAW in piezoelectric films. Furthermore, a SiO2 overlay is added on the top of the structure to gain an excellent zero temperature coefficient of frequency (TCF). Experimentally, we successfully fabricated SAW one-port resonators based on the proposed structure and good characteristics of high K2, low Vp, and small TCF as simulated were confirmed. Our results show that the proposed structure provides a viable route to design SAW devices with a large bandwidth, small size, and robust temperature compensation for practical use.