Analysis of bulk acoustic wave response in ZnO based structures using transmission-line method

Piezoelectric thin film ZnO and its ternary alloy MgZnO have broad applications in transducers, resonators, filters and sensors. In ZnO based multi-layer piezoelectric device structures, such as ZnO on r-Al₂O₃, multi-acoustic wave mode coupling between each layer in the multilayer structure must be considered. In this paper, we use transmission line representation to analyze frequency response of a structure based on piezoelectric Mg_xZn_1-xO. The structure is Al/Mg_xZn_1-xO/n⁺⁺ ZnO/r-sapphire, where the Al and n⁺⁺ ZnO layers serve as top and bottom electrodes, respectively. Due to the crystalline orientation of the n⁺⁺ ZnO electrode and r-plane sapphire used in this work, there exist quasi shear and longitudinal wave modes in the device. The simulation results and measured device response show general agreement.