Laterally-excited bulk acoustic wave resonator with an adjustable piezoelectric coupling coefficient

Abstract

This paper reports on a design journey for laterally-excited bulk acoustic wave resonator (XBAR) with adjustable piezoelectric coupling coefficient (K2). The vibration principle and resonant characteristics of XBAR are investigated by theoretical and simulation analysis, and the way to adjust K2 by introducing two grooves in the area between interdigital electrodes (IDEs) is proved to be effective by using finite element method (FEM) simulation and the Modified Butterworth-Van Dyke model with series capacitor Cr (MBVD-Cr) first, and then the impact of groove depth (Hg) and groove width (Wg) on K2 of XBAR is theoretically analyzed. Specifically, the K2 can be effectively adjusted by setting different values of Hg and Wg. After optimization, the maximum regulation range of K2 is from 2.02% to 45.05%. The fluted XBAR has a remarkable potential in building XBAR bandpass filter for specific frequency band, which greatly optimizes the XBAR filter design.