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

This paper reports on a design journey for a laterally-excited bulk acoustic wave resonator (XBAR) with an adjustable piezoelectric coupling coefficient (K (2)). The vibration principle and resonant characteristics of XBAR are investigated by theoretical and simulation analysis, and the way to adjust K (2) by introducing two grooves in the area between interdigital electrodes (IDEs) is proved to be effective by using the finite-element method (FEM) simulation and the Modified Butterworth-Van Dyke model with series capacitor C ( r ) (MBVD-C ( r )) first, and then the impact of groove depth (H (g)) and groove width (W (g)) on K (2) of XBAR is theoretically analyzed. Specifically, K (2) can be effectively adjusted by setting different values of H (g) and W (g). After optimization, the maximum regulation range of K (2) is from 2.02% to 45.05%. The fluted XBAR has remarkable potential in building an XBAR bandpass filter for specific frequency bands, which greatly optimizes the XBAR filter design.