An eigenmode superposition model for lateral acoustic coupling between thin film BAW resonators

A simple model is developed for calculating lateral acoustical coupling between adjacent thin film BAW resonators forming an electrical N-port. The model is based on plate wave dispersion properties of different regions of the device and solution of lateral eigenmodes and eigenfrequencies. Mechanical and electrical response of the device is calculated as a superposition of eigenmodes according to voltage drive at one electrical port at a time while extracting current induced in the other ports, leading to a full Y-parameter description of the device. Comparison of model prediction with experimental results from adjacent large square resonators and narrow finger-like resonators is performed. Large resonators exhibit comb-shaped oscillating transmission characteristics over wide frequency band, while narrow finger create a single pass-band. Fair qualitative agreement is obtained.