Modelling of 2-D lateral modes in solidly-mounted BAW resonators

Lateral resonances occurring in bulk acoustic wave resonators contribute to the device operation, e.g., by creating spurious electrical responses. Predicting lateral effects in two dimensions typically requires computationally heavy 3-D finite element modelling. Here, dispersion characteristics calculated using a 1-D transfer matrix model are used in a finite-element software to model lateral resonance modes of solidly-mounted bulk acoustic wave resonators. Based on the resulting spectrum of 2-D eigenmodes, electrical frequency response as well as mechanical displacement is then calculated using mode superposition. Resonators with elliptic and rectangular shapes are studied. Simulated results for ellipses are compared to measured electrical frequency response and mechanical displacement. Simulations are found to agree with measured data. Dependence of electrical spurious responses on resonator shape and eigenmode spectrum is studied.