Investigation of spurious resonances in thin film bulk acoustic wave resonators

A finite element analysis is performed to simulate thin film bulk acoustic wave (FBAR) structures, and a coupled finite element analysis/boundary integral method (FEA/BIM) is used to simulate accurately a radiation medium, like a Bragg mirror underneath a resonator, without having to mesh it entirely. Displacement fields are extracted from these calculations and analysed. In particular, dispersion curves are obtained by a Fourier analysis of these fields and are used to explain phenomena arising at electrode edges, like standing wave resonances under the electrodes or mode conversions.