Simulation of transverse effects in FBAR devices

Interest in thin-film bulk acoustic wave resonator (FBAR) devices is driven by their wide bandwidth and high frequency filtering applications. Fast one-dimensional simulations are widely used for designing resonators. Such models only consider the forced thickness-extensional vibrations in the layers. However, the existence of acoustic modes with a lateral wave vector is responsible for the appearance of parasitic resonances in the response of devices. The analysis of such modes is a key to the understanding and the improvement of industrial designs. We present a calculation of the dispersion curves of laterally propagating or standing acoustic waves. These are used to explain spurious responses observed in finite-element simulations of FBAR structures. The possibility of designing laterally coupled resonators is investigated on this basis.