Transverse Mode Spurious Resonance Suppression in Lamb Wave MEMS Resonators: Theory, Modeling, and Experiment

This paper presents a transverse mode suppression theory and its experimental verification through aluminum nitride Lamb wave resonators (LWRs) operating at 142 MHz. An effective 2-D approximation model of the LWR is proposed, based on which the origin of transverse modes in LWR is investigated. The displacement distribution, resonant frequencies, and electromechanical coupling coefficients (k2t) of the main mode and its auxiliary transverse modes are obtained. A spurious mode suppression theory in terms of the expression of k2tin the 2-D model is proposed. Three kinds of electrodes are designed to suppress the transverse mode adjacent to the main mode, including a novel interdigital transducer gap technique that is reported for the first time. With the applicable geometries, these methods reduce the spurious response from 11.8 to <;0.5 dB, without significantly affecting the figure of merit of the resonator.