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 (k²_t) of the main mode and its auxiliary transverse modes are obtained. A spurious mode suppression theory in terms of the expression of k²_t in 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.