Suppression of spurious modes via dummy electrodes and 2% frequency shift via cavity size selection for 1 GHz AlN MEMS contour-mode resonators

This paper reports on the application to 1 GHz AlN MEMS contour-mode resonators (CMR) of a spurious mode suppression technique based on the introduction of dummy electrodes and a method to shift the resonator center frequency by modifying its cavity size. The realization of wideband filters with CMRs is currently limited by the need to 1) enlarge the device capacitance (so as to minimize the inductive components in the matching network), 2) reduce in-band ripples and out-of-band spurs (which are introduced when the device capacitance is increased), and 3) shift the device center frequency by a large percentage (> 2%) to synthesize ladder/lattice configurations. This work addresses these 3 main challenges by optimizing the electromechanical response of AlN CMRs having a large static capacitance, synthesized by using thin AlN films of two different thicknesses (500 nm and 1 μm thick), sandwiched by Pt and Al electrodes and having a large number of fingers (up to 45). 3D COMSOL finite element model is used to analyze and/predict the resonator's behavior.