Micromachined aluminum nitride acoustic resonators with an epitaxial silicon carbide layer utilizing high-order Lamb wave modes

In this study, we present a composite plate composed of an aluminum nitride thin film and an epitaxial cubic silicon carbide layer has the remarkable capability to enable Lamb wave resonators with a high series resonance frequency (f_s) and a high quality factor (Q) simultaneously. The epitaxial cubic silicon carbide layer not only provides the Lamb wave resonator with a low acoustic loss layer to boost the Q´s but also enhances the electromechanical couplings of the high-order Lamb wave modes in the composite plate. Specifically, a micromachined acoustic resonator utilizing the third quasi-symmetric (QS₃) Lamb wave mode exhibits a Q of 5510 at 2.92 GHz, resulting in the highest f_s·Q product, 1.61×10¹³ Hz, among suspended piezoelectric thin film resonators to date.