GHz High- $Q$ Lateral Overmoded Bulk Acoustic-Wave Resonators Using Epitaxial SiC Thin Film

This letter presents the development of a lateral overmoded bulk acoustic-wave resonator (LOBAR) made out of epitaxial silicon carbide and piezoelectrically driven by an aluminum nitride transducer at radio frequencies. The 1.75-GHz SiC LOBAR constitutes a new class of resonant devices formed by a very small volume piezoelectric transducer on a high quality factor (Q) acoustic cavity. In operation, the AIN-based transducer excites multiple longitudinal vibrations in the SiC resonant cavity. A high Q of 4250 is obtained for a LOBAR with series resonances around 1.75 GHz. The impact of the AIN transducer coverage of the SiC cavity on device Q and impedance is also experimentally studied. Characterization of the LOBAR over temperature is performed to extrapolate the intrinsic loss limits in the epitaxial SiC. The integration of two materials, capable of offering high Q and high transduction efficiency in conjunction with their ability of sustaining operations at high temperature and in harsh environments, will enable the development of radio frequency microelectromechanical system components for a new realm of applications.