Tunable silicon bulk acoustic resonators with multi-face AlN transduction

This paper presents tunable width-extensional mode bulk acoustic resonators that are piezoelectrically-actuated and sensed using thin layers of AlN on the sidewalls as well as the top surface. By using both longitudinal and transverse piezoelectric effects of conformally-sputtered AlN layers on sidewalls and top surface of a 20 μm thick resonator, a low motional resistance of ~35 Ω was achieved for a 100 MHz silicon resonator operating in air. The motional resistance is improved by at least 10× compared to similar devices with capacitive transduction. Furthermore, it is shown that the resonance frequency of these piezoelectrically-transduced devices can be tuned by varying the electric signal power from 0 to 7 dBm.