Deep Trench capacitor drive of a 3.3 GHz unreleased Si MEMS resonator

This work presents unreleased RF bulk acoustic resonators using Deep Trench (DT) capacitors for both transduction and acoustic isolation. While the majority of Si MEMS resonators require a release step to freely suspend the resonant cavity, these unreleased resonators are formed entirely in solid media. This eliminates the need for complex release steps and costly packaging. The resonators use 1D periodic DT structures etched into a bulk Si substrate for both electrostatic transduction and to form Acoustic Bragg Reflectors (ABRs) for energy localization. In this paper, we introduce the concept of Deep Trenches as ABRs, and provide analysis, simulation, and experimental verification of their use for high-Q resonators. A 3.3 GHz unreleased Si resonator is demonstrated with Q of 2057 and motional impedance R_X of 1.2 kΩ. This realization of high-Q unreleased resonators in a bulk Si process provides a high yield, low cost, no packaging solution for on-chip clocking, wireless communication, and electromechanical signal processing.