Reduction of anchor loss in high quality factor silicon nano-resonator for gas sensors

Abstract

Micro / Nano electromechanical system (MEMS / NEMS) resonators can achieve high-resonance quality factor (Q-factor), which can be advantageous in applications for ultra-sensitive gas sensing. Q-factor is being considered as an important parameter of such sensing devices, and is enhanced by reducing the dissipation of mechanical energy stored in the resonator arising from various sources including air damping, thermoelastic damping, anchor loss, etc. In this study, anchor loss is investigated because it can emerge as the dominant mechanism of energy dissipation in ultra-high-quality factor resonators operated in high vacuum and low temperature. By numerical analysis via finite element method using perfectly matched layer (PML) technique, several anchor geometries are proposed to reduce anchor loss. Among them, a design with additional mass at the anchor point gives the highest simulated Q-factor. We also fabricated Si micro resonators having 300–500 μm length, 2 μm width and 7.5 μm thickness from silicon-on-insulator wafer. Q-factor of the fabricated micro resonators is evaluated in a vacuum chamber (~1 Pa) and at room temperature by the ring-down method with a digital lock-in-amplifier.