Dual-Mode AlN-on-Silicon Micromechanical Resonators for Temperature Sensing

摘要

In this paper, we present dual-mode (DM) AlN-on-silicon micromechanical resonators for self-temperature sensing. In-plane width-shear (WS) and width-extensional (WE) modes of $[110]$-oriented silicon resonators have been used as alternatives to first- and third-order modes to enhance DM temperature sensitivity by engineering device geometry, which reduces inherent beat frequency $f_{b}$ between the two modes. This configuration provides a $50times$ improvement in temperature coefficient of beat frequency $({rm TC}f_{b})$ compared with single-mode temperature measurement and eliminates the need for additional frequency multipliers to generate $f_{b}$ from its constituents. $[100]$-oriented WS/WE resonators provide $4times$ larger TCF difference between modes $(Delta{rm TCF})$ than first and third width-extensional resonators, which further contributes to ${rm TC}f_{b}$ enhancement. WS/WE mode resonators also demonstrate the capability of operating as a temperature-stable reference $f_{b}$. The proposed modes for DM operation have high $Q$ and low motional resistance, and are 180$^{circ}$ out-of-phase when operated in two-port configuration, thus enabling mode-selective low-power o- cillator interfacing for resonant temperature sensing.