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

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 50× improvement in temperature coefficient of beat frequency (TCf_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 4× larger TCF difference between modes (ΔTCF) than first and third width-extensional resonators, which further contributes to TCf_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 ^° out-of-phase when operated in two-port configuration, thus enabling mode-selective low-power oscillator interfacing for resonant temperature sensing.