A 7.25 μ K Ultrahigh Resolution MEMS Resonant Thermometer

This article proposes an ultrahigh-resolution MEMS resonant thermometer that exploits differences in Young's modulus and coefficient of thermal expansion (CTE) between structural layers to increase thermal stress due to temperature variation. The increased thermal stress eventually acts on the resonator to produce a large frequency shift, and the temperature coefficient of frequency (TCF) can be increased to 17.4 times the original, which is consistent with theoretical analysis and finite element method simulations. The MEMS resonator chip is manufactured by the standard silicon-on-insulator (SOI) process and stacked on a ceramic chip carrier through multiple layers of materials. A self-sustaining oscillator, mainly composed of a packaged MEMS resonator chip and a low-noise application-specific integrated circuit (ASIC), is built to track the resonant frequency shift of the resonator. This MEMS resonant thermometer prototype demonstrates a high TCF of −866.84 ppm/K from −50 °C to 40 °C and exhibits good linearity. An ultrahigh resolution of $7.25 ~\mu \text{K}$ is achieved in the closed-loop experimental test. This is the best result achieved for a MEMS thermometer employing the resonant sensing paradigm to date.