A Reliable Liquid-Based CMOS MEMS Micro Thermal Convective Accelerometer With Enhanced Sensitivity and Limit of Detection

In this paper, a liquid-based micro thermal convective accelerometer (MTCA) is optimized by the Rayleigh number ( Ra ) based compact model and fabricated using the $0.35\mu $ m CMOS MEMS technology. To achieve water-proof performance, the conformal Parylene C coating was adopted as the isolation layer with the accelerated life-testing results of a 9-year-lifetime for liquid-based MTCA. Then, the device performance was characterized considering sensitivity, response time, and noise. Both the theoretical and experimental results demonstrated that fluid with a larger Ra number can provide better performance for the MTCA. More significantly, Ra based model showed its advantage to make a more accurate prediction than the simple linear model to select suitable fluid to enhance the sensitivity and balance the linear range of the device. Accordingly, an alcohol-based MTCA was achieved with a two-order-of magnitude increase in sensitivity (43.8 mV/g) and one-order-of-magnitude decrease in the limit of detection (LOD) ( $61.9~\mu \text{g}$ ) compared with the air-based MTCA. [2021-0092]