Design and Manufacturing of Shear Stress Sensor for High-Temperature Applications With Embedded Capacitive Floating Unit

The shear stress sensor is a pivotal technical instrument for measuring wall shear stress in aerodynamic tests. Currently, MEMS-based shear stress sensors with floating unit capacitance structures have entered the commercial arena. However, a notable limitation of these typical capacitive shear stress sensors lies in their floating structure surface, which directly interfaces with the test fluid. Exposure to high-temperature, high-speed airflow, and particulate pollutants is prone to degrade the capacitive structure. To address this issue, our study focuses on the preparation of a novel design, which separates the capacitive unit located on the device layer from the sensitive structure residing on the handle layer of a silicon-on-insulator (SOI) wafer. This innovative approach aims to shield the capacitor from direct contact with the test fluid, thereby mitigating potential damage. We term this structural characteristic, which detects capacitance beneath the shear stress-sensitive surface, as "embedded capacitance detection." Key dimension parameters have been refined via rigorous theoretical analysis and electromechanical coupling simulations. Furthermore, a sensor circuit that integrates differential capacitance detection components was designed. Extensive testing of the shear stress sensor has been conducted in both room temperature (RT) and high-temperature fluid environments. Our findings reveal that at RT, the sensor exhibits a sensitivity of 10.26 mV/Pa, a nonlinear error of 3.26%, and a hysteresis error of 2.41%. Moreover, the high-temperature tests demonstrate that the sensor's temperature drift remains within 1.66 mV/degrees C across the range from 20 degrees C to 210 degrees C. Ultimately, the key technologies and challenges of high-temperature shear stress sensors were discussed.