Fabrication process of micro shear stress sensors

The research and testing technique of friction sensor is an important support for hypersonic aircraft. Compared with the conventional skin friction sensor, the micro shear stress sensor has the advantages of small size, high sensitivity, good stability, and good dynamic response. The micro shear stress sensor can be integrated with other flow field sensors whose process is compatible with that of the micro shear stress sensor to achieve multi-physical measurement of the flow field; and the micro-friction balance sensor array enables large area and accurate measurement for the near-wall flow. A micro shear stress sensor structure is proposed, whose sensing element does not directly contact with the flow field. The MEMS fabrication process of the sensing element is described in detail. The thermal silicon oxide is used as the mask to solve the selection ratio problem of silicon deep reactive ion etching(DRIE). The optimized process parameters of DRIE are etching power 1600 W/LF power 100 W, SF6 flux 360 cm3/min, C4F8 flux 300 cm3/min, O2 flux 300 cm3/min. With Cr/Au mask, etching depth of glass shallow groove can be controlled at 30 ℃ and low concentration HF solution; spray etching and wafer rotating improve the corrosion surface quality of glass shallow groove. The micro shear stress sensor samples were fabricated by the above MEMS process, and results show that the error of the length and width of the elastic cantilever is within 2 m, the depth error of the shallow groove is less than 0.03 m, and the static capacitance error is within 0.2 pF, which satisfy the design requirements.