Design and fabrication of sensitive elements of sublayer fence for wall shear stress sensor

MEMS sublayer fence provides a new method for wall shear stress measurement. In order to determine the influence of a fence's structural parameters on its natural frequency and piezoresistive sensitivity, the finite element method (FEM), orthogonal experimental design, and range analysis are adopted to optimize the parameters of the fence. The simulation results demonstrate that the natural frequency and sensitivity of a fence are more easily affected by its thickness than other parameters. Piezoresistive sensitivity can be improved more effectively than natural frequency by increasing the height of a sensitive element. The width of the element has less impact on the natural frequency and sensitivity of the fence. Inductive couple plasma etching process is used to form the structure of a sensitive element. The releasing process of the fence is accomplished by reactive ion etching technology. The dimension of the sublayer fence is 5.9 mm×10.1 mm×0.39 mm. Dynamic measurement results show that the natural frequency of the fence is 1453.1 Hz, featuring a deviation of less than 4.4% as compared with finite element simulation.