Design And Fabrication Of MEMS-Based Thermal Shear Stress Sensor

The accurate measurement of wall shear stress is of vital importance to a broad application spectrum, such as micro-fluidic control, industrial process control and biomedical applications. As one kind of MEMS-based sensors, which are considered as the most promising techniques for measuring wall shear stress, thermal shear stress sensor can be fabricated and integrated easily.This paper used FEA (finite element analysis) method to simulate thermal field of four different (silicon, glass, air cavity and vacuum cavity) substrates, and concluded that the glass substrate with a vacuum cavity has the most effective characteristic of thermal insulation. Meanwhile, the thermal field, pressure field, velocity field, and shear stress of the flow was analyzed using ANSYS. The process for the fabrication of silicon-based shear stress sensor and glass-based shear stress sensor were designed to fit with the conditions of our lab well; the scheme of back-side vacuum cavity and substituting poly-silicon resister with Pt were proposed; Using aluminum as the sacrifice layer, the Lift-Off process was improved; Finally, the glass-based and silicon-based thermal shear stress sensor, whose Pt electrodes had the minimum width 50μm and thickness 100μm, were fabricated successfully. The TCR (temperature coefficient of resistance) of Pt film was tested at 0.00257/℃, and their steady electro-thermal characteristics were also studied. Their V-I and P-T curves showed that the sensor with glass substrate had greatly reduced the heat transferred to the substrate, which testified the above simulation results.