Surface micromachined thermal shear stress sensor

We have designed, fabricated, and tested a new type of thermal shear-stress sensor. The sensor consists of a 2 m wide polysilicon thermistor (with a range of lengths, 80-200 m) on a 1.2 m thick silicon-nitride diaphragm, which is on top of a vacuum cavity 200 200 2 m in size. The vacuum cavity provides a good thermal isolation between the resistive element and the substrate; shear-stress sensitivity of 15 V/kPa at a power consumption of 12 mW (constant current = 2 mA) is obtained. The typical thermal time constant of our sensors is 350 s, which translates into a bandwidth of 500 Hz.

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