Surface Micromachined Thermal Shear Stress Sensor

Abstract

Abstract We have designed, fabricated, and tested a new type of thermal shear-stress sensor. The sensor consists of a 2 μm wide polysilicon thermistor (with a range of lengths, 80-200 μm) on a 1.2 μm thick silicon-nitride diaphragm, which is on top of a vacuum cavity 200×200×2 μm3 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 μs, which translates into a bandwidth of 500 Hz.