Characterization of a Micromachined Thermal Shear Stress Sensor

A detailed characterization is presented of a silicon-micromachined thermal shear-stress sensor employing a thin-film platinum-sensing element on top of a silicon-nitride membrane that is stretched over a vacuum cavity. The sensor was operated in a constant current mode and characterized using a four-point probe configuration to isolate the sensor response from the effects of external compensation circuitry. The characterization results consist of static sensitivity data at multiple overheat ratios (maximum of 11 mV/Pa at an overheat of 1.0), pressure sensitivity spectra (<1 uV/Pa), noise floor spectra (100 nV/Hz^0.5), and direct dynamic calibration data (up to 7 kHz). Noise floor measurements reveal a minimum detectable shear stress of 9 uPa/Hz, thus resulting in a sensor dynamic range of over 100 dB (9 uPa