Dielectrically-supported multi-element mass flow sensor

The author reports a monolithic transducer array for measuring the physical variables associated with gas flow. The transducers are supported on micromachined dielectric windows and measure flow velocity, flow direction, ambient gas temperature, and ambient pressure. The gas velocity sensor is based on a full-diaphragm structure and for a 1-mm × 1-mm window achieves an output voltage of 34 mV/V at 5 m/s flow velocity in air with an input heater power of 13.9 mW. The polysilicon pressure sensor has a sensitivity of 12 ppm/mm Hg and operates over a range of more than 800 mm Hg. Generic thermal models have been developed to describe the electrothermal characteristics of the planar diaphragm structure and to optimize the device designs. The process requires seven masks, and the overall die size is 3 mm × 4.5 mm.