MEMS Flow Sensor Based on a Sigma–Delta Modulator Embedded in the Thermal Domain

A system for gas flow measurement, based on MEMS flow sensing microstructures and a sigma–delta interface, is described. The sensing structures consist of double-heater differential microcalorimeters, obtained by means of a post-processing procedure applied to chips fabricated using the Bipolar-CMOS-DMOS process BCD6s of STMicroelectronics. Part of the sigma–delta modulator is implemented in the thermal domain by exploiting the versatility of the double-heater sensing structures. The measurements performed in nitrogen flow prove the effectiveness of the proposed approach.