A Single-Chip Pulse-Driven CMOS-MEMS Flow Sensing System With Sub-mm/s Flow Detection Limit

This paper presents a single-chip CMOS-MEMS flow sensing system for high-precision bidirectional gas flow detection, featuring a pulse-excited constant temperature difference (CTD) control scheme and a low-noise analog front-end using capacitively coupled chopper instrumentation amplifier (CCIA). The MEMS sensing structure is fabricated using a cost-effective surface micromachining process and thinned to 1.38 mu m, significantly enhancing system sensitivity and thermal efficiency. Two sensor prototypes, with MEMS opening sizes of 130 mu m and 170 mu m (named as Sensor 130 and Sensor 170), achieve record-high sensitivities of 24.74 mV/(m/s) and 30.84 mV/(m/s), respectively, within a linear flow range of +/- 5 m/s. Leveraging pulse excitation, the system dramatically reduces heating power down to 1.63 mW (Sensor 130) and 1.85 mW (Sensor 170). The CCIA readout circuit exhibits an ultra-low input-referred noise density of 5.86nV/ root Hz, with a 1/ f noise corner below 0.1 Hz, greatly improving low-flow detection capabilities of the sensor system. As a result, the overall system output noise density is measured at 1.93 mu V/ root Hz, enabling minimum detectable flow velocities (MDFV) of 0.51 mm/s (Sensor 130) and 0.41 mm/s (Sensor 170). With its compact design, low power, and exceptional circuit performance, this cost-effective CMOS-MEMS flow sensing system is well-suited for high-precision flow measurement in industrial and IoT applications.