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 µm, significantly enhancing system sensitivity and thermal efficiency. Two sensor prototypes, with MEMS opening sizes of 130 µm and 170 µm (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/ √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 _µV/ √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.