Integrated CMOS-MEMS Flow Sensor With High Sensitivity and Large Flow Range

We present an integrated complimentary metal-oxide-semiconductor (CMOS) MEMS flow sensor, which demonstrates a very compact system on chip (SoC) that can sense <inline-formula> <tex-math notation="LaTeX">$N_{\mathbf {2}}$ </tex-math></inline-formula> gas flow ranging from 0 to 26 m/s (0–50 sccm). Implemented in the proprietary InvenSense AlN process, our SoC features a very low-power current feedback instrumentation amplifier (CFIA) as a front-end readout circuit for a micro-calorimetric flow sensor configured in a Wheatstone bridge. To maintain a constant temperature difference of 56 K, an on-chip heater with off-chip op-amp feedback circuit is also implemented. The on-chip CFIA is chopped at 50 kHz to reduce its offset and flicker-noise and consumes <inline-formula> <tex-math notation="LaTeX">$250~\mu \text{A}$ </tex-math></inline-formula> current. The measured sensitivity of our CMOS MEMS flow sensor is 35 mV/sccm.