A CMOS MEMS Capacitive Flow Sensor for Respiratory Monitoring

This letter presents a novel complementary metal-oxide-semiconductor (CMOS) micromachined capacitive flow sensor for respiratory monitoring. Airflow induces a pressure change on the suspended sensing plate and causes a capacitance change with respect to the bottom electrode. The microstructure fabricated by post-CMOS metal etch occupies an area of 190 $,\times,$ 190 $\mu{\rm m}^{2}$ and possesses a sensing capacitance of 180 fF. Output waveform of consecutive breaths is successfully measured with an output noise of 14 $\mu{\rm V}$ for a measuring bandwidth of 0.5 Hz, which is equivalent to a minimum detectable capacitance change and airflow velocity of 0.13 aF and 0.2 mm/sec, respectively.