Abstract
The research studies a capacitive micro-sensor used for long-term respiratory monitoring of patients with breathing difficulties. By using CMOS-MEMS technology, we can integrate sensing structures and circuits into one chip. Parasitic effect is therefore reduced to enhance the signal-to-noise ratio. The chip size and fabrication cost are reduced as well. The capacitive flow sensor is fabricated by using the TSMC 0.35-μm 2P4M (two-polysilicon-four-metal) CMOS process. The differential sensing capacitances are formed by the metallization and polysilicon layers. Capacitance change is produced by momentum change of the air flow on the microstructure, which is released by wet-etching of metal-1 and metal-3. The sensor area is 320μm × 230μm. The sensing capacitances are about 124 fF. The total chip area is 2.46 × 2.46 mm^2. The sensing circuit is operated at 5 V with a total current consumption of 5 mA. The measured data shows the sensor has a sensitivity of 3.33 mV/(L⁄min) and a detection limit of 34.4 (mL/min) within a 1-Hz bandwidth. We have successfully measured the waveform from a subject’s nasal respiration.