Design and Characterization of a CMOS Micromachined Capacitive Acoustic Sensor

This work presents a CMOS micromachined capacitive sensor for detection of acoustic pressure transmitted through the air. The post micromachining steps performed at chip level start with a sacrificial metal etch, followed by a dielectric reactive ion etch. The fabricated device has a suspended plate of 65 mum in diameter with four support beams, producing an initial sensing capacitance of 35 fF. The suspended plate has a resonant frequency of 1.3 MHz. The measured input-referred circuit noise is 0.35 muV/Hz^1/2. The measured sensor output is 3.5 muV at an electrode bias of 10 V, which is equivalent to a capacitance change of 2.9x10² aF and a displacement of 0.31 pm. The corresponding acoustic force and pressure acting on the sensor are 0.33 nN and 0.075 Pa, respectively.