Design and fabrication of an integrated CMOS-MEMS 3-axis accelerometer

A monolithic integrated CMOS-MEMS three-axis accelerometer has been designed and fabricated. The sensor is a single structure that uses sidewall capacitors of comb fingers to sense acceleration in all three directions. The sensor plus on-chip CMOS circuitry is about 1 mm by 1 mm. in size and is fabricated by a post-CMOS micromachining process that uses interconnect metal layers as etching mask and has only dry-etch steps involved. The sensor structure incorporates both thin-film structures and bulk Si structures to achieve three-axis acceleration sensing without any extra masks, material deposition or wafer bonding. Both behavioral simulaton and finite element simulation were conducted to verify and optimize the sensor design. A noise floor of 50 mug/Hz(1/2) can be achieved.