A monolithic three-axis micro-g micromachined silicon capacitive accelerometer

A monolithic three-axis micro-g resolution silicon capacitive accelerometer system utilizing a combined surface and bulk micromachining technology is demonstrated. The accelerometer system consists of three individual single-axis accelerometers fabricated in a single substrate using a common fabrication process. All three devices have 475-μm-thick silicon proof-mass, large area polysilicon sense/ drive electrodes, and small sensing gap (< 1.5 μm) formed by a sacrificial oxide layer. The fabricated accelerometer is 7 × 9 mm² in size, has 100 Hz bandwidth, > ∼5 pF/g measured sensitivity and calculated sub-μg/ √Hz mechanical noise floor for all three axes. The total measured noise floor of the hybrid accelerometer assembled with a CMOS interface circuit is 1.60 μg/ √Hz (>1.5 kHz) and 1.08 μg/ √Hz (>600 Hz) for in-plane and out-of-plane devices, respectively.