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 a2004 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.