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-mu m-thick silicon proof-mass, large area polysilicon sense/drive electrodes, and small sensing gap (< 1.5 mu m) formed by a sacrificial oxide layer. The fabricated accelerometer is 7 x 9 mm(2) in size, has 160 Hz bandwidth, > similar to 5 pF/g measured sensitivity and calculated sub-mu g/root 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 mu g/root Hz (> 1.5 kHz) and 1.08 mu g/root Hz (> 600 Hz) for in-plane and out-of-plane devices, respectively.