A monolithic three-axis silicon capacitive accelerometer with micro-g resolution

A monolithic three-axis silicon capacitive accelerometer utilizing a combined surface and bulk micromachining technology is demonstrated with micro-g resolution. The accelerometer consists of three individual single-axis accelerometers. All three devices have full-wafer thick silicon proof-mass, large area polysilicon sense/drive electrodes, and small sensing gap (<1.5 /spl mu/m) formed by a sacrificial oxide layer. The fabricated accelerometer system is 7/spl times/9 mm/sup 2/ in size, has >5pF/g measured sensitivity and sub-/spl mu/g//spl radic/Hz mechanical noise floor for all three axes. The total measured noise floor of the accelerometer hybrid assembled with CMOS interface circuit is 1.60 /spl mu/g//spl radic/Hz, 1.08 /spl mu/g//spl radic/Hz for in-plane and out-of-plane devices, respectively.