Force-balanced accelerometer with mG resolution, fabricated using Silicon Fusion Bonding and Deep Reactive Ion Etching

A single crystal silicon accelerometer with mG resolution (1 G=9.81 m/s/sup 2/) has been fabricated using Silicon Fusion Bonding (SFB) and Deep Reactive Ion Etching (DRIE). This allows thick devices (up to several hundred /spl mu/m) to be defined with high aspect ratios (up to 25), resulting in high sensitivity and low cross-axis sensitivity. Prototypes use a hybrid approach, with a 1.0/spl times/1.5 mm/sup 2/ mechanical element and a capacitive sensor interface providing closed-loop force-balancing to minimize non-linearity. The bandwidth is 1 kHz and the sensitivity is 700 mV/G. The dynamic range is 44 dB, corresponding to a resolution of 35 mG for a 5 G (full scale) device and 7 mG for a 1 G device. The resolution is currently limited by 1/f noise in the electronic interface, but will be reduced with an improved design of the capacitive sensing interface (currently in fabrication), thus resulting in sub-mG resolution.