Low-g Area-changed MEMS Accelerometer Using Bulk Silicon Technique

A bulk micromachined accelerometer based on an area variation capacitive sensing for low-g applications was developed. The accelerometer was designed with ribbed-style fingers structure on the movable mass connected in parallel and suspended over stationary electrodes composed of differential comb fingers by means of suspension beams anchored onto the substrate. A folded, rigid truss suspension design with low spring constant and low cross-axis sensitivity was chosen. The simulation was performed using Coventorware software. A three-mask bulk micromachining wafer bonding fabrication process was utilized to realize the accelerometer. Silicon-on-glass was used to achieve high sensitivity and low mechanical noise while maintaining a simple structure. The general concept, main design considerations, fabrication procedure and performance of the resulted accelerometer was elaborated and presented. A linear relationship between the differential capacitance and acceleration was obtained. The accelerometer sensitivity was calculated to be 0.47 pF/g with an acceleration range of ±5 g.