Consideration of the fringe effects of capacitors in micro accelerometer design

Capacitive micro accelerometer, as one of promising micro devices, utilizes the parallel-plate capacitor arrays to covert input acceleration into differential capacitance, so its characteristics highly depend on an accurate capacitance evaluation. The traditional capacitance formula used in macro-scale systems design could not meet the requirement of micro-scale field because the fringe effects of capacitors have great contribution to the total measured capacitance under a few millimeters of separation distance. In this paper, the theoretical equation of capacitance with fringe effects is utilized to design the sensitivity and nonlinearity of a capacitive micro accelerometer. The proposed analytical method provides a quantitative evaluation of sensing capacitance of micro accelerometers. Experimental results indicate that the theoretical design with fringe effects has a better agreement with experiments than ideal parallel-plate capacitor principle.