A surface-micromachined accelerometer using a movable polysilicon gate FET

This paper presents a new accelerometer which detects applied acceleration by measuring the variation of the drain current of Field Effect Transistors(FETs). This proposed accelerometer consists of a polysilicon plate, supporting beams and source/drains of n-channel Metal Insulator Semiconductor FETs(MISFETs). The polysilicon plate used as the proof mass is suspended by four flexures and separated from the substrate. The comb finger structures at the polysilicon plate edge are used as gates of FETs. In the FET of the proposed accelerometer, gate oxide of a typical MOSFET is replaced with air gap between floating gate and substrate. As an acceleration perpendicular to the substrate is applied to the proposed accelerometer, the proof mass would have a displacement proportional to the acceleration, and the gap between proof mass and substrate would vary. This will change the drain current of the FET because the drain current of a FET is inversely proportional to the gap between a gate and a substrate.