Abstract
In this study, a displacement sensing mechanism is proposed using suspended gate field-effect transistor (SGFET) and integrated with comb-drive actuators to provide a position feedback signal. By utilizing SGFET, the proposed method has advantages of reduced chip size, simplicity in sensing structure, and compatibility with CMOS-MEMS fabrication process. The operating principle of SGFET is to sense the displacement of suspended gate via the output drain current. Design and analysis for SGFET and comb-drive actuators are presented. A sensing structure combining an SGFET with a comb-drive actuator is proposed, with two models describing the linear and nonlinear drain current of SGFET. Numerical simulation is carried out to investigate the relationship between drain current of SGFET and displacement of comb-drive actuator. To demonstrate the proposed sensing mechanism, the integrated device on a single chip was implemented using both TSMC 2P4M 0.35 um CMOS-MEMS fabrication process and a customized surface micromachining process.