Development of a Closed-loop MEMS Capacitive Force Sensor

force-balanced;feedback;capacitive sensor;MEMS

Guan, Changhong ; Fen Wu, Committee Member,Yong Zhu, Committee Chair,Paul I. Ro, Committee Member,Guan, Changhong ; Fen Wu ; Committee Member ; Yong Zhu ; Committee Chair ; Paul I. Ro ; Committee Member

University:North Carolina State University

关键词: force-balanced;    feedback;    capacitive sensor;    MEMS;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/460/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

This thesis describes a closed-loop microelectromechanical system (MEMS) basedon lumped-parameter modeling. Analytical models are derived for electrostatic comb driveactuator (CDA) under force-controlled actuation, electrothermal actuator (ETA) underdisplacement-controlled actuation, capacitive position sensor, including parallel plate capacitivesensor (PPCS) and torsional plate capacitive sensor (TPCS), mechanical equationof motion of a suspended shuttle, viscous air damping, folded exure. These models are implementedand simulated in finite element analysis softwares (ANSYS and FEMM). Systemlevel simulation, implementing PID difierential feedback loop, is simulated in a numericalsimulation program (MATLAB).The MEMS die is fabricated by following the standard PolyMUMPs process byMEMSCAP. A series of MEMS packaging process and storage are done in the lab. Allperipheral circuitries are self-made.A commercial capacitive readout IC (MS3110) is first used for open-loop capacitivesensing, which achieves the resolution of 0.05fF, equivalent to 1nm in displacement. Due tothe disadvantage of MS3110 in closed-loop, AC bridge capacitance measurement method isthen implemented for closed-loop integration. The resolution of AC bridge sensor reaches0.02fF, equivalent to 0.4nm in displacement. An additional function of AC bridge sensingis accomplished which is simultaneously sensing and actuation of CDA. In the feedbackloop, the traditional analog PID controller is designed to transfer the voltage signal ofcapacitance measurement to the voltage-force transducer which converts feedback voltagesto differential feedback force. Since the differential feedback force is limited by clampedvoltage, a force-balanced mode is observed under 5V actuation of CDA.