Design, Fabrication, Position Sensing, and Control of Electrostatic, Surface-Micromachined Polysilicon Microactuators

This dissertation describes the design, fabrication, position sensing, and control of an electrostatically-driven microactuator. The polysilicon microactuator, together with an on-chip electronic buffer, were fabricated by the Modular Integration of CMOS and microStructure (MICS) technology. The microactuator has a linear dimension of 300um x 300um x 1.7um and a "long throw" range of motion of +/-4um. The electrostatic comb fingers of the microactuator can generate up to 0.3uN of force, which is able to pull the microactuator across the substrate at an acceleration of over 270 G's. The lateral position of the microactuator, relative to the substrate, is sensed by measuring the change of capacitance in the sensing comb fingers with a Kalman filtering scheme, which achieves a position estimation error covariance below 0.01 um RMS. A state-variable feedback loop operates at a closed loop bandwidth of over 11 kHz, and enables the microactuator to settle to a position step input command within 0.12 msec. The microactuator was packaged and tested. Experimental results are given.
An electro-mechanical model of the microactuator is developed, and the model is identified and verified through experimentation. Several design issues are addressed, including the analysis and design of polysilicon micromachined microactuator suspensions, and the design and implementation of sensing and control schemes which linearize the microactuator's input/output dynamics. Noise models for the microactuator and the sensing circuits are developed, which are used in the Kalman-filter-based position sensing scheme. A method to tune the observer gains in order to balance measurement accuracy, feedback control systems disturbance rejection, and robustness is tested.
Patrick Ching-Pak Cheung
Roberto Horowitz
Publication date: 
May 31, 1995
Publication type: 
Ph.D. Dissertation
Cheung, P. C. (1995). Design, Fabrication, Position Sensing, and Control of Electrostatic, Surface-micromachined Polysilicon Microactuators. United States: University of California, Berkeley.

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