Effect of Space Charges on Micro- to Nanoscale Electrostatic Actuation
Wu, Yan
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Permalink
https://hdl.handle.net/2142/80911
Description
Title
Effect of Space Charges on Micro- to Nanoscale Electrostatic Actuation
Author(s)
Wu, Yan
Issue Date
2005
Doctoral Committee Chair(s)
Shannon, Mark A.
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
The effect of the space charges on the electrodes becomes important on micro- to nanoscale electrostatic actuations because the appropriate phenomenological electrostatic length scale is on the order of the physical scale of the system. A 1-D electromechanical model has been developed to provide quantitative analysis of the effect of the space charges. The electrostatic forces developed between doped silicon/gap/doped silicon electrodes are calculated based on this 1-D model. Departures well over two orders of magnitude in the predicted forces are possible with the consideration of the space charge effect. One key concept that comes out from the theoretical model is the characteristic voltage of a system. Through an example of an electrostatic actuator with a metal/gap/dielectric/doped silicon layered configuration, we demonstrated that when the applied voltage to the actuator is within one order of magnitude of the characteristic voltage, the real electric field within the gap can significantly differ from the 'ideal' electric field predicted without the consideration of the space charges. The characteristic voltage is determined by the surface potential of the space charge layer and the work function difference between the electrodes. Since the surface potential is a quantity that can be measured experimentally, the proposed model can be used to determine the electrostatic force affected by the space charge with an arbitrary charge distribution, without needing to know the exact form of charge distributions. Theoretical results are supported by a set of orthogonal experiments. In the first experiment, the electrostatic force is measured directly using a conductive AFM probe as force sensor. Experimental data demonstrating the effect of the characteristic voltage on the electrostatic force are presented. In the second experiment, the surface potential of the sample is measured using a scanning Kelvin force microscope (SKFM). Experimental data showed that SKFM measurements can be used to determine the characteristic voltage a system experimentally.
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