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Microfabricated tweezers with a large gripping force and a large range of motion

Chu, Wen-Hwa Martin
http://rave.ohiolink.edu/etdc/view?acc_num=case1057869514

Abstract Details

1994, Doctor of Philosophy, Case Western Reserve University, Electrical Engineering.
The objective of this thesis is to gain a basic understanding of bimetallic microactuation through a study of microfabricated bimetallic microtweezers. The microtweezers utilize two cantilevered gripping arms each 2000μm long and 100μm wide, connected to a square silicon support piece. The tweezer structure is fabricated by double-sided processing and bulk micromachining of a (100) silicon wafer. The tweezers' arms are created on the two sides of the wafer by using the p+ etch stop technique. One of the arms can be actuated to operate the tweezers, whose initial opening is typically 200μm. A method to determine the bending moment of a p+ cantilever in order to quantify the effects of the p+ diffusion conditions and of thermal oxidation on the residual stresses in p+ silicon is developed. It is demonstrated that thermal oxidation can significantly modify the residual stress distribution in the near-surface region of the p+ silicon films, even changing the sign of the bending moment of p+ cantilevers. Transmission electron microscopy (TEM) studies of p+ silicon show a thin surface layer which is dislocation free, while the rest of the p+ layer has a high density of dislocations. Analytical models for the curvature, neutral axis position, stress profile, and generated force of the bimetallic cantilever arm of the tweezers are derived. Initially, a constant temperature along the cantilever length is assumed. A 105°C increase in temperature results in a cantilever tip deflection of 200μm. This temperature increase results in an equivalent force of about 10μN if the cantilever tip is constrained against deflection. Finite element analysis (FEA) is used to verify the analytical model for the tip deflection. The thermal characteristics of the bimetallic cantilever arms are studied by FEA. The value of the heat transfer coefficient (htc) associated with the natural convection around the bimetallic cantilever arm is investigated. A htc of 263W/m2K is estimated from experiments using FEA. It is found from the FEA results that the temperature profile of a bimetallic cantilever microactuator is not a constant. The temperature decreases toward the silicon mechanical support which acts as a heat sink. The temperature profile along the length of the bimetallic cantilever arm is characterized experimentally. Two techniques are used for such measurements: an infrared scanning microscope and a thermocouple. The temperature measurements from both techniques are consistent at lower temperatures. The bimetallic cantilever arm tip deflection is measured as a function of input power. Near 30mW is required to fully close the tweezers (i.e., 200μm actuation arm tip deflection), corresponding to an actuation arm tip temperature of 170°C which is expectedly higher than the 105°C temperature predicted using a constant temperature profile along the length of the arm. (Abstract shortened by UMI.
Mehran Mehregany (Advisor)
165 p.
Microfabricated tweezers; large gripping force; large range of motion

Recommended Citations

Citations

  • Chu, W.-H. M. (1994). Microfabricated tweezers with a large gripping force and a large range of motion [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1057869514

    APA Style (7th edition)

  • Chu, Wen-Hwa. Microfabricated tweezers with a large gripping force and a large range of motion. 1994. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1057869514.

    MLA Style (8th edition)

  • Chu, Wen-Hwa. "Microfabricated tweezers with a large gripping force and a large range of motion." Doctoral dissertation, Case Western Reserve University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1057869514

    Chicago Manual of Style (17th edition)

case1057869514
919
© 1994, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.