Date on Master's Thesis/Doctoral Dissertation

5-2013

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Mechanical Engineering

Committee Chair

Berfield, Thomas Austin

Author's Keywords

MEMS; Bi-stable buckled membranes

Subject

Microelectromechanical systems; Diaphragms (Structural engineering)

Abstract

Bi-stable buckled MEMS (micro-electromechanical systems) diaphragms have a myriad of uses in the MEMS field for their large out-of-plane deflections. Buckling is a phenomenon brought upon by a compressive stress. Diaphragms are large aspect ratio, circular structures similar to membranes, where the thickness of the diaphragm is much smaller than its diameter. Diaphragms differ from membranes by the amount of bending stiffness. Membranes have negligible bending stiffness and are a common structure analyzed in mechanics of materials, whereas diaphragms have much larger stiffness. Diaphragms were created in the cleanroom by thermally growing silicon dioxide on a silicon wafer. A structural polyimide layer was added on top of the silicon dioxide. The created diaphragms demonstrate bi-stability, meaning that they can be switched either up or down using an applied pressure. After the pressure is removed the diaphragms remain in their new respective states. The pressure required to switch the membranes is known as the actuation or snap-through pressure, and is of primary interest. The vertical displacement of the center of the diaphragms, known as the buckled height, is also of interest. A finite element model of the diaphragm was created using ANSYS. This model was used to generate both actuation pressure and buckled height data. These two data sources are compared extensively in an attempt to further understand the behavior of the experimental system. Buckled height data between experimental data and the finite element model were found to match well. This information can be used in the production of micro-valves and micro-actuators in the future. Actuation pressure found from the finite element model follows the trend and closely models the values of experimental data for a range of membranes. Other effects not accounted for in the finite element model probably contribute to the difference between the two.

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