Mechanical Engineering ETDs

Publication Date

2-8-2011

Abstract

Among MicroElectroMechanical Systems (MEMS), the most common type of failure is stiction. Stiction is the unintended adhesion between two surfaces when they are in close proximity to each other. Various studies have been conducted in recent years to study stiction. Our research group has shown the in-service repair of the stiction failed MEMS devices is possible with structural vibrations. In order to further understand this phenomenon and better predict, theoretically, the onset of repair we have constructed an apparatus to determine the Mode I, II, and III interfacial adhesion energies of MEMS devices failed on a substrate. Though our method is general, we are specifically focused on devices created using the SUMMiT V process. An apparatus has been constructed that has 8 degrees-of-freedom between the MEMS device, the surface on which the device is failed, and a scanning interferometric microscope. Deflection profiles of stiction failed MEMS (micro-cantilevered beams 1000 microns long, 30 microns wide, and 2.3 microns thick) have their deflection profiles measured with nanometer resolution by a scanning interferometric microscope. Using the experimental apparatus that is constructed, we determine the Mode I and Mode II interfacial adhesion energies using two methodologies. The first method utilizes the peel test scheme to determine pure Mode-I and Mixed Mode (Mode I and II) interfacial adhesion energies. In order to determine the values for the interfacial adhesion energies a nonlinear model was developed for the deflection of a beam that accounts for its stretching. Energy methods are then utilized to determine interfacial adhesion energies. Using the same experimental apparatus Mode II interfacial adhesion energies are measured directly with a novel technique developed in this work. This experimental method for measuring the Mode II interfacial adhesion energies for stiction failed MEMS devices uses a microcantilever beam (1500 μm long, 30 μm wide and 2.3 μm thick) attached to MEMS actuator with fix-fix beam flexure. Deflection of the spring is measured with the vernier scale of the actuator. Then a nonlinear elastic model for the fix—fix beam flexure is used to determine the interfacial adhesion energy between the failed microcantilever beam and the surface. A theory is developed to measure the strain energy release rates with finite crack growth, which gives the upper bounds of interfacial adhesion energy for Mode II fracture problem. A separate theory is developed for infinitesimal crack growth, which gives the exact interfacial adhesion energy of the Mode II fracture problem. Because the surface roughness plays an important role in the adhesion of MEMS structures, the surfaces of all structures have been characterized with an Atomic Force Microscope (AFM).

Keywords

Stiction, Microelectromechanical Systems, Strain Energy, Cantilever, MEMS Actuator

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Shen, Yu-Lin

Second Committee Member

Luhrs, Claudia

Document Type

Thesis

Language

English

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