Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Dr. S. F. Asokanthan

Abstract

The aim of the present research is to understand the bouncing dynamic behavior of NEM/MEM switches in order to improve the switch performance and reliability. It is well known that the bouncing can dramatically degrade the switch performance and life; hence, in the present study, bouncing dynamics of a cantilever-based NME/MEM switch has been studied in detail. To this end, a model of a MEM switch that incorporates electrostatic force, squeeze film air damping force as well as asperity-based contact force has been proposed for an electrostatically actuated switch. An actuation force due to piezoelectric effects is further included in an alternative micro-switch model of combined actuation for the purposes of bounce mitigation. For a NEM switch, an asperity-based contact model along with repulsive van der Waals force are incorporated in a nano-switch to capture the contact dynamics. Intermolecular forces, surface effects, and gas rarefication effects are also included in the NEM switch model. Further, an intermolecular force, specifically the Casimir force, is also used to actuate this class of switches in addition to the classical electrostatic actuation. Euler-Bernoulli beam theory and an approximate approach based on Galerkin’s method have been employed for predicting transient dynamic responses. In the present study, performance parameters such as initial contact time, permanent contact time, major bounce height, and the number of bounces have been quantified in the presence of interactive system nonlinearities.

For a MEM switch, improvement of bouncing behavior has been investigated using harmonic dither in the actuation voltage of an electrostatically actuated switch or using harmonic dither in the secondary piezoelectric actuator voltage. Improvements have been achieved in both types of switches at specific frequency ranges. Uncertainty quantification of parameters that affect the bouncing is also performed since MEM switches are prone to uncertainties during the fabrication. Measure of performance in terms of second order statistics is predicted, particularly for the beam as well as beam tip parameters and the influence of uncertainty in parameters on the system performance has been quantified.

For a NEM switch, the performance parameters are also used to investigate the influence of surface effects and rarefication effects on the performance of an electrostatically actuated switch. Influence of some pull-in parameters on the switch bouncing behavior have also been investigated in the presence of surface effects at different vacuum conditions for purely Casimir actuated NEM switch. Recommended operating conditions or actuation parameters are suggested for the purposes of avoiding excessive bouncing for both types of NEM switches.

The present investigation on the bouncing dynamic behavior of a class of MEM/NEM switches is envisaged to yield greater insight into the design, reliability and performance predictions for this class of switches.

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