Free vibration of geometrically nonlinear micro-switches under electrostatic and Casimir forces-Research Proposal

Table of Contents

Background2

Problem Statement2

Purpose of the Study4

Objective of the Study4

Proposed Methodology4

Proposed References6

Free vibration of geometrically nonlinear micro-switches under electrostatic and Casimir forces-Research Proposal

Background

Micro-switches are important building blocks in micro-electro-mechanical-systems (MEMS). A typical elec-trostatic micro-switch comprises two parallel conducting electrodes, one is fixed and the other is movable. When an electrical potential difference is created between the two electrodes, the induced electrostatic charge gives rise to electrostatic force which deflects the movable electrode towards the fixed electrode. In addition, the intermolecular interaction force which is directly dependent on the gap between them also acts on the movable electrode, altering its deflection. Counteracting the electrostatic and intermolecular forces is the elastic force, which tries to restore the movable electrode to its original position. Obviously, the equilibrium position of the movable electrode is determined by the balance of the elastic, electrostatic, and intermolecular forces. When the voltage increases beyond a critical value, the movable electrode becomes unstable and collapses onto the fixed electrode and consequently, the micro-switch is in the ON state. The voltage and deflection at this state are known as the pull-in voltage and pull-in deflection which are of utmost importance in the design of MEMS devices.

Problem Statement

Since it is sometimes difficult for a single layer to meet all material and economical requirements posed to an MEMS structural layer, Witvrouw and Mehta proposed the use of a non-homogenous functionally graded material (FGM) layer to achieve the desired electrical and mechanical properties and suggested that a polycrystalline-SiGe (poly-SiGe) layer can be an appropriate choice. They and their co-workers also conducted an experimental study for the characterization and strain gradient optimization of PECVD poly-SiGe layers for MEMS applications. Recently, Hasanyan et al. studied the pull-in instabilities in functionally graded MEMS due to the heat produced by an electric current. The material properties of the two-phase MEMS are assumed to vary continuously in the thickness direction.

With continuing reduction in the size, the surface traction due to molecular interaction between two surfaces plays an important role in the deflection of micro-switches and can be described by the Casimir force or the van der Waals force, depending on the gap between the electrodes. At a large gap, which is typ-ically above 20 nm so that the retardation is pronounced, the intermolecular interaction can be described as Casimir force. Among the many previous studies, Serry et al. investigated how the Casimir force effect can deflect a thin micro-fabricated rectangular membrane strip and possibly collapse it onto a fixed surface. Buks and Roukes demonstrated experimentally how the electrostatic and Casimir interaction limit the range of positional stability of electrostatically actuated or capacitively coupled mechanical devices. A distributed parameter model was used by Ramezani et al. to study the free vibration of cantilever nanomechan-ical switches subjected to intermolecular and electrostatic forces.

Ramezani and Alasty later investigated the free vibration of cantilever arrays with the combined electrostatic and Casmir or van der Waals interac-tions between the neighbouring ...