Micro-Electro-Mechanical System

ELECTROSTATICALLY ACTUATED CANTILEVER BEAM

By-Vedavyas P.Burli

Introduction

• Elastic cantilever beam is an elementary structure in MEMS design.

• The electro mechanics interface to solve the coupled equations for the structural deformation and the electric field. Such structures are frequently tested by means of a low frequency capacitance voltage sweep.

• The bending of a beam due to electrostatic forces.

Model definition

• The dimensions of the beam are: Length: 300 μm; Width: 20 μm; and Thickness 2 μm.

• The beam is made of polysilicon with a Young’s modulus, E, of 153 GPa, and a Poisson’s ratio, ν, of 0.23.,

• It is fixed at one end but is otherwise free to move.

• The polysilicon is assumed to be heavily doped, so that electric field penetration into the structure can be neglected.

Result and discussion • There is positive feedback

between the electrostatic forces and the deformation of the cantilever beam.

• This action, in turn, increases the forces. At a certain voltage the electrostatic forces overcome the stress forces, the system becomes unstable, and the gap collapse

References • R.K. Gupta, Electrostatic Pull-In Structure Design for In-Situ Mechanical

Property Measurements of Microelectromechanical Systems (MEMS), Ph.D. thesis, MIT, 1997.

• Methodologies.V Vardhan K.J.Vinoy,S.Gopalkrishnan,Wiley.Smart Material systems and MEMS design and development

• Model gallery,COMSOL Multiphysics 4.3