Measurement and characterization of viscous damping in micromechanical dynamic structures

Abstract

The thesis presents the analysis, design, fabrication and testing of the damping test structures to characterize the viscous damping in the dynamic micromechanical structures. There are three types of damping test models such as the squeezing plate damping, tilting plate damping and squeezing strip damping, respectively. The planar structures of the squeeze damping have the closed plate and the perforated plates of the net area of 80×80μ㎡ The nine perforated plates are designed to investigate the change of the damping coefficients due to the change of the area of the perforations and their locations. Two straight tethers support the tilting plate. The viscous damping in the lateral narrow gaps formed by the movable finger electrodes and fixed ones will be analyzed in the squeezing strip damping. The test structures are fabricated through the surface micromachining using the 2.0㎛ sacrificial PSG and 4.3㎛ polysilicon as the structural layer. The fabricated damping test structures are tested under the ambient air condition of one atmospheric pressure and room temperature. The dynamic responses of the squeezing and tilting plate are measured by the optical vibrometer. The detection circuit for the small capacitance obtains the frequency response curve. The experimental damping coefficients of each test structure are compared with the estimated values from the analytic equations and finite element analysis. For the squeeze damping, the decrease rate of the damping coefficients becomes slow due to the increase of the edge length by the perforation holes. The lateral gap resistance in the squeezing strips agrees with the expected value.