Study of an eletrostatically actuated torsional micromirror with compliant planar springs

Abstract

This paper presents modelling, fabrication and testing of a torsional micromirror suspended by two compliant ortho-planar springs attached at the sides. The proposed cantilevered serpentine spring is a single-chain frame, composed of nine beam segments to form a serpentine together with an initial segment and a final segment. Castigliano theory is used to formulate the spring constants under certain loads. Two equivalent spring constants for the micromirror are obtained according to structure analysis. The 2-DOF model for torsion and bending of the micromirror is presented. Finite element analysis (FEA) of the coupled domain of the structure is performed to verify the analytical results. Further validation of the prediction is carried out through static testing of a fabricated micromirror using a PSD (position sensing detector) sensor based experimental set-up. Due to relative compliancy of the dominant torsion mode, the fabricated micromirror is actuated to some angle at a lower voltage. The comparison between FEA and analytical results shows good agreement, demonstrating the accuracy prediction by the derived model. Small deviation from experiments is expected due to the nonlinear nature of electrostatic field.