Theoretical and finite element analysis of dynamic deformation in resonating micromirrors

Dynamic deformation is one of the limiting factors in the design of high frequency resonating microscanners that are intended for high definition raster scanning display applications. Out-of-plane deformation resulting from high acceleration loads causes beam divergence, which will in turn reduce the optical resolution. This paper presents a detailed analysis on the mechanical design aspects contributing to dynamic deformation such as the micromirror layout and the micromirror-spring linkage design. The applicability of one-dimensional plate bending theory in evaluating micromirror deformation due to inertial loads is investigated using finite element analysis. Improved analytical dynamic deformation predictions, which take into consideration the two-dimensional mirror plate twist, will also be presented. A comparison among a number of layout designs was carried out with the aim of increasing micromirror bending stiffness in a direction parallel to the axis of rotation. Moreover, spring-linkage effects were also addressed and a significant improvement in dynamic deformation was achieved with the inclusion of a gimbal structure between the micromirror and the torsion springs. A parametric analysis was also carried out in order to optimise the gimbal frame design in order to comply with the Rayleigh diffraction limit criterion.