DEFORMATION AND WARPAGE ANALYSIS OF FLAT AND HEMISPHERICAL CENTER-ANCHORED DEFORMABLE FOCUSING MICROMIRROR WITH STRUCTURE DEPOSITING METAL LAYER

摘要

Deformable focusing micromirror is one of the important optical MEMS devices. The focusing length is determined by the profile of the micromirror surface. The profile of the micromirror is determined by the devices sizes, material properties, and depositing temperature. However, as the deformation is in the unstable regime, warpage will happen. Therefore, the deformation and warpage of two structure types of center-anchored deformable focusing micromirror are discussed. One is flat plate, and the other is semi-spherical shell. Criteria to determine the warpage condition of centered anchored deformable focusing mirrors of flat and hemispherical structure are obtained. The results show, in general, the thinner plate and the thicker metal layer will cause larger deformation. And the results also show that as the ratio of depositing metal and structure layer thickness increasing, the deformation will reach to a limit value due to the saturation of stress gradient. In warpage discussion, by the criteria from theoretical solution, the result shows when the thickness of depositing metal layer increasing, the temperature which induces warpage condition decreases. And the larger thickness of structure plate will cause the warpage temperature increasing nonlinearly. However, in some structure and depositing metal layer sizes, the focusing mirror would not become warpage. even the depositing temperature increases larger than the melting temperature of metal. The effect of outer radii of focusing micromirror on warpage temperature is also discussed. When the outer radii increasing, the depositing temperature causing warpage decreases fast and reaches a limit value. Compared to the theoretical solution, numerical results of finite element have the same tendency.