Design and analysis of micro electrostatic deformable focusing mirror actuated by hemispherical electrode

Deformable focusing micromirror is one of the important optical MEMS devices. The focusing length is determined by the profile of the micromirror surface. For uniform deformation, based on bulk microfabrication of isotropic etching and wafer bonding, a novel micro electrostatic deformable focusing mirror actuated by hemispherical electrode is designed and analyzed. Due to the coupling between elastic and electrostatic force, numerical method of finite element using ANASYS software is used to analyze the deformations and stresses of different structure sizes. The phenomenon that structures deform abruptly fast due to nonlinear increasing electrostatic force called pull-in is also discussed. Using the least square method, the profile of micro focusing mirror can be curve fitting as a parabola. And the focal length can be obtained. The results show deformation increases nonlinearly as applying voltages increasing. The stresses increase linearly when thickness also increase but nonlinearly when radius of mirror increases. The maximum stress happens in the region of bounded. The focal length decreases quasi-linearly as applying voltage increases. The mirror sizes and gaps have effect on pull-in voltages. Larger gap and smaller mirror radius will cause larger pull-in voltage.