Novel method to improve stroke of electrostatically actuated MEMS micromirror

In this paper, an electrostatically actuated MEMS micromirror with enhanced stroke is presented. Unlike traditional MEMS micromirror, the proposed micromirror achieves a large out-of-plane stroke through employing a larger air gap for the micromirror surface to move as well as eliminating the pull-in instability. This novel micromirror has a central reflective micromirror surface of 400 μm by 400 μm, an L-shaped arm that holds the micromirror to the anchor on all side and 3 fixed bottom electrodes beneath each L-shaped arms. The lateral electrostatic forces on the upper L-shaped arm are equal in magnitude but opposite in direction and they counteract to neutralize out each other. The electrostatic force produced on the top L-shaped arm is larger than on the bottom. Therefore, the net electrostatic force points in the upward direction. As a result, the upper plate of the micromirror moves upwards. COMSOL Multiphysics is used to simulate and design the device in order to optimize the stroke of the micromirror for a lower input voltage. The mirror is fabricated using PolyMUMPs fabrication technique where an air cavity of 2.75 μm was achieved by combining the two available sacrificial layers. In this proposed design, an out-of-plane stroke of 2.43 μm is achieved at a 110 V DC bias voltage.