Numerical analysis and demonstration of a 2-DOF large-size micromirror with sloped electrodes

We report on the numerical analysis and demonstration of a two-degree-of-freedom (2-DOF) micromirror with a large mirror plate and a reduced actuation voltage. The micromirror consists of two layers, namely, a top layer and a bottom layer. In the top layer, the flat reflection surface is comprised of single crystalline silicon, while the bottom layer has sloped electrodes allowing for a decrease in the actuation voltage. The sloped electrodes are fabricated by time-delayed electroplating using nickel. Two different types of electrodes, a cone-type electrode and a wedge-type electrode, are designed for the mirror plate actuation and for the frame actuation, respectively. The mirror size is 1.5 mm x 1.5 mm, and the distance between the top and bottom layers is 65 mu m. The slope angle of the bottom electrode is 10.3 degrees for the cone-type electrode and 11.3 degrees for the wedge-type electrode. The mechanical maximum tilt angles are measured at 2.7 degrees with 127 V and 3.1 degrees with 120 V for the cone-type electrode and wedge-type electrode, respectively. The cone-type electrode and the wedge-type electrode provide decreased actuation voltages of 49.3% and 62.1%, respectively, compared to a parallel-type electrode. This design is useful for building large-size mirrors actuated by electrostatic forces.