Pivot-stable electrostatic rotary MEMS structure for alignment-critical applications

This work presents a novel electrostatically actuated rotary MEMS structure optimized for high-precision in-plane rotation with low parasitic displacement. The design integrates curved comb-drive electrodes with symmetrical U-shaped suspension springs to enable controlled bidirectional rotation while minimizing undesirable lateral and out-of-plane motion. Analytical modeling, finite element simulations, and experimental measurements consistently demonstrate a maximum angular displacement of ± 2.2 ∘ at 150 V, with unwanted lateral translational motion confined below 190 nm along both the X and Y directions, and out-of-plane motion confined under 300 nm in the Z direction. The platform stable center of rotation and suppressed parasitic displacement make it highly suitable for applications such as MOEMS-based optical switches, where alignment precision is critical. In addition, the platform features a lateral gap-closing mechanism actuated electrostatically, enabling tunable displacement for alignment-critical optical applications while preventing pull-in through stopper integration. Furthermore, this work provides an analytical formulation of torque and stiffness. The proposed device occupies an area of 1 mm × 2 mm and is fabricated using the PiezoMUMPs process with a 10 µm thick device layer.