Analysis, Simulation and Testing of a Micromirror with Rotational Serpentine Springs

In this paper, a 2-DOF model for electrostatically actuated torsional micromirrors with relatively soft stiff rotational serpentine springs is presented. The analytical stiffness formulae for this rotational serpentine spring are also presented. FEA simulations for static performance have been verified by the experimental values. Such validation was implemented through fabrication of the micromirror on a SOI wafer by MicraGEM micromachining process, PSD sensor based test set-up for static properties, and the corresponding tests. Due to the soft stiffness of rotational serpentine springs designed, the fabricated torsional micromirror could be rotated to some angle under low applied bias. The simulated pull-in voltage 17.2 V is close to the actual value but much smaller than those of previously reported large size torsional micromirrors. The deviation of the simulated static displacements from experimental results could be mainly due to the tolerance of fabrication, the slender beam and linear structural assumptions. However, with relatively lower applied voltages of actuation, these torsional micromirrors that use the rotational serpentine springs can be integrated on the same microchip with CMOS circuits, showing their promising potential for industrial applications.