A study of the static characteristics of a torsional micromirror

Torsional micromirror has been widely used in many applications as diverse as optical communication, laser scanning related and spatial light modulator related applications. In different applications the torsional micromirror may have different arrangements. A general analysis of the static characteristics of the torsional micromirror, especially its snap-down effect, is able to simplify the design of torsional micromirror. This paper describes the static characteristics of an electrostatically-actuated torsional micromirror based on the parallel-plate capacitor model. First, a normalized equation that governs the static actuation property of the torsional micromirror device is derived, and the relationship between rotation angle and driving voltage are also determined. Thereafter, the snap-down effect is specially investigated, leading to the revealment of the direct relationships of the electrode size with the snap-down angle and the maximum driving voltage. Based on the model, a 100 μm × 100 μm torsional micromirror and a array of torsional micromirrors are fabricated using the three-layer-polysilicon micromachining process to verify the static actuation relation and the snap-down effect, respectively. The rotation angle of the micromirror is measured using an optical projection method. The experimental set-up and data are processed and analyzed in accordance with ISO guideline. It is shown that the experimental results are in good agreement with the theoretical analysis.