Study of snap-down phenomenon in an electrostatically-actuated torsional micromirror

In this paper, the snap-down phenomenon in an electrostatically-actuated torsional micromirror is investigated. Based on the static actuation relation of torsional micromirrors, the relationship between snap-down angle and the structural parameters of the torsional micromirror is derived. It is shown that the snap-down angle is mainly determined by the size and position of the electrodes. Most importantly, it is found that the product of the normalized snap-down angle and the normalized size of the electrode is equal to a constant of 0.4404, which is universal for all torsional micromirrors of this kind of configuration, and is very useful for micromirror design. The relationship between the maximum driving voltage and the snap-down angle is also studied. Finally, a group of torsional micromirrors has been fabricated using multi-layer polysilicon processes, and then been tested to verify the analysis.