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 modulato r related applications. In different applications the torsional micromirror may have different arrangements. A general analysis of the static characte ristics of the torsional micromirror, especially its snap-down effect, is a ble to simplify the design of torsional micromirror. This paper describes the static characteristics of an electrostatically-act uated torsional micromirror based on the parallel-plate capacitor model. Fi rst, a normalized equation that governs the static actuation property of th e torsional micromirror device is derived, and the relationship between rot ation angle and driving voltage are also determined. Thereafter, the snap-d own effect is specially investigated, leading to the revealment of the dire ct relationships of the electrode size with the snap-down angle and the max imum driving voltage. Based on the model, a 100 mum x 100 mum torsional mic romirror and a array of torsional micromirrors are fabricated using the thr ee-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 experimenta l set-up and data are processed and analyzed in accordance with ISO guideli ne. It is shown that the experimental results are in good agreement with th e theoretical analysis. (C) 2001 Elsevier Science B.V. All rights reserved.