Nonlinear Rotational Spring with Tension for Stabilizing Electrostatically Driven Micromirror

Thin film torsion bar with tension is introduced in the micromirror realizing the low-voltage driving. The rotational spring of this torsion bar shows the large nonlinearity which is observed in the change of the ringing frequency. The curve of the mirror rotation angle against the driving voltage becomes rather linear increasing the stable region. The origin of the nonlinearity is investigated. The combination between the tension and the vertical displacement of the torsion bar is considered for expressing the experimental result.