Nonlinear flexures for stable deflection of an electrostatically actuated micromirror

This paper describes how nonlinear force flexures can be used to increase the stable deflection distance of an electrostatically-operated micromirror. Traditional micromirrors have flexures that provide linear force as a function of deflection. Electrostatic attraction is a nonlinear force, so after a traditional micromirror has deflected one-third of the initial separation distance between the top and bottom electrode, the mirror's position becomes unstable, and the mirror quickly jumps down to the bottom electrode. This phenomenon is called ''snap-through,'' and it has been well-documented, A nonlinear second order flexure has a restorative force that is proportional to the square of the deflection distance. A second order flexure does not exhibit snap-through until the micromirror is deflected one-half the initial separation between the top and bottom electrode. Higher order flexures are capable of traveling a larger distance before snap-through. This paper presents a theoretical simulation of traditional and higher order flexures. Specific nonlinear flexure designs have been constructed and demonstrated.