Tilted folded-beam suspension for extending the stable travel range of comb-drive actuators

We investigate the electromechanical side instability and the stable travel range of comb-drive actuators. The stable travel range depends on the finger gap spacing, the initial finger overlap, and the spring stiffness ratio of the compliant suspension. Proper design of the suspension structure is the most effective way to stabilize the actuator and therefore to achieve a large deflection. In this paper, we propose an improved suspension design, the so-called tilted folded-beam suspension. Using such suspension, the stability of the comb-drive actuator is improved and the stable travel range is enhanced. We give the expressions for the spring constants of the proposed suspension, both in the stroke direction and perpendicular to it. The suspension designs are also studied numerically using the finite element method (FEM), in which the geometric nonlinearities, such as large deflections and stress stiffening, are considered. Analytical calculations and FEM simulations are compared. The results demonstrate that an enhanced stable travel range, compared to that of a comb-drive actuator with the most commonly used folded-beam flexure, can be achieved by using the proposed suspension design. Comb-drive actuators with various tilted folded-beam suspensions have also been fabricated using the standard surface micromachining technology and their operational performances have been characterized. The experimental results are in good agreement with the theoretical predictions.