A Bi-Directional Out-of-Plane Actuator by Electrostatic Force

Abstract

Presented in this paper is a bi-directional out-of-plane actuator which combines the merits of the electrostatic repulsive principle and the electrostatic attractive principle. By taking advantage of the electrostatic repulsive mode, the common "pull-in" instability can be lessened to enlarge the displacement, and by applying the electrostatic attractive mode, the out-of-plane displacement is further enlarged. The implications of changing the actuator's physical dimensions are discussed, along with the two-layer polysilicon surface microfabrication process used to fabricate such an actuator. The static characteristics of the out-of-plane displacement versus the voltage of both modes are tested, and displacements of 1.4 μm and 0.63 μm are obtained at 130 V and 15 V, respectively. Therefore, a total stroke of 2.03 μm is achieved, more than 3 fold that of the electrostatic attractive mode, making this actuator useful in optical Micro-Electro-Mechanical Systems (MEMS) and Radio Frequency (RF) MEMS applications.

Study of Electrostatic Actuator Voltage Reduction with a Tri-Electrode Actuator with Varying Pull-Down Voltage

“…Shai Shmulevich et al [1] proposed solving the pull-in issue with a nonlinear spring, thereby allowing closer electrode spacing. Toshiyuki Sugimoto et al [2] and Hao Ren et al [3] used bi-directional electrostatic actuators to expend the controllable stroke. J. I. Seeger et al [4] utilized a negative feedback with a capacitor in series with the electrostatic actuator as a solution to the pull-in.…”

Reduction of Electrostatic Control Voltage with a Tri-Electrode Actuator

“…However, this leads to significantly elevated driving voltage, since the electrostatic force is proportional to the square of the separation distance. Various researches have been carried out [2][3][4][5][6][7] to overcome the drawback. Shai Shmulevich et al [2] proposed a design with a nonlinear spring whose spring constant increases as the actuator closes, and an 18.6 µm out of 21 µm was achieved; Holger Conrad et al [3] came up with a v-shaped actuator design so that the displacement is amplified by angle between the pulling direction and actuation direction.…”

“…Shai Shmulevich et al [2] proposed a design with a nonlinear spring whose spring constant increases as the actuator closes, and an 18.6 µm out of 21 µm was achieved; Holger Conrad et al [3] came up with a v-shaped actuator design so that the displacement is amplified by angle between the pulling direction and actuation direction. Other methods also exist such as nonlinear driver electrodes [4] and bi-directional moving of the upper electrode [5,6]. In [7], a capacitor in series with the electrode power supply was explored to avoid pull-in.…”