A gimbal-less two-axis electrostatic scanner with tilted stationary vertical combs and serially connected springs via a microassembly process

Abstract

We propose a gimbal-less two-axis electrostatic microelectromechanical system (MEMS) scanner with tilted stationary vertical combs (TSVCs) fabricated via a microassembly process. The gimbal-less two-axis scanner has the advantage of being of a compact size and also does not need any additional fabrication sequence for electrical isolation. The TSVCs and coupled springs (T-shaped springs and folded springs) allow the mirror scanner to rotate around two axes with a large scanning angle. The fabrication steps for the proposed scanner can be remarkably reduced by employing a microassembly process, as there is no need to conduct a multistep etching process for height offset between two vertical combs. It was found that the width of the folded spring and the T-shaped spring dominated the resonant frequency of the fast axis and the slow axis, respectively. By modeling the capacitance change of TSVCs with respect to the rotational angle (theta), the effective tilted angle (ETA), as a new design criterion, was introduced to determine an adequate operation range. The optical scanning angle of the fabricated scanner was up to 7.8 degrees at 90 V for the slow axis in quasistatic mode and up to 17.3 degrees at 100 V for the fast axis in resonant mode at 2.84 kHz. The fabricated scanner can be used for various endoscopic optical applications.