IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 6, JUNE 2005 1193 A Metal-Coated Polymer Micromirror for Strain-Driven High-Speed Multiaxis Optical Scanning Yi-Chung Tung, Student Member, IEEE, and Katsuo Kurabayashi, Member, IEEE Abstract—We have developed a new polymer-based micro- mirror device capable of high-speed multiaxis out-of-plane scan- ning motion. The whole device structure integrates a metal-coated three-dimensional polydimethylsiloxane micromirror structure with an optically smooth surface and a single layer of silicon- on-insulator electrostatic comb-drive actuators. The high-strain mechanical elasticity of the polymer material allows for trans- lating the in-plane comb-drive motions into three-degree-of- freedom scanning motion with a single actuator layer. The simple structure design and rapid response characteristics of the demon- strated device may lead to high-yield high-performance scanning micromirror technology. Index Terms—Electrostatic actuation, microelectromechanical devices, multiaxis optical scanning, polymer micromirror, three- dimensional (3-D) elastomer microstructures. S CANNING micromirror technology plays a critical role in optical switching, imaging, and beam steering applica- tions that require miniaturization, light weight, low energy con- sumption, and reduced manufacturing complexity. With the ad- vancement of microelectromechanical systems (MEMS) tech- nology, a large number of scanning micromirrors have been demonstrated for a wide variety of applications including optical communications [1], optical microscopy [2], [3], display tech- nology, and biological detection [4]. The key functionality to the MEMS optical scanning mirror is micrometer-scale actuation of their mirror surface with multiple degrees of freedom [5], [6] and fast response [1]. One of the most common approaches to driving a MEMS scanning micromirror in previous work is elec- trostatic actuation using comb drives due to their complemen- tary metal–oxide–semiconductor (CMOS) compatibility, high speed, and low power consumption. There are two other major advantages with this approach: 1) both of the micromirror com- ponent and the actuator can be fabricated using standard silicon micromachining and 2) the force generated by comb drives is constant and well predicted regardless of the electrode engage- ment length, thus making it easy to control the motion of scan- ning mirror [7]. However, a single comb drive can only generate one-dimensional motion, which usually lies parallel to the sub- strate plane [6], [8]. Previous studies show that this approach has the shortcoming that it requires multilayer structures and rela- tively complex mechanisms to achieve multiaxis manipulation Manuscript received December 1, 2004; revised February 8, 2005. The authors are with the Department of Mechanical Engineering, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109-2125 USA (e-mail: tungy@umich.edu; katsuo@umich.edu). Digital Object Identifier 10.1109/LPT.2005.846613 Fig. 1. (a) Schematic drawing of polymer-based scanning micromirror with single-layer silicon comb drives. (b) Vertical motion of micromirror. (c) Rotational motion of micromirror. of the micromirror component [3], [5], [9], making the fabrica- tion processes challenging and time-consuming. In this letter, we demonstrate a new CMOS-compatible scanning micromirror technology. Our approach employs an elastomeric microstructure which is reversibly deformable under mechanical strain introduced by comb drives. The use of three-dimensional (3-D)-shaped elastomer in MEMS allows us to achieve multiaxis scanning motion without increasing the structural complexity of the silicon comb-drive system. Fig. 1 illustrates a device that we present in this letter. It consists of two major parts: 1) multiple comb drives on a silicon-on-insulator wafer and 2) a 3-D polydimethylsiloxane (PDMS) micromirror structure connected to each of the comb drives via its flexural joint. PDMS is an organic elastomer, and it has excellent me- chanical flexibility and large maximum strain limit near 40% (for silicon material, it is 1%.) The PDMS microstructure is fabricated using soft lithography [10]. The soft lithography al- lows us to fabricate 3-D PDMS microstructures based on replica molding. With its manufacturability, mechanical flexibility, and robustness, PDMS serves as an excellent structural material of the flexural joints, which are the key device components to achieve the multiaxis mirror motion in our device. The connections between the PDMS micromirror and the comb drives translate the in-plane motion of the comb drives 1041-1135/$20.00 © 2005 IEEE