A micromirror with large static rotation and piston actuation

Jin-Chern Chiou, C. F. Kuo, Y. J. Lin, H. P.D. Shieh

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


Recently, MEMS based micromirrors have been developed for various optical applications including displays, confocal microscopy, and optical switching. These MEMS based micromirrors have higher operating speed and lower mass than traditional fabricated technology, and potential for lower cost through MEMS fabrication process. In most cases, however, MEMS actuators have provided only in-wafe-plan motion. Thus, for many optical applications such as scanning micromirrors, a variety of methodologies are investigated to provide the needed additional out-of -wafer-plane degree of freedom (DoF) [1, 2]. Nevertheless, these methodologies often need complex fabrication process. For this consideration, a micromirror with large rotation and piston actuation is developed, and the design, fabrication and measurement result are also presented. In order to achieve out-of-plan actuation, the pre-stress comb actuator (PCA) was designed to actuate the micromirror [3], Figure 1(a) shows one end of the composite beam, which is clamped to the anchor, while the other end is elevated due to the residual stress between the two deposited materials. When a voltage, V, is applied between the movable and fixed comb, the movable composite beam can be pulled downward to the substrate by the electrostatic force induced by the fringe effect, as shown in figure 1(b). Compare to the parallel plate electrostatic actuator, the vertical comb drive exhibits no pull-in and hysteresis phenomenon. Notably, the electrostatic force is constrained when the movable comb finger is closed to the fixed comb finger, independently of the input driving voltage, as shown in figure 1(c). Figure 2 shows the fabricated micromirror device. The present micromirror device was fabricated through commercial available polyMUMPs. It contains two PCAs, springs, and a micromirror. The fabricated PCA consists of a 540×40 μm2 composite beam that is fixed to an anchor structure with 34 movable comb fingers orthogonally mounted on the composite beam, and 35 fixed comb fingers are mounted on the surface of the nitride. The diameter of the micromirror is 200 μm. After release process and post-heat treatment, the micromirror was elevated 60 μ m by the PCAs. By applying driving voltage to the single PCA or the PCA pair, the mocromirror could achieve rotation or piston motion. Figure 3 shows the rotation angle and vertical displacement of the fabricated micromirror respectively. The maximum rotation angle is ±12.5 degree with 200V actuating voltage, and the maximum vertical displacement is 45 μ m with 200V driving voltage.

Original languageEnglish
Title of host publicationIEEE/LEOS International Conference on Optical MEMS and Their Applications Conference, 2006
Number of pages2
StatePublished - 1 Dec 2006
EventIEEE/LEOS International Conference on Optical MEMS and Their Applications Conference, 2006 - Big Sky, MT, United States
Duration: 21 Aug 200624 Aug 2006

Publication series

NameIEEE/LEOS International Conference on Optical MEMS and Their Applications Conference, 2006


ConferenceIEEE/LEOS International Conference on Optical MEMS and Their Applications Conference, 2006
CountryUnited States
CityBig Sky, MT

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