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<nobr><strong> Laser Scanning Display Using a 2D Micromirror</strong></nobr></div>
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<nobr> Anthony Kopa, Ankur Jain, and Huikai Xie</nobr></div>
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<nobr>Dept. of Electrical and Computer Engineering, Univ. of Florida, 221 Benton Hall, P.O Box 116200, Gainesville, FL, 32611, (352) 846-0441</nobr></div>
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<nobr>Email: <a href="mailto:akopa@ufl.edu">akopa@ufl.edu</a>; <a href="mailto:ajain@ufl.edu">ajain@ufl.edu</a>; <a href="mailto:hkxie@ece.ufl.edu">hkxie@ece.ufl.edu</a></nobr></div>
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<nobr>The purpose of this study is to develop a small, low voltage, low power 2D optical scanning</nobr></div>
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<nobr>device to replace larger, conventional solutions. Such a device can greatly reduce the size of visual</nobr></div>
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<nobr>display units or go where its larger counterparts cannot, such as in vivo biomedical imaging. Other 2D</nobr></div>
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<nobr>MEMS scanners have been demonstrated by other groups [1,2], but usually use electrostatic actuation,</nobr></div>
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<nobr>requiring high voltages.</nobr></div>
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<nobr>This paper details the characterization and application of a 2D CMOS-MEMS micromirror device</nobr></div>
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<nobr>for a visual display. The device is thermally actuated by bimorph beams, shown in Fig. 1. This bimorph</nobr></div>
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<nobr>actuation technique has proved successful for a 1D micromirror [3] and was extended to a 2D design. For</nobr></div>
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<nobr>the 2D device, bimorph beams are used to connect an aluminum/silicon frame to the bulk silicon substrate</nobr></div>
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<nobr>and to connect an aluminum/silicon mirror surface to this frame (Fig. 2). The mirror surface is 1mm x</nobr></div>
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<nobr>1mm with a radius of curvature of 33cm.</nobr></div>
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<nobr>Angular deflection is linear with applied power (Fig. 3). The mirror actuator can safely (without</nobr></div>
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<nobr>risk of breakage) achieve a scanning angle of 30 degrees with an input power of 60mW. The frame</nobr></div>
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<nobr>actuator can achieve 16 degrees at 110mW. The frame and mirror actuators have resonant frequencies</nobr></div>
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<nobr>near 160Hz and 330Hz, respectively, with Q~20-50. It was observed that thermal coupling exists between</nobr></div>
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<nobr>the actuators due to the limited thermal isolation of silicon dioxide. Therefore, simply ramping the driving</nobr></div>
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<nobr>currents of the two actuators (raster scanning) will generate distorted images. It was also found that</nobr></div>
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<nobr>convection cooling is significant in dynamic operation. Thus, the micromirror package must be sealed to</nobr></div>
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<nobr>prevent airflow disturbance and yet remain transparent to the laser beam.</nobr></div>
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<nobr>In this study, a simple visual display was successfully demonstrated by using the 2D micromirror.</nobr></div>
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<nobr>The objective was to scan a pixel field with the mirror, stabilizing for each pixel, and illuminate selected</nobr></div>
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<nobr>pixels with a laser diode. Using a microprocessor to control the mirror and laser and a filter to flatten the</nobr></div>
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<nobr>resonance peaks, a display resolution of 4x4 pixels at 10 frames per second was demonstrated (Fig.4).</nobr></div>
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<nobr>This resolution was largely limited by attempting to stabilize the mirror for each pixel. A new technique is</nobr></div>
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<nobr>currently in development to use continuous resonant scanning, similar to a raster pattern, which should</nobr></div>
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<nobr>simplify the mirror’s motion and allow for drastic increases to both resolution and frame rate.</nobr></div>
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<nobr>References</nobr></div>
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<nobr>[1] </nobr><span class="Apple-style-span" style="white-space: nowrap; ">W. Piyawattanametha, L. Fan, S. S. Lee, John G. D. Su and M. C. Wu. “MEMS Technology for Optical</span></div>
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<nobr>Crosslink for Micro/Nano Satellites” in The International Conference on Integrated Nano/Microtechnology</nobr></div>
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<nobr>for space Applications (NanoSpace'98), Nov. 1-6, 1998, Houston, TX.</nobr></div>
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<nobr>[2] </nobr><span class="Apple-style-span" style="white-space: nowrap; ">R. Conant , P. Hagelin, U. Krishnamoorthy, O. Solgaard, K. Lau , and R. Muller. “A Raster-Scanning Full-</span></div>
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<nobr>Motion Video Display Using Polysilicon Micromachined Mirrors” in Sensors & Actuators A, Vol. 83, no.</nobr></div>
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<nobr>1-3, 22 May 2000, pp 291-296.</nobr></div>
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<nobr>[3] </nobr><span class="Apple-style-span" style="white-space: nowrap; ">H. Xie, A. Jain, T. Xie, Y. Pan, and G. Fedder. “A Single-Crystal Silicon-Based Micromirror with Large</span></div>
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<nobr>Scanning Angle for Biomedical Applications” in The 23rd annual Conference on Lasers and Electro-Optics</nobr></div>
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<nobr>(CLEO 2003), June 1-6, 2003, Baltimore, Maryland.</nobr></div>
