INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 13 (2003) 383–389 PII: S0960-1317(03)56653-0 Magnetically-driven bi-directional optical microscanner Hyoung J Cho 1 and Chong H Ahn 2 1 Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, PO Box 162450, Orlando, FL 32816-2450, USA 2 Microsystems and BioMEMS Laboratory, Department of Electrical and Computer Engineering and Computer Science, University of Cincinnati, PO Box 210030, Cincinnati, OH 45221-0030, USA E-mail: joecho@mail.ucf.edu and chong.ahn@uc.edu Received 26 November 2003, in final form 30 January 2003 Published 28 February 2003 Online at stacks.iop.org/JMM/13/383 Abstract A magnetically-driven bi-directional optical microscanner has been designed, fabricated and characterized. Magnetic and structural modeling and analysis has been applied to the design of the scanner. The micromachined scanner can be operated bi-directionally under the condition of static operation. Under dynamic operation, the prototype scanner has shown stable bi-directional scanning performance at the operating frequency of 30 Hz, corresponding to 60 Hz in the regular uni-directional scanner. Compared with a conventional scanner, the microscanner has the advantages of low power consumption due to its small size and high scanning efficiency as a result of unique bi-directional actuation. (Some figures in this article are in colour only in the electronic version) 1. Introduction For the miniaturization of optical scanners, there has been a growing interest in the fabrication of magnetically-driven micromirrors and optical switches, which allow millimeter- sized mirrors to be actuated with a low driving voltage [1–3]. Although electrostatic mirrors have been commonly used in microelectromechanical systems (MEMS) devices, there have been technical difficulties in realizing large electrostatic mirrors because of restrictions due to the electrode gap size and high driving voltage [4]. Furthermore, the positive attributes of magnetic MEMS devices involve simple packaging. Since magnetic actuators are driven by current and have low input impedances, leakage impedances due to the package do not affect the performance of devices as much as those in electrostatic actuators [5]. If properly designed, by eliminating the high voltage power source, the total device or system size with magnetic actuators could be smaller than that of electrostatic devices. The operation of magnetic MEMS devices is also less affected by dust and moisture in the air due to the use of a magnetic field. For the practical application of the micromachined mirror, Conant et al [6] and Urey et al [7] have studied a raster scanner. A raster scanner is composed of two mirrors scanning in orthogonal directions or one two-dimensional (2D) scanning mirror and a modulated light source to generate a 2D image. A frame-scan mirror performs a linear scan at a low frequency of 60 Hz for a typical display in one direction, whereas a line-scan mirror scans at a high frequency greater than 28 kHz in the other direction, to obtain a 640 × 480 VGA display [6]. For a frame scan, if a bi-directional scanner is used, the sweeping speed of the scanner can be reduced by half because of the doubled scanning efficiency. To determine the performance of the scanner, one simple measure is to evaluate the maximum deflection measured from the tip of the scanner, which is proportional to the size of the mirror and the scanning angle. According to Urey et al [7], the scan angle θ · D (deg · mm), as a measure of requirements for different display formats, is 3.75 for 320 × 240, QVGA and 7.50 for 640 × 480, VGA in a retinal scanning display device using a raster scanner. Because of this requirement, the smallest optical aperture has to be large enough to ensure sufficient image resolution. As a result, mirrors with lateral dimensions above 1 mm are required for specific applications in practical systems. Therefore, a magnetically driven optical scanner is one of the optimal candidates for this application. 0960-1317/03/030383+07$30.00 © 2003 IOP Publishing Ltd Printed in the UK 383