78 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 11, NO. 1, FEBRUARY 2002 A Bidirectional Magnetic Microactuator Using Electroplated Permanent Magnet Arrays Hyoung J. Cho and Chong H. Ahn, Member, IEEE Abstract—A novel bidirectional magnetic microactuator using electroplated permanent magnet arrays has been designed, fabri- cated and characterized in this work. To realize a bidirectional mi- croactuator, CoNiMnP-based permanent magnet arrays have been fabricated first on a silicon cantilever beam using a new electro- plating technique. In the fabricated permanent magnets, the ver- tical coercivity and retentivity have been achieved up to 87.6 kA/m (1100 Oe) and 190 mT (1900 G), respectively by applying magnetic field during electroplating. A prototype bidirectional magnetic mi- croactuator has been realized by integrating an electromagnet with a silicon cantilever beam, which has permanent magnet arrays on its tip. By applying a dc current of 100 mA and altering its polarity, bidirectional motion on the tip of the cantilever beam has been suc- cessfully achieved in the deflection range of 80 m. [656] Index Terms—Bidirectional actuator, electroplated magnet, magnetic microactuator, permanent magnet array. I. INTRODUCTION T HERE has been a growing interest in the realization of bidirectionally driven microactuators [1]–[5]. Specifically, optical switches and scanners, which are essential components for optical communication and image process, usually require a stable and long-range bidirectional microactuators. Among sev- eral driving principles available for the bidirectional actuation, magnetically driven bidirectional actuation can be considered as one of the appropriate actuations for a large deflection over sev- eral hundreds of m. Based on the magnetic actuation, bidirec- tional actuation can be achieved between a permanent magnet and an electromagnet. By altering the exciting direction of the current through the electromagnet, either attractive or repulsive force can be generated between the magnets, so the actuator has a relatively simple structure. In addition, permanent mag- nets allow favorable scaling factor and low power consumption in microscale compared to a variable reluctance-type electro- magnetic actuator [6]. Despite many advantages from the bidi- rectional magnetic actuators, the realization of the devices has been limited mainly by technical difficulties in fabricating pre- cise permanent magnets in microscale. Until recently, assembling of commercial magnets [1]–[3] or screen-printing of magnetic particles [4], [5] has been suggested as a way of fabricating thick permanent magnet structures on Manuscript received December 21, 2000; revised July 17, 2001. This work was supported in part by NASA-Glenn Microsystem Initiative (156264- N003327). Subject Editor E. Obermeier. The authors are with Microsystems and BioMEMS Lab, Center for Microelectronic Sensors and MEMS, Department of Electrical and Computer Engineering and Computer Science, University of Cincinnati, Cincinnati, OH 45221-0030 USA (e-mail: choh@email.uc.edu; chong.ahn@uc.edu). Publisher Item Identifier S 1057-7157(02)00077-X. the microactuators. Though relatively high coercivity and re- tentivity have been reported, the size of the magnet is limited by the processing condition and is usually in millimeter scale. In integrating the permanent magnets on the microactuators, however, processing temperature, geometry and alignment pre- cision of the fabricated permanent magnets will be a critical con- cern, since the fabrication process should be compatible with the other electronic devices such as complementary metal–oxide– semiconductor (CMOS) circuits and integrated electromagnets. To improve the fabrication capability of permanent magnets with CMOS, we have already introduced the electroplating tech- nique of CoNiMnP-based thick permanent magnet arrays [7]. Another goal of this work is to meet the magnetic requirement in fabricating the integrated permanent magnet component. The magnetic properties of the permanent magnets should be con- trollable in a given dimension. For this purpose, heat treatment has been commonly used in conventional permanent magnets such as Nd–Fe–B permanent magnets [8], [9]. Although this method is effective to align the magnetic moment in a hard mag- netic film through crystallization, the device should be heated up to a temperature of 600 C, which is usually not compatible with electronic devices and MEMS structures. In order to meet the requirements described the above, we have developed a new method to control the magnetic properties of the permanent magnet arrays by applying external magnetic field during electroplating without any heat treatment. Then, with the optimized plating condition, the permanent magnet ar- rays were incorporated as part of a prototype actuator to achieve bidirectional actuation. A bidirectional magnetic microactuator, which consists of a silicon cantilever beam with electroplated permanent magnets and an electromagnet, has been successfully fabricated and characterized in this work. The deflections at- tained from the fabricated bidirectional actuator have been com- pared with the simulated results. In this paper, we present a new bidirectional actuator using electroplated permanent magnets. II. DESIGN A prototype bidirectional magnetic actuator is composed of a silicon cantilever beam and an electromagnet. At the tip of the silicon cantilever beam, permanent magnet arrays are electro- plated so as to achieve the bidirectional actuation. A schematic diagram of the microactuator is shown in Fig. 1. Underneath the cantilever beam, permanent magnet arrays are placed along the axis of the electromagnet. Vertical magnetic anisotropy of the magnetic arrays produce bidirectional motion of the microactuator when a current is ap- plied to the electromagnet. The adaptation of array shapes in de- sign of permanent magnets allows suppression of the residual 1057–7157/02$17.00 © 2002 IEEE