JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 17, NO. 4, AUGUST 2008 823 Polymeric Thermal Microactuator With Embedded Silicon Skeleton: Part II—Fabrication, Characterization, and Application for 2-DOF Microgripper Trinh Chu Duc, Gih-Keong Lau, and Pasqualina M. Sarro, Fellow, IEEE Abstract—This paper presents the fabrication, characterization, and application of a novel silicon-polymer laterally stacked elec- trothermal microactuator. The actuator consists of a deep silicon skeleton structure with a thin-film aluminum heater on top and filled polymer in the trenches among the vertical silicon parts. The fabrication is based on deep reactive ion etching, aluminum sputtering, SU8 filling, and KOH etching. The actuator is 360 μm long, 125 μm wide, and 30 μm thick. It generates a large in-plane forward motion up to 9 μm at a driving voltage of 2.5 V using low power consumption and low operating temperature. A novel 2-D microgripper based on four such forward actuators is introduced. The microgripper jaws can be moved along both the x- and y-axes up to 17 and 11 μm, respectively. The microgripper can grasp a microobject with a diameter from 6 to 40 μm. In addition, the proposed design is suitable for rotation of the clamped object both clockwise and counterclockwise. [2007-0192] Index Terms—Electrothermal microactuator, polymeric mi- croactuator, SU8, 2-D microgripper. I. I NTRODUCTION P OLYMERIC electrothermal actuators are of great interest in microelectromechanical systems technology as they are capable of producing large displacements at a low driving volt- age and operating temperature [1]–[3]. Furthermore, the poly- meric electrothermal actuators are capable of operating in liquid and can be biocompatible. However, most of the developed Manuscript received July 31, 2007; revised January 10, 2008. First published June 13, 2008; last published August 1, 2008 (projected). Subject Editor S. M. Spearing. T. Chu Duc was with the Electronic Components, Technology and Materials Laboratory, Delft Institute of Microsystems and Nanoelectronics, Delft Univer- sity of Technology, 2624 CT Delft, The Netherlands. He is now with the Fac- ulty of Electronics and Telecommunication, College of Technology, Vietnam National University, Hanoi, Vietnam (e-mail: trinhcd@coltech.vnu.vn). G.-K. Lau was with the Department of Precision and Microsystems Engi- neering, Delft University of Technology, 2628 CD Delft, The Netherlands. He is now with the School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798 (e-mail: mgklau@ntu.edu.sg). P. M. Sarro is with the Electronic Components, Technology and Ma- terials Laboratory, Delft Institute of Microsystems and Nanoelectronics, Delft University of Technology, 2628 CT Delft, The Netherlands (e-mail: p.m.sarro@tudelft.nl). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2008.924275 polymeric electrothermal microactuators employ two-material structures. The metal heater is deposited on the top of a high coefficient of thermal expansion (CTE) polymer layer. The structures are bent when heated. The interface between the heat source and the polymer layer is rather limited by the surface area of the metal layer, and the heat transfer along the vertical dimension is not effective. Since the polymer layers have low thermal conductivity, the reported structures [1], [2] have limited movement. Moreover, the unintended vertical move- ment couples and interferes with the desired lateral movement [1], [2]. We propose a novel silicon-polymer laterally stacked electrothermal in-plane forward microactuator. The device is composed of three materials: a metal heating layer, a silicon structure as frame with high heat conductivity, and a polymer with a high CTE. The design and modeling of the actuator is described in detail in a companion paper [4]. During ac- tuation, heat is efficiently transferred from the heater to the polymer by employing the high thermal conduction of the deep silicon skeleton structure that provides a large interface with the surrounding polymer. Moreover, the polymer layer is constrained between two silicon plates. The thermal expansion of the constrained polymer is significantly larger than the no constraint one [4]–[6]. A very interesting application that largely benefits from the specific characteristics of these actuators is a novel 2-D silicon-polymer electrothermal microgripper. The development of microgrippers with large motion capability and low working temperature has become a great technological challenge for ad- vanced microassembly, micromanipulation, and microrobotics. Conventional microgrippers or pipettes are used to manipulate microparticles [7]. However, the developed microgrippers and pipettes cannot be used to rotate individual microparticles, a function which is highly desirable during microassembly or micromanipulation [3], [8]. The microgripper introduced here is based on four forward silicon-polymer electrothermal actua- tors. The actuator device is capable of providing displacement in two dimensions in a plane that is generally parallel to the surface of the substrate. Besides the regular grasping operation of conventional microgrippers, this proposed 2-D microgripper is suitable for rotation of the clamped object. The device is made on silicon-on-insulator (SOI) silicon wafers with a CMOS-compatible fabrication process. 1057-7157/$25.00 © 2008 IEEE Authorized licensed use limited to: Technische Universiteit Delft. Downloaded on April 29,2010 at 09:13:37 UTC from IEEE Xplore. Restrictions apply.