INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 15 (2005) 1294–1302 doi:10.1088/0960-1317/15/6/022 Comparison of microtweezers based on three lateral thermal actuator configurations J K Luo 1 , A J Flewitt 1 , S M Spearing 2,3 , N A Fleck 1 and W I Milne 1 1 Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, UK 2 Department of Aeronautics & Astronautics, MIT, Cambridge, MA 02139, USA 3 School of Engineering Science, University of Southampton, Southampton, SO17 1QJ, UK Received 26 November 2004, in final form 1 April 2005 Published 16 May 2005 Online at stacks.iop.org/JMM/15/1294 Abstract Thermal actuator-based microtweezers with three different driving configurations have been designed, fabricated and characterized. Finite element analysis has been used to model the device performance. It was found that one configuration of microtweezer, based on two lateral bimorph thermal actuators, has a small displacement (tip opening of the tweezers) and a very limited operating power range. An alternative configuration consisting of two horizontal hot bars with separated beams as the arms can deliver a larger displacement with a much-extended operating power range. This structure can withstand a higher temperature due to the wider beams used, and has flexible arms for increased displacement. Microtweezers driven by a number of chevron structures in parallel have similar maximum displacements but at a cost of higher power consumption. The measured temperature of the devices confirms that the device with the chevron structure can deliver the largest displacement for a given working temperature, while the bimorph thermal actuator design has the highest operating temperature at the same power due to its thin hot arm, and is prone to structural failure. (Some figures in this article are in colour only in the electronic version) 1. Introduction The advance of miniaturization technology has led to the development of microtools which are suitable for precisely manipulating objects at small scales. Applications exist in biomedical and biological fields, micro-assembly of microelectronics, communication devices and precision machining. There is a great demand for microgrippers or microtweezers with a controlled grasping force and accuracy. Such devices must be easy to operate with a large opening displacement at a low power consumption and low temperature. The driving mechanisms used in microtweezers include electrothermal, electrostatic, piezoelectric, pressure and the shape memory effect [1–10]. High voltages of up to hundreds of volts are generally required to operate electrostatically or piezo-electrically driven microtweezers [5, 6], which are thus unsuitable for biological applications. Devices actuated by gas pressure are normally large in size and the device structure is complicated [7]. Shape memory-based devices have problems of low efficiency, limited operating temperature and difficulty in position control [8, 9]. Although these devices are relatively large, with dimensions of up to a few millimetres, only small openings of a few tens of micrometers can be realized. Although microtweezers based on electrothermal actuators need a high current and are usually operated at high temperature [3], they are able to deliver a large force with large opening displacements, and are, therefore, one of the preferred driving mechanisms for microtweezers, especially for non-biological applications. Lateral bimorph thermal actuators based on differential heating 0960-1317/05/061294+09$30.00 © 2005 IOP Publishing Ltd Printed in the UK 1294