NANO ELECTRO MECHANICAL SYSTEMS WITH SINGLE WALLED CARBON NANOTUBES AS FUNCTIONAL ELEMENTS C. Hierold, C. Stampfer, T. Helbling, A. Jungen, D. Sarangi Micro and Nanosystems, ETH Zurich, Tannenstrasse 3, 8092 Zurich, Switzerland hierold@micro.mavt.ethz.ch , phone +41 44 63 23143, fax +41 44 63 21462 Abstract: Sensors are key components in mechatronic systems. Further system miniaturization will demand for continuous down-scaling of sensor functions in such systems most likely towards nano scale. Then new sensor device concepts will emerge to maintain performance, e.g. sensitivity, or to utilize unique functional properties of nano scale structures. This paper presents concepts to create nano electro mechanical sensors based on carbon nanotubes (CNTs). Suspended single walled CNT based cantilever and bridge structures and a membrane based CNT pressure sensor are introduced and discussed. Measurements on the pressure sensor prove metallic single walled CNTs as exceptional piezoresistive electro mechanical transducers with gauge factors above 200. Copyright © 2006 IFAC Keywords: nano electro mechanical systems, NEMS, carbon nanotubes, sensors, pressure sensor 1. INTRODUCTION Further system miniaturization in mechatronic systems will certainly create demands for a continuous down-scaling of sensor functions in a variety of different application fields (Hierold et.al., 2005). Further scaling of transducers in general and sensors in particular is mandatory for all applications where ultra-miniature size enables the exploration of the nano-cosmos. System biology for example, which is currently taking off as research discipline to explore the basic principles of living systems by quantitative modeling of inter and intra cellular processes (Klipp et.al., 2005), will starve for sensors to provide data for model verification. Implantable devices like future autonomous micro robots or multifunctional endoscopes (Kim et.al., 2005) for minimal invasive diagnostics (Allen, 2005), health monitoring (Cong et.al., 2005), drug delivery and many other intra-corporal tasks need ultra-miniature sensors to fulfill their missions while minimizing invasiveness. Last but not least, system miniaturization and device integration, based on reproducible fabrication processes and large scale production, are still the top pre-requisites for low cost products. However, limitations in down-scaling of conventional micro electro mechanical systems (MEMS) are foreseeable (Hierold, 2004). Therefore new materials with new properties on the nano scale will emerge to fulfill sensor tasks in ultra- miniaturized sensor systems. In this paper, first proposals to create electro mechanical sensors based on carbon nanotubes (CNTs) are discussed. 2. CARBON NANOTUBES AS ELECTRO MECHANICAL TRANSDUCERS Carbon nanotubes (Iijima, 1991) are one of the most intensely studied nanostructures to date (Dresselhaus et.al., 2001; Saito et.al., 2001; Reich et.al., 2003) and are very promising for the further miniaturization of sensors due to their unique properties. Single walled carbon nanotubes (SWNTs) are hollow cylinders of graphene, composed of a single layer of carbon atoms. The length of the tubes can be several micrometers and the diameters are on the order of 1 nm, owing to very high aspect ratios. Perfect SWNTs without distortions show ballistic conductance and may carry very high current densities (up to 10 9 A/cm 2 (Bushan, 2004)). Depending on the structural symmetry, which is described by the terms armchair, zig-zag or chiral type tubes, they can exhibit either metallic or semiconducting behavior. Moreover, they are highly elastic with Young’s modulus in the range of 1 TPa (Zhang et.al., 2002). Their extraordinary mechanical, electrical and electro mechanical properties will make them to promising candidates for very sensitive elements in nanosystems. Research on CNTs for transducers is taking off and first realizations of CNT-based nano mechanical systems have been recently published (Williams et.al., 2003; Miyashita et.al., 2003; Fennimore et.al., 2003). Some of the many application ideas for utilizing CNTs as structural mechanical elements include data storage (Rueckes et.al., 2000), relays (Lee et.al., 2004), oscillators (Papadakis et.al., 2004; Nishio et.al., 2005), switches (Cha et.al., 2005), and 97