Delivered by Ingenta to: Purdue University Libraries IP: 95.181.217.235 On: Tue, 07 Jun 2016 15:36:16 Copyright: American Scientific Publishers RESEARCH ARTICLE Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 11, 4919–4922, 2011 Carbon Nanotube Crossed Junction by Two Step Dielectrophoresis Anupama Arun, Paul Salet, and Adrian M. Ionescu ∗ ELB 335, Station 11, Nanolab, EPFL, Lausanne, 1015, Switzerland The crossed junction formed between a multi walled carbon nanotube (MWCNT) and a bundle of single walled carbon nanotube (SWCNT) is investigated. The junction is fabricated by orthogonally assembling the MWCNT and SWCNT by a two-step dielectrophoresis process. The conventional dielectrophoresis method to self-assemble carbon nanotubes has been modified to be able to align single MWCNT and SWCNT at predefined location on a substrate. At room temperature, the junction has an ohmic behavior with junction resistance of about 500 K or a conductance of 0.05 (e 2 /h). At 77 K, the onset of a Schottky-like behavior was observed. The resulting junction has an extremely tiny area of less than 20 nm 2 and yet supports a current density of 10 7 A/cm 2 at 1 V. The proposed fabrication technique is a convenient way to fabricate novel prototype devices to investigate material properties and new device architecture. Following further optimization, this cross-junction can be an interesting candidate for cross-bar like interconnects, with potential applications in dense logic and memory circuits. Keywords: Carbon Nanotubes, Crossed-Junction, Dielectrophoresis, Self-Assembly. 1. INTRODUCTION Carbon nanotubes (CNT) have been of significant inter- est for both fundamental research and for practical elec- tronic circuit applications. With Moore’s law reaching its physical limit, different device architectures and materials (CNTs, Si nanowires etc.) have been considered as alterna- tive solutions. In particular, cross bar architecture has been proposed for memory application, 1 nano-electromechnical systems 2 and quantum system. 3 Cross-bar architectures need ultra-scaled memory devices at the crossing points between nanowires and/or nanotubes. The purpose of this work is to fabricate such cross junctions between two carbon nanotubes and investigate their electrical property. Despite significant research in the field of CNT growth, it is still a challenge to fabricate high quality CNTs on silicon substrate with controlled orientation of growth. 4 CNT growth is a high temperature process and is often difficult to integrate CNTs for device application. CNT growth directly on the substrate is typically done by chem- ical vapor deposition process which results in more defec- tive tubes compared to arc-discharge technique. In the recent years dielectrophoresis technique has emerged as an alternative technique to orient the CNTs. 5–7 The critical ∗ Author to whom correspondence should be addressed. advantage with this technique is the possibility to locally deposit single walled carbon nanotubes (SWCNT) and multi walled carbon nanotubes (MWCNT). It is a low tem- perature process and hence is CMOS compatible. Apart from being a low temperature process dielectrophore- sis also provides the possibility to integrate high quality tubes produced by techniques such as arc discharge and laser ablation for device application. In Ref. [8] SWCNT– SWCNT junction was studied, where CNTs are randomly dispersed on the substrate and the eventual device fabri- cation involved a cumbersome step of locating the CNTs by AFM. In this work, a two-step dielectrophoresis has been used for the first time to form a SWCNT–MWCNT junction (MWCNT with diameter of ∼20 nm, and bun- dles of SWCNT with diameter of ∼10 nm), which pro- vides better control over the process than the technique used in Ref. [8]. The technology described here could be envisaged to fabricate nano-electromechanical systems as in Ref. [2]. 2. FABRICATION DETAILS Dielectrophoresis is defined as the motion of matter caused by polarization effects in non-uniform electric field. 9 Typ- ically an array of CNTs are aligned across two electrodes using this technique. 5 With a modified dielectrophoresis J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 6 1533-4880/2011/11/4919/004 doi:10.1166/jnn.2011.4116 4919