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0990-B04-01

Dielectrophoresis-Based Assembly and High-Frequency Characterization of Carbon Nanotube Bundles Michael Woodson, Alexander Tselev, and Jie Liu Department of Chemistry, Duke University, French Family Science Center, 124 Science Drive, Durham, NC, 27708 ABSTRACT As the size of integrated circuit elements decreases, the properties of carbon nanotubes (CNTs) become increasingly attractive for interconnect applications. To be used by industry, full characterization of the electronic properties of CNT aggregates is essential. Dielectrophoresis from CNTs suspended in liquid has been demonstrated as a simple route to bundles of aligned parallel nanotubes. We describe a method by which circuits including such bundles may be fabricated, and provide some high-frequency measurements of their electrical properties. The contributions of the contacts can be separated from those of the bundle itself. INTRODUCTION Interconnects are becoming an increasingly important aspect of integrated circuits. As the size of metal interconnects decreases, surface scattering becomes more important and resistance increases dramatically.1 Carbon nanotubes are ballistic conductors, and so can be used for interconnects at size levels that are unavailable to metals. To provide sufficiently low impedence however, many nanotubes must be used in parallel. At extremely small scales, aligned thin films are preferred while at more moderate scales a bundle of nanotubes is predicted to give better properties.2 Such predictions are based on idealized models, and actual bundles produced by some physical or chemical process will most likely diverge from this model. Experimental investigation of CNT interconnects is therefore critical so that the significance of this divergence can be determined and assembly methods evaluated. The particular physical process used in this study to assemble CNT bundles is dielectrophoresis (DEP). Briefly, DEP uses nonuniform electric fields to align and attract polarizable molecules or particles. If properly functionalized, CNTs can be dispersed in water or other solvents and from there assembled into high-density aligned bundles by a combination of dielectrophoretic forces and surface tension.3 Bundles formed in this way have demonstrated good mechanical stability and field-emission properties. Multiple bundles may even be formed in parallel. Bundles formed by DEP are therefore technologically significant, making them valid candidates for electrical characterization. To be technologically useful, the characterization must cover an appropriate frequency range. Since the future digital integrated circuits are envisioned to operate at clock frequencies above 10 GHz,4 we have performed the electrical characterization of the bundles at microwave frequencies (0.5-67 GHz). Additionally, as we show below, the microwave measurements allow us to separate contributions of the contacts from that of the bundle itself and to obtain the intrinsic electrical properties of the DEP-assembled bundle.

EXPERIMENT Few-walled nanotubes wit