2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Contact Structure Formation in Carbon Nanotube Electronic Devices and Its Effect on Electron Transport

W. Luo, K. Ravichandran, W. Windl, L.R.C. Fonseca
The Ohio State University, US

Keywords:
nano electronics, contact formation, electron transport

Abstract:
The down scaling of silicon devices has been an effective method to improve device performance for decades. However, several dimensions are approaching their physical limit (such as channel length and gate oxide thickness). Further minimization is not feasible for much longer without revising the device structure. Molecular devices with carbon nanotubes (CNTs) as a channel material in field effect transistors are currently under investigation as a possible replacement for Si-based devices. In CNT field effect transistors, the CNT/metal contact forms a crucial region which exerts considerable influence on the device characteristics, since the contact resistance has been suggested to dominate the device resistance. We perform molecular process modeling by ab-initio temperature-accelerated molecular dynamics simulations to study the contact formation between different metals and nanotubes of different size. The resulting change in the electron transport properties upon contact formation is calculated based on the Landauer formulation. Our results indicate that depending on the metal, the contact formation can range from small changes in the structure as compared to uncontacted metal and CNT to strong structural changes such as disintegration of (3,3) nanotubes on Ti contacts. We find that metals used as electrodes can be categorized into two types in terms of CNT/metal contact formation and the final contact structure, which are characterized by different types of charge transfer between the CNT and the metal. This finding may help to better understand the fact that CNT devices with different electrode materials exhibit quite different transport properties. The size of CNT is found to be important as well. Smaller CNTs are more likely to disintegrate on top of electrodes due to the higher strain energy. The effect of surface contamination such as oxygen on the contact formation is discussed as well.


Nanotech 2008 Conference Program Abstract