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Unformatted text preview: Thermal properties of carbon nanotube array used for integrated circuit cooling Yuan Xu, Yi Zhang, a ! and Ephraim Suhir Nanoconduction Inc., 1275 Reamwood Avenue, Sunnyvale, California 94089 Xinwei Wang Department of Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0656 s Received 19 January 2006; accepted 24 July 2006; published online 4 October 2006 d Carbon nanotubes s CNTs d , owing to their exceptionally high thermal conductivity, have a potential to be employed in micro- and optoelectronic devices for integrated circuit s IC d cooling. In this study we describe a photothermal metrology intended to evaluate the thermal conductivity of a vertically aligned CNT array s VCNTA d grown on a silicon s Si d substrate. Plasma-enhanced chemical vapor deposition, with nickel s Ni d as a catalyst, was used to grow CNT. The experimentally evaluated thermal conductivity of the VCNTA and the thermal contact resistance at the interface between the VCNTA and the “hot” surface was found to be in a satisfactory agreement with theoretical predictions. The measured effective thermal resistance is measured to be 0.12 , 0.16 cm 2 ·K/W. This resistance was compared to the measured resistance of commercially available thermal grease. Based on this comparison, we conclude that, although the thermal resistance of CNTs might not be as low as it might be desirable, there exists a definite incentive for using VCNTA of the type in question for IC cooling. © 2006 American Institute of Physics . f DOI: 10.1063/1.2337254 g I. INTRODUCTION Carbon nanotubes s CNTs d , since their discovery in 1991, 1 have attracted significant interest of a number of in- vestigators. CNTs possess unique structure, as well as ex- traordinary mechanical, electrical, and optical properties. 2–7 It has been shown that CNTs can be used as optoelectronic devices, 8–10 field effect transistors s FETs d , 11–13 and sensors. 14–17 It has been shown also that the thermal conduc- tivity of CNTs can be exceptionally high, even higher than that of the diamond. 18 Numerous studies, mostly theoretical, have been recently conducted to evaluate the thermal performance of CNTs and their applicability for heat removal in integrated circuit s IC d devices. Thermal conductivity of single wall carbon nano- tubes s SWCNTs d was investigated using various simulation techniques, such as molecular dynamics s MD d simulation, nonequilibrium simulation and theory of force field. 19–22 Al- though the obtained data are rather inconsistent and showed significant discrepancy, these data nonetheless confirmed that the expected level of CNT thermal conductivity could be quite high: 6000, 19 3750, 20 1600, 21 and 2980 W/m K, 22 i.e., much higher than that of the majority of the known materi- als. There exists, therefore, a significant interest in using CNTs as thermal interface materials s TIMs d for thermal man- agement of IC devices....
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