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Unformatted text preview: Proceedings of HT2005 2005 ASME Summer Heat Transfer Conference July 17-22, 2005, San Francisco, California, USA HT2005-72172 Thermal Transport in Nanotube Composites for Large-Area Macroelectronics Satish Kumar Department of Mechanical Engineering Purdue University 585 Purdue Mall W. Lafayette IN 47907 Mohammad A. Alam Department of Electrical and Computer Engineering Purdue University 465 Northwestern Avenue W. Lafayette IN 47907 Jayathi Y. Murthy Department of Mechanical Engineering Purdue University 585 Purdue Mall W. Lafayette IN 47907 ABSTRACT Thermal transport in a new class of nanocomposites composed of isotropic 2D ensembles of nanotubes or nanowires in a substrate is considered for use as the channel region of thin film transistors. The random ensemble is generated numerically and simulated using a finite volume scheme. The effective thermal conductivity of a nanotube network embedded in a thin substrate is computed. Percolating conduction in the composite is studied as a function of wire/tube densities and channel lengths. The conductance exponents are validated against available experimental data for long channels devices. The effect of tube-tube contact conductance, tube-substrate contact conductance and substrate-tube conductivity ratio is analyzed for various channel lengths. It is found that beyond a certain limiting value, contact parameters do not result in any significant change in the effective thermal conductivity of the composite. It is also observed that the effective thermal conductivity of the composite saturates beyond a limiting channel-length/tube length ratio for the range of contact parameters under consideration. INTRODUCTION In recent years, there has been growing interest in low-cost large-area manufacture of thin film transistors (TFTs) on flexible substrates for use in applications such as displays, e-paper, e-clothing, biological and chemical sensing, conformal radar, and others . TFTs based on amorphous silicon (a-Si) now dominate the market for large-area flat-panel displays [1-2]. When transistor performance is not critical, low-cost organic TFTs on flexible, lightweight, plastic substrates [3-7] are emerging as an alternative in many non- display applications. For high performance applications, however, the choices are limited: single crystal silicon or poly-silicon based TFTs [8,9] cannot be manufactured at low temperature (<200C) and are therefore not suitable for plastic substrates. As a result, researchers are exploring a new class of nano-composite TFTs based on bundles of silicon nanowires (Si-NWs) or carbon nanotubes (CNTs) [10-12]. Here, high- quality, nearly-crystalline NWs and CNTs are grown at high temperature on a temporary substrate, then released from the temporary substrate into a carrier fluid, and finally, the wire- saturated carrier fluid is spin-coated onto arbitrary (flexible) substrates at room temperature to form a thin film of randomly-oriented NWs or CNTs. Once the source/drain contacts are defined, this thin film of nearly crystalline...
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This note was uploaded on 12/29/2011 for the course ME 608 taught by Professor Na during the Fall '10 term at Purdue.
- Fall '10
- Heat Transfer