Carbon nanotube array thermal interfaces
Carbon nanotubes (CNTs) possess extremely high thermal conductivity in the axial direction. To take advantage of this property, new methods are needed to functionalize nanotubes across length scales of practical engineering relevance. In this research, a tri-layer catalyst configuration has been developed for well anchored and vertically oriented multi-walled carbon nanotube arrays synthesized on various substrates by plasma enhanced chemical vapor deposition system. Dense (108 to 109 CNTs/mm2) and tall (10 to 100μm) CNT arrays have been created over areas of order 1 to 10 cm2. The resulting arrays have been characterized for tube type, uniformity, density, and alignment with electron microscopy. ^ A reference calorimeter testing rig in a high vacuum environment with infrared temperature measurement has been set up and calibrated in this work for thermal contact resistance characterization. Experimental measurements of contact conductance between varieties of surfaces, CNT arrays, and combinations with other thermal interface materials have been performed to assess and to optimize the efficacy of CNT array interfaces. The investigation has demonstrated that with CNT arrays, copper-silicon interface resistance can be reduced by nearly an order of magnitude. Further, two-sided CNT interfaces and CNT wax composites can produce very low interface resistances of 4 and below 3mm 2K/W respectively. ^ A nano-contact resistance model (NCR) has been developed in this work to explain and predict CNT interface resistance. The effects of phonon ballistic transport and CNT array properties, e.g. diameter, density and distribution, have been explicitly incorporated into conductance. The model reveals that: (1) phonon ballistic transport resistance dominates at the CNT array interface; (2) the overall performance of CNT interfaces is governed by the resistance at the CNT-Cu contacts; and (3) the conformability and volume ratio have very important effects on CNT interface conductance. ^
Timothy Fisher, Purdue University.
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