(20a) Synthesis of Aligned Carbon Nanotubes on Double-Sided Metallic Substrate by Chemical Vapor Deposition

With the continually diminishing size of electronic devices, the heat generated by such devices can cause structural damage due to over-heating. It is highly desirable to design and fabricate thermal interface materials (TIMs) with exceptionally high thermal conductivity for transporting heat efficiently from electronic components to a heat sink.

In this study, the use of aligned CNTs as TIM was further explored in order to take advantage of the exceptional thermal conductivity of CNTs. Instead of growing the CNTs on silicon, they were grown on a metal surface by water vapor-assisted chemical vapor deposition (CVD). The proposed multilayer composite structure, with two films of aligned CNTs, was grown on the opposite faces of a suspended substrate. Provided that the substrate is sufficiently thin and highly conductive, this double-sided design for a TIM device has the distinct advantage that it can fit between the heat source and heat sink to minimize the resistance to heat flow due to the presence of an air gap. Aligned CNT films with thicknesses ranging from 1 to >100 µm were obtained. By manipulating various operating factors, namely, the position of the substrate in the reactor, the amount of water vapor, the amount of catalyst, the reactor temperature, and the growth time, the morphology and thickness of these carbon nanotube films could be adjusted. This technique was used to fabricate a thermal interface material, made up of a thin copper foil covered with Cr-Au-MWCNT on both sides, which has a thermal resistance as low as 12 mm2 K/W.