From the heat of a phone in your hand to the noise of an overburdened computer fan, most people are familiar with the effects of heat generation in electronics. This heat generation limits the performance improvements that our society has become used to, and for that reason improved thermal management is critically important for many applications. Within thermal management, thermal interfaces are one of the most significant bottlenecks. A thermal interface is the boundary between two surfaces in contact with each other, such as with a silicon chip and a heat sink, and since surfaces are never completely flat, the contact between the surfaces is limited, which severely restricts the heat flow.
Thermal interface materials (TIMs) are materials placed between these surfaces, and conform and fill out the gaps, allowing heat to flow better. A good TIM should have high thermal conductivity, conform well to the surfaces, and not break during the device lifetime. Within my research, I have been focused on achieving TIMs with these properties, based on two different concepts: metal composites and carbon nanotubes (CNTs).
Metals have generally high thermal conductivity, and by melting them, such as we do with solders, they can conform to surfaces very well but have high stiffness which can cause reliability issues. Part of this thesis describes our development a composite material consisting of polymer fibers in a metal matrix, combining the mechanical properties of polymers with the thermal properties of metals.
The other route is to utilize vertically aligned CNTs to bridge the interface. Carbon nanotubes have both high thermal conductivity and flexibility to conform to surfaces. In principle, these should also be soft enough for good reliability, but this had never been experimentally tested, until now. Our studies show that reliable CNT array TIM are possible, but only under certain conditions.
Thermal management is not the only application for CNTs, and during my research, I found that my work could have applications within more areas. Within this thesis, I have also utilized CNTs as supercapacitor electrodes, developed a new fabrication method and studied what happens to CNT arrays when they get really hot. In total, this work represents an explanation of the possibilities of using both metal composites and carbon nanotubes for thermal interfaces, and beyond.