Development and Characterization of Reliable Graphene-based Materials for Lightweight and Efficient Thermal Management in Electronics

Abstract: The semiconductor industry continuously aims to increase the transistor density in integrated circuits to improve performance of electronics. As performance and transistor density increases, so does the power density of integrated circuits. To help solve the future demand of thermal management in electronics it is necessary to work with new innovative materials, engineer advanced material structures and develop new cooling concepts. The carbon nanomaterial graphene has the right properties to be used for this purpose as it has an extremely high thermal conductivity and is very lightweight. One challenge with using graphene in thermal management solutions is to engineer macroscopic materials from the nanomaterial graphene without losing too much of the extraordinary properties that are exhibited on nanoscale. High-performance graphene-based thermal management products are already commercialized today. Products like thermal interface materials (TIMs) and heat spreaders are still novel, and some knowledge gaps exist. More understanding of these products regarding reliability, aging properties and how to optimize production processes can enable them on a broader market. Further, it is believed that graphene-based materials can replace more conventional metals in applications where they have not been used before. In this thesis, the thermal conductivity and heat dissipation capacity of a graphene-assembled film heat spreader has been shown to be improved by a newly developed annealing process. The effect of the annealing process was demonstrated in a thermal test rig where a high-power light emitting diode (LED) was used as a hot spot while the temperature was monitored with an infrared (IR) camera. Furthermore, a vertically aligned graphene-based TIM was tested with a new test method to gain a better understanding of the long-term reliability and aging properties. The TIM was subjected to thermal aging, thermal cycling and damp heat while regularly measuring the thermal resistance to see how the performance changes with time. Generally, it could be seen that the thermal resistance was stable, a result that paves way for this type of TIM to be used in applications with a need for high performance over a long time.     Additionally, a literature study on nano-enhanced wick structures was carried out to help determine the most promising nanomaterial-based wick to be used in a two-phase heat spreading device called vapor chamber. Lastly, prototypes of a novel graphene-enhanced vapor chamber were built with graphene assembled film as encapsulating material and they were characterized in a custom-made test rig. The lightweight prototype vapor chambers could outperform a conventional copper vapor chamber in terms of mass-based thermal resistance. However, leak tightness, working fluid and the wick structure were identified as three important future design improvements to further enhance performance and reliability.

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