The thermal effect of hexagonal boron nitride supports in graphene devices




Choi, David Seiji Kar Liang

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fundamental understanding of thermal dissipation and energy transport is necessary for designing robust electronic systems and energy conversion devices. In many of these systems, minimizing the operating temperature of the working components is required for increasing the performance, lifetime, efficiency, and reliability of the device. For example, hot spots in transistors caused by the conversion of electronic energy to thermal energy has become a bottleneck in the continued scaling of microelectronics. As the demand for compact, highly conformable and mobile electronics continues to push the limit of miniaturization, these phenomena increasingly occur at the nanoscale. At these length scales, the governing physical principles differ from classical laws based on continuum mechanics and instead require a quantum mechanical treatment. The thermal transport properties of traditional three-dimensional (3D) heat conducting materials such as the metal interconnects in nanoelectronic devices tend to degrade as the critical dimension is reduced. In contrast, the thermal properties of a new class of van der Waals-based two-dimensional (2D) materials can show different size confinement effects that can potentially be utilized for thermal management. First realized by the isolation of graphene, these materials have become attractive candidates for future-generation electronic and thermal components. Due to their atomic thinness, the properties of 2-D materials are highly sensitive to their operating environment. The studies in this dissertation therefore aim to answer critical questions surrounding the practical applicability of graphene and its dielectric isomorph hexagonal boron nitride as thermal materials in real devices. Specifically, the fundamental heat dissipation pathways of joule-heated graphene channels are inspected within the framework of silicon-based electronics as well as next-generation flexible electronic architectures. The study reveals that lateral heat spreading is essential to mitigating hot-spot formation. As a result, the inclusion of h-BN as a thermal interface material between the active graphene layer and the underlying support facilitates significant reductions in device operating temperatures due to enhanced lateral heat spreading. More than a passive thermal layer, an h-BN support increases the intrinsic thermal conductivity of graphene relative to other support materials based on an additional study in this work. An analytical solution of the phonon Boltzmann transport equation is derived to explain the observed phenomenon.


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