Thermal Transport in Graphene Multilayers and Nanoribbons

As the electronic industry aggressively moves towards nanometer designs thermal issues are becoming increasingly important for the high-end electronic chips. One of the approaches to mitigate the self-heating problems is the high-heat-flux hot-spot removal via incorporation into the chip designs of materials with the high thermal conductivity. Graphene is found to be one of the best known heat conductors, thus it can be used in nanoelectronic and optoelectronic devices as a heat spreader component. Graphene, the latest isolated allotrope of carbon made of individual atomic sheets bound in two dimensions, shows many remarkable properties. A non-contact method of measuring G peak position of the Raman spectrum as a function of both the temperature of the graphene sample and the power of the heat source was used to measure the thermal conductivity of graphene. The samples in the experiment had approximately rectangle geometry and the assumption about the plane heat wave was used for the data extraction. In this dissertation research we propose to develop a model and numerical procedure for the (i) accurate modeling-based data extraction for the thermal conductivity measurements; and (ii) simulate heat propagation in semiconductor device structures with graphene layers incorporated as heat spreaders. To achieve the goals of this dissertation research we simulated the heat transport in graphene using the finite element method (FEM) with the help of COMSOL software package, which solves numerically the partial differential equations. The modeling based data extraction was necessary to determine thermal conductivity of the graphene flakes of arbitrary shape. It also substantially improved the accuracy of the measurements. The simulation of heat propagation in device structures with graphene heat spreaders allows one to assess the feasibility of the graphene high-heat-flux thermal management. We focused on understanding how thermal transport is influenced by a surface geometry of the sample and geometries of the heat sources. The simulation results showed that the size, shape and heat source geometry impact heat propagation in different ways and have to be included in the experimental data extraction. The simulation procedure provided a necessary input for next experiments on heat conduction in graphene structures e.g., graphene multi-layers and graphene-heat sink structures and other device-level thermal management applications. It was found that the incorporation of graphene or few-layer graphene (FLG) layers with proper heat sinks can substantially lower the temperature of the localized hot spots. The developed model and obtained results are important for the design of graphene heat spreaders and interconnects and lead to a new method of heat removal from nanoelectronic and 3-D chips