EFRI 2DARE: Thermal Transport in 2D Materials for Next Generation Nanoelectronics- From Fundamentals to Devices

计算机和其他当前基于硅技术的微电子设备包含在执行计算和其他任务时产生多余热量的中央处理单元。这种热能迁移到硅芯片表面，并通过风扇或其他方式（例如，流体冷却）消散。然而，当工程师们试图增加每个芯片的晶体管数量以获得更大的计算机功率时，硅技术达到了极限，需要一种具有不同硬件架构的不同基础材料。最近，已经开发出只有一个原子层厚的材料片，可以用作半导体（过渡金属二硫族化物），导体（石墨烯）或绝缘体（氮化硼）。任何电子设备的主要元件。晶体管已经通过堆叠这些不同的原子层而被开发出来。然而，在如此小的规模下，这种器件的功率密度和过热趋势急剧增加。因此，在更好地理解这种尺度的传热物理和解决散热问题之前，这些材料的实际设备是不可能的。本提案旨在全面研究半导体、导体和绝缘体的原子层堆叠的热输运动力学，代表未来的纳米电子器件。这个多学科团队由来自三所不同大学的一名机械工程师、一名电气工程师、一名化学家和两名物理学家组成。每所大学都有专门的项目，让本科生和少数族裔学生参与研究。研究人员将让博士生、本科生和少数民族学生以及高中生参与这项结合实验和理论的研究，旨在通过全面了解未来二维设备中热传输的主要贡献和局限性，从而造福社会。本提案的主要目标是为社区提供对二维非均质材料中通过各种结和界面的耗散和散热动力学所设定的限制的更深入的理解。该团队旨在通过材料合成和器件级实验、原子级表征、热输运和声子光谱、理论建模和计算研究的紧密结合，建立多尺度热输运研究。转换合成/制造方法，如化学气相沉积和原子层沉积，将用于生产异质结构的兴趣作为任何电子设备的基本组件。合成结构的面内和面外导热系数将使用定制设计的电测温平台进行测量。利用外差瞬态光栅技术测量了热传导率的长度尺度依赖关系和载热声子的平均自由程分布。将进行原位扫描热显微镜表征，以研究所选半导体2D材料在高功率操作条件下在其接触金属电极处的自加热。原子分辨率扫描透射电子显微镜将用于表征二维材料界面和表面。表征结果将指导分子动力学模拟，以预测界面和晶界的原子结构，并量化小尺度结构变化对材料热输运性质的影响。热输运，包括声子MFPs的全谱，将使用声子玻尔兹曼输运方程计算，包括声子本征散射和界面散射。声子MFP分布的模拟结果和玻尔兹曼输运计算将以瞬态光栅测量和器件级数据为基准，建立二维非均质材料的热耗散预测模型。提出的研究具有变革潜力，在许多研究领域具有高度相关性。从热管理的角度来看，这项工作的更广泛影响将是为未来电子/光电子设计新型2D非均质材料。

Computers and other current microelectronic devices based on silicon technology contain central processing units that produce excess heat while performing calculations and other tasks. This thermal energy migrates to the surface of the silicon chip and is dissipated by fans or other means (e.g., fluid cooling). However, as engineers seek to increase the transistor count per chip for greater computer power, silicon technology reaches its limit, and a different base material with a different hardware architecture will be needed. Recently, sheets of material have been developed which are only one atomic layer thick and which may function as semiconductors (transition metal dichalcogenides), conductors (graphene), or insulators (boron nitride)?the main elements of any electronic device. Transistors have already been developed by stacking these different atomic layers. However, the power density and tendency for such devices to overheat increase dramatically at such a small scale. Therefore, no practical devices from these materials will be possible until the physics of heat transfer at this scale is better understood and the heat dissipation problem is solved. This proposal seeks to comprehensively study the thermal transport dynamics of stacks of atomic layers of semiconductors, conductors, and insulators representative of future nano-electronic devices. The multidisciplinary team consists of a mechanical engineer, an electrical engineer, a chemist, and two physicists from three different universities. Each university has special programs for involving undergraduate and underrepresented minority students in research. The investigators will engage PhD students and undergraduate minority students as well as high school students in this combined experimental and theoretical study aimed at benefiting society through the development of a comprehensive picture of the dominant contributions and limitations of heat transport in future 2D devices.The primary goal of this proposal is to provide the community with a deeper understanding of the limits set by the kinetics of dissipation and heat removal through various junctions and interfaces in two-dimensional heterogeneous materials. The team aims to establish a multiscale thermal transport study through a closely coupled combination of material synthesis and device-level experiments, atomic-level characterization, thermal transport and phonon spectroscopy, theoretical modelling, and computational studies. Transformative synthesis/fabrication methods, such as chemical vapor deposition and atomic layer deposition, will be used to produce hetero-structures of interest as fundamental components of any electronic devices. The in-plane and out-of-plane thermal conductivity of the synthesized structures will be measured using a custom-designed electrical thermometry platform. The length scale dependence of thermal conductivity and the mean free path (MFP) distribution of heat-carrying phonons will also be measured by heterodyne transient grating technique. In-situ scanning thermal microscopy characterization will be performed to study self-heating of selected semiconducting 2D materials at their contact metal electrodes under high-power operational conditions. Atomic-resolution scanning transmission electron microscopy will be used to characterize 2D material interfaces and surfaces. Characterization results will guide molecular dynamics simulations to predict the atomic structures of interfaces and grain boundaries and to quantify the effects of small-scale structural variations on thermal transport properties of the materials. Thermal transport, including the full spectrum of phonon MFPs, will be calculated using the phonon Boltzmann transport equations including intrinsic phonon scattering as well as scattering at interfaces. The simulation results and Boltzmann transport calculations of phonon MFP distributions will be benchmarked against the transient grating measurements and device level data to develop a predictive model for thermal dissipation in 2D heterogeneous materials. The proposed research has a transformative potential and is of high relevance across many research fields. The broader impacts of this work will be significant in enabling the design of new classes of 2D heterogeneous materials for future electronics/optoelectronics from a thermal management perspective.