Enhancement of interfacial thermal transport through evanescent electric field mediated acoustic phonon transmission for efficient cooling of high power Gallium Nitride devices

笔记本电脑、手机和高功率氮化镓(GaN)设备等电子设备的功耗不断增加，导致需要改进冷却，并将设备温度保持在允许的水平以下。最近的一种冷却策略涉及使用金刚石衬底来冷却电子器件，由于金刚石在300K时的超高导热系数超过2000W/MK，然而，金刚石与GaN电子元件之间的界面既有较差的界面结合，又有结构缺陷，这大大降低了界面上的热传递，加剧了热管理问题。这项研究的目的是探索界面电场的作用，以降低界面热阻，从而大幅增强电子设备-金刚石衬底界面的热传递。该项目将直接吸引研究生和本科生参与拟议的研究。高中生和代表不足的学生将通过夏令营计划和俄克拉何马州部落大学的外联活动被介绍给研究活动。众所周知，在极性介质之间的纳米间隙处，短暂的电场会导致黑体极限以上的换热增加几个数量级。基于声子极化子(电场与光学声子的耦合)的连续介质涨落-耗散定理充分地描述了这种热传递的增强。在大约2到4埃的间隙处，类似于在界面缺陷上遇到的间隙，最近的一项工作(通过原子形式论)证明了电场也可以使声学声子传输，从而增强热传递。该项目将结合原子格林函数方法、经典分子动力学和从头算分子动力学，探索这种库仑相互作用辅助的声学声子传输，以增强界面热导。同时，该项目将通过基于三声子和四声子散射的第一原理方法和玻尔兹曼输运方程的精确解，进一步探索在纳米到微米范围内具有相对于钻石更好的导热性能的材料。具有优异导热系数和界面导热系数的材料将导致具有更高可靠性和性能的新一代大功率GaN器件。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Increasing power dissipation in electronic devices such as laptops, mobile phones and high-power Gallium Nitride (GaN) devices has led to the need for improved cooling, and to maintain device temperatures below permissible levels. A recent cooling strategy involves using a diamond substrate to cool electronic devices, due to the ultra-high thermal conductivity of diamond exceeding 2000 W/mK at 300 K. However, the interface between the diamond and the GaN electronic component has both poor interfacial bonding and structure-defects, which greatly diminish heat transfer across the interface, exacerbating the thermal management problem. The goal of this research is to explore the role of electric fields across the interface to reduce the interface thermal resistance and thus enable large enhancement of heat transfer across the electronic device-diamond substrate interface. The project will engage graduate and undergraduate students directly in the proposed research. High school and underrepresented students will be introduced to research activities through a summer-camp program and through outreach to tribal colleges in Oklahoma. It is well known that at nanometer gaps between polar dielectrics, evanescent electric fields lead to several orders of magnitude enhancement in heat transfer above the black body limit. Such enhancement in heat transfer is adequately described by continuum fluctuation-dissipation theorem, based on phonon polaritons (coupling of electric fields with optical phonons). At gaps of around 2 to 4 Angstroms, similar to those encountered across interfacial defects, a recent work demonstrated (through an atomistic formalism) that electric fields can also enable transmission of acoustic phonons, enhancing heat transfer. The project will explore such Coulomb interaction assisted acoustic phonon transmission, for enhancement of interfacial thermal conductance, using a combination of atomistic Green’s function method and classical and ab initio molecular dynamics. Simultaneously, the project will further explore materials with superior thermal conductivity relative to diamond, at nanometer to micron range length scales, through a first-principles approach based on three and four phonon scattering and an exact solution of the Boltzmann transport equation. Materials with superior thermal conductivity and improved interfacial thermal conductance will lead to next generation high power GaN devices with improved reliability and performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.