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

在诸如膝上型计算机、移动的电话和高功率氮化镓（GaN）器件之类的电子器件中，功率耗散的增加导致了对改进的冷却以及将器件温度保持在允许水平以下的需求。最近的冷却策略涉及使用金刚石衬底来冷却电子器件，这是由于金刚石在300 K下的超高热导率超过2000 W/mK。然而，金刚石和GaN电子元件之间的界面具有较差的界面结合和结构缺陷，这大大减少了穿过界面的热传递，加剧了热管理问题。本研究的目的是探讨电场在界面上的作用，以降低界面热阻，从而使整个电子器件-金刚石衬底界面的热传递大大增强。该项目将使研究生和本科生直接参与拟议的研究。高中和代表性不足的学生将通过夏令营项目和俄克拉荷马州的部落学院的外联活动被介绍给研究活动。众所周知，在极间纳米间隙处，瞬逝电场导致高于黑体极限的几个数量级的传热增强。基于声子极化激元（电场与光学声子的耦合）的连续波动耗散定理充分描述了这种传热增强。在约2至4埃的间隙处，类似于在界面缺陷处遇到的间隙，最近的工作证明（通过原子形式主义）电场也可以使声学声子传输，从而增强热传递。 该项目将结合原子绿色函数方法和经典及从头算分子动力学，探索这种库仑相互作用辅助的声学声子传输，以提高界面热导率。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，进一步探索在纳米至微米范围长度尺度上具有比金刚石更上级热导率的材料。具有上级导热性和改进界面导热性的材料将导致下一代高功率GaN器件具有更高的可靠性和性能。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.