镓基液态金属热界面材料的制备与性能研究

Liquid metal gallium or its alloy working as a novel kind of thermal interface material (TIM) has many excellent advantages, such as non-toxic, environment friendly, low melting point, high thermal conductivity and so on. Especially, the theoretical thermal conductivity of liquid metal mixed with nano-particles owing higher thermal conductivities such as Ag, Au and Cu is as high as 60-80 W/(moK), which is one order higher in magnitude than that of traditional TIMs. It will play an important and critical role in heat transfer field, especially in thermal management of high-power electronics. However, the poor wettability of liquid metal with many substrate materials often brings serious technical problems such as overflowing easily, large contact thermal resistance, which significantly restrict the application and development of liquid metal working as TIMs in management fields. Here, in this subject we propose a micro-oxidation reaction method to prepare the gallium and its alloys based liquid metal TIMs with a controlled viscosity, which is expected to improve the wettability of liquid metal with any other materials fundamentally. The liquid metal TIMs will retain a semi-liquid state permanently and indefinitely under normal operating conditions and environment; We also make further investigation about the wettability and thermal properties of liquid metal TIMs by changing the experimental conditions, such as alloy components, oxidation temperature and time, stirring speed, content of gallium oxides and so on. Meanwhile, a scientific experimental platform is built for studying the relationship of heat load and temperature of chips or temperature difference between chip and heat transfer system so as to evaluate the heat transfer capability and stability of liquid metal TIMs. The experimental data and theoretical analysis reported in this subject will provide more valuable evidences for commercialization of liquid metal TIMs in future. The application of liquid metal TIMs will exploit a new way for heat transfer technology to cool military and civil electronics including high-performance computers, microelectronic equipments, and high-power optoelectronic in conjunction with a conventional fluid cooling system.

室温液态金属镓及其合金具有无毒环保，导热性好等优点，特别是加载高导热纳米颗粒后，其理论热导率远高于常规热界面材料1个量级，是一种十分理想的热界面材料。然而，液态金属与多种材料的润湿性较差，将其填充于界面后易存在溢出、接触热阻大等问题，严重束缚了其作为热界面材料的应用与发展。为此，本项目提出一种微氧化的方法，从根本上提高其润湿性；项目还将系统地研究影响液态金属热界面材料润湿性能、热物性能的各种因素及其作用机理，从而制备出综合性能优越的液态金属热界面材料；同时模拟芯片散热原理，从实验上考察加热功率与芯片温度以及与芯片和散热系统间温差的响应关系，以评估液态金属热界面材料的传热能力以及稳定性，为其实用化奠定坚实的理论基础与实验依据。本项目的实施将为我国高性能计算机、微电子产品以及光电器件等军民用产品散热技术的发展探索出一条新路，具有十分重要的基础科学价值和实际应用前景。

在该项目研究中，我们采用微氧化法成功制备出基于液态金属镓，镓铟二元合金以及镓铟锡三元合金的新型纯金属基热界面材料，并进一步研究了其润湿性，热物性以及传热能效。研究结果表明：微量Ga2O3的存在可有效提高液态金属对基底材料的润湿性能，是热界面材料的主要形成机制。通过大量实验发现，当氧化镓含量为1wt%时，粘附性完全满足热界面材料的需求，且仍能保持较高的导热率；研究上述三种液态金属基热界面材料的导热率，发现均大于市售性能最佳的导热硅脂（约7 W/mK），且其中GaIn10基热界面材料具有最高的导热率，约为19.2 W/mK；搭建一接触式传热测试平台，分别研究液态金属Ga及其二元、三元合金热界面材料的导热性能。对比市售导热硅脂，该新型镓基热界面材料，特别是其二元合金热界面材料，在大功率下工作时热源温度相对于导热硅脂下降约14 oC。当加热功率为100 W时，界面热阻只有4.3 Kmm2/W，显示出非常卓越的导热性能，即相对于导热硅脂而言，液态金属基热界面材料在大功率下表现出更大的优越性，尤其适合于大功率光电器件的散热。当对系统施加压力时，界面热阻随压力增加而降低，例如当压力为0.05MPa时，界面热阻只有2.2 Kmm2/W。介于液态金属基热界面材料的导电性，我们还研发了一种以室温液态金属流体作为导热填充材料、硅油为基体的新型复合导热硅脂。与液态金属基热界面材料不同的是，该材料中液态金属填料的体积分数为81.8时，复合硅脂的电阻率为1.07×107 Ω m，该材料的开发打破了液态金属基热界面材料在那些可能存在短路危险的电子器件散热领域的应用限制。该项目中的研究内容与实验结果为高性能室温液态金属基热界面材料的开发及未来产业化提供科学依据和指导性意见。相关研究结果已发表论文7篇，其中SCI收录5篇，授权发明专利2项。