微电子封装中聚噻吩纳米纤维作为热界面材料的机热电特性研究

The number of transistors in a single microelectronic chip has been increasing exponentially, giving rise to a continuous increase of packaging density in microelectronic devices. Thermal management issues faced by scientists and engineers, which influence the performance, reliability and lifetime of devices, become increasingly severe. The key role of thermal interface materials (TIMs), which are utilized to fill in the air gap between the silicon die and heat sink in order to improve the heat removal efficiency from inside, becomes more pronounced in microelectronic packaging. Conventional TIMs are mainly bulk polymer-based composites filled with materials with high thermal conductivity. The rapid advance of material synthesis and fabrication technologies enables vertically aligned nanofiber arrays to be a new research focus in TIMs fields, such as carbon nanotube arrays and polymer nanofiber arrays. It is demonstrated in our previous work that, polythiophene nanofiber arrays are capable of being used as new TIMs due to their superior properties. In this proposal, we will investigate the mechanical, thermal and electrical properties of individual polythiophene nanofibers by experimental measurements and computer simulations. We aim at not only presenting systematic measurement results on various physical properties of polythiophene nanofibers, but also analyzing the underlying mechanisms associated with these properties for the optimal design of TIMs, and further exploring their applications in flexible electronics and thermoelectric energy conversion fields.

单个微电子芯片上晶体管数目呈指数级的增长，使得微电子器件的封装密度持续增大，科学家和工程师所面临的影响器件性能、可靠性和寿命的热管理问题日益严峻。热界面材料，用来填补芯片与热沉间的空气间隙，提高芯片内的热移除率，其在微电子封装中的关键作用愈发得以凸显。传统的热界面材料主要是在体态聚合物基体中添加高导热填料而形成的复合材料。材料合成和制备技术的快速发展，使得垂直取向纳米纤维阵列成为热界面材料领域新的研究热点，如碳纳米管阵列和聚合物纳米纤维阵列。我们前期的研究工作表明，聚噻吩纳米纤维阵列性能优异，可用作新型热界面材料。本项目将以单根聚噻吩纳米纤维为研究对象，采用实验测试和计算机模拟方法，研究其机械、热学和电学等物理性能，旨在不但给出聚噻吩纳米纤维各物理参数的系统性测试数据，而且研究分析影响其物理特性的潜在机制，用于热界面材料的优化设计，并进一步拓展其在柔性电子和热电能量转换领域的应用前景。

本研究主要采用分子动力学模拟方法，以及飞秒激光、拉曼光谱和原子力显微镜等实验技术技术，研究微纳机电器件封装中的界面设计和聚合物纳米纤维的机械和黏附等力学性能，取得了较大的进展和创新性成果。主要有以下几点：.1）对于变截面的界面，分子动力学模拟结果表明，过渡角越大越有利于界面处的热传导；对于单轴应力作用下的石墨烯，拉曼光谱测试结果表明，应变小于3.3%时，石墨烯的面内导热系数几乎不变；飞秒激光瞬态热反射测试结果表明，石墨烯的氢化会导致 Au/graphene/Au的界面热导减小约50%，通过分子动力学模拟进一步发现，电子在Au/graphene/Au的界面热导的贡献，高达53%。.2）采用拉伸分子动力学模拟方法，对聚噻吩与硅、碳化硅和金刚石间的黏附性能研究表明，范德华能和静电能均对黏附性能起着积极作用，而熵变的增加则会极大削弱材料间的黏附作用；静电能在聚噻吩和碳化硅之间的黏附作用中贡献最大，而范德华能则对聚噻吩和金刚石之间的粘附起主要作用；三者中，聚噻吩与碳化硅之间的界面黏附作用最强。.3）分子动力学模拟结果表明，室温下聚乙烯分子链的杨氏模量约为247 GPa，远超过宏观聚乙烯的杨氏模量；而且，随着温度的升高，聚乙烯分子链的断裂应力由约80 GPa下降至约30 GPa，其杨氏模量相应由420.6 GPa降至201.5 GPa；基于三点弯曲法，采用原子力显微镜对聚噻吩纳米纤维机械性能的系列测试结果表明，对于有效长度约为3.083 μm和直径约为90 nm的系列纳米纤维，所测的杨氏模量约为64.48 GPa，远超过其体态值。