超短脉冲激光微纳尺度连接技术及其冶金结合机理研究

Materials joining at microscale and nanoscale (microjoining and nanojoining) is one of the essential fabrication steps in determining the properties of micro/nano components and their systems. The present micro/nano joining techniques, particularly nanojoining technologies such as electron beam joining, resistance heating joining, soldering/brazing, show various limitations. However, ultrashort pulse laser, including picosecond and femtosecond laser, possesses prominent features derived from its interaction with materials, such as non-linear energy absorption, ultra-low thermal effects, microscaled spots, multi-material adaptability. Based on above reasons, a study on the technology and interfacial bonding mechanism of ultrashort pulse laser joining at microscale and nanoscale is proposed. By the combining use of morphology observation, microscopic analysis, pump-probe ultrafast imaging technique, molecular dynamic simulation and numerical calculation, the law of ultrafast melting and ultrafast solidification of materials at nanoscale, microsacle and macroscale under the influence of ultrashort pulse laser will be investigated, and also the metallurgical behavior and nonequilibrium solidification microstructure characteristics of materials especially the dissimilar materials will be expounded. Microjoining and nanojoining of materials will be performed by the use of picosecond and femtosecond laser as heat source, and the effects of technological factors such as pulse energy, joining speed and base material properties, on the formation, microstructures, interface microstructure and performance of the joints will be studied, accompanied with the acquiring of optimal technologies. Further, technology design principle for high quality joints and metallurgical bonding mechanism will be proposed. And then, the newly developed ultrashort pulse laser joining technique at microscale and nanoscale will be further applied to typical nano-component fabrication and microsystem packaging, where the microjoining and nanojoining with high precision, slight thermal damage and high joint properties will be hopefully achieved. Through the project implement, the technique improvement in the fabrication of micro/nano components and the packaging of microsystem will be realized.

材料微纳尺度连接是决定微纳器件及其系统性能的关键环节之一。鉴于目前微纳连接特别是纳连接技术如电子束焊、钎焊、电阻加热焊等的局限性，基于超短脉冲（皮秒和飞秒）激光与物质作用时具有能量非线性吸收、多材料适应、斑点小、极低热效应等显著特性，提出超短脉冲激光微纳米尺度连接研究项目。采用形貌观测、显微分析、泵浦-探测超快成像技术与分子动力学模拟、数值计算相结合，探明纳、微、宏尺度材料超短脉冲激光超快加热熔化与凝固过程的规律，及材料特别是异种材料之间的冶金行为和非平衡凝固组织特征。用超短脉冲激光作热源进行材料微纳尺度连接，研究脉冲能量、焊接速度、材料特性等因素对接头的成形、显微组织、界面结构及其性能的影响并优化，提出获得高性能接头的工艺设计原则和界面冶金结合机理；将该微纳尺度连接新技术用于典型纳元器件制备和微系统封装，实现高精度、低热损伤、高性能接头的微纳连接。促进微纳元器件制造及其系统封装技术水平。

本项目系统地研究了超快激光微纳尺度的材料连接技术及其冶金结合机理。1）揭示了超快激光与纳-微-宏尺度材料的作用机理及其对纳米连接的影响：（1）超快激光辐照下金属-介电界面处产生的等离子激元效应会影响能量在纳米结构中的输入，呈现空间限制性输入特征。（2）超快激光辐照下纳米结构中“热点”处强场会对近距离内材料产生力的作用，Ag纳米颗粒受到Ag纳米线周围间隔分布“热点”作用而被吸引至纳米线表面并规则排布。（3）结构中的强场促进材料吸收高能量，使金属材料软化并促使材料发生变形，接头部位金属材料的延展会弥补间隙进而形成互连结构；而在介电材料中能破坏其稳定的晶体结构并产生缺陷，金属原子在其表面获得改善的润湿特性，增强接头界面强度，从而有助于实现同质及异质纳米线结构的连接。2）揭示了超快激光纳米连接成形特点、结合机理，提出了控制措施并用于微纳器件制造：（1）利用偏振激光辐照纳米结构时能量在其中的可控输入，并辅以飞秒激光的极高脉冲能量，研究了不同金属-金属及金属-介电材料体系的激光快速低损伤连接过程，阐明了纳米材料间等离子激元互连机理。（2）在金属-金属材料体系中实现了Ag纳米颗粒与Ag纳米线之间的自组装互连，以及Ag纳米线交叉结构的低损伤互连及初始分离结构的原位间隙自填充互连。（3）在金属-介电材料体系中实现了热平衡条件下冶金不兼容的Ag与TiO2、Ag与SiC纳米线互连，以及跨尺度的TiO2/SiC纳米线与Au电极之间互连。（4）间隔分布的纳米颗粒-纳米线结构可获得在特定波段激励下颗粒处选择性近场增强效果；而互连的Ag分枝结构由于接头间隙的弥补减小了耦合能量损失，在纳米线末端获能得更高的光发射分辨率。（5）异质接头处连接层可优化电传导，通过构造不同的Ag与TiO2纳米线接头可获得对称与非对称的整流特性，同时在TiO2纳米线-电极结构中得到可控的多级电阻记忆性能，且最大级数能达到8级；而在SiC纳米线-电极结构中可获得快速开关与状态短时维持特性。3）实现了飞秒激光对玻璃与玻璃、玻璃与硅的直接连接，获得了优化工艺，剪切强度最高分别达到40.4MPa、54.0MPa。本项目的成果丰富了纳米连接理论，为功能微纳器件的高性能制造提供了重要技术支撑。