高密度片外纳米孪晶铜连接在力-电-热耦合作用下的力学行为

项目名称： 高密度片外纳米孪晶铜连接在力-电-热耦合作用下的力学行为

项目编号： No.10802101

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 轻工业、手工业

项目作者： 刘立林

作者单位： 中山大学

项目金额： 22万元

中文摘要： 以厚金属薄膜作为LED芯片的自支撑衬底，要求强度高、韧性好、具有高的导热导电性，纳米孪晶Cu厚膜是理想选择之一。纳米孪晶Cu兼具高强度和高韧性，但是强度并非随着晶粒尺寸减小单调增大，而是存在一个软化点。为了研究纳米孪晶的强化机制，同时考虑与LED芯片工艺的兼容性，本项目采用脉冲喷镀的方法，分别以可溶性铜盐、银盐为主溶液，并配置了光亮剂HA和HB，电镀沉积了具有高密度纳米孪晶的Cu薄膜和Ag薄膜。透射电镜图像表明，Cu薄膜和Ag薄膜均由微/纳双尺度晶粒构成。实验表明，双尺度纳米孪晶结构提高了Cu薄膜的强度，但是对Ag薄膜的强度没有明显影响。在纳米孪晶Cu薄膜中，存在三种形变机制：(1)孪晶界迁移；(2)晶界位错分解；(3)孪晶晶内平行层错链。纳米孪晶Ag中存在一种独特的形变机制：Σ112}非共格孪晶界分解，纯刃位错在无外应力作用下进行集体滑移，产生9R结构，此形变过程不产生应变。Cu和Ag的层错能差别较大，这种零应变形变机制是否可以解释纳米孪晶Cu的软化点，以及其与层错能、晶界结构、晶粒尺寸等的关系有待深入研究。

中文关键词： 纳米孪晶;非共格孪晶晶界;位错;9R晶体结构;零应变形变

英文摘要： Cu films with high density nanotwins are an excellent choice for GaN-based light emitting diode chips as self-support substrates,due to their high strength, high ductility,excellent thermal conductivity and electric conductivity. However, the strength of nanotwinned Cu films does not increase monotonically with the decrease of grain sizes. There exists a strength-softening regime. In order to investigate the deformation mechanisms of nanotwins and also considering the compatibility with LED fabrication process, we employ pulse-electro-deposition method to fabricate Cu films and Ag films with high density nanotwins. Transmission electron microscope images show that the electro-deposited Cu films and Ag films both are composed of micro-grain/nano-twin hierarchy structures. Experimental results indicate that although the strength of nanotwinned Cu films is increased greatly, the strength of nanotwinned Ag films does present obvious enhancement. In the Cu films with nanotwins, three deformation mechanisms are observed:(1)coherent twin boundary migration;(2)twin dislocation's dissociation; (3)nucleation of a series of stacking faults parallel with the coherent twin boundary. Surprisingly, a new deformation mechanism is observed in Ag films with nanotwins, that is, Σ112}incoherent twin boundaries will dissociate into one pure edge shockley partial dislocation and two mixed-type shockley partial dislocations. Under zero applied stress or small applied stress, the pure edge partial dislocations will glide on the {111} planes collectively, while those mixed-type dislocations will remain near the original incoherent twin boundary. A 9R-type crystal structure thus are generated and there is no strain during the deformation process. The difference of stacking fault energy of Cu and Ag is great. The strength-softening regime in nanotwins may be related with the zero-strain deformation mechanism. The effects of stacking fault energy, grain boundary structure and grain size on the so-called zero-strain deformation need further investigation.

英文关键词： nanotwin;incoherent twin boundary; dislocation;9R crystal structure;zero-strain deformation