介观材料力学.ppt

材料的介观力学性能评价及尺度效应,参考书目： L. B. Freund and S. Suresh, Thin Film Materials: Stress, Defect Formation,and Surface Evolution Cambridge University Press, Cambridge,2003 (2) W. D. Nix, Metall. Trans. A 20 (1989) 2217.,2,什么是介观？,3,材料介观力学性能评价的意义,微米尺寸材料的广泛应用,MEMS,集成电路 互连导线,4,块体材料强度随晶粒尺寸的变化,微米尺寸下材料安全选择与性能预测的需要,材料介观力学性能评价的意义,5,强度,材料力学性能指标,延性,韧性,承载能力,可发生变形的能力,抵抗断裂的能力,疲劳！,6,提纲,1. 金属薄膜的准静态力学性能,2. 金属薄膜的疲劳性能,3. 微小柱状单晶试样的力学性能,7,弹性模量：弹性变形的抗力,1. 宏观材料的力学性能评价,强 度：承载能力,塑 性：变形能力,韧 性：变形功 能量概念,硬 度：材料软硬程度,万能材料实验机,常用试样形貌,8,块材压入测试简介,1. 金属薄膜的静态力学性能纳米压入仪测量,布氏硬度压痕,布氏：稳定/压痕大,洛氏硬度压痕,洛氏：压痕小/不稳定,维氏：兼有布氏和洛氏的优点,9,1. 金属薄膜的静态力学性能纳米压入仪测量,10,1. 金属薄膜的静态力学性能纳米压入仪测量,11,不足：,基体影响,压头周围材料堆积或塌陷,尺寸效应问题,残余应力影响,1. 金属薄膜的静态力学性能纳米压入仪测量,12,1. 金属薄膜的静态力学性能悬臂梁法,属于薄膜弯曲实验方法,13,1. 金属薄膜的静态力学性能悬臂梁法,14,1. 金属薄膜的静态力学性能悬臂梁法,屈服应力-悬臂梁厚度关系曲线,15,1. 金属薄膜的静态力学性能 悬臂梁法,可能原因：,残余应力,基体影响,压头滑动,16,1. 金属薄膜的静态力学性能 微桥法,17,1. 金属薄膜的静态力学性能单轴拉伸,获得材料应力-应变最直接的方法,自由膜,微加工,柔性基板,粘揭,溶去中间介质层,溶去基板,边缘损伤、卷曲,装样困难,试样规整,制备复杂,简单易行,数据可靠,18,1. 金属薄膜的静态力学性能单轴拉伸,膜基系统拉伸曲线,柔性基板,19,1. 金属薄膜的静态力学性能单轴拉伸,20,1. 金属薄膜的静态力学性能单轴拉伸,t ：薄膜厚度 尺寸效应,柔性基板,21,Cu薄膜/聚酰亚胺 晶粒尺寸 vs 薄膜厚度,磁控溅射薄膜沉积设备,t = 60 nm,t = 340 nm,t = 700 nm,22,1. 金属薄膜的静态力学性能单轴拉伸,表面、界面处位错受约束,23,1. 金属薄膜的静态力学性能 延性,自由膜：一旦颈缩，快速断裂,硬基底附着膜：基底脆断,软基底附着膜：可使薄膜延性完全表现,延性评价方法 ？,24,1. 金属薄膜的静态力学性能微裂纹统计及实时电阻法,裂纹萌生临界应变：C,薄膜表面微裂纹百分数统计,实时电阻法测试,25,实时电阻法测定临界应变,不同薄膜厚度,临界应变-屈服强度关系,Cu薄膜延性尺寸效应,26,微裂纹统计法测定临界应变,应变,薄膜厚度,薄膜越薄，应变越大，贯穿型大裂纹越多,27,不同薄膜厚度,微裂纹统计法测定临界应变,两种方法结果对比,微裂纹测定与实时电阻测定结果相近,金属薄膜延性评价方法,28,Flexible substrate (Polymer),Rigid substrate (Silicon),Good understanding of the fatigue properties are very important !,2. 金属薄膜的疲劳性能附着膜,29,Polymer substrate (Stretchable),Tension-tension fatigue (Microforce tester),Key point: Subtracting or avoiding the influence of deformed substrate,3 % elastic deformation,P = 250 N + 1 mN,polyimide,2. 金属薄膜的疲劳性能柔性基板,30,Previous methods on fatigue lifetime (Nf) measurement,Shortcomings: complicated and structurally instable at definition point,Strain range change (Kraft et al. 2001),Extrusion density counting (Volkert et al. 2008),Nf,Load-controlled,Saturated,Ex-situ measurement,2. 金属薄膜的疲劳性能柔性基板,31,Suggestion of a much more simple method,Fatigue lifetime for microcrack nucleation (Verified by SEM),Relative change in ER,Cu,In-situ measurement,2. 金属薄膜的疲劳性能柔性基板,32,Thin Cu and Al films: Nf Curves,Following the well-known Coffin-Manson relationship,Al films (80nm-800nm),Cu films (100nm-3.75 m),2. 金属薄膜的疲劳性能柔性基板,33,Thin Cu films: thickness dependent Nf,The thinner is the film, the longer is the Nf,Fatigue lifetime,Yield strength & ductility,2. 金属薄膜的疲劳性能柔性基板,34,Comparing with others results,Shorter than others experimental results,Nano-thick Cu film,Micro-thick Cu films,2. 金属薄膜的疲劳性能柔性基板,35,In-situ testing in a SEM chamber,Thermal fatigue,Time variant resistance and T,Based on the resistance-temperature relationship, T () can be determined,Monig, et al., Rev. Sci. Ins. 75 (2004) 4997,Electrical open: Nf, = x T,Mismatch in TEC,2. 金属薄膜的疲劳性能刚性基板,36,2. 金属导线的力学性能评价试样制备,微米级线宽,37,“工”字型试样,2. 金属导线的力学性能评价试样形貌,38,Previous work on the Thermal fatigue of Cu thin films,Nf vs T and ,Damage morphology,Park et al., Thin Solid Films 504 (2006) 321,Volkert et al., Thin Solid Films 515 (2007) 3253,300 nm-thick Cu 1.5 m GS,200 nm-thick Cu 0.5 m GS,In all the previous reports, the Cu films have a thickness 200 nm and an average grain size 500 nm, within this region dislocation is operative,So, how about the thermal fatigue of more thinner and more finer Cu films ?,2. 金属薄膜的疲劳性能刚性基板,39,Thickness: about 60 nm Grain size: about 55 nm,Resistance and temperature Measurement,60 nm-ultrathin Cu films/lines ( 5,10,15 m wide),A single layer of grain along the thickness,j = 3.2 26.5 MA/cm2,2. 金属薄膜的疲劳性能刚性基板,40,Current density dependent T and Nf,j vs T,j vs Nf,T j Nf,Size effect: the wider is the line, the longer is Nf,2. 金属薄膜的疲劳性能刚性基板,41,Two-stage fatigue lifetime curves,Low cycle region ( j 10 MA/cm2),High cycle region ( j 10 MA/cm2),Thermally controlled damage,Mechanically controlled damage,2. 金属薄膜的疲劳性能刚性基板,42,Damage mechanism,Low cycle region: Burst to electrical open,High cycle region: Formation of damage bands,2. 金属薄膜的疲劳性能刚性基板,43,Damage bands in high cycle region,Grain extrusion,TEM image,Different from all the previous reports !,2. 金属薄膜的疲劳性能刚性基板,44,AFM analyses,Two dimension AFM image,Three dimension AFM image,2. 金属薄膜的疲劳性能刚性基板,45,Damage band forming mechanism,Compressive-compressive fatigue,TEM,2. 金属薄膜的疲劳性能刚性基板,46,微小试样的力学性能评价试样