纳米沟槽表面黏着接触过程的分子动力学模拟研究

采用大规模分子动力学方法研究了刚性球型探头与具有不同纳米沟槽基体表面的黏着接触过程,探讨了表面沟槽结构对载荷-位移曲线、接触引力和拉离力以及材料转移的影响规律.研究结果表明:在相同的压入深度下,与原子级光滑表面的黏着接触过程相比,刚性探头与具有纳米沟槽结构基体表面的接触压力较小,接触加载过程中的引力作用范围较大,并伴随载荷的多次跳跃,且接触引力和拉离力均有减小;当沟槽深度相同时,随着沟槽宽度的增大,接触引力和拉离力逐渐减小,当沟槽宽度逐渐接近探头与光滑表面的接触直径时,接触引力和拉离力又逐渐增大,趋于接近探头与光滑表面的接触过程;当沟槽宽度相同时,随着沟槽深度的增大,接触引力相对减小,拉离力变化不大.     

Cu/Al引线键合界面金属间化合物生长过程的原位实验研究

铜引线键合由于在价格、电导率和热导率等方面的优势有望取代传统的金引线键合, 然而Cu/Al引线键合界面的金属间化合物(intermetallic compounds, IMC)的过量生长将增大接触电阻和降低键合强度, 从而影响器件的性能和可靠性. 针对以上问题, 本文基于原位高分辨透射电子显微镜技术, 研究了在50–220 ℃退火温度下, Cu/Al引线键合界面IMC的生长问题, 实时观测到了Cu/Al IMC的动态生长及结构演变过程. 实验结果表明, 退火前颗粒状的Cu/Al IMC 分布在键合界面, 主要成分为Cu₉Al₄, 少量成分为CuAl₂. 退火后Cu/Al IMC的成分是: 靠近Cu一端为Cu₉Al₄, 远离Cu的一端为CuAl₂. 同时基于原位观测Cu/Al IMC的动态生长过程, 计算得到了Cu/Al IMC 不同温度下的反应速率和激活能, 给出了基于原位实验结果的Cu/Al IMC的生长公式, 为优化Cu/Al引线键合工艺和提高Cu/Al引线键合的可靠性提供了指导.     

Interdiffusion of Al-Ni system enhanced by ultrasonic vibration at ambient temperature

At ambient temperature, Al–1%Si wire of 25 μm diameter was bonded successfully onto the Au/Ni/Cu pad by ultrasonic wedge bonding technology. Physical process of the bond formation and the interface joining essence were investigated. It is found that the wire was softened by ultrasonic vibration, at the same time, pressure was loaded on the wire and plastic flow was generated in the bonding wire, which promoted the diffusion for Ni into Al. Ultrasonic vibration enhanced the interdiffusion that resulted from the inner defects such as dislocations, vacancies, voids and so on, which ascribed to short circuit diffusion.     

Microstructural and mechanical analysis of Cu and Au interconnect on various bond pads

Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h.     

基于铅铟合金线的SFQ多芯片超导互连方法研究

用基于铅铟合金线的引线键合(WB)工艺对单磁通量子(SFQ)多芯片的超导互连方法进行了研究,将铅含量75％,铟含量25％的铅铟合金线制备成WB线材,用超声楔形焊工艺成功实现SFQ芯片I/O接口焊盘的超导互连.拉力测试表明室温下铅铟合金线键合强度与同线径金线相当,优于同线径铝线;用开尔文四端法测量了铅铟合金线互连的多级超...     

微米尺度结构最大抗扭强度的在线测试和研究

提出了一种新型的测试结构，对面积为微米量级下键合的最大抗扭强度进行了测试.实验设计一系列的单晶硅悬臂梁结构测试键合面积在微米量级时的最大剪切力，键合面为常用的矩形其边长从6μm到120μm，并根据实际移动距离计算得出的最大剪切力.并实验实际得出最大剪切扭矩和相应的键合面积的曲线，以及最大扭转剪切破坏应力与悬臂梁加载距离的关系，并针对60μm×60μm的矩形键合结构进行了加载和位移的重复性实验测量，两次测量结果符合较好.微电子机械系统(microelectromechanical system, MEMS)器件的设计人员可以根据结论曲线，针对所需的抗扭强度设计相应的键合面积，为MEMS器件工艺的在线定量测试与设计提供参考. 关键词： 阳极键合 硅深刻蚀 键合强度 最大抗扭强度     

Enhanced electron field emission characteristics of single-walled carbon nanotube films by ultrasonic bonding

A novel ultrasonic bonding process was used to fabricate the electron field emission cathode of single-walled nanotube film, which was deposited on an Al plate substrate by electrophoretic deposition. Electron field emission properties were improved remarkably after the cathode carbon nanotubes nanobonded with the Al substrate. Turn-on voltage showed a significant decrease and the emission current was much stabilized. This can be attributed to the reduction of the contact resistance in bonding area and easily moving electrons for field emission after ultrasonic bonding. In addition, the field emission performances of SWCNTs films formed at different bonding conditions were also studied. With a simple nano-bonding apparatus, this technique has low cost, and can be utilized for extensively roboticized fabrication of high performance field emission cathodes with short process time.     

Mechanical properties of hexagonal boron nitride synthesized from film of Cu/BN mixture by surface segregation

Hexagonal boron nitride (h-BN) has a low friction coefficient and weak surface attractive force similar to graphite. Furthermore, while graphite is conductive, BN is a good insulator. These properties make it suitable for application like lubricating coating or as an insulator/buffer layer in electronic devices. The synthesize of h-BN layer by surface segregation phenomena and mechanical properties of the h-BN surface segregated on Cu substrate have been investigated. During in situ annealing, the surface segregation of BN occurred on Cu/BN film deposited by deposition process with a rf magnetron co-sputtering system. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis showed that though the h-BN layer synthesized was not covered whole area of substrate but the h-BN layers partially covered substrate. And the concentration of oxygen on the surface after exposure in air is decreased with increase of BN concentration. The topography of atomic forces microscopy (AFM) showed that h-BN phases surface segregated are discontinuous droplet shape. The force curves of AFM and friction force of lateral force microscopy (LFM) showed that the h-BN droplet surface segregated have very weak attractive force and low friction coefficient equal to h-BN sintered plate.     

纳米接触过程中黏着规律的变化

本文应用大规模分子动力学方法, 模拟了两种具有不同粗糙形貌的、刚性球形探头与弹性平面基体之间的纳米尺度接触, 计算了探头与基体之间的拉离力和黏着功, 研究了接触过程中界面黏着力随载荷的变化规律, 分析了接触界面原子的法向应力分布. 研究发现, 原子级光滑接触的黏着力随着载荷的增大而线性增大, 而原子级粗糙接触的黏着力-载荷曲线分为以不同斜率增长的两个阶段. 相比于原子级光滑探头, 原子级粗糙探头与基体之间具有较小的拉离力和黏着功, 却在接触过程中形成了较大的黏着力. 因此, 拉离力和黏着功不能表征出纳米接触过程中原子吸引作用对界面法向力的贡献大小.     

表面黏附导致的接触行为转变

应用大规模分子动力学方法, 模拟了具有不同原子级粗糙形貌的两种刚性球形探头与弹性平面基体的黏附接触行为. 研究了载荷与真实接触面积、接触界面排斥力与真实接触面积, 以及黏附力与真实接触面积之间的关系. 分子模拟得到的载荷与真实接触面积的关系, 与连续力学接触理论预测很好地定性一致. 无论是原子级光滑探头还是粗糙探头, 黏附接触下的排斥力与真实接触面积的关系, 都与无黏附接触时的规律相一致, 即黏附力对接触行为的影响作用, 可以等效为附加在真实外载荷基础上的虚拟载荷, 将对黏附接触行为的分析转变为无黏附接触分析. 两种探头的黏附力随真实接触面积都呈幂函数形式的增长, 但是, 原子级光滑探头的幂指数大于1, 而原子级粗糙探头的幂指数小于1. 关键词： 接触行为 表面黏附 分子动力学模拟     

Cu互连应力迁移温度特性研究

提出了一种基于扩散-蠕变机制的空洞生长模型, 结合应力模拟计算和聚焦离子束分析技术研究了Cu互连应力诱生空洞失效现象, 探讨了应力诱生空洞的形成机制并分析了空洞生长速率与温度、应力梯度和扩散路径的关系. 研究结果表明, 在Cu M1互连顶端通孔拐角底部处应力和应力梯度达到极大值并观察到空洞出现. 应力梯度是决定空洞成核位置及空洞生长速率的关键因素. 应力迁移是空位在应力梯度作用下沿主导扩散路径进行的空位积聚与成核现象, 应力梯度的作用与扩散作用随温度变化方向相反, 并存在一个中值温度使得应力诱生空洞速率达到极大值. 关键词： Cu互连 应力迁移 应力诱生空洞 失效     

Molecular dynamic simulations of nanoindentation in aluminum thin film on silicon substrate

In the present work, the nanoindentation of aluminum thin film on silicon substrate is investigated by three-dimensional molecular dynamic (MD) simulation. The film/substrate system is modeled by taking Lennard-Jones (LJ) potential to describe the interaction at the film-substrate interface. Different loading rate from 50 to 250 m/s is carried out in the simulation. The results showed that the hardness of the film increased with the loading rate. In order to study the effect of substrate on the mechanical properties of thin film, nanoindentation process on monolithic Al material is also simulated. The simulation results revealed that indentation pile-up in the aluminum film is significantly enhanced by the substrate. The substrate also affects the loading force during the nanoindentation. At the beginning of the indentation, the loading force is not affected by the substrate. Then, it is getting smaller caused by the interface. As the film is penetrated, the loading force increased rapidly caused by the hard substrate. These results were coincident with the previous reported experiments.     

Underwater explosive compaction-sintering of tungsten–copper coating on a copper surface

This study investigated underwater explosive compaction-sintering for coating a high-density tungsten–copper composite on a copper surface. First, 50% W–50% Cu tungsten–copper composite powder was prepared by mechanical alloying. The composite powder was pre-compacted and sintered by hydrogen. Underwater explosive compaction was carried out. Finally, a high-density tungsten–copper coating was obtained by diffusion sintering of the specimen after explosive compaction. A simulation of the underwater explosive compaction process showed that the peak value of the pressure in the coating was between 3.0 and 4.8?GPa. The hardness values of the tungsten–copper layer and the copper substrate were in the range of 87–133 and 49?HV, respectively. The bonding strength between the coating and the substrate was approximately 100–105?MPa.     

粉末高速压制成形过程中的应力波分析

应用离散单元法,模拟了粉末高速压制成形过程中的压力传播过程.根据粉末高速压制成形的工艺特性,把一次压制过程分为弹性加载、塑性变形、弹性卸载三个阶段;基于离散单元法的基本理论,分别建立了三个阶段的控制方程;应用PFC2D软件对粉末高速压制过程模腔内部颗粒的运动状态进行了数值模拟,给出了压坯内部的压力分布,得出了实验中无法测量的压坯内部应力传播波形.数值模拟结果显示,压力作用曲线表现出明显的弛豫现象,形成了倾斜度不同的锯齿状加载波形和卸载波形,压坯底层的应力波与实验得到的应力波相符. 关键词： 高速压制成形 离散单元法 接触模型 应力波     

Effects of homogenous loading on silicon direct bonding

The effect of a homogenous loaded stress on the bonding quality of silicon wafer pairs was investigated by employing a Nano-Imprint System and a homogenous plane-stress applied over the entire surface area of pre-cleaned wafers. In addition, the effects of variations in the applied homogenous stress (1, 10, 100, 500 psi) on the interface energy of the bonded pairs were examined using a dynamic blade insertion (DBI) method. Infrared imaging was used to evaluate the quality of the bonded interface of each bonded pair immediately after the bonding process and after allowing the bonded pairs to rest at room temperature for 80 h after bonding. The results indicated that the homogenous loading with the Nano-Imprint System further improved the bonding condition of wafer pairs that had been pre-bonded using an anodic bonder. Furthermore, the bonded pairs exhibited almost identical interfacial energies of about 0.2 Jm⁻² when the homogenous stress was varied from 1 psi to 500 psi, which clearly indicates that the interfacial energy of bonded wafers is independent of the amount of stress applied by the homogenous loading process.     

Local probe of the interlayer coupling strength of few-layers SnSe by contact-resonance atomic force microscopy

The interlayer bonding in two-dimensional (2D) materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy (CR-AFM) in this study. Site-specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO₂/Si substrate comparatively. Based on the cantilever and contact mechanic models, the contact stiffness and vertical Young’s modulus are evaluated in comparison with SiO₂/Si as a reference material. The interlayer bonding of SnSe is further analyzed in combination with the semi-analytical model and density functional theory calculations. The direct characterization of interlayer interactions using this non-destructive methodology of CR-AFM would facilitate a better understanding of the physical and chemical properties of 2D layered materials, specifically for interlayer intercalation and vertical heterostructures.     

Contact electrification between polymers and steel

Electrification occurs when metals are put into contact with polymers, and the mechanism is still not fully understood. In this paper, experimental study of contact electrification between a metal and polymers was conducted. Effects of contact cycle, load, and nominal area on electrification were investigated. Results showed that electrification charge increased with real contact area. However, experimental results showed that charge density increased with nominal area and decreased with load. The key factor that determined the charge density was contact stress. Charge density decreased with contact stress linearly. A quantitative relationship between charge density and contact stress was proposed.     

Electrode metal penetration of amorphous indium gallium zinc oxide semiconductor thin film transistors

Penetration effects of various electrode materials, namely Al, Au, and Cu, on the physical and electrical characteristics of amorphous oxide semiconductor thin film transistors (TFTs) were investigated. Amorphous indium gallium zinc oxide (a-IGZO) TFTs were fabricated with conventional staggered bottom gate structures on a p-type Si substrate. X-ray photoemission spectroscopy (XPS) analysis under the electrode deposition area revealed variations in the oxygen bonding states and material compositions of the a-IGZO layer. Field-emission scanning electron microscopy (FE-SEM) with the line scan of energy dispersive spectroscopy (EDS) showed lateral penetration by the electrode metal. To compare the electrical characteristics of the tested TFTs, the initial current–voltage (I–V) transfer characteristics were examined. In addition, the tested TFTs fabricated using various electrode materials were tested under bias stress to verify the correlations between variations in TFT characteristics and both the metal work function and penetration-induced oxygen vacancies in the channel around the contact area.     

Modeling of the loading path dependent magnetomechanical behavior of Galfenol alloy

The magnetomechanical behavior of single-crystal Galfenol alloy was found to be strongly dependent on the loading paths. An energy-based anisotropic domain rotation model, assuming that the interaction between domains can be ignored and the probability of the magnetic moment pointing along a particular direction is related to the free energy along this direction, is used to simulate the magnetostriction versus magnetic field and stress curve and to track the magnetic domain motion trail. The main reason for loading path dependent effect is the rotation/flipping of the magnetic domains under different loading paths. The effect of loading and unloading paths on 90° magnetic domain motion was studied by choosing different loading and unloading state and paths. The results show that prior loading magnetic field can make the 90° magnetic domains flip to the directions of 45° domains because the magnetic field is the driving force to make the domains rotate, and the final loading state and the loading path both have great influence on the motion of 90° magnetic domains.     

Experimental analysis of interface contact behavior using a novel image processing method

The spatial and temporal evolution of real contact area of contact interface with loads is a challenge. It is generally believed that there is a positive linear correlation between real contact area and normal load. However, with the development of measuring instruments and methods, some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions, such as large-scale interface contact with small roughness surface,which is called the nonlinear phenomenon of real contact area. At present, there is no unified conclusion on the explanation of this phenomenon. We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism. An image processing method is proposed, which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon. The weighted superposition method is used to identify micro contact spots, to calculate the real contact area, and the color superimposed image is used to identify micro contact behaviors.Based on this method, the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed. Furthermore, the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally. It is found that the effects of fluid between contact interface, normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.