Finite element analysis of interface delamination and buckling in thin film systems by wedge indentation

A finite element method is used to study the interface delamination and buckling of thin film systems subject to microwedge indentation. In the formulation, the interface adjoining the thin film and substrate is assumed to be the only site where cracking may occur. Both the thin film and the substrate are taken to be ductile materials with finite deformation. A traction-separation law, with two major parameters: interface strength and interface energy, is introduced to simulate the adhesive and failure behaviors of the interface between the film and the substrate. The effects of the interface adhesive properties and the thickness of the thin film on the onset and growth of interface delamination and the film buckling are investigated.     

铁电薄膜与底电极之间界面的异质结效应

铁电薄膜与底电极之间由于高温扩散而形成了界面层，且观察到其对薄膜电性能的影响类似于硅衬底上铁电薄膜的异质结效应。基于能带理论的考虑，建立物理模型来解释其影响。该界面异质结模型不仅可以解释铁电薄膜的界面分层、电滞回线不对称等现象，而且还成功地解释了电滞回线中心在极化轴上的偏移和疲劳循环过程中的偏移增加，并探讨了这种偏移对铁电薄膜疲劳特性的影响。     

Disappearance of stress singularity at interface edge due to nanostructured thin film

The purpose of this study is to examine the stress distribution near the interface between a nanostructured thin film and a solid body. We focus on a nanostructured thin film that consists of Ta₂O₅ helical nanosprings fabricated on a Si substrate by dynamic oblique deposition. The mechanical properties of the thin film are obtained by vertical and lateral loading tests using a diamond tip built into an atomic force microscope. The apparent shear and Young’s moduli, G′ and E′, of the thin film are 2-3 orders of magnitude lower than those of a conventional solid Ta₂O₅ film. Moreover, the thin film shows strong anisotropy. A finite element analysis for two types of components with different interface edges between the thin film and an elastic solid body is conducted under uniform displacement. One has a free edge where the surface-interface angle is 90°-90°, and the other has a short interface crack. These analyses indicate the absence of not only stress singularity but also high stress concentration near the free edge and the interface crack tip. The characteristic stress distributions near the interface are due to the nanoscopically discrete structure of the thin film.     

Pre-cracking technique for fracture mechanics experiments along interface between thin film and substrate

Utilizing the difference in interface strength due to fabrication process, a technique for producing a sharp pre-crack between a thin film and a substrate is proposed. A cracked specimen for examining fracture toughness of interface between a sputtered copper (Cu) thin film and silicon (Si) is made by the method. A vacuum-evaporated Cu thin film, which has poor adhesion to Si, is inserted between the sputtered Cu thin film and the Si substrate as a release layer. The release layer debonds from the Si substrate at very low load, and the sharp pre-crack is successfully introduced along the interface. Using the pre-cracked specimen, the interface fracture toughness test is conducted and the critical J-integral, J_C, is evaluated as about 1 J/m² for the sputtered Cu/Si interface.     

On debonding of thin films

Debonding of a thin film from a large substrate is analyzed by an interface crack model. Based on a solution to interface cracks given by the author, energy release rate and stress intensity factors at the interface crack between the film and the substrate under general film edge loads are determined analytically. The solution is favorably compared with the result from the literature. Thermal stress intensities due to a uniform temperature change are also considered. The solution may be helpful for the analysis and testing of thin film debondings.     

Numerical simulation of laser-induced thin film delamination

Laser-induced thin film spallation has been developed to be one of the most powerful tools for quantitative measurement of thin film interfacial adhesion. High-energy laser pulse absorption generates stress pulse that can be used to delaminate a thin film-substrate interface. Interfacial strength is obtained from the measured surface motion of the thin film using elastic wave mechanics. Due to the short duration of the stress pulses, the dynamic interfacial debonding process usually happens within nanosecond duration, thus the interfacial strength measurement pertains to the intrinsic adhesion of the interface. In this paper, we performed detailed numerical simulations on various aspects of this experimental technique. Combining with experimental observations, the simulation results provide explanations of various phenomena and insights on the fundamental mechanisms of the laser-induced interface debonding process.     

Stability of thin solid films

A small amplitude perturbation analysis is used to determine the conditions under which a solid film several hundred ångströms thick on a substrate will rupture. If the perturbation grows with time the film is unstable and rupture may occur, whereas if the perturbation decays the film is stable. Film rupture is caused essentially by diffusion of atoms along the free interface of the film which can, under certain conditions, amplify a perturbation applied to the film-gas interface. This surface diffusion is generated by a gradient of the chemical potential along the free interface. The chemical potential is affected by the curvature of the interface, by the pre-existing internal stresses normally found in thin films (they generate a strain energy term in the chemical potential) and by interaction forces between the atoms at the gas-solid interface with those of the film and substrate. The thin film is assumed to behave like an elastic body. The difference in the forces which act on a volume element in a film thinner than the range of interaction forces between the atoms of the film and substrate and the forces in a bulk solid is accounted for by introducing a body force into the equations of displacement of an elastic solid. Because of the difficulties in writing boundary conditions at the film-substrate interface, two limiting situations are considered: (1) a thin film on a rigid substrate and (2) a thin free film. A critical internal stress necessary for rupture is identified. The time of rupture is estimated from the inverse of the maximum growth coefficient of the perturbation. The dominant wavelength corresponding to the maximum growth coefficient gives an idea as to the size of the islands formed through rupture.     

Numerical simulations of conduction and low-frequency noise in polysilicon thin film transistors

Numerical simulations of static conduction and low-frequency noise are carried out in N-channel polysilicon thin film transistors. The Meyer-Neldel effect associated with the drain current is related to trapping/detrapping processes of carriers from dangling bonds located at the interface. Low-frequency noise is simulated by generation-recombination processes. The sources responsible of noise in the thin film transistors are mainly located close to the interface. The microscopic parameter deduced from numerical simulation is lower than the macroscopic one deduced from noise measurements. The ratio of these two parameters is considered as a factor of merit to qualify thin film transistor technology.     

用于Si基片上外延BST薄膜的缓冲层的研究进展

由于界面之间的扩散,很难取得在Si基片上BST薄膜的外延.在这种异质结之间,稳定的缓冲层起着良好的阻挡作用以及结构上的延伸功能.综述了用于外延BST薄膜的缓冲层材料的意义和要求,及国内外通过缓冲层来控制界面以及薄膜的外延取向而获得高质量薄膜的最新研究动态,展望了今后用于外延BST薄膜的缓冲层材料发展的趋势.     

蒸发薄液膜非等温界面处电场强化传热的数值分析

电场能够强化微通道中延展弯月面处蒸发薄液膜区域非等温界面处的换热。分析在扩展的拉普拉斯方程及Wayner界面传质方程的蒸发毛细弯月面薄液膜区热质传输模型的基础上,加入电场力后电场强化蒸发薄液膜的换热效果。运用数值方法,讨论电场力对薄液膜固有弯月面处的曲率、蒸发质量流量、液相压力梯度、热流密度和传热系数的影响。数值计算结果表明,电场的存在可以显著提高微通道中薄液膜区域的换热系数,进而提高换热效率。     

Monte Carlo simulation of nucleation and growth of thin films

We study thin film growth using a lattice-gas, solid-on-solid model employing the Monte Carlo technique. The model is applied to chemical vapour deposition (CVD) by including the rate of arrival of the precursor molecules and their dissociation. We include several types of migration energies including the edge migration energy which allows the diffusive movement of the monomer along the interface of the growing film, as well as a migration energy which allows for motion transverse to the interface. Several well-known features of thin film growth are mimicked by this model, including some features of thin copper films growth by CVD. Other features reproduced are—compact clusters, fractal-like clusters, Frank-van der Merwe layer-by-layer growth and Volmer-Weber island growth. This method is applicable to film growth both by CVD and by physical vapour deposition (PVD).     

Magnesium metallic interlayer as an oxygen-diffusion-barrier between high-κ dielectric thin films and silicon substrate

The deposition of a thin magnesium metallic interlayer on an Si substrate prior to the deposition of an oxide thin film using rf-sputtering was investigated. The deposition of high-κ HfO₂ thin film was more particularly studied and it was demonstrated that the metallic interlayer acts as an oxygen barrier, preventing the formation of a low-κ layer at the high-κ/Si interface during the deposition. A post-deposition annealing treatment performed on the films induced the diffusion of the metal barrier into the HfO₂ film and allowed obtaining a sharp interface. However, the degree of diffusion depends not only on the interlayer thickness, but also on the thickness of the high-κ film. X-ray photoelectron spectroscopy was used to study the degree of oxidation of the Mg interlayer. High resolution transmission electron microscopy and energy filtered transmission electron microscopy were used to characterize the films and the diffusion of the Mg interlayer into the high-κ film after annealing. In this work we will stress on the engineering of the interface via the diffusion of the Mg interlayer during the growth process and on annealing.     

Plasma assisted and manipulated deposition of thin film electrodes for micro batteries

The properties of the thin film electrodes have been the main factors for the performances of lithium or lithium ion micro batteries, i.e. thin film batteries. In this paper, plasma assisted and manipulated techniques have been developed for the fabrication of polycrystalline thin film cathodes, and of amorphous/nano-crystalline thin film anodes. The thin film electrodes were deposited by magnetron sputtering under precisely controlled plasma conditions. The deposition apparatuses were designed to obtain the desired film properties by equipping a long anode-shield or an inductive coil. Polycrystalline LiMn₂O₄ thin film cathodes with a smooth surface were deposited, which greatly reduced the cathode/electrolyte interface resistances. Amorphous/nano-crystalline Sn thin film anodes were obtained free of plasma induced large grains, which enhanced the cycling stability. The results have demonstrated that by careful designs of deposition apparatus the plasma conditions can be precisely controlled and therefore the thin film electrodes of desired properties can be obtained.     

Hybrid spectral/finite element analysis of dynamic delamination of patterned thin films

A combined spectral and finite element analysis is performed to investigate the dynamic edge delamination of patterned thin films from a substrate. The analysis is motivated by an emerging experimental technique in which high-amplitude laser-induced stress waves initiate progressive interfacial debonding of thin film interfaces. The numerical method relies on the spectral representation of the elastodynamic solutions for the substrate and the finite element model for the thin film. A cohesive model is introduced along the interface of the bimaterial system to capture the decohesion process. The important role of the film inertia on the crack extension and the appearance of the mixed-mode failure are demonstrated by observing the traction stress evolution at various points along the bond line. Parametric studies on the effect of film thickness, interface fracture toughness, loading pulse shape and amplitude on the debonding process are performed. A semi-analytical investigation on the inertial effect is carried out to predict the final crack length as a function of the film thickness and pulse amplitude.     

金刚石薄膜涂层硬质合金刀具的界面表征

采用SEM对金刚石薄膜涂层硬质合金刀具的金刚石薄膜表面、背面及金刚石薄膜剥落后的硬质合金刀片表面的典型形貌进行了观察,并采用TEM对金刚石薄膜／硬质合金刀片横截面的微观组织进行了研究,还采用FT—Raman光谱法对金刚石薄膜表面及金刚石薄膜剥落后的硬质合金刀片表面的微观结构进行了表征．结果表明：经适当的化学侵蚀脱钻和等离子体刻蚀脱碳预处理后,金刚石薄膜涂层硬质合金刀具的界面通常存在薄的（数十nm）石墨碳层;局部区域见到金刚石粒子直接生长在WC颗粒上,金刚石膜／基横截面的典型组织层次为：金刚石薄膜／薄的石墨碳层／细小的WC层／残留的脱碳层（η相＋W相）／原始的硬质合金基体．     

6H-SiC单晶表面ZnO薄膜的制备及其结构表征

利用脉冲激光淀积(PLD)技术在6H-SiC单晶衬底上制备了ZnO薄膜. 利用X射线衍射(XRD), 反射式高能电子衍射(RHEED)和同步辐射掠入射X射线衍射(SRGID)φ扫描等实验技术研究了ZnO薄膜的结构. 结果表明:在单晶6H-SiC衬底上制备的ZnO薄膜已经达到单晶水平, 不同入射角的SRGID结果, 显示了ZnO薄膜内部不同深度处a方向的晶格弛豫是不一致的, 从接近衬底界面处到薄膜的中间部分再到薄膜的表面处, a方向的晶格常数分别为0.3264、0.3272和0.3223nm. 通过计算得到ZnO薄膜的泊松比为0.504, ZnO薄膜与单晶6H-SiC衬底在平行于衬底表面a轴方向的实际晶格失配度为5.84%.     

A laboratory technique for the evaluation of electrochemical transparent conductive oxide delamination from glass substrates

A rapid laboratory technique has been developed to evaluate the susceptibility of the transparent conductive oxide (TCO) layer to delaminate from its glass substrate in a thin film PV module. The test sample is stressed through the use of heat, humidity, and a DC bias to drive sodium ions to the TCO-glass interface. Delamination reactions occur at the interface causing the TCO to lose adhesion. The technique takes less than 15 min to complete and is useful in predicting the propensity of a thin film module to fail via electrochemical delamination of the TCO. Potential mechanisms for the adhesion failure are discussed.     

TiO2薄膜与玻璃基板横断截面的TEM及TEM—EDX分析

对玻璃基板上ＴｉＯ２薄膜与基板横断截面进行了ＴＥＭ形貌及ＴＥＭ－ＥＤＸ成分分析．结果表明,薄膜与基板结合致密,Ｎａ＋从基板向ＴｉＯ２薄膜的扩散为负扩散     

Interface Engineering of Inorganic Thin‐Film Solar Cells – Materials‐Science Challenges for Advanced Physical Concepts

The challenges and research needs for the interface engineering of thin‐film solar cells using inorganic‐compound semiconductors are discussed from a materials‐science point of view. It is, in principle, easily possible to define optimized device structures from physical considerations. However, to realize these structures, many materials' limitations must be overcome by complex processing strategies. In this paper, interface properties and growth morphology are discussed using CdTe solar cells as an example. The need for a better fundamental understanding of cause–effect relationships for improving thin‐film solar cells is emphasized.