Thickness dependent mechanical behavior of submicron aluminum films

Mechanical behavior of thin metallic films has been investigated on aluminum films deposited on a flexible polyimide substrate. Aluminum thin films exhibit a higher tensile strength than bulk aluminum. As film thickness decreases from 480 to 60 nm tensile strength increases from 196 to 408 MPa. These mechanical behaviors are correlated with the microstructure and its evolution with the thickness of aluminum thin films. Films are consisted of fine columnar grains and average grain size increases monotonically with the film thickness. The volume fraction of (111)-textured grains increases and the dispersion of texture axis becomes narrow as the film thickens. The relative contributions of the film thickness, grain size, and texture to the strength of aluminum thin films are estimated using an empirical strengthening model. The result indicates that the high strength of aluminum thin films is due largely to their small grain size, followed by the strengthening due to the film thickness and texture.     

Flexible Inorganic Ferroelectric Thin Films for Nonvolatile Memory Devices

Next‐generation wearable electronics call for flexible nonvolatile devices for ubiquitous data storage. Thus far, only organic ferroelectric materials have shown intrinsic flexibility and processability on plastic substrates. Here, it is shown that by controlling the heating rate, ferroelectric hafnia films can be grown on plastic substrates. The resulting highly flexible capacitor with a film thickness of 30 nm yields a remnant polarization of 10 µC cm^?2. Bending tests show that the film ferroelectricity can be retained under a bending radius below 8 mm with up to 1000 bending cycles. The excellent flexibility is due to the extremely thin hafnia film thickness. Using the ferroelectric film as a gate insulator, a low voltage nonvolatile vertical organic transistor is demonstrated on a plastic substrate with an extrapolated date retention time of up to 10 years.     

Interfacial Strain‐Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin Films

To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub‐300‐nm EuBa₂Cu₃O_7?δ thin films deposited on SrTiO₃ substrates are studied by X‐ray diffraction and electrical transport measurements. The out‐of‐plane crystallographic mosaic tilt and the out‐of‐plane microstrain both increase with decreasing film thickness. The calculated density of c‐axis threading dislocations matches the extent of the observed low‐field enhancement in critical current density for fields applied parallel to c. The in‐plane mosaic twist and in‐plane microstrain are both around twice the magnitude of the out‐of‐plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in‐plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film‐substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties.     

Plastic deformation and interfacial sliding in Al and Cu thin film: Si substrate systems due to thermal cycling

As a result of the large difference in thermal expansion coefficients between metal and Si, high stresses can develop in thin metallic films attached to Si substrates in microelectronic devices during thermal excursions experienced in processing steps or during usage. These stresses may induce plastic deformation of the thin films accompanied by creep and interfacial sliding, and have a pronounced effect on the reliability of microelectronic devices and components. Even though various methods have been proposed to study thermal stress, methodologies for studying plastic deformation of thin films are not well established. Here, we report the results of a study of plastic deformation and interfacial sliding of thin Al and Cu films on Si substrates during thermal cycling. Cross-sectional profiles of pattern-grown Al and Cu films of nominally 250 nm thickness were measured before and after thermal cycling by employing an atomic force microscope. Through statistical analysis, the size changes of the thin films induced by thermal cycling were determined. Finite element (FE) analyses were conducted to compute the stress and strain states within the thin film and at the interface, and the results were utilized to interpret the atomic force microscopy (AFM) observations. Experiments revealed that, following thermal cycling, Al films expanded relative to the Si substrate, whereas Cu films shrank, resulting in an alteration of the film-footprint on the substrate in both cases. Based on the FE calculations, this was attributed to net inelastic deformation of the thin films via creep and yielding, with the deformation being accommodated at the interface by diffusion-controlled interfacial sliding.     

Stress development during evaporation of Cu and Ag on silicon

This work presents results of stress measurements during deposition of thin silver and copper films on 100 μm Si substrate. The stress in thin films has been determined by means of an optical system for the measurement of sample’s curvature. This system was applied in situ in a high vacuum deposition system. For Ag films the stress occurring during deposition goes from a low compressive value to tensile for thickness less than 30 nm and to compressive above this. For Cu films we observe tensile stress for thickness less 20 nm and above 50 nm. The same general trend of stress evolution with thickness is present in all cases at initial stage. There is the same growth mode for Cu and Ag because of the similar shapes of stress curves for thickness lower than 30 nm The behavior of stress evolution was explained by island nucleation and growth, island coalescence and continuous film growth. The difference in the stress evolution above 30 nm is caused by the fact that silver may be less sensitive than copper to adsorption of impurities. Adsorbed contamination inhibits compressive stress increase generated by grain boundary and defects remaining in the film.     

Substrate‐Dependent Spin–Orbit Coupling in Hybrid Perovskite Thin Films

Solution‐processing hybrid metal halide perovskites are promising materials for developing flexible thin‐film devices. This work reports the substrate effects on the spin–orbit coupling (SOC) in perovskite films through thermal expansion under thermal annealing. X‐ray diffraction (XRD) measurements show that using a flexible polyethylene naphthalate (PEN) substrate introduces a smaller mechanical strain in perovskite MAPbI_3?xCl_x films, as compared to conventional glass substrates. Interestingly, the linear/circular photoexcitation‐modulated photocurrent studies find that decreasing mechanical strain gives rise to a weaker orbit–orbit interaction toward decreasing the SOC in the MAPbI_3?xCl_x films prepared on flexible PEN substrates relative to rigid glass substrates. Simultaneously, decreasing the mechanical strain causes a reduction in the internal magnetic parameter inside the MAPbI_3?xCl_x films, providing further evidence to show that introducing mechanical strain can affect the SOC in hybrid perovskite films upon using flexible substrates toward developing flexible perovskite thin‐film devices. Furthermore, thermal admittance spectroscopy indicates that the trap states are increased in the perovskite films prepared on flexible PEN substrates as compared to glass substrates. Consequently, PEN and rigid glass substrates lead to shorter and longer photoluminescence lifetimes, respectively. Clearly, these findings provide an insightful understanding on substrate effects on optoelectronic properties in flexible perovskite thin‐film devices.     

金属薄膜附着性的改进

根据薄膜附着机理,综述了影响金属薄膜附着性的因素。通过引入中间过渡层,减少应力来提高薄膜与衬底之间的结合强度,改善金属薄膜的性能。适当的热处理不仅能消除内应力,增强界面反应,而且对薄膜的性能有一定的影响。     

An ac microcalorimeter for measuring specific heat of thin films

Microcalorimeter based on suspended SiO₂ membrane structures has been designed and fabricated. The geometry of suspension arms is optimized by ANSYS simulation to ensure that it provides maximum thermal isolation between the membrane structure and the supporting substrate. The microcalorimeter is intended to be a sample carrier onto which other thin films can be deposited for thermal property measurement. An ac modulation method has been used to measure the specific heat of aluminum thin film with thickness from 13.5 to 370 nm. The measurements demonstrated clearly the dependence of specific heat on thin film thickness.     

磁控溅射制备Zr膜的应力研究

为了研究磁控溅射方法制备的Zr膜的应力分布情况,采用探针轮廓仪测量镀膜前后基片在1维方向上的形变,根据镀膜前后基片曲率半径的变化和Stoney公式,用自编应力计算软件计算出薄膜的内应力。结果表明,Zr膜中主要存在的是压应力,且分布不均匀;工作气压对Zr膜内应力影响不大,但膜厚对Zr膜内应力影响较大,且随膜厚的增加,Zr膜中压应力减小。     

Residual stress in silicon nitride films

The mechanical stress caused by Si₃N₄ films on (111) oriented Si wafers was studied as a function of the Si₃N₄ film thickness, deposition rate, deposition temperature and film composition. The Si₃N₄ films were prepared by the reaction of gaseous SiH₄ and NH₃ in the temperature range 700–1000°C. The curvature of the Si substrates caused by the Si₃N₄. films is related to the film stress; the substrate curvature was measured by an optical interference technique. The measured Si₃N₄. film stress was found to be highly tensile with a magnitude of about 10¹⁰ dynes/cm². For the thickness range of 2000–5000Å, there was no change in the measured stress. The total film stress was observed to decrease for decreasing deposition rate and increasing deposition temperature. A large change in film stress was observed for films containing excess Si; the stress decreased with increasing Si content. Based on published values for the thermal expansion coefficients for Si and Si₃N₄, a published value for Young’s Modulus for Si₃N₄, and the measured total stress values, a consistent argument is developed in which the total stress consists of a compressive component due to thermal expansion coefficient mismatch and a larger tensile intrinsic stress component. Both the thermal and intrinsic stress components vary with film deposition temperature in directions which decrease the total room temperature stress for higher deposition temperatures.     

Effect of Ar ion irradiation on structural and optical properties of e-beam evaporated cadmium telluride thin films

CdTe thin films were prepared using e-beam evaporation technique. The prepared films were irradiated by Ar⁺ ions at different fluencies using multipurpose aluminum (Al) probe as in-situ. This could also be used in ion bombardment for cleaning the substrate prior to coating. The as grown and Ar⁺ ion irradiated films were confirmed to be of polycrystalline nature with X-ray technique. Ar⁺ ion irradiation enhances the growth of (1 1 1) oriented CdTe crystals and the Cd enrichment on the surface of CdTe thin films. Higher Ar⁺ ion flux helps to grow (2 2 0) oriented CdTe thin film. A considerable change in structural parameters like crystallite size, lattice parameter, internal strain, etc. could be observed as a result of high Ar⁺ ion flux. The applied in-plan stress in both as grown and irradiated film was identified to be of tensile nature. The applied stress was observed between 0.016 and 0.067 GPa for all Ar⁺ ion irradiated samples. As a result of the Ar⁺ ion irradiation, the in-plan stress varies between 1.38×10⁹ and 5.58×10⁹ dyn/cm². The observed bad gap was increased for higher Ar⁺ ion flux. It shows the effect of Ar⁺ ion irradiation on the modifications of optical properties. The observed results were encouraging on the use of simple multipurpose Al probe for Ar⁺ ion irradiation process as in-situ.     

Tensile properties of aluminum/alumina multi-layered thin films

Thin, free standing aluminum and alumina films were produced by physical vapor deposition and tensile properties were measured. Young’s modulus of the aluminum was microstructure insensitive, but the plastic behavior was very structure sensitive. The natural surface oxide of the aluminum had no apparent affect on the measured value ofYoung’s modulus. The alumina films showed true brittle behavior, but Young’s modulus was lower than bulk. Impurities residing at the grain boundaries were observed in the aluminum films using transverse Auger electron spectroscopy (AES). The films were well characterized using AES, transmission electron microscopy, Rutherford backscattering spectroscopy, and secondary electron microscopy. Well characterized, thin three-layered aluminum/alumina compositionally modulated films were produced by alternate depositions and tensile properties were measured. Young’s modulus was found to be less than a weighted thickness average of Young’s modulus of the individual constituents. Otherwise, the mechanical measurements yielded typical bulk behavior.     

The effect of thin film structure and properties on gold ball bonding

The gold ball bonding process is widely used for making interconnections between integrated circuit chips and package lead frames, yet the relationships between the wire/substrate materials properties and the bond formation processes are not yet well understood. While the creation of a metallurgical bond at the interface between the wire and substrate is required, the deformation of the wire and substrate also play an important role in bond formation. Bonding to thin film substrates is of particular interest, since thin films often exhibit mechanical behavior distinctly different from bulk materials. In the present study, a systematic investigation has been conducted to understand the effects of the structure and properties of aluminum thin films on the quality of gold ball bonds. A series of aluminum thin films was fabricated with systematic variations in hardness, roughness, thickness, and composition. Gold wires were ball bonded to these substrates, and the bondability and bond shear strengths were assessed. Metallographic sections of several of these specimens were made and examined in the scanning electron microscope. The results show that the film thickness has the most dominant effect on the bondability and bond strength; films that were 0.5 μm thick often exhibited low strength or poor bondability. Very hard films also gave poor results. Ultimately, these results can be used to predict the wire bond reliability expected from various types of thin film metallization.     

Substrate‐Dependent Molecular and Nanostructural Orientation of Nafion Thin Films

The effects of film thickness and substrate composition on the ionomer structure in porous electrodes are critical in understanding pathways toward developing higher performance electrochemical devices, including fuel cells and batteries. Insights are gained into the molecular and nanostructural orientation dependence for thin Nafion films (12–300 nm thick) on gold, platinum, and SiO₂ model substrates. Molecular orientation is determined from the birefringence measured using spectroscopic ellipsometry, while the nanostructural orientation of the ionic domains is measured using grazing‐incidence small‐angle X‐ray scattering. Density functional theory calculations for the molecular polarizability of the Nafion backbone and side chain show complimentary contributions to the measured birefringence values for the material. Nafion films prepared on SiO₂ substrates exhibit a nearly isotropic molecular and nanostructural orientation. Films on gold and platinum display parallel backbone orientations, relative to the substrate, with decreasing film thickness. However, a birefringence transition toward molecular isotropy is observed for 30 nm thick films on Au and Pt; while the ionic nanostructured domains continuously align parallel to the substrate. This apparent isotropic molecular orientation with increasing domain orientation highlights the difference between the backbone and side chain orientation, a key finding for elucidating transport in confined films at the interfaces.     

不锈钢表面溅射氮化铝陶瓷膜工艺参数的研究

工业生产中需要测量机械零件的润滑油膜厚度,利用超声波检测可实现无损检测的目的。利用氮化铝(AlN)陶瓷膜制成的压电换能器对超声波发射和接收。利用射频磁控溅射技术,在不锈钢表面沉积AlN薄膜。利用X线衍射仪(XRD)和原子力显微镜(AFM)等设备对AlN薄膜结构表征,并对结果进行了讨论。     

多层四面体非晶碳膜的热稳定性

为了获得具有一定厚度的四面体非晶碳薄膜,利用过滤阴极真空电弧(FCVA)沉积技术,通过交替改变衬底偏压的方法制备了多层四面体非晶碳(ta?鄄C)薄膜。多层膜由富sp2子膜层Ai与富sp3子膜层Bi交替组成(i=1,2,3),各子膜层厚度比dAi/dBi约为1.0,总的膜厚约为1 m。根据Stoney公式计算多层膜的各子膜层压应力呈交替起伏变化。多层四面体非晶碳膜在500 ℃以下的真空退火处理后,可见光Raman谱表明,多层膜的富sp3杂化结构基本保持不变,纳米压痕测量的薄膜硬度与杨氏模量略微增加,纳米划擦实验表明,多层膜具有优良的耐磨性与附着性。因此,多层ta?鄄C膜具有优良的力学性能和热稳定性,是一种优异的航空航天用光学元件的表面保护膜。     

Ferroelastic Strain Induced Antiferroelectric‐Ferroelectric Phase Transformation in Multilayer Thin Film Structures

Coupling effects among mechanical, electrical and magnetic parameters in thin film structures including ferroic thin films provide exciting opportunity for creating device functionalities. For thin films deposited on a substrate, their mechanical stress and microstructure are usually determined by the composition and processing of the films and the lattice and thermal mismatch with the substrate. Here it is found that the stress and structure of an antiferroelectric (Pb_0.97,La_0.02)(Zr_0.90,Sn_0.05,Ti_0.05)O₃ (PLZST) thin film are changed completely by a ferroelastic strain in a magnetic shape memory (MSM) alloy Ni‐Mn‐Ga (NMG) thin film on the top of the PLZST, despite the existence of the substrate constraint. The ferroelastic strain in the NMG film results in antiferroelectric (AFE) to ferroelectric (FE) phase transformation in the PLZST layer underneath. This finding indicates a different strategy to modulate the structure and function for multilayer thin films and to create unprecedented devices with ferroic thin films.     

Tensile Behaviors and Ratcheting Effects of Partially Sintered Chip-Attachment Films of a Nanoscale Silver Paste

The mechanical behaviors of partially sintered thick films of a nanoscale silver paste used for attaching semiconductor chips are studied. The films, about 150 μm thick, were made by repeatedly stencil-printing the paste on a ceramic substrate and sintering by a recommended heating profile suitable for device attachment. The partially sintered films were lifted off the substrate, and their tensile behaviors, i.e., stress–strain curves, were measured at temperatures between −60°C and 300°C using a dynamic mechanical analyzer (DMA). The elastic modulus and tensile strength of the sintered silver films decreased with increasing temperature. Ratcheting behaviors of the films under cyclic tension at 150°C were also tested by using the DMA by examining the effects of loading rate, mean stress, and stress amplitude. The ratcheting strain grew with increasing mean stress or stress amplitude and with decreasing loading rate.     

退火对用PLD法制备ZnO薄膜的发光影响

用脉冲激光沉积(PLD)方法在Si(111)和蓝宝石衬底上制备的氧化锌薄膜,在不同的退火温度和不同的退火氛围中进行了退火处理.退火温度及退火氛围对ZnO薄膜的结构和发光特性的影响用X射线衍射(XRD)谱和光致发光谱进行了表征.实验结果表明,随着退火温度的提高,ZnO薄膜的压应力减小,并向张应力转化.在不同的退火温度退火...     

Formation of Thick Porous Anodic Alumina Films and Nanowire Arrays on Silicon Wafers and Glass

A method for the fabrication of thick films of porous anodic alumina on rigid substrates is described. The anodic alumina film was generated by the anodization of an aluminum film evaporated on the substrate. The morphology of the barrier layer between the porous film and the substrate was different from that of anodic films grown on aluminum substrates. The removal of the barrier layer and the electrochemical growth of nanowires within the ordered pores were accomplished without the need to remove the anodic film from the substrate. We fabricated porous anodic alumina samples over large areas (up to 70 cm²), and deposited in them nanowire arrays of various materials. Long nanowires were obtained with lengths of at least 9 μm and aspect ratios as high as 300. Due to their mechanical robustness and the built‐in contact between the conducting substrate and the nanowires, the structures were useful for electrical transport measurements on the arrays. The method was also demonstrated on patterned and non‐planar substrates, further expanding the range of applications of these porous alumina and nanowire assemblies.