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.     

Formation process of the bonding joint in Ti/Al diffusion bonding

The process of the formation of Ti/Al diffusion bonding joints was studied by means of scanning electron microscopy (SEM), X-ray diffractometry (XRD) and shear strength measurement. Pure titanium and pure aluminum were used as bonding couples. The results show that the process of joint formation can be separated into four stages, and the product of the diffusion reaction is only TiAl₃ under a particular range of holding time. There is a delay time t_D before TiAl₃ is generated, which is mainly affected by temperature. The joint strength depends on the metallurgical combination percentage and the interface structure in the diffusion zone, and it can reach or even exceed the strength of pure aluminum after TiAl₃ forms a layer. The position where shear fracture occurs depends on interface structure in the diffusion zone.     

Growth mechanism of Si nodules on BPSG

Si nodules that appear in the metal electrodes of integrated circuits often reduce their reliability. The growth process of Si nodules generated on boro-phospho silicate glass (BPSG) in the Al-1 wt.% Si film electrode has been investigated. The Al-1 wt.% Si films sputter deposited on BPSG films were annealed at 723 K for 30 min according to the usual integrated circuit procedure. Scanning electron microscopy and atomic force microscopy observations revealed that the Si nodules seemed to precipitate along Al grain boundaries particularly on the BPSG film and their shape appeared pyramidal. To make clear the mechanism of the growth of the Si nodule on the BPSG film, the interface between the Si nodule and the BPSG film was investigated in detail by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. As the result, it was found that there existed an amorphous silicon oxide region in the central part of the interface under the Si nodule. The amorphous silicon oxide is considered to be formed by diffusion of oxygen from the BPSG film to the Si nodule during the annealing. The amorphous silicon oxide may act as an embryo for the formation of the Si nodule and the migration of Si atoms dissolved in Al towards the embryo seems to enhance the growth of the Si nodule.     

Microstructure Evolution of Zr50Cu18Ni17Al10Ti5 Bulk Metallic Glass during Cold-rolling

Zr50Cu18Ni17Al10Ti5 bulk metallic glass has been rolled at room temperature up to 95% in thickness reduction, and the dependence of microstructure on the strain was investigated. With increasing thickness reduction, the full width at half maximum (FWHM) and crystallization enthalpy decrease gradually till 80%, and then increase evidently at 95%. It is revealed that the reversible transition between the ordered and disordered atomic configurations was found in the metallic glass as the deformation proceeds, which is further verified by the high-resolution transmission electron microscopy images. The final microstructure in metallic glass during cold-rolling is the net result of two competing processes between shear-induced disordering and diffusion controlled reordering.     

Modelling behaviour of oxide film during vibration diffusion bonding of SiCp/A356 composite in air

Abstract

The vibration liquid phase diffusion bonding of SiC_p/A356 composite in air has been investigated. The surface of specimens to be bonded was treated with and without vibration under the bonding condition. It was found by atomic force microscopy analysis that some of the oxide film could be broken down when ridges on the surface of the matrix were ground down. Dissolution of the base metal by the filler metal occurred with removal of the oxide film during vibration liquid phase bonding, and SiC particles in the base metal entered the bond region. A removal process model for vibration bonding has been established with and without filler metal. Results show that shearing and impacting actions are the two main breaking mechanisms during vibration; the oxide film bulk is generally broken down by shear, and dissolution of the base metal by the filler metal promotes particle segregation from the matrix and their entry into the bond region.     

Direct diffusion bonding of Ti3SiC2 and Ti3AlC2

Two typical layered ternary compounds, Ti₃SiC₂ and Ti₃AlC₂, were joined directly by solid-state diffusion bonding method. By various bonding tests at 1100-1300 °C for 30-120 min under 10-30 MPa, and characterizing the microstructure and diffusion reactive phases of the joints by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD), the optimal condition for direct joining of Ti₃SiC₂ and Ti₃AlC₂ was obtained. Strong joints of Ti₃SiC₂/Ti₃AlC₂ can be achieved via diffusion bonding, which is attributed to remarkable interdiffusion of Si and Al at the joint interface. The shear strength of the Ti₃SiC₂/Ti₃AlC₂ joints was determined.     

Microstructure and properties of diffusion bonded Ti-6Al-4V parts using brazing-assisted hot isostatic pressing

Ti-6Al-4V couples have been diffusion bonded by hot isostatic pressing (HIPping) after vacuum brazing was used to seal the periphery of the bonding samples so that no encapsulation was required during HIPping. Analytical scanning electron microscopy was used to assess the microstructure of the HIPped interface and tensile and fatigue properties of bonded samples were compared with those of the bulk starting material. The tensile properties of the bonds were shown to be comparable with those of the bulk material, but the fatigue life was slightly downgraded. The fatigue fractures were initiated by inclusions on the bonding interface, caused by contamination before bonding, but the fatigue cracks did not propagate along the bonding interface indicating a strong bond. It is concluded that this technique of vacuum brazing plus HIPping could be used for encapsulation-free HIPping to produce complex-shaped components.     

Investigations of diffusion behaviour in Al-doped zinc oxide and zinc stannate coatings

Multi-layer dielectric/silver/dielectric coating systems have excellent proprieties as heat insulators and for solar energy reflection and electrical conductivity. The largest market is dominated by low-emissivity (low-E) coatings, which are applied to large area architectural glazing to reduce heat losses from buildings. They combine high visible transparency with high reflectance in the far-infrared region, where the thin (~ 10 nm) silver layer reflects long wavelength IR back into the building and the dielectric layers both protect the silver and act as anti reflectance layers.In this study, a range of dielectric coatings has been deposited onto soda-lime glass substrates by reactive sputtering from metallic targets. The magnetrons were driven in DC mode and also in mid-frequency pulsed DC and AC modes. Process variables investigated include operating pressure, oxygen flow rate and magnetron configuration. Selected coatings were annealed at 650 °C and analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM).The oxide samples were then over-coated with silver and annealed for a second time. These coatings were analysed by secondary ion mass spectroscopy (SIMS) to determine the diffusion rates of silver and sodium (from the substrate) through the oxide coatings.The results to date, presented here, show the diffusion of silver and sodium atoms through zinc oxide and zinc stannate thin films deposited under a vast range of conditions. Preliminary attempts have been made to estimate diffusion coefficients for these coating systems and to relate these values to processing conditions and the structural variations observed.     

Effects of surface roughness on the diffusion bonding of Al alloy 6061 in air

The effect of surface roughness on the properties of Al6061 joints fabricated by diffusion bonding in air at 450°C was studied. It was found that rougher surfaces yield superior ultimate tensile strength and linearized bonded ratio. Joints with ultimate tensile strength comparable to that of bulk metal were obtained for holding times of 75 min using rougher surfaces; however, the maximum linearized bonded ratio obtained was only about 75%. Incomplete bonding was attributed to air entrapment along the bond interface. This was due to good bonding occurring at the periphery of the bonded specimens during the early part of the bonding process.     

Microstructure and strength of diffusion-bonded joints of TiAl base alloy to steel

Diffusion bonding of TiAl-based alloy to steel was carried out at 850–1100 °C for 1–60 min under a pressure of 5–40 MPa in this paper. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. When products are diffusion-bonded, the optimum bond parameters are as follows: bonding temperature is 930–960 °C, bonding pressure is 20–25 MPa, bonding time is 5–6 min. The maximum tensile strength of the joint is 170–185 MPa. The reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA) and X-ray diffraction (XRD). Three kinds of reaction products were observed to have formed during the diffusion bonding of TiAl-based alloy to steel, namely Ti₃Al+FeAl+FeAl₂ intermetallic compounds formed close to the TiAl-based alloy. A decarbonised layer formed close to the steel and a face-centered cubic TiC formed in the middle. The interface structure of diffusion-bonded TiAl/steel joints is TiAl/Ti₃Al+FeAl+FeAl₂/TiC/decarbonised layer/steel, and this structure will not change with bond time once it forms. The formation of the intermetallic compounds results in the embrittlement of the joint and poor joint properties. The thickness of each reaction layer increases with bonding time according to a parabolic law. The activation energy Q and the growth velocity K₀ of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC in the diffusion-bonded joints of TiAl base alloy to steel are 203 kJ/mol and 6.07 mm²/s, respectively. Careful control of the growth of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC can influence the final joint strength.     

Growth of nano-needles of manganese(IV) oxide by atomic layer deposition

Needles of manganese (IV) oxide in the nanometer range have been synthesised using the atomic layer deposition technique. Traditionally the atomic layer deposition technique is used for the fabrication of thin films, however, we find that needles of beta-MnO2 are formed when manganese (IV) oxide is deposited as relatively thick (ca. 800 nm) thin films on substrates of alpha-Al2O3 [(001) and (012) oriented]. There is no formation of needles when the film is deposited on substrates such as Si(100) or soda lime glass. The film is formed using Mn(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione) and ozone as precursors. While thin films (ca. 100 nm) consist of epsilon'-MnO2, the same process applied to thicker films results in the formation of nano-needles of beta-MnO2. These needles of beta-MnO2 have dimensions ranging from approximately 1.5 microm at the base down to very sharp tips. The nano-needles and the bulk of the films have been analysed by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy.     

Diffusion Bonding of Ti-6Al-4V to QAl 10-3-1.5 with Ni/Cu Interlayers

Ti-6Al-4V and QAl 10-3-1.5 diffusion bonding has been carried out with Ni/Cu interlayers. The diffusion-bonded joints are evaluated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and microhardness test. Intermetallic compounds at the interface zone are detected by X-ray diffraction (XRD). Interfacial microstructure of TiNi+CuTis+α-Ti forms at the Ni/Ti-6Al-4V transition zone and Cu (ss. Ni) solid solution forms between Ni/Cu interlayers. The thickness of reaction layer (TiNi) increases with bonding time by a parabolic law: y2=K0exp(-150000/RT)t, and K0=2.9×10~7 m2/s is figured out from the experiment data.     

Stability of nanocrystallites dispersed in Cu50Zr45Ti5 metallic glass under electron irradiation

Effect of electron irradiation on stability of nanocrystallites dispersed in a glassy matrix of a Cu50Zr45Ti5 bulk metallic glass (BMG) alloy was investigated. Microstructural evolution during electron irradiation was observed and analyzed by means of conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) and X-ray energy dispersive spectroscopy (EDS). The crystalline nanoparticles of monoclinic CuZr phase formed in-situ in as-cast Cu50Zr45Ti5 alloy exhibited a high stability against electron irradiation. No obvious changes in their size, morphology, and crystal structure were observed during electron irradiation, though new crystalline nanoparticles nucleated and precipitated in the glassy matrix under electron irradiation. The new nanoparticles formed upon irradiation have a similar composition and crystal structure to those formed in-situ in the as-cast alloy. The nanocrystalline precipitates in the glassy matrix are proposed to be mainly due to electron knock-on effect under electron irradiation, which promotes atomic diffusion and assists the crystallization of the glassy phase. The present result indicates that electron irradiation to metallic glasses has potential for producing nanocrystalline structure and nanocrystalline-glassy composite structure.     

Deposition of biomimetic biocompatible oxides on metallic glass surface by electro-discharge coating process

Bulk metallic glass demonstrates superior mechanical properties and excellent bio-mechanical stability compared to routinely used biomaterials like titanium, cobalt-chromium, stainless steel, et cetera. However, the metallic glass surface do not easily adhere to the leaving tissues due to native bio-inert oxide layer, which have poor wear resistance and low hardness. In this current study an innovative method for surface coating of bulk metallic glass by mixing hydroxyapatite powder during electro-discharge machining has been employed. A biomimetic nano-porous bio-ceramic layer of oxides and carbides was deposited on metallic glass surface. The modified surface integrity and composition were investigated by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction characterization techniques. The characterization results confirmed the formation of a natural bone-like nano-porous surface topography on the metallic glass surface using a novel hydroxyapatite-mixed electro-discharge coating process. In addition, a favourable surface chemistry in the form of bioceramic carbides (zirconium carbide, titanium carbide) and zirconium oxide layers, was achieved.     

熔态镁合金在空气/SF6保护气氛中形成的膜特征

镁及其合金的铸造、熔炼需要在SF6的保护气氛中进行,目前对其研究还不完善.为此,用SEM,TEM和XRD研究了熔态AZ91D镁合金在空气/SF6保护气氛中形成的表面膜特征.结果表明:保护性表面膜分为两层,最外层主要为疏松多晶的MgO及含有少量Al的氧化物和微量的氟化物;内层为结晶MgF2;随着AZ91D在保护气氛中暴露时间的增加,表面膜中F/O原子比显著增加,表面粗糙度增加;表面膜超过一定厚度后,主要为F和Mg发生反应;表面膜表面弥散着大小不一的白色片状物,其主要成分为MgO,内含少量MgF2.部分近表面区域断面中有不连续的白亮富F(原子分数约为70%)小半圆区域,富F的小半圆亮区之间F含量显著降低;部分为一条厚度不均匀的白亮带,其中F原子分数也很不均匀.富F区中F/Mg原子比显著大于MgF2中的2/1,F可能通过富F区域不断从保护气氛向AZ91D镁合金内部扩散形成MgF2.     

Electric field induced interfacial reaction of Au-Ag bimetal film on SiO2 surface

Interface evolution of nanometer scale Au-Ag bimetal film on SiO₂ substrate surface during electromigration was investigated by angle resolved X-ray photoelectronspectroscopy (ARXPS). ARXPS spectra showed that a chemical reaction between Au-Ag filmand SiO₂ layer occurred at interface, which caused Au, Ag and Si having differentdistribution and chemical states across the film. This result as well as previousobservation by atomic force microscopy (AFM) demonstrate that electromigration of Au-Agbimetal film on SiO₂ surface is accompanied with strong interfacial chemicalreaction rather than a simple lateral physical diffusion process.     

An effective approach for bonding of TZM and Nb-Zr system:Microstructure evolution,mechanical properties,and bonding mechanism

A novel method of liquid metallic film(LMF)bonding was developed to join titanium zirconium molyb-denum alloy(TZM)and Nb-Zr alloy with a Ni interlayer.Using this method,a Ni-Zr liquid phase was formed by the eutectic reaction and then squeezed out from the gap due to a transient pressure,leaving an LMF.It not only achieved a reliable metallurgical bonding but also served as a transition layer between TZM and Nb-Zr alloy to reduce the mismatch between them thus further improving its performance.The bonding mechanism of the TZM and Nb-Zr system was discussed based on theoretical calculation and high-resolution microscopy analysis.The advantages of this method were established by comparing the microstructure and mechanical properties of LMF bonded joints with that of traditional contact-reaction brazing and direct diffusion bonding.Additionally,the feasibility of the LMF bonding method was also demonstrated by the reliable joining of other high-temperature and immiscible systems.     

Crystallization and thermally induced surface relief effects in a Mg<Subscript>65</Subscript>Cu<Subscript>25</Subscript>Y<Subscript>10</Subscript> bulk metallic glass

The crystallization behaviour of Mg₆₅Cu₂₅Y₁₀ bulk metallic glass (BMG) under different reheating conditions was investigated. X-ray diffraction spectrometery (XRD), differential scanning calorimetery (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to examine the crystallization of different samples and the surface relief generated on as-polished surfaces during heat treatment. Different phase constituents were found in samples that experienced different reheating stages. It is proposed that both the reheating temperature and holding time have a significant effect on the phase constituents. The BMG was found to generate surface corrugations of amplitude 1–2 μm during annealing above its crystallization temperature. Such thermally induced surface relief effects are probably a result of the development of surface stresses generated by volumetric changes associated with crystallization of the residual amorphous phase.     

An Evaluation of Quality of Joints of Two Dissimilar Metals by Diffusion Bonding using Ultrasonic C Scan

Diffusion bonding of commercially available pure aluminum/copper was carried out between the temperatures of 400°C and 500°C for 60 min under the pressure of 5–15 MPa in vacuum. The effects of temperature and pressure on the microstructure of aluminum/copper diffusion bonded joints were analyzed. The interface micrographs of the bonded samples were observed in optical and scanning electron microscope (SEM) images. The soundness of the bond was evaluated by destructive and nondestructive (ultrasonic C scan) testing methods. The quality of the bonded joints was evaluated by the intensity of the echo and its images of ultrasonic testing and was correlated with destructive parameters such as the strength ratio. Chemical compositions of the interface and the fractured surface of the bonded samples were characterized by energy dispersive spectroscopy (EDS). EDS patterns were confirmed by the formation of the different compositions at the interface of the bonded samples. Better bonding characteristics were observed by diffusion bonding optimum parameters at 450°C with an applied pressure of 15 MPa for 60 min.     

The oxidation behavior of Cu42Zr42Al8Ag8 bulk metallic glasses

The oxidation behavior of Cu₄₂Zr₄₂Al₈Ag₈ bulk metallic glass was studied in synthetic air over the temperature range of 330–460 °C. The oxidation kinetics of the metallic glass follows a single parabolic rate law at 330 and 390 °C and a two-stage parabolic rate law from 420 to 460 °C. Silver precipitates on the topmost oxide layer of the metallic glass were revealed by energy-dispersive X-ray spectroscopy together with X-ray diffraction pattern. Observation using scanning electron microscopy shows that silver metal precipitated at all temperatures and some islands were formed on the outermost copper oxide layer at high temperatures. Multilayered oxide scales were also observed with silver precipitates sandwiched between copper- and zirconium-rich oxides layers.