Metallization of polytetrafluoroethylene substrates by ion plating

The paper deals with the adhesion of copper films deposited using the ion plating technique onto polytetrafluoroethylene (PTFE) substrates. The substrates were biased by an r.f. voltage; copper was evaporated by electron bombardment. The results showed that careful sputter cleaning in an argon-oxygen (or helium- oxygen) mixture is essential to achieve good adhesion.Diagnostics by IR spectroscopy indicated that sputter cleaning in pure argon induced some damage at the substrate surface and that PTFE chains were broken. Microscopic inspection gave evidence that sputter cleaning in an argon-oxygen mixture increased the roughness of the substrate surface. Results of adhesion strength measurements for silver films on PTFE substrates after reactive sputter cleaning are presented and discussed. The formation of CuOCbonds at the interface is assumed to play an essential role.     

The contributions of morphological and surface chemical modifications to the elevated-temperature ageing of copper–epoxy interfaces

Adhesion experiments were performed using both morphological and surface chemical modifications to identify whether one is dominant in controlling copper–epoxy adhesion and durability. Surface preparation procedures included sanding and etching copper surfaces which were thermally oxidized and a surface plating treatment that formed oxidized nodules on the copper surface. Further surface chemical modification used benzotriazole primary and chromium ion implantation on copper oxide. All prepared surfaces were laminated to an epoxy–glass resin cloth and the interfaces were aged in an air oven at 150°C. Adhesion with ageing time was measured by a floating roller peeler assembly attached to a mechanical load frame. Interfaces formed when copper was oxidized in air had significantly lower peel strength than interfaces prepared by the plating treatment. Furthermore, peel adhesion was significantly reduced by elevated temperature conditioning. Adhesion degradation kinetics were applied to the transitional peel adhesion data and kinetic parameters associated with degradation at 150°C were calculated. The results suggest that peel failure for the thermally oxidized samples occurs within the oxide layer, and that surface treatments on the oxide layer are not effective in altering adhesion. The peel adhesion of the electroplated surfaces was affected by the surface chemistry. No difference was observed in the fracture surface as a function of chemistry or ageing time. © 1997 Chapman & Hall     

本底真空度对磁控溅射Cr/C镀层微观形貌及结合强度的影响

采用闭合场非平衡磁控溅射离子镀技术于不同本底真空度下制备了Cr/C镀层。利用TEM、划痕仪分析了不同真空度下镀层微观截面形貌与结合强度的变化。结果表明,随本底真空度的降低,Cr/C镀层中物理混合界面层和Cr金属打底层的厚度显著减小;镀层结合强度随本底真空度的降低显著下降,物理混合界面层、Cr金属打底层厚度的减小以及镀层表面孔洞等缺陷增多、致密度变差等共同导致了其结合强度的下降。     

Evidence for a solid state reaction at the a-SiSnOx interface: An x-ray photoelectron spectroscopy study

X-ray photoelectron spectroscopy together with argon ion sputtering were used to investigate the depth distribution of tin and silicon suboxides formed during thermal annealing of an amorphous silicon (a-Si) film vacuum evaporated onto a conducting tin oxide surface. The presence of multicomponent silicon suboxides together with free tin was observed at the a-SiSnO_x interface. The presence of these components is attributed to a solid state reaction between silicon and SnO_x.     

Raman and X-ray absorption study of selenium incorporated into the channels of mordenite: Dependence on the ion exchange and the method of incorporation

Influence of ion exchange and method of selenium incorporation into mordenite channels on the structure of incorporated selenium species are studied by Raman and X-ray absorption spectroscopy. It is shown that Se chains prepared by Se vapor adsorption are more regular than Se chains prepared by pressure injection of liquid Se. Concentration ratio between Se chains and Se₆ rings is found to be practically independent of the method of preparation but dependent on the type of cations in mordenite channels. Substitution of Na cations by larger monovalent cations leads to a decrease in Se chains concentration compared to Se₆ rings concentration and to an increase in average SeSe bond length. X-ray absorption spectrum of M-Se for polarization of radiation perpendicular to the channels is shown to be determined mainly by Se6 rings, and that for polarization parallel to the channels is a superposition of the absorption of chains and rings. Selenium incorporated into H-form of mordenite is found to be located not only in the original mordenite channels, but also in meso-channels organized due to partial destruction of the interchannel walls.     

On the mechanical weakness of glass seals to nickel-plated Remendur (Fe-Co-2 to 3% V) wire

Poor surface quality of wire can result in leaking glass-to-metal seals in sealed reed contacts. Nickel plating of Remendur reeds can be effective in eliminating this problem. However, the mechanical strength with nickel plated Remendur seals is significantly inferior to that for unplated reed seals. Measurement of breaking loads required for various types of sealed contacts, followed by examination of the fracture interfaces in a scanning electron microscope, indicates that the greater strength of seals with unplated reeds is due to a chemical bond at the Remendur/glass interface caused by interaction of constituents in the alloy with the glass. Furthermore, evolution or production of gases from the nickel plating during sealing causes the formation of large bubbles at the nickel/glass interface which reduce the area of contact and contribute to weakening. Outgassing of the nickel-plated Remendur reeds prior to sealing is impractical because the temperature required to achieve this results in degradation of the magnetic properties of the reeds. Seals made with barium oxide glasses, regardless of the reed material, appear to be stronger than those with the conventional lead oxide glass.     

Secondary ion mass spectrometry depth profiling and simultaneous electrical investigation of MOS structures

A comparative study of the electrical behaviour of MOS structures and the composition of the oxide layer was carried out by means of secondary ion mass spectrometry depth profiling and simultaneous electrical measurements. The width of the SiSiO₂ interface region was determined for wet, dry and HCl oxide layers using a special method for definition of the virtual SiSiO₂ interface of the depth profiles. A good correlation was found between the interface region width and the electrical parameters such as fixed oxide charge density and minimum surface state density for the samples analysed. The secondary ion intensity distributions of different contaminating species show a maximum at a distance of 20–80 Å from the interface. The incorporation of chlorine during HCl oxidation was monitored and a direct identification of migrating sodium ions in the HCl oxide layers was accomplished by comparing ²³Na⁺ depth profiles before and after positive bias- temperature stress.     

界面形貌对热障涂层残余应力分布的影响

用ABAQUS有限元软件建立了热障涂层模型,计算得出,在热载荷作用下,界面形貌对热障涂层材料残余应力分布影响很大,σ22主要集中在热生长氧化层和过渡层波峰处,随着热生长氧化层变厚、波长变小、振幅变大,σ22变大,且最大值产生在热生长氧化层/过渡层界面的波峰处.     

Aging properties of gold layers with different adhesion layers

Adhesion layers of nickel-chromium, titanium and molybdenum were sputtered and evaporated onto thermally oxidized silicon wafers. On these adhesion layers pure gold layers were sputtered, evaporated or electroless-deposited. The layer composited were patterned by a photoresist process and were taken through isochronal and isothermal heat treatments at temperatures up to 350°C in vacuo and in corrosive atmospheres. Measurements of d.c. resistivity changes gave thermal activation energies between 0.8 and 2.4 eV. For the systems AuMo, AuTi and AuNiCr three aging mechanisms were identified: recrystallization; volume diffusion; volume diffusion with surface corrosion. A three-step aging model for metallic sandwich layer composites was established: (1) atomistic defect recovery; (2) structure transformation and adhesion losses; (3) layer degradation. The steady state creep stability of bonds on the films can be correlated to the aging process.     

Bending fatigue failure of atmospheric-plasma-sprayed CoNiCrAlY + YSZ thermal barrier coatings

Bending fatigue failure of conventional atmospheric-plasma-sprayed CoNiCrAlY + ZrO₂–8 wt.% Y₂O₃ thermal barrier coatings with/without the thermally grown oxide layer generated between the bond coat and the top coat was experimentally studied at room temperature. Microscopical and profilometrical characterization of as-received and fractured specimens and a simplified finite element study of cooling thermal stresses show that the same fatigue strength of both the as-coated and the oxidized specimens (i.e. its insensitivity to the presence of the thermally grown oxide) is most likely caused by a preferential through-the-thickness cracking of the thermally grown oxide layer. Moreover, the bond-coat/substrate interface is identified as the weakest part of the studied thermal barrier system under both low and high crack growth rates.     

Hybrid epoxy-silyl modified polymer adhesives for CFRP sheets bonded to a steel substrate

This paper presents an experimental study examining the interfacial behavior between a steel substrate and carbon fiber reinforced polymer (CFRP) sheets bonded with hybrid epoxy-silyl modified polymer (SMP) adhesives. The epoxy adhesive has high modulus and strength characteristics, while the SMP adhesive possesses a low modulus with permanent elastic nature. The hypothesis tested is that a combination of these two distinct materials can alleviate interfacial stresses along the bond line with maintaining adequate strength. Two types of double-lap tension tests are conducted to evaluate the bond-capacity of the epoxy and SMP adhesives and to study the effect of various hybrid bond schemes. Test results show that the specimens bonded with homogeneous epoxy demonstrate abrupt failure, whereas those with SMP exhibit gradual load-softening at failure. The load-carrying capacity and stiffness of the CFRP–steel interface are not influenced by hybrid bond configurations. The degree of CFRP-debonding is, however, affected by the hybrid bond scheme. Stress transfer from the steel substrate to the CFRP is well maintained along the hybrid bond line with significant local deformability of the interface layer. Analytical models report that shear stresses along the CFRP–steel interface are noticeably mitigated at geometric discontinuities and the proposed hybrid bond technique can be used for structure-level application.     

An inorganic-organic passivation double layer for thin film circuits

If not hermetically encapsulated, thin film hybrid circuits require passivation for various reasons: protection against mechanical attack, long-term humidity diffusion, oxidation of metal films during heat treatment and destruction of oxide layers in electroless plating baths. An inorganic (Al₂O₃, SiO₂ etc.) or organic (photoresist, polyimide) passivation alone cannot meet all requirements simultaneously since most organic coatings do not resist temperatures of more than 150°C whereas evaporated oxide layers are too thin (1 μm or less) for mechanical protection and are often destroyed by non-neutral plating baths.We present a double-layer protective coating for thin film circuits consisting of an evaporated Al₂O₃ thin film and a photoresist layer baked at temperatures near the solder bath temperature. This passivation layer sequence is shown to avoid all the shortcomings of its constituents.     

Effect of rolling temperature on interface and bond strength development of roll bonded copper/aluminium metal laminates

Copper/aluminium laminates were prepared by roll bonding at different temperatures between 350 and 500°C. The effect of the roll bonding temperature on the interface reactions and bond strength development of the laminates was investigated. It was found that the bond strength of the laminates was generally enhanced with increased roll bonding temperature up to 430°C. Optimum roll bonding conditions, in terms of maximum bond strength were identified. It is shown that the development of the optimum bonding between the metal laminates is related to the creation of physical contact between the metals in the roll bonding stage and the formation of various intermetallic phases at the interface during the subsequent sintering process. The formation of intermetallic phases is greatly affected by the diffusivity of the metallic elements across the interface. It has been identified that dissolution of the interfacial oxide layer, formed in the roll bonding stage, has a great influence on the diffusivity of metallic elements across the interface which in turn determines the bond strength development of the material.     

On the bonding of porcelain on titanium

The interface structure and bond strength between Ti and porcelain were studied using various firing times and vacuum levels. During firing an interfacial oxide layer was formed between Ti and porcelain. Fracture occurred between this oxide layer and Ti. A correlation was observed between the thickness of the interfacial layer and the bond strength: the thicker the layer, the weaker was bonding. An improved vacuum was found to increase the bond strength. Oxygen was observed by ESCA to dissolve into Ti, causing brittleness in the uppermost Ti layer with prolonged firing time.     

Mechanical behavior of segmented oxide protective coatings

Mechanically and thermally induced fractures were examined in sputtered coatings consisting of an NiCrAlY underlayer, either a thin or a thick transition layer grading from NiCrAlY to ZrO₂, and an outer ZrO₂ layer. A pronounced columnar (fibrous) microstructure was obtained, although the columnar boundaries in the ZrO₂ layers and in the thick transition layers were much more open than in the NiCrAlY, effectively producing a more segmented structure. Some coatings also included a continuous fine-grained outer NiCrAlY sealing or close-out layer.For this complex metal and ceramic coating, a stress applied parallel to the layer plane always resulted in fracture perpendicular to the layer plane along open columnar boundaries. If the transition layer was thick, no fractures other than those at columnar boundaries were observed. If the transition layer was thin, fracture parallel to the layer plane occured in the ZrO₂-rich portion of this layer. When stress was perpendicular to the layer plane, fracture parallel to the layer plane occurred first at the outer ZrO₂(NiCrAlY) interface if an outer NiCrAlY sealing layer was present. Otherwise the ZrO₂-rich portion of the transition layer failed first, followed by fracture in the ZrO₂ layer.     

2.5 Behaviour of amorphous Ge contacts to monocrystalline silicon

The performance of evaporated amorphous Ge films (thickness $\text{～-500}\text{A}\text{?}$) contacts to etched n-and p-type silicon crystals of different resistivities are discussed. The Ge was 3 Ωcm n-type was also used but gave no difference), and as external contact to the Ge film an Au layer was evaporated. The behaviour of the aGeSi junction seems to be largely governed by interface effects (and thus depends on surface preparation), as is often the case with metal-Si junctions, but Ge gives more reproducible and less time-varying results.In the process of clarifying the function of the contact the following structures were investigated (1) aGe_pⁿSiIn (Hg), where the latter is an ohmic contact, (2) amSi_pⁿSi-metal where amSi is a surface region of the crystal which has been rendered amorphous by ion bombardment, (3) aGe_pⁿSi-metal. I-V and C-V measurements were performed. From the results we conclude that aGeSi junctions act as low-resistance contacts when fed by electron or hole currents from the crystal. The currents (holes and electrons) that are injected into the crystal from the film are limited by barriers to small current densities, usually in the range 10^?6 A cm^?2. It is suggested that the small hole currents are explained by an increase in the hole barrier, effected by positive charges at the interface or in the Ge film, which are built up when positive carriers (holes) are injected by the contact.     

Preface

The reliability of GaAs microwave devices is directly related to the integrity of Schottky and ohmic contacts for Schottky barrier devices and metal/semiconductor field effect transistor devices. The interface analysis of these device structures using surface analysis techniques has become extremely important in the study of the degradation of these devices. The research reported here focuses on three different metallic systems, namely Au/In, Au-12 wt.% Ge and Ni/AuGe, for both Schottky and ohmic contacts. The three metallic systems were evaporated onto 〈100;〉- oriented GaAs substrates (N_D=3×10¹⁷cm^-3) in an ultrahigh vacuum system. These samples were thermally aged by keeping them at 150°C for 500h. Current-voltage and capacitance-voltage measurements were made on as-deposited and thermally aged samples. The ideality factor decreased in all the samples. There was an apparent large increase in barrier height in AuGe/GaAs and Ni/AuGe/GaAs Schottky diodes. There was an insignificant change in the contact resistivity of ohmic contacts after thermal aging.The changes in the electrical characteristics of these device structures are explained on the basis of the formation of an oxide layer after thermal aging. A comparison of the Auger depth profiles of the as-deposited and the thermally aged samples substantiates the electrical observations. However, Au/In/GaAs Schottky diodes do not show the existence of an oxide layer at the interface. The out-diffusion of indium to the surface might have removed the oxygen from the interface to result in an Au-GaAs interface in the thermally aged sample. A slight increase in the barrier height of this sample is due to the Au-GaAs interface rather than the In-GaAs interface.     

Crack formation in sapphire/niobium/sapphire joints under compression

Compression tests were carried out on UHV diffusion bonded single crystalline sapphire/Nb/sapphire joints to investigate their mechanical properties, the mechanisms that lead to the failure of the joints and the dislocation-interface interaction. The tests were performed for different orientation relationships (OR) at the interface to study the influence of different bond strength on the mechanical behavior. Additionally, the metal layer thickness was varied for each OR to alter the influence of the interface. The experimental results showed, that with decreasing metal layer thickness the stress needed to form a crack increases drastically, whereas for the Nb/sapphire system the bond strength at the interface seems to have no significant influence on the mechanical behavior of the joint. A theoretical model will be presented that explains the experimentally observed relationship between metal layer thickness and crack stress.     

Preparation of a tantalum-based MoSi2-Mo coating resistant to ultra-high-temperature thermal shock by a new two-step process

To develop an ultra-high-temperature resistant coating for a reusable thermal protection system,the preparation of a tantalum-based MoSi2-Mo coating by a new two-step process of multi-arc ion plating and halide activated pack cementation is presented.The coating has a dense structure and is well compatible with the tantalum substrate,which can be thermally shocked from room temperature to 1750℃ for 360 cycles without failure.The mechanism of the coating's excellent resistance to high-temperature thermal shocks is that a strong-binding gradient interface and a dense SiO2 oxide scale with good oxygen resistance are formed by the high-temperature self-diffusion of Si.     

Einfluss einer PVD‐Al‐Zwischenschicht auf die Eigenschaften eines thermisch gespritzten Wärmedämmschichtsystems nach Temperaturwechselbelastung

Thermal barrier coatings (TBC) generally consist of a metallic bond coat (BC) and a ceramic top coat (TC). Co–Ni–Cr–Al–Y metallic super alloys and Yttria stabilised zirconia (YSZ) have been widely used as bond coat and top coat for thermal barrier coatings systems, respectively. As a result of long‐term exposure of thermal barrier coatings systems to oxygen‐containing atmospheres at high temperatures, a diffusion of oxygen through the porous ceramic layer occurs and consequently an oxidation zone is formed in the interface between ceramic top coat and metallic bond coat. Alloying components of the BC layer create a so‐called thermally grown oxides layer (TGO). One included oxide type is α‐Al₂O₃. α‐Al₂O₃ lowers oxygen diffusion and thus slows down the oxidation process of the bond coat and consequently affects the service life of the coating system positively. The distribution of the alloying elements in the bond coat layer, however, generally causes the formation of mixed oxide phases. The different oxide phases have different growth rates, which cause local stresses, micro‐cracking and, finally, delamination and failure of the ceramic top coat layer. In the present study, a thin Al inter‐layer was deposited by DC‐Magnetron Sputtering on top of the Co–Ni–Cr–Al–Y metallic bond coat, followed by thermal spraying of yttria‐stabilised zirconia (YSZ) as a top coat layer. The deposited Al inter‐layer is meant to transform under operating conditions into a closed layer with high share of α‐Al₂O₃ that slows down the growth rate of the resulting thermally grown oxides layer. Surface morphology and microstructure characteristics as well as thermal cycling behaviour were investigated to study the effect of the intermediate Al layer on the oxidation of the bond coat compared to standard system. The system with Al inter‐layer shows a smaller thermally grown oxides layer thickness compared to standard system after thermal cycling under same conditions.