Growth Of Interfacial Layer Research Articles

A dual-phase-lag diffusion model for interfacial layer growth in metal matrix composites

The time dependence of a reinforcement-matrix interfacial layer growth (RMILG) in most metal matrix composites (MMC's) is not t1/2 as described by Fick's law. Moreover, the RMILG vs. t1/2 could be linear for relatively short and long times, and an anomaloustransition behavior exhibits in between. In this paper, a dual-phase-lag diffusion (DPLD) model is proposed to characterize the RMILG kinetics. Unlike Fick's law, it accounts for the two lagging times required for the processes of interdiffusion and chemical reaction. This unique feature empowers the DPLD model to capture the multiple stages response over the entire RMILG history. Model validation is verified with the experimental results of seven different MMC systems.

Growth kinetic studies of Cu–Sn intermetallic compound and its effect on shear strength of LCCC SMT solder joints

Growth kinetics of interfacial Cu–Sn intermetallic (IMC) layer and its effect on the shear strength on practical LCCC surface mount solder joints were studied for isothermal aging at 70, 120, 155 and 170°C. Only normal Cu 6Sn 5 ( η-phase) intermetallic was found in the interfacial IMC layer of as-soldered solder joint, whereas the duplex structure of both η-phase and ε-phase Cu 3Sn existed in all annealed joints. The growth kinetics of the overall interfacial IMC layer can simply be described by classical kinetic theory for solid-state diffusional growth with an activation energy of 1.09 eV and interdiffusion coefficient of 1.61×10 −4 m 2 s −1. The relatively higher activation energy, as compared with that found for bi-metallic couple of eutectic Sn–Pb solder on copper, is attributed to the dissolution of Ni from the component metallization into the bulk Sn–Pb solder. In addition, the shear fractures in all the solder joints investigated are shown to be ductile in nature and confined in the bulk solder rather than through the interfacial IMC layer. A linear reduction in shear joint strength was observed with an increase in intermetallic layer thickness up to ∼5.6 μm. Such a reduction in joint strength is due to a continuous removal of Sn from the bulk solder for the growth of interfacial IMC layer and flattening of the solder/IMC layer during isothermal aging of the solder joint.

Aging studies of Cu-Sn intermetallic compounds in annealed surface mount solder joints

This is the second in a series of investigations aimed at studying the effect of Cu-Sn intermetallic compound on the reliability of surface mount solder joints. Our previous investigation revealed the formation kinetics and characteristics of Cu-Sn intermetallic compounds in LCCC surface mount solder joints during IR-reflow soldering. The present study focuses on the solid state growth of the interfacial Cu-Sn intermetallic compound in LCCC surface mount solder joints under prolonged annealing at elevated temperature. A thick Cu-Sn IMC layer at the Sn-Pb solder/Cu interface of a surface mount solder joint (which can be achieved by prolonged storage at high temperature or after long term operation of modern SMT electronic assemblies) makes the interface more sensitive to stress and may eventually lead to fatigue failure of all SMT solder joint. The microstructural morphology of the Cu-Sn IMC layer at the solder/Cu pad interface in all annealed LCCC surface mount solder joints is duplex and consists of /spl eta/-phase Cu/sub 6/Sn/sub 5/ and /spl epsi/-phase Cu/sub 3/Sn IMC. Both Cu-Sn IMC phases thicken as the aging time increases. On the other hand, at the interface close to the component metallization, the growth of both the /spl eta/- and /spl epsi/-phase were showed to be suppressed, with more pronounced effect on /spl epsi/-phase, by Ni originating from the metallization. The mean total layer thickness was found to increase linearly with the square root of aging time and the growth was faster for higher annealing temperature. The activation energy for the growth of interfacial Cu-Sn IMC layers and the pre-exponential factor, D/sub o/, for diffusion were calculated to be 1.09 eV and 1.68/spl times/10/sup -4/ m/sup 2//s respectively for the 0805 LCCC surface mount solder joint using eutectic Sn-Pb solder. These values are useful in predicting the thickness of interfacial Cu-Sn IMC layers in real surface mount solder joints in electronic assemblies after prolonged operation and hence the reliability factor of the solder joint attributed to the interfacial Cu-Sn IMC layer. Finally, the pad size and quantity of Sn-Pb solder employed in LCCC surface mount solder joints were shown to have an insignificant effect on the solid state growth rate for the interfacial Cu-Sn IMC layers.

Influence of Interfacial Layer Growth on the Kinetics of Iron Enrichment in Hot-dip Galvanneal Coatings on IF Steel Sheets.

Influence of Interfacial Layer Growth on the Kinetics of Iron Enrichment in Hot-dip Galvanneal Coatings on IF Steel Sheets.

Origin of cathodic degradation and new phase formation at the La 0.9Sr 0.1MnO 3/YSZ interface

New phase formation at the La 0.9Sr 0.1MnO 3/YSZ interface and its effects on the cathodic performances were studied at 900 °C in air. The resistance caused by the interfacial product layer kept increasing with time to reach up to 40% of the total resistance after 500 h. The interfacial product was identified as La 2Zr 2O 7 by XRD measurement. The electrical conductivity of La 2Zr 2O 7 (2.4 × 10 −5 S cm −1 at 1000 °C), measured by AC impedance and current interruption methods, was 4 to 7 orders of magnitude smaller than those of La 0.9Sr 0.1MnO 3 electrode or YSZ electrolyte. Either the electronic conductivity or the electrochemical O 2 reduction activity of La 2Zr 2O 7 was negligible. Combining these results, a conclusion was made that the cathodic degradation comes mainly from the growth of interfacial product layer and its contribution to the cell resistance increment is ohmic in nature.

Effects of annealing in O2 and N2 on the electrical properties of tantalum oxide thin films prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition

The tantalum oxide thin films with a thickness of 14 nm were deposited at 95°C by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD), and annealed at various temperatures (700∼850°C) in O2 and N2 ambients. The microstructure and composition of the tantalum oxide thin films and the growth of interfacial silicon oxide layer were investigated and were related to the electrical characteristics of the film. Annealing in an O2 ambient led to a high dielectric constant (er(Ta2O5) = 24) as well as a small leakage current (Ebd = 2.3 MV/cm), which were due to the improved stoichiometry and the decreased impurity carbon content. Annealing in an N2 ambient resulted in poor and nonuniform leakage current characteristics. The as-deposited tantalum oxide films were crystallized into δ-Ta2O5 after annealing at above 750°C regardless of the ambient. The leakage current of the film abruptly increased after annealing at 850°C probably because of the stress caused by thermal expansion or contraction.

Interfacial layer development in hot-dip galvanneal coatings on interstitial free (IF) steel

During the annealing of hot-dip galvanized coatings on interstitial free (IF) steel, an interfacial layer was found to develop and grow at the steel/coating interface. The interfacial layer followed a three-step growth process in which there was initial rapid growth up to a thickness of approximately 1.0 µm, followed by a period of essentially no growth with continued zinc and iron interdiffusion into the coating, and finally renewed growth at long time (60 second) anneals. The interfacial layer did not inhibit zinc and iron interdiffusion or the development of the Fe-Zn alloy layer. Coating iron content increased rapidly before the interfacial layer grew to a thickness of 1.0 µm, however, once the coating reached a total iron content in excess of 11.0 wt pct, interfacial layer growth became active and coating iron content increased only slightly with continued annealing. Although powdering of the coating as evaluated by a 60 deg bend test was generally found to increase with an increase in interfacial layer thickness, particularly in excess of 1.0 µm, no definitive relationship between interfacial layer thickness and powdering was found. The thickness of this interfacial layer, however, can be used as an indicator of formability performance.

Solid state intermetallic compound growth between copper and high temperature, tin-rich solders—part II: Modeling

The solder/base metal interfacial chemistry characterizing solder joints impacts the manufacturability and reliability of electronic components. A model was developed to predict the long-term diffusion-controlled growth of interfacial intermetallic compound layers using short-term experimental data. The model included terms for both constant and variable diffusion coefficients. Application of the model was demonstrated using parameter values for 100Sn/Cu system and comparing calculated layer thicknesses with the experimentally observed values. The early time data for the 100Sn/Cu system that were used to predict growth at longer times were characterized using a variable diffusion coefficient that was an empirical function of layer thickness.

Oxidation behaviour of titanium-containing brazing filler metals

Brazements on alumina or partially stabilized zirconia (PSZ) of four silver- or copper-based brazing filler metals that contain titanium to promote wetting of and adherence to structural ceramics, were exposed in a thermogravimetric analyser at temperatures up to 700°C to atmospheres of 100% O2, Ar-20% O2 and Ar-3 p.p.m. O2. The alloys included Cu-41.1Ag-3.6Sn-7.2Ti, Ag-44.4Cu-8.4Sn-0.9Ti, Ag-41.6Cu-9.7Sn-5.0Ti and Ag-37.4Cu-10.8In-1,4Ti, at%. All formed external oxides that were more or less protective under all of the test conditions studied. The growth of the oxides followed a parabolic time law. The gains in weight due to oxidation observed were small, ranging (for 45 h exposure at 400 °C to Ar-20% O2) from 0.20 mgcm−2 for the Ag-37.4Cu-10.8In-1.4Ti alloy to 0.46 mgcm−2 for Cu-41.1Ag-3.6Sn-7.2Ti. As expected, weight gain increased with increasing temperature or {ie4067-01}. Unexpectedly, the titanium played a minor role in the scale formed on any of the filler metals with a titanium oxide, TiO2, being found on only one alloy — Ag-41.6Cu-9.7Sn-5.0Ti. The brazements on PSZ gained weight at a higher rate than comparative brazements on alumina. We attribute this behaviour to oxygen transport through the zirconia resulting in the growth of an interfacial layer of titanium oxide.

Growth, shrinkage, and stability of interfacial oxide layers between directly bonded silicon wafers

Models for the growth and shrinkage of an interfacial oxide layer and for the stability of the interfacial oxide layer are formulated. Predictions of these models are compared to results obtained by high-resolution transmission electron microscopy. Wafers containing different concentrations of oxygen interstitials are bonded. Depending on the starting concentration of oxygen interstitials in the wafers, the interfacial oxide layer grows or shrinks during long-time annealing at high temperatures. For much shorter annealing times, local disintegration of the oxide layer may occur, which is less severely influenced by the concentration of oxygen interstitials. Rather, it depends on the thickness of the interfacial oxide layer. The influence of rotational misorientation is examined by rotating wafers around their common axes perpendicular to a wafer plane and subsequent bonding. Above a critical angle of about 1–3°, a continuous oxide layer is formed, whereas below this critical angle, sufficiently thin oxide layers disintegrate.

Heat treatment effects on an In-GaAs ohmic contact

Heat treatment effects on an In-GaAs ohmic contact are reported. Our finding is that the contact resistance of In to GaAs exhibits a practically insignificant increase after a heat treatment at a temperature of up to 900 °C. Results of secondary ion mass spectroscopy analysis show that the diffusion constant of In in GaAs is 3.3×10−5 exp(−1.9/kT) cm2/s. Moreover, a thermodynamic analysis gives the result that an InGaAs layer is formed between GaAs and In during the course of the heat treatment process. It is concluded from the above two analyses that the high stability of the contact resistance we have found is attributable to the low diffusion constant of In in GaAs and to the growth of an InGaAs interfacial layer.

Influence of beam energy, flux, and composition on junction parameters in ion beam tunnel barrier processing

An ion beam process was used to fabricate planar and edge-defined niobium-lead alloy Josephson junctions. Critical current density was found to be determined primarily by the dose of oxygen ions delivered during tunnel barrier growth. Comparison of spatial distributions of critical currents with ion flux profiles indicated that both preclean and oxidation were important in determining the magnitude of the on-wafer spatial variations. Uniformity of angle of incidence of the ion beam was very important in fabrication of edge junctions. The first ion beam experiments involving intentional additions of carbon-containing ions to the beam, to facilitate controlled growth of a carbide interfacial layer which is important in high quality devices, are also reported.

Pd2Si on Si(111) Growth Kinetics Studied by X-Ray Diffraction

AbstractResults are presented for the kinetics of growth of Pd2Si interfacial layers obtained by an X-ray diffraction technique. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222°C. The parabolic rate law observed is in qualitative agreement with those reported by investigators using other techniques (RBS, AES, Electron Microprobe). There appear to be two kinetics regimes distinquished by diffusion paths with different activation energies (1.35±0.10 eV vs. 1.05± 0.10 eV). The presence of impurities and the detailed Pd 2Si microstructure will influence how the reacting species are transported through the lattice.

Accelerated life tests of SnO2—Si heterojunction solar cells

The series resistance of SnO 2 -Si heterojunction solar cells increases with time on-shelf after fabrication, but tends to stabilize after a few weeks. This degradation is enhanced at elevated temperatures. The open-circuit voltage may increase or decrease with time. It is concluded that the degradation results from the spontaneous growth of a high-resistance interfacial layer (probably SiO 2 ) at the SnO 2 -Si interface. Degradation proceeds in two steps. The first step is relatively rapid and accounts for the degradation on-shelf. The second step is slower, is observed only at elevated temperatures, and is believed to be limited by the rate of transport of oxygen across the existing SiO 2 layer. Under prolonged illumination, the series resistance and open-circuit Voltage both decrease, Although the second stage of degradation is too slow to affect the practical life of these cells, it is not clear if the initial rapid stage and/or degradation under illumination will preclude the practical use of these cells.

Technology of GaAs metal—Oxide—Semiconductor solar cells

The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> ) and efficiency by up to 60 percent in GaAs metal-semiconductor solar cells. Several oxidation techniques have been developed which will provide the necessary oxide thickness and chemical structure. Details of these techniques using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> predominantly have As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> in the arsenic oxide rather than As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+5</sup> . A major difficulty at this time is a reduction in open-circuit Voltage by 100-200 mv when the antireflection coating is vacuum deposited. Without this effect, values of about 750 mV for V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> and 15-percent efficiency with air mass of 1 sun can be obtained with single-crystal GaAs. All techniques are compatible with polycrystalline GaAs thin films.

On the Growth of Interface layer of Oxide Coated Cathodes

On the Growth of Interface layer of Oxide Coated Cathodes