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Tin rich surfaces inside Pb-free electronics are more prone to tin whisker growth, thereby resulting in electrical failure of components. Conformal polyurethane (PU) coatings, which can be used as a mitigation strategy for such whisker growth, were investigated in this study. Nanoparticles of silica (∼20 nm in diameter) were added via liquid suspension to the PU resin to improve its mechanical properties. Four compositions of functionalized nanosilica suspensions, 10 wt.%, 20 wt.%, 30 wt.% and 50 wt.% (corresponding to the solid silica weight of 3.50%, 6.74%, 9.75%, and 15.17%, respectively) were evaluated to establish the relationship between microstructure developments and mechanical properties. Fourier-transform infrared spectroscopy (FTIR) and low-kV field emission scanning electron microscopy (FE-SEM) were used to examine the effects of nanosilica suspension addition to the PU resin. Mechanical properties of the coating were not only evaluated by nanoindentation for localized PU matrix properties but also by uniaxial tensile testing for composite properties. Results from both scales show that the addition of the particle suspension up to 20 wt.% (corresponding to 9.75 wt.% nanosilica) makes optimum mechanical performance consisting of good modulus, strength and ductility. This conclusion is also supported from microstructural, as well as chemical aspects of the PU coatings with the addition of nanosilica suspension.

We show that sandblasting can be employed to effectively enhance the oxidation resistance of copper by suppressing the interfacial delamination between copper and its oxide by modifying the surface roughness of Cu. Increasing sandblasting treatment time from 0 to 120 s increases the surface roughness of Cu from 0.12 ± 0.003 μm to 2.89 ± 0.176 μm, which results in improved oxidation resistance of the Cu surfaces and enhances the oxide/substrate interfacial fracture energy from 0.035 J/m 2 to 3.1 J/m 2 determined using nanoindentation. The sandblasting treatment has no appreciable effect on the Young's moduli of the Cu oxide film, which remain nearly constant at around 36 GPa. The improved oxidation resistance is ascribed to the enhanced interfacial adhesion of the sandblasted copper owing to the concave shape of craters generated by sandblasting, which results in a net downward force from the compressive stresses in the oxide film that forces the film to adhere to the Cu substrate.

Nanostructured TiO2 thin films were prepared via a low-temperature solution processing. We have previously calculated the degree of supersaturation (s) for TiO2 precursor solution to systematically tailor the development of TiO2 nanostructures in the range of s = 70–200. In this article, we focused more on a lower supersaturation regime (s < 70), from which we were able to obtain various shapes and sizes of nanostructures of TiO2 thin films. A film consisting of “rutile” phase nanoblades was observed when the degree of supersaturation was s = 15–70. To further lower the supersaturation (s < 15), hydrothermal processing had to be used, for which a film consisting of “rutile” phase nanorods was obtained. The resulting thin films were evaluated for band gap energies and dielectric properties. The band gap energy for those rutile thin films decreased from 3.22 to 2.99 eV when the supersaturation was lowered from s = 70 to 15. The dielectric constant (k) of the rutile film processed from s = 50 showed the best performance with k~50 at 1 MHz.

The self-assembly of tyrosyl bolaamphiphiles is exploited to create a colloidal protein-like host matrix, upon which sacrificial electron-donor molecules associate to create a photosystem II (PSII) mimetic electron-relay system. This system harnesses the tyrosine phenol groups abundant on the surface of the assemblies to mediate photoinduced intermolecular electron transfer. Compared with the l-tyrosine molecules, the tyrosyl bolaamphiphile assembly facilitates electron transfer from the sacrificial electron donor to the oxidized photosensitizer. The enhanced electron relay is likely to be driven by the host function of the assembly associated with the sacrificial electron donor and by the suppression of the oxidative cross-linking of phenoxyl radicals. The tyrosyl bolaamphiphile assembly is advantageous in the construction of a PSII mimetic system with a protein-like nature and displaying biochemical functions.

Predominant high melting point solders for high-temperature and harsh environment electronics (operating temperatures from 200 to 250 °C) are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt % to 20 wt %) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. Reflow processes were developed to make die-attach samples made from the cast Bi alloys. Die-attach joints made from Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. These alloy compositions also retained original shear strength even after thermal shock (TS) between −55 °C and +200 °C and high-temperature storage (HTS) at 200 °C. Brittle interfacial fracture sometimes occurred along the interfacial NiSb layer formed between Bi(Sb) matrix and Ni metallized surface. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly and were compared to the corresponding bulk alloys. The thermal conductivity of all the Bi–Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi–15Sb–10Cu alloy has so far shown the most promising performance as a die-attach material for high-temperature applications (operated over 200 °C). Hence, this alloy was further studied to evaluate its potential for plastic deformation. Bi–15Sb–10Cu alloy has shown limited plastic deformation in room temperature tensile testing in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175 °C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high-temperature test.

Predominant high melting point solders for high temperature electronics contain lead (Pb), which will soon be banned by environmental regulations as in most of consumer electronics. In an effort to replace the Pb-based solders with a new high-temperature capable material, we developed a transient liquid phase (TLP) bonding of bismuth (Bi) and nickel (Ni). A molten Bi (m.p. of 271°C) strongly reacts with Ni to form a Bi3Ni or BiNi intermetallic layer, both of which can withstand over 400°C. To study microstructural developments and their influences on reliability performance, the die attached coupons were assembled using Bi-Ni TLP bonds. It was shown that Bi3Ni is the first phase to form, after which the diffusion of Bi controls the growth kinetics of this intermetallic phase with the activation energy of 65.5 kJ/mol for the temperature range from 160 to 240°C. The solid-state transformation of Bi3Ni to BiNi follows, which is a slower process and only occurs at a long-term aging (activation energy of 17.8 kJ/mol, for the temperature range from 260 to 300°C). When tested at high temperatures (up to 350°C) or exposed under long-term storage at 200°C over 1000 hours, such bonds showed no degradation in die shear strength. It indicates the potential of the Bi-Ni TLB bonds as a Pb-free alternative to replace high-Pb solders for high temperature electronics that operate at 200°C or higher.

Bolaamphiphilic molecules with tyrosyl end groups formed interior-filled spherical self-assemblies, which are distinct from the vesicular or tubular structures of other similar peptidic bolaamphiphile assemblies reported in the literature. In this study, the self-assembly mechanism of these tyrosyl bolaamphiphiles was investigated taking into consideration the solvent effects on the molecular interaction forces using molecular modeling. The dissipative particle dynamics simulation of an aqueous tyrosyl bolaamphiphile solution suggested that the interior-filled assemblies were produced by a solvent-regulated assembly of small aggregates of bolaamphiphiles. These small aggregates were generated by hydrophobic interactions at an early stage, and then further assembled to form large spherical assemblies through intermolecular forces, including hydrogen bonds between the intermediate aggregates. Additional experiments and density functional theory calculations based on solvent variations proved that smaller assembled structures could be obtained by disrupting the hydrogen bonds between the intermediates. The assembly mechanism of these peptidic bolaamphiphiles afforded a facile way to create condensed supramolecular structures with controlled sizes.

We present a comparison study of the microstructure developments during aqueous solution deposition of SnO2, particularly, through chemical bath deposition (CBD) and liquid phase deposition (LPD) at very low temperatures (40–75 °C). The effects of solution chemistry on the microstructural details and electrical properties of SnO2 thin films are presented and discussed. Smooth, nanoparticulate SnO2 films were obtained from supersaturated precursor solutions with lower precursor concentrations while more aggregated SnO2 films were generated from higher precursor concentrations. Loosely-packed and porous structures were obtained from low supersaturation solutions with very low pHs. The deposition rates were also evaluated under various deposition conditions. XRD result shows that annealing process helps improve the degree of crystallinity of the as-deposited films that are composed of 3–10 nm nanocrystalline particles. One advantage of LPD of SnO2 films is in-situ fluorine doping during deposition. The resulting electrical resistivity of F-doped SnO2 films was about 18.7 Ω cm after the films were annealed at 450 °C.

We propose an efficient computational method to acquire diffuse and specular normal map with three types of illumination patterns by removing the redundancy of the conventional method. By analyzing the relationship between four reflectances under XY Z-gradient and constant patterns, the number of patterns needed is reduced to three patterns.

Predominant high melting point solders for high temperature electronics (operating temperatures over 200°C) are high Pb containing alloys. The new regulation will have banned the use of Pb in all electronics by 2019. We designed a "new" class of solder alloys with high bismuth (Bi) content (≥ 70 wt.%) to evaluate their potential as a high temperature Pb-free solder. Although having high melting point (271°C), pure Bi exhibits poor thermal conductivity, limited plasticity and wetting issues on common metallized surface such as Ni and Cu. In this work, alloying elements such as Sb and Cu were added to Bi in an attempt to negate such shortcomings by creating innovative alloy microstructures and optimum alloy compositions. As an extension to this work, a transient liquid phase (TLP) bonding between Bi and Ni was also investigated as Bi in a molten state reacts strongly with Ni to be converted into a Bi3Ni or BiNi intermetallic layer. Once formed, these phases can be stable until reaching ~ 470°C (with Bi3Ni), or ~ 617°C (with BiNi). We tested the reliability of the die attached coupons using Bi-Sb-Cu solders and Bi-Ni TLP bonds under high temperatures (up to 200°C for Bi solders and up to 350°C for TLP bonds), thermal shock (from -55 to 200°C), and high temperature storage (at 200°C). The resultant data indicate the potential of these two Bi systems as Pb-free alternatives for high temperature electronics.

We have developed a “two-step” solution-based processing to deposit high-k ceramic thin films. Electrochemically pre-coated amorphous titania layers were “hydrothermally” or “hydrothermal-electrochemically” converted to crystalline BaTiO3 films at ≤90°C. In hydrothermal process, an in situ electrochemical protection (ECP) mechanism enables utilization of common metallic substrates (e.g., Cu), which otherwise suffer corrosion from the precursor. Microstructural evolution of BaTiO3 films along with the effectiveness of ECP is discussed in this article. Derived BaTiO3 shows a dielectric constant of ~80 at 100 kHz, which makes it a promising candidate for high-density microelectronic capacitor applications.

This study presents a systematic investigation of the microstructure dependence of liquid phase deposition (LPD) of SiO2 films on solution parameters and deposition temperature. The corresponding deposition rate and film roughness were also evaluated under various deposition conditions. Smooth and sufficiently dense SiO2 films, which are the prerequisite for reliable low-k dielectric applications, were deposited on both silicon and fluorine-doped tin oxide coated glass substrates from supersaturated hydrofluorosilicic acid (H2SiF6) solution with the addition of boric acid (H3BO3). It is shown that H2SiF6 acid controls the surface morphology and grain structure through surface reaction while H3BO3 acid prompts bulk precipitation in solution. For the 208-nm thick SiO2 film, the breakdown field exceeded 1.9 MV/cm and the leakage current density was on the order of 10− 9 A/cm2 at 4 V, indicating excellent insulating properties of LPD SiO2 films. The strong presence of Si–O–Si and some Si–F with little Si–OH bond as shown in FT-IR spectra indicate that the LPD SiO2 films have mostly a silica network with some fluorine (F) content. F-doping was self-incorporated into the silica films from the H2SiF6 solution during deposition process.

This study examines the high temperature creep behavior of several Pb-based alloys. All compositions tested were found to follow power-law dislocation creep in the strain rate range of 10 −9 –10 −3 s −1 . Both the stress exponent and activation energy were measured from 298 to 473 K to identify the rate controlling mechanism for creep deformation. Creep of 95Pb–5In, 92.5Pb–5Sn–2.5Ag, 93Pb–3Sn–2Ag–2In was rate limited by dislocation climb from the observed stress exponent. A transition in the controlling climb mechanism from pipe diffusion to lattice diffusion was observed around 0.7 T m . Creep of 90Pb–10Sn was, however, rate limited by viscous solute drag rather than dislocation climb due to the greater concentration of Sn in Pb. The enhancement in self-diffusion of Pb was dependent on the degree of solid solution with solute atoms. The outcome of this work identifies variables related to the alloy elements that control creep behavior of Pb-based alloys used in high temperature applications where traditional solders cannot be used.

Conductive atomic force microscopy (C-AFM) has been widely used to map the nanoscale electrical properties of conducting polymers, nanomaterials, and organic electronic devices. While these measurements provide valuable insight into the spatial dependence of electrical performance, reported current densities and electrical conductivities measured by C-AFM are consistently much higher than those measured at the macroscopic scale. Here, we demonstrate that these anomalously high current densities and conductivities arise from ignoring current spreading and hence underestimating the current-carrying area. We present a simple experimental means of estimating the effective charge collection area during C-AFM measurements. Using semiconducting polymer poly(3-hexylthiophene) films as a test case, we find that the effective charge collection area can be as much as three orders of magnitude larger than the mechanical contact area between the probe and the film. Calibrated conductivity maps are obtained, with a quantitative correspondence with accepted values, and C-AFM photocurrent measurements of a nanostructured hybrid organic-inorganic solar cell active layer yield short-circuit current densities that match those reported for macroscopic devices. Finally, we address the observation that current spreading increases the effective charge collection area beyond the size of the probe-sample contact but does not preclude an imaging resolution below 10 nm.Conductive atomic force microscopy (C-AFM) has been widely used to map the nanoscale electrical properties of conducting polymers, nanomaterials, and organic electronic devices. While these measurements provide valuable insight into the spatial dependence of electrical performance, reported current densities and electrical conductivities measured by C-AFM are consistently much higher than those measured at the macroscopic scale. Here, we demonstrate that these anomalously high current densities and conductivities arise from ignoring current spreading and hence underestimating the current-carrying area. We present a simple experimental means of estimating the effective charge collection area during C-AFM measurements. Using semiconducting polymer poly(3-hexylthiophene) films as a test case, we find that the effective charge collection area can be as much as three orders of magnitude larger than the mechanical contact area between the probe and the film. Calibrated conductivity maps are obtained, with a qua...

Current microelectronics devices based on flexible as well as rigid substrates demand high dielectric constant (k) films to be grown on conductive substrate from a low-cost, low-temperature deposition technique. In this study, we produced high-k titania (TiO 2 ) fihns through an affordable electrodeposition protocol from the electrochemical bath maintained at about 0°C. The deposition occurs through a rapid hydrolysis mechanism of titanium containing ions in the precursor solution aided by electrochemically generated hydroxyl ions formed near the cathode surface (copper (Cu) substrate). Upon attaining a sufficient supersaturation level, such hydrolyzed species precipitate to form a titania thin film on the cathode surface. While depositing from a highly acidic precursor solution, Cu substrate was protected by a cathodic potential (-3 to ―5 V against the counter electrode). The resultant titania films show nanoparticulate structures evolved from nucleation and growth events of the in situ precipitated particles. Much higher deposition rate (about 1 μm/ min) was observed compared with that of typical chemical bath deposition. The resultant fihns with a thickness of 1500 nm grown on Cu exhibit very high dielectric properties (e.g., k ∼ 30, capacitance density > 110 nF/in. 2 at 100 kHz) and moderate breakdown voltage (V B ) (∼17.5 V). These properties indicate the potential of electrodeposited titania films to be used as a small-area thin-film capacitor for miniaturized electronic devices.

Both the electrical and mechanical properties of silica thin films deposited by liquid phase deposition (LPD) have been evaluated in this study. Silica thin films have been prepared on glass surface by immersing it in a supersaturated Hexafluorosilicic acid (H 2 SiF 6 )-based solution at a low temperature of 50°C. The as-deposited LPD silica fihns exhibit a low dielectric constant (k) that varies from 1.7 to 2.7 depending on the film morphology and fluorine content of the film. Young's modulus of these films was measured in the range of 18.9-24.5 GPa by a nanoindentation technique. The combination of extremely low k and fairly high modulus made this low-temperature-processed LPD silica films a very promising candidate for an interlayer dielectric film for the next-generation semiconductor devices.

Flagella isolated from Salmonella typhimurium were used as a template for the formation of TiO 2 nanotubes, which was accomplished through recent advances in low temperature ceramic film processing. TiO 2 is precipitated onto or attracted to the flagellar surface in aqueous solution. The mechanism of mineral film formation is similar to that of biominerals in nacre, sea urchin spine, and sponge spicule. This process is advantageous over other mineralization processes, as no genetic modification of the flagella is necessary and the mineralization is done at low temperature in aqueous solution.

This study characterized the temperature-dependent constitutive parameters (yield strength, ultimate tensile strength, elastic modulus, strain hardening exponent) from the mechanical behavior of five high-temperature solders, 95Sn-5Sb, 95Pb-5In, 90Pb-10Sn, 92.5Pb-5Sn-2.5Ag, and 93Pb-3Sn-2In-2Ag, chosen such that T m > 518 K. To model appropriately their mechanical responses under high-temperature thermal cycling, where the temperatures exceed 473 K, the material’s parameters must be determined as a function of temperature. Uni-axial tensile tests were, therefore, carried out between 298 K and 473 K to determine the constitutive behavior of each solder. 95Sn-5Sb exhibited the highest strength over the temperature range tested except near 473 K. Pb-based alloys with a higher degree of solid solution (>5%) showed greater strengthening than those primarily strengthened by coarse precipitates. Additionally, microstructure changes in 90Pb-10Sn and 95Sn-5Sb were shown to be responsible for unexpected mechanical behavior at elevated temperatures.

Titanium oxide (TiO{sub 2}) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl{sub 4}) precursor in an aqueous solution at temperatures below 100 C. As part of an effort to understand the formation of such TiO{sub 2} films, the kinetics of the nucleation, growth, and aggregation of TiO{sub 2} nanoparticles in aqueous solutions of TiCl{sub 4} were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl{sub 4}, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO{sub 2} nanoparticles was found to be 0.072 J/m{sup 2} from the homogeneous nucleation theory. Further investigations by a high-resolution scanning electron microscope (SEM) and TEM for the as-deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO{sub 2} nanoparticles can provide useful guidance for tailoring of microstructures of the TiO{sub 2} films.

Aligned Cr-doped ZnO nanorods have been successfully fabricated at 600 °C by in situ doping of Cr into ZnO nanorods using a vapor transport approach. Comprehensive structural analyses indicate that dopant Cr occupies Zn sites in ZnO and nanorods align along the [0001] direction. Photoluminescence spectra reveal unusual features peaked at 401 and 488 nm, respectively. Magnetic measurements have shown that nanorod arrays exhibit ferromagnetism at 10 and 293 K, which is likely due to defect-mediated exchange interactions. Nanomechanical studies have revealed a critical buckling load of 517 μN and a buckling energy of ca. 4.2 × 10−11 J, respectively, for the Cr-doped ZnO nanorod arrays.

The fluxless solderability of pure indium on gold-coated surfaces is investigated in this study using measurements of wetting angle and joint strength. This study focuses on the effects of indium’s native oxides and those which form during heat treatment. The initial oxide thicknesses are obtained by heating indium samples at various temperatures, and then, during the reflow above the melting temperature, oxidation at the interface is either allowed in open air or prevented by reflowing in an inert environment. The testing results presented include characterization of indium oxide (In2O3), the effects of indium oxide on joint strength, and the effect of hot pressing during reflow process.

Reconstructing 3D models given a single-view 2D information is inherently an ill-posed problem and requires additional information such as shape prior or user input.We introduce a method to generate multiple 3D models of a particular category given corresponding photographs when the topological information is known. While there is a wide range of shapes for an object of a particular category, the basic topology usually remains constant.In consequence, the topological prior needs to be provided only once for each category and can be easily acquired by consulting an existing database of 3D models or by user input. The input of topological description is only connectivity information between parts; this is in contrast to previous approaches that have required users to interactively mark individual parts. Given the silhouette of an object and the topology, our system automatically finds a skeleton and generates a textured 3D model by jointly fitting multiple parts. The proposed method, therefore, opens the possibility of generating a large number of 3D models by consulting a massive number of photographs. We demonstrate examples of the topological prior and reconstructed 3D models using photos.

Objective:To investigate whether reduced radiation dose abdominal CT images reconstructed with adaptive statistical iterative reconstruction V (ASIR-V) compromise the depiction of clinically competent features when compared with the currently used routine radiation dose CT images reconstructed with ASIR.Methods:27 consecutive patients (mean body mass index: 23.55 kg m−2 underwent CT of the abdomen at two time points. At the first time point, abdominal CT was scanned at 21.45 noise index levels of automatic current modulation at 120 kV. Images were reconstructed with 40% ASIR, the routine protocol of Dong-A University Hospital. At the second time point, follow-up scans were performed at 30 noise index levels. Images were reconstructed with filtered back projection (FBP), 40% ASIR, 30% ASIR-V, 50% ASIR-V and 70% ASIR-V for the reduced radiation dose. Both quantitative and qualitative analyses of image quality were conducted. The CT dose index was also recorded.Results:At the follow-up study, the mean dose r...

The device performance of microelectromechanical system (MEMS) inertial sensors such as accelerometers and gyroscopes is strongly influenced by the stress developed in the silicon die during packaging processes. This is due to the die warpage in the presence of the stress. It has previously been shown that most of the stress is generated during a die-attach process. In this study, we employ both experimental and theoretical approaches to gain a better understanding in a stress development induced during the packaging processes of a small silicon die (3.5times3.5 mm2). The former approach is accompanied with an optical profilometer while the latter part by a finite element analysis and an analytical model. A specific emphasis is given to the effects of structural parameters such as the die-attach adhesive thickness and material properties on the stress development. The results from all three approaches show good agreement, in that more compliant and thicker adhesives offer great relief in the stress development, as well as bend the die convex downward from its central location. A stress model proposed from this study not only provides a diagnostic tool for very small stress-sensitive devices, but it will also present a design tool for low-stress MEMS packaging systems

Zirconium oxide thin films were deposited on a phosphonate-terminated self-assembled monolayer (SAM) on a single crystal silicon substrate by a hydrolysis of zirconium sulfate solution in acid environment at 80 °C. The ZrO2 films consist of tetragonal ZrO2 crystallites with a size of 5–10 nm. Surface nucleation and attraction between the SAM surface and bulk precipitates in solution can explain the film formation. In both mechanisms, the surface functionality of the SAM plays a crucial role. This deposition approach was inspired by biomineralization through controlled deposition of inorganic solids on an ordered organic matrix. Microstructures and mechanical properties of the ZrO2 thin films were studied using scanning electron microscope (SEM), cross-sectional transmission electron microscope (TEM) and nanoindentation. Microstructures were tailored at different stages of the film growth, as well as with processing parameters and substrate surface conditions. The nanoindentation modulus and hardness of the as-deposited ZrO2 films were much lower than those of the bulk ZrO2. The addition of extra pressure during this process, however, restores mechanical properties of ZrO2 films.

Ceramic/self-assembled monolayer (SAM) bilayer coatings can provide adequate protection for silicon devices, or act as a multipurpose coating for other electronic applications, due to synergistic effects by forming a hybrid coating structure. The organic SAM layer acts as a “template” for the growth of the ceramic layer, while the ceramic layer can provide protection from environmental and mechanical impact. Low-temperature solution-based deposition techniques, namely, an in-situ solution method (biomimetic) and a hydrothermal method, have been employed in this study. Specifically, phosphonate-based (diethyl phosphatoethyl triethoxy silane) SAMs were used as a template to generate a zirconia ceramic layer at low temperatures. Other organic templates such as -SiCl3-, -OH-, -HSO3-, or -CH3-terminated SAMs were also examined. The reactions to grow the ceramic film were found to be pH sensitive. The ceramic and SAM coatings were characterized by a variety of analytical techniques. A pathway for the formation of the ceramic coating is also discussed.

The tensile creep behavior of two rare-earth dopant systems, lanthanum- and yttrium-doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior. It was found that, despite some microstructural differences, these systems displayed qualitatively a similar improvement in creep resistance, supporting the hypothesis that creep is strongly influenced by segregation. Differences in primary creep behavior and activation energy for steady-state creep were, however, observed for these systems. Given these results, it is expected that creep behavior can be further optimized by adjusting the dopant level and by controlling the microstructure.

Oversized dopant ions such as yttrium and lanthanum segregate to grain boundaries and reduce the tensile creep rate of α-Al 2 O 3 by 2-3 orders of magnitude. One explanation for this behavior is that the oversized segregants give rise to a site-blocking effect for grain boundary diffusion. It has also been speculated that the dopant ions modify the grain boundary structure in alumina and reduce the creep rate by promoting the formation of special (e.g., coincidence site lattice (CSL)) grain boundaries. In order to test the latter hypothesis, we have used electron backscattered Kikuchi diffraction to characterize the misorientation and special grain boundary distribution for undoped and 1000-ppm-yttrium-doped alumina. The results show that the grain boundary structure in alumina (as characterized by the frequency of selected CSLs and misorientation distribution) was not significantly changed by the addition of yttrium, indicating that creep retardation results mainly from site-blocking.

Film growth by physical vapor deposition on rotating substrates is modeled via a kinetic Monte Carlo algorithm on a two-dimensional hexagonal lattice. The motivation is to provide insight on the evolution of porosity during the deposition of thermal barrier coatings (TBCs). The model is implemented on an atomic scale that incorporates the effect of surface diffusion as well as the interplay between surface topography and the changing vapor incidence angle. It is shown that substrate rotation generates voids with a periodicity dependent on the amount of material deposited per revolution. The onset of pore formation and morphology of the pores are linked to the presence of shadowing features on the surface, either in the form of stochastic or crystallographic peaks and valleys evolving during columnar growth, or pre-existing roughness typical of polycrystalline oxide substrates. In addition, various forms of anisotropy develop in the microstructure as a result of the “sunrise–sunset” pattern of vapor incidence characteristic of TBC deposition on, for example, turbine airfoils. Comparison with observations on actual TBCs reveals that the simulations, in spite of their simplicity, capture several key microstructural features characteristic of these complex films.

High-spatial-resolution analytical electron microscopy using energy-dispersive X-ray (EDX) and electron energy-loss spectrometry (EELS) of yttrium- and lanthanum-doped Al2O3 has been conducted to ascertain the level of segregation of these impurities to grain boundaries. Line profile analyses indicate that the segregation is confined to a layer thickness of

It is believed that the segregation of oversized dopant ions to grain boundaries in Al 2 O 3 hinders grain-boundary diffusion, thereby reducing the tensile creep rate in this system by ∼2-3 orders of magnitude. In order to explain this improvement in creep behavior, it is helpful to characterize both the effective cation and interstitial volumes at grain boundaries, because the relative openness of some boundary structures suggests a great accommodation of oversized ions. In this study, the boundary volume is determined by a spatially local Voronoi construction, which highlights cation (Al 3+ ) substitutional sites as well as large interstitial voids. In particular, we examine the spatial distribution of free volume near grain boundaries and, in addition, the dependence of the driving force for segregation on misfit strain in doped Al 2 O 3 . We interpret our results in light of recent evidence that selective codoping can provide a more efficient means of filling available space near boundaries, thereby further enhancing creep resistance.

Oversized rare-earth dopant ions such as Y3+, Nd3+, and La3+ segregate to grain boundaries and reduce the tensile creep rate of α-Al2O3 by 2-3 orders of magnitude. It has been speculated that these dopant ions can modify the grain boundary structure in alumina by promoting the formation of special grain boundaries. If this were indeed the case, it would provide a possible explanation for the aforementioned creep rate retardation. In order to test this hypothesis, electron backscatter diffraction (EBSD) has been used to assess both the proportion of coincidence-site lattice boundaries, and the grain boundary misorientation distribution, in aluminas doped with various ions (Zr, Y, Nd, La, Nd/Zr). The results show that the grain boundary structure in alumina is not significantly altered by the addition of the above dopants, implying that the change in grain boundary chemistry is primarily responsible for the observed creep behavior.

Predominant high melting point solders for high temperature electronics (operating temperatures from 200 to 250°C) are Pb-based but these are hazardous to environment. In our previous study, we have shown the alloy design and characterization of the ‘new’ bismuth (Bi) - based solder alloys; 78Bi-14Cu-8Sn, 70Bi-20Sb-10Cu. It was shown that these solders have strong reactivities with Ni (forming intermetallic phases containing Bi or Sb), and with Cu (forming Cu 2 Sb, Cu 4 Sb). Of the two alloys, 70Bi-20Sb-10Cu exhibited the potential for forming good bonding with both Ni and Cu surfaces. The aim of this study was to establish the microstructure - property relationship by exploring the microstructure features involving solid solution behavior between Bi and Sb and the interfacial intermetallic layers. For this, the sandwiched coupons were fabricated using high Bi solders to bond the silicon die having Ti/Ni/Au backside metallization to the Cu substrate. These sandwich samples were then tested for thermal conductivity, die shear testing and liquid thermal shock between −50°C and 150°C. The current alloy matched the performance of high Pb alloys in thermal and die shear testing. In particular, the role of interfacial intermetallic layer on the reliability of the solder joint was investigated. From the findings of this study, Bi solder alloys showed some potential as an alternative to high-temperature Pb-free solders.

The microstructural features and tensile creep behavior of Al 2 O 3 doped with Nd 2 O 3 at levels ranging from 100 to 1000 ppm (Nd:Al atomic ratio) were systematically investigated. Compositional mapping, using both high-resolution scanning transmission electron microscopy and secondary ion mass spectroscopy revealed that, for all of the compositions studied, the Nd 3+ ions were strongly segregated to the Al 2 O 3 grain boundaries. Microstructural observations revealed that the solubility of Nd 2 O 3 was between 100 and 350 ppm. Tensile creep tests were conducted over a range of temperatures (1200°-1350°C) and stresses (20-75 MPa). Both the stress and grain-size exponents were analyzed. In selected experiments, controlled grain-growth anneals were used to enable creep testing of samples of the same average grain size but different neodymium concentrations. Independent of dopant level, the neodymium additions decreased the creep rate by 2-3 orders of magnitude, compared with that of undoped Al 2 O 3 . The value of the apparent creep activation energy increased with increased dopant concentration and then saturated at dopant levels exceeding the solubility limit. Overall, the results of the present study were consistent with a creep-inhibition mechanism whereby oversized segregant ions reduce grain-boundary diffusivity by a site-blocking mechanism.

The tensile creep behavior of yttrium- and lanthanum-doped alumina (at dopant levels below the solubility limit) was examined. Both compositions (100 ppm yttrium, 100 ppm lanthanum) exhibited a uniform microstructure consisting of fine, equiaxed grains. The creep resistance of both doped aluminas was enhanced, compared with undoped alumina, by about two orders of magnitude, which was almost the same degree of improvement as for materials with higher dopant levels (in excess of the solubility limit). In addition, measured creep rupture curves exhibited predominantly steady-state creep behavior. Our results, therefore, verified that the creep improvement in these rare-earth doped aluminas was primarily a solid-solution effect.

Recent studies have demonstrated that p.p.m. levels of rare-earth dopant ions (e.g. Y, La, Nd) wield a beneficial and highly potent influence on the creep properties of alumina. In addition, codoping with ions of disparate sizes (Nd, Zr) resulted in even further enhancement of the creep behavior. In all cases, the dopant ions were found to strongly segregate to grain boundaries. Creep rates were not influenced by the presence of second phase precipitates, verifying that the creep improvement is a solid solution effect. In an attempt to clarify the exact mechanism(s) that controls creep behavior of the doped aluminas, various advanced characterization techniques have been applied including: secondary ion mass spectrometry, scanning transmission electron microscopy, orientation image microscopy, and extended X-ray absorption fine structure as well as atomistic computer simulation and studies of the creep kinetics. Although no definitive mechanism has been established, a logical explanation is that outsize ions segregate to more energetically favorable grain boundary sites, and improve creep resistance by blocking a few critical diffusive pathways. This mechanism is sufficiently general that it may be applicable to other ceramic systems.

Dopants Y and Zr at 100 p.p.m. level (Y or Zr to Al atomic ratio) in ultra-high purity polycrystalline alumina have been found to be mainly segregated to the alumina grain boundaries. The atomic structural environments around the Y and Zr segregants have been investigated by Extended X-ray Absorption Fine Structure (EXAFS). On average, Y ions in α -Al 2 O 3 grain boundaries are coordinated by four oxygens, at a distance of 2.30 A, which corresponds nearly to the Y–O bond length in cubic Y 2 O 3 , and Zr ions are coordinated by five oxygens at a distance of 2.14 A, which is approximately the same as the average Zr–O bond length in monoclinic ZrO 2 . However, in the EXAFS radial distribution function, the Y-cation and Zr-cation next nearest neighbor shell cannot be clearly identified. These results suggest that Y and Zr at 100 p.p.m. concentrations in α -Al 2 O 3 occupy grain boundary sites with well defined nearest neighbor cation–oxygen bond lengths similar to those in their parent oxides but with the next nearest neighbor cation–cation distances varying considerably from site to site. From EXAFS, the Y grain boundary saturation concentration is estimated to be 6.0 atoms/nm 2 , which is consistent with the estimate from STEM of 4.4 atoms/nm 2 . The differences in the Zr–O and Y–O nearest neighbor distances and coordination numbers in Al 2 O 3 grain boundaries are related to the Y–Al and Zr–Al size mismatches.

In this paper, two types of permanent-magnet-assisted switched reluctance motors (SRMs) characterized by placing permanent magnets in either common or excitation poles are comparatively investigated in terms of performance such as torque production and efficiency improvement with respect to switch-on and switch-off angles through dynamic performance estimation. Four conditions for angle control are employed to predict dynamic performance in the two proposed permanent-magnet-assisted SRMs compared to the design of no permanent magnets, and the conditions are the increase of advance angle with a fixed turn-off angle (Condition A), the increase of advance angle with a fixed dwell angle (Condition B), the increase of dwell angle with a fixed advance angle (Condition C), and finally, the decrease of advance angle with a fixed dwell angle (Condition D). The permanent-magnet-assisted SRMs are always superior to the no-permanent-magnet design in terms of efficiency regardless of the condition of switching angles, and torque performance is overall in the same situation except for condition C due to a gradual boost in the negative torque of the permanent-magnet-assisted SRMs. Also, the placement of permanent magnets in either common or excitation poles is critical in condition C, and regarding the increase of power density, condition A is the best. The permanent-magnet-assisted SRMs are higher than the no-permanent-magnet structure by approximately 30% in power density under the condition of the same efficiency. The prototype of two permanent-magnet-assisted SRMs and their drive system have been built up.

Cu-Cu direct bonding is the leading method for fine pitch (10 μm) chip-to-chip interconnects. We performed several measurements on blanket Cu film samples in an effort to determine the impact of the Cu film properties on wafer-to-wafer Cu-Cu direct bonding. X-ray photoelectron spectroscopy (XPS) measurements were performed on uncleaned and cleaned samples to evaluate the effectiveness of three surface cleaning methods, Ar sputtering in vacuum, forming gas annealing and N2 annealing (NA). The XPS results were correlated with the bonding quality of the wafers cleaned by above mentioned methods using a C-mode scanning acoustic microscope (CSAM) and four-point bending test. The grain structure and texture information of the Cu surface were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) and the residual stress of Cu films was measured by X-ray diffraction (XRD). The roles that these microstructural variables may play in Cu-Cu direct bonding were also discussed.

e-AIRS[1,2], an abbreviation of ‘e-Science Aerospace Integrated Research System,’ is a virtual organization designed to support aerodynamic flow analyses in aerospace engineering using the e-Science environment. As the first step toward a virtual aerospace engineering organization, e-AIRS intends to give a full support of aerodynamic research process. Currently, e-AIRS can handle both the computational and experimental aerodynamic research on the e-Science infrastructure. In detail, users can conduct a full CFD (Computational Fluid Dynamics) research process, request wind tunnel experiment, perform comparative analysis between computational prediction and experimental measurement, and finally, collaborate with other researchers using the web portal. The present paper describes those services and the internal architecture of the e-AIRS system.

When flexible organic substrates are used for organic light emitting diodes (OLEDs), a barrier layer is required for the substrate to protect the enclosed functional materials from oxygen and water penetration. In this study, barrier coatings consisting of organic and inorganic films were developed for the organic substrate to ensure sufficient hermetic protection. As a model system, we chose the 'Parylene-C/TiO2' grown on the polyethylene terephthalate (PET) substrates. Parylene C films, which were vapor deposited at room temperature, have been known for a superior conformal coverage. The oxide films were biomimetically formed from in- situ precipitated particles in aqueous solutions and displayed nanoparticulate, dense structures. Since these oxides are processed at very low temperatures (< 70degC) in aqueous solutions, the processes can be applicable to organic structures, cheap and environment-friendly. Further, plasma treatments were employed to adjust the functionality of the organic surfaces and their effects on microstructure evolution of subsequent depositing layers are discussed. In order to evaluate the mechanical properties and film adhesion of the inorganic-organic hybrid coatings, in-situ AFM coupled nanoindentation techniques were introduced. Preliminary results on the dye penetration test indicated that the hermeticity of the barrier coatings was improved by having the hybrid films consisting of parylene-C and TiO2.

This research into new packaging materials and methods for elevated temperatures and harsh environment electronics focused on gaining a basic understanding of current state-of-the-art in electronics packaging used in industry today, formulating the thermal-mechanical models of the material interactions and developing test structures to confirm these models. Discussions were initiated with the major General Electric (GE) businesses that currently sell into markets requiring high temperature electronics and packaging. They related the major modes of failure they encounter routinely and the hurdles needed to be overcome in order to improve the temperature specifications of these products. We consulted with our GE business partners about the reliability specifications and investigated specifications and guidelines that from IPC and the SAE body that is currently developing guidelines for electronics package reliability. Following this, a risk analysis was conducted for the program to identify the critical risks which need to be mitigated in order to demonstrate a flex-based packaging approach under these conditions. This process identified metal/polyimide adhesion, via reliability for flex substrates and high temperature interconnect as important technical areas for reliability improvement.

This study focuses on microelectronic package design for the oil and natural gas drilling of wells with depths in excess of 20,000 ft, where package temperatures can exceed 204°C. At these high temperatures, solder interconnect sites are subject to fatigue and creep failures due to the stress generated by the thermal expansion mismatch between various components in the package. Typically this phenomenon is modeled by finite element analysis (FEA) to predict the number of cycles to failure. To ensure meaningful model results, however, accurate time and temperature-dependent mechanical properties are needed. This study examines five solders suitable for high temperature: 90Pb-10Sn, 95Sn-5Sb, 92.5Pb-5Sn-2.5Ag, 95Pb-5In, and 93Pb-3Sn-2Ag-2In. Uniaxial tension tests of the solder wires are carried out on a MTS servohydraulic machine using wedge grips. To evaluate the time-dependence on deformation, a strain rate study was carried out at 0.5%/sec, 1%/sec, and 5%/sec. Nanoindentation of solder wire is performed and compared to the corresponding solder wires tested through uniaxial tension tests. Dynamic nanoindentation through continuous stiffness measurement is performed on the wires to obtain the indentation data less sensitive to creep of the material, as well as to assess the effect of indentation depth on elastic modulus for each solder. One purpose of nanoindentation testing is to determine its suitability for the mechanical testing of soft solders. Mechanical properties obtained from these tests will be used in future modeling studies to estimate the cyclic fatigue life of these solders under thermal loading.Copyright © 2007 by ASME

Protection from oxygen and moisture is crucial for organic light emitting diodes (OLED) used in flexible display applications. The surface coating is an effective way to protect the enclosed functional materials and organic substrates in order to ensure their device functionality. Parylene films, which can be vapor deposited at room temperature, are known as a superior conformal polymeric material. In fact, a few attempts have shown that the parylene can be a good barrier coating for the OLED devices. This polymer film cannot, however, provide a long-term reliability due to nature of the polymer degradation in the presence of oxygen and moisture. In order to compensate such a drawback, we have explored the ‘biomimetic’ solution processing to deposit the oxide films on the organic substrate. Oxide films can provide a better protection and more robust surface. In this study, polyethylene terephthalate (PET) commonly used for an organic substrate, is deposited with the TiO2 films with or without the parylene underlying layer. Importantly, the oxide coating is processed at very low temperatures (< 60 °C) in aqueous solution, so the process can avoid premature failure due to high-temperature processes, and is applicable to organic structures, cheap and environment-friendly. In addition, hermeticity tests are devised to measure the moisture and oxygen permeation. Interfacial structure and mechanical properties of the resultant coatings are tested via scanning electron microscope (SEM), atomic force microscope (AFM), optical microscope (OM) and nanoindentation.Copyright © 2007 by ASME