bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Reliability Underfill for Flip-Chip Application
Authors: Sumita K. , Kumagae K. , Dobashi K. , Shiobara T. , Kuroda M. 
Published: April 2011

AbstractA new underfill was developed for a flip chip application with a large VLSI die. The new underfill is resistant to hydrolysis, exhibits a significantly lower moisture saturation level than widely used carboxylic anhydride cured underfills, demonstrates superb penetration capability between such a large die and an organic substrate without void formation, and delivers excellent adhesion characteristics and reliability performance during temperature cycling test and PCT (pressure cooker test).The new underfill utilizes amine catalyzed ring opening polymerization of epoxides, forms ether linkages during cure rather than ester linkages which anhydride cured underfills form, and strongly resists to hydrolysis. The underfill is less sensitive to moisture contamination and provides improved floor life as well as storage life in contrast to anhydride cured underfills as well. Unique low stress performance and penetration capability of the underfill are attributed to the use of proprietary silicone modified epoxy resin as well as highly loaded filler of optimized size, shape and size distribution in reference to the gap between a die and an organic substrate.An optimum cure schedule and a desirable viscosity range have also been identified for the new underfill to minimize filler segregation. Proper preheating of a die‐substrate has effectively reduced void formation while facilitating the removal of volatile from an organic substrate.
Development of New High-Mounting Density Packages
Authors: Kasai J. , Tsuji K. , Yoneda Y. 
Published: April 2011

AbstractIn low pin-count packages mounted with a device for portable electronics equipment, we have developed the CSP(Chip Size Package), which guarantees the reliability similar to the former SSOP (Shrink Small Outline Package) despite its drastic miniaturization in size than SSOP. The BCC (Bump Chip Carrier) we developed this time, as the name suggests, is a package with bumps, having the following structure: resin bumps covered with metal film are laid out in the base peripherally as mounted terminals. This resin bump can be formed by molding monolithically with resin sealing, and the connection between the bump and metal film has been implemented using lead frame manufacturing technology and etching technology we have developed. In this paper, we outline the structure and manufacturing technology of BCC as well as the results of reliability evaluation for BCC.
InN-Based Ohmic Contacts to AlInN
Authors: Donovan S. M. , Ren F. , MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Jones K. 
Published: April 2011

ABSTRACTIn order to maximize the performance of III-Nitride devices, it is necessary to develop thermally stable low resistance Ohmic contacts to III-N based electronic structures. This paper reports on the utility of InN as an aid to contact formation on widegap materials such as InAIN. For n-type materials, several questions relating to the growth conditions have been explored. Specifically, the impact of substrate type (GaAs vs. Sapphire), cap layer growth temperature and V/III ratio on contact resistance has been investigated. It was found that the use of sapphire substrates combined with high growth temperatures (575°C) and high V/III ratios produced acceptable contact resistances (∼10−6Ohm-cm2) to InAIN.
Nitride-Based Thin-Film Cold Cathode Emitters
Authors: Christman James A , Sowers Andrew T , Bremser Michael D , Ward Brandon L , Davis Robert F , Nemanich Robert J 
Published: April 2011

ABSTRACTCold cathodes have been fabricated using two different nitride structures as a thin film emitting layer. The A1N and graded AlGaN structures are prepared by metalorganic chemical vapor deposition (MOCVD) on an n-type 6H-SiC substrate. Individual aluminum grids are perforated with an array of either 1, 3, or 5μm holes through which the emitting surface is exposed. After device fabrication, a hydrogen plasma exposure was found to be necessary to activate the cathode. The devices have displayed a limited lifetime and a small percentage of the devices operate, although half of the devices with 5μm holes functioned. The highest measured collector currents are 0.1μA for A1N and l0nA for AlGaN at grid voltages of 110V and 20V, respectively. The grid currents are typically 10 to 104 times the collector currents.
A Microstructural Analysis of Orientation Variation in Epitaxial AlN on Si, Its Probable Origin, and Effect on Subsequent GaN Growth
Authors: Beye R. , George T. , Yang J. W. , Khan M. A. 
Published: April 2011

ABSTRACTA structural examination of aluminum nitride growth on [111 ] silicon was carried out using transmission electron microscopy. Electron diffraction indicates that the basal planes of the wurtzitic overlayer mimic the orientation of the close-packed planes of the substrate. However, considerable, random rotation in the basal plane and random out of plane tilts of about ±3–4$ are evident. The orientation variations were traced to the Si interface, where crystallites and an amorphous-like background were present. A strong relationship between these phenomena and substrates containing Si is established by comparing the present growth results with those reported elsewhere. Crystalline quality of the overgrown GaN on the AIN layer is described, with suggestions for the relation between surface pyramids or peaks and the mis-oriented buffer layer.
In Situ Reflection High-Energy Electron Diffraction Study of Structure and Morphology Evolution of AlN Thin Films During Growth
Authors: Jin F. , Auner G. W. , Naik R. , Zatyko P. , Rao U. 
Published: April 2011

ABSTRACTAIN films were grown on Si (111) substrates using a PSMBE deposition system. Two types of growth methods were used: (i) a continuous growth at one temperature and (ii) a two stage growth where a buffer layer at low temperature is followed by deposition at higher temperature. The structure and morphology of the films grown at different temperatures are compared. The evolution of surface structure and morphology of the film during the growth were studied using in-situ RHEED, X-ray diffraction, and AFM.
High Resolution X-ray Diffraction from Epitaxial Gallium Nitride Films
Authors: Lafford T. , Loxley N. , Tanner BK 
Published: April 2011

ABSTRACTThe width of double axis X-ray rocking curves of epitaxial GaN layers is shown to be critically dependent on the width of the detector aperture. We show that triple axis diffraction measurements using a crystal analyser before the detector enables the instrument function to be defined and the tilt and dilation distributions separated. All GaN samples examined showed a mosaic structure of misoriented sub-grains with little dilation within the mosaic blocks. In reciprocal space maps this was revealed as a wide distribution of intensity in a direction perpendicular to the reciprocal lattice vector.
Deep Levels in GaN Studied by Extrinsic Photoconductivity Measurement
Authors: Zhang Rong , Huang Zhenchun , Guo Bo , Chen J. C. , Yan Li , Zheng Youdou , Kuech T. F. 
Published: April 2011

ABSTRACTModulation Extrinsic photoconductivity spectra between 1.44eV and 1.75eV of unintentionally n-doped high resistance GaN film grown by MOCVD are measured at room temperature by using wavelength adjustable Ti:Sapphire laser. We find that there are two major deep levels in the GaN material in the used photon energy range. The relaxation time of excess carriers controlled by those levels are in the order of 10−4sec. The concentration of localized states are determined as 1.8×108cm−3 and 2.5×109cm−3, respectively. A physical model is developed to explain the results and process the data. Using a new method we have determined the optical absorption cross section of deep levels are 1.5×10−17cm2 and 2.7×10−18cm2, respectively.
Analytical Theory of Electron Mobility and Drift Velocity in GaN
Authors: Gelmont B. L. , Shur M. S. , Stroscio M. 
Published: April 2011

ABSTRACTWe derive balance transport equations for the electron mobility and drift velocity, which are applicable at any degeneracy of the electron gas. These equations account for the polar optical phonon scattering and ionized impurity scattering and include the effects of screening. These equations are valid only for very high concentrations (above 1019 cm-3 for GaN). However, the comparison with the results of Monte Carlo simulations shows that they fairly accurately reproduce the field-velocity curves in GaN in moderate electric fields (up to 100 kV/cm). The comparison with the electron mobility calculated using the two-step model [1] shows a much larger difference but allows us to illustrate the trends in mobility dependencies caused by electron-electron collisions. We also derive the balance transport equations accounting for the polar optical phonon scattering in a two-dimensional electron gas. The calculations based on these equations, show that the unscreened polar optical scattering mobility is smaller in the two-dimensional gas than in the bulk intrinsic semiconductor and that the mobility decreases with the decrease of the quantum well thickness.
Study of Traps in GaN by Thermally-Stimulated Current
Authors: Zhang Rong , Huang Zhenchun , Chen J. C. , Zheng Youdou , Kuech T. F. 
Published: April 2011

ABSTRACTIn this paper we employed the TSC method to investigate the traps in GaN. The measured sample was a M-S-M UV-detector of high-resistance GaN on sapphire grown by LP-MOCVD. The relation of dark conductance to temperature clearly showed three major donor levels at 0.019, 0.13 and 0.74eV respectively. TSC measurements from 60 to 380K indicated that there were at least 11 traps in the GaN material. The active energy of those traps were 0.15, 0.19, 0.25, 0.28, 0.33, 0.39, 0.47, 0.55, 0.60, 0.63 and 0.67eV. The range of trap density is from 6 × l014cm-3 to 2 × l018cm-3. By comparing TSC spectrum to dark current, we consider there are at least 4 hole traps in the measured range with energy of 0.25, 0.28, 0.33 and 0.39eV. The illumination time effect was studied and discussed.
Relaxations at GaN (1010) and (110) Surfaces
Authors: Filipetti Alessio , Menchi Manuela , Bosin Andrea , Cappellini Giancarlo 
Published: April 2011

ABSTRACTWe present anab-initiocalculation of GaN wurtzite (1010) and zinc-blende (110) surface structures and formation energies. Our method employs ultrasoft pseudopotentials and plane-wave basis. These features enable us to obtain accurate results using small energy cut-off and large supercells. The (110) surface shows a Ga-N surface dimer rotation of ∼ 14°, i.e. about one half that of the ordinary III–V non-nitride compounds, and a 5% contraction of the surface bond-length (more than the double that occurring in GaAs). For the (1010) surface, a layer rotation angle of about 11° and a bond-length contraction of 6% has been found. Zinc-blende GaAs (110) and wurtzite ZnO (1010) surfaces have been studied as well, for the sake of comparison. GaAs results are in good agreement with the experimental findings. For ZnO a large bond contraction and a rotation angle of around 11% result. Thus, our findings place GaN closer in behaviour to the highly ionic II–VI compounds than to the non-nitride III–V semiconductors.
Characterization of SiGe Alloy Nanocrystallites Prepared by Pulsed Laser Ablation in Inert Gas Ambient
Authors: Yamada Yuka , Orii Takaaki , Yoshjda Takehito 
Published: April 2011

AbstractWe report nanometer-sized silicon germanium (SiGe) alloy crystallites prepared by excimer laser ablation in constant-pressure inert gas. Size distribution of the SixGelxultrafine particles decreases with decreasing x under fixed conditions of deposition such as ambient gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks intrinsic to crystalline SiGe alloys, and the linewidths of these peaks broaden due to the reduced size of the crystallites. Furthermore, a visible photoluminescence (PL) band with a peak at around 2.2 eV is obtained at room temperature after an annealing process.
Luminescence Properties of Silicon Nanocrystals
Authors: Li Shoutian , Silvers Stuart J. , Samy El-Shall M. 
Published: April 2011

AbstractWeblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization -controlled condensation technique. SEM micrographs show particles with ∼ 10 nm diameters but the Raman shift suggests the presence of particles as small as ∼ 4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending and rocking vibrations of the Si-O-Si bonds indicating the presence of a surface oxidized layer SiOx (x<2).The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiOx passivated coating. They show a short-lived blue emission characteristic of the SiO2 coating and a biexponential longer-lived red emission. The short lifetime component of the red emission, about 12 μs, does not depend on emission wavelength. The longer-lived component has a lifetime that ranges from 90 to over 130 μs (at 300 K), increasing with emission wavelength. The results are consistent with the quantum confinement mechanism as the source of the red photoluminescence.
Deposition of Polypyrrole into Porous Silicon
Authors: Moreno J. D. , Agullo-Rueda F. , Guerrero-Lemus R. , Martinpalma R. J. , Martinez-Duart J. M. , Marcos M. L. , Gonzalez-Velasco J. 
Published: April 2011

AbstractPolypyrrole has been electrocleposited in the interior of the pores that form the Porous Silicon structure, and a very significant increase of the electrical conductivity of the samples has been observed. The degree of filling by the polymer has been found to be highly dependent on the electropolymerization conditions. Micro-Raman Spectroscopy experiments have allowed us to measure the amount of polymer as a function to the distance from the outer PS surface.
Growth of Thin <p> μc-Si:H on Intrinsic a-Si:H for <nip> Solar Cells Application
Authors: Pemet P. , Goetz M. , Keppner H. , Shah A. 
Published: April 2011

AbstractThe <p> μc-SiC:H / <i> a-Si:H junction can be considered to be a sub-system of a n/i/p solar cell. Optimised performance of this junction can be assumed to be a key feature for obtaining high efficiency solar cells.In this paper the authors present results on the conductivity of boron doped microcrystalline hydrogenated silicon (<p> μc-Si:H) thin films deposited on amorphous substrates (e.g. glass or glass/<i> a-Si:H). It is shown that, without any treatment of the substrate or of the underlying surface, the <p> layers showed a strongly reduced conductivity. This indicates either a bad nucleation or a poor microcrystalline behaviour. By using an appropriate surface treatment of the substrate, a gain in photoconductivity of about three orders of magnitude could be obtained (σ > 3 S/cm at a layer thickness of 400Å). We conclude from this, that for thin <p> type μc-Si:H layers the nucleation conditions are essential for obtaining best electric properties of the film w.r.t. solar cell performance.Based on these results, interface treatment was successfully implemented in n/i/p solar cells deposited on TCO coated glass and stainless steel. The results of these experiments are also presented.
Epitaxy-Like Growth of Polycrystalline Silicon on the Seed Crystallites Grown on Glass
Authors: Miyamoto Y. , Miida A. , Shimizu I. 
Published: April 2011

AbstractPolycrystalline silicon thin films were grown on glass by two-steps, i.e., deposition of seeds on glass (1) and growth epitaxy-like on the seeds (2). For the growth of seeds, the surface reaction was intentionally enhanced by impingment of atomic hydrogen at rather high temperature (450 °C). Strongly textured polycrystalline Si exhibiting (220) preferential orientation was grown epitaxy-like on the seeds.
Nanocomposite Thin Films of Transition Metal Carbides Fabricated Using Pulsed Laser Deposition
Authors: Brock W. F. , Krzanowski J. E. , Leuchtner R. E. 
Published: April 2011

ABSTRACTA study has been conducted on the pulsed laser deposition (PLD) of transition metal carbides in order to examine alloying and phase formation in binary systems. Alternating layers of TiC/ZrC and ZrC/VC were deposited at 400 C and 5 mTorr Ar with nominal period thicknesses of 0.6 nm, 10.0 nm, and 50.0 nm. ZrC/VC x-ray diffraction analysis showed that the alloys were amorphous and the TiC/ZrC alloys were crystalline. The thicker films showed a higher degree of phase separation of the two compounds. Transmission electron microscopy confirmed the amorphous structure in the 0.6 nm ZrC/VC film, while the 50.0 nm film showed a layered structure and extremely fine grain size.
Preparation and Characterization of Nanocomposite Composed of TiO2 as Active Matrix
Authors: Sasaki T. , Rozbicki R. , Matsumoto Y. , Koshizaki N. , Terauchi S. , Umehara H. 
Published: April 2011

ABSTRACTPt/TiO2 nanocomposite films were deposited on quartz glass and ITO glass substrates by the co-sputtering method. As-deposited composite films were amorphous and content of Pt in the films could be easily controlled by the amount Pt wire placed on the TiO2 target. Pt/Ti atomic ratio in the nanocomposite increased as the length of Pt wire on the TiO2 target increased. It was determined by XPS that the chemical states of Pt in as-deposited nanocomposites were Pt metal, Pt-O-Ti and PtO2, which were dependent on the Pt/Ti atomic ratio in the nanocomposite. The size of Pt nanoparticles in the composite films increased as the temperature of heat-treatment and Pt/Ti atomic ratio in the composite films increased. Pt nanoparticles in the nanocomposite films inhibited grain growth of TiO2 during heat-treatment.
Synthesis and Characterization of Aerogel-derived Cation-substituted Hexaaluminates
Authors: Yan Lin-chiuan , Thompson Levi T. 
Published: April 2011

ABSTRACTNew methods have been developed for the synthesis of high surface area cation-substituted hexaaluminates. These materials were prepared by calcining high temperature (ethanol extraction) or low temperature (CO2 extraction) aerogels at temperatures up to 1600°C. Cation-substituted hexaaluminates have emerged as promising catalysts for use in high temperature catalytic combustion. In comparing unsubstituted and cation-substituted hexaaluminates, we found that the phase transformations were much cleaner for the cation-substituted materials. BaCO3 and BaAl2O4 were intermediates during transformation of the unsubstituted materials, while the cation-substituted materials transformed directly from an amorphous phase to crystalline hexaaluminate. Moreover, the presence of substitution cations caused the transformation to occur at lower temperatures. Mn seems to be a better substitution cation than Co since the Mn-substituted materials exhibited higher surface areas and better heat resistances than the Co-substituted materials. The low temperature aerogel-derived materials possessed quite different characteristics from the high temperature aerogel-derived materials. For example, phase transformation pathways were different.
Electrical Conductivity of Pure and Doped Nanocrystalline Cerium Oxide
Authors: Lavik E. B. , Chiang Y.-M. 
Published: April 2011

ABSTRACTWe have previously shown that dense nanocrystalline CeO2−x of approximately 10 nm grain size exhibits enhanced electrical conductivity and an enthalpy of reduction that is more than 2.4 eV lower than that for conventional ceria [1, 2]. These effects were attributed to preferential interface reduction. In this work, we investigated the relationship between interfacial area, heat treatment conditions, and conductivity by varying the grain size of dense samples through annealing at various temperatures. It is shown that the conductivity does not scale in direct proportion to interfacial area. Moderate temperature (700 °C) anneals which change the grain size by only a few nanometers reduce the conductivity by three orders of magnitude. It is suggested that atomistic relaxation occurs at the interfaces, and eliminates many low energy defect sites.
Monotonic and Transient Creep Experiments for Single Phase Gamma TiAl at Intermediate Temperatures
Authors: Lu Min , Hemker K. J. 
Published: April 2011

ABSTRACTMonotonie creep experiments (constant stress and constant temperature) of a single phase γ Ti47Al51Mn2 were conducted within a temperature region where the yield stress anomaly is observed (500°C - 600°C). The creep strength was found to have a normal temperature dependence. In addition to the monotonie creep experiments, temperature change experiments were performed. The creep activation energy obtained by the transient experiments was found to be significantly lower than that obtained from the monotonie experiments. TEM observations indicate that the microstructure evolves throughout creep, and no evidence of the formation of subgrains was observed. Instead, the mobility and the multiplication of ordinary dislocations were found to play a dominant role in intermediate temperature creep of single phase γ TiAl.
Effect of Stress on Creep of Lamellar Near γ-TiAl
Authors: Beddoes J. , Triantafillou J. , Zhao L. 
Published: April 2011

ABSTRACTThe creep behaviour of a binary Ti-48%A1 intermetallic is presented as a function of stress for two fully lamellar microstructures. The two lamellar conditions differ in terms of the lamellar interface spacing and grain boundary morphology. Air cooling (AC) from the single phase a region causes planar grain boundaries and lamellar spacing of 90 to 130 nm, while furnace cooling (FC) causes interlocked lamellae along grain boundaries and 350 to 550 nm lamellar spacing. Monotonie and stress increment creep tests at 760°C indicate that the AC condition exhibits a lower mimimum creep strain rate at stresses between 105 MPa and 290 MPa. The stress exponent increases from ∼ 1 at low stress to ∼ 10 at high stress. Consecutive stress reduction creep tests indicate that the internal stress required for dislocation glide is higher for the AC condition. The results suggest that at low stress the creep rate is controlled by recovery mechanisms, while at high stress the creep rate is predominantly controlled by dislocation glide. It is postulated that at high stresses the lower creep rate of the AC condition, compared to the FC condition, results from the reduced lamellar interface spacing, which increases the internal stress required for dislocation glide.
Microstructure Control in Iron Aluminides by Phase Decomposition or by Mechanical Alloying for Improved Strength and Ductility
Authors: Morris D. G. , Gunther S. 
Published: April 2011

ABSTRACTThe iron aluminides based on Fe3Al or FeAl being developed for intermediate temperature applications suffer from mediocre room temperature strength and ductility and poor high temperature tensile and creep strength. Attempts to overcome these problems have been restricted by the limited possibilities of structure modification by, for example, precipitation of stable strengthening particles. The present study examines two approaches to obtaining two-phase mixtures for improved strength and ductility: by adjusting chemical compositions such that two-phase order-disorder (α-α″) mixtures are obtained, and by mechanical alloying. Two-phase α-α″ mixtures are obtained by heat treatment of Fe-Al alloys with Al content near 20–24% and in ternary Fe-Al-Si alloys with suitably adjusted Al and Si contents. Microstructures of such alloys can be modified during heat treatments by ordering, precipitation or decomposition, and two-phase mixtures similar to those in the γ-γ superalloys obtained. Such two-phase alloys show good high temperature tensile and creep strength with some indication of reasonable ductility and reduced environmental sensitivity. Mechanical alloying can easily produce FeAl alloys of fine grain size reinforced with stable oxide particles. These structures lead to high room temperature strength with some ductility: controlled recrystallization can significantly modify both strength and ductility.