bluuebunny/crossref_metadata_2025 huggingface dataset:
Continuous Synthesis of Inorganic Magnetic Nanocomposites by Laser Pyrolysis for Biomedical Applications
Authors: Veintemillas Sabino , Bouchet-Fabre Brigitte , Morales Maria Puerto , Leconte Yann , Costo R , Bonville Pierre , Herlin-Boime Nathalie C
Published: April 2011

Nanocomposite particles made from encapsulation of magnetic nanoparticles in an inorganic matrix have a real interest in biomedicine due to their high resistance against biodegradation compared with nanoparticles encapsulated in an organic matrix and little work has been published concerning such materials. In this work we use the laser pyrolysis method for the preparation of magnetic composites of Fe-based nanoparticles dispersed in silica and carbon. The precursor is an aerosol of a precursor which can be easily used in a safe way. Important advantages of the laser pyrolysis method are the reproducibility, simplicity (one step method) and continuity which allows producing significant amounts of nanoparticles. The short reaction times (ms) involved in the nucleation of the powders insure the nanometric particle size of both the magnetic component and the inorganic matrix.

This paper is focused on the synthesis and characterization of the Fe@SiO2 and Fe@C nanopowders generated by laser pyrolysis of ferrocene diluted in toluene and carried to the reaction zone in aerosol form. The silica coating was formed by the addition of tetraethoxysilane (TEOS) to the reactant. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), specific surface area determination (BET) and magnetic measurements. In the case of Fe@SiO2 the process generates rather homogeneous iron/magnetite particles smaller than 10 nm in diameter surrounded by a SiO2 coating of about 20 nm. In the case Fe@C the process generate iron based magnetic nanoparticles of complex composition smaller than 11 nm surrounded by a graphitic carbon layer of 50 nm. Stable aqueous dispersions at physiological pH were produced for both systems by means of strong oxidation in aqueous solutions, which is a very encouraging result for application in the field of living tissues.
Negative Refractive Index of Meta-materials at Optical Frequencies
Authors: Ramakrishna S. Anantha , Chakrabarti Sangeeta
Published: April 2011

Scaling the performance of metamaterials to obtain negative refractive index at optical frequencies has been of great interest. One of the great barriers to the scaling is that real currents cannot be driven at very high frequencies and one is more dependent on displacement currents to generate negative magnetic permeability. Moreover to keep the dimensions of the metamaterials physically accessible, the structural lengthscales of the metamaterials begin approach the wavelength of the radiation in free space and homogenisation is often questionable. Here we will show that metamaterials such as Split ring resonators in these high frequency limits exhibit complex behaviour. Magnetic activity and Negative refractive index behaviour can, indeed, be obtained at optical frequencies but will need to be interpreted very carefully. The plasmonic nature of the metallic system and excitation needs to be considered in detail.
Negative Index Metamaterials with Deeply Subwavelength Structural Dimensions from Near Infrared to Visible Based on Thin Filmsββ
Authors: Lomakin Vitaliy , Fainman Yeshaiahu , Shvets Gennady
Published: April 2011

Novel two and three-dimensional doubly negative metamaterials (DNM), viz. metamaterial with simultaneously negative permittivity, permeability, and index of refraction, are introduced. The metamaterials comprise deeply subwavelength periodic unit cells, can be tuned to operate in the near infra-red and visible spectra, and can be manufactured using standard nanofabrication methods with compatible materials. The DNMs' unit cell comprises an optically thin metal film sandwiched between two thin metal strips or patches residing at a small distance from the film. The cavity formed between the strips or patches supports resonances with magnetic and electric response that can be tuned to exist in overlapping frequency bands thus leading to the DNM operation.
Enhancement of Ferroelectricity and Magnetoelectric Effect of BiFeO3 Thin Films on Membrane Structure
Authors: Nakashima Seiji , Yun Kwi-Young , Nakamura Yoshitaka , Okuyama Masanori
Published: April 2011

Multiferroic BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/thick (200 μm) and membrane (15 μm) Si substrate by pulsed laser deposition (PLD) to confirm the influence of stress from substrate. Si membrane was obtained by etching using reactive ion etching (RIE) until thickness is to be 15 μm. The X-ray diffraction peaks of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane substrate slightly shift to lower angles, compared to those on Pt/TiO2/SiO2/Si (200 μm) substrate. Ferroelectric hysteresis loops were also measured at 150 K before and after Si etching by RIE. The BiFeO3 thin film on the Pt/TiO2/SiO2/Si (15 μm) membrane structure shows remanent polarization (Pr) of 95 μC/cm2 for a maximum applied voltage of 18 V, which is larger than Pr = 71 μC/cm2 of BiFeO3 thin film on Pt/TiO2/SiO2/Si (200 μm) substrate at the same measurement conditions. Under magnetic field of 1.1 T, remanent polarization (Pr) of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane structure increased from 95 μC/cm2 to 101 μC/cm2 at 150 K due to stress relaxation of BiFeO3 thin film.
Thermal Analysis at Low and High Temperature and Evidence of Structural Transition Induced by Praseodymium in SrTiO3
Authors: Durán Alejandro , Morales Francisco , Fuentes Luis , Castro Javier , Siqueiros Jesus
Published: April 2011

To explore the nature of ferroelectric behavior induced by Pr ion in the SrTiO3 ceramic, we brought together a combination of Synchrotron x-ray powder diffraction and thermal analysis. Rietveld analysis shows a clear peak splitting strongly suggesting a cubic-tetragonal structural transition when 15 % Pr substitutes the Sr site. To determine the temperature of the structural instability differential thermal analysis at high temperatures (30-900 °C) and specific heat at low temperatures (2-300 K) were performed. The difference in the heat capacity for Pr doped and undoped samples are very small. A plateau in Cp/T vs T at 110 K is a clear evidence of the competing effect of two kinds of order parameters, one represented by the polarization and the other by the rotation of the oxygen octahedral in the perovskite structure. Upon heating, DTA analysis shows an unexpected single endothermal broad anomaly at about 118 °C. The occurrence of this thermal anomaly could be related to displacive structural contributions providing unambiguous evidence of diffuse phase transition.
Molecular Beam Epitaxial Growth and Dielectric Characterization of Ba0.6Sr0.4TiO3 Films
Authors: Fisher P. , Skowronski M. , Salvador P. A. , Snyder M. , Xu J. , Lanagan M. , Maksimov O. , Heydemann V. D.
Published: April 2011

Ba0.6Sr0.4TiO3 films were grown by molecular beam epitaxy on MgO(001) and LaAlO3(001) substrates. The growth mode was determined to be two-dimensional by in-situ reflection high-energy electron diffraction. The films were structurally and dielectrically characterized ex-situ using X-ray diffraction, Rutherford backscattering spectrometry, and split cavity resonance mode dielectrometry. The structural and dielectric properties of the Ba0.6Sr0.4TiO3 film grown on MgO were determined to be inferior to the film grown on LaAlO3, as was indicated by the broader rocking curve (0.59 deg. vs. 0.17 deg.) and higher dielectric loss (0.29 vs. 0.12).
Conduction Characteristics of Charge Ordering Type Ferroelectrics,YFe2O4
Authors: Imamura Ken , Horibe Yoichi , Yoshimura Takeshi , Fujimura Norifumi , Mori Shigeo , Ikeda Naoshi
Published: April 2011

Electrical conduction properties of charge ordering type ferroelectrics YFe2O4 were investigated. YFe2O4 was synthesized in reduced atmosphere at 1200 °C. Oxygen partial pressure of the reduced atmosphere was controlled by the equilibrium state of CO and CO2. YFe2O4 is paramagnetic at room temperature and has Néel temperature around 250K. The Néel temperature was decreased with increasing the amount of oxygen deficiency. Moreover, YFe2O4 showed ohmic conduction from 260 to 100 K. The temperature dependence of the DC conductivity showed an inflection point at the Néel temperature, which indicated the development of charge ordering of Fe2+ and Fe3+ ions. From the complex impedance measurements, the equivalent circuits of YFe2O4 with different oxygen deficiency were determined at various temperatures.
Evaluation and Modeling of Power Generator with Bimorph PZT Cantilever
Authors: Shen Dongna , Ajitsria Jyoti , Choe Song-Yul , Kim Dong-Joo
Published: April 2011

Battery, the traditional power source in present wireless remote sensor systems, has large volume and requires large amount of maintenance. Therefore, piezoelectric power generator has been studied for a potential alternative to battery by scavenging or harvesting energy from its operating environment. The efforts for investigating such piezoelectric device have been especially enhanced by the miniaturization requirement and low energy consumption of advanced devices as well as the sufficient vibration energy sources and its high conversion efficiency. To utilize piezoelectric material as energy conversion transducer, the device should be designed to operate with high efficiency and simple configuration. PZT (Lead Zirconium Titanate) is an excellent candidate for energy conversion because of its large piezoelectric constant and coupling coefficient.

In this study, power generators based on bimorph cantilever structure were designed and fabricated using PZT ceramic benders due to accessible large strain or energy. The parameters influencing the output energy of piezoelectric bimorph cantilevers including the dimensions of the cantilever and the proof mass, the loading ways of the proof mass, and the resonant frequency of the cantilever were systematically investigated. The robustness of cantilever structure was also considered for implementing piezoelectric power conversion devices in harsh environments. The final optimal design was realized by considering the balance between the output power and the safety factor through numerical analysis. The energy density generated by the optimized piezoelectric devices was higher than 1 mW at 1-g vibration, which could be enough to operate microsensor systems. To broaden the operation conditions, multiple-resonant frequency device was also explored.
Comparison of Piezoelectric Materials for Vibration Energy Conversion Devices
Authors: Shen Dongna , Choe Song-Yul , Kim Dong-Joo
Published: April 2011

Piezoelectric materials have been investigated as vibration energy converters to power wireless devices or MEMS devices due to recent low power requirement of such devices and the development of miniaturization technology. It has shown the potential that piezoelectric power generator can be an alternative to the traditional power source-battery because of facile vibration sources in our environment and the potential elimination of maintenance required for large volume batteries. To date, PZT (Lead Zirconium Titanate) has been commonly exploited as a piezoelectric material for energy conversion since it can generate higher power density even at low-g (< 1 g) vibration environment. Its high fragility, however, can limit its applicability at high-g conditions. Therefore, other types of piezoelectric materials such as polymer and composite are necessary to investigate the applicability at severe vibration conditions. In this study, piezoelectric power generators based on cantilever beam structure were designed, optimized, and fabricated by considering matching the resonant frequency with environmental vibration, achieving maximum output power, and reaching maximum g-value without device failure. As piezoelectric materials, ceramic PZT, polymer PVDF (Polyvinylidene fluoride) and composite MFC (Macro Fiber Composite) were utilized. The energy conversion of all three types of generator devices was systematically evaluated. All three devices were measured to generate enough power density for providing electric energy to wireless sensor or MEMS device. The PZT device shows the highest output energy density and PVDF device has the highest durability to operate at high-g vibration condition.
Peculiar Features of the Dielectric Response in Lead Scandium Tantalate Pb(Sc1/2Ta1/2)O3 Thin Films
Authors: Brinkman Kyle , Tagantsev Alexander , Cherman Vladimir , Wang Yongli , Setter Nava , Kamba Stanislav , Petzelt Jan
Published: April 2011

An examination of the low temperature (20 K) dielectric permittivity revealed dispersion between the MHz and THz frequencies in both disordered and ordered Pb(Sc1/2Ta1/2)O3 (PST) thin films. The difference between the lattice contribution in the THz regime and that measured in the MHz regime at extremely low temperatures points to the peculiar contribution of polar regions which maintain their mobility on cooling. Experiments measuring the permittivity upon cooling under an electric bias field revealed an additional peculiar feature of polar regions in disordered PST thin films: the application of a DC field of 30kV/cm failed to induce a phase transition to a long range polar state.
Simultaneous Observation of Surface Morphology and Dielectric Properties Using Non-Contact Scanning Nonlinear Dielectric Microscopy with Atomic Resolution
Authors: Hirose Ryusuke , Cho Yasuo
Published: April 2011

Recently, we have developed Non-Contact Scanning Nonlinear Dielectric Microscopy (NC-SNDM) with a new height-control technique utilizing higher order nonlinear dielectric constant detection (ε(4) signal). In theoretically, NC-SNDM has quite high height sensitivity against the gap between tip and sample as well as STM technique and the simultaneous observation of the topography and ferroelectric polarization (local dipole moment) distribution with atomic resolution has been expected. To confirm such performance of NC-SNDM with atomic resolution, UHV-SNDM was developed and Si(111) cleaned surface was chosen as a specimen. As a result, we have succeeded in observing Si(111) 7×7 atomic structure. Moreover, distribution of tunneling current and lowest order nonlinear dielectric signal ε(3) could be observed simultaneously. To the best our knowledge, this is the first successful demonstration of the atomic resolution achievement in dielectric microscopy techniques.
Microwave Magneto-Electric Interactions in Multiferroics
Authors: Srinivasan Gopalan , Tatarenko A.S. , Fetisov Y. K. , Gheevarughese V. , Bichurin M.I.
Published: April 2011

Investigations on microwave magneto-electric (ME) interactions at 1-10 GHz have been carried out on yttrium iron garnet (YIG)-lead zirconate titanate (PZT) and YIG-lead magnesium niobate lead titanate (PMN-PT) bilayers. Ferromagnetic resonance is a powerful tool for such studies. An electric field E applied to the composite produces a mechanical deformation in PZT or PMN-PT, resulting in a shift in the resonance field for YIG. Information on the nature of high frequency ME coupling has been obtained from data on resonance field shift vs E. A cavity resonator or stripline structure was used. The measured ME interactions are in the range 1-5 Oe cm/kV. The coupling strength has been found to be dependent on magnetic field orientation. The strongest interaction is measured in YIG-PZT systems. The design and characterization of ferromagnetic resonance based, electric field tunable ME resonators and filters are discussed.
The Electronic Structure of 1,7-PCB10H11 Molecular Films
Authors: Balaz Snjezana , Boag Neil M , Platt Neil P , Dimov Dimtcho I , Brand Jennifer I , Dowben Peter A
Published: April 2011

The electronic structure and highest occupied to lowest unoccupied molecular orbital gap of undoped films of the molecular icosahedra of closo-1-phospha-7-carbadodecaborane (1,7-PCB10H11, meta-phosphacarborane) are reported. For 1,7-PCB10H11 adsorbed on Au and Ag, the Fermi level is placed closer to the lowest unoccupied molecular orbital than has been observed with closo-1-phospha-2-carbadodecaborane (1,2-PCB10H11, ortho-phosphacarborane) adsorbed on Au and Ag.
Dielectric Properties of PCB Embedded Bismuth-Zinc-Niobium Films Prepared using RF Magnetron Sputtering
Authors: Lee Seungeun , Lee Jung Won , Lee Inhyung , Chung Yul Kyo
Published: April 2011

Dielectric properties of bismuth-zinc-niobium oxide (Bi1.5Zn1.0Nb1.5O7, BZN) thin films have been investigated for embedded capacitor. Crystalline BZN has a pyrochlore structure in nature and shows a dielectric constant of ∼ 200 and very low leakage current when crystallized. Since the process temperature is limited to < 200 due to an organic based substrate in printed circuit board, as-deposited BZN film is composed of an amorphous phase, confirmed by XRD analysis. However, it shows remarkably high dielectric constant of 113. It makes BZN to be a proper candidate as a decoupling embedded capacitor in power delivery circuits. Effects of post treatment such as oxygen plasma treatment and low temperature thermal annealing on dielectric properties of BZN thin films are studied. By optimizing deposition conditions, amorphous BZN thin film is well processed in the current PCB process and provides a capacitance density as high as 218 nF/cm2 and leakage current less than 1 μA/cm2 at 3V.
Strategy for the Integration of PLZT Thin Films on Base-Metal Foils for High Voltage Embedded Passives
Authors: Ma Beihai , Balachandran U. , Kaufman David Y , Uprety Krishna
Published: April 2011

Evolution of electronic devices towards higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). A “film-on-foil” approach is the most viable fabrication method. A high permittivity of lead lanthanum zirconate titanate (PLZT) thin film was coated on nickel foil by chemical solution deposition. Such a prefabricated capacitor sheet can be embedded into a PWB. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. To eliminate this parasitic effect, conductive buffer layer of lanthanum nickel oxide (LNO) was coated by chemical solution deposition on nickel foil. We produced PLZT film-on-foil capacitors with capacitance densities as high as 1.5 μF/cm2 and breakdown field strength >1.4 MV/cm. With the desirable volumetric character, PLZT film-on-foil capacitors hold particular promise for use in high voltage embedded passives.
Layered Compound Semiconductor GaSe and GaTe Crystals for THz Applications
Authors: Mandal Krishna C. , Kang Sung H. , Choi Michael K.
Published: April 2011

The single crystal growth of layered semiconductors GaSe and GaTe by vertical Bridgman technique using zone refined selenium (Se), tellurium (Te) and high purity (HP) gallium (Ga) have been described. The grown crystals (2.5 cm diameter and ∼10 cm long) have demonstrated efficient broadband tunable THz emission and as sensitive THz detectors. The crystals have shown promising characteristics with good optical quality, high dark resistivity, wide band gap (GaSe-2.01 eV and GaTe-1.66 eV at 300 K), good anisotropic (parallel, p & perpendicular, pa) electrical properties (σ∥ vs σ⊥ and μ∥ vs σ⊥) and long term stability. Different steps involved in processing GaSe and GaTe crystals as THz sources and sensors are described.
Single-Mode Polymer Optical Fiber Sensors for Large Strain Applications
Authors: Kiesel Sharon M. , Peters Kara , Hassan Tasnim , Kowalsky Mervyn
Published: April 2011

This paper characterizes an intrinsic, single-mode, polymer optical fiber (POF) sensor for use in large-strain applications such as civil infrastructures subjected to earthquake loading or systems with large shape changes such as morphing aircraft. The opto-mechanical response was formulated for the POF including a second-order (in strain) photoelastic effect as well as a second-order (in strain) solution for the deformation of the POF during loading. It is shown that four independent mechanical and opto-mechanical constants are required for the small deformation regime and six additional independent mechanical and opto-mechanical constants are required for the large deformation regime. The mechanical nonlinearity of a typical polymer optical fiber was experimentally measured in tension at various loading rates. The secant modulus of elasticity measured at small strains, roughly up to 2% strain, was measured to be ∼4GPa whereas at larger strains, roughly up to 4.5% strain, the secant modulus was measured to be ∼4.8GPa. As the loading rate was increased the yield strain increased, ranging from ∼3.2% at 1mm/min to ∼5% at 305 mm/min.
CMOS-Compatible Through Silicon Vias for 3D Process Integration
Authors: Tsang Cornelia K. , Andry Paul S. , Sprogis Edmund J. , Patel Chirag S. , Webb Bucknell C. , Manzer Dennis G. , Knickerbocker John U.
Published: April 2011

As the limits of traditional CMOS scaling are approached, process integration has become increasingly difficult and resulting in a diminished rate of performance improvement over time. Consequently, the search for new two- and three- dimensional sub-system solutions has been pursued. One such solution is a silicon carrier-based System-on-Package (SOP) that enables high-density interconnection of heterogeneous die beyond current first level packaging densities. Silicon carrier packaging contains through silicon vias (TSV), fine pitch Cu wiring and high-density solder pads/joins, all of which are compatible with traditional semiconductor methods and tools. These same technology elements, especially the through silicon via process, also enable three dimensional stacking and integration. An approach to fabricating electrical through-vias in silicon is described, featuring annular-shaped vias instead of the more conventional cylindrical via. This difference enables large-area, uniform arrays to be produced with high yield as it is simpler to integrate into a conventional CMOS back-end-of-line (BEOL) process flow. Furthermore, the CTE-matched silicon core provides improved mechanical stability and the dimensions of the annular via allows for metallization by various means including copper electroplating or CVD tungsten deposition. An annular metal conductor process flow will be described. Through-via resistance measurements of 50, 90, and 150μm deep tungsten-filled annular vias will be compared. Two silicon carrier test vehicle designs, containing more than 2,200 and 9,600 electrical through-vias, respectively, were built to determine process yield and uniformity of via resistance. Through silicon via resistances range from 15-40 mΩ, and yields in excess of 99.99% have been demonstrated.
Exploration of the Scaling Limits of 3D Integration
Authors: Pozder Scott , Jones Robert , Adams Vance , Li Hui-Feng , Canonico Michael , Zollner Stefan , Lee Sang Hwui , Gutmann Ronald J. , Lu Jian-Qiang
Published: April 2011

Three dimensional (3D) wafer bonding is an emerging technology that may be used to increase transistor densities by stacking devices over devices. The alignment of the wafers and the devices on them is a function of the mechanical capability of the wafer to wafer alignment tool and the thermal conditions of each wafer when bonded. However, as bonded wafers are thinned to 1% or less of their starting thickness the processes of bonding and thinning as well as previous process history affect wafer planarity and silicon stress. The drive to vertically interconnect circuit blocks at the sub-micron scale requires a high density of vertical interconnects and thinning a wafer to less than 5 μm enables through wafer via processing at a scale found in the first layers of the interconnect stack. In this paper the measurement of wafer to wafer alignment was done by comparing a metal pattern on a face down bonded silicon on insulator (SOI) wafer to a complementary metal pattern on the bulk wafer to which it was bonded. The effect of aggressive thinning is evaluated using thinned back to face bonded SOI wafers with functional devices and face down bonded non-patterned SOI wafers thinned after bonding. The face up bonded SOI wafers with functional devices were temporarily bonded face down to a Si-wafer I, thinned to the buried oxide (BOX), face up bonded with benzocyclobutene (BCB) on a Si-wafer II, followed by release of the temporary bond and electrical test. Raman and XRD stress measurements of the non-patterned SOI wafer silicon 70 nm and 110 nm thick SOI Si were taken before and after thinning, and the radius of curvature of the SOI wafers and the bulk wafer substrates was monitored. Thermo-mechanical models of SOI Si stress and bonded wafer curvature are compared to the measured results.
Thermo-Mechanical Reliability of 3D-integrated Microstructures in Stacked Silicon
Authors: Wunderle Bernhard , Mrossko R. , Wittler O. , Kaulfersch E. , Ramm P. , Michel B. , Reichl H.
Published: April 2011

This paper investigates the thermo-mechanical reliability of inter-chip-vias (ICV) for 3D chip stacking after processing and under external thermal loads relevant for the envisaged field of application (mobile, automotive) by Finite Element simulation. First the materials are characterised by nano-indentation to determine elasto-plastic data. Finite Element simulations are used to reproduce these data and to extract local material properties like E-modulus and yield stress. Accumulated plastic strain is used as failure indicator under periodic thermal loading of an ICV. Geometrical, material and process-related parameters are varied to obtain first design guidelines for this new technology. The locations of stress and strain accumulation are given.
Three-Dimensional Integration of Silicon Chips for Automotive Applications
Authors: Weber Werner
Published: April 2011

Currently, 3D integration of semiconductor chips is introduced into high-volume products. While memory and communication will be leading fields of application, automotive will require specific non-standard solutions some of which are in research or development whereas others have already been introduced to production. This paper elaborates on the different opportunities and constraints of automotive applications, presents different technological options and discusses specific solutions considered in research or found in already existing products.
Current and Future Three-Dimensional LSI Integration Technology by “chip on chip”, “chip on wafer” and “wafer on wafer”
Authors: Bonkohara Manabu , Motoyoshi Makoto , Kamibayashi Kazutoshi , Koyanagi Mitsumasa
Published: April 2011

Recently the development of three dimensional LSI (3D-LSI) has been accelerated and its stage has changed from the research level or limited production level to the investigation level with a view to mass production. This paper describes the current and the future 3D-LSI technologies which we have considered and imagined. The current technology is taken our Chip Size Package (CSP) for sensor device, for instance. In the future technology, there are the five key technologies are described. And considering con and pro of the current 3D LSI stacked approach, such as CoC (Chip on Chip), CoW (Chip on Wafer) and WoW (Wafer on Wafer), We confirmed that CoW combined with Super-Smart-Stack (SSS™) technology will shorten the process time per chip at the same level as WoW approach and is effective to minimize process cost.
Low Temperature Copper-Nanorod Bonding for 3D Integration
Authors: Wang Pei-I , Karabacak Tansel , Yu Jian , Li Hui-Feng , Pethuraja Gopal G. , Lee Sang Hwui , Liu Michael Z. , Lu J.-Q. , Lu T.-M.
Published: April 2011

Wafer bonding is an emerging technology for fabrication of complex three-dimensional (3D) structures; particularly it enables monolithic wafer-level 3D integration of high performance, multi-function microelectronic systems. For such a 3D integrated circuits, low-temperature wafer bonding is required to be compatible with the back-end-of-the-line processing conditions. Recently our investigation on surface melting characteristics of copper nanorod arrays showed that the threshold of the morphological changes of the nano-rod arrays occurs at a temperature significantly below the copper bulk melting point. With this unique property of the copper nanorod arrays, wafer bonding using copper nanorod arrays as a bonding intermediate layer was investigated at low temperatures (400 °C and lower). 200 mm Wafers, each with a copper nanorod array layer, were bonded at 200 – 400 °C and with a bonding down-force of 10 kN in a vacuum chamber. Bonding results were evaluated by razor blade test, mechanical grinding and polishing, and cross-section imaging using a focus ion beam/scanning electron microscope (FIB/SEM). The FIB/SEM images show that the copper nanorod arrays fused together accompanying by a grain growth at a bonding temperature of as low as 200 °C. A dense copper bonding layer was achieved at 400 °C where copper grains grew throughout the copper structure and the original bonding interface was eliminated. The sintering of such nanostructures depends not only on their feature size, but also significantly influenced by the bonding pressure. These two factors both contribute to the mass transport in the nanostructure, leading to the formation of a dense bonding layer.
Multi-Stacked Flip Chips with Copper Plated Through Silicon Vias and Re-distribution for 3D System-in-Package Integration
Authors: Lee Shi-Wei Ricky , Hon Ronald
Published: April 2011

The study is a prototype design and fabrication of multi-stacked flip chip three dimensional packaging (3DP) with TSVs for interconnection. Three chips are stacked together to make a 3DP with solder bumped flip chips. TSVs are fabricated and distributed along the periphery of the middle chip. The TSVs are formed by dry etching, deep reactive ions etching (DRIE), with dimensions of 150 × 100 microns. The TSVs are plugged by copper plating. The filled TSVs are connected to the solder pads by extended pad patterns surrounding the top and the bottom of TSVs on both sides of the wafer for the middle chip. After pad patterning passivation and solder bumping, the wafer is sawed into chips for subsequent 3D stacked die assembly. Because the TSVs are located at the periphery of the middle chips and stretch across the saw street between adjacent chips, they will be sawed through their center to form two open TSVs (with half of the original size) for electrical interconnection between the front side and the back side of the middle chip. The top chip is made by the conventional solder bumped flip chip processes and the bottom chip is a carrier with some routing patterns. The three middle chips and top chip are stacked by a flip chip bonder and the solder balls are reflowed to form the 3DP structure. Lead-free soldering and wafer thinning are also implemented in this prototype. In addition to the conceptual design, all wafer level fabrication processes are described and the subsequent die stacking assembly is also presented.
Through-Silicon-Via Copper Deposition for Vertical Chip Integration
Authors: Kim Bioh
Published: April 2011

Consumers are demanding smaller, lighter electronic devices with higher performance and more features. The continuous pressure to reduce size, weight, and cost, while increasing the functionality of portable products, has created innovative, cost-effective 3D packaging concepts. Among all kinds of 3D packaging techniques, through-silicon-via (TSV) electrodes can provide vertical connections that are the shortest and most plentiful with several benefits (1). Connection lengths can be as short as the thickness of a chip. High density, high aspect ratio connections are available. TSV interconnections also overcome the RC delays and reduce power consumption by bringing out-of-plane logic blocks much closer electrically.

The technologies engaged with TSV chip connection include TSV formation, insulator/barrier/seed deposition, via filling, surface copper removal, wafer thinning, bonding/stacking, inspection, test, etc. Process robustness and speed of copper deposition are among the most important technologies to realize TSV chip integration. There are generally three types of via filling processes; lining along the sidewall of vias, full filling within vias, and full filling with stud formation above the via. Here, the stud works as a mini-bump for solder bonding. Two methodologies have been generally adopted for via filling process; (a) via-first approach : blind-via filling with 3-dimensional seed layer, followed by wafer thinning and (b) thinning-first approach : through-via filling with 2-dimensional seed layer at the wafer bottom after wafer thinning. Currently, the first approach is more popular than the second approach due to difficulty in handling and plating thinned wafers (2).

We examined the impact of varying deposition conditions on the overall filling capability within high aspect ratio, deep, blind vias. We tested the impacts of seed layer conformality, surface wettablity, bath composition (organic and inorganic components), waveform (direct current, pulse current, and pulse reverse current), current density, flow conditions, etc. Most deposition conditions affected the filling capability and profile to some extent. We found that reducing current crowding at the via mouth and mass transfer limitation at the via bottom is critical in achieving a super-conformal filling profile. This condition can be only achieved with a proper combination of aforementioned process conditions. With optimized conditions, we can repeatedly achieve void-free, bottom-up filling with various via sizes (5-40μm in width and 25-150μm in depth).
Research on Computer Optimization of Low-Cost Hydrogen Storage Alloy Containing Boron Prepared by Strip Casting and its Microstructure and Performance
Authors: Guo Hong , Weiping Han , Ximin Zhang , Likai Shi
Published: April 2011

A kind of low-cost hydrogen storage alloy containing B has been prepared by near rapid solidification strip casting. And computer optimization has been carried out with MASTER software through mode identification and neuro-network. The alloy microstructure, the alloy performance and the battery performance have been evaluated through optical microscope, TEM and X-ray diffraction. The results indicate that the alloy microstructure is fine columnar crystal and there exists the second phase of CeCo4B on the crystal interface, which increases the diffusion channels for hydrogen atoms and improves the alloy activation. The MmNi3.9Co0.37Mn0.4Al0.3B alloy has excellent performance at room, high and low temperatures prepared by strip casting.
Role of Annealing for Improving Hydrogen Storage Properties of Ti-Cr-V Alloy
Authors: Munekata Yasuhiro , Washio Kota , Suda Takanori , Hashimoto Naoyuki , Ohnuki Somei , Arashima Hironobu , Ito Hideaki
Published: April 2011

One of impotent materials issues of Ti-Cr-V based hydrogen storage alloys is to improve cyclic degradation of storage capacity, which has been assumed to be the effect of internal stress. We focused on the sub-micron structure of this material, which can be accumulated during cyclic use. We used 24Ti-36Cr-40V alloy for the specimens, after FZ melting. Powered samples were fabricated by mechanical grinding under Ar environment. Vacuum annealing was carried out for reducing residual stress and lattice defects. PCT properties were tested at 293 K under 4.5 MPa. XRD and TEM were carried out for important samples. In the first cycle, the annealing resulted in the increasing of storage capacity, but in the second cycle the improving was disappeared. Comparing microstructures with and without annealing, complex dislocation structures were observed after cyclic hydrogenation. It is notable that dislocation free structure was some time observed in the fine grains of less than 0.1 micron, which suggests the possibility of fine structure without defect accumulation.
Proton Diffusion in Hydrated Acceptor-Doped Barium Zirconate
Authors: Wilmer Dirk , Seydel Tilo , Kreuer Klaus-Dieter
Published: April 2011

Quasielastic neutron scattering experiments have been performed on proton-conducting hydrated Y-doped BaZrO3at temperatures between 473 K and 673 K. Quasielastic broadening is observed at all temperatures, but only at the higher ones the scattering exhibits the characteristics of the proton transport process. Attempts to interpret our data in the framework of the two-state model yield unconvincing results. A simpler approach using the isotropic Chudley-Elliott model yields reasonable values for the proton self-diffusivities but also unusually high values for the jump distance which are close to the mean distance between dopants.
Cell Performance Stability of HMFC using Ba(Ce1-xZrx)0.8Y0.2O3 Perovskite Type Proton Conductor as Electrolyte
Authors: Iijima Masahiko , Ito Naoki , Matsumoto Shinichi , Iguchi Satoshi
Published: April 2011

We have developed a new type of FC which shows high performance at intermediate temperatures to solve the disadvantage of using hydrocarbon as fuel to FC system. This new FC is an ultra-thin proton conductor electrolyte supported by a metal hydrogen membrane. We have named itHydrogenMembraneFuelCell

The HMFC using BaCe0.8Y0.2O3 (BCY) as the electrolyte and pure Palladium as the substrate exhibits a high cell performance of 2.7 A/cm2 @0.5V, 873K and 1.8 A/cm2 @0.5V, 673K. But the BCY cell performance drops rapidly during several hours. It was inferred that this phenomenon is caused by BCY electrolyte dissolved by hydrothermal reaction with H2O vapor which was generated by the fuel cell reaction.

We studied the possibility as HMFC electrolyte of Ba(Ce0.5Zr0.5)0.8YO3 (BCZY) and BaZr0.8Y0.2O3 (BZY) which are exchanged the B site of BCY perovskite ceramic from Ce to Zr to improve the resistance against the hydrothermal dissolution. BCZY and BZY confirmed the resistance against the hydrothermal dissolution improved compared with BCY by analyzing after the hydrothermal treatment. The BCZY cell shows the same level of the performance as the BCY cell and the performance stability has improved over the BCY cell.
Mixed-Conducting Membranes for Hydrogen Production and Separation
Authors: Balachandran U. , Ma Beihai , Lee Tae H , Song Sun-Ju , Chen Ling , Dorris Stephen E
Published: April 2011

Mixed-conducting oxides, possessing both ionic and electronic charge carriers, have found wide application in recent years in solid-state electrochemical devices that operate at high temperatures, e.g., solid-oxide fuel cells, batteries, and sensors. These materials also hold promise as dense ceramic membranes that separate gases such as oxygen and hydrogen from mixed-gas streams. We are developing Sr-Fe-Co oxide (SFC) as a membrane that selectively transports oxygen during partial oxidation of methane to syngas (mixture of CO and H2) because of SFC's high combined electronic and ionic conductivities. We have evaluated extruded tubes of SFC for conversion of methane to syngas in a reactor that was operated at ≈900°C. Methane conversion efficiencies were >90%, and some of the reactor tubes were operated for >1000 h. We are also developing dense proton-conducting oxides to separate pure hydrogen from product streams that are generated during methane reforming and coal gasification. Hydrogen selectivity in these membranes is nearly 100%, because they are free of interconnected porosity. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, we have developed cermet (i.e., ceramic-metal composite) membranes in which metal powder is mixed with these oxides in order to increase their hydrogen permeability. Using several feed gas mixtures, we measured the nongalvanic hydrogen permeation rate, or flux, for the cermet membranes in the temperature range of 500-900°C. This rate varied linearly with the inverse of membrane thickness. The highest rate, ≈32 cm3(STP)/min-cm2, was measured at 900°C for an ≈15-μm-thick membrane on a porous support structure when 100% H2 at ambient pressure was used as the feed gas.
Synthesis and Densification of Nanometric Ce0.8Sm0.2O1.9-δ
Authors: Esposito Vincenzo , Fronzi Marco , Traversa Enrico
Published: April 2011

Nanometric 20% molar Sm-doped ceria (SDC20) powders were synthesized by tetrametylethylen ammine (TMDA) co-precipitation method. SDC20 was sintered in several conditions to control the final microstructure. Fast firing and conventional sintering were performed. LiNO3was used as an additive to promote liquid phase sintering of ceria at low temperatures (900-1200°C). Powders and dense pellets were analysed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) measurements were performed on dense pellets in air to estimate the contribution of grain boundary and bulk to the electrical conductivity. Liquid phase sintering produced the densest samples with the highest conductivity.
Design of Anodes for IT SOFC: Effect of Complex Oxide Promoters and Pd on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets
Authors: Sadykov Vladislav A , Mezentseva Natalia V , Bunina Rimma v , Alikina Galina M , Lukashevich Anton I , Rogov Vladimir A , Moroz Ella M , Zaikovskii Vladimir I , Ishchenko Arcady , Bobrenok Oleg F , Smirnova Alevtina , Irvine John , Vasylyev Oleksandr
Published: April 2011

Effect of fluorite-like or perovskite-like complex oxide promoters and Pd on the performance of Ni/YSZ and Ni/ScSZ cermets in methane steam reforming or selective oxidation by O2 into syngas at short contact times was studied. Spatial uniformity of dopants distribution in composites was controlled by TEM combined with EDX, while the lattice oxygen mobility and reactivity was elucidated by CH4 and H2 TPR. Oxide promoters allow to operate even at stoichiometric H2O/CH4 ratio by suppressing coke deposition through modification of Ni surface, while doping by Pd ensures reasonable performance at moderate (∼550 °C) temperatures required for Intermediate–Temperature Solid Oxide Fuel Cells (IT SOFC).
Sintering Behavior and Phase Characterisation of Composite Perovskite/Fluorite Ceramics for Intermediate Temperature SOFCs and Oxygen Separation Membranes
Authors: Tangtrakam Natee , Swanson Matthew , Moran Peter , Kuebler Jakob , Kapat Jayanta , Orlovskaya Nina
Published: April 2011

The sintering behavior and structural changes of fluorite Gd0.2Ce0.8O2-δ(GDC) with one of three perovskites: LaMnO3 (LMO), (La0.7Sr0.3)0.98MnO3 (LSM) and La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) composite ceramics were studied. Sintering was carried out for two hours at five different temperatures: 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C. The highest sinterability has been found in LSFC + GDC. LSM + GDC appear to undergo two-step sintering mechanisms. Of all types of ceramics, only sintered LMO experiences a phase change, from rhombohedral R C to orthorhombic Pnma structure, with respect to its powder phase at sintering temperatures ≥1200 °C. The transition is notably suppressed when LMO is part of an LMO + GDC composite. GDC in a fluorite and/perovskite composite, when sintered, undergoes a temperature-dependent expansion in its unit cell that is not observed in pure GDC ceramics. This structural change will impact the function of composite ceramics as a fuel cell cathode, or oxygen separation membranes.
Electrochemical Properties of Nanocrystalline Y2-xPrxRu2O7 Pyrochlore for Electrodic Application in IT-SOFCS
Authors: Abate Chiara , Duncan Keith , Traversa Enrico , Wachsman Eric
Published: April 2011

Nanocrystalline powders of Y2-xPrxRu2O7 were prepared by a co-precipitation method, and were tested as electrode on ESB and GDC electrolytes by electrochemical impedance spectroscopy in the 300-750°C temperatures range. The electrode polarization was studied as a function of the amount of praseodymium in the cathode material. Both systems, Y2-xPrxRu2O7/ESB and Y2-xPrxRu2O7/GDC, showed a similar variation of the electrode area specific resistance (ASR). Y1.5Pr0.5Ru2O7 cathode material presented the best performance, with ASR value of 0.19 Ωcm2 on ESB and 4.23 Ωcm2 on GDC at 700°C. Furthermore, the change in ASR with the oxygen partial pressure suggested that the rate limiting step is the surface diffusion of the adsorbed oxygen at the electrode surface to the triple-phase boundary. Thus, the low value of resistivity of the Y1.5Pr0.5Ru2O7 in contact with ESB results from a much lower charge transfer resistance compared to the Y2-xPrxRu2O7/GDC system, and a partial solid diffusion at the interface electrode/electrolyte that increases the effective triple phase boundary length. This suggests that Y2-xPrxRu2O7 is a promising material for cathode application in ESB-based electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs).
Ab Initio Study of Oxygen-Vacancy Ordering in Oxygen Conducting Ba2In2O5
Authors: Lee Yueh-Lin , Morgan Dane
Published: April 2011

The thermodynamic properties of Ba2In2O5 are studied using Monte Carlo simulation of an ab initio based cluster expansion. The simulations predict a first-order orthorhombic to tetragonal phase transition, followed by a second-order tetragonal to cubic phase transition, which is in good agreement with experiments. It is predicted that the orthorhombic to tetragonal transition is associated with major disordering in the O(3) plane as well as some introduction of vacancies in the O(2) plane.
Nanosized Amorphous Materials as Anodes for Lithium Batteries
Authors: Fan Quan , Whittingham M. Stanley
Published: April 2011

The carbon anode presently used in commercial lithium ion batteries has a relatively low capacity and may pose safety problems particularly under fast charging. Nanosized amorphous materials have excellent electrochemical behavior when applied as anodes for lithium ion batteries; especially they have advantages over bulk materials on capacity retention and rate capability. The initial studies on some amorphous compounds are promising. A commercialized tin-cobalt-carbon amorphous material, which is composed of ∼5nm nanoparticles, shows a capacity retention of >350 mAh/g for 50+ cycles. Manganese oxide nanofibers were synthesized by polymer templated electrospinning followed by calcinations. The fibers have 200-500 nm diameter and the main composition is Mn3O4. The capacity remains 400 mAh/g for at least 50 cycles.
Room-Temperature Synthesis and Electrical Properties of La, Nd and Gd Apatite-type Silicates
Authors: Fuentes Antonio F. , Martinez-Gonzalez Luis G. , Moreno Karla J. , Rodriguez-Reyna Evelyn , Amador Ulises
Published: April 2011

We show in this paper the possibility of using mechanical milling to prepare apatite-type La, Nd and Gd silicates starting from stoichiometric mixtures of the constituent oxides. XRD patterns collected after grinding the starting mixtures for 9 hours contain only the characteristic reflections of the target materials with no other phase apparently present. Electrical conductivity data were successfully fitted to a Jonscher-type empirical expression with fractional exponent n included in the 0.35-0.75 range. Activation energies for oxygen migration were found to decrease as the size of the rare-earth cation increases. Therefore, the highest conductivity values were found for the apatite-type lanthanum silicate.
Characterization of the Carbon-Coating of LiFePO4 by Transmission Electron Microscopy and Raman Spectroscopy
Authors: Massot Michel , Zaghib Karim , Mauger Alain , Gendron François , Julien Christian M
Published: April 2011

We present the properties of the carbon layer deposited at the surface of the LiFePO4 particles. Characterizations include scanning electron microscopy, high-resolution transmission electron microscopy, and Raman scattering spectroscopy. Analuysis of Raman spectra reveals that the carbon deposit is hydrogenated with very small hydrogen/carbon ratio, so that it belongs to the family of the amorphous graphitic carbon. It is expected to have the same properties (small hardness, high electronic conductivity) that favor both the Li diffusion from the LiFePO4 bulk and the charge-discharge rate of the cell.