bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of OUM Phase Change Materials and Devices for High Density Nonvolatile Commodity and Embedded Memory Applications
Authors: Lowrey Tyler A. , Hudgens Stephen J. , Czubatyj Wally , Dennison Charles H. , Kostylev Sergey A. , Wicker Guy C.
Published: April 2011

Phase change memory devices were originally reported by S. R.Ovshinsky [1] in 1968. A 256-bit phase-change memory array based on chalcogenide materials was reported in 1970 [2] Recent advances in phase change materials, memory device designs, and process technology have resulted in significant advances in phase change device performance, and a new memory device, called Ovonic Unified Memory (OUM), has been developed. This paper will discuss various device and materials characteristics of OUM phase change memory materials of interest in applications for nonvolatile high-density memories. These materials are generally Te chalcogenide based, exploiting the congruent crystallization of the FCC phase and the associated reduction in resistivity that results from crystallization from the quenched amorphous state. Data storage is a thermally initiated, rapid, reversible structural phase change in the film. While rewriteable DVD disks employ laser heat to induce the phase change and modulate reflectivity, OUM technology uses a short electrical current pulse to modulate resistivity. The device geometry and thermal environment dictate the power and energy required for memory state programming.
Simulation of Crystallization Processes in Phase Change Optical Discs
Authors: Hyot Bérangère , Poupinet Ludovic , Desré Pierre
Published: April 2011

Future development of erasable phase change recording requires a thorough understanding of the fundamental mechanisms involved in crystallization processes to be able to forecast the behavior of a new material or to guide its optimization when submitted to specific conditions. In this paper, we emphasize that a predictive simulation is valuable only if a good modeling and accurate values of the involved parameters are used. We will present the main characteristics of our phase change model (effect of the short-pulse laser excitation, chemical influence of the materials in contact with the PC layer, stabilization of the amorphous state for very thin film layers) and we will discuss experimental and simulated crystallization behaviors.
TEM study of InSbTe crystal morphology as a function of crystallization conditions
Authors: Verheijen Marcel A. , Mijiritskii Andrei , Kooi Bart J.
Published: April 2011

In this work crystallization of an InSbTe alloy in Blu-ray Disc rewritable (BD-RE) media is studied using Transmission Electron Microscopy (TEM). Two different crystalline states can be formed in a thin InSbTe layer depending on crystallization conditions. These two states give rise to different reflectivity levels of the recording stack as well as a different level of normalized media noise. It is shown that the two states correspond to the same phase (R 3 m), but that they show clear differences in morphology as well as in texture.
Microgravimetric Corrosion Studies on UO2
Authors: Wegen Detlef H. , Gouder T. , Eckle M. , Wiss T. , Glatz J.-P.
Published: April 2011

For the first time at ITU electrochemical quartz crystal micro-balance has been used for the investigation of UO2 thin film oxidation. The combination of cyclic voltammetry with nano-gram weight change measurements in-situ has shown at least two steps in the initial stages of UO2 dissolution under oxidising conditions relevant to spent fuel storage.
Development of Siting Factors and Commencement of Open Solicitation for Preliminary Investigation Areas of HLW disposal in Japan
Authors: Tsuchi Hiroyuki , Kobayashi Masanori , Kondo Hirofumi , Koike Akihisa , Hatamoto Hiroki , Seo Toshihiro
Published: April 2011

The Nuclear Waste Management Organization of Japan (NUMO) has developed a set of “Siting Factors (SFs)” to guide choice of preliminary investigation areas (PIAs) of HLW disposal. A call for municipalities to volunteer PIAs was initiated, which included published SFs, in December 2002 as the first stage of a stepwise site selection procedure. This paper describes the way that SFs were developed and the outlines how they will be applied.
The Role of Water Diffusion in the Corrosion of the French Nuclear Waste Glass SON 68 under Solution Saturation Conditions
Authors: Ferrand Karine , Abdelouas Abdesselam , Grambow Bernd , Crovisier Jean-Louis
Published: April 2011

The alteration kinetics of the French borosilicate glass SON 68 have been investigated in a dynamic system at 50°C and 90°C under solution saturation conditions. The pH was adjusted to 4.8, 7.2 and 9.8 with addition of chemical buffers or/and by bubbling CO2 in solution. In all experiments, Li and Cs leaching seems to be controlled by a diffusion process. The Li- and Cs-concentrations were used to calculate the sum of ionic exchange and matrix dissolution rates of the glass while Mo-concentrations indicate matrix dissolution. The final leaching rates in saturation condition of Mo were in the order of 10–4–10- g.m-2.d-1 in good agreement with those given in literature for static tests. The glass surface was studied by scanning and transmission electron microscopy (SEM, STEM) for analysis of the corrosion products and by infrared spectroscopy (FTIR) for water speciation and concentration. A good inverse correlation between the water content and the alkali concentrations released from the glass has been obtained. About three hydrogen ions replaced one alkali ion. Modeling of the experimental data using GM 2001 model gives water diffusion coefficients between 10–20 and 10–22 m2.s-1.
Ceramics for the Immobilization of Plutonium and Americium: Current Progress of R&D of the V.G. Khlopin Radium Institute
Authors: Anderson Evgeniy B. , Burakov Boris E.
Published: April 2011

Since 1990, the Laboratory of Applied Mineralogy and Radiogeochemistry of the V.G. Khlopin Radium Institute (KRI) has been developing several different types of crystalline host-phases acceptable for the economically feasible and environmentally safe immobilization of actinide wastes. We proposed that ceramics that are based on host phases similar to naturally occurring accessory minerals including zircon, (Zr,Hf,…)SiO4; hafnon, (Hf,Zr,…)SiO4; baddeleyite (monoclinic zirconia), (Zr,Hf,…)O2; tazheranite (cubic zirconia), (Zr,Hf,Ca,Ti,…)O2; garnet, (Ca,Fe,Gd,…)3(Al,Fe,Si,…)5O12; perovskite, (Ca,Gd,…)(Al,Fe,Ti,…)O3, and monazite, (La,Ce,…)PO4, are the most efficient materials for actinide immobilization in deep geological formations. Solid solution of Pu in zirconia, (Zr,Pu)O2, could be used as a ceramic nuclear fuel that is competitive with mixed oxide fuel (MOX). To date, the following crystalline materials doped with 239Pu, 238Pu and 243Am have been successfully synthesized and studied at KRI: zircon; hafnon; cubic and tetragonal zirconia; monazite; aluminate garnet and perovskite. The maximum actinide loading was (in wt.% el.): 239Pu -37; 238Pu-10; 243Am-23. All Pu-Am-doped samples were made in air atmosphere under glove boxes conditions. Polycrystalline (ceramic) materials were made by sintering or melting of sol-gel, co-precipitated hydroxides, oxalates and phosphates or ground oxide precursors; single crystals were grown by a flux method. It was demonstrated that all ceramic samples obtained are characterized by high chemical durability and typical normalized actinide losses in deionized water at 90°C do not exceed 10−2–10−3 g/m2 (without correction for ceramic porosity). However, investigation of long-term behavior of ceramic waste forms requires taking into account the results of accelerated radiation damage study and modeling of ceramic alteration by underground solutions. The principal features of Pu-Am-doped samples obtained so far at KRI and their synthesis conditions are discussed.
Behavior of 238Pu-Doped Cubic Zirconia under Self-Irradiation
Authors: Burakov Boris E. , Yagovkina Maria A. , Zamoryanskaya Maria V. , Kitsay Alexander A. , Garbuzov Vladimir M. , Anderson Evgeniy B. , Pankov Alexey S.
Published: April 2011

To investigate the resistance of cubic zirconia to accelerated radiation damage, which simulates effects of long term storage, 238Pu-doped polycrystalline samples of cubic zirconia, (Zr,Gd,Pu)O2, were obtained and studied using X-ray diffraction analysis (XRD), electron probe microanalysis (EPMA), optical and scanning electron microscopy (SEM), and modified MCC-1 static leach test. The ceramic material was characterized by the following chemical composition (from EPMA in wt.% element): Zr = 50.2, Gd = 15.4, Pu = 12.2. This corresponds to the estimated formula, Zr0.79Gd0.14Pu0.07O1.99. The content of 238Pu estimated was approximately 9.9 wt.%. The XRD measurements were carried out after the following cumulative doses (in alpha decay/m3 × 1023): 3, 27, 62, 110, 134, 188, 234, and 277. Even after extremely high self-irradiation, cubic zirconia retained its crystalline structure. All XRD analyses showed no phases other than a cubic fluorite-type structure. The following results of normalized Pu mass loss (NL, in g/m2, without correction for ceramic porosity) were obtained from static leach tests (in deionized water at 90°C for 28 days) for 4 cumulative doses (in alpha decay/m3 × 1023):

The results obtained confirm the high resistance of cubic zirconia to self-irradiation. This allows us to consider zirconia-based ceramic as the universal material that is suitable for actinide transmutation and geological disposal.
Study of the Effects of Potential Impurities from Actinide Flux on the Zirconolite Microstructure
Authors: Leturcq G. , Auzemerie B.
Published: April 2011

Zirconolite ceramics are candidate hosts for the containment of minor actinides from the reprocessing of spent fuel in France. Although actinide-doped or rare earth-doped zirconolite ceramics have been successfully produced from pure chemical precursors, there has been little focus on the effect of impurities on the zirconolite microstructure. However, this aspect is crucial for technical feasibility to guarantee a microstructure acceptable for nuclear waste management needs.

First, chemical elements from the reprocessing process that could enter into the actinide flux as impurities were listed. We considered rare earths, zirconium, platinoids (Ru, Rh, Pd), molybdenum, barium, cadmium, silver, caesium, iron, and strontium. As we know rare earths and zirconium entering into the zirconolite microstructure they were not included in the study. For each other impurity listed, a zirconolite batch containing 1 wt% oxide impurity, and enriched in Nd simulating minor actinides, was synthesised then examined by SEM. Impurities were then categorised into those digested into the zirconolite microstructure, those partially digested into the zirconolite microstructure but also forming their own phases, and those that did not enter into zirconolite and formed their own separate phases.

A sample was then produced containing all the impurities, to assess any interference effects. Three minor phases were observed: barium molybdenum oxide, noble metal alloy and zirconium titanium dioxide. These minor phases should not decrease the chemical durability of the ceramic, and therefore, we can conclude that zirconolite is not seriously affected by the impurities introduced.
Measurement of Dissolution Rates of UO2 Matrix with the Isotope Dilution Method
Authors: Ollila K. , Oversby V.
Published: April 2011

The objective of this work was to measure the actual rates of matrix dissolution of UO2 in synthetic groundwater by using an isotope dilution method to provide a quantitative estimate of precipitation effects. A preliminary series of tests was performed under oxidising conditions, in contact with air. The second series of tests was under reducing conditions produced by actively corroding iron. The solid phases were fragments of unirradiated fuel pellets and intact pellets. The aqueous phase was a dilute, synthetic groundwater - so-called modified Allard water that is buffered by sodium bicarbonate/carbonate. This paper gives results for the experiments under oxidising conditions and preliminary tests under reducing conditions. In contact with air, the U concentrations reached higher levels than measured in previous experiments with spent fuel or with UO2 pellets. The comparison of the U concentrations calculated from isotopicratios with the experimental results suggests precipitation has begun at later stages of restarted tests. The measurements in the presence of actively corroding iron gave very low concentrations in the aqueous phase. At contact times longer than one week, all U seemed to disappear from solution and sorb or precipitate on UO2 or Fe surfaces in the test vessel.
Representation of Fracture Zone Interpretation Uncertainty in 3D Geological Models of the Mizunami Underground Research Laboratory, Japan
Authors: White Matthew J. , Saegus Hiromitsu
Published: April 2011

The Japan Nuclear Cycle Development Institute (JNC) is undertaking research into the deep geological environment in Japan in the Tono area of Japan. In the Mizunami Underground Research Laboratory (MIU) Project, located in the Tono area, JNC is carrying out surface-based investigations and will excavate an Underground Research Laboratory (URL) in order to establish comprehensive techniques for investigating and characterising the geological environment. The MIU Project focuses on the investigation of the granitic rocks of the Toki Granite. The geological structure and hydrogeological properties of the Toki Granite are closely affected by the regional fracture zones and faults. The interpretation of these features is undertaken in 3D and directly linked into 3D hydrogeological models. Significant uncertainty exists in the 3D interpretation of the fracture zones, and geologists must make several assumptions regarding the 3D structure in order to develop the 3D interpretation. In order that these assumptions are communicated to the hydrogeologists, a methodology has been developed for representing uncertainty in the 3D geological models. An important part of the uncertainty representation, is the development of a fracture zone classification in which the uncertainty in both the presence and the geometry of the fracture zone is assigned. Other elements include the development of alternative models, visualisation of raw data, development of conceptual models, development of bounding models, and suitable quality assurance and archiving of modelling projects.
Mineralogical Characterisation of Sediments at the Drigg Low Level Radioactive Waste Disposal Site and the Influence on Groundwater Chemistry
Authors: Randall M. G. , Trivedi D. P. , Graham J. , Small J. S. , Hughes C.
Published: April 2011

Petrographic microscopy, scanning and transmission electron microscopy, X-ray diffractometry, surface area and cation exchange analyses have been undertaken on a suite of ‘bulk’ and size separated sediment fractions from the Drigg site. The data indicate a complex phyllosilicate assemblage consisting of illitic and vermiculite material derived from the complex weathering history of the siliceous, micaceous, feldspathic and chloritic parent clasts. Coarse grains range from clean fresh looking ‘polished’ clasts to heavily coated with iron oxides and oxyhydroxides. The surfaces of most igneous clasts (granites and volcanics) are usually highly altered to micaceous (‘illitic’), chloritic and vermiculitic clays. Carbonates, such as calcite, dolomite and siderite, are present, particularly in the more shallow formations. The properties of the sediments have a clear impact on the evolution of groundwater chemistry. Redox conditions are consistent with equilibrium between iron oxyhdroxides and siderite, both present in Drigg sediments. Drigg groundwater samples are close to equilibrium with calcite, which not only controls the concentration of dissolved calcium and bicarbonate ions, but also the groundwater pH. Concentrations of potassium and magnesium are controlled by ion exchange reactions, while both mineralogical and groundwater evidence show that some weathering of aluminosilicate minerals is occurring, although equilibrium is not reached.
Solubility of Plutonium in Water Containing Carbonate under Reducing Conditions
Authors: Ödegaard-Jensen Arvid , Albinsson Yngve , Nilsson Hans
Published: April 2011

In order to investigate the dissolution of plutonium(III) under reducing condition and in a carbonate rich water solid phases of plutonium hydroxide and carbonate were made. The still wet solid phases were placed in vessels which contained 1 M NaClO4. The atmosphere in the vessels was either H2 or a mixture of H2 and 0.03% CO2.

The preliminary results shows that after some time the plutonium concentration in the solutions reached a value between 10−9 M and 10−7 M. The pH in the solutions is dependent of the atmosphere. In a pure H2 atmosphere the pH is changing over time whereas in the H2+CO2 atmosphere the pH stays between 7 and 7.5. At pH 8 the total carbonate concentration in the water was between 10−4 M and 10−3 M. This is the same order of magnitude as the ground water surrounding the proposed repository.
Dissolution of Plutonium (III) Hydroxide at 50 bar H2
Authors: Nilsson Hans , Albinsson Yngve , Skarnemark Gunnar
Published: April 2011

In the proposed Swedish nuclear fuel repository, intended to be placed some 500 meters down in granitic bedrock, the aquatic conditions will be reducing. In order to investigate the plutonium dissolution properties under near repository conditions Pu(III) was prepared using H2bubbling in the presence of a platinum wire. The plutonium oxidation state was checked by spectrophotometry and a blue Pu(OH)3precipitate was produced using deoxygenated NaOH. During drying the precipitate turned brownish and was then put in 0.1 M NaCl in pressure vessels. X-ray powder diffraction (XPD) showed no crystallinity of the precipitate. Solubility experiments were performed in pressure vessels that have an insert of PEEK (polyether-etherketone) and two valves, one for gas application and one with a PEEK tube reaching down into the vessel content for sample withdrawal. A small piece of platinum wire was put in each vessel and 50 bar H2was applied. The pH was adjusted to range from about 3 to 10. All handling was performed in an inert gas (N2) glove box with active oxygen removal yielding oxygen concentrations of <10 ppm. The results after about one year showed concentrations from 10−8M to 10−5M at pH 10 and pH 3 respectively.
A New Modelling of the Kinetics of Uranium Dioxide Oxidation in Air
Authors: Desgranges L. , Poinssot C.
Published: April 2011

A finite difference based modelling of the oxidation of uranium oxide is presented. This modelling involves only oxygen diffusion from the atmosphere into the solid and then inside the solid described with Fick's law. Some calculations performed with this modelling evidenced that the shape of the weight gain curves observed experimentally could be reproduced. This modelling is compared to the formula previously used to interpret the thermograms.
Structural Analyses of Layer Structure in Na-Montmorillonite using NMR
Authors: Ohkubo Takahiro , Kanehashi Koji , Saito Koji , Ikeda Yasuhisa
Published: April 2011

The analyses of layer structure in Na-montmorillonite have been performed using 27Al MAS and 27Al Multi Quantum (MQ) MAS NMR techniques. In 27Al 5QMAS NMR spectra measured at higher magnetic field of 16.4 T, two peaks were observed at 74.2 and 62.9 ppm. Hence, it has been suggested that the 4-coordinated Al site in Na-montmorillonite has two different structures. For detail assignment of the two peaks due to such 4-coordinated Al sites in Na-montmorillonite, 27Al MAS NMR measurements have been carried out for Na-montmorillonites with different water contents. The ratio of two 4-coordinated Al sites was found to be affected by water in the interlayer space of Na-montmorillonite, because the area ratio of peaks corresponding to two 4-coordinated Al sites changes with the water content, i.e., the peak area at around 69 ppm is increased sensitively with an increase in water content. Moreover, Cross Polarization/MAS (CP/MAS) NMR measurements have been carried out. As a result, the enhancement of peak at around 69 ppm was observed. Therefore, the two peaks observed by 27Al 5QMAS methods are assigned to AlO4 in the vicinity of water bound to tetrahedral sheets and the remote AlO4 from such water, respectively.
Fluid Flow and Solute Transport though a Fracture Intersecting a Canister - Analytical Solutions for the Parallel Plate Model
Authors: Liu L. , Neretnieks I.
Published: April 2011

In this paper, we are concerned with a specific scenario where a large fracture intersects, at its center, a canister that contains spent nuclear fuel. Assuming that a nuclide is free to release from the canister into groundwater flowing through the fracture, a detailed formulation of the volumetric flow rate and the equivalent flow rate are made for the parallel plate model. The formulas proposed have been validated by numerical examinations; they are not only simple in forms but also universal in applications where the flow may be taken normal, inclined or parallel to the axis of the canister. Of great importance, they provide a convenient way to predict the average properties of fluid flow and solute transport through a single fracture with spatially variable apertures.
Application of the M3 code for modelling groundwater chemistry
Authors: Laaksoharju Marcus , Gascoyne Mel , Gurban Ioana
Published: April 2011

The need to decode the complex groundwater information in terms of origin, mixing (transport) and reactions at site scale, necessitated the development of a new modelling tool. This new modelling concept was named M3 (Multivariate Mixing and Mass-balance calculations). Initially, the method quantifies the contribution from the flow system. Subsequently, contributions from reactions are calculated. The M3 code has been used for the following types of modelling: to calculate the mixing portions at different sites and to quantify the contribution from inorganic and organic reactions. For instance, the groundwaters at many sites have been calculated to consist of complex mixtures of different water types such as meteoric water, biogenetically modified water, modern and ancient sea water, glacial meltwater and brine water. Examples from modelling of data from Äspö in Sweden, Oklo in Gabon and the URL in Canada are given.
Near-field/Far-field Interface of a Near-Surface Low-Level Radioactive Waste Site
Authors: Beadle I. R. , Graham J. , Boult S. , Hand V. L. , Warwick P. , Randall M. G. , Trivedi D. P. , Humphreys P. N.
Published: April 2011

Experimental and Modelling studies have been used to investigate the biogeochemical processes occurring at the interface zone between the near-field and far-field of the Drigg Low-Level radioactive Waste (LLW) trenches. These have led to a conceptual model of interface biogeochemistry, which has subsequently been modelled by the BNFL code known as the Generalised Repository Model (GRM). GRM simulations suggest that as organic rich leachate migrates into the far-field, iron III minerals such as iron hydroxide will dissolve, and reduced iron minerals such as siderite will precipitate due to microbial processes. Batch and column experimental studies have verified this conceptual understanding. Some unexpected processes, such as the presence of nitrate enhancing sulphate reduction, were also observed
Geochemical Model of the Granite-Bentonite-Groundwater at Äspö (LOT Experiment)
Authors: Domènech C. , Arcos D. , Bruno J. , Karnland O. , Muurinen A.
Published: April 2011

A geochemical modelling of one of the experimental parcels of the LOT experiment (Äspö, Sweden) is presented. The model consists on a 2D reactive transport model of a perpendicular section of the experimental borehole with a stationary temperature gradient ranging from 130 to 15°C. The results of the model show that temperature has an important effect on the geochemical evolution of the system. Due to the temperature effect, anhydrite replaces gypsum and hematite precipitates instead of Fe(OH)3(am). Calcite and siderite dissolve in the warmer part of bentonite; whereas a major replacement of Na by Ca in the bentonite takes place close to the bentonite-granite boundary. pH is buffered by the equilibrium with calcite, although the effect of temperature leads to a decrease in pH.
Modeling of Aluminum Induced Lateral Crystallization of Hydrogenated Amorphous Silicon
Authors: Abbasi Mohammad Saad , Abu-Safe Husam , Naseem Hameed , Brown W. D.
Published: April 2011

Metal induced lateral crystallization (MILC) of hydrogenated amorphous silicon (a-Si:H) was studied and a model was developed based on the resistance measurement of the films. Hydrogenated amorphous silicon films of 300 nm thickness were deposited using plasma enhanced chemical vapor deposition (PECVD) on oxidized p-type (100) silicon wafers. Thermally evaporated 200 nm thick aluminum layer was deposited over amorphous silicon and patterned using photolithography. The samples were annealed at different temperatures for different time periods. After annealing the resistance of amorphous silicon between aluminum pads was measured. Based on these measurements, a model was developed to predict the lateral crystallization velocity. In this model, the resistance change due to loss of hydrogen from the film was also taken into account. For this purpose, another set of experiments was conducted. In this set, hydrogenated amorphous silicon films of 300 nm thickness were deposited on Corning 7059 glass. The samples were annealed for different period of time at different temperatures. After annealing, parallel bars of silver paint were formed on the samples and the resistance of each sample was measured. The theoretically determined lateral crystallization velocity was verified using optical microscope observations and X-ray diffraction analysis and was found to be in close agreement.
Phase diagram and microstructure of microcrystalline and amorphous silicon: a numerical growth simulation
Authors: Bailat Julien , Vallat-Sauvain Evelyne , Vallat André , Shah Arvind
Published: April 2011

Growth dynamics and microstructure of thin-film silicon simulated by a 3D dynamical numerical model are investigated. The model, recently introduced, is characterized here with its phase diagram. It reproduces the main features of the growth and microstructure of thin film silicon: amorphous to crystalline phase transition, conical/columnar shape of the conglomerates of nanocrystals, surface roughness evolution of the layer. It is observed that preferential etching of the amorphous silicon is sufficient to reproduce qualitatively the surface evolution observed experimentally. In the presence of preferential etching, nucleation of the microcrystalline phase in the simulated layers always coincides with a surface roughness increase as observed experimentally. This model opens new perspectives for the simulation of thin-film microstructure and surface morphology.
An Investigation of Silicon Oxide Thin Film by Atomic Layer Deposition
Authors: Lee Joo-Hyeon , Han Chang-Hee , Kim Un-Jung , Park Chong-Ook , Rha Sa-Kyun , Lee Won-Jun
Published: April 2011

SiO2 thin films were prepared on p-type Si (100) substrates by atomic layer deposition (ALD) using SiH2Cl2 and O3(1.5 at.%)/O2 as precursors at 300. The growth rate of the deposited films increased linearly with increasing amount of simultaneous SiH2Cl2 and O3 exposures, and was saturated at about 0.35 nm/cycle with the reactant exposures of more than 3.6×109L. A larger amount of O3/O2 than that of SiH2Cl2 was required to obtain a saturated deposition reaction. The composition of the deposited film also varied with O3/O2 exposure at a fixed SiH2Cl2 exposure. The Si/O ratio gradually decreased to 0.5 with increasing amount of O3/O2 exposure. Finally, we also compared the physical and electrical characteristics of the ALD films with those of the films deposited by conventional chemical vapor deposition (CVD) methods. In spite of low process temperature, the SiO2 film prepared by the ALD method was in wet etch rate, surface roughness, leakage current and breakdown voltage superior to that by other several CVD methods.
Development of Top-Gate Nanocrystalline Si:H Thin Film Transistors
Authors: McDonald Jarrod , Dalal Vikram L. , Noack Max
Published: April 2011

We report on the growth and fabrication of top gate thin film transistors at low temperatures in nanocrystalline Si:H. The nanocrystalline Si:H was deposited using a VHF-PECVD plasma process at 45 MHz in a diode reactor. The material was deposited from a mixture of silane and hydrogen at a temperature of 250-300°C. Higher temperatures resulted in a loss of hydrogen from the material. The properties of the nanocrystalline Si:H were studied using x-ray diffraction and Raman spectroscopy. The material showed a high ratio (3.8) between the crystalline and amorphous peaks in the Raman spectrum. X-ray diffraction data showed the films to be predominantly oriented in <111> direction, and the grain size estimated from Scherer's formula was in the range of 12-15 nm. The doping of the material could be changed by introducing ppm levels of Boron or Phosphorus. The as-grown material was generally n type. By adding controlled amounts of B, the material could be made p type. The devices made were n-channel MISFET's with p body. The n+ source and drain layers were made from amorphous Si:H. A systematic investigation of the appropriate oxide/nitride layer to be used was undertaken. The nitride layers were grown at 250-300°C using mixtures of silane and ammonia, with a high degree of dilution by helium. The presence of helium dilution, along with post-deposition passivation by a hydrogen plasma, was found to produce reproducible, low interface defect density nitride materials. Interface state densities were measured using capacitance spectroscopy at different frequencies and temperatures and found to be in the range of 4.5x1011/cm2-eV. The breakdown strength of the nitride was measured and found to be 4 MV/cm. Proof-of-concept TFT devices were fabricated using reactive ion etching. The threshold voltage was in the range of 13-15 V, and the on/off ratio was in the range of 103.
Influence of catalyzer area and design on the growth of intrinsic hot-wire CVD thin-film silicon for photovoltaic applications
Authors: Kupich Markus , Grunsky Dmitry , Hofferberth Bernd , Schröder Bernd
Published: April 2011

Recently, hot-wire deposited microcrystalline silicon has attracted increasing attention. The use of hot-wire deposited intrinsic μc-Si:H for high efficiency solar cells was demonstrated by Klein et al. [1]. Integration of high-quality intrinsic μc-Si:H into all-hot-wire nip solar cells, prepared close to the transition to amorphous growth using a tantalum catalyzer, resulted in initial and stable efficiencies of 5.4 % on simple stainless steel substrates [2]. However, the deposition rates for the absorber material in both cases remained low, at values around 1 Å/s.

In the present study we report on the dependence of deposition rate and material quality on the design and area of the tantalum catalyzer. It was found that different filament geometries require considerable changes in certain deposition conditions to optimize material properties. So, for example, enlarging the catalyzer surface made it necessary to decrease the hydrogen dilution of the process gas, in order to obtain the desired microcrystalline material close to the phase transition. These changes might be understood in terms of alterations of the gas decomposition relations on the catalyzer surface. For these modified conditions, deposition rates in the range of 2.5-10 Å/s could be achieved for μc-Si:H due to the fact that a higher silane fraction of the process gas could be used. For different wire geometries, the optimized intrinsic layers were incorporated into solar cells. Using a catalyzer with modified geometry and enlarged surface area, conversion efficiencies of ν = 4.4 % could be achieved for all-μc-Si:H, all-HWCVD solar cells at a rate of about 3 Å/s.
Measurement of the Electric Potential on Amorphous Silicon and Amorphous Silicon Germanium Alloy Thin-Film Solar Cells by Scanning Kelvin Probe Microscopy
Authors: Jiang C.-S. , Moutinho H. R. , Wang Q. , Al-Jassim M. M. , Yan B. , Yang J. , Guha S.
Published: April 2011

We report on direct measurements of surface potentials on cross sections of a-Si:H and a-SiGe:H n-i-p solar cells using scanning Kelvin probe microscopy. External bias voltage (Vb)induced changes in the electric field distributions in the i layer were further deduced by taking the derivative of the Vb-induced potential changes. This procedure avoids the effect of surface charges or surface Fermi-level pinning on the potential measurement. We found that the electric field does not distribute uniformly through the i layer of a-Si:H cells, but it is stronger in the regions near the n and p layers than in the middle of the i layer. The non-uniformity is reduced by incorporating buffer layers at the n/i and i/p interfaces in the a-Si:H solar cells. For a-SiGe:H solar cells, the electric field at the p side of the i layer is much stronger than at the n side and the middle. The non-uniformity becomes more severe when a profiled Ge content is incorporated with a high Ge content on the p side. We speculate that the increase in defect density with increasing of Ge content causes charge accumulation at the i/p interface.
Electric-Field Dependence of Photocarrier Properties in the Steady-State Photocarrier Grating Experiment
Authors: Brüggemann R. , Badran R.I.
Published: April 2011

We apply an experimental variation of the steady-state photocarrier grating technique by monitoring the photoresponse at higher electric fields and thus changing from diffusion to drift determined transport. Evaluation of the field-dependen experimental data is achieved with the analysis by Abel et al. [C.-D. Anel, G.H. Bauer and W. Bloss, Philos. Mag. B 72, 551 (1995)]. We study the photoelectronic properties of microcrystalline silicon samples and deduce the minority carrier diffusion length. From the variation in electric field the trapped charge density, responsible for charge neutrality under illumination, can also be determined. Thus additional information is gained which can be related to the density of states in the material.
Boron Diffusion and Silicon Self-Interstitial Recycling between SiGeC layers
Authors: Carroll M. S. , Sturm J. C.
Published: April 2011

Substitutional carbon is known to locally reduce silicon self-interstitial concentrations and act as a barrier to self-interstitial migration through the carbon rich regions. A silicon spacer between two carbon rich SiGe layers is fabricated in this work to examine self-interstitial generation in a region that is isolated from self-interstitial formation at the surface or in the silicon bulk. Boron marker layers above, below and in between two SiGeC layers are used to monitor the self-interstitial concentration between the substitutional carbon. No evidence of self- interstitial depletion in the silicon spacer is observed, despite annealing in conditions believed sufficient to allow the self-interstitials to reach and react with surrounding substitutional carbon. Simulations of the self-interstitial and carbon indicate that the silicon self interstitial concentration in the spacer layer can be sustained in part due to a silicon self-interstitial recycling process through a reverse “kick-out” reaction.
Suppression of Ni Silicide Formation by Se Passivation of Si(001)
Authors: Shanmugam Janadass , Coviello Michael , Udeshi Darshak , Kirk Wiley P. , Nano Meng Tao
Published: April 2011

Valence mending of a semiconductor surface, such as the Se-passivated Si(001) surface, improves the chemical and thermal stability of the surface as compared to the bare Si(001) surface. In this paper, we report the suppression of Ni silicide formation between Ni and Si(001) through monolayer passivation of Si(001) by Se. Ni was deposited on both Se-passivated and bare Si(001) surfaces. The samples were annealed at temperatures from 400°C to 700°C. Cross-sectional TEM (Transmission Electron Microscopy) revealed that Ni on bare samples reacted with Si at 400°C and formed silicide, whereas Ni on Se-passivated samples did not react with Si at 500°C. Surface composition analysis by XPS (X-Ray Photoelectron Spectroscopy) showed pure Ni surface on Se-passivated samples annealed at 400°C and 500°C, but silicide surface on bare samples annealed at the same temperatures. Hence, Se passivation suppresses the formation of Ni silicide on the Si(001) surface by over 100°C as compared to the bare Si(001) surface. These results may have important implications in source/drain engineering in sub-100 nm Si CMOS (Complementary Metal Oxide Semiconductor) devices.
The Use of SiGe Barriers During the Formation of p+ Shallow Junctions by Ion Implantation
Authors: Thompson Phillip E. , Bennett Joe , Felch Susan
Published: April 2011

Ultra-shallow p+ junctions are required for next generation electronics. We present a technique for the formation of ultra-shallow p+ junctions that increases the thermal stability of the junctions formed by ion implantation. By using a 10 nm Si1−xGex barrier layer, the diffusion of B is inhibited during high temperature processes. Alloys having a composition from x = 0 to 0.4 were investigated and it is shown that the most effective barrier had the maximum Ge fraction. The junction depth decreased to 36.7 nm for a 5×1015/cm2 1kV BF3 plasma implant spike annealed at 1050°C, compared to a junction depth of 48 nm for a Si control sample having the identical implant and anneal. It is hypothesized that the inhibition of B diffusion in the alloy layer is caused by a reduction of the Si self-interstitials in the alloy.
Lattice strain and composition of Boron-Interstitial Clusters in Crystalline Silicon
Authors: Salvador D. De , Bisognin G. , Napolitani E. , Aldegheri L. , Drigo A.V. , Carnera A. , Mirabella S. , Bruno E. , Impellizzeri G. , Priolo F.
Published: April 2011

In this work we have investigated the average composition of Boron Interstitials Clusters (BICs) and the strain induced in the Si crystal by BICs. We have formed BICs by Si implantation and subsequent annealing of two Si samples, grown by molecular beam epitaxy, containing thin buried layers doped with different B concentrations (1019 and 1020at/cm3). By B chemical profiles diffusion analysis, we have extracted the doses of Si self-interstitials (I) and Boron atoms trapped at the BICs. The B/I stoichiometric ratio is about 1 for the low B concentration and about 3.5 for the high B concentration sample. High-resolution x-ray diffraction analyses provided an estimate of strain profile. While in the low B concentration sample no appreciable strain was detected after BIC formation, at the higher B concentration we found that the tensile strain present in the as grown B doped layer changes to a strong compressive strain as a consequence of BICs formation. For this kind of clusters, the mean volume expansion with respect to the Si matrix is of (29 ± 6) Å3 for each B atom trapped at the BICs.
Effect of Annealing on the Structural, Mechanical and Tribological Properties of Electroplated Cu Thin Films
Authors: Shukla P. , Sikder A. K. , Zantye P.B. , Kumar Ashok , Sanganaria M.
Published: April 2011

The increasing demand for faster and more reliable integrated circuits (ICs) has promoted the integration of Copper-based metallization. Electroplated Cu films demonstrate a microstructural transition at room temperature, known as self annealing. In this paper we intend to investigate the annealing behavior of electroplated Cu films grown on a seed Cu layer on top of the barrier layers over a single crystal silicon substrate. All the samples were undergone through a multistep annealing process. Grazing incident x-ray diffraction pattern shows stronger x-ray reflections from Cu (111) and (220) planes but weaker reflections from (200), (311) and (222) planes in all the electroplated Cu samples. Transmission electron microscopy was performed on the cross section of the samples and the diffraction pattern showed the crystalline behavior of both seed layer and electroplated Cu. Nanoindentation was performed on all the samples using the continuous stiffness measurement (CSM) technique and it was found that the elastic modulus varies from 110 to 130 GPa while the hardness varies from 1 to 1.6 GPa depending on the annealing conditions. The tribological properties of all the copper films were also measured using the Bench Top CMP tester. Subsequently, Nanoindentation was performed on the samples after polishing the top surface in order to investigate the work hardening and an increase in hardness and modulus was observed. Finite Element Modeling was performed in order to investigate the stress behavior during nanoindentation.
Morphology of Ti37Al63 Thin-Films Deposited by Magnetron Sputtering
Authors: Theodore N. David , Kim Hyunchul C. , Gadre Kaustubh S. , Mayer James W. , Alford Terry L.
Published: April 2011

TiAl based thin-films possess high oxidation-resistance and high melting points, making them possible candidates for application in electronics. The behavior of the films upon exposure to various temperatures is of interest for such application. In the present study, Ti37Al63 thin films were deposited onto SiO2 substrates using RF magnetron sputtering from a compound target. Anneals were performed in vacuum at temperatures ranging from 400 °C to 700 °C. The phases and microstructural behavior of the films were evaluated as a function of annealing. Microstructural behavior was correlated with resistivity changes in the films. The behavior of Ti-Al films as potential under-layers for silver metallization was also evaluated. The Ti-Al was observed to enhance the thermal stability of pure Al thin-films. The results are relevant for potential application of the films to electronics.
3-dimensional evaluation of nm-pores in porous low-k films using TEM stereoscopic / electron tomographic observation method
Authors: Shimanuki J. , Inoue Y. , Shimada M. , Ogawa S.
Published: April 2011

Stereoscopic and electron tomographic observation methods using Transmission Electron Microscope (TEM) were examined to characterize three-dimensionally a shape and size of pores and spatial distribution in porous low dielectric constant (low-k) films. In a case of TEM observation, nm size pores in an amorphous film are difficult to be imaged since contrast from the amorphous layer affect the pore imaging. An optimum image capture method at a modified electron beam condition was studied in which the amorphous contrast from the porous low-k film is weakened to enhance scattering contrast from the pores and a matrix. As a result, a stereoscopic observation and 3-D reconstruction images clarified that the shape of pores was not spherical but distorted and almost pores were partially connected. For measuring pore size and spatial distribution, connected pores were segmented into smaller pores by separating at the narrowest part. From images after segmentation, it is indicated that there existed more and larger pores at interfaces than a center area. It was found that the pores did not homogeneously distribute in the film but concentrated at the interfaces.
Coupling Between Precipitation and Plastic Deformation During Electromigration in a Passivated Al (0.5wt%Cu) Interconnect
Authors: Barabash R.I. , Ice G.E. , Tamura N. , Valek B.C. , Spolenak R. , Bravman J.C. , Patel J.R.
Published: April 2011

In the present paper the evolution of the dislocation structure during electromigration in different regions along the Al(Cu) interconnect line is considered. It is shown that plastic deformation increases in the regions close to cathode end of the interconnect line. A coupling between the dissolution, growth and re-precipitation of Al2Cu precipitates and the electromigration-induced plastic deformation of grains in interconnects is observed. Possible mechanism of the Cu doping effect on the improved electromigration resistance of the Al(Cu) interconnects is discussed.
MEMS Metallization
Authors: Lohmann Christian , Gottfried Knut , Bertz Andreas , Reuter Danny , Hiller Karla , Kuhn Michael , Gessner Thomas
Published: April 2011

Silicon is the dominating material for the fabrication of MEMS devices, especially in high volume production. However, metals with their typical properties are used to enhance or enable the functionality of MEMS. In contrast to microelectronic technologies, not only the electrical but also the mechanical and optical behavior of metals could be helpful. New requirements in MEMS technologies demand optimized processes in metallization for the fabrication of microstructures.

This paper presents some metallization applications and related technology development in the field of MEMS.
Interface Nanochemistry in Mg-Doped Al2O3
Authors: Petot-Ervas Georgette , Baldinozzi Gianguido , Petot Claude , Graham Mike J. , Sproule Irwin G. , Tebtoub Moussa , Raulot Jean-Marc
Published: April 2011

In this experimental paper the influence of the grain size, of the thermal history and of the nominal composition on the nanochemistry at the interfaces in α-alumina submicronic powders are analyzed. The consequences on the physical and chemical properties are also discussed. Nanocrystalline Mg-doped α-alumina powders (550 and 1650 ppm by wt MgO) were prepared by the alum process. These powders (10-400 nm) were characterized by X-ray diffraction, SEM, TEM, XPS and surface area measurements (BET). In agreement with BET analysis, SEM observations show that the grain size increases with annealing time and annealing temperature. This effect is less pronounced in the highly doped samples. The less doped samples are also less aggregated and sintering bridges between the grains are still observed. XPS shows that Mg segregates at the periphery of the grains on a depth ≤0.5 nm. The dopant segregation is stronger when the nominal amount of Mg increases, leading eventually to the formation of MgAl2O4 precipitates near the grain surface. It is possible to observe an increase of the dopant segregation with grain size in the low Mg concentration powders. Other impurities like Si or higher cooling rates also favour this Mg segregation. However, the rate of cooling is so effective that it can overshadow all the other parameters (grain size, impurities,…), suggesting that this is certainly the key parameter for obtaining a perfect sintering of these ceramics, as experimentally shown.
Recrystallization Processing of Cold-Rolled Nickel
Authors: Baker I. , Chang H. , Li J.
Published: April 2011

We have examined the effects of isothermal annealing, at a variety of temperatures, and directional annealing, under a range of conditions, on both primary recrystallization and secondary recrystallization in 90% cold-rolled 99.5% nickel of two different textures. The initial texture is shown to influence the rolling texture and, hence, the results of subsequent annealing. It was found that one alloy showed a cube texture after primary recrystallization, underwent abnormal grain growth upon annealing at high temperatures, and could be directionally (secondary) recrystallized to give large columnar grains. In contrast, the other alloy produce a weak cube texture after primary recrystallization, showed only normal grain growth upon annealing at higher temperatures, and could not be directionally annealed to produce columnar grains. The implications of these results are discussed for producing columnar grains.