bluuebunny/crossref_metadata_2025 huggingface dataset:
Porous Structure and Mechanical Properties of the Cellular Metallic Materials Fabricated by Sintering Al Powder Coated with Sn
Authors: Sonoda Tsutomu , Katou Kiyotaka , Asahina Tadashi
Published: March 2009

The deposition of pure tin onto pure aluminum powder in its self-convective
motion by magnetron DC sputtering was examined in order to prepare Al-Sn composite
powder and thereby to improve the sintering of the aluminum particles, aiming at the
development of highly structure-controlled porous aluminum materials. The fabrication of
porous aluminum materials was carried out by space-holder method using the prepared Al-Sn
composite powder in ordinary powder metallurgy processing. The effects of the sputterdeposition
of tin on porous structure and mechanical properties of the sintered compact were
investigated. It was found that the porous structure of the sintered porous materials with the
porosity 80% was better regulated by the sputter-deposition, compared to that without the
deposition. Regarding their compressive properties, it was found that the plateau stress of the
sintered porous materials reached by the sputter-deposition twice as high as that without the
deposition. Therefore it was concluded that coating of aluminum powder with tin deposits
enables the porous-structure to be controlled more effectively in fabricating sintered highly
porous aluminum materials, as well as improves their mechanical property.
Filtration on Hydrocyclone of Optimized Geometric Relationships
Authors: Vieira Luiz Gustavo Martins , Damasceno João Jorge Ribeiro , Barrozo Marcos A.S.
Published: March 2009

The filtering hydrocyclone is a solid-liquid separation device patented by the Chemical
Engineering School of the Federal University of Uberlândia, which consists of a hydrocyclone
whose conical section was replaced by a conical filtering wall. During the operation of these
separators, besides underflow and overflow streams, the existence of a filtrate stream generated by
the filtering process is found in the permeable conical region of the hydrocyclones. Vieira et al.
(2006) got a filtering hydrocyclone that simultaneously presented low Euler Number and cut size
diameter because its geometric relationships has been optimized. The objective of this work was to
analyze the behavior of this optimized filtering hydrocyclone through computational fluid dynamics
and experimental studies. In the same operational conditions of the conventional hydrocyclone, the
performance of this optimized filtering hydrocyclone was significantly influenced by the filtration.
The filtration caused decreases in the Euler number and increment in the total efficiency.
Developing of Ceramic Roof Tiles Process by Powder Pressing and Firing in Roller Kiln
Authors: Neckel Lorenço , Prette André L.G. , Alarcon Orestes Estevam , Fredel Márcio Celso
Published: March 2009

In this work, it was investigated the behavior of a ceramic composition in pressing and
firing process, related to its pyroplasticity, to permit the production of roof tiles in roller kiln.
Experiments were realized varying the parameters of pressing, sintering and composition, adding a
refractory material. With this study, it became possible to select the optimal parameters of pressing
and firing, and to start the pilot industrial tests. The developed process has advantages, in the
process and the final product, related with the standard process (extrusion and firing in tunnel kiln).
The process is energetically more efficient, because there are no movable in the kiln. It was
measured a flexural strength above 40 MPa with 12mm thickness, saving material. Also, the
product has a higher quality in size, shape and dimensional precision (linear thermal shrinkage
lower than 1,5%); tonality, porosity (water absorption lower than 10%), and frost resistance.
Characterization of the Apatite Formation on the Surfaces of Zirconia and Alumina Ceramics in Body Environments
Authors: Aguiar Amanda Abati , Ussui Valter , Ribeiro Christiane , Scapin Marcos A. , Ribeiro Ricci Dolores , de Lima Nelson Batista
Published: March 2009

Induction of an apatite-forming ability on a 100% Y2O3-ZrO2, 100% Al2O3, and 80/20 and
20/80 wt% of zirconia-alumina (Y2O3-ZrO2-Al2O3) composite polycrystals via chemical treatment
with 5M H3PO4 have been investigated. The chemical treatments produced Zr-O surface functional
groups, which are known to be effective for apatite nucleation in simulated body fluid. It’s believed
that Al-OH surface functional groups are not effective for apatite nucleation. I this work was shown
that apatite nucleates in substrate of alumina treat and untreated chemically. This implies that Al-
OH functional groups are effective for apatite nucleation.
Use of Aggregates from Recycled Concrete Mixer Trucks Waste in Concrete
Authors: Correia Sivaldo Leite , Souza F.L. , Dienstmann G. , Folgueras Marilena Valadares , Hotza Dachamir
Published: March 2009

This paper presents some of the results of an investigation on the possible applications of
use of waste concrete aggregates from mixer trucks concrete productions (WCA) in concrete. The
investigation has been carried out using factorial design for experimental design. For the study, the
physical and mechanical properties along their durability of concrete produced with WCA were
investigated and the results presented. Concrete mixtures were prepared using WCA as the
replacement of natural fine aggregate at the level 10%, 20% and 30 wt.% with water/cement ratios
of 0.40, 0.50 and 0.60. Properties of fresh and hardened concrete were evaluated: fresh unit weight,
consistency, 7-day and 28-day compressive strength were carried out in specimens. The necessary
data for establishing a mix proportion design and a quality control method are obtained using a full
factorial design 32. The influence of level of WCA on the mineralogical composition has been
established, and its suitability for use in a concrete application has been assessed. Empirical contour
plots for the physical-mechanical properties of fresh and hardened concrete with WCA were
obtained via regression analysis, which predict that as the amount of waste increases, has no or little
effect on the compressive strength of concrete mixes. The results form confirmation experiments
justify the prediction from the statistical approach.
Collaborative Environment Development for the Supported CAD/CAM
Authors: Su Jian Jun , Liao Xiao Ping , Zhou Xiao Rong , Wang Shuang Fei
Published: March 2009

Collaborations abstract the interactions among a group of objects above the level of an
individual object-oriented programming (OOP) message send for an integrated design/manufacture
process, they can realize information share and system integration, and can be viewed as a type of
systematic approach. This paper proposes the collaborative mode in the interior of an enterprise and
among enterprises and a novel knowledge-based intensive CAD/CAM framework for collaborative
environment development, which integrates product design, design for process planning, NC codes
auto-generation and manufacturing simulation. A unified class of knowledge intensive data structures
is defined using the blackboard and OO knowledge-based approach for handling both the design and
the process planning problems. The detailed knowledge-intensive framework with integration of
multi-cooperative knowledge sources and software is given. Thus, product design, process planning
and NC codes auto-generation can be carried out simultaneously and collaboratively in an entirely
computer-aided collaborative environment.
The Effect of Additional Elements on Oxide Scale Evolution of Fe-20at.%Cr-10at.%Al Alloy at 900 °C in Air
Authors: Kitajima Yuri , Hayashi Shigenari , Ukai Shigeharu , Narita Toshio
Published: March 2009

The oxidation behavior of Fe-20at.%Cr-10at.%Al alloys with a small amount of an
additional element such as W, Cu, Mn, Nb, Mo, Re, Co or Ti was investigated at 900 °C for up to
625hr. The fourth element addition to the FeCrAl alloy could be classified into two groups;
elements (Mn, Nb, Ti) that are contained in the Al2O3 scale, and elements (W, Mo, Re, Co) which
are not present in the scale. In the latter case, the elements (W, Cu) caused scale spallation. The
rumpling of alloys with Mn, Nb or Ti was smaller than that of the other alloys. The surface of the
alloy with Ti was the smooth. Pt marker experiments suggested that the Al2O3 scale formed on the
alloy with Ti grew by inward diffusion of O, whilst the Al2O3 scale formed on the FeCrAl alloy
grew by both outward diffusion of Al and inward diffusion of O. This different growth behavior due
to the elements incorporated in the Al2O3 scale could have an effect on the surface rumpling
behavior.
Chemistry of Ash-Deposits on Gas Turbines Hot Parts: Reactivity of Nickel, Zinc and Iron Oxides in (Na, V, S) Molten Salts
Authors: Rocca Emmanuel , Aranda Lionel , Molière Michel
Published: March 2009

When ash-forming oils or contaminated distillate oils are used as fuels in land-based,
marine or aero gas turbines, the hot gas path components, mainly the partition vanes and the blades
of the expansion turbine are subjected to the deposition of slags that are corrosive at high
temperature due to their low liquidus temperature. This hot corrosion process - if not properly
inhibited - entails a dramatic life reduction of the hot gas path parts. MgO is a traditional, efficient
inhibitor. Recently, it has been found that NiO also suppresses the corrosiveness of the (Na,S,V)
melts by trapping vanadium in a refractory vanadate (Ni3V2O8); this compound is friable and does
not tend to accumulate on turbine blades. The use of inhibitors entails losses in both machine
performance and availability. Moreover, other metals can interfere with the inhibition process. In
particular, zinc and iron are often inadvertently introduced in gas turbines fuels during their
transportation or storage and they can significantly interact with nickel. This paper distinguishes the
interactions between NiO on one hand and both ZnO and Fe2O3 on the other hand in the general
complex chemistry of ash.
The thermochemical study of (Na,S,V) melts in presence of Ni confirms that nickel is a good
"trapper" of vanadium oxide at high temperature. However, they also show that nickel can react
with iron to form the very stable ferrite NiFe2O4 and a low melting point vanadate phase. On the
contrary, the presence of zinc affects to a lesser extent the reactivity of NiO versus V2O5 despite the
formation of Ni1-xZnxO solid solutions.
Microstructural Evolution of Slurry Fe Aluminide Coatings during High Temperature Steam Oxidation
Authors: Agüero Alina , Spiradek Krystina , Höfinger S. , Gutiérrez Marcos , Muelas Raúl
Published: March 2009

Slurry iron aluminide coatings are very resistant to steam oxidation at 600-650º C. These
coatings can be used to protect new generation Ultra Super Critical (USC) steam power plant
ferritic/martensitic steel components. The microstructure of the initially deposited coating changes
as a function of time, mainly due to coating-substrate interdiffusion, going from mostly Fe2Al5 to
FeAl, causing the precipitation of AlN in those substrates containing a minimum content of N and
moreover, developing Kirkendall porosity at the coating-substrate interface. Steam oxidation at 650º
C causes the formation of a protective thin layer of hexagonal χ-Al2O3 phase along with some α-
and γ-Al2O3 after the first few hours of exposure. However, despite the relatively low temperature,
and after several thousands hours the protective layer was mostly composed of α-Al2O3. A study of
the evolution of the microstructure of slurry aluminide coatings deposited on P92 and exposed to
steam at 650º C has been carried out by scanning and transmission electron microscopy and X ray
diffraction.
A Review of Haynes® 230® and 617 Alloys for High Temperature Gas Cooled Reactors
Authors: Katcher Michael , Klarstrom Dwaine L.
Published: March 2009

HAYNES® 230® and 617 alloys are competing for use on Generation IV, high temperature
gas cooled reactor components because of good high temperature creep strength in the temperature
range between 760°C and 982°C and resistance to oxidation in the gas cooled reactor environment.
A review of the metallurgy affecting the properties in each alloy will be discussed. Grain size and
carbide precipitation developed during fabrication effect short term and long term ductility, fatigue,
and creep. For example, 230 alloy has a finer grained structure which promotes fatigue strength
with a slight sacrifice in creep strength. The 617 alloy has a coarser grain structure which provides
slightly higher creep resistance while sacrificing some fatigue strength. Thermal aging also
introduces gamma prime precipitation to the 617 alloy as well as grain boundary carbides, and this,
in addition to grain boundary oxidation, reduces the low cycle fatigue strength of 617 alloy
compared to 230 alloy. Independent studies have shown that 230 alloy possesses higher resistance
to thermal fatigue than 617 alloy. However, welds of both base metals with similar weld
composition have about the same thermal fatigue life. Cooling rates from solution annealing
temperatures during processing effect the ductility and creep strength of these alloys with the
highest cooling rates preferred for retention of ductility and creep strength. The reason; slow
cooling rates promote carbide precipitation in the grain boundaries which reduces ductility and
creep strength.
The Kinetics of Oxidation of Ru-Bearing Nickel-Based Superalloys
Authors: Edmonds I.M. , Evans Hugh E. , Jones C.N. , Broomfield Robert W.
Published: March 2009

Oxidation tests have been undertaken in air on two experimental fourth-generation Nibased
superalloys containing, respectively, 3 and 5 wt.% Ru. A Ru-free, third generation alloy
(CMSX-10K) was also included in the test programme which used temperatures covering the range
750-1100°C. Where possible, comparisons were also made with literature data on the secondgeneration
CMSX-4 alloy and with IN738. After an initial period of transient oxidation, the
subsequent parabolic rate constants for the 3%-Ru alloy were similar to those for CMSX-4 at all
temperatures above 750°C. At 1000 and 1100°C these were consistent with the formation and
growth of an α-alumina layer. At 950°C and lower, protective oxidation was obtained through the
formation of an Al-rich spinel rather than alumina but, again, no deleterious influence of Ru
additions could be found, at least in the temperature range of 800-950°C. Anomalous behaviour was
found, however, at 750°C in that the Ru-bearing alloys oxidised non-protectively through the
formation of sub-surface pits in which the γ΄ phase within the alloy was oxidised in situ.
On the Loss of Protective Scale Formation in Creep-Resistant, Alumina-Forming Austenitic Stainless Steels at 900°C in Air
Authors: Brady M.P. , Yamamoto Yukinori , Pint Bruce A. , Santella M.L. , Maziasz P.J. , Walker L.R.
Published: March 2009

A family of creep-resistant, Al2O3-forming austenitic (AFA) stainless steels was recently
developed. The alloys exhibit excellent oxidation resistance up to ∼800°C, but are susceptible to
internal attack of Al at higher temperatures. In the present work, higher levels of Ni, Cr, Al, and Nb
additions were found to correlate with improved oxidation behavior at 900°C in air. The alloys
generally appeared to be initially capable of external Al2O3 scale formation, with a subsequent
transition to internal attack of Al (internal oxidation and internal nitridation) that is dependent on
alloy composition. Compositional profiles at the alloy/scale interface suggest that the transition to
internal oxidation is preceded by subsurface depletion of Al in the lower-Al compositions. In higher
Al-containing compositions, NiAl second-phase precipitates act as an Al reservoir, and Al depletion
may not be a key factor. Alloy design directions to increase the upper-temperature limit of
protective Al2O3 scale formation in these alloys are discussed.
Microstructure Influence on Residual Stresses in Growing Chromia Oxide Films as Determined by In Situ High Temperature Raman Spectroscopy
Authors: Kemdehoundja Mbaihoudou , Grosseau-Poussard Jean Luc , Dinhut J.F. , Bonnet G.
Published: March 2009

In this work, growth stresses have been investigated in relation with the microstructure in
the case of α-Cr2O3 growing oxide films on NiCr30 alloy. The equibiaxial growth stresses have been
measured thanks to a technique coupling Raman spectroscopy and in situ high temperature
oxidation of the NiCr30 alloy in the temperature range [700°C-900°C]. The low acquisition time
necessary to obtain a Raman spectrum allows to follow the chromia growth kinetic with sufficient
accuracy. It is demonstrated that the growth stress in such oxide films can attain more than 2 GPa,
before additional thermal stress arises on cooling. Moreover, the growth stress kinetic - subsequent
establishment and relaxation - are highly microstructure sensitive: in particular, as the oxidation
temperature rises, the chromia grain size also increases, and it consequently retards the occurrence
of the creep relaxation phenomena which needs an additional stress to start.
Relation between Synthesis Process, Microstructure and Corrosion Resistance of Two Yttrium Silicates
Authors: Courcot Emilie , Rebillat Francis , Louchet-Pouillerie Caroline
Published: March 2009

Silicon-based ceramics are among the main candidates for high temperature structural
components in aeronautic applications. One key drawback of silicon-based ceramics for these
applications is the volatilization of the protective silica scale, in moisture and the resulting ceramic
recession. Therefore, the further use of these ceramics components depends on the development of
external protection against water vapour attack. Some of the most promising materials seem to be
rare earth silicates. Based on much richer data in the bibliography, the purpose of this work is to
investigate the influence of two yttrium silicates elaboration processes on both the capability to
crystallize and the corrosion resistance in an oxidative moist atmosphere at high temperature.
Taking into account the material’s morphology, composition and degree of crystallization, the
composition (Y2SiO5 or Y2Si2O7) and the preferable synthesis process are discussed.
Thermal Fatigue of Anticorrosive Coatings and Multilayer Coatings: A Performance Index Approach
Authors: D'Ans Pierre , Bondoux Céline , Degrandcourt Christophe , Bakrim Mohamed , Dille Jean , Segers Luc , Degrez Marc
Published: March 2009

A strategy is proposed to cope with combined thermal fatigue and hot corrosion
resistance affecting industrial coatings. It allows comparing different materials, coatings and
geometries with respect to thermal cracking and then properly selecting protective coatings. It uses
a thermo-mechanical model combining the heat transfer conditions, thermal and mechanical
properties of the materials and the system geometry. The model is applied to two cases: (i) borided
steel, with experimental support; (ii) multilayer coating made of a thermal barrier layer, aimed at
reducing thermal gradients in the system, and a corrosion layer.
Chemical Characterization and Comparison of Thermally Treated Beech and Ash Wood
Authors: Windeisen Elisabeth , Wegener Gerd
Published: March 2009

Thermal treatments of two wood species were examined. The temperature load at 200 °C on the wood causes characteristic changes in the chemical composition. The determination of specific alterations was carried out by means of suitable methods, both wet chemical and instrumental analyses. The heat treated wood specimens of beech (Fagus sylvatica) and ash (Fraxinus excelsior) were characterized by means of Carbon analysis. The samples were extracted with organic solvents, cold and hot water. The pH-values were determined in the cold water extracts. Sugar analyses were performed after hydrolysis by means of ion-exchange chromatography. Lignin analyses after thioacidolysis were carried out by means of GC and GC/MS.
Self-Heating of 4H-SiC PiN Diodes at High Current Densities
Authors: Levinshtein Michael E. , Mnatsakanov Tigran T. , Ivanov Pavel A. , Palmour John W. , Das Mrinal K. , Hull Brett A.
Published: March 2009

Self-heating in high-voltage 4H-SiC PiN diodes has been studied experimentally and
theoretically in dc and 8-ms single pulse modes. To simulate the self-heating, an electro-thermal
model was used to calculate non-isothermal current-voltage characteristics at dc and current-time
dependences at pulsed measurements. The dynamic instability of N-type was observed: the current
decreases in spite of increasing of bias applied to the structure. At dc, irreversible diode degradation
was found to occur at a current density of about 1700 A/cm2. Under a single current surge 8-ms
pulse, the loss of thermal stability has been found at a current density of approximately 9000 A/cm2.
Comparison of experimental data and simulations showed that the local temperature in the diode
base at the end of the 8-ms, 9000-A/cm2 pulse reaches 2000 – 2300 K.
Impact of RIE Etching on the Breakdown Voltage of 4H-SiC Mesa Diodes
Authors: Vang H. , Scharnholz Sigo , Raynaud Christophe , Lazar Mihai , Pâques Gontran , Planson Dominique
Published: March 2009

This paper presents a comparison of the reverse characteristics of mesa terminated PiN
diodes fabricated on n- and p-type 4H-SiC substrates. For n-type the attained breakdown voltages are
higher and for p-type lower than expected. This is likely to be explained by the presence of negative
charges at the interface between passivation oxide and SiC. Supported by XPS data we come to the
conclusion that the RIE process creates surface charges which have an impact on the breakdown
voltage of the fabricated diodes.
Comparison of 10 kV 4H-SiC Power MOSFETs and IGBTs for High Frequency Power Conversion
Authors: Walden Ginger G. , McNutt Ty , Sherwin Marc , Van Campen Stephen , Singh Ranbir , Howell Rob
Published: March 2009

For the first time, large area 10 kV SiC power devices are being produced capable of
yielding power modules for high-frequency megawatt power conversion. To this end, the switching
performance and power dissipation of silicon carbide (SiC) n-channel IGBTs and MOSFETs are
evaluated using numerical simulations software over an extended current range to determine the
best device suitable for 10 kV applications. Each device is also optimized for minimal forward
voltage drop in the on-state.
Electron Irradiation Lifetime Control for SiC Bipolar Devices of 200 kVA High Power SiC Inverters
Authors: Sugawara Yoshitaka , Ogata Shuuji , Miyanagi Yoichi , Asano Katsunori , Okada Shinichi , Tanaka Atsushi , Nakayama Koji , Izumi Toru
Published: March 2009

To reduce the switching power losses of SiC bipolar devices, an electron irradiation
lifetime control method was investigated and was successfully applied to the development of
200kVA full SiC inverters, in which SiCGTs and SiC pn diodes irradiated electrons were used at the
condition required to minimize inverter power loss.
Hydrogen Gas Sensors Fabricated on Atomically Flat 4H-SiC Webbed Cantilevers
Authors: Neudeck Philip G. , Spry David J. , Trunek Andrew J. , Evans Laura J. , Chen Liang Yu , Hunter Gary W. , Androjna D.
Published: March 2009

This paper reports on initial results from the first device tested of a “second generation”
Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC
webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper
selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20
ppm was achieved. A stable sensor current gain of 125 ± 11 standard deviation was demonstrated
during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.
Efficiency Improvement of PV-Inverters with SiC-DMOSFETs
Authors: Burger Bruno , Kranzer Dirk , Stalter Olivier
Published: March 2009

The new MOSFET-generation with SiC-materials seems well suited for power electronic
converters up to 1200 V operating-voltage, and particularly for grid-feeding PhotoVoltaic-inverters,
which transfer the DC power of the solar panel to the AC grid. Their high switching speed and low
on-resistance RDS(on) allow the use of higher switching frequencies, which could mainly reduce the
costs and weight of the converters. This paper shows a comparison between IGBT and SiC
DMOSFET devices and first measurements of some 1200 V / 10 A SiC-DMOSFET samples made
by CREE®.
LPE Growth of Bulk GaN Crystal by Alkali-Metal Flux Method
Authors: Kawamura Fumio , Umeda Hidekazu , Morishita Masanori , Gejo Ryohei , Tanpo Masaki , Imade Mamoru , Miyoshi Naoya , Yoshimura Masashi , Mori Yusuke , Sasaki Takatomo , Kitaoka Yasuo
Published: March 2009

We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the
Na flux method. Our success is due to the development of a new apparatus for growing large GaN
single crystals. The crystal grown in this study has a low dislocation density of 2.3×105 (cm-2), The
secondary ion mass spectrometry (SIMS) technique demonstrates that the Na element is difficult to be
taken in the crystal in both the + and – c directions, resulting in a Na concentration of 4.2 × 1014 (cm-3)
in the crystal. Our success in growing a two-inch GaN substrate with a low impurity content and low
dislocation density should pave the way for the Na flux method to become a practical application.
Thin SiC-4H Epitaxial Layer Growth by Trichlorosilane (TCS) as Silicon Precursor with Very Abrupt Junctions
Authors: Condorelli Giuseppe , Mauceri Marco , Pistone Giuseppe , Perdicaro L.M.S. , Abbondanza Giuseppe , Portuese F. , Valente Gian Luca , Crippa Danilo , Giannazzo Filippo , La Via Francesco
Published: March 2009

A process has been developed to grow multi-epy high doped structure. Trichlorosilane (TCS) and Ethylene have been used as precursor; Nitrogen (N2) and trimethylaluminum (TMA) as doping source. The SIMS and SCM analysis show that using this silicon precursor very abrupt N++/P+/N+ junctions (40-60 nm) can be obtained with low background doping concentration in a single epitaxial growth run.
Optical Characterization of Defect-Related Carrier Recombination and Transport Features in GaN Substrates and CVD Diamonds
Authors: Jarašiūnas Kęstutis , Malinauskas T. , Aleksiejunas R. , Monemar Bo , Ralchenko V. , Gontar A. , Ivakin E.
Published: March 2009

Defect related carrier recombination and transport properties have been investigated in
differently doped HVPE GaN substrates and CVD diamond layers. Carrier generation by interband
transitions or by deep-defect photoexcitation were realized for studies of GaN samples by using
picosecond pulses at 351 nm or 527 nm. This allowed to create favorable conditions for radiative and
nonradiative recombination in the crystals and reveal peculiarities of photoelectrical properties of
high and low density plasma in undoped, doped, and compensated GaN. In CVD diamonds, carrier
diffusion length was found equal to ~ 0.5 μm and non-dependent on nitrogen density, while the carrier
lifetime varied from 0.2 to 0.6 ns.
Current Collapse Characteristic of AlGaN/GaN MIS-HEMT
Authors: Yagi Shuichi , Shimizu Mitsuaki , Yano Yoshiki , Ubukata Akinori , Akutsu Nakao
Published: March 2009

We investigated the current collapse characteristics of the fabricated MIS-HEMT with the
SiO2, SiN and high-k gate insulator. TiO2 was employed as the high-k material. We found the
significant drain current change in the switching characteristic when the insulator changes. The SiN
MIS-HEMT showed good switching characteristic. On the other hand, the MIS-HEMTs with oxide
insulator film showed large drain current reduction. We considered that the degradation of the
switching characteristic is due to the current collapse.
Growth Mechanism and 2D Aluminum Dopant Distribution of Embedded Trench 4H-SiC Region
Authors: Sugiyama Naohiro , Takeuchi Yuuichi , Kataoka Mitsuhiro , Schöner Adolf , Malhan Rajesh Kumar
Published: March 2009

The migration enhanced embedded epitaxy (ME3) mechanism and 2D dopant distribution of the embedded trench region is investigated with the aim to realize the all-epitaxial, normally-off junction field effect transistor (JFET). We found that the embedded growth consists of two main components. First one is the direct supply without gas scattering and the other one is the surface migration supply via the trench opening edge, which dominate the ME3 process. An inhomogeneous 2D distribution of Aluminum (Al) concentration was revealed for the first time in the 4H-SiC embedded trench regions by the combined analysis of secondary ion mass spectrometry (SIMS) and scanning spreading resistance microscopy (SSRM) results. The maximum variation of Al concentration in the trench is estimated to be about 4-times, which suggests that the Al concentration is highest for the (0001) plane and lowest for the trench corner (1-10x) plane. Al concentration in the (1-100) plane, which determines the JFET p-gate doping level is 1.5-times lower than (0001) plane for trench region fabricated on Si-face wafers.
Void Formation in Differently Oriented Si in the Early Stage of SiC Growth
Authors: Severino Andrea , Bongiorno Corrado , Anzalone Ruggero , Abbondanza Giuseppe , Mauceri Marco , Condorelli Giuseppe , Foti Gaetano , La Via Francesco
Published: March 2009

This study refers, through different microscopies, about the carbonization effects on differently oriented Si surfaces. A statistical study on the relationship between some process parameters (such as temperature, process time) and void dimensions and density, for three Si substrate orientations, is reported.
Influence of Growth Parameters on the Residual Strain in 3C-SiC Epitaxial Layers on (001) Silicon
Authors: Wagner Günter , Schwarzkopf J. , Schmidbauer M. , Fornari R.
Published: March 2009

3C-SiC epitaxial layers were grown on on-axis Si (001) substrates by low-pressure hot-wall chemical vapour deposition. Depending on the growth parameters, the residual strain in the 3C-SiC layer was seen to be tensile or compressive. In this work, the influence of parameters, such as growth temperature and C/Si ratio in the vapour phase, on residual strain and macroscopic layer bow is investigated. We found that the wafer bow changes from convex, at a deposition temperature of 1270° C, to concave at 1370° C. High resolution x-ray diffraction data indicate that the crystal-line perfection of the layers is lower for decreasing deposition temperature and increasing compres-sive strain. No remarkable influence of the C/Si ratio in the gaseous atmosphere on the FWHM of the rocking curve was observed.
Island Formation of SiC Film on Striated Si(001) Substrates
Authors: Kato Yoshimine , Sakumoto Kazuo
Published: March 2009

SiC growth on as-received and striated Si(001) substrates was studied. SiC films were grown by pulsed-jet chemical vapor deposition using monomethylsilane as a gas source at 780°C. Two kinds of Si surfaces were prepared. One was an as-received Si(001) surface and the other was an striated (scratched) Si(001) surface. It was found that nucleation rate of SiC is quite different between these two kinds of surfaces. The film growth rate was very low for the as-received Si(001) surface compared with the striated surface, and after 8 hours of growth hardly any film was grown and only square-shaped islands were observed. On the other hand, for the undulant substrate about 100nm thick 3C-SiC film was grown after 8 hours of deposition. This film growth rate difference appears to be due to the difference in density of nucleation sites. For the as-received Si(001) surface, nucleation site density appears to be quite small due to the atomically flat surface. On the other hand, for the undulant surface, nucleation site density was large enough for the film to grow faster.
Observation of Misfit Dislocations Introduced by Epi-Layer Growth on 4H-SiC
Authors: Matsuhata Hirofumi , Yamaguchi Hirotaka , Nagai Ichiro , Ohno Toshiyuki , Kosugi Ryouji , Kinoshita Akimasa
Published: March 2009

4H-SiC substrate wafers with epi-layers were observed using monochromatic synchrotron
X-ray topography in grazing incidence geometries, to investigate the defects in the epi-layer. Misfit
dislocations with b=+1/3[11 2 0] caused by the difference in lattice parameter between the epi-layer
and the substrate were observed. The misfit dislocations are located near the interface as edge
dislocations, and appear at the top surface as screw dislocations on basal planes. It was observed that
more than half of them were introduced from the growing epi-layer surface. The misfit dislocations
and some screw dislocations with b=+1/3[11 2 0] are observed to remain as basal plane dislocations
at the surface, while other basal plane dislocations were converted to threading edge dislocations in
the epi-layer.
Structural Analysis of Off-Axis SiC Planes for the Growth of SiC and AlGaN Films
Authors: Jones Kenneth A.
Published: March 2009

An orientation relationship between the cubic 3C and nH hexagonal structures was
developed to identify low surface energy, close packed, conducive to growth hexagonal semi-polar
planes. This was done to identify planes on which micropipe free SiC crystals, and/or hetero-epitaxial
AlGaN structures with a reduced piezoelectric field and a smaller lattice mismatch could be grown.
The nH (33 0 2n)H and (33 0 n )H hexagonal planes, which correspond to the (100)C and (111)C cubic
planes are identified, and equations are developed to determine their planar structure and packing
density to assess whether there is a reasonable chance that high quality material can be grown on these
surfaces and whether it is likely that stacking faults will be formed. It is shown that stacking faults
will likely form in SiC crystals; it is also shown that good epitaxy of AlGaN films should be possible
on these planes although it is likely stacking faults will be formed.
Delineation of Defects Reducing Schottky Barrier Heights on 4H-SiC by the Electrochemical Deposition
Authors: Kato Masashi , Ogawa Kazuya , Ichimura Masaya
Published: March 2009

We identified regions with low Schottky barrier height on 4H-SiC surfaces by the
electrochemical deposition of ZnO. When we adopt an appropriate deposition voltage, ZnO grew
preferentially at the regions with the low Schottky barrier height. Thus, we were able to identify the
ZnO film only at these regions if we stopped the deposition at a proper time. We compared positions
of the deposited film and etch pit after molten NaOH etching. As a result, in a bulk 4H-SiC, the films
were deposited around some of micropipe positions. On the other hand, in an epitaxial 4H-SiC layer,
although approximately a half of deposited films seemed to grow at the etch-pit defect positions, other
deposited films were grown at positions without etch-pit defects. Therefore the Schottky barrier
heights were reduced by not only defects emerging as etch pits but also other kind of origins in
epitaxial 4H-SiC.
The Observation and Explanation of Electricity Switch Phenomena in PVT Grown SiC Bulk
Authors: Hao Jian Min , Wang Li Jie , Fen Bin , Wang Xiang Quan , Hong Ying , Meng Da Lei , Guo Jun Min , Yan Ru Yue
Published: March 2009

An unusual contrast in SEM secondary electron imaging for PVT grown silicon carbide with vanadium doped was observed. An explanation in point of the compensation of different type of dopant was drawn. And the relationship between the doping properties of vanadium and orientation of SiC domains was investigated.
Nitrogen Passivation of (0001) 4H-SiC Dangling Bonds
Authors: Pennington Gary , Ashman C.R.
Published: March 2009

We report a density functional theory study of N and NO passivation of surface dangling
bonds at the Si-face of (0001) 4H-SiC. Results agree with many key experimental findings in
nitrogen processed devices including: observed interface N coverage and characteristic changes in Dit.
Dangling bonds at the SiC surface are fully passivated by 1/3 ML N or NO coverage. Upon
passivation the surface is found to incur negligible strain and no reconstruction. Allowing atomic O
to interact with the 1/3 ML N or NO passivated surface, we find oxygen prefers to incorporate into
SiO2 rather than adsorb to the surface. This indicates the possibility of oxide deposition onto
nitrogen passivated (0001) 4H-SiC surfaces.
Generation and Recombination Carrier Lifetimes in 4H SiC Epitaxial Wafers
Authors: Chung Gil Yong , Loboda Mark J. , Marinella M.J. , Schroder D.K. , Klein Paul B. , Isaacs-Smith Tamara , Williams J.W.
Published: March 2009

Compared to silicon, there have been relatively few comparative studies of
recombination and carrier lifetimes in SiC. For the first time, both generation and recombination
carrier lifetimes are reported from the same areas in 20 m thick 4H SiC n-/n+ epi-wafer structures.
The ratio of the generation to recombination lifetime is much different in SiC compared to Si.
Activation energy calculated from SiC generation lifetimes shows that traps with energy levels near
mid-gap dominate the generation lifetime. Comparison of both generation and recombination
lifetimes and dislocation counts measured in the device area show no correlation in either case.
Investigation of the Internal Carrier Distribution in 4H-SiC Pin-Diodes by Laser Absorption Experiments
Authors: Werber Dorothea , Aigner Martin , Denoth D. , Wittmann F. , Wachutka Gerhard
Published: March 2009

We present an experimental equipment for studying the charge carrier distribution in the
interior of bipolar 4H-SiC high power devices by means of laser absorption measurements. Since the
light absorption coefficient in a semiconductor depends on the electron and hole concentration, the
attenuation of a laser beam transmitted through a sample is an integral function of the local charge
carrier density. In order to detect the tiny changes in the light intensity caused by the plasma-optical
effect, a highly sensitive measurement set-up has been developed. Its crucial components are a
low-noise blue laser and a high-speed and broad-band photo-diode amplifier circuit. Sample
preparation is sophisticated and requires special care. We investigated charge carrier profiles in
4H-SiC pin-diodes in the high-injection regime at current densities between 175 A/cm² and 350
A/cm². The measured charge carrier profiles are in good agreement with computer simulations.
The Specific Features of High-Field Transport in SiC Polytypes
Authors: Sankin Vladimir Ilich , Shkrebiy Pavel P. , Lepneva Alla A. , Ramm M.S.
Published: March 2009

A natural superlattice (NSL) in silicon carbide polytypes is shown to introduce a
miniband structure into the conduction band, which leads to a number of effects in phenomena of
quantum-mechanical transport and impact ionization when the electric field directed along an axis
of NSL (axis C in crystal). These processes are absolutely traditional when the electric field is
perpendicularly to this axis. The parallel field phenomena are explained by the effects of the
Wannier–Stark localization (WSL) among them the Bloch oscillations effect is most prominent
today.
Thermal Expansion Coefficients of 6H Silicon Carbide
Authors: Stockmeier Matthias , Sakwe Sakwe Aloysius , Hens Philip , Wellmann Peter J. , Hock Rainer , Magerl Andreas
Published: March 2009

The thermal expansion of 6H Silicon Carbide with different dopant concentrations of
aluminum and nitrogen was determined by lattice parameter measurements at temperatures from
300 K to 1575 K. All samples have a volume of at least 6 x 6 x 6 mm3 to ensure that bulk properties
are measured. The measurements were performed with a triple axis diffractometer with high energy
x-rays with a photon energy of 60 keV. The values for the thermal expansion coefficients along the
a- and c-direction, α11 and α33, are in the range of 3·10-6 K-1 for 300 K and 6·10-6 K-1 for 1550 K. At
high temperatures the coefficients for aluminum doped samples are approximately 0.5·10-6 K-1
lower than for the nitrogen doped crystal. α11 and α33 appear to be isotropic.
Studies of Thermal Anisotropy in 4H-, 6H-SiC Bulk Single Crystal Wafers by Photopyroelectric (PPE) Method
Authors: Wutimakun Passapong , Miyazaki Hisashi , Okamoto Yoichi , Morimoto Jun , Hayashi Toshihiko , Shiomi Hiromu
Published: March 2009

Thermal anisotropy in 4H-, and 6H-SiC bulk single crystal wafers was studied by the
PPE method. The thermal diffusivities of the [1-100] and [11-20] orientations (^c-axis) samples
were higher than those of the [0001] orientation (//c-axis) samples. Moreover, the thermal
anisotropies of the lattice component and the carrier component were analyzed by Raman
measurement.
Evolution and Structure of Graphene Layers on SiC(0001)
Authors: Riedl Christian , Bernardt J. , Heinz K. , Starke Ulrich
Published: March 2009

The evolution and structure of graphene layers on 4H-SiC(0001) and the corresponding
interface are investigated by scanning tunneling microscopy (STM) and low energy electron diffraction
(LEED). The surface is characterized by the so-called (6p3£6p3)R30± reconstruction, whose
structural properties are still unclear but at the same time are crucial for the controlled growth of
homogeneous high-quality large-terrace graphene surfaces. We analyse the properties of three phases
in this reconstruction with periodicities (6p3£6p3)R30±, (6£6) and (5£5). Their LEED intensities
strongly depend on the surface preparation procedure applied. The graphitization process imprints
distinct features in the STM images as well as in the LEED spectra. An easy and practicable determination
of the number of graphene layers is outlined by means of LEED intensities.
Depth Profiling of Al Ion-Implantation Damage in SiC Crystals by Cathodoluminescence Spectroscopy
Authors: Mitani Takeshi , Hattori Ryo , Yoshikawa Masanobu
Published: March 2009

Cross-sectional CL measurements have been performed on the cleaved surface of the
Al-ion implanted 4H-SiC. The strong L1 luminescence that originates from the DI defect has been
observed even in the deep region (~10 μm) where implanted ions do not penetrate. In the implanted
layer, CL results show that high-density non-radiative defects remain even after activation annealing.
Generation of the DI defect in the deep region is presumably attributed to the diffusion of point defects
from the implanted layer.
Structure and Lattice Location of Ge Implanted 4H-SiC
Authors: Kups Thomas , Tonisch Katja , Voelskow M. , Skorupa Wolfgang , Konkin Alexander , Pezoldt Joerg
Published: March 2009

Pseudomorphic 4H-(Si1-xC1-y)Gex+y solid solutions were formed by ion implantation at
600°C and rapid thermal annealing at implanted Ge concentrations below 10%. At higher implantation
doses followed by annealing 3C-SiC inclusion and SiGe precipitates are formed. Transmission
electron microscopy investigations accompanied with “atomic location by channeling enhanced microanalysis”
of the annealed samples revealed an increasing incorporation of Ge on Si lattice sites.
Comparison of Electrical Properties of Ohmic Contact Realized on p-Type 4H-SiC
Authors: Nguyen Duy Minh , Raynaud Christophe , Lazar Mihai , Vang Heu , Planson Dominique
Published: March 2009

N+ 4H-SiC commercial substrates with n-type epilayers have been used to realize bipolar
diodes and TLM structures. The p-type emitter of diodes was realized by Al implantations followed
by a post-implantation annealing with or without a graphite capping layer. Ohmic contacts were
formed by depositing Ti/Ni on the backside and Ni/Al on the topside of the wafer. It appears that
capping the sample during the annealing reduces considerably the surface roughness and the specific
contact resistance. Sheet resistance and specific contact resistance as low as 2kΩ/□ and respectively
1.75×10-4 Ωcm² at 300 K have been obtained. I-V measurements as a function of temperature have
been performed from ~100 to ~500 K. The variations of the series resistance vs. temperature can be
explained by the freeze-out of carriers and by the variation of carrier mobility.
4H Silicon Carbide Etching Using Chlorine Trifluoride Gas
Authors: Habuka Hitoshi , Katsumi Yusuke , Miura Yutaka , Tanaka Keiko , Fukai Yasushi , Fukae Takaya , Gao Yuan , Kato Tomohisa , Okumura Hajime , Arai Kazuo
Published: March 2009

The etching technology for 4H-silicon carbide (SiC) was studied using ClF3 gas at
673-973K, 100 % and atmospheric pressure in a horizontal reactor. The etch rate, greater than 10
um/min, can be obtained for both the C-face and Si-face at substrate temperatures higher than 723
K. The etch rate increases with the increasing ClF3 gas flow rate. The etch rate of the Si-face is
smaller than that of the C-face. The etched surface of the Si-face shows many hexagonal-shaped
etch pits. The C-face after the etching is very smooth with a very small number of round shaped
shallow pits. The average roughness of the etched surface tends to be small at the higher
temperatures.
Enhanced Channel Mobility in 4H-SiC MISFETs by Utilizing Deposited SiN/SiO2 Stack Gate Structures
Authors: Noborio Masato , Suda Jun , Kimoto Tsunenobu
Published: March 2009

Deposited SiN/SiO2 stack gate structures have been investigated to improve the 4H-SiC
MOS interface quality. Capacitance-voltage measurements on fabricated SiN/SiO2 stack gate MIS
capacitors have indicated that the interface state density is reduced by post-deposition annealing in
N2O at 1300°C. The usage of thin SiN and increase in N2O-annealing time lead to a low interface state
density of 1×1011 cm-2eV-1 at EC – 0.2 eV. Oxidation of the SiN during N2O annealing has resulted in
improvement of SiC MIS interface. The fabricated SiN/SiO2 stack gate MISFETs demonstrate a high
channel mobility of 32 cm2/Vs on (0001)Si face and 40 cm2/Vs on (000-1)C face.
Effects of Fabrication Process on the Electrical Characteristics of n-Channel MOSFETs Irradiated with Gamma-Rays
Authors: Hishiki Shigeomi , Iwamoto Naoya , Ohshima Takeshi , Itoh Hisayoshi , Kojima Kazu , Kawano K.
Published: March 2009

The effect of the fabrication process of n-channel 6H-SiC MOSFETs on their radiation
resistance is investigated. MOSFETs that post implantation annealing for source and drain was
carried out with carbon coating on the sample surface are compared to MOSFETs that post
implantation annealing was carried out without carbon coating. The radiation resistance
(gamma-rays) of the carbon-coated MOSFETs is higher than that of non-coated ones. The channel
mobility for MOSFETs whose gate oxide was formed using pyrogenic or dry oxidation process dose
not change by gamma-ray irradiation below 1x105 Gy. The value of channel mobility slightly
increases with increasing dose above 1x105 Gy. No significant increase in irradiation induced
interface traps is observed.
Comparative Study of Differently Grown 3C-SiC Single Crystals with Birefringence Microscopy
Authors: Chaussende Didier , Mercier Frédéric , Madar Roland , Pons Michel
Published: March 2009

We have investigated through birefringence microscopy, a set of 3C-SiC crystals grown with the CF-PVT process, starting from different seeds and under different growth conditions. Through self nucleation experiments, the stable growth of very high quality 3C-SiC crystals at high temperature (2100°C) and at high rate (roughly 0.2 mm/h) is demonstrated. The possibility to develop bulk growth of 3C-SiC crystals is discussed.
Influence of Ambient, Gate Metal and Oxide Thickness on Interface State Density and Time Constant in MOSiC Capacitor
Authors: Nakagomi Shinji , Sato Kenta , Suzuki Shun , Kokubun Yoshihiro
Published: March 2009

A metal-oxide-semiconductor (MOS) capacitor was fabricated using 4H-SiC epitaxial
layer, and the interface state was evaluated in oxygen and hydrogen ambient under high-temperature
conditions by the AC conductance technique. The relationships between interface state density (Dit),
and corresponding time constant (tit) were obtained. Influences of oxide thickness and of gate metal
(Pt or Al) were studied. Dit of Pt gate capacitor is influenced by ambient gas at higher temperature but
Dit of Al gate capacitor is little affected by ambient gas. Dit of capacitor with thicker oxide layer tends
to be lower than that of capacitor with thinner oxide layer. Interface states with larger time constant
are decreased for hydrogen ambient comparing with oxygen ambient in the Pt gate capacitor.