bluuebunny/crossref_metadata_2025 huggingface dataset:
Design, Fabrication and Application of 4H-SiC Trenched-and-Implanted Vertical JFETs
Authors: Zhao Jian Hui , Alexandrov Peter , Li Yu Zhu , Li Larry X. , Sheng Kuang , Lebron-Velilla Ramon
Published: March 2009

This paper reports recent progress in the development of a vertical JFET, the purely vertical
JFET based on trenched-and-implanted vertical JFET (TI-VJFET) approach that eliminates the need
of epitaxial regrowth at middle of device fabrication and the need of a merged lateral JFET to control
the vertical JFET. Different structures have been designed to target breakdown voltages ranging from
600V to 1.2kV. Vertical channel width uniformity has been studied, showing the feasibility of
achieving below 0.1um variation for reasonably flat wafers of good thickness uniformity. Pitch size of
the designs has been reduced compared to early report. Gate trench width has been reduced from
3.8um to 2.3um, aimed at increasing the device current capability. Fabricated device cells have been
tested and packaged into multi-cell 30A TI-VJFETs which have been characterized of DC and
switching characteristics at room and elevated temperatures. Very fast current rise/fall times of <10ns
were observed from RT to 200°C. PSpice model for TI-VJFET has been developed and applied to the
performance prediction of 3-phase SiC power inverter, suggesting a high efficiency 97.7% at 200°C
junction temperature without using soft-switching scheme. Preliminary experimental demonstration
of a PWM-controlled three-phase inverter based on SiC TI-VJFET power board is reported.
High-Frequency SiC MESFETs with Silicon Dioxide/Silicon Nitride Passivation
Authors: Matocha Kevin , Kaminsky Ed , Vertiatchikh Alexey , Casady Jeff B.
Published: March 2009

4H-SiC MESFETs were fabricated using a bilayer dry thermal oxide/low-pressure
chemical vapor deposited (LPCVD) silicon nitride for surface passivation. The passivation
dielectric consists of a 20 nm thick dry thermal oxide covered by a 45 nm thick LPCVD silicon
nitride layer. Devices utilize a recessed-channel architecture with 0.6 micron T-gates. Devices with
the bilayer SiO2/SiNx passivation achieved a ft=9.3 GHz and fmax=15.5 GHz (WG=1.5 mm). The
device transconductance was 34 mS/mm, drain current density was 235 mA/mm, and pinchoff
voltage was –8V. Devices were load-pull characterized at 3 GHz with a 10% duty cycle and 100 μs
repetition rate and a Class AB quiescent bias of IDS=100 mA/mm, and VDS=30V. Large devices
with a 9.6 mm gate-periphery deliver an output power of 43.2 dBm (20.9 W=2.2W/mm) with a
power-added-efficiency of 59% at a gain of 8.8 dB.
SiC Power MOSFETs – Status, Trends and Challenges
Authors: Peters Dethard , Schörner Reinhold , Friedrichs Peter , Stephani Dietrich
Published: March 2009

SiC power MOSFETs are attractive electronic power switches for innovative power
supply and motor drive solutions. The paper discusses this statement and specifies market
segments offering the best chances for a commercialization. Due to well-known difficulties in
achieving adequate channel conductivity, a lot of SiC-MOSFET publications focus on the
channel mobility. However, for a power MOSFET this is only one important parameter
affecting the performance. Other characteristics have to be considered too for an honest
evaluation: transfer characteristics and blocking capability over the standard operation
temperature range, handling of gate oxide stress and related reliability issues, capability of
paralleling, dynamic stability, body diode characteristics, reproducibility of the fabrication
process and device size. Various attempts have been made in recent years in order to address
these features. Approaches differ in the use of different crystal orientations and polytypes,
accumulation or inversion channel, implanted or epitaxially grown channels and novel
oxidation techniques. Worldwide a trend to the planar DIMOS concept can be observed. Our
present results are shown for a power SiC MOSFET designed for 10 A / 1200 V. Key data are
a specific on-resistance of 12 m1cm2, the desired low but positive increase of the onresistance
with temperature, static avalanche (20 mA DC @1574 V), short-circuit stability at
600 V for 20 9s and robust switching behavior.
Optimum Design of Short-Channel 4H-SiC Power DMOSFETs
Authors: Saha Asmita , Cooper James A.
Published: March 2009

We describe an optimized design for the 1 kV short-channel 4H-SiC power DMOSFET,
obtained from numerical simulations using the Taguchi method. Three new structural features are
employed: (1) a current spreading layer (CSL) below the p-well, (2) a heavily-doped, narrow JFET
region, and (3) a segmented p-well contact.
High Power-Density 4H-SiC RF MOSFETs
Authors: Gudjónsson G. , Allerstam Fredrik , Ólafsson H.Ö. , Nilsson Per Åke , Hjelmgren Hans , Andersson Kristoffer , Sveinbjörnsson E.Ö. , Zirath Herbert , Rödle T. , Jos R.
Published: March 2009

We have made a 4H-SiC RF power MOSFETs with cutoff frequency up to 12 GHz,
delivering RF power of 1.9 W/mm at 3 GHz. The transistors withstand 200 V drain voltage, are
normally-off, and show no gate lag, which is often encountered in SiC MESFETs. The measured
devices have a single drain finger and a double gate finger and a total gate width of 0.8 mm. To our
knowledge this is the first time that power densities above 1 W/mm at 3 GHz are reported for SiC
MOSFETs.
Bias Stress-Induced Threshold-Voltage Instability of SiC MOSFETs
Authors: Lelis Aivars J. , Habersat Daniel B. , Lopez G. , McGarrity J.M. , McLean F. Barry , Goldsman Neil
Published: March 2009

We have observed instability in the threshold voltage, VT, of SiC metal-oxide
semiconductor field-effect transistors (MOSFETs) due to gate-bias stressing. This effect has
routinely been observed by us in all 4H and 6H SiC MOSFETs from three different
manufacturers—even at room temperature. A positive-bias stress, applying an electric field of
about 1 to 2 MV/cm across the gate oxide, for 3 minutes followed by a negative-bias stress for
another 3 minutes typically results in a shift of the ID-VGS current-voltage characteristic in the range
of 0.25 to 0.5 V and is repeatable. We speculate that this effect is due to the presence of a large
number of near-interfacial oxide traps that presumably lie in the oxide transition region that extends
several nm into the oxide from the SiC interface, caused by the presence of C and strained SiO2.
This instability is consistent with charge tunneling in and out of these near-interfacial oxide traps,
which in irradiated Si MOSFETs has been attributed to border traps. Also consistent with charge
tunneling is the observed linear increase in the magnitude of the SiC VT instability with log (time).
A 1cm × 1cm, 5kV, 100A, 4H-SiC Thyristor Chip for High Current Modules
Authors: Agarwal Anant K. , Krishnaswami Sumi , Damsky Ben , Richmond Jim , Capell Craig , Palmour John W. , Ryu Sei Hyung
Published: March 2009

We report on the development of the first 1 cm x 1 cm SiC Thyristor chip capable of
blocking 5 kV. This demonstrates the present quality of the SiC substrate and epitaxial material. A
forward drop of 4.1 V at 100 A and 25°C has been measured. The turn-on delay is found to be a
strong function of the gate current. At a gate current of 0.5 A, a turn-on delay of 250 ns is observed
for an anode to cathode current of 200 A. The turn-on delay reduces to 72 ns for an IG = 1.5 A. The
turn-on rise time is a strong function of the anode to cathode voltage, VAK. At VAK =230 V, the
turn-on rise-time is 300 ns for IAK =200 A. The rise-time reduces to 26 ns for VAK = 500 V.
Analysis of the Effect of Temperature on Base Current Gain in Power 4H-SiC BJTs
Authors: Ivanov Pavel A. , Levinshtein Michael E. , Agarwal Anant K. , Krishnaswami Sumi , Palmour John W.
Published: March 2009

For 1-kV, 30-A 4H-SiC epitaxial emitter npn bipolar junction transistors, the dependence
of the common-emitter current gain β on the collector current IC were measured at elevated
temperatures. The collector-emitter voltage was fixed (at 100 V voltage) to provide an active
operation mode at all collector currents varying in a wide range from 150 mA to 40 A (current
densities 24 - 6350 A/cm2). The maximum room temperature current gain was measured to be βmax
= 40 (IC = 7 A) while βmax = 32 (IC = 10 A) at 250oC. The β-IC dependences were simulated using a
model which takes into account the main processes affecting the current gain. Minority carrier
lifetimes and surface recombination velocity were obtained by means of those considerations.
Radiation Hard Devices Based on SiC
Authors: Kalinina Evgenia V. , Strel'chuk Anatoly M. , Lebedev Alexander A. , Strokan Nikita B. , Ivanov Alexander M. , Kholuyanov G.
Published: March 2009

The effect of irradiation with protons, electrons, neutrons, x-ray radiation and gamma-ray
photons as well as with different ions on properties of starting SiC material and devices based on it
was studied. The rectifying properties of the diode structures, which degraded as a result of irradiation
with high energy particles, were recovered at higher operation temperatures. The transistor structure
SiC-based detectors were realized with the signal amplification by a factor of tens under irradiation.
The energy resolution of 0.34 %, commensurable with Si-detectors, has been achieved for SiC
detectors and is correct for all classes of short range ions. The maximum signal amplitude
corresponds, in SiC, to a mean electron-hole pair creation energy of 7.7 eV.
Molecular Beam Epitaxy of Cubic Group III-Nitrides on Free-Standing 3C-SiC Substrates
Authors: As Donat J. , Potthast S. , Schörmann J. , Li S.F. , Lischka K. , Nagasawa Hiroyuki , Abe Masayuki
Published: March 2009

Cubic GaN, AlxGa1-xN/GaN and InyGa1-yN/GaN multiple quantum well (MQW) layers
were grown by plasma assisted molecular beam epitaxy on 200 &m thick free standing 3C-SiC
substrates. The influence of the surface roughness of the 3C-SiC substrates and the influence of
metal coverage during growth are discussed. Optimum growth conditions of c-III nitrides exist,
when a one monolayer Ga coverage is formed at the growing surface. The improvement of the
structural properties of cubic III-nitride layers and multilayers grown on 3C-SiC substrates is
demonstrated by 1 μm thick c-GaN layers with a minimum x-ray rocking curve width of 16 arcmin,
and by c-AlGaN/GaN and c-InGaN/GaN MQWs which showed up to five satellite peaks in X-ray
diffraction, respectively.
Growth of AlN and AlN-SiC Solid Solution by Sublimation Method
Authors: Anikin Mikhail , Chaussende Didier , Pernot Etienne , Chaix-Pluchery O. , Roussel H. , Pons Michel , Madar Roland
Published: March 2009

AlN is considered as the most suitable substrate material for further development of high
quality and high performance nitride-based micro- and opto-electronics. AlN ingots are often grown
on SiC seeds. To solve the formation of cracks due to the difference in lattice parameters between
seed and crystal we chose to “adapt” the lattice mismatch by a buffer layer of the (AlN)x(SiC)1-x
solid solution. This paper gives some inputs on the growth of AlN and the solid solution by the
sublimation technique, in terms of materials compatibility, hetero- and homo-epitaxial growth of
AlN and on the preparation of crack-free solid solution single crystals.
GaN Resistive Gas Sensors for Hydrogen Detection
Authors: Yun F. , Fawcett T.J. , Chevtchenko S. , Moon Y.T. , Morkoç Hadis , Wolan J.T.
Published: March 2009

We report on the fabrication and testing of GaN resistive gas sensors for hydrogen
detection. The Si-doped n-type GaN was grown by organometallic vapor phase epitaxy (OMVPE)
on c-plane sapphire substrates. The device structure is simply a pair of metal ohmic contact pads.
The sensors are sensitive to H2 gas over a wide range of concentration: the lowest concentration
tested being ~0.1% H2 (in Ar), well below the lower combustion limit in air. No saturation of the
signal is observed up to 100% H2 flow. In the continuous operation mode with varying H2
concentration, a clear and sharp response was recorded with no memory effects during ramping up
and down cycles of H2 concentration. The change in current at a fixed voltage to hydrogen was
found to change with sensor geometry. The possible gas sensing mechanisms are still under
investigation.
Hetero-Epitaxial Growth of 3C-SiC on Silicon Substrates by Plasma Assisted CVD
Authors: Shimizu Hideki , Aoyama Yosuke
Published: March 2009

3C-SiC films grown on carbonized Si (100) by plasma-assisted CVD have been
investigated with systematic changes in flow rate of monosilane (SiH4) and propane (C3H8) as
source gases. The deposition rate of the films increased monotonously and the microstructures of
the films changed from 3C-SiC single crystal to 3C-SiC polycrystal with increasing flow rate of
SiH4. Increasing C3H8 keeps single crystalline structure but results in contamination of α-W2C,
which is a serious problem for the epitaxial growth. To obtain high quality 3C-SiC films, the effects
of C3H8 on the microstructures of the films have been investigated by reducing the concentration of
C3H8. Good quality 3C-SiC single crystal on Si (100) is grown at low net flow rate of C3H8 and
SiH4, while 3C-SiC single crystal on Si (111) is grown at low net flow rate of C3H8 and high net
flow rate of SiH4. It is expected that 3C-SiC epitaxial growth on Si (111) will take placed at a
higher deposition rate and lower substrate temperature than that on Si (100).
Multi-Scale Simulation of MBE-Grown SiC/Si Nanostructures
Authors: Schmidt Alexander A. , Trushin Yuri V. , Safonov K.L. , Kharlamov V.S. , Kulikov Dmitri V. , Ambacher Oliver , Pezoldt Joerg
Published: March 2009

The main obstacle for the implementation of numerical simulation for the prediction of
the epitaxial growth is the variety of physical processes with considerable differences in time and
spatial scales taking place during epitaxy: deposition of atoms, surface and bulk diffusion, nucleation
of two-dimensional and three-dimensional clusters, etc. Thus, it is not possible to describe all
of them in the framework of a single physical model. In this work there was developed a multi-scale
simulation method for molecular beam epitaxy (MBE) of silicon carbide nanostructures on silicon.
Three numerical methods were used in a complex: Molecular Dynamics (MD), kinetic Monte Carlo
(KMC), and the Rate Equations (RE). MD was used for the estimation of kinetic parameters of
atoms at the surface, which are input parameters for other simulation methods. The KMC allowed
the atomic-scale simulation of the cluster formation, which is the initial stage of the SiC growth,
while the RE method gave the ability to study the growth process on a longer time scale. As a result,
a full-scale description of the surface evolution during SiC formation on Si substrates was
developed.
Observation of Free Carrier Redistribution Resulting from Stacking Fault Formation in Annealed 4H-SiC
Authors: Glembocki Orest J. , Skowronski Marek , Prokes S.M. , Gaskill D. Kurt , Caldwell Joshua D.
Published: March 2009

Bulk n+-4H-SiC wafers (n=1-2×1019 cm-3) containing annealing-induced
stacking faults were examined by Raman scattering. The coupled plasmon-LO mode
was observed to shift in a manner consistent with 1018 cm-3 doping in the 4H-SiC.
Numerical simulations were performed using a self-consistent Poisson-Schrödinger
solver and agree well with the experimental observations of carrier transfer from the
4H-SiC into the 3C-SiC stacking faults. The Raman data also shows that the 3C
stacking faults induce a tensile strain on the surrounding 4H-SiC regions.
Deep Electron and Hole Traps in 6H-SiC Bulk Crystals Grown by the Halide Chemical Vapor Deposition
Authors: Huh Sung Wook , Polyakov A.Y. , Chung Hun Jae , Nigam Saurav , Skowronski Marek , Glaser E.R. , Carlos W.E. , Fanton Mark A. , Smirnov N.B.
Published: March 2009

Deep electron and hole traps were studied in a series of high purity 6H-SiC single crystals
grown by Halide Chemical Vapor Deposition (HCVD) method at various C/Si flow ratios and at
temperatures between 2000 oC and 2100 oC. Characterization included Low Temperature
Photoluminescence (LTPL), Deep Level Transient Spectroscopy (DLTS), Minority Carrier Transient
Spectroscopy (MCTS), and Thermal Admittance Spectroscopy (TAS) measurements. Concentrations
of all deep traps were shown to strongly decrease with increased C/Si flow ratio and with increased
growth temperature. The results indicate that the majority of deep centers in 6H-SiC crystals grown by
HCVD are due to native defects or complexes of native defects promoted by Si-rich growth
conditions. The observed growth temperature dependence of residual donor concentration and traps
density is explained by increasing the effective C/Si ratio at higher temperatures for the same nominal
ratio of C and Si flows.
Deep Level near EC – 0.55 eV in Undoped 4H-SiC Substrates
Authors: Mitchel W.C. , Mitchell William D. , Smith S.R. , Landis G.R. , Evwaraye A.O. , Fang Z.Q. , Look David C. , Sizelove J.R.
Published: March 2009

A variety of 4H-SiC samples from undoped crystals grown by the physical vapor
transport technique have been studied by temperature dependent Hall effect, optical and thermal
admittance spectroscopy and thermally stimulated current. In most samples studied the activation
energies were in the range 0.9 - 1.6 eV expected for commercial grade HPSI 4H-SiC. However, in
several samples from developmental crystals a previously unreported deep level at EC-0.55 ± 0.01
eV was observed. Thermal admittance spectroscopy detected one level with an energy of about
0.53 eV while optical admittance spectroscopy measurements resolved two levels at 0.56 and 0.64
eV. Thermally stimulated current measurements made to study compensated levels in the material
detected several peaks at energies in the range 0.2 to 0.6 eV.
Divacancy Model for P6/P7 Centers in 4H- and 6H-SiC
Authors: Son Nguyen Tien , Umeda T. , Isoya Junichi , Gali Adam , Bockstedte M. , Magnusson Björn , Ellison Alexsandre , Morishita Norio , Ohshima Takeshi , Itoh Hisayoshi , Janzén Erik
Published: March 2009

Electron paramagnetic resonance (EPR) studies of the P6/P7 centers in 4H- and 6H-SiC
are reported. The obtained principal values of the hyperfine tensors of C and Si neighbors are in
good agreement with the values of the neutral divacancy (VCVSi
0) calculated by ab initio supercell
calculations. The results suggest that the P6/P7 centers, which were previously assigned to the
photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge
state (VCCSi
2+), are related to the triplet ground states of the C3v/C1h configurations of VCVSi
0.
Identification of Deep Level Defects in SiC Bipolar Junction Transistors
Authors: Lenahan Patrick M. , Pfeiffenberger N.T. , Pribicko T.G. , Lelis Aivars J.
Published: March 2009

In this study, we report on the observation of recombination center defects in the base of
4H-SiC bipolar junction transistors. The defects are observed through a very sensitive electrically
detected electron spin resonance technique called spin dependent recombination. To the best of our
knowledge, these results represent the first electron spin resonance results of any kind reported in a
fully processed SiC bipolar junction transistor and provide the first direct observations of the
chemical and physical nature of recombination centers in SiC bipolar junction transistors. Our
results clearly demonstrate the power of SDR techniques in the detection of recombination centers
in SiC bipolar junction transistors.
Evidence for Phosphorus on Carbon and Silicon Sites in 6H and 4H SiC
Authors: Yan Fei , Devaty Robert P. , Choyke Wolfgang J. , Gali Adam , Bhat I. , Larkin David J.
Published: March 2009

New lines are observed in the photoluminescence of 6H and 4H SiC epitaxial layers grown
in cold wall CVD reactors and doped with phosphorus. These lines are associated with neutral
phosphorus donor four particle bound exciton complexes with the phosphorus substituting on both
the carbon and silicon sublattices. Assignments are made for the (h) hexagonal and (k) cubic sites of
the phosphorus donor substituting on the two SiC sublattices.
Dependence of the Ionization Energy of Phosphorous Donor in 4H-SiC on Doping Concentration
Authors: Rao Sunil , Chow T. Paul , Bhat I.
Published: March 2009

4H-SiC implanted with high dose of phosphorus has been shown to exhibit lower sheet
resistance than 4H-SiC implanted with high dose of nitrogen. In this paper, we have implanted
various doses (1x1014cm-2, 2x1014cm-2, 1x1015cm-2 and 4x1015cm-2) of phosphorus into 4H-SiC in
order to extract the ionization energy of phosphorus in 4H-SiC as a function of the doping
concentration. Variable temperature Hall effect measurements were performed in the temperature
range from 60-600K. Least square fits using the charge neutrality equation with two donor levels
were used to extract the ionization energies and donor concentrations from the measured data. The
ionization energies for both, the hexagonal (53meV, 49meV and 26meV) and the cubic (109meV,
101meV and 74meV) site decreased as the donor concentration (5x1018cm-3, 9.8x1018cm-3 and
3.4x1019cm-3) increased.
Evaluating and Improving SIMS Method for Measuring Nitrogen in SiC
Authors: Smith Howard E. , Eyink Kurt G. , Mitchel W.C. , Wood M.C. , Fanton Mark A.
Published: March 2009

A multiple data point version of the industry standard, two data point raster-changing
procedure is employed to measure low levels (< 1 x 1017 atoms/cm3) of nitrogen (N) in silicon
carbide (SiC) by SIMS (Secondary Ion Mass Spectrometry). A current-changing procedure is also
employed. Together, these are used evaluate the assumptions of the standard method, to separate
and measure the components of background signal, and to improve upon the precision and accuracy
of the standard method. The risk of poor precision in the two-point method is demonstrated, as is
the improvement provided by the multiple-point method. Results show that, in addition to the wellknown
N memory background, adsorption background can contribute significantly to the N signal.
In general, establishing the presence of adsorption gas in this way can be used to warn of the
presence of ionization background, which is not measurable per se.
Electrical Properties of Undoped 6H- and 4H-SiC Bulk Crystals Grown by Halide Chemical Vapor Deposition
Authors: Chung Hun Jae , Huh Sung Wook , Polyakov A.Y. , Nigam Saurav , Li Qiang , Grim J.R. , Skowronski Marek , Glaser E.R. , Carlos W.E. , Freitas Jaime A. , Fanton Mark A.
Published: March 2009

Undoped 6H- and 4H-SiC crystals were grown by Halide Chemical Vapor Deposition
(HCVD). Concentrations of impurities were measured by various methods including
secondary-ion-mass spectrometry (SIMS). With increasing C/Si ratio, nitrogen concentration
decreased and boron concentration increased as expected for the site-competition effect. Hall-effect
measurements on 6H-SiC crystals showed that with the increase of C/Si ratio from 0.06 to 0.7, the
Fermi level was shifted from Ec-0.14 eV (nitrogen donors) to Ev+0.6 eV (B-related deep centers).
Crystals grown with C/Si > 0.36 showed high resistivities between 1053 and 1010 4cm at room
temperature. The high resistivities are attributed to close values of the nitrogen and boron
concentrations and compensation by deep defects present in low densities.
Electronic Structure and Magnetic Properties of Transition Metal Doped Silicon Carbide in Different Polytypes
Authors: Miao M.S. , Lambrecht Walter R.L.
Published: March 2009

We report density functional calculations using the full-potential linearized muffin-tin
orbital method on early first row transition metal doped Silicon Carbide in both cubic (3C) and
hexagonal (4H) polytypes. The energy levels in the gap for Ti, V and Cr are in good agreement with
the available photoluminescence experiments. Our calculation shows that the Ti impurity is active
for 4H but not for 3C, while V and Cr impurities are active for both polytypes. The magnetic
interactions are very different for Cr and Mn. Cr shows a very local exchange interaction that decays
rapidly, which is similar for different polytypes and different sites. The exchange interaction for Mn
is quite long range and is very sensitive to the location of the Mn pairs.
Phonons in SiC from INS, IXS, and Ab-Initio Calculations
Authors: Strauch Dieter , Dorner B. , Ivanov A.A. , Krisch M. , Serrano J. , Bosak Alexey , Choyke Wolfgang J. , Stojetz B. , Malorny Michael
Published: March 2009

Preliminary results for the phonon dispersion curves of hexagonal 4H-SiC from
experimental inelastic neutron (INS) and X-ray scattering (IXS) are reported and contrasted with
those of cubic 3C-SiC and silicon. The experimental frequencies and scattering intensities are in
excellent agreement with those from first-principles calculations using density-functional methods.
The relative merits of the two experimental techniques and aspects of the density functional
perturbation theory and the so-called frozen phonon method for the determination of the basic
phonon properties are briefly outlined.
Infrared Reflectance Study of 3C-SiC Grown on Si by Chemical Vapor Deposition
Authors: Feng Zhe Chuan , Huang C.W. , Chang W.Y. , Zhao Jie , Tin Chin Che , Lu Wei Jie , Collins W.E.
Published: March 2009

We have performed a combined investigation of experiment and theory on the infrared
reflectance from cubic SiC grown on Si by chemical vapor deposition. A damping behavior of the
interference fringes away from the reststrahlen band and a dip or notch within the “flat top” are
observed from some samples while they does not occur in high quality 3C-SiC/Si samples. The
former is interpreted due to an interfacial transition layer existed between SiC-Si and a rough surface,
while the latter can be demonstrated by a three-component effective medium model.
Precise Determination of Thermal Expansion Coefficients Observed in 4H-SiC Single Crystals
Authors: Nakabayashi Masashi , Fujimoto Tatsuo , Katsuno Masakazu , Ohtani Noboru
Published: March 2009

The coefficient of thermal expansion (CTE) of SiC single crystals is important, in
particular, for both designing device assembly and controlling stress distributions in heteroepitaxial
thin film structures grown onto SiC substrates. We have performed very precise measurements of
the CTEs for SiC single crystals comprising of single 4H polytype PVT-grown in NIPPON Steel
Corporation for a temperature range from 123 K to 473 K using a laser interferometry method. This
method allows us to directly measure the temperature dependent variation in thermal expansion of
the crystal volume with much higher accuracy, and enables us to straightforwardly obtain practical
information of CTE data. Furthermore in order to discuss the CTE behavior for a wider temperature
range the CTEs at higher temperatures up to 1573 K have been also measured using dilatometer
method. The CTE obtained for a nitrogen-doped 4H-SiC single crystal increases continuously from
0.8 ppm/K to 3.1 ppm/K for temperatures of 273 K and 423 K respectively, and further increases to
5.4 ppm/K at 1273 K. We conclude from our data that the CTE variations are likely to be almost
independent of the crystal axis directions of SiC from 123 K up to 1573 K.
Impact of Annealing Temperature Ramps on the Electrical Activation of N+ and P+ Co-Implanted SiC Layers
Authors: Blanqué Servane , Pérez R. , Mestres Narcis , Contreras Sylvie , Camassel Jean , Godignon Philippe
Published: March 2009

We have performed nitrogen and phosphorus co-implants at room temperature to obtain
high n-type carrier concentration layers in SiC. An inductive heating RTA furnace has been used
for the activation annealing. The influence of the temperature ramp parameters such as rise/decrease
temperature speed and intermediate annealing steps on the dopant activation rate and surface
morphology have been investigated. A reduction of the temperature ramp slope reduces the surface
roughness by 50%. Inclusion of a pre-activation annealing step at low temperatures (1300°C)
further reduces the surface roughness. However, the use of slower ramps or an intermediate
annealing step during ramp up reduces the free carrier concentration. The faster the ramp up, the
higher the activation rate and the resulting doping. We also demonstrate that the inclusion of a postactivation
annealing at intermediate temperatures (1150°C) reduces significantly the surface
roughness. In addition, the use of this post-annealing treatment does not degrade the activation rate
nor the carrier Hall mobility, and activation rates close to 100% have been obtained.
High Dose High Temperature Ion Implantation of Ge into 4H-SiC
Authors: Kups Thomas , Weih Petia , Voelskow M. , Skorupa Wolfgang , Pezoldt Joerg
Published: March 2009

A box like Ge distribution was formed by ion implantation at 600°C. The Ge concentration
was varied from 1 to 20 %. The TEM investigations revealed an increasing damage formation
with increasing implantation dose. No polytype inclusions were observed in the implanted regions.
A detailed analysis showed different types of lattice distortion identified as insertion stacking faults.
The lattice site location analysis by “atomic location by channelling enhanced microanalysis” revealed
that the implanted Ge is mainly located at interstitial positions.
An Approach to Improving the Morphology and Reliability of n-SiC Ohmic Contacts to SiC Using Second-Metal Contacts
Authors: Ervin Matthew H. , Jones Kenneth A. , Lee Un Chul , Das Taniya , Wood M.C.
Published: March 2009

While nickel ohmic contacts to n-type silicon carbide have good electrical properties, the
physical contact, and therefore the reliability, can be poor. An approach is described for using the
good electrical properties of Ni ohmic contacts while using another metal for its desired
mechanical, thermal and/or chemical properties. In the present work, once the Ni contacts have
been annealed forming nickel silicides and achieving low contact resistance, they are etched off.
Removing the primary Ni contacts also eliminates the poor morphology, voids, and at least some of
the excess carbon produced by the Ni/SiC reaction. The Ni contacts are then replaced by a second
contact metal. This second metal displays low contact resistance as-deposited, indicating that the
critical feature responsible for the ohmic contact has not been removed by the primary contact etch.
Not only does this approach provide more flexibility for optimizing the contact for a given
application, it also provides some insight into the ohmic contact formation mechanism.
Diffusion Welding Techniques for Power SiC Schottky Packaging
Authors: Korolkov Oleg , Rang Toomas , Syrkin A. , Dmitriev V.
Published: March 2009

This paper is devoted to the results of a diffusion welding technique applied to solve the
problem of packaging for large area SiC Schottky diodes. To supply low defect density substrates
for fabrication of 0.3 cm2 Schottky diodes TDI defect-reducing technology was used. Diodes were
fabricated on CVD grown low-doped 4H-SiC single epitaxial layer without edge termination.
Double layer Ni-Au and triple layer Ti-Ni-Au sputter metallization were used for Schottky contacts
fabrication. Non-rectifying backside contacts were provided by Ni-Au metallization. Diodes were
tested on-wafer and delivered for dicing, and packaging. To decrease the parasitic spreading
resistance the thickness of initial sputter metallization was increased by diffusion welded 30 μm
metal foil. Combined thick and plane metal layers make it possible to perform the clamp mode
package used in power electronics. This scheme of packaging ensures current takeoff from the
whole contact area and allows operating temperatures up to 600°C. The forward current-voltage
characteristics measured at 75 A measured for packaged diodes yields 250 A/cm2 (70A) at 1.9 V
forward voltage. Reverse recovery time for packaged diodes was in the range of 29-36 ns.
High Channel Mobility 4H-SiC MOSFETs
Authors: Sveinbjörnsson E.Ö. , Gudjónsson G. , Allerstam Fredrik , Ólafsson H.Ö. , Nilsson Per Åke , Zirath Herbert , Rödle T. , Jos R.
Published: March 2009

We report investigations of MOS and MOSFET devices using a gate oxide grown in the
presence of sintered alumina. In contrast to conventionally grown dry or wet oxides these oxides
contain orders of magnitude lower density of near-interface traps at the SiO2/SiC interface. The
reduction of interface traps is correlated with enhanced oxidation rate. The absence of near-interface
traps makes possible fabrication of Si face 4H-SiC MOSFETs with peak field effect mobility of
about 150 cm2/Vs. A clear correlation is observed between the field effect mobility in n-channel
MOSFETs and the density of interface states near the SiC conduction band edge in n-type MOS
capacitors. Stable operation of such normally-off 4H-SiC MOSFET transistors is observed from
room temperature up to 150°C with positive threshold voltage shift less than 1 V. A small decrease
in current with temperature up to 150°C is related to a decrease in the field effect mobility due to
phonon scattering. However, the gate oxides contain sodium, which originates from the sintered
alumina, resulting in severe device instabilities during negative gate bias stressing.
Improved Dielectric and Interface Properties of 4H-SiC MOS Structures Processed by Oxide Deposition and N2O Annealing
Authors: Kimoto Tsunenobu , Kawano H. , Noborio Masato , Suda Jun , Matsunami Hiroyuki
Published: March 2009

Oxide deposition followed by high-temperature annealing in N2O has been investigated to
improve the quality of 4H-SiC MOS structures. Annealing of deposited oxides in N2O at 1300oC
significantly enhances the breakdown strength and decreases the interface state density to 3x1011
cm-2eV-1 at EC – 0.2 eV. As a result, high channel mobility of 34 cm2/Vs and 52 cm2/Vs has been
attained for inversion-type MOSFETs fabricated on 4H-SiC(0001)Si and (000-1)C faces, respectively.
The channel mobility shows a maximum when the increase of oxide thickness during N2O annealing
is approximately 5 nm. A lateral RESURF MOSFET with gate oxides formed by the proposed process
has blocked 1450 V and showed a low on-resistance of 75 mcm2, which is one of the best
performances among lateral SiC MOSFETs reported.
Process-Dependent Charges and Traps in Dielectrics on SiC
Authors: Krishnan Bharat , Das Hrishikesh , Koshka Yaroslav , Sankin Igor , Martin P.A. , Mazzola Michael S.
Published: March 2009

Dielectric charges and charge stability were compared in different dielectrics formed on
SiC by different processing techniques. The concentration and transient behavior of the interface
and trapped charges were investigated. Strong hysteresis and flat-band voltage drift under applied
bias were observed in some of the samples. They are attributed to the trapping of the charge injected
in the dielectrics. Differences in charge injection, charge trapping, and capture/emission of carriers
by interface traps were pronounced for the investigated SiO2 and Si3N4 dielectrics.
Modelling the Heat Treatment of Sintered SmCo5 Magnets
Authors: de Campos Marcos Flavio , de Castro José Adilson , Rios Paulo Rangel
Published: March 2009

The processing of SmCo5 sintered magnets involves a post-sintering heat treatment,
where the intrinsic coercivity of the magnets may increase more than one order of magnitude.
Variables of the heat treatment like time, temperature and cooling rate have strong influence on
coercivity. We describe a method for modeling the heat treatment, which includes microstructural
features as precipitate size and 2nd phase volume fraction. The numerical solution was obtained
using the Finite Volume Method to solve Fick´s second law. Experimental data like the diffusion
coefficient of Sm into SmCo5 phase and the Sm-Co phase Diagram are used for the modeling.
Densification and Microstructural Behaviour on the Sintering of Blended Elemental Ti-35Nb-7Zr-5Ta Alloy
Authors: Taddei Elisa B. , Henriques Vinicius André Rodrigues , Silva Cosme Roberto Moreira , Cairo Carlos Alberto Alves
Published: March 2009

Beta titanium alloys, e.g., are now the main target for medical materials. Ti-35Nb-7Zr-
5Ta alloy were manufactured by blended elemental (BE) powder method, which appears to be one
of the most promising technique for titanium parts production at reduced cost. The process employs
hydrided powders as raw materials with low production costs and oxygen content. Among the
titanium alloys recently developed, Ti-35Nb-7Zr-5Ta is distinguished for presenting low modulus
of elasticity, high mechanical resistance and superior biocompatibility. Samples were produced by
mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent
densification by sintering among 800 at 1500 °C, in vacuum. Sintering behavior was studied by
means of dilatometry. Sintered samples were characterized for phase composition, microstructure
and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation,
respectively. Density was measured by Archimedes method. In this work, an alternative blending
technique (with planetary mill) was used. The samples presented a good densification and a totally
β-type microstructure, with complete dissolution of alloying elements in the titanium matrix with
the temperature increase with low pore content.
Study on Characteristics and Principium of Rare Earth Carbide Tools
Authors: Fu Tie , Yu Qi Xun , Pang Si Qin
Published: March 2009

Carbide tools play key roles in present machine manufacture. The mechanical property and
cutting performance of carbide tools are improved obviously when adding micro rare earth (RE)
elements into carbide tools. By means of some apparatus, such as materials testing machine,
Scanning Electron Microscope (SEM), dynamometer, microscope and electron probe microanalyser,
the traditional and RE carbide tools, P30 (YT5 and YT5R), P20 (YT14 and YT14R), M10 (YW1 and
YW1R), K30 (YG8 and YG8R), are studied and compared by doing a lot of experiments. These
experiments show that the bending strength, fracture toughness and anti-impact capability of RE
carbide tools are improved remarkably, and their hardness increased a little. Moreover, the cutting
force, tool-chip friction coefficient and wear of RE carbide tools decreased in cutting. In addition, the
effect and cutting principium of RE element to carbide tools are analyzed and discussed, which is
beneficial to the research and application of RE carbide tools.
A Study on Machining Quality of a Kind of Functional Hollow Lightweight Metallic Micro-Helixes by Bio-Limited Forming
Authors: Chen Bo , Cai Jun , Lian Zhi Yang , Zhang De Yuan
Published: March 2009

Helical structure plays an important role in many fields and the machining quality is
important for its applications. In this paper, a kind of functional hollow lightweight metallic
micro-helixes based on cells of spirulina was manufactured by bio-limited forming. Then the
impurity degree and the un-metallization degree, two important parameters to evaluate the machining
quality of the functional micro-helixes in the application to chiral microwave absorbing material were
investigated. Numeric models were established and the regularities were researched on how the two
parameters are influenced by metallization technology factors. The results showed that the values of
these two parameters could be reduced by adjusting the volume of the original deposition solution for
1g filtered wet activated cells, the diluted multiples of the original deposition solution, the
temperature of reaction and the time of reaction so as to improve the machining quality.
Rotary Ultrasonic Machining of Advanced Ceramics
Authors: Zeng Wei Min , Xu Xi Peng , Pei Zhi Jian
Published: March 2009

Rotary ultrasonic machining (RUM) is one of the cost-effective machining methods for
advanced ceramics, which is a hybrid machining process that combines the material removal
mechanisms of diamond grinding and ultrasonic machining (USM). This paper presents an
overview of the investigations on RUM of advanced ceramics. The issues about the material
removal mechanisms, process modeling, material removal rate, and tool wear in RUM are
reviewed. Directions of future research on RUM are also presented.
Induction Brazing Diamond Grinding Wheel with Ni-Cr Filler Alloy
Authors: Xu Zheng Yang , Xu Hong Jun , Fu Yu Can , Xiao Bing , Xu Jiu Hua
Published: March 2009

An experimental study on induction brazing diamond grinding wheel with Ni-Cr filler
alloy was carried out. Brazing trial was conducted at the temperature range of 1020-1080 oC and the
brazing time were 10, 20, 30 and 40 seconds in a flowing argon environment with a flow rate of
5000cm3/min. The scanning electron microscopic (SEM) results indicate that good wetting existed
between the brazing alloy and diamond. The element distribution of C, Cr, Si and Ni were examined
by energy dispersive spectrometer (EDS), the results demonstrated an intermediate layer rich in the
chromium formed between the filler metal and diamond. Kinds of compounds formed in the interface
were detected by means of x-ray diffraction (XRD), and the graphitization of the brazed diamond grits
was determined by Raman spectroscopy. The monolayer induction brazing diamond grinding wheels
were used in grinding of nature granite, experimental results show that induction brazing wheels
performed better than vacuum brazing diamond wheels, and no pullout of diamond grits or peeling of
the filler metal layer took place.
Fabrication of Ultra-Fine Abrasive Polishing Pads by Gel Technique
Authors: Liu Juan , Yu Yi Qing , Xu Xi Peng
Published: March 2009

In this paper, an experimental study was carried out to fabricate a new kind of ultra-fine
abrasive polishing pad by means of gel technology. The polishing pad was then used to polish
silicon wafer on a nano-polishing machine. Optical microscope and ZYGO 3D surface analyzer
were applied to observe the surface morphologies of the silicon wafer. Meanwhile, surface
morphology of ultra-fine abrasive polishing pad was observed by ESEM. No obvious gathering of
ultra-fine grains were found on the ultra-fine abrasive pad. The surface roughness (Ra) of the silicon
wafer was reduced to 0.3nm after being polished by the abrasives with average grain size of 10μm.
Mirror surface can be realized after being polished with the polishing pad.
Variable Radius Conformal Cooling Channel for Rapid Tool
Authors: Au Kin Man , Yu Kai Ming
Published: March 2009

The cooling system of a plastic injection mould is important as it affects the quality and
productivity of the polymeric components or assemblies. Contemporary cooling channel design is
confined to simple configurations of straight-drilled coolant passageway around the mould insert.
Undesirable defects resulted during injection moulding, such as warpage, are inevitable. The
application of rapid tool (RT) based on solid freeform fabrication (SFF) technologies with conformal
cooling channel (CCC) design has provided a profound opportunity in quality improvement of
polymeric components. In this study, a novel design of variable radius conformal cooling channel
(VRCCC) is proposed to achieve better uniform cooling performance. Thermal-FEA and melt flow
analysis are used to validate the method.
Research of Surface Hardening Based on Transverse Feed Grinding
Authors: Liu Ju Dong , Wang Gui Cheng , Li Qin Feng , Pei Hong Jie , Jia Zhi Hong , Wang Zhi
Published: March 2009

The structure and performance of the hardened layer in this paper has been researched by means of transverse feed grinding 40Cr steel on a plane grinding machine, the result shows that under the action of the grinding temperature field, there are different structural change rules and distributing characteristics of micro-hardness. Although there is always a softened band, which is made up of a transitional area and an unhardened area or a temper area in the hardened layer, the reasonable softened band is conducive to the improvement of wear-resistant quality of a hardened layer under the condition of oil lubrication.
Modeling of Virtual Machining System for Contour Milling of Gear Indexing Cam
Authors: Guo Pei Quan , Huang Chuan Zhen , Shi Jin Ping , Li Xiao Xia
Published: March 2009

Geometrical model of virtual machining system was introduced. Based on the analysis of
the machining system, it was divided into workpiece subsystem and tool subsystem. Dynamic models
of subsystems have been established by means of simplification of machining system. Dynamic
analysis and simulation have been done. Model of virtual machining system is the combination of
geometrical model and dynamic model. Based on the dynamic analysis and simulation of virtual
machining system, conclusion was drawn: (1) In cutting process, as cutter feeds into cutting zone,
vibration appears and becomes stronger and stronger. As cutter tends to leave cutting zone, vibration
becomes weaker and weaker and disappears finally. The most violent vibration occurs as cutter has
engaged into cutting zone and as cutter tends to leave cutting zone. (2) As machining corresponding to
dwell of indexing plate, dynamic response is smooth and steady. (3) Vibration will attenuate sharply
after cutter leaving cutting zone. The operation of virtual machining system accords with the
appearance in real machining process. Properties of product model are very close to those of real
machined cam.
The Kinematic Analysis of a Novel Parallel Machine Tool with 3-HSS Structure
Authors: Gao Tie Hong , Yu Chang Juan , Qi Jiang Bo , Cao Jun Yi
Published: March 2009

A novel parallel machine tool(PMT) with 3-HSS structure is presented in this paper. The
three ball screws and guiding-parallels of this PMT are horizontally and parallel set. The three helix
joints are driving components connected to and driven by servos, and the corresponding parameters
of the cutter position can be obtained. The kinematics modeling is simple and the direct and inverse
kinematics can be easily obtained for this PMT. It also has other advantages, such as spacious
workspace in horizon direction, simple structure, easy controlling, etc. This PMT can be used in
three-dimensional carving, milling and other machining processing. This kind of PMT has been
designed and manufactured in our institution, and has also been tested successfully. Besides, it’s
easy to get the 5-DOF series-parallel machine tool through fixing two more revolving structure on
the mobile platform. It’s also easy to furnish complex surface processing using a rotary table. This
paper studies mainly on DOF analysis, derivation of the kinematical equation, direct and inverse
kinematics, workspace and other kinematical problems of the parallel machine.
The Prediction of Earing and the Design of Initial Shape of Blank in Cylindrical Cup Drawing
Authors: Yang Tung Sheng , Hsu Yuan Chuan
Published: March 2009

The parameters such as aniotropic property, blank holder force and friction coefficient
between tool and blank are not only effect on the forming force, stress and strain distribution of the
worpiece, but also on the earing in products. In this paper, the finite element method is used to
investigate the earing of the deep drawing process. In order to verify the prediction of FEM
simulation of the earing in the cylindrical cup drawing process, the experimental data are compared
with the results of the current simulation. A finite element analysis is also utilized to reduce the earing
profile of the drawn products, a reverse forming method for obtaining the initial blank’s shape
according to the forward cup deep drawing simulation is proposed.
Experiment Study on Shape Defect of Cylinder Shallow Shell
Authors: Yang Yu Ying , Zhao Li Hong , Sun Zhen Zhong
Published: March 2009

In this paper, the shape defect is studied by the experiment of drawing parts before and
after trimming for the rectangle cylinder shallow shell. The mechanism of shape defect and the effect
of forming condition and trimming on shape defect are discussed. And the influence laws of forming
conditions on shape defect are achieved. Such as binder force, curvature radius, sheet thickness, yield
strength and residual stress after trimming.