bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Evaluation of Thermally Oxidized and Deposited Dielectric in NMOS-PMOS devices
Authors: Weng Ming Hung , Idris Muhammad I. , Chan H.K. , Murphy A.E. , Smith D.A. , Clark D.T. , Young R.A.R. , Ramsay E.P. , Horsfall Alton B.
Published: May 2016

We demonstrate the influence of enhancing the dielectric film used to form the gate in complimentary MOS circuits, designed for high temperature operation. The data show that the characteristics of both n-MOS and p-MOS capacitors and transistors have degraded capacitance characteristics in terms of the trapped charge in the dielectric, although the interface state density is dictated by the underlying stub oxide, at around 5×1012 cm-2eV-1. The use of a deposited oxide also reduces the variability in the critical electric field in the oxide, whilst maintaining a value of approximately 10MV cm-1. The channel mobility extracted from n-and pMOS transistors fabricated alongside the capacitors showed similar values, of approximately 3.8 cm2V-1s-1, which are limited by the high doping level in the epilayers used in this study.
Effect of Activation Annealing and Reactive Ion Etching on MOS Channel Properties of (11-20) Oriented 4H-SiC
Authors: Chowdhury Sauvik , Yamamoto Kensaku , Chow T. Paul
Published: May 2016

In this paper we have investigated the effect of two key processing steps for the fabrication of 4H-SiC trench gate power MOSFETs, namely activation annealing and reactive ion etching on the MOS interface properties of a-face (11-20) 4H-SiC. By optimizing activation annealing conditions, high channel mobility (µfe) of 111 cm2/V.s, threshold voltage (VT) of 3.5V and subthreshold slope (S) of 194 mV/dec was obtained. However, after reactive ion etching (RIE) of the surface, µfe reduced to 81 cm2/V.s with increase in VT to 5V and S to 331 mV/dec. This is possibly due to increase in interface trap density from 1.8×1012 cm-2 to 3.3×1012 cm-2 after RIE treatment estimated from by MOS gated diode characteristics. Increased trap density contributes to higher coulombic scattering as indicated by the weaker temperature dependence of high field mobility in RIE etched sample.
Influence of Oxide Processing on the Defects at the SiC-SiO2 Interface Measured by Electrically Detected Magnetic Resonance
Authors: Gruber Gernot , Aichinger Thomas , Pobegen Gregor , Peters Dethard , Koch Markus , Hadley Peter
Published: May 2016

Anneals in nitrogen (N) containing atmosphere have been proven as efficient means of improving the channel mobility of SiC MOSFETs. It has been demonstrated that simultaneously the density of interface traps is reduced. However, this process is not yet fully understood. In this study we show a comparison of MOSFETs annealed in different atmospheres and compare their electrically detected magnetic resonance (EDMR) spectra with electrical parameters. We find hints for the N incorporation not only passivating but also creating or transforming defects.
Investigation of the Interface Quality and Reliability of 4H-SiC MOS Structure with NO and Forming Gas Annealing Treatment
Authors: Peng Zhao Yang , Wang Yi Yu , Shen Hua Jun , Bai Yun , Tang Yi Dan , Wu Jia , Li Chengzhan , Liu Kean , Liu Xin Yu
Published: May 2016

Effects of NO and forming gas annealing treatment on the interface quality and reliability of 4H-SiC MOS were systematically studied by low temperature conductance measurements in combination with time-zero dielectric breakdown and time-dependent dielectric breakdown methods. The interface trap density (Dit) showed no obvious reduction after forming gas annealing, and the values of Dit decreased significantly after combined NO and forming gas annealing treatment. The F-N barrier height, electric field to breakdown (Ebd) and charge to breakdown (Qbd) of the MOS structure increased from 2.42 eV, 10 MV/cm, 1mC/cm2 to 2.62 eV, 10.7 MV/cm, 78mC/cm2 after forming gas annealing. The values of F-N barrier height, Ebd and Qbd for MOS capacitors with combined NO and forming gas annealing treatment are 2.69 eV, 10.2 MV/cm, and 24mC/cm2. These results suggest that forming gas annealing is more effective in reliability improvement. While when considering the interface trap density, it seems that combined NO and forming gas annealing treatment is a better choice.
High Channel Mobility 4H-SiC MOSFETs by As and P Implantation Prior to Thermal Oxidation in N2O Atmosphere
Authors: Mikhaylov Aleksey I. , Reshanov Sergey A. , Schöner Adolf , Afanasyev Alexey V. , Luchinin Victor V. , Knoll Lars , Minamisawa Renato A. , Alfieri Giovanni , Bartolf Holger
Published: May 2016

High channel mobility 4H-SiC MOSFETs have been demonstrated by phosphorus and arsenic implantation prior to thermal oxidation in N2O. The maximum field-effect mobility of 81 and 114 cm2/Vs were achieved, respectively. The MOSFET fabrication was done on lightly aluminium doped p-type epitaxial layers and on heavily aluminium implanted p-well.
Flatband Voltage Shift Depending on SiO2/SiC Interface Charges in 4H-SiC MOS Capacitors with AlON/SiO2 Stacked Gate Dielectrics
Authors: Hosoi Takuji , Azumo Shuji , Yamamoto Kenji , Aketa Masatoshi , Kashiwagi Yusaku , Hosaka Shigetoshi , Asahara Hirokazu , Nakamura Takashi , Shimura Takayoshi , Watanabe Heiji
Published: May 2016

The mechanism of flatband voltage shift in SiC metal-oxide-semiconductor (MOS) capacitors with stacked gate dielectrics consisting of aluminum oxynitride (AlON) layers and SiO2 underlayers was investigated by varying the AlON and SiO2 thicknesses. The flatband voltages of the fabricated capacitors with fixed SiO2 underlayer thicknesses were almost independent of the AlON thickness, indicating the negligible charges in AlON layer. On the other hand, when varying SiO2 underlayer thickness, the flatband voltage decreased with an increase in capacitance equivalent thickness (CET), and the slope of their linear fit was comparable to that for SiC MOS capacitors without AlON layer. These observations can be well explained by assuming interface charges at AlON/SiO2 interface with an amount comparable, but a polarity opposite to, those at SiO2/SiC interface.
Interface Analysis of P-Type 4H-SiC/Al2O3 Using Synchrotron-Based XPS
Authors: Suvanam Sethu Saveda , Yazdi Milad Ghadami , Usman Muhammad , Götelid Mats , Hallén Anders
Published: May 2016

In this paper, the interface between Al2O3 and p-type 4H-SiC is evaluated using x-ray photoelectron spectroscopy (XPS) measurements. These studies are made on dielectric-semiconductor test structures with Al2O3 as dielectric with different pre-and post-deposition treatments. XPS measurements on the as-deposited samples with two different pre-surface cleaning have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60s, a SiO2 interlayer is formed. The surface band bending was determined from Si 2p core level peak shifts measured using XPS. These results suggest that Al2O3 deposited on the p-type 4H-SiC have a net positive oxide charge which is complementary to that of n-type 4H-SiC. From these shifts it was found that the as-deposited RCA cleaned sample had an oxide charge of 5.6×1013 q/cm-2, as compared to standard cleaned samples, having 4.6×1013 q/cm-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N2O, down to a value of 4×1013 q/cm-2.
Impact of Phosphorus Implantation on the Electrical Properties of SiO2/4H-SiC Interfaces Annealed in N2O
Authors: Fiorenza Patrick , Di Franco Salvatore , Giannazzo Filippo , Rascunà Simone , Saggio Mario , Roccaforte Fabrizio
Published: May 2016

In this work, the combined effect of a shallow phosphorus (P) pre-implantation and of a nitridation annealing in N2O on the properties of the SiO2/4H-SiC interface has been investigated. The peak carrier concentration and depth extension of the electrically active dopants introduced by the nitridation and by the combination of P pre-implantation and nitridation were determined by high resolution scanning capacitance microscopy (SCM). Macroscopic capacitance-voltage (C-V) measurements on metal oxide semiconductor (MOS) capacitors and nanoscale C-V analyses by SCM allowed to quantify the electrical effect of the donors introduced underneath the SiO2/4H-SiC interface. Phosphorous pre-implantation and subsequent high temperature electrical activation has been shown not only to produce an increased doping in the 4H-SiC surface region but also a better homogeneity of surface potential with respect to the use of N2O annealing only.
3C-SiC Microdisks for Visible Photonics
Authors: Radulaski Marina , Babinec Thomas , Zhang Jing Yuan Linda , Buckley Sonia , Kelaita Yousif , Müller Kai , Lagoudakis Konstantinos , Alassaad Kassem , Ferro Gabriel , Vučković Jelena
Published: May 2016

We fabricated and characterized record small microdisk resonators in thin (210 nm) 3C-SiC film grown on Si (100) substrate. It was found to support high quality factor whispering gallery modes at visible wavelengths. We demonstrated room temperature coupling of these modes to the intrinsic photoluminescence of 3C-SiC at room temperatures and identified their polarization. Finally, we discussed applications for quasi-phasematched second harmonic generation from infrared visible wavelengths.
Etching Rate Behavior of 4H-Silicon Carbide Epitaxial Film Using Chlorine Trifluoride Gas
Authors: Hirooka Asumi , Habuka Hitoshi , Kato Tomohisa
Published: May 2016

4H-silicon carbide epitaxial film was etched using chlorine trifluoride gas. The etch rate of C-face at 2-100 % and at various temperatures was 0.8 – 10 μm min-1, which was comparable to those of the silicon carbide substrates. The surface morphology observed after the etching was very smooth, in contrast to that of the substrate showing many pits.
Development of “Si-Vapor Etching” and “Si Vapor Ambient Anneal” in TaC/Ta Composite Materials
Authors: Yabuki Norihito , Torimi Satoshi , Nogami Satoru , Kitabatake Makoto , Kaneko Tadaaki
Published: May 2016

We propose the thermal chemical etching process for Silicon Carbide (SiC) under the Si-vapor ambient using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this process, the high-rate “Si-vapor etching” method is applied to the removal of the surface damage and the formation of epi-ready surface. Over 10μm of “Si-vapor etching” provides smooth surface without latent scratch and low stacking faults density as same as on the CMP after epitaxial growth, which are observed by confocal microscope with differential interference contrast (C-DIC) microscope and Photo-Luminescence (PL) imaging measurement. Furthermore, the low-rate Si-vapor etching method, “Si-vapor ambient annealing” is applied to post-implantation activation annealing process without conventional C-cap. “Si-vapor ambient annealing” provides lower sheet resistance and smoother surface than the C-cap annealing after very high temperature annealing up to 2000 °C.
Design of Area-Efficient, Robust and Reliable Junction Termination Extension in SiC Devices
Authors: Bolotnikov Alexander , Losee Peter A. , Deeb Peter , Wang Meng Li , Dunne Greg , Kretchmer James , Arthur Stephen , Stevanovic Ljubisa
Published: May 2016

This paper discusses SiC JTE design tradeoffs required to maximize device performance while minimizing consumed die area, fabrication cost and maintaining good reliability. Modeling and experimental results are provided.
Electrical Performance of 4H-SiC Based Drift Step Recovery Diodes
Authors: Ivanov Pavel A. , Kon'kov Oleg , Samsonova Tatyana , Potapov Alexander , Grekhov Igor
Published: May 2016

Mesa-epitaxial 4H-SiC p+-p-no-n+-diodes were fabricated from commercial epitaxial wafers. Reverse recovery characteristics of the diodes were measured in pulse regimes to be relevant to operation of drift step recovery diodes (DSRDs) [1]. When injecting the minority carriers by forward current pulse followed by applying a reverse voltage pulse, the diodes are able to break the reverse current in a subnanosecond time (DSRD-mode). Different regimes of diode operation in DSRD-mode are investigated such as variable reverse voltage amplitude, forward current amplitude and duration, time delay between forward and reverse pulses.
Forward Current of Al+ Implanted 4H-SiC Diodes: A Study on Periphery and Area Components
Authors: Puzzanghera Maurizio , Nipoti Roberta
Published: May 2016

The temperature dependence of the bulk and periphery forward current components of vertical 4H-SiC p+-i-n diodes, with Al+ implanted circular anodes of diameters in the range 150-1000 mm, have been obtained from the analysis of the results of forward current-voltage measurements in the temperature range 30-290°C. The zero voltage bulk and periphery current densities at different temperatures have been used to compute the temperature dependence of: (i) the effective carrier lifetime in the space charge region, (ii) the minority carrier diffusion coefficient to lifetime ratio in the base region, and (iii) a surface quality parameter.
Silicon Carbide Schottky Rectifiers with Improved Avalanche Ruggedness
Authors: Konstantinov Andrei , Jinman Song , Young Sungmo , Lee Brian , Allerstam Fredrik , Neyer Thomas , Akram Sal
Published: May 2016

Silicon carbide Schottky-barrier diode (SBD) rectifiers have been manufactured with low on-state voltages, high surge currents and high avalanche ruggedness. Non-destructive unclamped inductive switching currents of 188 A (mean) are achieved for the 1200 V 15 A rectifier. Very tight distribution of maximum sustained UIS current is confirmed. We relate improved avalanche ruggedness to bulk avalanche breakdown and show the breakdown pattern of the new Schottky rectifier being the same type as that for the p-n diode.
Advanced SiC Power MOSFETs Manufactured on 150mm SiC Wafers
Authors: Matocha Kevin , Banerjee Sujit , Chatty Kiran
Published: May 2016

An advanced silicon carbide power MOSFET process was developed and implemented on a high-volume 150mm silicon production line. SiC power MOSFETs fabricated on this 150mm silicon production line were demonstrated with blocking voltage of 1700V with VGS=0V. These SiC MOSFETs have a specific on-resistance as low as 3.1 mΩ-cm2 at room temperature, increasing to 6.7 mΩ-cm2 at 175°C. Devices were packaged in TO-247 package and measured to have on-resistance of 45 mΩ with VGS=20V at room temperature. Clamped inductive switching characterization of these SiC MOSFETs shows turn-off losses as low as 110 uJ (700V, 19.5A). The high-temperature gate bias stability was characterized at positive (+20) and negative gate bias (-10V) at 175°C. After 750 hours of gate stress at a gate bias of VGS=+20V and 175°C, we observe less than a 250mV shift in the threshold voltage. After 750 hours of stress at VGS=-10V and 175°C, we characterize a threshold voltage shift less than 100mV. This shows promise for high-volume production of reliable SiC MOSFETs on 150mm wafers.
Potential of 4H-SiC CMOS for High Temperature Applications Using Advanced Lateral p-MOSFETs
Authors: Albrecht Matthaeus , Erlbacher Tobias , Bauer Anton J. , Frey Lothar
Published: May 2016

In this work, the impact of the n-well doping concentration on the channel mobility and threshold voltage of p-MOSFETs and their applications in CMOS-devices is evaluated. For this purpose lateral p-channel MOSFETs with different channel lengths (L = 800 μm, 10 μm, 5 μm, and 3 μm) and doping concentrations (ND = 1015 cm-3 and 8·1015 cm-3) were fabricated and the respective field-effect mobility was extracted from the transfer-characteristics. Comparable to n-MOSFETs the mobility of p-MOSFETs was found to be the highest for the lowest doping concentration in the channel and the absolute value of the threshold voltage increases with increasing doping concentration [4]. To investigate its suitability for CMOS applications, inverters with different doping concentrations for n-MOSFET (NA = 1015 cm-3 and 1017 cm-3) und p-MOSFET (ND = 1015 cm-3 and 8·1015 cm-3) were built. For logic levels of 0 V and 10 V, the voltage transfer characteristic with the highest input ranges was obtained for a low p-MOSFET and a high n-MOSFET doping concentration. The lowest propagation delay time could be achieved with a low p-MOSFET and a low n-MOSFET doping concentration. At room temperature as well as at high temperatures T = 573 K the drain current of p-MOSFETs with channel lengths below 3 μm is hampered by the series resistance of the source and drain region which limits the performance of CMOS devices.
Analytical Description of the Input Capacitance of 4H-SiC DMOSFET’s in Presence of Oxide-Semiconductor Interface Traps
Authors: Licciardo Gian Domenico , di Benedetto Luigi , Bellone Salvatore
Published: May 2016

An analytical model of the input capacitance of Vertical DMOSFETs in 4H-SiC is presented, in order to provide an accurate instrument for the quantitative analysis and synthesis of the device and for accurate interpretations of C-V measurements. The model describes the charge dynamics into the channel and the accumulation region of the device, in presence of the energy dependent oxide-semiconductor interface trapped charge. Comparisons with numerical simulations show that the model correctly describes the variations of the surface potential induced by the gate voltage in all the device regions covered by the oxide, from accumulation to strong inversion of the channel, and to correctly relate them to the capacitance variations.
Characteristics of High-Threshold-Voltage Low-Loss 4H-SiC MOSFETs with Improved MOS Cell Structure
Authors: Ebiike Yuji , Tanioka Toshikazu , Furuhashi Masayuki , Osawa Ai , Imaizumi Masayuki
Published: May 2016

High threshold voltage low loss 600 V 4H-SiC MOSFETs have been fabricated successfully using a re-oxidation technique for gate oxides and an n-type doping in the Junction Field Effect Transistor region of the MOSFET with shrunk MOS cells. The MOSFET has exhibited a high threshold voltage of more than 4 V and a low specific on resistance of 5.2 mΩ·cm2 at 25 °C. The MOSFET has also exhibited a sufficient blocking characteristic at VG of 0 V at 150 °C. High speed switching with low switching losses has been demonstrated successfully using the MOSFET at 150 °C.
Trench-MOSFETs on 4H-SiC
Authors: Banzhaf Christian T. , Schwaiger Stephan , Scholten Dick , Noll Stefan , Grieb Michael
Published: May 2016

This paper introduces n-channel normally-off Trench-MOSFETs on 4H-SiC featuring a blocking voltage of 600 V and 1200 V. The Trench-MOSFETs exhibit a specific room temperature on-state resistance RDS,on of 1.5 mΩ cm² and 2.7 mΩ cm², respectively. It is shown that a further reduction of the RDS,on by approximately 25 % can be achieved using square-shaped or hexagonal unit cells instead of stripe-shaped unit cells. The Trench-MOSFET switching characteristics using a double pulse setup with a switching current Isw of 100 A and a switching voltage Vsw of 450 V is presented and discussed. The short turn-off and turn-on times in the range of several ten nanoseconds yield large maximum disw/dt and dvsw/dt values, which enable highly efficient power conversion with low switching losses.
Effect of Electron Irradiation on 1700V 4H-SiC MOSFET Characteristics
Authors: Popelka Stanislav , Hazdra Pavel
Published: May 2016

The effect of 4.5 MeV electron irradiation on static characteristics of commercially available 5 A/1700 V SiC power MOSFETs is investigated. Results show that in the low dose range (up to 20 kGy) the threshold voltage decreases rapidly with irradiation dose but devices keep full functionality. This effect is caused by embedding of the positive charge into the gate oxide. When electron dose reaches 200 kGy, the threshold voltage moves back close to its original value, however, the ON‑state resistivity increases and transconductance is lowered. This is caused by introduction of deep acceptor centers into the low doped drift region of MOSFET. This effect can be considered as a cause of the final failure of the device (the lost of the ON-state capability).
Using SiC MOSFET’s Full Potential – Switching Faster than 200 kV/μs
Authors: Kreutzer Otto , Heckel Thomas , Maerz Martin
Published: May 2016

SiC-MOSFETs are available since several years, but unlike SiC diodes they have not arrived in the mass market yet. The main reason is that the higher costs do not get compensated by the technical advantages in common applications. This lack is not only caused by the SiC-MOSFETs itself, but also by the packaging and the gate drivers. Consequently the main challenge for getting SiC-MOSFETs to a wider acceptance by application engineers is to show how all benefits of the new technology can be used. This paper demonstrates how SiC-MOSFETs can be operated in a standard half bridge application with exceptional switching speeds of less than 4 ns, resulting in slopes of more than 200 kV/μs and lowest possible switching losses. Previous publications have claimed to use “the full potential of the SiC devices for power conversion applications” achieving switching times of 20 ns [1].
Readiness of SiC MOSFETs for Aerospace and Industrial Applications
Authors: Stevanovic Ljubisa , Losee Peter A. , Kennerly Stacey , Bolotnikov Alexander , Rowden Brian , Smolenski Joseph , Harfman-Todorovic Maja , Datta Rajib , Arthur Stephen , Lilienfeld David , Schuetz Tobias , Carastro Fabio , Tao Feng Feng , Esler David , Raju Ravi , Dunne Greg , Cioffi Philip , Yu Liang Chun
Published: May 2016

This paper highlights ongoing efforts to validate performance, reliability and robustness of GE SiC MOSFETs for Aerospace and Industrial applications. After summarizing ruggedness and reliability testing performed on 1.2kV MOSFETs, two application examples are highlighted. The first demonstrates the 1.2kV device performance in a prototype high frequency 75kW Aviation motor drive. The second highlights the experimental demonstration of a 99% efficient 1.0MW solar inverter using 1.7kV MOSFET modules in a two-level topology switching at 8kHz. Both applications illustrate that SiC advantage is not only in improved performance, but also in significant system cost savings through simplifications in topology, controls, cooling and filtering.
Experimental and Theoretical Study of 4H-SiC JFET Threshold Voltage Body Bias Effect from 25 °C to 500 °C
Authors: Neudeck Philip G. , Spry David J. , Chen Liang Yu
Published: May 2016

This work reports a theoretical and experimental study of 4H-SiC JFET threshold voltage as a function of substrate body bias, device position on the wafer, and temperature from 25 °C (298K) to 500 °C (773K). Based on these results, an alternative approach to SPICE circuit simulation of body effect for SiC JFETs is proposed.
A 500 °C Monolithic SiC BJT Latched Comparator
Authors: Tian Ye , Lanni Luigia , Rusu Ana , Zetterling Carl Mikael
Published: May 2016

This paper presents a monolithic 4H-SiC BJT latched emitter-coupled logic (ECL) comparator for high temperature analog-to-digital conversion. The comparator consists of a low-gain pre-amplifier, a track and latch stage and an output buffer. For low-speed input signals, the comparator input offset voltage is 3.9 mV at 27 °C and monotonically increases up to 9.1 mV at 500 °C. The single-ended output swing is 5.5 V at 27 °C and 3.9 V at 500 °C. The minimum comparison time is around 1μs from 27 °C to 500 °C. The whole comparator dissipates 464 mW in average over the considered temperature range with a 15 V power supply. It consumes 2.25 × 0.84 mm2 chip area (with the bond pads included).
Design Impact on the Static and Short-Circuit Characteristics of SiC-SIT with Non-Uniformly Doped Channel
Authors: Niu Shi Qin , Berthou Maxime , Tournier Dominique
Published: May 2016

The static characteristics and short-circuit capabilities of SIT (Static Induction Transistor) depend strongly on its channel design. Analysis show that the doping concentration and the width of the channel are crucial parameters in determining the specific on-resistance, threshold voltage and saturation capabilities of the device. Classically SIT is designed with a uniformly doped channel. Improving the saturation capability of such a device comes along with increasing its on resistance. This drawback can be overcome by using non-uniformly doped channel. This paper shows that this technique achieves a 12.3% decrease in saturation current without changing its on-resistance compared to uniformly doped channel case. This result allows a significant increase of 31% in terms of short-circuit withstanding time of SIT.
Current Gain Stability of SiC Junction Transistors Subjected to Long-Duration DC and Pulsed Current Stress
Authors: Sundaresan Siddarth G. , Grummel Brian , Singh Ranbir
Published: May 2016

The current gain stability of a second generation of 1200 V rated SiC Junction Transistors (SJTs) under long-term DC and pulsed current operation is investigated. A 1000-hour long, 200 A/cm2 DC current stress results in a ≈ 10% reduction of the current gain (β) during the early stages of the stress test, while the β is perfectly stable for the remainder (>90%) of the stress duration. The same amount of stress charge applied as a pulsed current in lieu of DC current results in similar extent of β degradation for the Gen-II SJTs. The pulsed current stressing is conducted at frequencies ranging from 50 kHz to 200 kHz, at a fixed duty cycle of 0.5.
Stress in SiC Single Crystal Caused by the Difference of CTE of SiC Seed and Graphite Holder and Role of the Elastic Moduli
Authors: Fadeev Alexey , Lebedev Andrey , Tairov Yuri
Published: May 2016

The specific elastic energy (SEE) of the system "SiC single crystal on graphite holder", caused by cooling process due to difference in coefficients of thermal expansion (CTE), is simulated. The dependence of SEE and corresponding elastic stress of SiC single crystal attached to the graphite holder on thickness of holder and SiC crystal is considered. The parameters of the synthetic graphite that can be used for the minimizing the stress are analyzed.
4H-SiC n-Channel DMOS IGBTs on (0001) and (000-1) Oriented Lightly Doped Free-Standing Substrates
Authors: Chowdhury Sauvik , Hitchcock Collin W. , Dahal Rajendra P. , Bhat I. , Chow T. Paul
Published: May 2016

We experimentally demonstrate 4H-SiC n-channel, DMOS Insulated Gate Bipolar Transistors (IGBTs) on 180 µm thick lightly doped free-standing n- substrates with an ion-implanted collector region, and metal-oxide-semiconductor (MOS) gate on (0001) and (000-1) surfaces. The IGBTs show an on-state current of 20A/cm2 at a power dissipation of 300W/cm2. Threshold voltage of 7.5V and 10.5V was obtained on Si-face and C-face respectively. Both IGBTs show a small positive temperature coefficient of the forward voltage drop, which is useful for easy parallelization of devices.
3.3 kV-Class 4H-SiC UMOSFET by Double-Trench with Tilt Angle Ion Implantation
Authors: Kobayashi Yusuke , Harada Shinsuke , Ishimori Hiroshi , Takasu Shinji , Kojima Takahito , Ariyoshi Keiko , Sometani Mitsuru , Senzaki Junji , Takei Manabu , Tanaka Yasunori , Okumura Hajime
Published: May 2016

A 3.3 kV trench MOSFET with double-trench structure was demonstrated. The deep buried p-base regions were fabricated using tilt angle ion implantation into the sidewalls of the trench contacts. The distance between the trench gate and trench contact was determined through simulation, in order to optimize the trade-off between on-resistance (RonA) and the electrical field in the oxide (Eox). A tapered trench was located in the connective area between the edge termination and the active area, in order to maintain breakdown voltage. We achieved a RonA of 10.3 mWcm2 and a breakdown voltage of 3843 V and the maximum Eox at breakdown voltage was estimated to be 3.2 MV/cm.
Modification of Etched Junction Termination Extension for the High Voltage 4H-SiC Power Devices
Authors: Elahipanah Hossein , Salemi Arash , Zetterling Carl Mikael , Östling Mikael
Published: May 2016

High voltage 4H-SiC bipolar junction transistors (BJTs) with modified etched junction termination extension (JTE) were fabricated and optimized in terms of the length (LJTE) and remaining dose (DJTE) of JTEs. It is found that for a given total termination length (Σ LJTEi), a decremental JTE length from the innermost edge to the outermost mesa edge of the device will result in better modification of the electric field. A breakdown voltage (BV) of 4.95 kV is measured for the modified device which shows ~20% improvement of the termination efficiency for no extra cost or extra process step. Equal-size BJTs by interdigitated-emitter with different number of fingers and cell pitches were fabricated. The maximum current gain of 40 is achieved for a single finger device with the emitter width of 40 µm at IC = 0.25 A (JC = 310 A/cm2) which corresponds to RON = 33 mΩ.cm2. It is presented that the current gain decreases by having more fingers while the maximum current gain is achieved at higher current density.
Vertical Termination Filled with Adequate Dielectric for SiC Devices in HVDC Applications
Authors: Nguyen Thi Thanh Huyen , Lazar Mihai , Augé Jean Louis , Morel Hervé , Phung Luong Viet , Planson Dominique
Published: May 2016

Recently, thanks to the advancement in SiC process technology, the deep trench termination (DT2) technique becomes an appropriate choice for future high voltage SiC power device. This technique termination is based on the use of a wide and deep trench, which is filled by a dielectric and associated with a field plate. DT2 technique increases the breakdown voltage (VBR) to a value near to the ideal one that can be obtained in a plan case; and at the same time, reduces drastically the chip area comparing to the previous conventional techniques. In this work, the DT2 used for a 3 kV 4H-SiC bipolar vertical diode is presented. Simulations using TCAD SENTAURUS software show that a maximum breakdown voltage of 3286 V at room temperature can be achieved with a deep trench of 20μm corresponding to 98 % of a parallel plane breakdown voltage for the drift layer of 18 μm. Those simulations also point out the important impact of the structure of the trench; the dielectric critical electric filled (Ec), the permittivity (εr) of the dielectric filled, etching defects as microtrench, fixed charges at the interfaces...on the VBR of power device.
NOx Sensing with SiC Field Effect Transistors
Authors: Möller Peter , Andersson Mike , Lloyd Spetz Anita , Puustinen Jarkko , Lappalainen Jyrki , Eriksson Jens
Published: May 2016

In this paper, we investigated the nitrogen oxides (NO, NO2) detection capability of strontium titanate (SrTiO3) when used as sensing layer on gas sensitive silicon carbide field effect transistors (SiC-FETs). Sensitivity, selectivity and response times for NO, NO2, and NH3 were characterized, to determine the possibility for diesel exhaust after treatment control applications. It was found that NOx can be detected down to single digit ppm levels at sensor temperatures in the 550°C - 600°C range. In addition, the results indicate that it is possible to suppress sensitivity to ammonia by selecting an operating temperature around 530°C.
Dynamic Colour Change of Multifunctional Thermochromic-Fluorescent Pigments
Authors: Panák Ondrej , Držková Markéta , Kaplanová Marie , Klanjšek Gunde Marta
Published: May 2016

The aim of presented paper was to prepare and characterise multifunctional thermochromic-fluorescent pigments with potential application in anti-counterfeiting patterns in security printing. Pigments were prepared by microencapsulation of chosen thermochromic system into melamine formaldehyde resin and the resin was modified with Uranine and Acid Red 52 fluorescent dyes, respectively. The fluorescence at low and high temperature was measured by spectrofluorometer. The concentration of 2.3 × 10–5 grams of fluorescent dye per one gram of polymer is sufficient for detection of fluorescence of modified polymeric shell. The dynamic colour change of prepared pigments was analysed in terms of cumulative colour difference obtained from reflectance measurements. Resulting multifunctional pigments exhibit much lower colour contrast and wider temperature sensitive interval in comparison with the bulk thermochromic system. However, the concept of two levels of verification based on two types of colour change embodied in one pigment has been approved.
Effect of Annealing on Room Temperature Multiferroics of BiFe1-xCoxO3
Authors: Wang Yang , Fu De Xiang , Li Wen Zhi , Wang Jian Hua , Zhang Wen Hao , Li Yong Tao , Liu Sheng Li , Xie Liang , Zhang Hong Guang
Published: May 2016

We studied the effect of annealing and Co ion doping on the structure, leakage current, ferroelectric polarization and magnetism of BiFeO3 samples. X-ray diffraction patterns demonstrate that an appropriate Co doping concentration is favor of suppressing the secondary phase but annealing treatment is apt to the growth of both the main and the secondary phases. The current density as a function of an electric field indicates that Co doping increases the leakage current density as samples before annealing but suppresses it after annealing. Annealing treatment improves the leakage for Co-doped sample and reduces it for the undoped sample. Ferroelectric hysteresis loops reflect that Co ions doping is liable to increase the ferroelectric polarization, while the sample is annealed it will do opposite effect. However the annealing treatment do improve the ferroelectricity for pure BiFeO3 sample. The magnetic hysteresis at room temperature shows the obvious enhancement of ferromagnetic properties with the sample after annealing.
Ag-Enhanced Antibacterial Property of MgO Film
Authors: Alajmi Zafer , Fu Tao , Zhao Yan Tao , Yang Shui Yun , Sun Jia Mao
Published: May 2016

MgO and silver-containing MgO (AgMgO, 3.3, 9.1 at% Ag) films were sol-gel coated on titanium to improve its antibacterial property. Thermal analyses of MgAc2·4H2O powder revealed that MgO was crystallized at 400 °C. X-ray diffraction analysis showed that MgO was converted to Mg(OH)2 or Mg5(CO3)4(OH)2·4H2O during the ageing in air. Silver nanoparticles at the surface of AgMgO films were identified by scanning electron microscopy and x-ray photoelectron spectroscopy. The MgO film was about 1.5 um thick. The potentiodynamic polarization test in the Ca-free Hank’s balanced salt solution showed that the coated titanium samples had better corrosion resistance than the polished one. The dissolution of silver nanoparticles resulted in a current peak in the polarization plots. In the antibacterial test against E. Coli, the inhibition zone width was 0.3, 1.6, 2.0 mm for the films with 0, 3.3, 9.1 at% Ag, respectively. The bactericidal mechanisms of the MgO and AgMgO films were discussed. The present work would provide a facile method for antibacterial surface modification of titanium based osteo-implants.
Tsunami intensity mapping: applying the integrated Tsunami Intensity Scale (ITIS2012) on Ishinomaki Bay Coast after the mega-tsunami of Tohoku, March 11, 2011
Authors: Katsetsiadou Katerina-Navsika , Andreadakis Emmanuel , Lekkas Efthimis
Published: May 2016

The study applies the Integrated Tsunami Intensity Scale (ITIS2012) criteria to map the tsunami intensities distribution in the broader Ishinomaki area, for the 9 Mw March 11, 2011 event offshore Tohoku, Japan. Based on reports, satellite imagery and published information, impact data was mapped, intensity values were assigned and thematic impact maps (layers) were created for each of the ITIS2012 six criteria categories. Most of the criteria result in a mosaic of intensities, which is in many cases due to lack of data, depending on the land use. Two methodologies were used to produce the final map. A land-use-based weighted overlay was applied integrating the six layers, resulting in a final map that rather shows damage tsunami assessment on Ishinomaki area. The second final map was produced using the maximum intensity grade throughout the six layers for each pixel. This map showed an excellent zoning filling in any gaps due to information lack in some layers and areas, with maximum intensity data from the others, highlighting the ITIS2012 criteria complementarity and is the tsunami intensity map of the study area.
Prevalence of brucellosis in the human, livestock and wildlife interface areas of Serengeti National Park, Tanzania
Authors: Shirima Gabriel M. , Kunda John S.
Published: May 2016

Between 2005 and 2006, a cross-sectional survey was carried out in domestic ruminants in agropastoral communities of Serengeti district, Tanzania to determine the seroprevalence of brucellosis in domestic–wildlife interface villages. Both the Rose Bengal Plate Test (RBPT) and Competitive Enzyme Linked-immunosorbent Assay (c-ELISA) were used to analyse 82 human and 413 livestock sera from four randomly selected villages located along game reserve areas of Serengeti National Park. Although both cattle (288) and small ruminants (125) were screened, seropositivity was detected only in cattle. The overall seroprevalence based on c-ELISA as a confirmatory test was 5.6%. In cattle both age and sex were not statistically associated with brucellosis seropositivity (P = 0.63; 95% CI = 0.03, 0.8 and 0.33; 95% CI = 0.6, 3.7, respectively). Overall herd level seropositivity was 46.7% (n = 7), ranging from 25% to 66.7% (n = 4–10). Each village had at least one brucellosis seropositive herd. None of the 82 humans tested with both RBPT and c-ELISA were seropositive. Detecting Brucella infection in cattle in such areas warrants further investigation to establish the circulating strains for eventual appropriate control interventions in domestic animals.
Serodiagnosis of Acute Typhoid Fever in Nigerian Pediatric Cases by Detection of Serum IgA and IgG Against Hemolysin E and Lipopolysaccharide
Authors: Davies D. Huw , Jain Aarti , Nakajima Rie , Liang Li , Jasinskis Algis , Supnet Medalyn , Felgner Philip L. , Teng Andy , Pablo Jozelyn , Molina Douglas M. , Obaro Stephen K.
Published: May 2016

Inexpensive, easy-to-use, and highly sensitive diagnostic tests are currently unavailable for typhoid fever. To identify candidate serodiagnostic markers, we have probed microarrays displaying the full Salmonella enterica serovar Typhi (S. Typhi) proteome of 4,352 different proteins + lipopolysaccharides (LPSs), with sera from Nigerian pediatric typhoid and other febrile cases, Nigerian healthy controls, and healthy U.S. adults. Nigerian antibody profiles were broad (∼500 seropositive antigens) and mainly low level, with a small number of stronger “hits,” whereas the profile in U.S. adults was < 1/5 as broad, consistent with endemic exposure in Nigeria. Nigerian profiles were largely unaffected by clinical diagnosis, although the response against t1477 (hemolysin E) consistently emerged as stronger in typhoid cases. The response to LPS was also a strong discriminator of healthy controls and typhoid, although LPS did not discriminate between typhoid and nontyphoidal Salmonella (NTS) disease. As a first step toward the development of a point-of-care diagnostic, t1477 and LPS were evaluated on immunostrips. Both provided good discrimination between healthy controls and typhoid/NTS disease. Such a test could provide a useful screen for salmonellosis (typhoid and NTS disease) in suspected pediatric cases that present with undefined febrile disease.
Fast descent routes from within or near the stratosphere to the surface at Fukuoka, Japan, studied using 7Be measurements and trajectory calculations
Authors: Itoh Hisanori , Narazaki Yukinori
Published: May 2016

Abstract. By using high concentrations of 7Be as an indicator, we clarify fast descent routes from within or near the stratosphere to Earth's surface, with the study site being in Fukuoka, Japan. Most routes arise from high latitudes through the following processes. First, the descent associated with a tropopause fold occurs, followed by southward movement with slow descent at the rear side of a strong trough. Because this motion occurs along an isentropic surface, the descending air parcels nearly conserve the potential temperature. As an extension, a strong descent associated with a sharp drop in the isentropic-surface height occurs at the southern edge of the trough; this transports air parcels to low altitudes. This process involves irreversible phenomena such as filamentation and cutoff of potential vorticity. Finally, upon meeting appropriate near-surface disturbances, parcels at low altitudes are transported to Earth's surface.In some cases, parcels descend within midlatitudes. In such routes, because the potential temperature is much higher at high altitudes than at low altitudes, descent with conservation of the potential temperature is impossible, and the potential temperature decreases along the trajectories through mixing.The prevalence of the high-latitude route is explained as follows. In the midlatitude route, because parcels at high and relatively low altitudes mix, the high concentrations of 7Be included in high-altitude parcels are difficult to maintain. Therefore, for parcels to arrive at low altitudes in the midlatitude while maintaining high concentrations of 7Be, i.e., conserving the potential temperature, their area of origin should be high altitudes in high latitudes where the potential temperature is almost the same as that in the arrival area.In spring, tropopause folds are frequent in high latitudes, disturbances in the southward transport of parcels are strong, and disturbances occur by which parcels descend to the surface. Therefore, high concentrations of 7Be occur most frequently in spring.
Error apportionment for atmospheric chemistry-transport models – a new approach to model evaluation
Authors: Solazzo Efisio , Galmarini Stefano
Published: May 2016

Abstract. In this study, methods are proposed to diagnose the causes of errors in air quality (AQ) modelling systems. We investigate the deviation between modelled and observed time series of surface ozone through a revised formulation for breaking down the mean square error (MSE) into bias, variance and the minimum achievable MSE (mMSE). The bias measures the accuracy and implies the existence of systematic errors and poor representation of data complexity, the variance measures the precision and provides an estimate of the variability of the modelling results in relation to the observed data, and the mMSE reflects unsystematic errors and provides a measure of the associativity between the modelled and the observed fields through the correlation coefficient. Each of the error components is analysed independently and apportioned to resolved processes based on the corresponding timescale (long scale, synoptic, diurnal, and intra-day) and as a function of model complexity.The apportionment of the error is applied to the AQMEII (Air Quality Model Evaluation International Initiative) group of models, which embrace the majority of regional AQ modelling systems currently used in Europe and North America.The proposed technique has proven to be a compact estimator of the operational metrics commonly used for model evaluation (bias, variance, and correlation coefficient), and has the further benefit of apportioning the error to the originating timescale, thus allowing for a clearer diagnosis of the processes that caused the error.
Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea
Authors: Nausch Monika , Bach Lennart Thomas , Czerny Jan , Goldstein Josephine , Grossart Hans-Peter , Hellemann Dana , Hornick Thomas , Achterberg Eric Pieter , Schulz Kai-Georg , Riebesell Ulf
Published: May 2016

Abstract. Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26 ± 0.03 and 0.23 ± 0.04 µmol L−1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15 ± 0.02 in the mesocosms and 0.17 ± 0.07 µmol L−1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82 % of PO4 was converted into DOP whereby only 18 % of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9 nmol L−1 h−1. About 86 % of them was realized by the size fraction < 3 µm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27 % of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments > 1000 µatm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO2 conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.
Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica
Authors: Yu Hongju , Rignot Eric , Morlighem Mathieu , Seroussi Helene
Published: May 2016

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and iceberg calving.