bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid Oxide Fuel Cells Based on Perovskite Components for Intermediate Temperature Operation
Authors: Monforte Giuseppe , Lo Faro Massimiliano , Antonucci Vincenzo , Aricò Antonino S.
Published: October 2013

A solid oxide fuel cell (SOFC) has been manufactured using a Ni-modified perovskite and perovskite-based electrolyte and cathode. The SOFC has been investigated for operation at intermediate temperatures. In this regard, we have first studied the electrical properties of La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) and gadolinia-doped ceria (GDC) electrolytes and afterwards we have investigated the reliability of the Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 based anode operation in combination with LSGM electrolyte and La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode. A 50 h electrochemical test for the SOFC operation under different fuel feed is presented to show the fuel-flexibility characteristics of this SOFC structure.
Crystal and Electronic Structures of LaP3O9-Based Protonic Conductors Synthesized by Liquid-Phase Method
Authors: Kitamura Naoto , Yamamoto Junpei , Idemoto Yasushi
Published: October 2013

La1-xSrxP3O9 with nominal compositions of x=0 and 0.03 were prepared by means of a coprecipitation method, and were characterized by X-ray diffraction, scanning electron microscopy and conductivity measurements. In addition, their crystal and electronic structures were investigated based on the Rietveld and maximum entropy method. As a result, it was found that a single phase of La1-xSrxP3O9 was successfully prepared with this method and the electrical conductivity was increased by partial substitution of Sr for La. H/D isotope effect on the conductivity also demonstrated that the Sr-substituted specimen exhibit significant protonic conduction. From the structure analysis using synchrotron X-ray diffractions, it was indicated that electron density distribution around oxygen depended on its crystallographic site slightly, and oxygen with weaker P-O bond had larger atomic displacement parameter and longer P-O distance.
Increasing Conductivity in Proton Conductors BaCeO3-δ Doped with Pr
Authors: Basbus Juan Felipe , Caneiro Alberto , Mogni Liliana Veronica
Published: October 2013

In this work we explore the effect of partial substitution of Ce for Pr ions in BaCe1-xPrxO3-
δ (0 ≤ x ≤0.8) perovskites with the aim of increasing the oxygen vacancies concentration and H+ charge carriers. The oxides were obtained by Pechini combustion method and sintered at 1350 °C. The Pr incorporation improves the capability of to obtain dense samples at this temperature. Crystal structure were studied by X-ray diffraction, while morphology by SEM. The conductivity was studied by Electrical Impedance Spectroscopy (EIS) under 20 % O2/Ar and 10 % H2/Ar, both with 2% humidity. We found that the Pr content diminished the lattice parameters, increase the sintering capacity and the conductivity under wet oxidant atmosphere, but it decreases the stability under reducing atmosphere.
The Soft Chemical Route Improving IT-SOFC Cathode Performance: The Lanthanum Barium Cobaltite Case
Authors: Garcés Diana , Mogni Liliana Veronica
Published: October 2013

In this work we studied the oxygen reduction mechanism in three cathodes: cubic La0.5Ba0.5CoO3-δ obtained by Solid State Reaction (SSR) in air at 1100 ºC; a phase with cationic order, laminar structure and tetragonal symmetry, LaBaCo2O6-δ, was obtained by SSR under inert gas at 1150 ºC. An intermediate compound with the same nominal composition was obtained at lower temperature by a soft chemical route involving a sol-gel process. Despite that the crystal structures of the oxides obtained by SSR are different, their microstructures are similar but quite different to that obtained by the soft chemical route. The area specific resistance (ASR) as a function of pO2 was studied at 700 °C by Electrochemical Impedance Spectroscopy (EIS). We found that both, crystal structure and microstructure affect strongly the ASR. Whereas cubic perovskite showed lower ASR than tetragonal, the ASR of the oxide obtained by the chemical route decreased almost one order of magnitude at higher pO2, respect to that obtained by conventional SSR.
Simulations of the Irradiation and Temperature Dependence of the Efficiency of Tandem Photoelectrochemical Water-splitting Systems
Authors: Haussener Sophia , Hu Shu , Xiang Chengxiang , Weber Adam Z. , Lewis Nathan S.
Published: October 2013

The efficiency of an operating photoelectrochemical solar-fuels-generator system is determined by the system design, the properties and morphology of the system’s components, and the operational conditions. We used a previously developed model comprising of i) the detailed balance limit to describe the currentpotential performance of the photoabsorber component, and ii) the detailed multi-physics device model solving for the governing conservation equations (mass, momentum, species and charge) spatially resolved in the device, to quantify the performance of photoelectrochemical devices. The investigated the performance and its variations as a function of operational conditions, i.e. daily and seasonal irradiation variations, concentration factor of irradiation, and isothermal device temperature. Additionally, the difference in performance of an integrated photoelectrochemical system and a photovoltaic array connected electrically to a standalone electrolyzer system was quantified.
(Invited) Novel Applications of Knudsen Effusion Mass Spectrometry
Authors: Jacobson Nathan S. , Hurowitz Joel A. , Farley Ken A. , Asimow Paul D. , Cartwright Julia A.
Published: October 2013

Knudsen effusion mass spectrometry (KEMS) is a valuable and versatile tool in physical chemistry, materials science, and geology. Most of the applications center on thermodynamic measurements. In this paper two novel applications of KEMS are discussed. The first is the determination of K isotope ratios for application to K-Ar dating. The second is the determination of silica thermodynamic activities in silicates via a reducing agent to increase signals without changing the condensed phase composition. This also involves the measurement of vaporization coefficient via a multi-cell KEMS method.
Observation of Nickel Oxidation Using Transmission X-ray Microscopy
Authors: Kiss Andrew M , Harris William M , Nakajo Arata , Wang Steve , Vila-Comamala Joan , Deriy Alex , Chiu Wilson K. S.
Published: October 2013

Changes in the microstructure of solid oxide fuel cell electrodes have been known to contribute to performance degradation. One degradation mechanism is the conversion of the nickel to nickel oxide in the anode. This conversion causes a volume increase and can increase stresses in the anode which could lead to performance loss. In order to study the reaction kinetics for nickel oxidation, a full field transmission x-ray microscope was used to image the reaction in situ. The conversion can be monitored based on the optical density of the sample and complete conversion can be confirmed with x-ray absorption near edge spectroscopy. The conversion data is used to calculate reaction rates as a function of temperature and activation energies for the reactions.
Applications of Nonlinear Electrochemical Impedance Spectroscopy (NLEIS)
Authors: Adler Stuart B.
Published: October 2013

This paper reviews the use of nonlinear electrochemical impedance spectroscopy (NLEIS) in the analysis of SOFC electrode reactions. By combining EIS and NLEIS, as well as other independent information about an electrode material, it becomes possible to establish quantitative links between electrochemical kinetics and materials properties, even when systems are unstable with time. After a brief review of the method, this paper summarizes recent results analyzing the effects of Sr segregation in thin-film LSC electrodes.
Iso-Octane Internal Reforming in a Solid Oxide Fuel Cell Using Co/CeO2 as Anode
Authors: Al-Musa Abdullah Abdulaziz , Kyriakou Vasileios , Al-Saleh Mohammed , Al-Shehri Riyadh , Kaklidis Nikolaos , Marnellos George
Published: October 2013

In the present work the cell performance of an i-C8H18 internal steam reforming solid oxide fuel cell (SOFC) with Co/CeO2 as anodic electrode is presented. Initially, the catalytic activity of bi-metallic Cu-Co ceria-supported catalysts for i-C8H18 steam reforming was examined. In all cases, gas mixtures rich in Η2, CO, CO2 and CH4 were produced. Among all samples tested, the 20wt%Co/CeO2 catalyst exhibited the optimum catalytic performance achieving Η2 yields well exceeding 75% at 700 oC. In addition, the excellent durability of this catalyst was proven by long-term (23 h) stability experiments. To this end, the mono-metallic Co/CeO2 catalyst was selected to serve as the anodic electrode in the electro-catalytic and fuel cell tests. During the fuel cell measurements, the power output was found similar to that obtained when 10% H2/Ar mixtures were fed to the cell, indicating that Co/CeO2 can be considered as a promising anodic composite for direct hydrocarbon fed SOFCs.
Nonlinear Analysis of Porous La0.9Ca0.1FeO3-δ Electrodes in Oxygen Environments
Authors: Geary Tim C. , Adler Stuart B.
Published: October 2013

Nonlinear electrochemical impedance spectroscopy (NLEIS) was performed on porous La0.9Ca0.1FeO3-δ electrodes at 700, 750, and 800°C and 0.01, 0.21, and 1 atm O2. The measured response was compared to a simplified one-dimensional porous electrode model assuming a co-limitation of kinetic and transport phenomena. The observed nonlinear trends were inconsistent with a bulk vacancy-only transport pathway or surface thermodynamics held at the independently-measured bulk values.
Metal-Doped Pyrochlore as Novel Electrode Materials for Intermediate Temperature Solid Oxide Fuel Cell
Authors: Hao Chia-Kan , Lee Chi-Shen
Published: October 2013

In this study, the high ionic conducting La2Zr2O7 (LZO) pyrochlore structure oxides with W on the B-site doping, were synthesized by Pechini sol-gel method and characterized by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). There was a solubility of W around x=0.1-0.15 in La2(Zr1-xWx)2O7 (LZWO). Temperature-programmed reduction (TPR) shown that the W-doped LZO structure didn’t react with H2. The XPS results indicated that the valence state of La3+, Zr4+, and W(5+, 6+) with the oxygen excess type. And the ionic, electronic- conductivity were measured to sort if the W-doped LZO could be used as electrolyte material. Above all, the sample powders compare with the commercial intermediate-temperature electrolyte material GDC. The 15% W-doped LZO ionic conducting value is with similar 2.2×10-3 - 1.9×10-2 S/cm at 400 - 700¢ªC and more structure stable even through in high temperature (below 1400¢ªC) or highly reductive atmosphere. Finally, we fabricated the single cell with the electrolyte, GDC and 15% W-doped LZO. The results shown that the La2(Zr1-xWx)2O7+δ will be high potential to be a novel electrolyte in IT-SOFC area.
The Stability and Ionic Conductivity in Cr Doped Y2Ti2O7 in the Search for Potential SOFC Electrolyte Materials
Authors: Hung Hao-En , Hao Chia-Kan , Lee Chi-Shen
Published: October 2013

In this study, a series of Y2Ti2-xCrxO7 were synthesized by sol-gel method and characterized by powder X-ray diffraction (PXRD), scanning electron microscope energy dispersive spectroscopy (SEM-EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), temperature-programmed reduction (TPR), and AC-impedance to investigate their properties for the application of intermediate temperature solid oxide fuel cell (IT-SOFC). Y2Ti2-xCrxO7 existed single-phase in a range of 0 < x ≤ 0.8. The refined cell parameters decreased as the amount of doped Cr concentration increased. In addition, the TPR profiles showed that the as-prepared materials started to react with hydrogen in the temperature range of 350 - 450 ºC. The analyzed results of XPS suggested that the average oxidation state of Cr decreased with the increased Cr content. Measurements of ionic conductivities induced that the optimized performance was observed at x = 0.2 with 0.01 S/cm at 700 ºC due to an optimized condition of carrier concentration and carrier mobility. The ionic conductivity dropped under reducing condition, indicative of a p-type semiconductor. The as-prepared Y2Ti1.8Cr0.2O7 exhibits low electrical conductivity (0.0004 S/cm at 700 ºC) and good ionic conductivity, which is potentially suitable to be utilized as an electrolyte material for IT-SOFC.
Characterization of (La,Sr)(Ti,Co)O3 Oxides for Symmetrical Solid Oxide Fuel Cell Electrodes
Authors: Napolitano Federico , Soldati Analía , Geck Jochen , Suescun Leopoldo , Acuña Leandro , Fernandez Zuvich Afra , Lamas Diego German , Serquis Adriana
Published: October 2013

In this work, a combined synchrotron X-ray diffraction (XPD), X-ray absorption near edge spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) study of La0.4Sr0.6Ti1-yCoyO3±δ (0 ≤ y ≤ 0.5), intended as symmetric solid oxide fuel cells electrode, is presented. Charge compensation mechanisms were characterized by room temperature measurements; LSTC has a perovskite pseudocubic structure with an A-site vacancy concentration related with Co doping level. This result seems to be triggered by the fact that Ti remains in a higher formal valence (around 4+) independent of the Co concentrations. On the contrary, Co K-edge XANES spectra show a dependency with the doping level but this seems to be related to structural changes. In-situ measurements simulating a symmetric SOFC working environment show that LSTC undergoes a rhombohedral to cubic perovskite phase transition with critical temperature dependent of the structural distortion level.
A Thermodynamic Interpretation of PVT Growth of Single Crystal SiC Material and Challenges in Reducing Dislocations
Authors: Fujimoto Tatsuo , Katsuno Masakazu , Tsuge Hiroshi , Sato Shinya , Ushio Shohji , Tani Komomo , Yashiro Hirokatsu , Hirano Hohsei , Yano Takayuki
Published: October 2013

The issues regarding the methods for the reduction of the densities of elemental dislocations such as the basal plane dislocation (BPD) and the threading screw dislocation (TSD) are discussed. We show that the pressure-dependent Si-C binary phase diagram is useful for the suppression of dislocation-generating foreign phases. In addition, recent progress on dislocation reduction in viewpoint of both the process control of PVT growth and the dislocation engineering is briefly reviewed. In particular, a specific behavior of 1c TSDs observed in the PVT growth of 4H-SiC is described in detail.
Growth of High-Quality GaN Template from Nanometer-Size Lattice Channels by Hydride Vapor Phase Epitaxy
Authors: Usui Akira , Goto Hiroki , Matsueda Toshiharu , Sunakawa Haruo , Nakagawa Takuya , Okada Akiko , Mizuno Jun , Yamaguchi Atsushi A. , Shinohara Hidetoshi , Goto Hiroshi
Published: October 2013

GaN are an attractive material in power devices for energy-saving measures in consumer products, automobiles, and industrial machines. To realize such GaN devices, however, high-quality GaN substrates are indispensable. In this paper, we describe the growth of high-crystalline-quality GaN template by HVPE with the nano-FIELO technique, where GaN growth starts by forming facet structures from nanometer-size channels which are opened on SiO2 layer deposited on GaN/sapphire substrate. The lattice pattern consisting of 500 nm × 500 nm square SiO2 masks surrounded by 80-nm-wide channels is used in this study. A nanoimprinting technique is applied followed by dry etching to fabricate lattice channels. From cross-sectional TEM observation, it is shown that the dislocation density is significantly reduced by the lattice pattern. Uniform GaN growth over 2-inch-diameter wafer is realized.
Channel Transport in 4H-SiC MOSFETs: A Brief Review
Authors: Dhar Sarit
Published: October 2013

This paper reviews the channel mobility problem in 4H-SiC MOSFETs. The importance of fundamental investigations on dielectric-SiC interfaces for next generation SiC power devices are highlighted and state-of-the-art interface passivation processes are discussed. Transport limiting mechanisms in current 4H-SiC MOSFETs are discussed and some key areas that need to be investigated for further improvement of this technology are identified. A necessary shift of focus from interface trap density reduction to other transport limiting mechanisms is motivated by discussing recent results.
Influence of Ion Implantation in SiC on the Channel Mobility in Lateral N-Channel MOSFETs
Authors: Strenger Christian , Uhnevionak Viktoryia , Burenkov Alex , Bauer Anton , Pichler Peter , Erlbacher Tobias , Ryssel Heiner , Frey Lothar
Published: October 2013

In this work, the impact of ion implantation into the MOSFET channel region on the channel mobility of electrons is investigated. For this purpose, a systematic investigation of the interface trap density, the interface trapped charge and the field-effect mobility is carried out for MOSFETs with different doping profiles and concentrations in the channel region. It will be demonstrated that implantation into the SiC MOSFET channel does not increase the amount of bulk defects. It leads, however, to a change of the doping concentration, and consequently of the bulk potential (ϕB). The latter crucially determines the amount of charged interface states, and as a result, represents one determining factor for the channel electron mobility. The experimental data indicates that bulk traps as suggested by Agarwal and Haney (1), are insufficient to explain the low electron mobility in SiC MOSFET inversion channels.
On the Temperature Dependence of the Hall Factor in n-Channel 4H-SiC MOSFETs
Authors: Uhnevionak Viktoryia , Burenkov Alex , Strenger Christian , Bauer Anton , Pichler Peter
Published: October 2013

To interpret Hall-effect measurements in a range of temperatures, the Hall factor for the electron transport in the channel of a SiC MOSFETs was evaluated. The method of the Hall factor calculation is based on the interdependence with mobility components via the respective scattering relaxation times. For the first time, the temperature dependence of the Hall factor in n-channel 4H-SiC MOSFETs was calculated. The results of the calculation reveal a strong reduction of the Hall factor with increasing temperature. Depending on gate voltage and temperature, the values of the Hall factor vary between 1.2 and 1.5. In addition, the sheet carrier densities and drift mobilities derived from the Hall-effect measurements using our new temperature-dependent Hall factor show very good agreement with independent simulation results.
Key Reliability Issues for SiC Power MOSFETs
Authors: Lelis A. , Habersat D. , Green R. , Mooro E.
Published: October 2013

Even with the successful introduction of SiC power MOSFETs into the commercial market place, several key reliability issues have not been fully resolved. The main two issues are the stability of the device threshold voltage, VT
, and the reliability of the gate oxide. This work focuses on the VT
stability issue, which has been investigated by a number of different research groups in recent years [1-12].
3C-SiC on Si Hetero-Epitaxial Growth for Electronic and Biomedical Applications
Authors: Reyes Meralys , Frewin Chris , Ward P. J. , Saddow S. E.
Published: October 2013

The growth of cubic silicon carbide on silicon, namely 3C-SiC/Si, has been extensively studied at the University of South Florida over the past decade and numerous electronic and biomedical applications explored using this material system. The key step to 3C-SiC devices is the growth of high-quality epitaxial layers of 3C-SiC. In order to improve the manufacturability of future 3CSiC devices, a simplified 3C-SiC growth process on 50 and 100 mm Si (100) substrates has been developed in a low-pressure horizontal hot-wall chemical vapor deposition (CVD) reactor. A simplified growth process consists of a single thermal ramp to the growth temperature followed by the 3C-SiC growth. The 3C-SiC epitaxial layers were characterized via optical microscopy, secondary electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and secondary ion mass spectrometry (SIMS). Examples of biomedical devices realized with this material system are also introduced, including neural probes and in-vitro recording devices, as well as myoglobin and glucose biosensors.
III-Nitride Materials and Devices for Power Electronics
Authors: Dobrinsky Alex , Simin Grigory , Gaska Remis , Shur Michael
Published: October 2013

Group III-Nitride based devices are expected to compete and possibly outperform state of the art silicon carbide based devices for power electronic applications. GaN, AlGaN, AlInGaN and other III-Nitride compound materials offer a very high breakdown field. Devices based on III-Nitride compounds have very high electron density and mobility in the device channel, leading to record low device on-resistance, high temperature stability and low gate capacitance enabling high switching speed and low switching loss. In order to enable III-Nitride based devices for power applications continuous efforts are underway in the area of material growth, novel power device concepts, designs, modeling and simulations.
Normally-Off GaN Transistors for Power Switching Applications
Authors: Hilt Oliver , Bahat-Treidel Eldad , Brunner Frank , Knauer Arne , Zhytnytska Rimma , Kotara Przemyslaw , Wuerfl Joachim
Published: October 2013

Normally-off high voltage GaN-HFETs for switching applications are presented. Normally-off operation with threshold voltages of more than 1 V and 6 V gate swing has been obtained by using p-type GaN as gate. Different (Al)GaN-based buffer compositions using intentional doping and potential barriers have been used to obtain high blocking voltages. 1000 V blocking was obtained for devices with carbon-doped buffer structures, however, they suffer from a stronger increased dynamic on-state resistance as compared to devices based on an iron-doped GaN-buffer or an AlGaN-buffer. The best trade-off between low dispersion and high blocking strength was obtained for a modified carbon-doped GaN-buffer that showed only a 2.6x increase of the dynamic on-state resistance for 500 V switching.
High Performance Normally-off GaN MOSFETs on Si Substrates
Authors: Kambayashi Hiroshi , Ikeda Nariaki , Nomura Takehiko , Ueda Hirokazu , Morozumi Y. , Harada Katsushige , Hasebe Kazuhide , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: October 2013

The enhancement mode AlGaN/GaN hybrid MOS-HFETs on Si substrates have been demonstrated. The breakdown voltage of over 1.71 kV was achieved by investigating the epitaxial structure. Furthermore, a high integrity SiO2/Al2O3 gate stack has been demonstrated for GaN MOSFETs. The SiO2 film formed on GaN by the MW-PECVD exhibits good properties compared that by the LP-CVD. Then, by incorporating the advantages of both of SiO2 with a high insulating characteristics and Al2O3 with good interface characteristics, the SiO2/Al2O3 gate stack structure has been employed in GaN MOS devices. It is shown that a low interface state density between gate insulator and GaN, a high breakdown field, and a large charge-to-breakdown by applying 3-nm Al2O3 in this structure. The SiO2/Al2O3 gate stack has also been applied to AlGaN/GaN hybrid MOS-HFET and excellent properties with the threshold voltage of 4.2 V and the maximum field-effect mobility of 192 cm2/Vs are shown in the transistor.
Voltage Switching Limits of Lateral GaN Power Devices
Authors: Shenai Krishna
Published: October 2013

The dv/dt switching limitations of power semiconductor devices are evaluated in a boost (PFC) power converter using circuit simulations. State-of-the-art commercial silicon CoolMOS devices, commercial Silicon Carbide (SiC) Junction Barrier Schottky (JBS) diodes, and emerging Gallium Nitride (GaN) lateral power transistors are considered. It is shown that although SiC and GaN power devices have low stored charge and small capacitances, they experience high switching dv/dt stresses which may pose serious switching limitations especially in high-frequency power converters. This problem is likely to be further exacerbated by the presence of a high density of crystal defects in SiC and GaN materials which will manifest in the form of poor field-reliability. Specific guidelines for device selection are recommended in order to optimize both performance and field-reliability.
GaN-Based Power HEMTs: Parasitic, Reliability and High Field Issues
Authors: Meneghesso Gaudenzio , Meneghini Matteo , Bisi Davide , Silvestri Riccardo , Zanandrea Alberto , Hilt Oliver , Bahat-Treidel Eldad , Brunner F. , Knauer A. , Wuerfl Joachim , Zanoni Enrico
Published: October 2013

This paper reviews the main mechanisms responsible for trapping and breakdown in power HEMTs based on gallium nitride. With regard to the trapping mechanisms, we describe the role of carbon and iron buffer doping compensation in determining the dynamic Ron. We also demonstrate how the use of double heterostructure without doping or a single-heterostructure with proper buffer doping compensation can effectively reduce trapping phenomena. In addition, we investigate the breakdown limits of single and double heterostructure (DH) HEMTs, by electrical and electroluminescence characterization. Results indicate that, for the devices adopting double heterostructure without doping or singleheterostructure with proper buffer doping compensation, the breakdown voltage linearly scales with the gate-drain distance, and provides information on the origin of breakdown current components for different bias levels and epitaxial structures.
True Figure of Merit (FOM) of a Power Semiconductor Switch
Authors: Shenai Krishna
Published: October 2013

Wide Band Gap (WBG) semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are known to be superior materials for the fabrication of power electronics switching devices compared to the industry work-horse silicon. This advantage primarily stems from wider energy bandgap, higher electric field strength for avalanche breakdown, and improved thermal conductivity of SiC and GaN semiconductors compared to silicon. This paper reviews the various “Figures of Merit (FOM)” proposed in the literature for the WBG power semiconductors. Unipolar power transistors with MOS channel conduction as well as transistors that employ two-dimensional electron gas (2DEG) channels are considered. A true FOM for a power semiconductor switching device needs to take into account all electrical power losses and thermal limitations. A new Safe Operating Area (SOA) limit that relates material defect density (Dit) to the switching current density (Jon) for a specified maximum junction temperature limit (Tjmax) is proposed as the true FOM for a power semiconductor switching device.
Systems-Driven Power Semiconductor Education
Authors: Shenai Krishna
Published: October 2013

Today’s power electronics curriculum practiced at most universities world-wide primarily focuses on power converters and power systems with little or no emphasis given to power electronics components and their interaction at the systems level. Consequently, graduates are trained to design power converters and power systems without adequate background on the physics and technology of power electronics components; graduate are often unable to understand and optimize component and systems technologies. The result is a widening disconnect that exists between the users and manufacturers of power electronics components. This paper discusses the challenges and approaches needed to bridge this educational gap and proposes a “systems-driven” power semiconductor educational curriculum in order to rapidly promote the power electronics industry.
Power Semiconductor Device Education: Which Topics and What Depth
Authors: Robbins William P. , Mohan Ned
Published: October 2013

Power electronics is a significant enabling technology in many areas of electrical engineering and the introduction of wide bandgap power devices utilizing silicon carbide and gallium nitride will make it even more important and pervasive in the future. In developing the power electronics workforce going forward, two major questions arise concerning power semiconductor devices. First what device topics should be covered and second what should be the depth of the topical coverage? One example discussed in the paper are the power semiconductor device topics are taught at the undergraduate and graduate level at the University of Minnesota and to what depth. The topical details of a graduate level device physics and device design course at the graduate level are also considered.
Ammonothermal Bulk GaN Substrates for Power Electronics
Authors: D'Evelyn Mark P. , Ehrentraut Dirk , Jiang Wenkan , Kamber Derrick S. , Downey Bradley C. , Pakalapati Rajeev T. , Yoo Hak Do
Published: October 2013

Soraa has developed a novel ammonothermal approach for growth of high quality, true bulk GaN crystals at a greatly reduced cost, known as SCoRA (Scalable Compact Rapid Ammonothermal). SCoRA GaN growth has been performed on seed crystals with diameters between 5 mm and 2" to thicknesses of 0.5-4 mm. The highest growth rates are greater than 40 um/h and rates in the 10-30 mm/h range are routinely observed. Two-inch diameter, crack-free, free-standing, n-type bulk GaN crystals have been grown. The crystals have been characterized by a range of techniques, including x-ray diffraction rocking-curve (XRC) analysis, optical microscopy, cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is very good, with FWHM values of 15-80 arc-sec and average dislocation densities below 5x105 cm-2.
Manufacturing Challenges in Wide Band Gap (WBG) Power Electronics
Authors: Shenai Krishna
Published: October 2013

Wide bandgap (WBG) semiconductors, Silicon Carbide (SiC) and Gallium Nitride (GaN), have enormous potential for transformative impact on electric utility and transportation infrastructures. However, commercialization of WBG power electronics switching devices has been slow primarily due to high cost and unproven field-reliability. This paper reviews the manufacturing challenges facing the WBG power electronics industry in order to “unlock” the true potential of this “game changing” solid-state energy conversion technology.
Basal Plane Dislocation Mitigation Using High Temperature Annealing in 4H-SiC Epitaxy
Authors: Mahadik Nadeemullah A , Nath Anindya , Imhoff Eugene A , Stahlbush Robert E , Nipoti Roberta
Published: October 2013

Basal plane dislocations (BPD) were mostly eliminated in 4H-SiC epitaxy using post growth high temperature annealing in the range of 1600 oC - 1950 oC for 30s - 2 mins. The samples annealed at temperatures >1700 oC showed the best BPD reduction. However, surface morphology was degraded for samples annealed >1850 oC, and new BPDs were generated. A better capping technique was developed to improve the surface morphology and avoid generation of new BPDs, while significantly reducing the existing BPDs in the SiC epitaxial layers.
High Voltage InAlN/GaN HFETs Achieved by Schottky-Contact Technology for Power Applications
Authors: Zhou Qi , Chen Wanjun , Liu Shenghou , Zhang Bo , Feng Zhihong , Cai Shujun , Chen Kevin J.
Published: October 2013

In this paper, a novel approach of Schottky-contact technology for high voltage InAlN/GaN power transistors is demonstrated. The improved breakdown voltage (BV) attributes to the effectively suppressed source carrier injection achieved by the Schottky source metallization featuring excellent metal morphology. Without using field-plate structure and buffer engineering technique, the record three-terminal off-state BV of 650 V is obtained for InAlN/GaN HFET featuring a Schottky source. The corresponding specific on-resistance is as low as 3.4 mΩ·cm2. Moreover, the proposed Schottky-contact technology enables the removal of conventional alloyed Ohmic contact which is beneficial to device scaling. The BV of 58 V is measured in an InAlN/GaN HFET with L
GD of 250 nm, which is the highest BV reported on GaN-based HFETs with such a short drift region. With simple fabrication process as well as the device structure while achieving a significant breakdown voltage enhancement the proposed technology opens up new perspectives for designing high voltage InAlN/GaN HFET for power applications.
Interaction of Defects with Quantum Well States: Electrostatic-Dependant Response Time for Traps in AlGaN/GaN HEMTs
Authors: Marinella Matthew J. , DasGupta Sandeepan , Kaplar Robert J. , Sun Min , Atcitty Stan , Palacios Tomas
Published: October 2013

Recovery transients in high-voltage AlGaN/GaN HEMTs following both blocking voltage and ON-state stress show strong dependence on stress time. The defect time constant spectra exhibit a temperature-dependant component (TG1, Ea = 0.6 eV) and a temperature-independent component (TG2). With increased stress time and larger current collapse, the time constants for TG2 become progressively longer. The stress-time-dependent behavior of TG2 is shown to be consistent with the capture of trapped carriers in the AlGaN barrier directly by quantum well states, originating from the same defect giving rise to the 0.6 eV behavior. By modulating this alternate recombination pathway, the electric field normal to the AlGaN/GaN interface is shown to have a strong effect on reducing the response time of the trap to several orders of magnitude below its bulk response time. This demonstrates that barrier design may be utilized to tune the recovery characteristics of the HEMT.
Power Semiconductor Device Modeling and Simulation
Authors: Mantooth H Alan , Ahmed Shamim , Ang Simon S.
Published: October 2013

Power semiconductor devices continue to be an active area of research and development. With the emergence of wide bandgap technologies this area has blossomed over the past decade beyond silicon boundaries. A brief survey of courses available around the world on the topic of power semiconductor device modeling and simulation is provided. An exemplar course at the University of Arkansas is described to demonstrate its applicability to power electronics students interested in circuit design, controls, device design, electronic packaging, and compact modeling of devices. This course is built on model-based engineering principles that are applicable to any area of electronic design.
Studying the Performance of Series-Connected GaN FETs in Higher Voltage Switching Applications
Authors: Hasanzadeh Amin , Khaligh Alireza
Published: October 2013

This manuscript investigates cascading of gallium-nitride (GaN) field-effect transistors (FETs) to accommodate for higher voltage switching operation, beyond the ratings of commercially available single switches. The current GaN FETs present substantial advantages over corresponding silicon (Si) and silicon-carbide (SiC) FETs in terms of switching speed, conduction and switching loss, and thermal capability. However, currently GaN based switching semiconductor devices are not available in high voltage ratings, which could be a limiting factor in their use for high voltage applications. This paper presents the study, design, simulation, and implementation of cascading enhancement-mode GaN (eGaN) devices to demonstrate their superior performance capabilities in comparison to their Si-counter parts. The presented study in this manuscript paves out a way to utilize future high-voltage GaN semiconductor devices in plasma technologies, pulsed microwave tubes, and high voltage direct current transmission applications, which need very high voltages.
Electrochemical Hydrogenation of Dimensional Carbon
Authors: Daniels Kevin M. , Shetu Shamaita , Staser John , Weidner John W. , Williams Christopher , Sudarshan Tangali , Chandrashekhar M.V.S.
Published: October 2013

The hydrogen adsorption and electrochemical properties of epitaxial graphene (EG) grown on silicon carbide (SiC) and bulk graphite in dilute sulfuric acid (H2SO4) and perchloric acid (HClO4) solutions were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). According to EIS, electrochemical activity is dependent on starting I(D)/I(G) ratio suggesting a dependence on point defects in the material for successful hydrogenation. Electrochemical hydrogen loading and unloading on epitaxial graphene was also demonstrated and confirmed by Raman spectroscopy and CV. These results show that hydrogenation of graphene is electrochemically reversible and history dependent impacting H loading. This process demonstrates a new pathway to hydrocarbon bond formation for synthesis of advanced organic/inorganic carbon-based compounds.
Growth of GaN by MOCVD on Rare Earth Oxide on Si(111)
Authors: Arkun F. Erdem , Dargis Rytis , Clark Andrew , Smith Robin S. , Lebby Michael , Leathersich Jeffrey M. , Shahedipour-Sandvik F.
Published: October 2013

Growth of GaN on rare earth oxide (REO) buffers grown on silicon (111) was performed. A novel low temperature buffer layer was developed in order to suppress the decomposition of the REO buffer under hydrogen flow during MOCVD. GaN films, grown by this technique, exhibit smooth surface morphologies. XRD studies reveal the formation of an ErN layer during growth.
(Invited) Storage Class Memory and NAND Flash Memory Hybrid Solid-State Drives (SSD)
Authors: Takeuchi Ken
Published: October 2013

SSDs and emerging storage class non-volatile semiconductor memories (SCM) such as PCRAM, FeRAM, ReRAM and MRAM have enabled innovations in various nano-scale VLSI memory systems for personal computers, multimedia applications and enterprise servers. This paper provides a comprehensive review on state-ofthe-art data management technologies of storage class memory and NAND flash memory hybrid solid-state drives (SSDs)
(Invited) Opportunities and Challenges of Atom Switch for Low-Power Programmable Logic
Authors: Tada Munehiro , Sakamoto Toshitsugu , Hada Hiromitsu
Published: October 2013

Opportunities and challenges of atom switch featuring Cunanometer-scale conducting bridge in the solid-electrolyte arediscussed with comparing the other emerging memories. Atomswitch having the high on/off conductance ratio is suitable todirectly replace the conventional CMOS switch element, realizingthe low-power, nonvolatile programmable logic. Reliabilitychallenges of the atom switch are also discussed in the view pointof the stabilization of the on- and off-states.
In Situ TEM Observation of Cu/MoOx ReRAM Switching
Authors: Kudo Masaki , Ohno Yuuki , Hamada Kouichi , Arita Masashi , Takahashi Yasuo
Published: October 2013

In-situ TEM observation was applied to a miniaturized Cu / MoOx / TiN ReRAM device shaped by the ion-shadow method. Applying a positive voltage to the Cu top electrode, resistive switching from the high-resistance state (HRS) to the low-resistance state (LRS) occurred, and a precipitation appeared in the switching layer of MoOx. On the other hand, negative voltage to Cu erased the precipitation, and the resistance state was converted from LRS to HRS. Growth or contraction of the precipitation was recognized during further voltage application after the switching operation. The precipitation observed in this work is thought to correlate with the resistive switching, and its formation and rupture phenomenon agrees to the switching mechanism based on conductive filaments.
Temperature Dependence of Resistance in Conductive Filament Formed With Dielectric Breakdown of Ni/TiO2/Pt Structure
Authors: Otsuka Shintaro , Hamada Yoshifumi , Shimizu Tomohiro , Shingubara Shoso
Published: October 2013

We investigated resistive switching (RS) characteristics and temperature dependences of a resistance of the Ni/TiO2/Pt resistive switching memory. The device was operated in a unipolar mode. From the temperature dependence of resistance, it is shown that the conductive filament in the low resistance state (LRS) is metallic. Fabricated Pt/NiO/Pt RS memory to compare the RS characteristics showed similar RS phenomenon. The conductive mechanism of the Pt/NiO/Pt RS memory is also metallic. Temperature coefficients of resistance of various RS memory were compared.
Investigation of Thomson Effect in Cu/TaOx/Pt Resistive Switching Memory
Authors: Liu Tong , Potnis Tanmay , Kang Yuhong , El-Helw Sarah , Orlowski Marius
Published: October 2013

Conductive bridge random access memory (CBRAM) shows strong potential for replacing flash memory on the sub-20 nm technology nodes. The switching mechanism is primarily attributed to the electrochemical formation and rupture of conductive filaments. In Cu/TaOx/Pt devices, high electric current in the RESET process can cause significant local heating. Thomson heating effect has to be considered due to conical or cylindrical filament geometries giving cause for strong temperature gradients. The thermoelectric effect is evaluated for the Cu and oxygen vacancy nanofilaments in bipolar and unipolar switching modes. The Thomson coefficient for oxygen vacancy filament is extracted from the difference of SET voltages between two switching modes.
(Invited) Programmable Metallization Cells in Memory and Switching Applications
Authors: Kozicki Michael N , Dandamudi Pradeep , Barnaby Hugh J , Gonzalez-Velo Yago
Published: October 2013

This paper describes programmable metallization cell (PMC) technology, which utilizes a high resistance ion conducting materials between oxidizable and inert electrodes. These cells exhibit resistance switching which is based on the combination of bias dependent ion transport through the solid-state ion conductor and reduction/oxidation (redox) reactions occurring at the electrodes. PMC structures promise a wide range of applications and PMC-based resistive random access memory (ReRAM) has already entered the nonvolatile memory marketplace. The paper briefly reviews PMC device operation and discusses research findings on memory cells that utilize Ag-Ge-S ion conducting films for commercial memory and radiation-hard applications.
Impact of STI Gap-Fill Process Deposited by HDP-CVD in Flash Memory
Authors: Park Hyoung-sun , Kim Ki-yong , Hong Ok-cheon , Kim Hong-sig , Lee Haebum , Lee Kyu-pil , Cho In-soo , Choi Byoung-deog
Published: October 2013

This paper presents an evaluation of different oxides for shallow trench isolation (STI) gap-filling in flash memory devices. We have investigated that plasma induced degradation mechanism of high density chemical vapor deposition (HDP-CVD) oxide compared to non-plasma TEOS+O3 undoped silicate glass (USG) for STI gap-filling process. HDP-CVD has more hydrogen contents due to H+ penetration into underlying layer in plasma which generates more interface state density. Hydrogen depassivation model has been suggested to demonstrate the degradation mechanism of HDP-CVD device.
Voltage-Induced Nonvolatile Change of Magnetic Anisotropy of CoFeB Ultrathin Films Stacked With Multivalent Oxides
Authors: Koba Jiro , Kita Koji
Published: October 2013

Voltage-induced nonvolatile control of magnetic anisotropy was demonstrated with TiOx/CoFeB/Ta stacks. We observed a nonvolatile change of interface anisotropy energy at TiOx/CoFeB, probably caused by a motion of positively-charged oxygen vacancies in ultrathin TiOx layer. Our results indicate a possible application of this phenomenon to a new type of nonvolatile memories.
Special Electric Characteristics of Superlattice Phase Change Memory
Authors: Ohyanagi Takasumi , Kitamura Masahito , Takaura Norikatsu
Published: October 2013

The sample preparation of superlattice films for a phase change memory (PCM) and the electrical characteristics of superlattice PCM are reported. Superlattice films with no inclusion of alloy were obtained. The strong RESET pulse width dependence is discussed.
A Study of Nanoparticle Removal on Patterned Surfaces
Authors: Pacco Antoine , Holsteyns Frank , De Gendt Stefan
Published: October 2013

In this paper a novel method is presented whereby both the damage and the particle removal efficiency on one patterned substrate can be assessed. The method is based on defect inspection by an automated brightfield inspection tool and its successive defect classification. In order to evaluate the method, a representative and common cleaning technique, aerosol spray cleaning, was used. The performance of this method was compared with particle removal efficiency evaluation on non-patterned substrates. Interestingly, particle removal efficiencies on patterned surfaces were much lower than on blanket silicon wafers.
Numerical Calculation Model of Single Wafer Wet Etcher Using Swinging Nozzle
Authors: Habuka Hitoshi , Ohashi Shintaro , Mizuno Kosuke , Kinoshita Tetsuo
Published: October 2013

A numerical calculation model for a single wafer wet etching rate using a swinging nozzle was developed on the basis of computational fluid dynamics and the rate theory. This model was validated using the etching rate of a silicon dioxide film by hydrogen fluoride aqueous solution, which was injected from a center and a non-center nozzle onto a rotating 200-mm diameter silicon wafer surface. The injection nozzle at the non-center position was accounted as a cylindrically-shaped inlet. Calculation showed the maximum etching rate at the outside edge position of the swinging nozzle, consistent with the trend of measurement.
Si and SiGe Alloys Wet Etching Using TMAH Chemistry
Authors: Loup Virginie , Gabette Laurence , Roure Marie-Christine , Kachtouli Riadh , Jourdan Marine , Besson Pascal , Petitdidier Sebastien
Published: October 2013

From MEMS to CMOS applications, silicon wet anisotropic etching is nowadays considered as an interesting alternative to face new and various technological challenges. This paper focuses on the TMAH chemistry and its use for Si and Si1-xGex alloys etching. Comparing two different dispense modes (immersion and spin-on), the impact of TMAH experimental conditions on the etching kinetics as well as on the surface morphology is discussed. We demonstrated that alleviating TMAH-induced Si surface degradation can be obtained by transferring the TMAH etching process on a spray dispense tool. We also highlight the drastic impact of germanium incorporation on the silicon etch rate which opens the scope to TMAH for many applications.
Numerical Study of Single Bubble Dynamics in Megasonic Field for New Physical Cleaning Method
Authors: Ochiai Naoya , Ishimoto Jun
Published: October 2013

The clarification of the mechanism and the control of a megasonic cleaning are necessary for the megasonic cleaning without pattern damage. In the present study, the numerical analysis of the bubble behavior in a megasonic field is performed to clarify the mechanism of the particle removal of megasonic cleaning. The bubble behavior in the standing wave of a megasonic wave is analysed using a compressible locally homogeneous model of a gas-liquid two-phase medium. The results show that the present numerical method is found to can simulate the characteristic of the bubble translational motion in a standing wave that the direction of the movement due to the primary Bjerknes force changes at the resonant radius. And the calculated wall pressure is higher than the exposed megasonic pressure, and the cavitation is confirmed to influence the particle removal of megasonic cleaning.
Integration of Wet Cleaning in 45 Nm Pitch BEOL Processing
Authors: Kesters Els , Le Quoc Toan , Lazzarino Frederic , Decoster Stefan , Wilson Chris , Simms Ihsan , Holsteyns Frank , De Gendt Stefan
Published: October 2013

A partial-trench via first with self-aligned double patterning (SADP) approach is used to realize a 45 nm pitch using a dual damascene compatible hardmask. This back-end of line (BEOL) integration approach is used to investigate the ability to integrate advanced low-k materials and more specifically to assess their patterning performance. Throughout this SADP integration approach, different specific cleaning steps are required. A first cleaning process is needed after spacer etch and amorphous-carbon (a-C) strip to remove the spacer etch residues that are formed. Further in the integration flow, a TiN clean is needed together with a post-etch residue removal (PERR) after low-k etch.