bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Vapor Exchange Flow Channels to Enhance the Performance of Polymer Electrolyte Fuel Cells without Cathode Humidification
Authors: Nakajima Hironori , Kitahara Tatsumi , Tsuda Kazuto
Published: October 2013

Polymer electrolyte fuel cells (PEFCs) generally have external humidifiers to feed humidified hydrogen and air for membrane hydration. The external humidifiers should be omitted to develop a very simplified PEFC system with increased total efficiency and reduced cost. In the present study, a water vapor exchange flow channels installed in the PEFC thus has been developed to enhance the performance without cathode humidification. A gas diffusion layer (GDL) coated with a hydrophilic microporous layer (MPL) consisting of polyvinyl alcohol (PVA) and carbon black is employed for the cathode water exchange flow channels to promote water transport from the cathode outlet wet gas to the anode inlet dry gas. This is effective for the membrane hydration, enhancing PEFC performance. Addition of hydrophilicity to the MPL is effective to water transport from the cathode to the anode.
Composite Carbon Nanotube and Titania Catalyst Supports for Enhanced Activity and Durability
Authors: Rigdon William A. , Larrabee Diana , Huang Xinyu
Published: October 2013

In polymer electrolyte cells, an approach is shown for construction of resilient electrocatalysts. In the anode where the hydrogen oxidation reaction is subject to poisoning from fuel impurities like carbon monoxide (CO), increased tolerance and stability for the catalyst is revealed by modification of the support structure and properties. A carbon nanotube framework serves as the foundation for metal oxide addition, namely titania and niobium doped form. The corrosion resistant transition metal oxides form a strong bond with platinum catalysts through unique electronic interactions, measured by XPS. Several other material characterizations are also included to make comparisons between composites. Composite supports contribute improved reactivity towards oxidation of CO, especially in reduced titania. Carbon corrosion resistance is also measured and shown to be the greatest for this support. Synergistic combination of effects is observed directly by preparation of electrocatalysts into working membrane electrode assemblies measured for their performance & durability.
Iridium-Titanium Oxide as Support for Pt Catalyst in PEFC Cathodes
Authors: Binninger Tobias , Fabbri Emiliana , Kötz Ruediger , Schmidt Thomas J.
Published: October 2013

Platinum supported on iridium-titanium oxide was investigated as cathode catalyst under polymer electrolyte fuel cell relevant conditions. Degradation of the cathode catalyst layer during automotive fuel cell operation was simulated by performing 1000 cyclic voltammetry scans between 0.5 V vs. RHE and 1.5 V vs. RHE in 0.1 M perchloric acid at room temperature. The electrochemically active platinum surface area was determined by CO stripping voltammetry with a novel method of baseline subtraction, and was found to reduce by 42% under these conditions. The activity of the metal oxide supported platinum catalyst towards oxygen reduction reaction was determined before and after the degradation test by rotating disk electrode measurements. The absolute kinetic current suffered a loss of 36% during the start / stop cycling. In contrast, the specific kinetic current was found to increase, which could be explained with a particle size effect due to platinum nanoparticle growth during potential cycling.
Highly Durable Metal-Oxides as an Alternative Catalyst Supports for PEFCs
Authors: Cilingir Dogan Didem , Hwang Sun-Mi , Yim Sung-Dae , Sohn Young-Jun , Yang Tae-Hyun , Park Gu-Gon
Published: October 2013

High surface area Magnèli Phase Titanium Oxides (MPTOs), synthesized by high temperature reduction and mechanical milling of TiO2 as a catalyst support material for a polymer electrolyte fuel cells (PEFCs). Pt as an active metal distributed on the prepared supports by impregnation-reduction method. The catalyst structure and composition of the Pt/HS_MPTO were determined by X-ray diffractometer (XRD), Field Emission Transmission Electron Spectroscopy (FE-TEM) and Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP). The catalytic activity for the oxygen reduction reaction (ORR) and stability against high potential were examined and compared with commercial Pt/C catalyst. The durability of Pt/HS_MPTO catalysts was examined by potential holding at 1.3 V for 24 h. Pt/HS_MPTO catalyst showed nearly no changes in the half-wave potentials representing much higher durability compared to the commercial Pt/C catalysts.
Electrochemical Hydrogen Separation Via Solid Acid Membranes
Authors: Papandrew Alexander B. , Wilson David L. , Hawks Samantha A. , Goenaga Gabriel , Zawodzinski Thomas A.
Published: October 2013

The inorganic proton conductor CsH2PO4 (CDP) was investigated as a proton exchange membrane for electrochemical hydrogen separation at temperatures from 230 °C to 250 °C. In pure hydrogen, electrodes based on carbon-supported Pt reversibly oxidize and evolve hydrogen at 550 mA/cm2. In a simulated reformate stream containing 7% CO, a maximum hydrogen oxidation current of 260 mA/cm2 was observed.
Electrocatalytic Oxygen Evolution Reaction on Iridium Oxide Model Film Catalysts: Influence of Oxide Type and Catalyst Substrate Interactions
Authors: Reier Tobias , Weidinger Inez , Hildebrandt Peter , Kraehnert Ralph , Strasser Peter
Published: October 2013

Different iridium oxides and their interactions with a titanium substrate were investigated with regard to their electrocatalytic oxygen evolution activities. Smooth iridium oxide thin-film model catalysts were synthesized at different temperatures. Thin-film catalysts minimize mass transport limitations, which tend to impede catalytic studies. Prior to the electrocatalytic investigation, the iridium oxide films were characterized by SEM, EDX, XRD, Raman spectroscopy and cyclic voltammetry. Temperature programmed reduction was applied to identify the oxide species formed as function of the calcination temperature. The TPR study was performed on inert silicon and titanium substrates to study iridium oxide properties alone and their interaction with the titanium substrate. Thus, it was possible to relate electrocatalytic oxygen evolution activity with the formation of the various oxide species.
Electrochemical Reduction of CO2 Using Supported Cu2O Nanoparticles
Authors: Bugayong Joel , Griffin Gregory L
Published: October 2013

We have studied the electrochemical reduction of CO2 using Cu2O catalysts prepared by nanoparticle synthesis (i.e., chemical reduction) and by electrochemical deposition. Both preparation methods give catalysts that exhibit high formation rates for CO and C2H4 relative to CH4, compared to Cu foil electrodes. The main difference is a higher relative rate of CO formation using the nanoparticle catalysts. Highly loaded nanoparticle catalysts give the highest overall rates for CO2 product formation, most likely because of their greater surface area. Lower loaded catalysts show evidence that product selectivity is affected by the competing H2 reaction on the carbon fiber support. Characterization using SEM and XRD together with transient current behavior suggests that Cu2O is reduced in two stages, with the initial formation of dispersed Cu clusters occurring rapidly on the oxide surface, followed by a much slower reduction of the interior of the oxide.
Electrochemical Systems for Production of Syngas and Co-Products
Authors: Lister Tedd E. , Dufek Eric J. , Stone Simon G.
Published: October 2013

This paper describes the development of bench-scale systems for the electrochemical reduction of CO2 to synthesis gas (syngas). Syngas is a significant building block chemical currently derived from fossil energy. Conventional methods create syngas using fossil resources which releases carbon into the atmosphere. Electrochemical reduction of CO2 is a process that could integrate intermittent alternative energy sources into the electric grid by using excess electricity to convert CO2 and H2O to a useful product. The paper describes applied electrochemical development of systems to reduce CO2 and H2O using technical data from previous work. This paper will describe three developed processes: 1) ambient pressure production of syn-gas, 2) pressurized CO2 reduction and 3) Cl2 and syngas co-production.
Effect of Composition and Atmosphere on Electrical Properties of Donor-doped BaCe1-(x+y)ZrxNbyO3
Authors: Gore Colin M. , White Joseph O. , Singh Harmanpreet , Thangadurai Venkataraman , Wachsman Eric D.
Published: October 2013

The properties of donor-doped barium cerate perovskites have recently gained attention as electrode or electrolyte materials for high temperature solid-state devices utilizing CO2 containing gas streams due to their excellent chemical stability. In this study, the effect of co-doping BaCeO3 with Nb and Zr on electrical conductivity from 300-700 ˚C in air and in H2 is investigated. Small doping levels give rise to a significant increase in total conductivity in both air and hydrogen environments compared to BaCeO3. In air, activation energies for conduction are ~1 eV. In a reducing environment, the Nb appears to be the species more easily reduced in order to give rise to increased total conductivity, and there is a discontinuous change in total activation energy from ~0.55 eV to ~0.3 eV at low temperatures in H2. The transition temperature is dependent on dopant concentration. These materials may provide chemically-stable mixed conducting anode materials for high temperature proton conductors.
Validation of Nd2NiO4+
δ as Oxygen Electrode Material for Intermediate Temperature Solid Oxide Cells with LSGM Electrolyte
Authors: Montenegro-Hernández Alejandra , Mogni Liliana Veronica , Caneiro Alberto
Published: October 2013

The oxygen reduction reaction (ORR) was studied by Electrochemical Impedance Spectroscopy (EIS) for Nd2NiO4+δ (NNO) electrodes deposited on La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) electrolyte. The influence of NNO microstructure on the electrochemical performance was evaluated. The EIS measurements were carried out as a function of temperature (500<T<750ºC) and oxygen partial pressure (10-4<pO2<1atm). Three contributions associated with the ORR were identified: at high (HF), medium (MF) and low frequencies (LF). The HF contribution was associated with oxygen ion transfer trough electrode/electrolyte interphase. The MF contribution was attributed to oxygen ions diffusion within the NNO. The LF contribution was related to O2-dissociative adsorption for NNO obtained by chemical routes, where the particle sizes are smaller. If NNO were obtained by Solid State Reaction, the LF element was associated with a convolution of dissociative adsorption and gas diffusion processes.
In-Situ Monitoring of Solid Oxide Electrolysis Cells
Authors: Cumming Denis J , Taylor Rebecca , Manerova Jevgenija , Sinclair Derek C , Hardacre Chris , Elder Rachael H
Published: October 2013

High temperature co-electrolysis of steam and carbon dioxide using a solid oxide cell (SOC) has been shown to be an efficient route to produce syngas (CO + H2), which can then be converted to synthetic fuel. Optimization of co-electrolysis requires detailed understanding of the complex reactions, transport processes and degradation mechanisms occurring in the SOC during operation. Thermal imaging, Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy are being developed to probe in-situ both the reactions occurring during operation and any associated changes within the structure of the electrodes and electrolyte. Here we discuss the challenges in designing experimental apparatus suitable for high temperature operation with optical spectroscopic access to the areas of the SOC that are of interest. In particular, issues with sealing, temperature gradients, signal strength and cell configuration are discussed and final designs are presented. Preliminary results obtained during co-electrolysis operation are also presented.
Reduced-Temperature Firing of Anode-Supported Solid Oxide Fuel Cells
Authors: Gao Zhan , Barnett Scott A
Published: October 2013

Anode-supported solid oxide fuel cells (SOFCs) with yttria-stabilized zirconia (YSZ) electrolytes were successfully co-sintered at a temperature as low as 1250oC, substantially lower than the usual 1400oC, by using 1 mol.% Fe2O3 sintering aid. The effect of sintering temperature on cell electrochemical performance was investigated for cells with two different composite cathodes: (La0.8Sr0.2)0.98MnO3-δ (LSM) – YSZ or La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) – Gd-doped ceria (GDC). For the latter case, the electrolyte included a 3-µm-thick GDC layer that was co-sintered with the YSZ electrolyte and Ni-YSZ anode. Open-circuit voltages were near theoretical values within measurement accuracy for all cells. The LSM-cathode cell maximum power densities increased with decreasing sintering temperature, due to an anode resistance decrease. Cells with LSCF cathodes had substantially lower cathode polarization resistance than the LSM cells, yielding lower total resistance and higher power density. This was despite slightly higher than expected ohmic resistance for the GDC/YSZ bi-layer electrolytes; although this might be explained by the formation of a low-conductivity ceria-zirconia mixed phase by GDC/YSZ interdiffusion, energy-dispersive x-ray analysis did not detect interdiffusion. Micro-chemical analysis did not detect any zirconate formation in the LSCF/GDC/YSZ region.
Effect of Temperature Treatment on CoTiOx Catalyst for the Oxygen Evolution Reaction
Authors: Seitz Linsey C , Pinaud Blaise A , Nordlund Dennis , Jaramillo Thomas Francisco
Published: October 2013

Developing improved catalysts for the oxygen evolution reaction (OER) to boost the efficiency of hydrogen production via electrochemical water splitting is a crucial step for advancing this attractive renewable energy technology. In this work, we identify CoTiOx as a novel nonprecious metal catalyst for the OER and explore the effect of temperature treatments on its activity, structure, and electronic state. Using a simple and scalable sol-gel synthesis we can deposit this catalyst on a wide variety of substrates. Extended electrochemical testing reveals good stability and physical and electronic characterization of this catalyst reveals an amorphous structure and an oxidation state similar to that of other active cobalt catalysts.
Mass Spectrometric Study of the Ln-LnI3 (Ln = La, Ce) Systems
Authors: Ivanov Dmitry A. , Sergeev Dmitry N. , Dunaev Anatoliy M. , Kudin Lev S. , Butman Mikhail F.
Published: October 2013

The Ln−LnI3 (Ln = La, Ce) systems and their individual components LaI3 and CeI3 have been studied by the Knudsen effusion mass spectrometry (KEMS). Monomer LnI2, LnI3, dimmer Ln2I6 molecules and positive and negative ions have been identified in the saturated vapor over these systems. The formation of LnI2 in the Ln−LnI3 systems during high temperature experiments has been determined.
Low Temperature Lanthanum Strontium Ferrite Thin Film Stress and Oxygen Surface Exchange Coefficient Measurements
Authors: Yang Qing , Lunt Richard R. , Nicholas Jason D.
Published: October 2013

Mechano-chemical coupling of La0.6Sr0.4FeO3-δ thin films were observed below 500oC for the first time using a curvature relaxation technique. Chemical oxygen surface exchange coefficients (k’s) were measured by fitting the transient curvature of the thin film|substrate bilayer specimens under controlled temperature and oxygen partial pressure. Reproducible k values and their activation energies were obtained and are consistent with bulk sample k’s extrapolated from the literature.
(Invited) Probing Surface and Bulk States of Cathode Materials with Synchrotron-Based Soft X-Rays in a Functioning Solid Oxide Fuel Cell
Authors: McDaniel Anthony H. , Chueh William C , Shavorskiy Andrey , Tyliszczak Tolek , Bluhm Hendrik , McCarty Kevin F. , El Gabaly Farid
Published: October 2013

We discuss the development of a research platform designed to investigate surface and bulk properties of electrocatalysts in an operating solid oxide fuel cell using synchrotron-based soft X-ray spectroscopies. This novel platform realizes a fully functioning galvanic cell capable of supporting a Nernst potential, and incorporates both ambient pressure X-ray photoemission and X-ray absorption spectroscopies. Thus, surface compositions, surface electronic states, and bulk electronic states can be measured while manipulating the electrode environment; i.e., varying the gas composition, pressure, temperature, and cell potential. We will demonstrate the utility of this approach by presenting results of an experimental campaign focused on understanding what gives rise to the enhanced oxygen reduction reaction rates observed on a Ba0.5Sr0.5Co0.8Fe0.2O3 perovskite cathode.
Feasibility of Dual-Perturbation Electrochemical Impedance, Employing Simultaneous Chemical and Electrochemical Perturbations
Authors: McDonald TJ , Adler Stuart B.
Published: October 2013

An expansion of existing electrochemical impedance techniques to include both electrically and chemically driven perturbations is proposed. The advantage of this technique, called Dual-Perturbation EIS, is due to the dual perturbations originating at different interfaces, which can be used to yield additional insights into solid oxide fuel cell behavior. The feasibility of a Dual-Perturbation EIS measurement is established by design and fabrication of a prototype system, which yields measurable perturbation interaction terms in the Fourier Transformed response.
Synthesis and Electrochemical Characterization of T* La0.84Sm0.96Sr0.2CuO4 as a Cathode Material for IT-SOFC
Authors: Satapathy Akshaya Kumar , Irvine John T. S.
Published: October 2013

The synthesis and electrochemical characterisation of T* based La0.84Sm0.96Sr0.2CuO4 (LSSCu) has been carried out in order to use as a cathode material for intermediate temperature solid oxide fuel cell application. XRD studies shows, the phase pure material and matches with the JCPDF (# 79-1861), belong to space group of P4/nmm. The electrical conductivity value decreases from 52 Scm-1 at room temperature to 18.3 Scm-1 at 850 oC showing metallic behaviour in all temperature range. A decrease in conductivity, decreasing the partial pressure of oxygen implying the above material is p-type conductor. The Coefficient of thermal expansion value measured from Dilatometry is 14.4 * 10 -6 K-1 which matches with La0.9Sr0.1Ga0.8Mg0.2 (LSGM). Symmetrical cell testing results shows that the area specific resistance is 0.02 Ω.cm2 at 800 oC when the 1:1 weight ratio of the LSSCu and LSGM composite was screen printed on LSGM electrolyte and sintered at 900 oC for 1 hr.
Correlation between Defects and Electrical Characteristics/Reliability Analyzed by Integrated Evaluation Platform for SiC
Authors: Kitabatake Makoto
Published: October 2013

The Integrated Evaluation Platform for SiC wafers and epitaxial films is established. It provides information about the correlation between step-bunching defects and SiO2/SiC electrical characteristics/reliability. The Observation-Recognition System discovers that the step bunching on the epitaxial wafer partly spreads along the scratches. The Qbd measured in the Electrical-Characteristics Analyses has three types of distribution denoted as D1 (ideal SiO2/SiC without defects), D2 (average Qbd value half of D1 with step bunching), and D3 (small Qbd value with large defects). The Defect-Structure Analyses elucidate that the oxide thickness fluctuates on the step bunching line. The local electric field concentration at thinner spots causes degradation of SiO2/SiC reliability.
Packaging Techniques for Compact SiC Power Modules Operable in an Extended Tj Range
Authors: Tanimoto Satoshi , Watanabe Kinuyo , Tanisawa Hidekazu , Matsui Kohei , Sato Shinji
Published: October 2013

Packaging technology applicable to SiC power devices operated in an extended junction temperature range (Tjmax > 200°C) must be developed in order to create much more compact and cost-effective SiC power modules. This paper describes some of the technical challenges involved in improving the reliability of the critical package components—die attachment system, Al wire bonds and encapsulation—in direct contact with SiC devices inside the power module. Two numerical targets, (I) 3000 hours for a storage test at 250°C and (II) 3000 cycles for thermal cycling between -40°C and 250°C, were achieved through optimization and various improvements.
Reducing the Wafer Off Angle for 4H-SiC Homoepitaxy
Authors: Kojima Kazutoshi , Masumoto K. , Ito S. , Nagata A. , Okumura H.
Published: October 2013

We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer in whole 3-inch vicinal off angled substrate. The results suggested that the control of surface energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4o off-axis substrates. These results suggest that the wafer off angle for epitaxial growth can be reduced to less than 4 degrees.
Progress in SiC MOSFET Reliability
Authors: Hughart David R. , Flicker Jack D. , DasGupta Sandeepan , Atcitty Stan , Kaplar Robert J. , Marinella Matthew J.
Published: October 2013

Bias-temperature stress experiments performed on two generations of SiC power MOSFETs from the same manufacturer show reductions in threshold voltage (VT) shift at elevated temperatures from first- to second-generation. The negative VT shift is reduced from a range of -1 V to -1.6 V to a range of -100 mV to -300 mV for temperatures from 125°C to 175°C. Plastic-packaged parts show a gate-bias-independent junction leakage current at temperatures above the rated temperature, suggesting that the plastic packaging introduces an extrinsic leakage path. Junction leakage in metal-packaged parts can be significantly reduced by applying a small negative gate bias at elevated temperatures. Switching gate bias temperature stresses show VT shifts dependent on duty cycle, with a higher duty cycle resulting in a higher rate of VT shift. Cumulative damage effects may be observed between switching gate bias stresses.
Power Semiconductor Device, Course Contents Revisited
Authors: Abdel-Motaleb Ibrahim M.
Published: October 2013

The skills needed to build the next-generation of power semiconductor devices and to integrate them into power electronic systems require proper education and training of engineering students, both at the undergraduate and graduate levels. To assess the current state of power electronics education, a study of curricular offering in power electronics in the U.S. universities is conducted. The study shows that there is a lack of course offering in semiconductor power devices and almost nonexistence of critical topics in the curriculum, especially thermal management, temperature effects, reliability, power packaging, modeling, systems integration, and failure analysis. To remedy these deficiencies, new power electronics tracks/concentrations for undergraduate and graduate programs are proposed. The proposed curricular modifications are designed to be rigorous to meet the future needs of the power electronic industry, but they remained flexible enough to be easily adopted by many institutions.
III-N High-Power Bipolar Transistors
Authors: Dupuis Russell D , Kim Jeomoh , Lee Yi-Che , Lochner Zachary , Ji Mi-Hee , Kao Tsung-Ting , Ryou Jae-Hyun , Detchphrom Theeradetch , Shen Shyh-Chiang
Published: October 2013

We report state-of-the-art d.c. and RF performance of GaN/InGaN npn DHBTs grown by the MOCVD technology on sapphire substrates. The fabricated GaN/InGaN HBTs achieved a collector current density greater than 50 kA/cm2 and a d.c. current gain of 60 at the collector voltage of 13 V. A open-base collector-emitter breakdown voltage of greater than 90 V was measured. Using the same layer structure and device fabrication techniques, we also demonstrated state-of-the-art RF performance of GaN/InGaN HBTs with fT
greater than 8 GHz and fmax
greater than 1.8 GHz at the collector current density of 11 kA/cm2. These d.c. and RF measurement results demonstrated the capability and feasibility of III-N HBTs for high-power circuit applications.
AlGaN/GaN MIS-HEMT Gate Structure Improvement Using Al2O3 Deposited by PEALD and BCl3 Gate Recess Etching
Authors: Meunier Richard , Torres A. , Charles M. , Morvan E. , Plissonier M. , Morancho F.
Published: October 2013

The enhancement of electric properties of MIS structures on an AlGaN/GaN heterostructure using Al2O3 a gate dielectric are investigated using C(V) and Id(Vg) measurements. The Al2O3 layer was deposited using two types of atomic layer deposition (ALD) techniques: thermal ALD and plasma enhanced ALD. Using PEALD over thermal ALD led to an increase of the threshold voltage Vth of 4V, and the suppression of non-uniform C(V) behavior by reducing traps at the Al2O3/AlGaN interface. Gate leakage current was also reduced by 6 decades and an Ion/Ioff ratio of 109 was achieved, with a subthreshold slope of 81mV/decades. Further improvements were achieved by gate recess etching before the high-k deposition through BCl3 reactive ion etching (RIE). We were able to further increase Vth by 4V while reducing gate leakage current, achieving a 1010 Ion/Ioff ratio, without degrading the subthreshold slope and the abruptness of the transition.
Production Readiness of AlGaN/GaN HEMT on 6”/8” Si
Authors: Lee Dong Seung , Su Jie , Krishnan Balakrishnan , Papasouliotis George D. , Paranjpe Ajit
Published: October 2013

Growth of crack-free AlGaN/GaN heterostructures on 6 and 8 inch Si(111) by 5x6” and 3x8” multi-wafer K465i production MOCVD system is presented. The two-dimensional-electron-gas is formed at the AlGaN/GaN interface with average Hall mobility values more than 1800 cm2/v.s and sheet resistance less than 400 Ohm/sq. Run to run repeatability of AlGaN/GaN structural qualities, wafer bow, and 2DEG properties shows the potential manufacturing possibility with the epitaxial process stability and longevity.
Synchrotron X-ray Topography Studies of the Evolution of the Defect Microstructure in Physical Vapor Transport Grown 4H-SiC Single Crystals
Authors: Dudley Michael , Raghothamachar Balaji , Wang Huanhuan , Wu Fangzhen , Byrappa Shayan , Chung Gil , Sanchez Edward K , Mueller Stephan , Hansen Darren , Loboda Mark
Published: October 2013

Synchrotron White Beam X-ray Topography studies are presented of dislocation behavior and interactions in a new generation of 100mm diameter, 4H-SiC wafers grown using Physical Vapor Transport under specially designed low stress conditions. Such low stress growth conditions have enabled reductions of dislocation density by two or three orders of magnitude from lowest previously reported levels of 104-105cm-2 down to current levels of 102-103 cm-2. This provides a unique opportunity to discern the details of dislocation configurations and interactions which were previously precluded due to complications of image overlap at higher dislocation densities. Detailed topography analysis have revealed dislocation multiplication by the hopping Frank-Read source mechanism, interactions between threading c, a and c+a dislocations and deflections of threading dislocations resulting in stacking fault formation. These insights greatly aid in eliminating such undesirable defects or engineering their structures to minimize their impact leading to improved performance in device applications.
Heat Dissipation in GaN Based Power Electronics
Authors: Su Zonghui , Malen Jonathan A
Published: October 2013

Gallium Nitride (GaN) possesses superior electronic properties for RF power electronics that play critical roles in various wireless communication technologies and military applications [1]. Heat generated as a byproduct of operation in these devices, increases their operating temperature and degrades their performance and lifetime. While bulk GaN has a high thermal conductivity (k) approaching 250 W/m-K, [2, 3] GaN thin films and devices experience a much lower k due to the presence of additional phonon scattering mechanisms and departures from Fourier transport [4, 5]. We will review thermal transport in GaN based devices, broadly addressing the impact of heat source dimensions, film thicknesses, interfaces, and defects.
Monolithic Integration of High Temperature Silicon Carbide Integrated Circuits
Authors: Alexandru Mihaela , Banu Viorel , Montserrat Josep , Godignon Philippe , Millán José
Published: October 2013

This paper deals with the design, the fabrication and the characterization of SiC ICs able to work at high temperature. The key SiC device is a planar MESFET specially designed for high temperature and high integration density. The other element required for integrating the basic cells library is a SiC resistor built in the same epilayer than the MESFET. Our preference for the MESFET is due to the already proved temperature stability of its Tungsten-Schottky barrier. The SPICE models of these two components are based on experimental measurements in the 25ºC-300ºC temperature range. The process technology setup is also analyzed, which contains three metal levels fully compatible with a standard CMOS technology. The digital library allows implementing multi-stage logic embedded in power management circuitry. The fabrication and the testing of the elementary logic gates library are also analyzed at high temperature and high frequencies. Furthermore, the standard CMOS topologies can be transferred to various Flip-Flops based on 4H-SiC MESFET basic logic gates. The multi-stage SiC ICs show a similar behavior as the logic gates at room and high temperatures, and at high frequency. The functionality of multi-stage SiC ICs has been proved.
Application Engineering of Wide Bandgap Semiconductors
Authors: Sarlioglu Bulent , Han Di , Noppakunkajorn Jukkrit , Ogale Anuradha
Published: October 2013

This paper will address the importance and benefits of wide bandgap (WBG) semiconductors and provide example research results on utilization of these new devices in power electronic circuits. The paper will elaborate on device and circuit level opportunities, challenges, and potential solutions for various power electronic applications using WBG semiconductors. The paper will also present the current power electronic curriculum and education for undergraduate, graduate, and outreach education. Furthermore, suggestions are included on changes that can be made to include and promote WBG devices in power engineering education to develop a new workforce.
First-Principles Study of Oxygen Vacancy and Hydrogen Impurity Effects in the Pseudo-Hexagonal Ta2O5
Authors: Kim J. Y. , Magyari-Köpe B. , Hazeghi A. , Lee K. J. , Kim H. S. , Lee S. H. , Nishi Y.
Published: October 2013

The structures and electronic properties of Ta2O5 polymorphs were calculated using density-functional theory employing the generalized gradient approximation with on-site Coulomb corrections. Using this approach, a pseudo-hexagonal structure was found to be a stable polymorph of Ta2O5 over the

14Î´' type="#_x0000_t75"> - and

14Î²' type="#_x0000_t75"> -Ta2O5 and is proposed as a new candidate structure which might be formed during the resistive switching process in random access memory devices. Its diffraction spectrum is shown to successfully match the recently indexed experimental structure and its band-gap energy is also in good agreement with available experimental data. A neutral oxygen vacancy is shown to induce an occupied defect state at 2.5 eV above the top of the valence band, as also found by x-ray photoelectron spectroscopy spectrum measurement. Furthermore, the effects of the hydrogen impurity on the electronic structures were investigated.
A CMOS Compatible, Forming Free TaOx ReRAM
Authors: Lohn Andrew J , Stevens James E , Mickel Patrick R , Hughart David R , Marinella Matthew J.
Published: October 2013

Resistive random access memory (ReRAM) has become a promising candidate for next-generation high-performance non-volatile memory that operates by electrically tuning resistance states via modulating vacancy concentrations. We demonstrate a wafer-scale process for resistive switching in tantalum oxide that is completely CMOS compatible. The resulting devices are forming-free and with greater than 1x105 cycle endurance.
(Invited) Improved Operation Characteristics in Charge-Trapping Flash Memory Devices with Engineered Dielectric Stack and SiGe Channel
Authors: Ye Zong-Hao , Liu Li-Jung , Chang-Liao Kuei-Shu
Published: October 2013

Programming and retention characteristics of charge-trapping (CT) non-volatile memory (NVM) devices can be enhanced by inserting Al2O3 between Si3N4 and HfO2 as the charge-trapping layer. This is because most of the injecting charges are trapped at Si3N4/Al2O3 interface and Al2O3 also provides a high barrier for electron detrapping. In addition, Compare to those with conventional Si-channel, both programming and erasing speeds are significantly improved by employing a Si0.7Ge0.3 buried channel. Satisfactory retention and excellent endurance characteristics up to 106 P/E cycles with 4.1 V memory window show that the degradation on reliability properties, if it exists, is negligible when SiGe buried channel is introduced.
Optimized Contact Engineering to Maximize Cell Current in NAND Flash Memory Technology
Authors: Yoon Joong Ho , Kim Hong-Sig , Kim Yung Sam , Lee Jun Kyoung , Han Eui Sung , Jeong YeonUn , Lee Young Ik , Jang Sung Jin , Kim Hyun Gil , Park Sung Wook , Park Sae Hui , Lee Hae-Bum , Lee Kyu-Pil , Cho In-soo
Published: October 2013

In this research we have confirmed that Nand flash cell current increases by optimization of contact barrier metal (BM) deposition and plug implantation (IIP) doping condition, which result in improved contact resistance (Rc) and cell leakage. Plug IIP dopant, BF2, which has been applied to P-type Transistor (Tr) for lowering Rc sacrifices contact process margin in cell area of n-type occurred by cell leakage. We could dramatically improve P-type Contact Rc and contact process margin by lowering BM deposition process temperature and adopting plug IIP doping with phosphorous (Ph.) respectively
(Invited) Particle Cleaning Technologies to Meet Advanced Semiconductor Device Process Requirements
Authors: Okorn-Schmidt Harald F. , Holsteyns Frank , Lippert Alexander , Mui David , Kawaguchi Mark , Lechner Christiane , Frommhold Philipp E. , Nowak Till , Mettin Robert
Published: October 2013

Dealing with nanometer-sized particulate contamination is still one of the major challenges during the manufacturing of yielding semiconductor devices. This is especially true for the increasing number of critical processing steps, where residues of particulate matter need to be removed without mechanically damaging sensitive device patterns and, at the same time, achieve the lowest possible substrate loss. If higher substrate loss would be permitted, pure chemical mechanism could be employed (e.g. particle undercut and lift-off). However, being only permitted to have statistical sub-Angstrom material loss, physical forces need to be integrated jointly with the appropriate chemical support. This paper provides an overview of prospective techniques being currently investigated to meet present and future industry requirements.
Surface Cleaning Using CO2 Gas Cluster for Semiconductor Device
Authors: Cho Yujin , Choi Hoomi , Kim Taesung
Published: October 2013

The present semiconductor cleaning technology is based upon chemical cleaning, a high-temperature process that consumes vast amounts of chemicals and ultrapure water. Therefore, this technology gives rise to many environmental issues, and some alternatives are being evaluated. Herein we report, gas cluster cleaning method for cleaning semiconductor devices. Two types of particles such as Ceria (CeO2) and Silica (SiO2) were used to evaluate particle removal efficiency (PRE). It is observed from the field emission scanning electron microscopy (FE-SEM) images that most of particles were removed with PRE more than 90% under various experimental conditions. Further, the pattern damage evaluation is carried out for poly-Si patterns which have width of pattern in the range of 60 to 100 nm. It is observed that there is no pattern damage for various experimental conditions.
A Multi-Frequency Megasonic System for Nano-Particle Removal
Authors: Kim Hyunse , Lee Yanglae , Lim Euisu
Published: October 2013

A multi-frequency megasonic system for nano-particle removal was developed. In design process, finite element analysis was performed and anti-resonance frequency for 1 MHz actuating, was predicted as 995 kHz with 0.5% error compared with the measured value of 1000 kHz. In addition, anti-resonance frequency of 2998 kHz was obtained for 3 MHz, which coincided with the measured value. For the verification of the system performance, acoustic pressures of the developed waveguide were measured and compared with a commercial megasonic system. The result revealed that the developed one can show relatively better distributions. To assess cleaning ability, particle removal efficiency (PRE) tests were processed and 56.1% PRE improvement was achieved compared with a conventional product. Considering these results, the developed system can be applied to nano-particle cleaning process with higher efficiency.
A Study on the Removal Method of Si Residue during Si Wet Etching
Authors: Ko Kihyung , Jeon Hayoung , Song Myunggeun , Han Jeongnam , Yoon Boun , Choi Siyoung , Kang Hokyu , Lee Chilgi , Kim Taesung
Published: October 2013

In this paper, problems that can occur during the poly-Si wet etch in the semiconductor process are used and methods to solve these problems are introduced. In order to prevent the substrate from being damaged, we generally use a wet etching process that uses alkali solutions rather than dry etching process. If poly si residues remain after etch process in this critical step, it bring about a huge impact on the wafer yield.
Effect of Surface Wettability on Frictional Conditions of PVA Roll Brushes
Authors: Hara Yoshitaka , Sanada Toshiyuki , Fukunaga Akira , Hiyama Hirokuni
Published: October 2013

In order to gain insight into the mechanisms of polyvinyl acetal (PVA) roll brush cleaning in semiconductor device fabrication, we measure the coefficient of friction (COF) between the PVA brush and a substrate. In particular, we focus on the brush rotation speed and the surface wettability. The COF is found to decrease and approach 0.5 as the brush rotation speed increases. For the case of low rotation speeds, the COF of hydrophobic surfaces has a large value, almost 1.0, while that of hydrophilic surfaces is small. These results imply that the brush and the surface directly contact and the real contact area of the PVA brush increases over the duration of the contact time.
Use of a Simple Cavitation Cell Set-Up with Replaceable Single Band Filters for Analysis of Sonoluminescence Signal from Megasonic Irradiated Gasified Aqueous Solutions
Authors: Han Zhenxing , Keswani Manish , Liebscher Eric , Beck Mark , Raghavan Srini
Published: October 2013

A simple method to resolve the features that are characteristic of hydroxyl radicals in sonoluminescence (SL) spectra from aqueous solutions has been developed. Using a modified version of cavitation threshold (CT) cell in which single band filters were sandwiched between the UV grade fused silica window and the photomultiplier tube (PMT) in the cell, photon emission in the wavelength range of 280 to 400 nm was measured. Four different single band filters, 280 – 305.5 nm, 300 – 340 nm, 335 – 375 nm and 374.5 – 397.5 nm were used. The results for air and Ar saturated DI water are consistent with those reported in the literature and obtained using expensive spectrometers. The SL signal collected in ammonium hydroxide solutions indicated that at higher power densities the signal intensity may not be relatable to the generation rate of hydroxyl radicals in their ground state.
Challenges and Solutions for 450mm FEOL Wet Clean Tool
Authors: Yu Bill , Ku Felix , Taft Charles , Larrea Anne-Sophie , Lin John , Hayashi Toyohide , Morita Akira , Arai Kenichiro , Naohara Hideji
Published: October 2013

Wafer size transition from 300mm to 450mm has been started to address the higher manufacturing cost issue. Major challenges for front end of line (FEOL) clean are listed. From preliminary results, cleanness and etching uniformity are very positive with comparable or even better particle adder performance. Pattern collapse and damage become more and more critical to advanced technology node, but currently they couldn’t be tested due to the lack of 450mm pattern wafer. For 450mm wafer recycling, it will be done in single wafer processing tool instead of batch tool, good results in terms of short process time and low surface roughness were obtained on SiO2 and Si3N4 recycling wafers. Same as 300mm, single wafer processing tool for Si3N4 wet etching is requested.
Chemical Improvement of EUV Ruthenium Capping Layer Against Active Oxygen and Hydroxyl Radicals
Authors: Lee Hanshin , Choi Jaehyuck , Koh Soowan , Kim Jinsu , Kim Dohyung , Choi Junyoul , Kim Hyoyeon , Ko Hyungho , Kim Byung Gook , Jeon Chan-Uk
Published: October 2013

It has been challenging to find suitable chemistries for cleaning of EUV mask consisting of various materials including multilayer, absorber, and capping layers. Recent investigation reveals that active oxygen or hydroxyl radical cleaning, which is more effective than SPM in removal of organic contaminant, turns out to cause serious damages on ruthenium capping layer. It is hypothesized that ruthenium layer damage is mainly caused by chemical oxidation (degradation) and physical rupture of ruthenium layer. Oxygen radicals not only oxidize ruthenium top surface but also diffuse into the layer where they oxidize ruthenium on inner surface. In this work, we try to understand root-causes of ruthenium damage using of qualitative analysis of TEM, EDX, and XPS. Based on the analysis, we propose innovative and robust technology of ruthenium surface treatment to mitigate diffusion of oxygen radicals into ruthenium layer, thereby reducing oxidation and damage of ruthenium capping layer.
Influence of Geometry, Edges and Roughness on Liquid Penetration and Removal During Wet Cleaning
Authors: Extrand C. W. , Moon Sung In
Published: October 2013

We examined how edges and roughness influence the penetration and removal of wet cleaning liquids from model vias. First, we demonstrated the influence of edges on the pinning of liquids. Next, we used this knowledge to construct models for estimating the influence of roughness on the inception of liquid movement. Our findings suggest that roughening of via walls reduces the ability of liquids to penetrate and impedes their removal.
Micro Unetched Oxide Defect during Buffered Oxide Etchant Process
Authors: Lim SeungTaek , Ahn Dukmin , Kim Kihyun , Jung Heechan , Lee Byoungsu , Lee Huihwan , Hwang Hasub
Published: October 2013

There are two oxide regions, high and low voltage in NAND flash memory devices, in order to improve program speed and reliability. Generally, the two regions are achieved with pattern blocking by using PR(Photo Resistor) followed by etching of low voltage oxide with BOE(Buffered Oxide Etchant). However, as the 10nm scale NAND flash devices are massively manufactured, 0.2um size defects after oxide etching with BOE are newly detected. Partially unetched oxide defects in low voltage oxide region causes the thicker tunnel oxide and influences abnormal electron’s tunneling. As the result, program and erase speed are declined on the relevant transistor, and it causes a yield drop by the electronic characteristics. As possible sources of the defects, the micro impurities in chemical or the micro bubbles from surfactant are suspected, but correct root cause is not yet known. In this study, the effects of filter pore size and nozzle movement of cleaning equipment are examined in other to reduce the defects.
Effective Defect Control in TiN Metal Hard Mask Cu/Low-k Dual Damascene Process
Authors: Kabansky Alexander , Tan Samantha S.H. , Hudson Eric A. , Delgadino Gerardo , Gancs Lajos , Marks Jeffrey
Published: October 2013

Metallic hard masks (MHM) are routinely employed in Cu/low k dual damascene (DD) etching, but can create defectivity problem. N2 plasma post-etch treatment (N2PET) based on high substrate temperature has been developed to provide effective TiFx residue reduction and MHM defect prevention without low k damage and productivity concerns. Strong gains in surface de-fluorination with substrate temperature and N2PET time was determined. SLIC, XPS, SEM data show 90% reduction of F residue on TiN and no defects on pattern at optimized N2PET. AES and EELS data show that “TiFx” defects are actually TiOx crystals covered by TiFx residue catalyzing the crystal growth. N2PET de-fluorination and defect growth are in focus of this study. An alternative approach in preventing defect growth by surface passivation in CF4/C4F8 etch chemistry was also studied. Both methods, N2PET cleaning and surface passivation, provide effective defect control in TiN MHM Cu/low-k DD etch process.
Advanced Wafer Drying Technology for 1x Node and Beyond Using Surface Modification Method
Authors: Watanabe Tsukasa , Toshima Takayuki , Nakamori Mitsunori , Egashira Keisuke , Ido Yasuyuki , Matsumoto Nobuaki , Orii Takehiko
Published: October 2013

IPA dry has been used as a method to prevent pattern collapse instead of spin dry since it is easy to install for single wafer tools. However, it is reaching the limit of process margin since IPA surface tension is only one third that of water. We focused on the other parameter which decides Laplace force: contact angle. When the contact angle is close to 90deg, the force approaches zero, which enables larger process margin for next generation structures. We call this concept of drying ‘Monolayer Dry’. We compared the potential of IPA dry, F-based solvent (with very low surface tension) and Monolayer Dry by calculating the threshold aspect ratio (AR) of generating pattern collapse. Compared the performance of Monolayer Dry to IPA dry by observing the cross-section surface after cleaning and drying. No collapse was found by Monolayer Dry using 1x node pattern sample.
All Wet Resist Strip for Improved Semiconductor Process and Product Improvement
Authors: Bashyam Murli , Satterfield M. , Gupta R.
Published: October 2013

Conventionally, plasma ash followed by a wet clean has been used to strip implanted photoresists on all semiconductor technology process flows and nodes. This paper describes the theory and implementation of an All Wet Strip (AWS) process at various post implant levels in the process flow, thus eliminating the need for a plasma treatment. Plasma treatment post implants have shown to add product yield limiting defects most likely eliminated by an All Wet Strip (AWS) process; successfully contributing to cycle time, capacity, cost and yield improvement for semiconductor chips. AWS involves the use of a sulfuric acid and hydrogen peroxide mixture for stripping implanted photo resists, the effectiveness of which has a dependency on the ion implant dose, energy and photo resist type. The paper describes the unique challenges that were overcome to bring the concept from an experimental stage to actual implementation, the process integration plus device sensitivities involved in ramping a process, in a volume 300mm semiconductor wafer fab for complex technologies.