bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Towards a Fundamental Understanding of the Cathode Degradation Mechanisms
Authors: Wachsman Eric D. , Huang Yi-Lin , Pellegrinelli Christopher , Taillon Joshua A. , Salamanca-Riba Lourdes G.
Published: May 2014

While impressive solid oxide fuel cell (SOFC) performance has been achieved, durability under “real world” conditions is still an issue for commercial deployment. In particular cathode exposure to H2O and CO2 can result in long-term performance degradation issues. Therefore, we have embarked on a multi-faceted fundamental investigation of the effect of these contaminants on cathode degradation mechanisms in order to establish cathode composition/structures and operational conditions to enhance cathode durability. Using a Focused Ion Beam (FIB)/SEM we are quantifying in 3-D the microstructural changes of the cathode before and after the onset of cathode performance degradation. This includes changes in TPB density, phase-connectivity, and tortuosity, as well as tertiary phase formation. This is then linked to heterogeneous catalysis methods to elucidate the cathode oxygen reduction reaction (ORR) mechanism to determine how H2O and CO2 affect the ORR as a function of temperature, time, and composition. By use of in-situ
18O-isotope exchange of labeled contaminants we are investigating whether oxygen incorporated in the lattice of LSM and LSCF, and their composites with YSZ and GDC, respectively, originated from ambient O2 or the contaminant, as well as intermediate adsorbed species and mechanisms that lead to degradation. The results will be used to develop a cohesive and overarching theory that explains the microstructural and compositional cathode performance degradation mechanisms.
Reactions and Transport Pathways in Syngas Fueled Ni/YSZ SOFC Anodes: Experiments and Modeling
Authors: Kromp Alexander , Geisler Helge , Weber André , Ivers-Tiffée Ellen
Published: May 2014

This paper reports a comprehensive understanding of the reactions and transport processes that determine the performance of syngas fueled Solid Oxide Fuel Cells with Ni/8YSZ anodes. With a combined electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) study the individual polarization processes for syngas operation are identified. Complex non-linear least squares (CNLS) fitting of a subsequently developed physically meaningful equivalent circuit enables quantitative analyses of the individual loss contributions. A detailed kinetic analysis of the high-frequency activation polarization processes has revealed the mechanism of the electrochemical fuel oxidation. For syngas operation, only H2 is electrochemically oxidized at the Ni/8YSZ anode. Consequently, the syngas fuel is transported through Ni/8YSZ anodes via (i) a H2/H2O diffusion pathway and (ii) a CO/CO2 diffusion pathway, which is activated by heterogeneous reforming chemistry. Transient numerical simulation validates this reaction-diffusion model and further helps to assign the measured low-frequency polarization processes to the identified transport pathways.
Tailoring Mixed Ionic Electronic Conducting Nano-Particle Size through Desiccation and/or Doped Ceria Oxide Pre-Infiltration
Authors: Burye Theodore , Nicholas Jason D.
Published: May 2014

Mixed Ionic Electronic Conducting (MIEC) multi-cation oxide nano-particles are commonly used to enhance the performance of Solid Oxide Fuel Cell (SOFC) Nano-Composite Cathodes (NCCs) electrodes. The average MIEC NCC nano-particle size produced by the infiltration method are typically 50-60 nm in diameter and result in SOFC operating temperatures in excess of 600°C. Since MIEC particle size directly correlates with the surface area available for oxygen incorporation and hence NCC performance, the objective of this study was to determine if MIEC infiltrate particle size could be reduced through nitrate gel desiccation and/or the pre-infiltration of a nitrate decomposition catalyst (in this case nano-Gd0.1Ce0.9O1.95 (GDC)). For the La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) infiltrate particles examined here, average nano-particle sizes were reduced from 50 nm to 20 nm using both desiccation and/or pre-infiltration processing techniques. These reduced LSCF nano-particle sizes lowered the 550°C NCC polarization resistance from 0.33 Ωcm2 to 0.16 Ωcm2 with desiccation and from 0.33 Ωcm2 to 0.11 Ωcm2 with nitrate decomposition catalyst pre-infiltration.
A Model for Extracting Fundamental Kinetic Rates of SOFC Cathode Materials from Oxygen Isotope Exchange Experiments
Authors: Huang Yi-Lin , Pellegrinelli Christopher , Wachsman Eric D.
Published: May 2014

A fundamental understanding of the oxygen reduction reaction (ORR) mechanisms on SOFC cathodes is essential for the development of lower temperature SOFCs with high performance. Isotope exchange is a powerful tool for analyzing the oxygen exchange process (1,2,3,4,5). In this study, we attempt to determine the ORR mechanism and extract fundamental kinetic rates for La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) and (La0.8Sr0.2)0.95MnO3-x (LSM) using isothermal isotope exchange (IIE)(6,7). IIE experiments were conducted at various temperatures and oxygen partial pressures. To extract fundamental kinetic rates from in-situ isotope exchange experiments on LSM and LSCF, a model was been developed based on a two-step reaction mechanism across the heterogeneous gas-solid interface. The coupled reactions can be shown in two elementary steps: dissociative adsorption and incorporation. The relation between the fundamental kinetic rates and surface exchange coefficient (kex) can be directly linked (8,9). In this paper we have developed a mathematic model to unify extracted surface exchange rates between techniques, including isotope exchange, conductivity relaxation experiments, etc. These results can lead to a better understanding of the ORR mechanisms and help design better cathode materials for SOFCs.
Three Dimensional Microstructural Characterization of Cathode Degradation in SOFCs Using Focused Ion Beam and SEM
Authors: Taillon Joshua A. , Pellegrinelli Christopher , Huang Yilin , Wachsman Eric D. , Salamanca-Riba Lourdes G.
Published: May 2014

Composite cathodes in solid oxide fuel cells (SOFCs) improve performance by increasing the triple phase boundary length and providing a more continuous pathway through the electrolyte for oxygen ion transport. These cathodes however, are susceptible to performance degradation from exposure to contaminants such as H2O and CO2 vapor. The microstructure and connectivity of yttria-stabilized zirconia (YSZ)/lanthanum strontium manganite (LSM) composite cathodes were examined and quantified using a dual beam focused ion beam/scanning electron microscope (FIB/SEM) in order to determine the effect of various contaminants on the performance of the SOFCs. Three-dimensional reconstructions of multiple composite cathodes allowed for microstructure quantification at nanometer resolution. Further analysis of triple phase boundary length (L
TPB) demonstrated how the available active sites changed as a function of cell operation and contamination. This sort of analysis allows for a direct comparison between cathode microstructure and polarization resistance.
(Invited) Increased Oxide Ion Diffusivity and Surface Exchange on Pr2NiO4 Base Oxide by Au Dispersion
Authors: Hyodo Junji , Tominaga K. , Ju Young-Wan , Ida Shintaro , Ishihara Tatsumi
Published: May 2014

Influence of the metal dispersion in the dense Pr2NiO4-base oxides on the charge and mass transport was investigated in this study. Ag, Au, Pd, and Pt metal particles were dispersed into the Cu- and Ga-doped Pr2NiO4, and it was found that Au dispersion improves the electric conductivity. In addition, Au dispersion also enhances the oxide ion diffusivity and oxygen surface exchange property.
Conduction Properties and Ionic Transference Behavior of CaTi1-XScxO3-δ (x=0.05, 0.1)
Authors: Hong Hyun-Jin , Yashiro Keiji , Hashimoto Shin-ichi , Kawada Tatsuya
Published: May 2014

Sc doped CaTiO3, CaTi1-xScxO3-δ (x=0.05, 0.1) was fabricated by a solid state reaction method and their conduction properties were investigated systematically investigated using a 4-terminal method at various temperature (1000ºC to 500ºC). Oxygen partial pressure dependence of the conductivity was analyzed from a defect chemical point of view in order to estimate the ionic and the electronic partial conductivities. The ionic conductivity of CaTi1-xScxO3-δ for x=0.05 and 0.1 were 0.018 S∙cm-1 and 0.033 S∙cm-1, respectively at 1073K and their ionic transference numbers were higher than 0.95 in the electrolytic domain range as function of P(O2) at 1073K. From these results, Sc doped CaTiO3, CaTi1-xScxO3-δ (x=0.05, 0.1) system has high potential for alternative electrolyte material especially in IT-SOFCs.
(Invited) Proton Transport in Inorganic Phosphates
Authors: Garzon Fernando , Kreller Cortney R. , Wilson Mahlon S. , Mukundan Randachary , Pham Hieu , Henson Neil J. , Hartl Monika , Daemen Luke
Published: May 2014

The proton conduction mechanism of well-characterized SnP2O7 and Sn1-xInxP2O7 materials was investigated using AC impedance spectroscopy and inelastic neutron scattering. Samples with minimal amounts of excess phosphate do not possess appreciable conductivity at room temperature. Indium doping appears to increase the high temperature proton conductivity of the materials. Inelastic neutron scattering data indicates that no appreciable changes in proton concentration occur between hydrated and dehydrated samples of SnP2O7 while changes in proton vibrational mode amplitudes occur with indium doping, or upon hydration, of samples that contain excess phosphate.
Concepts for Ultra-High Power Density Solid Oxide Fuel Cells (SOFC)
Authors: Zhu Liangzhu , Zhang Lei , Zhao Feng , Virkar Anil V.
Published: May 2014

A parametric equation for describing polarization in solid oxide fuel cells (SOFC) is presented in terms of experimentally measurable parameters. The equation explicitly describes activation and concentration polarizations at the two electrodes, and the ohmic loss as a function of current density. Using the equation and known values of experimentally measured parameters, determined by in-cell and out-of-cell tests, various polarizations are estimated as functions of current density, and the maximum possible performance characteristics are assessed. Using the model, prospects for ultra-high power density SOFC at intermediate temperatures (<800oC) are examined. The results show that even in thin electrolyte film, anode-supported cells, ohmic contribution can be substantial, not all of it being attributable to the electrolyte. The results also show that the electrode particle size has a substantial effect on activation polarization.
Fermi Potential across Working Solid Oxide Cells with Zirconia or Ceria Electrolytes
Authors: Jacobsen Torben , Chatzichristodoulou Christodoulos , Mogensen Mogens Bjerg
Published: May 2014

Two kinds of electrochemical relevant potentials are important in order to describe several observed phenomena in operating electrochemical cells with solid electrolytes. This paper gives illustrative examples of how the profiles of the two potential types, the Galvani potential, f, and the electromotive – also called the Fermi potential, p, will vary across the electrolyte, and of how the electron leak current density though the electrolyte, which is related to p, will be affected by temperature and cell voltage across the electrolyte in cells based on gadolinia doped ceria (CGO) and on yttria stabilized zirconia (YSZ) electrolytes. The nature of the two potential types and the importance of each of them for the cell operation are explained.
Catalytic Enhancement of Solid Carbon Oxidation in HDCFCs
Authors: Deleebeeck Lisa , Ippolito Davide , Hansen Kent Kammer
Published: May 2014

Hybrid direct carbon fuel cells consisting of a solid carbon (carbon black)-molten carbonate ((62-38 wt% Li-K)2CO3) mixtures in the anode chamber of an anode-supported solid oxide fuel cell type full-cell are tested for their electrochemical performance between 700 and 800°C. Performance was investigated using current-potential-power density curves. In the anode chamber, catalysts are mixed with the carbon-carbonate mixture. These catalysts include various manganese oxides (MnO2, Mn2O3, and Mn3O4) and doped-ceria (CeO2, Ce1-xGdxO2-x/2, Ce1-xRExO2-δ (RE = Pr, Sm)), the effectiveness of these families of catalysts are discussed with respect to electrochemical, chemical and post-mortem analysis.
Effect of CeO2 Infiltration on the Hybrid Direct Carbon Fuel Cell Performance
Authors: Ippolito Davide , Deleebeeck Lisa , Hansen Kent Kammer
Published: May 2014

The effect of CeO2 infiltration into the anode or CeO2 mixed with the carbon-fuel on the performance of a Hybrid Direct Carbon Fuel Cell (HDCFC) was studied through the use of polarization curves and electrochemical impedance spectroscopy. The use CeO2 in both ways helped to increase the cell performance. In particular, mixing CeO2 with carbon represents the best strategy to increase the cell power output.
Zirconia Sensor Device for In Situ Monitoring of Metalpowder Oxidation for Energy Storage Applications
Authors: Milshtein Jarrod David , Basu Soumendra Nath , Gopalan Srikanth , Pal Uday Bhanu
Published: May 2014

A zirconia oxygen sensor was designed to monitor the gas-solid oxidation reaction characteristics of metal/metal-oxide powder beds. This in-situ monitoring device allows for determination of the oxidation state of the metal oxides during reactions in real time, as well as calculation of the chemical reaction rate constants. The signal output of the sensor was analyzed for oxidation of and diffusion of oxygen into the powder bed. The oxygen transport mechanisms occurring inside the sensor were described to further understand the signal outputs from the powder bed. A model metal/metal-oxide system is examined using this device to demonstrate its performance. The simple Ni/NiO system was chosen to demonstrate feasibility.
Electrochemical, Catalytic and O2-Permeation Studies of Iron-Doped Barium Zirconates for Membrane Reactor Applications
Authors: Zhang Haomiao , Suresh Aravind , Carter C. Barry , Wilhite Benjamin A
Published: May 2014

An Fe-doped Barium Zirconate perovskite (Ba0.9Fe0.1Zr0.9O3-δ) is investigated for electrochemical and catalytic activity at 800oC via combination of gas effluent mass spectroscopy and electrochemical impedance spectroscopy (EIS). Results confirm competitive reaction rates for both CO2 reduction to CO and O2 under dry-gas conditions and CO oxidation to CO2 and H2 in the presence of steam. A combination of both p-type and n-type semiconduction behavior is suggested to explain the complex dependence of electrical conductivity upon individual gas species partial pressure. Separate gas permeation measurements confirm an O2 permeability of 9.52×10-12 mol.m-1.s-1.Pa-1, which is competitive with similarly reported zirconate-based perovskite materials.
Carbon Ceramic Electrodes Modified with Alpha-Nickel Hydroxide Applied to the Electro-Oxidation of Methanol in Alkaline Medium
Authors: Módolo Márcio Luiz , Danczuk Marins , Anaissi Fauze Jacó , Araki Koiti , Fujiwara Sergio Toshio
Published: May 2014

The preparation of alpha nickel hydroxide and its incorporation into the carbon ceramic electrodes (CCEs) was reported. The nickel hydroxide was obtained by mixing nickel acetate and glycerin, the obtained solution was mixed with a solution of NaOH/butanol. Carbon ceramic (CC) was obtained by the sol-gel process, and it was mixed with nickel hydroxide, in various proportions. The material obtained was used as an electrode for electro-oxidation of methanol in alkaline medium. The CCE has no catalytic activity for the electro-oxidation of methanol, but the CCE/α-Ni(OH)2 promotes the electro-oxidation of methanol potential of 0.53 V vs. Ag/AgCl, yielding a current density of about 100 mA.cm-2. The highest oxidation current was obtained with 1.90 mol.L-1 of methanol. The CCE has no signs of poisoning. All results indicate that the CCE/α-Ni(OH)2 is a promising material for electro-oxidation of methanol in alkaline medium, to obtain high current densities.
Proton-Conducting Ce0.9Mn0.1P2O7 Composite Electrolytes for Low Temperature Ceramic Electrolyte Fuel Cells
Authors: Singh Bhupendra , Kim Ji-Hye , Jeon Sang-Yun , Park Jun-Young , Song Sun-Ju
Published: May 2014

Composites of 10% Mn2+-doped cerium pyrophosphate with excess phosphates were synthesized by a digestion method with different P/(Ce+Mn) molar ratios. The sintering at 400 oC leads to the formation of a proton-conducting composite of pyrophosphate, metaphosphate, polyphosphate and orthophosphate. The composites with high phosphate content become denser on sintering. The variation of ionic conductivity with temperature is studied in unhumidified and humidified air for the potential application as electrolytes in proton-conducting ceramic-electrolyte fuel cells (PCFCs). Among various samples, Ce0.9Mn0.1P2O7 with P/(Ce+Mn)=2.8 shows maximum conductivity of 7.49´10-6 S cm-1 at 450 oC in unhumidified air. In humidified atmosphere (pH2O=0.12 atm), Ce0.9Mn0.1P2O7 with P/(Ce+Mn)=2.3 shows maximum ionic conductivity (9.58´10-3 S cm-1) at 90 oC while those with P/(Ce+Mn)=2.7 and 2.8 show maximum ionic conductivities (1.78´10-2 and 1.86´10-2 S cm-1, respectively) at 170 oC.
Effect of Sintering Atmosphere and Particle Size on the Ionic Conductivity of Gadolinia-Doped Ceria
Authors: Batista Rafael Morgado , Muccillo Eliana Navarro Santos
Published: May 2014

The effects of sintering under oxidizing, inert and reducing atmospheres on the microstructure and ionic conductivity of gadolinia-doped ceria were investigated. Commercial powders with specific surface areas from ~7 to 210 m2.g-1 were used as received. The sintering experiments were carried out in air, nitrogen, argon and in a mixture of argon-4% hydrogen. Powder compacts were isothermally sintered at 1523 K for 2 h. After isothermal treatments the relative density of compacts sintered at several atmospheres ranged from 92-97%. The linear shrinkage in air of powders with different particle sizes behave differently, but after the isothermal treatment their microstructure is homogenized and no significant difference was observed, except for the compacts sintered under reduced atmosphere. The total ionic conductivity of specimens sintered under oxidizing and inert atmospheres is similar. The specimens sintered under reducing atmosphere exhibits larger grain size and lower total ionic conductivity.
(Invited) High Pressure Sputtering for High-K Dielectric Deposition. Is It Worth Trying
Authors: San Andrés Enrique , Feijoo Pedro Carlos , Pampillón María Ángela , Lucía María Luisa , del Prado Álvaro
Published: May 2014

Our research group studies the deposition of high permittivity dielectrics by a non-standard method: high-pressure sputtering. The dielectrics studied here are gadolinium scandate deposited from dielectric targets, and gadolinium oxide deposited from a metallic target, with an in situ plasma oxidation. The stoichiometric gadolinium scandate presents a slight permittivity boost after annealing, but with gadolinium-rich scandate (grown with an annealing of a nanolaminate) the dielectric shows a high effective permittivity of 21 and no noticeable SiO2 layer at the interface with Si. On the other hand, the stacks fabricated with the metallic Gd target have a SiO2 interface less than 0.7 nm thick that can be further reduced by scavenging with Ti gates. In fact, this scavenging effect is also demonstrated for the first time with indium phosphide substrates, obtaining a low capacitance equivalent thickness of only 2.1 nm.
(Invited) Passivation Schemes for Ge High-K Metal Gate MOSFETs on Si for VLSI Production
Authors: Tapily Kandabara , Ngai Tat , Clark Robert , O'meara David , Consiglio Steve , Gaylord Richard , Wajda Cory , Veksler Dmitry , Hobbs Chris , Matthews Ken , Gilmer David , Kirsch Paul , Leusink Gert
Published: May 2014

We report progress on surface passivation and functionalization of Ge channel surfaces, as well as high-k dielectric layer growth by atomic layer deposition (ALD) and the resulting electrical properties measured in transistor (MOSFET) and metal oxide semiconducting capacitor (MOSCAP) structures. Epitaxial Si and Al2O3 passivation of Ge show improved performance with 3 times reduction in interface states density (Dit), higher conductance, reduced hysteresis and sub-1nm EOT as opposed to non-passivated interface. A 3 times drive current improvement to Si MOSFET was achieved with thin Al2O3 passivation layer.
(Invited) Atomic-Order Thermal Nitridation of Si, Si1-xGex and Ge by NH3
Authors: Murota Junichi , Sakuraba Masao , Tillack Bernd
Published: May 2014

One of the main requirements for Si-based ultrasmall device is atomic-order control of process technology. Here, we show the concept of atomically controlled processing for group IV semiconductors based on atomic-order surface reaction control in Si-based CVD epitaxial growth. On the atomic-order surface nitridation of Si1-xGex by NH3, it is suggested that nitridation of Si atoms proceeds by transfer of N atoms from Ge atoms by heat-treatment. In the case of epitaxial Ge film, the crystallinity change is not observed by NH3 treatment and N atoms diffuse through nm-order thick Ge layer into Si (100) substrate and form Si nitride even at 500 oC. It is also suggested that N diffusion in Ge layer is suppressed by the formation of Si nitride. These results demonstrate the capability of CVD technology for atomically controlled nitridation of Si, Si1-xGex and Ge for ultralarge scale integration.
Characterization of a Novel Radical Nitrogen Plasma Source for Semiconductor Nitridation
Authors: Lucero Antonio Tomas , Cho Taiheui , Kim Jiyoung
Published: May 2014

Semiconductor nitridation for interface passivation has a subject of study for many years. Numerous techniques have been used, with plasma and thermal nitridation being the most common and successful. There are, however, disadvantages to both: thermal techniques can exceed the thermal budget for III-V materials and plasma subjects samples to damaging, high energy ions. This work aims to investigate a newly developed, fully remote, radical nitrogen plasma source. The system allows for low process temperatures and is damage free. Ultrathin nitridation films grown on silicon with this system have been characterized using x-ray photoelectron spectroscopy (XPS). The effects of both time and temperature on film growth were studied. Zirconium oxide on silicon metal-oxide-semiconductor capacitors (MOSCAPs) were fabricated to study the passivation effectiveness of the nitridation layer.
Dielectric/Si Interface Quality Characterization Using Room Temperature Photoluminescence
Authors: Yoo Woo Sik , Kim Byoung Gyu , Jin Seung Woo , Ishigaki Toshikazu , Kang Kitaek
Published: May 2014

Room temperature photoluminescence (RTPL) spectroscopy was proposed as an in-line monitoring technique for characterizing the dielectric/Si interface. Specifically, Si lattice stress beneath dielectric films and overall quality of the dielectric/Si interface (including passivation characteristics) are investigated. As an application example, ~7.0 nm thick ultra-thin SiO2 films on 300 mm Si wafers, prepared by various oxidation techniques and conditions, were characterized using multiwavelength RTPL spectroscopy. The overall SiO2/Si interface quality was seen to be very dependent on oxidation technique and process condition. Within wafer and wafer-to-wafer variations of SiO2/Si interface quality were successfully characterized by RTPL spectrum measurement and intensity wafer mapping under different excitation wavelengths.
(Invited) Scanning Probe Microscopes for Subsurface Imaging
Authors: Kopanski Joseph J. , You Lin , Ahn Jung-Joon , Hitz Emily , Obeng Yaw S.
Published: May 2014

Scanning probe microscopes (SPMs) have some ability to image sub-surface structures. This paper describes the theoretical and practical basis for imaging metal lines buried beneath insulating layers and for imaging insulating regions or voids within metal with SPMs. Three techniques are discussed: scanning Kelvin force microscopy (SKFM) to image the potential of buried metal lines, scanning microwave microscopy (SMM) to image the capacitance of buried metal lines, and SMM to image voids in metals through the frequency dependence of the skin depth. A test chip, designed at NIST, and that contains buried structures to precisely produce electric potential and magnetic field variations at the surface to test the presumptions is described, along with some preliminary results.
Comparison between Equilibrium Voltage Step and Charge Pumping Techniques for Characterizing near Si-SiO2 Interface Traps
Authors: Guenifi Naima , Bauza Daniel
Published: May 2014

The Equilibrium Voltage Step (EVS) technique has been used for extraction of depth and energy concentration profile of traps situated in the oxide of a lightly stressed metal-oxide-semiconductor (MOS) structure. This has been achieved up to the very near Si-SiO2 interface. The results are discussed and compared with those obtained using charge pumping (CP) technique. A good agreement is achieved between the trap densities extracted using the two methods even though differences in the shape of the profiles can be observed. The results also very well agree with those published previously using current deep level transient spectroscopy (C-DLTS).
Dependence of the Multi-Component Nature of Bias Temperature Instability in MOSFETs on Oxide and Device Type
Authors: Nguyen Duc , Kambour Kenneth , Kouhestani Camron , Devine Roderick A.B.
Published: May 2014

We have performed negative and positive bias temperature instability (NBTI and PBTI) measurements on devices having different gate oxide types and thicknesses. The devices used for the study include 130nm and 90 nm oxynitrided gate dielectric bulk Si technology and devices with pure SiO2 gate dielectric. NBTI and PBTI were studied for both p-channel and n-channel MOSFETs for each of the oxide types and thicknesses, this requires the measurements be made in both accumulation and inversion modes. Using “Pseudo DC” measurements at 120 oC on p-channel and n-channel devices, we have extracted at least three distinct components of BTI. We find evidence for the existence of positive charge injection for PMOS under PBTI and more puzzling results for NMOS under PBTI, where unexpected interface state creation was observed.
Integration of Advanced MOSFET Device with Dual Effective Band Edge Work Function Metals Using Both HK and MG Last Scheme
Authors: Tang Zhaoyun , Tang Bo , Xu Jing , Xu Yefeng , Wang Hongli , Li Junfeng , Yan Jiang , Zhao Chao
Published: May 2014

A 22nm MOSFET device was presented with bulk Si planar process integration in this paper. We have achieved NFET and PFET drive current of 539μA/μm and 801μA /μm respectively with novel high k and metal gate stack. Excellent DIBL and Swing performance were achieved with 78mV/V and 82mV/V and 62mV/dec and 64mV/dec for NFET and PFET respectively. TiAl alloy with optimized Al concentration and process power as NFET work function metal and TiN with optimized process power, bias and concentration as PFET work function metal were chosen in our experiments. Effective work functions for both NFET and PFET were adjusted to band edge with 4.15eV and 5.04eV respectively by process optimization.
(Invited) Characteristics of Charge Trap Flash Memory with Al2O3/(Ta/Nb)Ox/Al2O3 Multi-Layer
Authors: Nabatame Toshihide , Ohi Akihiko , Ito Kazuhiro , Takahashi Makoto , Chikyo Toyohiro
Published: May 2014

In this paper we studied characteristics of the Pt/Al2O3/(Ta/Nb)Ox/ Al2O3/SiO2/p-Si capacitors, fabricated by using atomic layer deposition at 200 °C. Note that a large flatband voltage shift (ΔVfb) value of more than 8 V appears after programming at 1 mC/cm2 because large amount of charge is trapped in the Al2O3/(Ta/Nb)Ox/Al2O3 structure. The ΔVfb which occurred after programming decreases with increasing retention time under bias voltage at -5 MV/cm. We found that the electron detrapping occurs easily across the tunneling layer rather than the blocking layer.
(Invited) Dielectrics for Graphene Transistors for Emerging Integrated Circuits
Authors: Srivastava Ashok , Banadaki Yaser M. , Fahad Md. S.
Published: May 2014

In this work, we present the use of high-k dielectric material in designing a novel structure of graphene nanoribbon field-effect transistor (GNR FET) to reduce short channel effects (SCE) for emerging integrated circuits. We have also studied influence of high-k dielectric on ON-state current density, threshold voltage and subthreshold slope of GNR tunneling field effect transistors (TFET). In the GNR FET structure, two side metal gates with lower work function than the main gate on top of the silicon dioxide (SiO2) and hafnium oxide (HfO2) insulating layers are used in a conventional double-gate (DG) GNR FET topology to provide virtual extensions to source and drain regions while these are fixed biased and independent of the main gate bias. We have found that the application of HfO2 in combination with SiO2 in the proposed GNR FET not only shifts the drain source leakage current to the lower values by several orders of magnitude but also makes the leakage current sensitive to the proportionality of thicknesses of SiO2 and HfO2 layers. This improvement makes the structure a more suitable configuration than the typical GNR FET for the integrated circuit design. In GNR TFET structure, SiO2, Al2O3 and HfO2 are considered as dielectric material and their corresponding effects on transistor are studied. By changing dielectric parameters the oxide capacitance changes, followed by the change in threshold voltage. With semi-classical current transport model such variations are closely observed for the proposed GNR TFET model.
(Invited) Nano-Derived Microsensors for Monitoring Gas Species in Harsh-Environments
Authors: Sabolsky Edward M , Çiftyürek Engin , Wildfire Christina , Sabolsky Katarzyna , Taub Jonathan , Sierros Kostas , Evans Thomas H.
Published: May 2014

The objective of our work is to develop nano-derived, micro-scale sensors to monitor various gases within extreme or harsh-environments. These environments include high temperature and pressure applications, where sensors are required to monitor emissions in applications such as coal gasifiers and turbine generators. The environment may also include applications in extreme cold and low-pressure applications, where sensors are required to monitor chemical leaks, as possible on the International Space Station and satellite servicing operations. Our research focuses on the development of microsensors for both of these extreme temperatures and pressure environments, but the current paper will only focus upon the high-temperature sensor application. In the case of the high-temperature gas sensing, nanomaterials for detecting gases such as H2 and SO2 within high-temperature environments were investigated at 1000°C. The microsensors developed in this work are based upon a resistive-type (chemiresistive) sensor platform.
(Invited) Thermochromic Phase Transitions in VO2-Based Thin Films for Energy-Saving Applications
Authors: Barron S C , Gorham J M , Green M. L.
Published: May 2014

The thermochromic transition in vanadium dioxide (VO2) has potential application as a smart energy-saving window coating, but the temperature of the transition must be depressed from 68 °C to Earth ambient temperatures by the incorporation of transition metal impurities. In this paper, we describe a high throughput combinatorial experiment to characterize the V1-xMxO2 phase space, in which M is another metal, for thermochromic transitions. Thin film combinatorial libraries were prepared by pulsed laser deposition on hot silicon substrates, and the M impurities were found to substitute into the VO2 crystalline lattice on the V-site. For M = Ta, Nb, and W, the thermochromic transition temperature was depressed with increasing M concentration. Doping with multiple M atoms is also easily accomplished by combinatorial synthesis and was found to have unexpected effects on the thermochromic transition.
An Etch Stop and Sacrificial Materials Study for 3D NEMS-CMOS Co-Integration
Authors: Philippe Julien , Ouerghi Issam , Pollet Olivier , Hentz Sébastien , Arcamone Julien , Ernst Thomas
Published: May 2014

This paper studies and compares different materials proposed as sacrificial and etch-stop layers for a 3D above Integrated Circuits (IC) Nano Electro Mechanical Systems (NEMS) integration. The latter constitutes a powerful approach to build highly sensitive sensors dedicated to gas detection or mass spectrometry. However, this strategy makes the mechanical part release process complex. Indeed, this step, performed by hydrofluoric acid (HF) vapor etching, must not damage the electronic part located below the mechanical one. This paper compares the behavior of materials under HF vapor presence and shows that tetraethyl orthosilicate (TEOS) and boron nitride (BN) materials constitute respectively good sacrificial and etch-stop layers for this integration strategy.
Flattening Technique of (551) Silicon Surface Using Xe/H2 Plasma
Authors: Suwa Tomoyuki , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: May 2014

In order to flatten Si(551) surface the thermal annealing in Ar ambience at the atmospheric pressure was performed. The surface roughness of Si(551) is very flat after annealing at 600 °C. It is considered that Si atoms on Si(551) surface easily migrate at lower temperature than Si(100). However because the very roughened spot are locally appeared, the atomically flat silicon surface cannot be obtained on Si(551) yet. Xe/H2 plasma process is also performed at low temperature less than 600 °C At the H2 concentration of 10 % and at the process pressure of 266 Pa, Ra of Si(551) surface has a very flat value of 0.068 nm. It is considered that the surface migration of Si atoms on Si(551) surface increasingly progresses because Si(551) surface became activated by Xe/H2 plasma.
Effect of Composition Ratio on Erbium Silicide Work Function on Different Morphology of Si(100) Surface Changed by Alkaline Etching
Authors: Tanaka Hiroaki , Suwa Tomoyuki , Teramoto Akinobu , Motoya Tsukasa , Sugawa Shigetoshi , Ohmi Tadahiro
Published: May 2014

Electrical and physical properties of ErSix on n-type Si(100) surfaces with an alkaline solution etching are investigated. The (111) facet of Si surface affects the SBH between ErSix and n-type Si, because the SBH depends on the surface orientation of Si. A controlling the facet of orientation is a key parameter for a reducing contact resistance for high performance MISFETs. These silicidation reactions are very important to develop the high current drivability devices.
(Invited) Vertical Tunnel FETs Using III-V Nanowire/Si Heterojunctions
Authors: Tomioka Katsuhiro , Fukui Takashi
Published: May 2014

We report on vertical tunnel field-effect transistors (TFETs) using III-V nanowire (NW)/Si heterojunctions. III-V nanowire (NW) was heterogeneously integrated on Si by selective-area growth with precise positioning. The III-V NW/Si heterojunction consisting of a few misfit dislocations shows a large Zener tunnel current under positive bias and band-to-band tunneling current under forward bias. The vertical TFET using InGaAs NW/Si heterojunction, which is vertical surrounding-gate architecture, demonstrated a steep turn-on behavior and very low parasitic leakage current.
Back Gate Bias Stressing on Extremely Thin SOI (ETSOI) MOSFETs with Gate Last Process Integration
Authors: Tang Zhaoyun , Tang Bo , Zhao Lichuan , Wang Guilei , Xu Jing , Xu Yefeng , Wang Hongli , Wang Dahai , Li Junfeng , Yan Jiang , Zhao Chao
Published: May 2014

In this paper, ETSOI transistors fabricated with gate last process scheme with thin channel layers of 4 to 11nm are provided with superior device performance. For a given gate length less than 30nm, DIBL and Swing are achieved with 48mV/V and 65mV/Dec respectively with stressing of back gate bias. Threshold voltage can be tuned within range of 0.8 volts (Vdd=-0.05v). It is large enough for adjusting device performance. Back gate bias stressing would enhance carrier confinement to top gate while large electrical field is induced in the ultra-thin channel layer which would impact on the performance of DIBL. Also, from our results, it is shown that device with thicker channel layer of 11nm are more sensitive to back gate bias comparing with that with thinner channel layer of 4nm.
(Invited) Strained Germanium Nanowire MOSFET with Low-Parasitic Resistance Metal Source/Drain
Authors: Ikeda Keiji , Kamimuta Yuuichi , Moriyama Yoshihiko , Ono Mizuki , Oda Minoru , Irisawa Toshifumi , Tezuka Tsutomu
Published: May 2014

We demonstrate metal S/D nanowire pFETs having a high-mobility strained Ge channel formed by doping-free processes. The large compressive strain as high as -3.9% resulted in a record high hole mobility (μ
eff = 1992 cm2/Vs @ N
s = 1.7x1012 cm-2) and a low contact resistivity (ρ
c ~ 3.8x10-8 Ω cm2). Inserting a plasma-oxide (GeOx) inter-layer between the high-k dielectric and the strained Ge nanowire channel greatly improved not only the mobility but the cut-off characteristics. A low off-current (2.7x10-9 A/μm at V
d = -0.5 V) was achieved for the device with the gate length of 45 nm thanks to the reduced interface state density.
(Invited) MOCVD of III-V Compounds on Silicon Substrate-Status and Challenges
Authors: Heuken Michael
Published: May 2014

III/V-on-Silicon technology for electronic applications demands sophisticated MOCVD reactor design. To address these challenges we developed horizontal MOCVD reactors for 5x200 mm III/V-on-Si applications utilizing planetary motion of the wafer around the center gas inlet. The showerhead technology opens the path to grow compound semiconductor on 300/450 mm wafer. This paper discusses the different developments in the field of MOCVD to facilitate further reduction in production cost and simultaneously improve the device characteristics by using larger wafer size.
(Invited) A High-Power Handling Tunable Low-Pass Filter Using Switched Capacitor in 0.5 μm GaN-on-Silicon HEMT
Authors: Huang Fan-Hsiu , Chiu Hsien-Chin
Published: May 2014

A tunable low-pass filter (LPF) is developed and fabricated in 0.5 μm GaN-on-Si HEMT process. By using HEMT device to be a switch, the shunt-type switched capacitors can be presented. The performances of switching low/high capacitance ratio and power handling can be also determined with a proper arrangement of capacitors and HEMT device size. The on-chip spiral inductors are used for designing a compact 3-order LC low-pass filter. The 3-dB bandwidth of the filter is ranging from 3 GHz to 7 GHz by varying the gate bias from 0 V to -6 V. The low frequency insertion loss is 0.4 dB. The measured power handling performance is up to 36 dBm at 2 GHz under on-wafer testing.
(Invited) Nanocrystalline Diamond for Near Junction Heat Spreading in GaN Power HEMTs
Authors: Anderson Travis J , Hobart Karl D , Tadjer Marko J , Koehler Andrew D. , Feygelson Tatyana I , Pate Bradford B , Hite Jennifer K. , Kub Fritz J , Eddy Charles R.
Published: May 2014

Reduced performance in Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) as a result of self-heating has been well-documented. A new approach, termed “gate after diamond,” is shown to improve the thermal budget of the deposition process and enable large-area diamond in a reliable and scalable way without degrading the gate metal. This work will highlight initial assessments of top-side diamond integration in GaN HEMTs as well as development efforts on back-side diamond coatings and diamond contacts for further improvements to the thermal management scheme.
(Invited) Rapid C-reactive Protein Detection with AlGaN/GaN High Electron Mobility Transistors in an Integrated Microfluidic System
Authors: Kang Yen-Wen , Lin Chih-Lin , Chang Ko-Wei , Chang Wen-Hsin , Lee Gwo-Bin , Wang Yu-Lin
Published: May 2014

Cardiovascular diseases are one of the most serious diseases worldwide and cause about 25 million deaths every year. C-reactive protein (CRP) in human blood is a well-known biomarker related to the cardiovascular diseases. The concentration of CRP identifies the risk for cardiovascular diseases. To measure the concentration of CRP, the CRP-specific aptamer immobilized AlGaN/GaN high electro mobility transistors (HEMTs) were used to recognize CRP and transfer it into electric signals. The AlGaN/GaN HEMT was further integrated with a multifunctional microfluidic system. The integrated microfluidic system enhanced the detection accuracy with stable detecting environment. It may be promising for on-site monitoring of CRP in the near future.
(Invited) Fundamental Modeling of Radiation Effects in AlGaN/GaN HEMTs
Authors: Patrick Erin , Law Mark E , Li Shun , Hwang Ya-Hsi , Ren Fan , Pearton Stephen J.
Published: May 2014

We model the effect of radiation damage on AlGaN/GaN HEMTs in FLOODS. While excellent fits are obtained for threshold voltage shift, the models do not fully explain the increased reliability observed experimentally. In short, the addition of negatively-charged traps in the GaN buffer layer does not significantly change the electric field at the gate edges at radiation fluence levels seen in this study. We propose that negative trapped charge at the nitride/AlGaN interface actually produces the virtual-gate effect that results in decreasing the magnitude of the electric field at the gate edges and thus the increase in critical voltage. Simulation results including nitride interface charge show significant changes in electric field profiles while the I-V device characteristics do not change.
Current Confinement Effect of InGaN Devices by Forming Photoelectrochemical-Oxidized GaN Nanoporous Structures
Authors: Lin Chia-Feng , Lee Wen-Che , Chen Yen-Lun , Tseng Yi-Hui , Dai Jing-Jie , Han Jung
Published: May 2014

InGaN LED structure with a nanoporous structure was fabricated through a laser drilling hole process and a focused ion beam drilling process. GaN nanoporous structure was formed around the drilled holes through a electrochemical wet etching and oxidation processes on a n-type GaN:Si layer under the InGaN active layer. The insulated GaOx layers were formed on the surface of GaN nanoporous structures. At the treated-sidewall region, the high light extraction efficiency and the compressive strain released phenomenon were observed at the InGaN active layer with bottom nanoporous structure. In the disk-array structure, the branch-like nanoporous structure was formed along the lateral etched direction to steer the injection current.
(Invited) Structural and Optical Properties of InN Quantum Dots Grown by an Alternating Supply of Source Precursors
Authors: Ke Wen-Cheng , Houng Wei-Chung , Huang Hao-Ping
Published: May 2014

The high density 2×1010 cm−
2 InN quantum dots (QDs) was grown by the two-step growth method. The InN nucleation, InN decomposition and In adatom diffusion in the step-1, annealing and the step-2 process, respectively, determined the density, shape and size distribution of the InN QDs. Especially in the InN nucleation density in step-1 process dominate the size distribution of the InN QDs. The bimodal size distribution of the two-step growth InN QDs can be suppressed by increasing the InN QDs nucleation density. The photoluminescence (PL) peak energy at 1.137 eV for InN QDs with average height of 6 nm the calculated confinement energy is ~ 356 meV and the electron concentration is estimated to be 2×1018 cm−
3. The two-step growth method can maintain both the InN QDs density and the optical quality, indicating a potential technique for future optoelectronic device applications.
Effect of O Impurity on the Properties of InGaN/GaN Multiple Quantum Well and Light Emitting Diode Structures
Authors: Li Ying , Berkman Erkan Acar , Stokes E. B.
Published: May 2014

InGaN/GaN multiple quantum well (MQW) and light emitting diode (LED) structures with different GaN barrier growth temperatures have been grown by metalorganic chemical vapor deposition (MOCVD). Atomic Force Microscopy (AFM)-Conductive AFM (CAFM) analysis has been performed to study the submicron scale structural and electrical properties of the LED structures. The effect of high O impurity concentration, introduced during the low temperature barrier layer growth, on the MQW LED structure has been explored. It is observed that (VGa-ON)2- point defects formed in the MQW layer serve as deep-level traps and lead to defect-assisted tunneling. Increasing barrier growth temperature decreases O impurity incorporation and thus improves the device performance.
(Invited) Hydrogen Sensing Characteristics of Gallium Nitrides with Various Crystal Planes
Authors: Kim Hyonwoong , Baik Kwang Hyeon , Ren Fan , Pearton Stephen J. , Jang Soohwan
Published: May 2014

We investigated hydrogen sensing characteristics of semipolar (11-22) GaN Schottky diode, and compared to various crystal planes of GaN including conventional gallium polar c-plane (0001), nitrogen polar c-plane (000-1), and a-plane (11-20). The semipolar GaN diode showed remarkable current change to 4% hydrogen in nitrogen and the device exhibited full recovery into original current level under nitrogen ambient. Each plane has its own surface configuration and shows different hydrogen responsivity. In case of (11-22) plane GaN, its current response to hydrogen is very large even though its surface is terminated with gallium atoms, since active nitrogens position beneath the gallium atoms.
Research on Charge Accumulation and Transport in Hole-Conductor-Free Perovskite (CH3NH3PbI2Cl) -based Nanostructure Solar Cells
Authors: Ma Shuai , Cao Lei , Li Yang , Sun Qiong , Dong Hongzhou , Dong Lifeng
Published: May 2014

In this paper, we propose a new kind of nanostructure solar cell involving perovskite CH3NH3PbI2Cl and metal-oxide semiconductor TiO2. Taking advantage of the promising properties of this solution-processed perovskite material such as good light absorption and ambipolar transport of charge carriers, we choose CH3NH3PbI2Cl as both a light absorber for TiO2 nanoparticle sensitization and hole transport material, which helps to constitute a solid-state sensitized solar cell with much simpler construction. Specifically, the cell fabrication and characterization are reported; the analysis based on small-signal electrochemical measurements is in particular provided, in order to investigate internal mechanisms of this photovoltaic device, mainly including charge accumulation, recombination and transport through it.
Magnéli Phase Titanium Oxide: Electrochemical Routes and Characterisation
Authors: Dunne Peter , Mieszala Maxime , Le Nader Victor , Philippe Laetitia , Michler Johann
Published: May 2014

Composite thin films of crystalline titanium oxide on an amorphous underlayer have been fabricated by electrodeposition. Optical, XRD, and Raman characterisation indicate the formation of one or more of the Magnéli phases. Optimal growth conditions were found to be at high pH close to 60°C.
(Invited) Novel Luminescent Materials Based on Semiconductor Nanowires
Authors: LaPierre Ray R , Gustafsson Anders , Kuyanov Paul , Haapamaki Chris
Published: May 2014

Recent work on the photoluminescence (PL) properties of InAsP/InP nanowires are reported. InP nanowires were grown on <111> Si substrates by the Au-assisted vapor-liquid-solid process in a gas source molecular beam epitaxy system. InAsyP1-y segments were grown within the InP nanowires, creating single or multiple quantum dots structures. The quantum dot dimensions and composition were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX). PL from the quantum dot structures could be tuned by the InAsyP1-y composition (y), or by the size of the quantum dot via the quantum confinement effect. Cathodoluminescence (CL) measurements confirmed localized emission from the quantum dots. To reduce detrimental surface states, the nanowires were passivated with an AlInP shell, which resulted in strong PL emission.