bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry Strip Removal of Si-Containing Anti-Reflective Coating Photo Resist Stacks
Authors: Mattson David T. , DeLuca James , Luo Shijian , Tracy John , Roh Dwight
Published: October 2011

Removal of SiARC containing photo resist stacks presents significant challenges to conventional plasma dry strip tools. Due to the high Si content (35-45% Si), the SiARC removal process must typically be done with a combination of dry and wet processes or done entirely in an etcher. As both the Dry-Wet-Dry and the Etcher approach to SiARC stack removal are long and high cost processes, a single chamber, dry-only solution to SiARC stack removal is highly desirable. This paper reports the dry strip process developed at Axcelis Technologies, Inc. to remove the SiARC stack layer by layer which results in a residue free oxide substrate.
Characterization of Post Etch Residues on Patterned Porous Low-k Dielectric Using Multiple Internal Reflection Infrared Spectroscopy
Authors: Rimal Sirish , Ross Nick , Pillai Karthikeyan S. , Singh Kanwal Jit , Chyan Oliver
Published: October 2011

Plasma etching and ashing processes on intricate porous low-k dielectrics are known to introduce high levels of defects that may cause serious reliability issues. Post etch cleans to remove polymer residues could also further damage the porous low-k dielectrics. Compounding the difficulty of handling weak porous ULK materials, a lack of sensitive metrology to evaluate such damage is a serious hindrance to systematic development of plasma etching, restoration and cleaning processes. In this paper, a new metrology tool using Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) was developed and tested using silicon wafer based IR waveguides. Our data demonstrates the capability of MIR-IR spectroscopy to monitor removal of thin polymeric post-plasma etch residues from porous low-k dielectrics and characterize plasma-induced dielectric damage.
(Invited) An Update on High Voltage SiC Power Devices
Authors: Agarwal Anant K. , Zhang Q. , Das Mrinal , Ryu Sei-Hyung , Cheng Lin , O'Loughlin Michael , Burk Al , Palmour John W.
Published: October 2011

The development of high voltage power devices based on Silicon Carbide (SiC) will be a critical component in building the next generation power systems. Bipolar devices are preferable due to their low on-resistance. In this paper, a detailed review of the state-of-the-art of SiC power switches, namely Bipolar Junction Transistors (BJTs), Gate Turn-Off thyristors (GTOs), and Insulated Gate Bipolar Transistors (IGBTs), is given with an emphasis on the device design, characterization and stability assessments.
(Invited) GaN Power Electron Devices
Authors: Otsuka Nobuyuki , Nagai Shuichi , Ishida Hidetoshi , Uemoto Yasuhiro , Ueda Tetsuzo , Tanaka Tsuyoshi , Ueda Daisuke
Published: October 2011

Recent progress in GaN-based power electron devices and advanced thermal management techniques for high performance GaN power devices are described. Recent advances in high performance GaN-based transistors are reviewed. The reduction of junction temperatures in low-pressure direct liquid cooling of GaN power devices for high-power and high-voltage applications are demonstrated using perfluorocarbon and perfluoroether as a working fluid, for the first time.
(Invited) III-Nitride Heterojunction Field-Effect Transistors and Heterojunction Bipolar Transistors for Next-Generation Power Electronics
Authors: Dupuis Russell D. , Shen Shyh-Chiang , Lochner Zachary M. , Kim Hee-Jin , Lee Yi-Chi , Zhang Yun , Wang Cheng-Yin , Ryou Jae-Hyun
Published: October 2011

This paper will discuss recent progress in technology development for two key III-Nitride (III-N) transistor technologies: high-voltage AlGaN/GaN heterojunction field-effect transistors (HFETs) and GaN/InGaN RF heterojunction bipolar transistors (HBTs).
(Invited) High Power Normally-Off GaN MOSFET
Authors: Kambayashi Hiroshi , Satoh Yoshihiro , Kokawa Takuya , Ikeda Nariaki , Nomura Takehiko , Kato Sadahiro , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: October 2011

The enhancement mode n-channel GaN-based MOSFETs on Si substrates have been demonstrated. We achieved a low interface state density between SiO2 and GaN, a high breakdown field, and a high reliability of SiO2 by annealing after SiO2 deposition on GaN. The SiO2 was applied for the gate oxide of GaN MOSFET. The fabricated GaN MOSFETs using an ion implantation technique showed good normally-off operation with threshold voltage of 2.7 V, the maximum output current of over 3.5 A, and a high-temperature operation up to 300oC. Furthermore, AlGaN/GaN hybrid MOS-HFETs were fabricated. The MOS-HFET has the merits of both a MOS channel and an AlGaN/GaN heterostructure with high mobility two dimensional electron gases. The maximum drain current of over 100 A was performed. The specific on-state resistance was 9.3 mΩ-cm2. The fabricated device also exhibited good normally-off operation and the breakdown voltage of over 600 V.
(Invited) Implications for Robust Reliability Testing of Power SiC MOSFETs
Authors: Green Ronald , Lelis Aivars , Habersat Daniel
Published: October 2011

Threshold voltage (VT) instability remains an important issue for the performance, reliability, and qualification of large-area SiC power MOSFET devices. The direct application of existing reliability test standards to SiC power MOSFETs can in some cases result in an inconsistent pass/fail response for a given device. Significant variations in the ID-VGS characteristics, with accompanying shift in VT and change in leakage current, can result when these prescribed standards are applied as written. These variations are likely due to the complex time, temperature, and bias dependent nature of the charging and discharging of significant numbers of near-interfacial oxide traps that exists in as-processed SiC MOSFET devices. The significant increase in this VT instability at elevated temperature may suggest the activation of additional performance limiting oxide defects. If the negative shift in VT is large enough, it may increase the OFF-state drain leakage current and limit the long-term device reliability.
(Invited) Degradation of SiC Bipolar Devices: A Review of Likely Causes and Recent Advances in its Understanding
Authors: Pirouz Pirouz , Galeckas Augustinas
Published: October 2011

Degradation of 4H-SiC PiN diodes - a rapid increase in the forward voltage drop with operation time - has been a focus of research since it was observed a decade ago. A combination of electrical studies and microstructural characterization of the diodes revealed early on that associated with this degradation is a rapid increase in the number and extent of intrinsic stacking faults in the active region of the device. Because PiN diode is a bipolar device, and the degradation occurs under forward biasing, it was suspected that the expansion of stacking faults is driven by injection of electron-hole pairs (ehps). In many ways, this effect is similar to a phenomenon known as recombination-induced dislocation glide (REDG) that occurs in some other semiconductors, including in SiC. In this paper, after a review of the basic materials science issues regarding extended defects in SiC, recent explanations of degradation of PIN diodes are discussed.
(Invited) High Quality 3C-SiC for MOS Applications
Authors: Severino Andrea , Locke Christopher , La Via Francesco , Saddow Stephen E.
Published: October 2011

In this work, the growth of high quality 3C-SiC films on Si substrates grown by a hot-wall chemical vapor deposition (CVD) reactor is presented. An increased crystal quality means a reduced crystallographic defect density affecting 3C-SiC films which can be achieved by reducing the growth rate during 3C-SiC heteroepitaxy. In particular, the micro-twin density was observed to decrease with decreasing growth rate allowing for the reduction of theboth the rocking curve and transverse optical Raman mode peak width. Si substrates, both of on- and off-axis orientation, are considered with improvement in crystal quality observed when off-axis substrates are used. Finally, stacking faults and microtwins at the SiC/SiO2 interface are seen to cause non-uniformity in the oxide layer due to the different oxidation rate observed.
(Invited) Integrated Microinductors on Semiconductor Substrates for Power Supply on Chip
Authors: Rohan J. F. , Casey Declan , O'Brien Joe , Hegarty Margaret , Kelleher Anne-Marie , Wang Ningning , Jamieson Brice , Waldron Finbarr , Kulkarni Santosh , Roy Saibal , O'Mathuna S. Cian
Published: October 2011

Microinductors were fabricated using electrodeposition for integration on semiconductor substrates. The process was optimised through validated models developed to focus on efficiency and footprint. Lithographic processing was performed to microfabricate Cu coils over a magnetic core. A racetrack design was used to maximise the high frequency response, yielding high inductance density and low DC resistance. The magnetic core was subsequently closed using a magnetic thin film deposition over a dielectric deposited on the Cu coils. Homogeneous ferromagnetic alloy, Ni45Fe55 of uniform thickness over a high aspect-ratio 3D structure has been achieved. Ni45Fe55 was chosen for the fabrication of micromagnetic cores due to its relatively high saturation flux density (1.6 T), resistivity (48 mΩ cm) and anisotropy field (9.5 Oe). The rationale, design, microfabrication process and characterisation results are presented.
Effect of Plasma Treatment on Stress Reduction Induced by Shallow Trench Isolation Filled with Spin-on-Glass Dielectric
Authors: Hashiguchi Hiroki , Nagata Kohki , Sameshima Takashi , Mizukami Yuki , Ogura Atsushi , Kuroda Takeshi , Sato Yoshihiro , Ishizuka Syuuichi , Hirota Yoshihiro
Published: October 2011

We used Raman spectroscopy to evaluate the stress induced by shallow trench isolation (STI) filled with spin-on-glass (SOG) dielectric material. We investigated the novel processes, such as the nitrogen into the liner oxide, and the plasma treatment before and/or after cure annealing to suppress the strain introduced by the STI with SOG. We clarified that a nitrogen incorporated liner oxide suppressed the stress in the active area caused by the SOG film shrinkage, and the plasma treatments were also effective at suppressing the stress induction in the active area.
Deposition Mechanism and Electrical Property of CeO2 Thin Films by MOCVD with H2O Introduction
Authors: Tada Naohiro , Izu Takanori , Kitaru Tomoya , Shimada Hiroki , Suzuki Setsu , Ishibashi Keiji , Yamamoto Yasuhiro
Published: October 2011

Cerium dioxide (CeO2) thin films are prepared by means of the metal organic chemical vapor deposition (MOCVD) using tetrakis (3-methyl-3-pentoxy) cerium with and without H2O vapor introduction. A large amount of H2O (more than 2 sccm) acts as an oxidant and as a result the deposition rate increases by up to four times at the deposition pressure of 2.0 Pa, leading to the temperature independence of the deposition rate. At the low deposition temperature of 270 åC, a small amount of H2O (0.1-0.2 sccm) suppresses the deposition because of its preferential occupation of the surface sites. The CeO2 film annealed at 600 åC in the oxidizing ambient shows steep C-V characteristics with no flat band voltage shift nor hysteresis.
SF6 Plasma Treated High κ Dielectrics Engineering on InP Metal-Oxide-Semiconductor Field-Effect-Transistors
Authors: Wang Yanzhen , Zhao Han , Chen Yen-Ting , Xue Fei , Zhou Fei , Lee Jack
Published: October 2011

The device performance of HfO2-based InP MOSFETs with or without Al2O3 interfacial passivation layer and SF6 plasma treatment is investigated. With both Al2O3 interfacial passivation layer (IPL) and SF6 plasma treatment, the transconductance, mobility, and drain current are improved by 50%, 56%, 100% respectively compared with those of a single HfO2 gate oxide layer without SF6 plasma treatment. Also we have investigated SF6 plasma treatment in two ways: 1) 4 minutes treatment from the middle of 5 nm HfO2 oxide, 2) 4 minutes treatment from the top of 5 nm HfO2 oxide. Results show that treatment in the middle introduces more F into the high κ layer and drive current can be further enhanced by over 20% compared with treatment at the top of gate oxide stack.
Effect of Various Surface Treatments on Chemical Bonding State at La2O3/In0.53Ga0.47As and on In0.53Ga0.47As Surface
Authors: Yamashita Koji , Komatsu Arata , Watanabe Masato , Numajiri Yuuya , Zade Darius , Kakushima Kuniyuki , Iwai Hiroshi , Nohira Hiroshi
Published: October 2011

We have investigated the influence of HF, (NH4)2S and Hexa Methy Disilazane (HMDS) treatments on thermal stability of high-k/In0.53Ga0.47As interface and the chemical bonding states at high-k/In0.53Ga0.47As interface by the X-ray (hv= 1486.6eV) photoemission spectroscopy. The control of the oxide formation on In0.53Ga0.47As surface was tried by surface treatment. Analyses of As 3d, Ga 3p, In 3d, S 1s, Si 2p, N 1s, O 1s and C 1s spectra show that the oxidation of In0.53Ga0.47As was suppressed by various surface treatments.
Comparison of the Optical Properties of Tantalum Pentoxide, Ta2O5, Anodically Grown from E-beam Deposited Tantalum, Ta, with Ta2O5 E-beam Deposited from a Ta2O5 Source
Authors: Kulpa Alina , Jaeger Nicolas A.
Published: October 2011

The optical properties of Ta2O5 anodically grown from e-beam deposited Ta have been compared with Ta2O5 e-beam deposited from a Ta2O5 source. Optical data were collected with a J. V. Woollam Co., Inc., Spectroscopic Ellipsometer, VASE. Measurements were conducted under the same conditions for both types of samples. Within the precision limits of our ellipsometer and for the thicknesses of the films studied, the absorption coefficient, α, was zero for anodically grown Ta2O5 over a very wide range of wavelengths, including the 1310 nm and 1550 nm telecommunications windows. By contrast, the e-beam deposited Ta2O5 layers had only a very narrow window in the visible range. Both types had the absorption coefficient of zero at some wavelengths in the ultraviolet range. The anodically grown Ta2O5 layers had a calculated average energy gap of 4.23 eV +/- 0.02 eV and a maximum dielectric constant of 28.73.
Impact of ALD Gate Dielectrics (SiO2, HfO2, and SiO2/HAH) on Device Electrical Characteristics and Reliability of AlGaN/GaN MOSHFET Devices
Authors: Lee Bongmook , Kirkpatrick Casey , Choi Young-Hwan , Yang Xiangyu , Wang Yalin , Yang Xingchen , Huang Alex , Misra Veena
Published: October 2011

GaN/AlGaN metal oxide semiconductor heterojunction field effect transistors (MOSHFET) with various gate dielectrics have been fabricated and studied. It was found that gate oxides formed by atomic layer deposition (ALD) provides improved device electrical characteristics over the conventional SiO2 formed by PECVD method. It was also found that there is no additional Ga oxide growth during the ALD process resulting in good and smooth interface. Conductance measurements showed that the trap state density is reduced with ALD dielectrics as compared to Schottky HFET device. Stacked dielectrics can provide large gate over drive voltage enabling low on-state resistance and high drain current.
Resistive Switching Characteristics of Core-Shell Nanoparticles of Metal-Oxide on Flexible Substrate
Authors: Yoo Jae-Woo , Hu Quanli , Baek Yoon-Jae , Kang Chi Jung , Lee Hyun Ho , Yoon Tae-Sik
Published: October 2011

Resistive switching characteristics of FePt/γ-Fe2O3 core- shell nanoparticle (NP) assembly on flexible substrate of polyethersulfone (PES) as being sandwiched by top and bottom Al electrodes were investigated for the potential as a flexible resistive switching memory. The NPs assembly was formed by solution process of dip-coating. The initial bipolar switching was observed in the voltage range < ±3 V, and the subsequent voltage sweep to higher voltage led to the increase of resistance, which is not typically observed in γ-Fe2O3 NP or other metal-oxide layer structure. Though the fundamental principle of resistive change in core-shell NPs is not clear, it demonstrated the feasibility of flexible memory application through solution-based processes.
Vertical 3D NAND Flash Memory Technology
Authors: Nitayama Akihiro , Aochi Hideaki
Published: October 2011

We've developed Bit Cost Scalable (BiCS) flash technology as a three-dimensional memory for the future ultra high density storage devices, which extremely reduces the chip costs by vertically stacking memory arrays with punch and plug process. We've advanced it into Pipe-shaped BiCS flash memory introducing U-shaped NAND string structure, to improve operation window, speed and reliability. 32 G bit test chips with 16 stacked layers by 60nm P-BiCS flash process have been fabricated, and the functionality of Multi-Level-Cell (MLC) operation has been successfully demonstrated. P-BiCS is the most promising candidate of three-dimensional ultra high density data storage memories.
Extension of Moore's Law via Strained Technologies- The Strategies and Challenges
Authors: Chung Steve
Published: October 2011

In this paper, we will first give an overview on the strain-silicon technology, such as eSiGe, eSi:C, stress memorization technique (SMT), dual stress liners (DSL), and high-k/metal gate replacement gate (RMG) process, after the 90nm generation. Then, the reliability and the design guideline for a trade-off between performance and reliability will be addressed. A technology roadmap in terms of the ballistic transport theory will be outlined. Then, the variability of the strained CMOS devices with focus on the discrete dopant profiling will be demonstrated. Finally, the strategies of strained-silicon device on advanced 3D device structure and IC will be introduced.
High Mobility Epitaxial Graphene for Carbon-based Nanoelectronics
Authors: Berger Claire , Ruan Ming , Palmer James , Hankinson John , Hu Yike , Guo Zelei , Dong Rui , Conrad Edward H. , De Heer Walt A.
Published: October 2011

Epitaxial graphene has demonstrated a great potential for carbon-based electronic. Multiple nanoscale devices can be patterned on a scalable platform with high electronic mobility, large conductivity, and conductance modulation by an electrostatic gate. High quality seamless epitaxial graphene layers are grown on the entire surface of SiC substrates by thermal decomposition of the SiC crystal. For multilayer epitaxial graphene grown on the 4H-SiC (000-1) surface, transport and spectroscopy measurements demonstrate an effective decoupling of the adjacent graphene layers due to a non-graphitic ordered rotational stacking. Large switching ratios require a band gap but graphene is a gapless semimetal. Transport gaps have been demonstrated in chemical functionalized graphene and in narrow ribbons. But patterning techniques severely degrade graphene. Transport data on narrow graphene ribbons directly grown on silicon carbide substrate step edges at high temperature indicate reduced edge scattering and open the way to non diffusive electronics.
(Invited) MEMS Module Integration into SiGe BiCMOS Technology for Embedded System Applications
Authors: Kaynak Mehmet , Wietstruck Matthias , Zhang Wogong , Scholz Rene , Drews J. , Marschmeyer S. , Knoll D. , Korndorfer F. , Schulz K. , Wipf C. , Wolansky D. , Kaletta Katrin , Wegner M. , Ehrmann Oswin , Tillack Bernd
Published: October 2011

Different MEMS process techniques have been integrated to 0.25 µm BiCMOS process for embedded system applications. Back-End-Off-Line (BEOL) integration technique was developed using standard metallization layers of BiCMOS process with additional MEMS process steps. As an example, an RF-MEMS capacitive switch was realized using BEOL embedded MEMS module. Back-side substrate etch method was developed as another MEMS integration technique. This technique is demonstrated by several high-Q passive components which can prevent from substrate losses and on-chip antennas/sensors for multi-GHz applications. Lastly, thick copper metallization with low-k BCB dielectric material was developed and processed on top of BiCMOS BEOL. It provides 2 additional thick copper metallization layers and allows realizing high-Q passives and on-chip THz resonators. Several design examples realized by using developed MEMS modules and processing techniques were also analyzed.
(Invited) III-V Tunnel Field-Effect Transistors
Authors: Seabaugh Alan , Chae Soo Doo , Fay Patrick , Hwang Wan Sik , Kosel Tom , Li Rui , Liu Qingmin , Lu Yeqing , Vasen Tim , Wistey Mark , Xing Grace (Huili) , Zhou Guangle , Zhang Qin
Published: October 2011

Current progress in the development of compound semiconductor tunnel field-effect transistors (TFETs) for low-voltage, high performance logic applications is reviewed.
Biaxial and Uniaxial Compressive Stress Implemented in Ge(Sn) pMOSFET Channels by Advanced Reduced Pressure Chemical Vapor Deposition Developments
Authors: Vincent Benjamin , Gencarelli Federica , Lin Denis , Nyns Laura , Richard Olivier , Bender Hugo , Douhard Bastien , Moussa Alain , Merckling Clement , Witters Liesbeth , Vandervorst Wilfried , Loo Roger , Caymax Matty , Heyns Marc
Published: October 2011

Three advanced architectures for ultimate progress in Ge p-Metal Oxide Semiconductor Field Effect Transistors are discussed in this paper. Different routes for stress implementations in Ge channels, either biaxial or uniaxial, are proposed by advanced selective Chemical Vapor Deposition techniques. Selective SiGe Strained Relaxed Buffer growth in Shallow Trench Isolation is first discussed to implement biaxial compressive strained Ge Quantum Wells on top of it. Next, innovative GeSn chemical vapor deposition technique is described in order to build either uniaxial strained Ge channel with GeSn Source/Drain stressors or compressively biaxial strained GeSn Quantum Well channels on Ge buffer layers.
(Invited) Selective Area Growth of InP on On-Axis Si(001) Substrates with Low Antiphase Boundary Formation
Authors: Loo Roger , Wang Gang , Orzali Tommaso , Waldron Niamh , Merckling Clement , Leys Maarten , Richard Olivier , Bender Hugo , Eyben Pierre , Vandervorst Wilfried , Caymax Matty
Published: October 2011

We discuss the selective epitaxial growth of InP on patterned Si (001) substrates with Shallow Trench Isolation using a thin Ge buffer to facilitate InP nucleation. The main focus is the defect formation mechanism during epitaxial growth and to develop solutions to reduce defect density so that device-quality III-V virtual substrates can be realized on large-scale Si substrates. We compare the InP growth on on-axis and off-axis Si substrates. In the case of off-axis wafers, the formation of stacking faults / twins cannot be avoided, at least not at one of the four STI side-walls. The formation of antiphase domain boundaries is reduced (but not yet completely eliminated) by engineering the local Ge surface profile. Further, the high density of Ge surface steps promotes step-flow growth mode instead of 3D growth during the growth of the InP seed layer. Finally, high aspect ratios (>2) allow to confine threading dislocations in the bottom of the trench.
CMOS Integration Using Low Thermal Budget Dopant-Segregated Metallic S/D Junctions on Thin-Body SOI
Authors: Larrieu Guilhem , Dubois Emmanuel , Ducatteau Damien
Published: October 2011

As segregated PtSi contacts using implant-through-silicide technique have been studied. A thermal activation at 600°C gives a As pile-up at the PtSi/Si interface of 4x1020 cm-3 resulting in a Schottky barrier to electrons below 0.1 eV. As and B segregated PtSi contacts have been integrated in a low temperature CMOS process and functional 90 nm inverters have been demonstrated. Inverters with nearly ideal DC voltage transfer characteristics and large voltage gains have been obtained down to 0.5V of supply voltage with excellent noise margins (~VDD/2). This approach provides a low temperature S/D module suitable for a viable and low-cost manufacturing approach for future CMOS technology nodes.
Optimization of Resist Ash Processes on Si0.45Ge0.55 Substrates for Post Extension-Halo Ion Implantation
Authors: Mannaert Geert , Vos Rita , Tsvetanova Diana , Altamirano Efrain , Witters Liesbeth , Demand Marc , Sonnemans Roger , Berry Ivan
Published: October 2011

State-of-the-art and conventional post extension-halo resist ash and clean sequences for SixGe1-x channels have been studied. The main goal of this work was to assess the effect of post ion implant ash plasma chemistry exposure on Si0.45Ge0.55 substrate oxidation and loss. Ashing photoresist with widely used oxidizing and F- containing plasma's, result in the formation of thermally unstable and chemical reactive GeO2. By reducing the oxygen flow or applying "controlled oxygen diffusion" plasma's (COD's) one can suppress Si0.45Ge0.55 substrate oxidation, resulting in better dopant retention and as a consequence improved junction performance in real devices.
Atomically Controlled Formation of Strained Si1-xGex/Si Quantum Heterostructure for Room-Temperature Resonant Tunneling Diode
Authors: Sakuraba Masao , Murota Junichi
Published: October 2011

Atomically controlled formation of strained Si1-xGex/Si quantum heterostructure was investigated in order to improve negative differential conductance (NDC) characteristics of high-Ge-fraction strained Si1-xGex/Si hole resonant tunneling diode with nanometer-order thick strained Si1-xGex and unstrained Si layers. Recently, especially to suppress the roughness generation at heterointerfaces for higher Ge fraction, Si barriers were deposited using Si2H6 reaction at a lower temperature of 400 oC instead of SiH4 reaction at 500 oC after the Si0.42Ge0.58 growth. NDC characteristics show that difference between peak and valley currents is effectively enhanced at 11-295 K by using Si2H6 at 400 oC, compared with that using SiH4 at 500 oC. Thermionic-emission dominant characteristics suggests a possibility that introduction of larger barrier height enhances the NDC at room temperature by suppression of thermionic-emission current. In this paper, based on our results, advanced epitaxial growth process of RTDs with atomically controlled Si/strained Si1-xGex heterostructures on Si(100) are reviewed.
Atomically Controlled Plasma Processing for Quantum Heterointegration of Group IV Semiconductors
Authors: Sakuraba Masao , Murota Junichi
Published: October 2011

For the purpose of quantum heterointegration of group IV semiconductors, atomically controlled plasma processing by utilizing an electron-cyclotron-resonance (ECR) plasma enhanced chemical vapor deposition (CVD) at low temperature has been developed to achieve atomic-layer doping and heterostructure formation with nanometer-order thickness control as well as smooth and abrupt interfaces. In this paper, recent typical achievements in the plasma processing are reviewed: (1) By N and B atomic-layer formation and Si epitaxial growth on Si(100), heavy atomic-layer doping was demonstrated. Most of the incorporated N or B atoms can be confined in an about 2 nm-thick region. (2) highly-strained and relaxed Ge films on Si(100) with atomic-order flatness can be epitaxially grown. (3) Using a 84% relaxed Ge buffer layer formed on Si(100), formation of a highly strained Si film with nanometer-order thickness was achieved.
(Invited) Current and Future Applications of ALD in Micro-Electronics
Authors: Raaijmakers Ivo J.
Published: October 2011

This paper describes the status of current and future applications of Atomic Layer Deposition (ALD) and Plasma Enhanced ALD (PEALD) in the field of Micro-electronics. Substantial expansion of the ALD market is expected in the coming decade, both in IC manufacturing, but also in adjacent non-IC applications. Several techniques will be described that work around the relatively slow deposition rate of ALD.
Plasma-Assisted Atomic Layer Deposition of SrTiO3: Stoichiometry and Crystallinity Study by Spectroscopic Ellipsometry
Authors: Longo Valentino , Leick Noemi , Roozeboom F. , Kessels W.M.M.
Published: October 2011

Strontium titanate (SrTiO3, STO) films were deposited by plasma-assisted ALD using cyclopentadienyl-based Sr and Ti precursors with O2 plasma as the oxidizing agent. As determined from Rutherford backscattering spectroscopy (RBS), [Sr]/[Ti] ratios ranging from 0.73 to 2.13 were achieved for 30-40 nm thick films by tuning the [SrO]/[TiO2] ALD cycle ratio. Films deposited at 250 °C were amorphous and required post-deposition annealing to crystallize into the ultrahigh-k perovskite structure. The crystallization temperature strongly depended on the film composition as observed by X-ray diffraction (XRD) measurements after rapid thermal annealing (RTA). Using RBS and XRD data as a combined-cross reference, it was shown that the film stoichiometry and the crystallinity can be probed directly by spectroscopic ellipsometry (SE).
Optimizing ALD HfO2 for Advanced Gate Stacks with Interspersed UV and Thermal Treatments- DADA and MDMA Variations, Combinations, and Optimization
Authors: Clark Robert D. , Consiglio Steven , Nakamura Genji , Trickett Ying , Leusink Gert J.
Published: October 2011

We have recently reported electrical performance improvements of atomic layer deposited (ALD) HfO2 films grown by use of a cyclical deposition and annealing scheme (termed DADA) compared to a single deposition with or without a post-deposition anneal (PDA). Likewise, a process for improving leakage and reliability characteristics of ALD HfZrO by use of an interspersed room temperature ultraviolet ozone (RTUVO) treatments, referred to as multi-deposition multi-room temperature annealing (MDMA), has recently been reported. We have developed a version of this MDMA process on our 300 mm clustered tool with in situ RTUVO treatments interspersed between ALD HfO2 depositions. In this report we compare these two processes (DADA vs. MDMA) for HfO2 dielectric formation in a low temperature MOSCAP flow with in-line measurements of the HfO2 and interface layer thicknesses.
(Invited) Aluminum Oxide and Other ALD Materials for Si Surface Passivation
Authors: Dingemans G. , Kessels W.M.M.
Published: October 2011

The high level of passivation of Si surfaces afforded by Al2O3 synthesized by atomic layer deposition (ALD) was the incentive to test.
Application of Neutron Imaging in PEFC Research
Authors: Boillat Pierre , Oberholzer Pierre , Perego Raffaella , Siegrist Raphael , Kaestner Anders , Lehmann Eberhard H. , Scherer Günther G. , Wokaun Alexander
Published: October 2011

Recent work at PSI based on anisotropic resolution improvement allowed reaching a combination of 20 μm of effective spatial resolution with 10 s exposure times for neutron imaging. This new setup was applied to dynamic in plane imaging of PEFCs in different applications such as the characterization of bulk and interfacial water transport parameters of membranes using 1H-2H contrast imaging, the study of water/ice behavior during sub-zero startup, and the correlation between water accumulation and diffusive voltage loss by combining neutron imaging with transient Helox operation. Future studies will take advantage of a new setup allowing the simultaneous operation and neutron imaging of 6 small scale differential cells.
Simultaneous Water Uptake, Diffusivity and Permeability Measurement of Perfluorinated Sulfonic Acid Polymer Electrolyte Membranes
Authors: Mittelsteadt Cortney K. , Staser John
Published: October 2011

Water diffusivity in perfluorinated sulfonic acid polymer exchange membranes (PEMs) is tested using two new methods. In the first "static" method the membrane is placed in a water activity gradient in a previously evacuated chamber to eliminate all gas/gas diffusion. In a second "dynamic" method the membrane is placed in an evacuated chamber, and known quantities of water vapor are added to the chamber. Diffusivity and water uptake are calculated by monitoring the change in chamber pressure. Rates of diffusivity were found to be identical regardless of method, or if the membrane was undergoing adsorption or desorption.
Random Pore Network Modeling of GDLs Using Voronoi and Delaunay Tessellations
Authors: Gostick Jeff T.
Published: October 2011

A random pore network model of a fibrous gas diffusion layer for fuel cell electrodes based on Voronoi and Delaunay tessellations is presented. This framework not only allows a random distribution of pores in space but provides a full geometric description of pore and throat sizes, connectivity and path lengths, as well as fiber backbone information. In this work the feasibility of this approach to predict capillary and transport properties of gas diffusion layers is assessed and promising results are obtained.
A Representative Volume Element Approach for Pore-Scale Modeling of Fuel Cell Materials
Authors: Wargo Eric A. , Hanna Anne C. , Cecen Ahmet , Kalidindi Surya R. , Kumbur Emin C.
Published: October 2011

The objective of this work is to utilize the recent advances in microstructure quantification to select small volumes (referred to as representative volume elements, or "RVEs") for use in pore scale modeling, which accurately reflect the overall microstructure and transport properties of large fuel cell material datasets. The micro-porous layer (MPL) of polymer electrolyte fuel cells is chosen for demonstration. Focused ion beam scanning electron microscopy is utilized to obtain a 3-D structural dataset for the selected MPL sample. Using n-point statistics, RVEs are selected from the full dataset to reflect the ensemble averaged statistics of the full dataset to within acceptable tolerance. Metric comparisons between RVEs and the full dataset indicate that the selected RVEs offer a very good representation of the full dataset, albeit in a volume that is significantly smaller in spatial extent, therefore providing a computationally efficient and reliable model domain for pore-scale modeling efforts.
Incorporation of Evaporation and Vapor Transport in Pore Level Models of Fuel Cell Porous Media
Authors: Medici Ezequiel F. , Allen Jeffrey S.
Published: October 2011

Evaporation within fuel cell porous media is a complex, conjugate phenomenon that is highly dependent upon the local morphology and wetting conditions. The effect of phase change, vapor transport and temperature gradient on the liquid-vapor water movement inside the porous transport layer is being investigated through a series of numerical simulations using a network model. Viscous models are used for the flow of liquid water and for the air-vapor mixture. Thermal transport is included by performing an energy balance at each pore. Existing models for vapor transport and evaporation are adapted for incorporation into the network model. The focus of this paper is on the methodology for effectively incorporating evaporation into a local pore model. The uncertainty in these transport modes relative to the fuel cell operating conditions such as working temperature and relative humidity are highlighted.
Modeling Two-Phase Transport in PEM Fuel Cell Channels
Authors: Wang Yun , Chen Ken S.
Published: October 2011

The ability to model and simulate polymer electrolyte fuel cells (PEFCs) is of paramount importance to the fundamental study and advancement of the technology as well as engineering design and optimization of PEFCs. Despite the great efforts made in past years, a challenge still remains in the area of two-phase sub-model in channels which simulate two-phase behavior in channels and can be incorporated to a full PEFC fuel cell model due to the lack of efficient numerical methods to track the two-phase interface. The objective of this paper is to make one of the first attempts at developing a sub-model of channel flows and couple it with other phenomena occurring in a PEM fuel cell, including those in the anode side. The boundary conditions at the channel and gas diffusion layer interface are briefly discussed. Comparison is also made between the single-phase channel sub-model and two-phase one, as well as between different model parameters in terms of liquid water saturation distributions.
PEMFC Contamination Model: Neutral Species Sorption by Ionomer
Authors: St-Pierre Jean
Published: October 2011

A mathematical and transient model was developed for the case of a neutral species penetrating an ionomer. It is assumed that transport in the gas or liquid water phases is rate determining. A limited number of equations are used to ensure that the model has an analytic solution. These equations include Fick's first law, a distribution of the neutral species between the gas/liquid phases and the ionomer phase described by a separation factor, a neutral species in the ionomer mass balance, an empirical relationship between the ionomer conductivity and the equivalent foreign neutral species mole fraction in the ionomer phase, and a cell voltage balance. Both separation factor and conductivity relations were experimentally validated. The model solution shows that the dimensionless current density reaches a steady state, recovery is eventually complete after removing the contaminant source, and, contamination and recovery time scales are equal.
Isolation of Transport Mechanisms in PEFCs with High Resolution Neutron Imaging
Authors: LaManna Jake , Chakraborty Subhadeep , Zhang FengYuan , Gagliardo Jeffrey , Owejan Jon P. , Mench Matthew
Published: October 2011

Cell water balance and anode to cathode water transport were investigated using high resolution neutron radiography in the through-plane direction. Induced pressure and relative humidity gradients were imposed across the membrane electrode assembly to determine how these gradients alter saturation profiles in the diffusion media. The asymmetric anode/cathode channel pitch used in this study resulted in large anode water saturation changes with applied gradients while cathode saturation remained more constant. A new low-cost core-shell diffusion media is introduced as a potential replacement of current diffusion media. This new material was found to reduce overall cell water content, but suffers poor overall performance due to excessive ohmic losses, and more work is needed to develop this concept.
In Situ Two-Phase Flow Investigation of Proton Exchange Membrane (PEM) Electrolyzer by Simultaneous Optical and Neutron Imaging
Authors: Selamet Omer F. , Pasaogullari Ugur , Spernjak Dusan , Hussey Daniel S. , Jacobson David L. , Mat Mahmut
Published: October 2011

In PEM electrolyzers, oxygen evolution in the anode and flooding due to water cross-over results in two distinct two-phase transport conditions, and these two phenomena were found to strongly affect the performance. A comprehensive understanding of two-phase flow in PEM electrolyzer is required to increase efficiency and aid in material selection and flow field design. In this study, two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data are used as complementary to aid in understanding of the two-phase behavior. Behavior of gas bubbles is investigated and two different gas bubble evolution and departure mechanism is found. It is also found that there is a strong non-uniformity in the gas bubble distribution across the active area, suggesting the importance of the flow field design.
Image Measurement of Water Droplets in Cathode of PEFC Based on Background Subtraction Method
Authors: Nishida Kosuke , Tanaka Shintaro , Tsushima Shohji , Hirai Shuichiro
Published: October 2011

To alleviate water flooding in polymer electrolyte fuel cells (PEFCs), it is essential to investigate the fundamental phenomena of liquid water transport in cathode electrode of operating fuel cell. This paper presented a novel imaging technique for quantitatively evaluating the dynamic behavior of water droplets on the cathode gas diffusion layer (GDL) of a PEFC based on background subtraction method. Furthermore, the current density measurement in the cathode was performed using segment cell structure concept, and the water balance in the membrane electrode assembly (MEA) was investigated. It was noted that the liquid water distribution on the cathode GDL surface has the maximum value in the midstream region of the counter-flow fuel cell.
Accelerated Testing Validation
Authors: Mukundan Rangachary , James Greg , Davey John , Langlois David , Torraco Dennis , Yoon Wonseok , Weber Adam Z. , Borup Rodney
Published: October 2011

Accelerated Stress Tests (ASTs) were performed on 2 different MEAs (designated P5 and HD6) from Ballard Power Systems. These MEAs were also incorporated into stacks and operated in fuel cell bus modules that were either operated in the field (three P5 buses) in Hamburg, or on an Orange county transit authority drive cycle in the laboratory (HD6 bus module). Qualitative agreement was found in the degradation mechanisms and rates observed in the AST and in the field. The HD6 based MEAs exhibited lower voltage degradation rates (due to catalyst corrosion) and slower membrane degradation rates in the field as reflected by their superior performance in the high potential hold and open-circuit potential AST tests. To quantitatively correlate lab ASTs to field degradation rates, various degradation stressors including temperature, RH, start/stops and voltage cycles, which are not constant in the field, must be accounted for.
Diagnostics for PEMFC Peformance and Durability
Authors: Fuller Thomas F.
Published: October 2011

A critical aspect of life-testing is rapidly and accurately diagnosing issues with materials and designs. Key diagnostic tests for proton exchange membrane fuel cells are reviewed. Catalyst stability, oxidation of supports, and membrane durability challenges are highlighted.
On the Determination of PEM Fuel Cell Catalyst Layer Resistance from Impedance Measurement in H2/N2 Cells
Authors: Malevich Dzmitry , Pharoah Jon , Peppley Brant , Karan Kunal
Published: October 2011

Impedance measurements of H2/N2 cell for the determination of PEMFC catalyst layer (CL) resistance can exhibit significant deviation from those predicted assuming homogeneous CL structure with uniform resistance and capacitance. Predictions from model with homogeneous structure but distributed resistance and/or capacitance shows deviation from the ideal mid-frequency response (45o line) but expected low-frequency response (vertical line). A distributed model considering agglomerate-type structure shows deviation from ideal mid-frequency response ((45o line) as well as from ideal vertical-line like response at experimentally employed frequencies although a vertical-line response is predicted at frequencies significantly lower than typically accessible in experiments.
Characterization of Carbon Corrosion in a Segmented PEM Fuel Cell
Authors: Spernjak Dusan , Fairweather Joseph D. , Rockward Tommy , Mukundan Rangachary , Borup Rodney
Published: October 2011

Corrosion of the catalyst support is an important degradation mechanism in PEM fuel cells because it reduces the overall cell performance by decreasing the active catalyst surface area, catalyst connectivity, and the porosity and hydrophobicity of the catalyst layer. Carbon corrosion rates were investigated in a segmented cell with and without a microporous layer (MPL) on the cathode. The cells were aged in-situ using a protocol for accelerated stress testing (AST) for carbon-support corrosion consisting of consecutive holds at 1.3 V. Carbon corrosion was quantified by measuring CO2 evolution during the potential holds. Although more carbon was corroded in the cell with the MPL on the cathode, corrosion in the catalyst layer was lower than in the cell without the MPL because a portion of the evolved CO2 originated from the MPL rather than from the catalyst layer. This was corroborated by the higher remaining ECSA and lower kinetic losses after prolonged corrosion for the MPL case. Both GDL cases exhibited substantial performance degradation and ECSA loss. Cell with the MPL was more resistant to prolonged carbon corrosion.
The Platinum/Titanium Nitride Interface: X-ray Photoelectron Spectroscopy Studies
Authors: Matic Nikola , Chottiner Gary , Ernst Frank , Scherson Daniel
Published: October 2011

This contribution presents the results of an X-ray photoelectron spectroscopy (XPS) study aimed at gaining further insight into the interactions between Si, Ti, TiN, and Pt. Our approach involves the sequential deposition of Ti, TiN, and Pt onto a clean, well-characterized Si(111) surface, a substrate known to react with Pt . These depositions were carried out in situ under ultra-high vacuum (UHV) in a chamber equipped to perform angle-resolved XPS (ARXPS) and various other types of characterization. It will be shown that layers of TiN only ca. 1 nm thick are sufficient to prevent interdiffusion between Pt and Si.
Nanofiber Cathodes for Low and High Humidity Hydrogen Fuel Cell Operation
Authors: Zhang Wenjing , Brodt Matthew W. , Pintauro Peter N.
Published: October 2011

A new fuel cell electrode fabrication scheme based on nanofiber electrospinning has been devised and nanofiber cathode membrane-electrode-assemblies (MEAs) were evaluated in a hydrogen/air fuel cell at 80ºC for low and high feed gas humidification conditions. MEAs were constructed from an electrospun mat with a fiber composition of 72wt% Pt/C, 15wt% poly(acrylic acid), and 13wt% Nafion. The Pt loading of the mat was 0.1 mg/cm². Mats were hot-pressed onto Nafion 212 membranes with a decal anode (at 0.4 mg/cm²). Under fully humidified conditions, the nanofiber cathode MEA generated very high power densities (e.g., 485mW/cm² at 0.6V vs. 345mW/cm² for a 0.1 mgPt/cm² decal cathode MEA). At lower feed gas humidities, the difference in power output for the nanofiber and decal MEAs was more pronounced, e.g., at 40%RH, the power density with the nanofiber cathode was more than double that for the decal MEA (132mW/cm² vs. 58mW/cm² at 0.6V).
Pt-Oxide Coverage-Dependent Oxygen Reduction Reaction (ORR) Kinetics
Authors: Subramanian Nalini P. , Greszler Thomas , Zhang Junliang , Gu Wenbin , Makharia Rohit R.
Published: October 2011

Oxygen Reduction Reaction (ORR) currents have been measured under the potential range of an operating fuel cell (0.72-0.9 Volts) while keeping proton and oxygen transport-related overpotentials insignificant by testing with pure O2, at 100%RH and at low current densities. Low potential points are achieved by reducing the platinum loading on the cathode and operating under sub-ambient (<101.3 kPaabs) pressure. The resulting experimental data is fit to Pt-oxide-coverage-dependent kinetics and the kinetic parameters extracted.
Transient Platinum Oxide Formation and Oxygen Reduction on Carbon-Supported Platinum and Platinum-Alloy Electrocatalysts
Authors: Huang Yan , Zhang Junliang , Liu Yuxiu , Subramanian Nalini P. , Wagner Frederick T. , Jorne Jacob , Li James
Published: October 2011

Chronoamperometry studies at a fixed potential of 0.9V vs. the reversible hydrogen electrode (RHE) have been performed on three PEM fuel cell catalysts (50 wt.% Pt/C, 30 wt. % PtM1/C and 30 wt. % PtM2/C) on both rotating disk electrodes (RDEs) and membrane electrode assemblies (MEAs), in order to investigate similarities and differences between Pt and Pt-alloy catalysts for transient behavior of the oxygen reduction reaction (ORR). Similar trends of reversible activity degradation were shown for both RDEs and MEAs. Compared to the baseline Pt/C catalyst, alloy catalysts under potential hold were found to have higher oxide coverage and faster oxide-growth rate, with the latter related to their faster transient ORR activity degradation rate. In addition, PtM1/C showed a higher ORR activity than PtM2/C in MEA tests, while the opposite trend was found in RDE tests, which could be attributed to their different transient stability under potential hold.