bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development And Demonstration Of Technology On The Path To Commercially Viable PEM Fuel Cell Stacks
Authors: Chiem Bien H. , Beattie Paul , Colbow Kevin
Published: October 2008

Ballard's Technology "Road Map" (TRM) highlighted the automotive fuel cell performance targets Ballard planned to meet on an annual basis, as the company progressed toward its goal of developing commercially viable fuel cell stack technology. These evaluation activities culminated in the most recent demonstration of a stack design in 2007 that met the cost (< US$57/kWnet), power density (>1900 Watts/Litre), durability (>5000 hours under a dynamic load profile and freeze-start capability (from -30C to 50% power in <130 seconds) targets that were on the path to satisfy the 2010 interim objectives. The stack technologies developed as part of the TRM initiative were leveraged into other product areas such as materials handling. Ballard recently completed the sale of its automotive fuel cell assets. As a result, the company is now shifting focus to the development of stack technology for non-automotive applications.
Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs
Authors: Rodgers Marianne , Agarwal Rohit , Pearman Benjamin P. , Li Bo , Slattery Darlene , Choi Pyoungho , Mohajeri Nahid , Bonville Leonard , Kunz H. R. , Fenton James M.
Published: October 2008

Durability studies were carried out on membrane electrode assemblies (MEA)s containing commercial Nafion® and perfluorinated ionomer/PTFE composite membranes that include the incorporation of phosphotungstic acid (PTA). Fuel cells were run for 100 hours at 30% relative humidity, 90 and 100 oC, and open circuit voltage. The voltage was monitored during the durability test, as was the condensate water for presence of fluoride ions. Crossover current, electrochemical active areas, and polarization curves were evaluated pre- and post- test. Improved degradation behavior was observed for the perfluorinated ionomer/PTA/PTFE composite membranes compared to the commercial Nafion® membranes under both testing conditions. Knowledge of the effect of operating conditions on the properties of a MEA over time provides important degradation information that can be used in the design of long-lasting MEAs.
Electrode and Membrane Durability Issues of PEFCs
Authors: Hatanaka Tatsuya , Takeshita Tomohiro , Murata Hajime , Hasegawa Naoki , Asano Takashi , Kawasumi Masaya , Morimoto Yu
Published: October 2008

Our approach focusing on Pt catalyst degradation, carbon corrosion and membrane degradation is reviewed in this paper. For Pt catalyst degradation in potential cycle test, the quantitative TEM image analysis and 1-D chemical engineering model was applied. The Pt particle distribution after the durability test could be explained by the Pt ion diffusion model. For carbon corrosion mitigation, vertically aligned carbon nanotube electrodes were applied. For membrane degradation understanding, membranes with intentionally introduced Pt-band was applied and revealed their higher fluoride emission rate. These results and further efforts would lead us to develop more durable PEFC system.
Two-dimensional Anisotropic Interfacial Delamination Model for Polymer Electrolyte Fuel Cell Performance Loss
Authors: Kim Soowhan , Khandelwal Manish , Chacko Charles , Mench Matthew
Published: October 2008

Performance loss can result from local or partial interfacial delamination between the catalyst layer and diffusion media, or peeling of the catalyst layer from the membrane. Under frozen conditions, experimental freeze/thaw testing of a polymer electrolyte fuel cell (PEFC) has revealed damage due to a local delamination in the soft goods, resulting in an increase of ohmic resistance. To study the impact of local delamination on performance, a two-dimensional anisotropic model was developed. To identify key parameters independently of particular material properties, a dimensionless ratio approach was taken. The model was then validated with experimental results from a model cell designed to simulate a gap between diffusion media and catalyst layers. Localized interfacial delamination of the polymer electrolyte membrane (PEM)|catalyst layer(CL) and CL|diffusion media were found to increase ohmic resistance significantly. The main engineering parameters which control the extent of damage when anomalous delamination occurs were determined with parametric study.
The Use of Ultrasound (20kHz) as a Novel Method for Preparing Proton Exchange Membrane Fuel Cell Electrodes
Authors: Pollet Bruno G.
Published: October 2008

A novel Sonoelectrochemical method for preparing catalyst layers for Proton Exchange Membrane Fuel Cell (PEMFC) is described. In order to optimize the system, initial studies focused on potentiostatic platinum electrodeposition on glassy carbon (GC) disc electrodes in the absence and presence of ultrasound (20 kHz, up to 29 W.cm-2) and at (313 {plus minus} 1) K. It was found that ultrasound affects significantly the electrodeposition process of Pt on GC electrodes, i.e. increased limiting currents were observed compared to those obtained under 'silent' conditions (no agitation). Platinum loaded on Nafion-bonded carbon anodes were prepared in K2PtCl4 aqueous solutions by galvanostatic pulse electrodeposition in the absence and presence of low-frequency high-power ultrasound; and MEAs were fabricated by conventional method. It was found that electrodes prepared sonoelectrochemically showed better performance compared to those prepared by (i) galvanostatic pulse method only (i.e. in the absence of ultrasound) and (ii) conventional method.
Viologen Catalyst for Direct-Carbohydrate Fuel Cell
Authors: Hansen Dane C. , Watt Gerald , Nichols Joey , Andrus Merrit B. , Wheeler Dean R. , Choi Sang H.
Published: October 2008

Investigation of viologen-based organic catalysts has shown them to be capable of directly oxidizing various sugars. Methyl viologen has been studied using oxygen uptake vial experiments, NMR analysis, and electrochemical methods. We have found that under appropriate conditions this catalyst is capable of completely oxidizing glucose to form carbonate. The preliminary performance of this catalyst in an alkaline fuel cell is also demonstrated.
Fullerene-Based Proton-Conductive Material for the Electrolyte Membrane and Electrode of a Direct Methanol Fuel Cell
Authors: Hirakimoto Takuro , Fukushima Kazuaki , Li Yongming , Takizawa Shuichi , Hinokuma Koichiro , Senoo Tadashi
Published: October 2008

A fullerene-based compound with proton-conductive functional groups was synthesized and characterized for fuel cell applications. The fullerene-based proton conductor was mixed with polyvinylidene difluoride (PVdF) as a binder to form the electrolyte membranes. The film property can be tuned by changing the ratio of the fullerene derivatives. The proton conductivity of the electrolyte membranes with 67 wt % fullerene derivative was higher than 4.5 × 10-3 S cm-1 at 25 {degree sign}C under relative humidity (RH) of 70%. The membrane-electrolyte assemblies with these materials showed high DMFC performance under ambient conditions.
Cathodes for Proton-Exchange-Membrane Fuel Cells based on Ordered Mesoporous Carbon Supports
Authors: Lebedeva Natalia P. , Booij Arend S. , Janssen Gaby J.
Published: October 2008

Electrodes for the PEMFC were made from 40 wt% Pt on ordered mesoporous carbon (OMC) and their performance as cathodes in PEMFC fuel cells was evaluated. Good activity for the oxygen reduction reaction was found resulting in mass activities better than observed with commercial catalysts. The mesopores in the OMC were in the order of 3.6 nm, which did not prevent a high utilization of the Pt. However, the oxygen transport was very poor in these electrodes, suggesting the mesopores are easily blocked by ionomer and water.
Electrochemical Stability and Oxidation Mechanism of Carbon Support for PEM Fuel Cell
Authors: Yadav Amar P. , Sugawara Yuu , Nishikata Atsushi , Tsuru Tooru
Published: October 2008

The oxidation behavior of a sputtered carbon electrode has been investigated in 0.5 M H2SO4 solution with the help of an electrochemical quartz crystal microbalance (EQCM). The mass change response of the carbon coated Au-QCM during potential cycling showed an increase of mass due to adsorption of water or bisulfate ion just after observation of an anodic peak for the oxidation of hydroquinone. A mass loss due probably to the evolution of CO2 gas was observed at potential above 1.3 V vs. SHE during anodic scan. During cathodic scan, a loss of mass due to release of water or bisulfate ion was accompanied by the reduction of quinone to hydroquinone. By comparing the result of carbon coated QCM with that of highly ordered pyrolytic graphite (HOPG), the mechanism for the oxidation of carbon in acidic medium is discussed.
PEM Fuel Cell Catalysts: The Importance of Catalyst Support
Authors: Ye Siyu , Hall Miho , He Ping
Published: October 2008

Cost and durability are major challenges for the commercialization of polymer electrolyte membrane (PEM) fuel cells. Accordingly, there remains a need in the art to understand the degradation of fuel cell components and to develop design improvements to mitigate or eliminate such degradation. Carbon support corrosion and Pt dissolution/aggregation are considered as the major contributors to the degradation of the carbon-supported Pt or Pt alloy catalysts. This paper will provide recent advances at Ballard in the performance and stability improvement of the carbon supported Pt and Pt alloy catalysts in PEM fuel cells. An accelerated stress test (AST) has been developed and used to evaluate the degradation resistance of different cathode catalyst materials and structures. It is demonstrated that the morphology, physical and chemical characteristics of these carbon supports have significant effects on the performance and stability of the electrocatalysts.
Estimation of Water Layer Thickness Adjacent to the Cathode Catalyst Layer of a PEFC (Analysis Using Electrochemical Impedance Spectroscopy)
Authors: Hoshiko Takuya , Nakajima Hironori , Konomi Toshiaki , Kitahara Tatsumi , Kita Shoichiro
Published: October 2008

We have analyzed the impedance of the cathode of a polymer electrolyte fuel cell (PEFC) to estimate oxygen diffusion distance, d. Assuming planar oxygen diffusion in a thin liquid water layer at the cathode unconventionally, we can regard d as water layer thickness adjacent to the cathode catalyst layer. Calculated values of d agree well with our previous experimental result of liquid water accumulation amount at the cathode. Measurement of impedance variation with time reveals that d initially tends to be almost constant with time after start-up from dry condition, but that excessive water accumulation due to long time operation causes an increase in d. From the viewpoint of the diagnosis, an exceeding increase in d can be used to indicate the flooding at the catalyst layer.
Mesoscopic Modeling of Liquid Water Transport in Polymer Electrolyte Fuel Cells
Authors: Mukherjee Partha P. , Wang Chao-Yang
Published: October 2008

A key performance limitation in polymer electrolyte fuel cells (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. Liquid water leads to the coverage of the electrochemically active sites in the catalyst layer (CL) rendering reduced catalytic activity and blockage of the available pore space in the porous CL and fibrous gas diffusion layer (GDL) resulting in hindered oxygen transport to the active reaction sites. The cathode CL and the GDL therefore play a major role in the mass transport loss and hence in the water management of a PEFC. In this article, we present the development of a mesoscopic modeling formalism coupled with realistic microstructural delineation to study the profound influence of the pore structure and surface wettability on liquid water transport and interfacial dynamics in the PEFC catalyst layer and gas diffusion layer.
Reactions of Chemical Hydrides with Polyhydroxyl Compounds for Onsite Hydrogen Production
Authors: Stanic Vesna
Published: October 2008

Hydrogen production in the reactions of sodium brorhydride with various polyhyroxyl compounds was investigated. The reactions were carried out at room temperature and ambient pressure with glycol, glycerol, fructose, and sucrose. The volume of hydrogen was measured during the reactions and compared with the theoretically predicted values. The results show that the hydrogen yield in the reactions of glycol or glycerol is 100%; however, the reactions with fructose and sucrose generated 40% and 70%, respectively, of the expected hydrogen amount.
Effect of Equivalent Weight of Phosphotungstic Acid-Incorporated Composite Membranes on the High Temperature Operation of PEM Fuel Cells
Authors: Choi Pyoungho , Li Bo , Agarwal Rohit , Pearman Benjamin P. , Mohajeri Nahid , Rodgers Marianne , Slattery Darlene , Bonville Leonard , Kunz H. R. , Fenton James M.
Published: October 2008

Two types of composite membrane were prepared by incorporating phosphotungstic acid (PTA) into host NafionO` membranes; one with 1100 EW of NafionO` and 15% PTA, namely FSEC1, and the other with 750 EW of NafionO` and 15% PTA, namely FSEC3. Catalyst-coated membranes (CCMs) were made using the composite membranes with the 32 wt.% and 25 wt.% ionomer contents in the catalyst layer for FSEC1 and FSEC3 membranes, respectively. The composite membranes were tested in a 25 cm2 single cell at the temperature of 80 oC, 100 oC, and 120 oC and compared to NafionO`112. At 80 oC and 100 oC, the performance of FSEC1 membrane showed the highest and followed by NafionO`112 and FSEC3 membranes. However, both the composite membranes, FSEC1 and FSEC3, outperformed NafionO`112 at 120 oC, showing great potential for their application in the high temperature (~120 oC) operations. At 400 mA/cm2, the potentials maintained were 0.47V, 0.55V, and 0.51V for NafionO`, FSEC1 and FSEC3 membranes, respectively. The resistance of oxygen mass transfer in FSEC3 was pronounced at high temperature as evidenced by oxygen gain at the temperature.
New Synthesis Routes for Indium-Doped Tin Pyrophosphate Proton Conductors
Authors: Einsla Melinda , Mukundan R. , Brosha Eric L. , Garzon Fernando H.
Published: October 2008

We have synthesized various indium-tin pyrophosphates using the traditional high-temperature method described in the literature as well as a novel solution-precipitation process developed in our laboratory. An ammonium-based precursor was used in an attempt to achieve a lower crystallization temperature. The use of this precursor in the solution-precipitation of indium-tin pyrophosphate gels resulted in precursors that could be crystallized at less than 600{degree sign}C. Inelastic neutron scattering studies indicate the presence of phosphate rich grain boundary phases that may be responsible for the high conductivity of the materials.
In-Situ Assessment of Macropore Growth in Low-Doped n-Type Silicon
Authors: Carstensen Jürgen , Cojocaru Ala , Leisner Malte , Föll Helmut
Published: October 2008

Understanding pore growth in semiconductors in detail needs some in-situ information about the processes occurring in a growing pore. It is shown that dual-mode in-situ FFT impedance spectroscopy can provide useful data for macropore etching in n-type Si under back side illumination. A new illumination mode is used alternating with the conventional current-voltage mode, and data evaluation is based on an advanced model developed for this kind of pore etching. The principles of the technique and the basics of the model are introduced and illustrated by a number of examples, some of which show new kinds of pore growth modes.
Design and Fabrication of Extended-Bandwidth Rugate Filters Made of Porous Silicon
Authors: Ishikura Nobuyuki , Fujii Minoru , Nishida Kohei , Hayashi Shinji , Diener Joachim , Mizuhata Minoru , Deki Shigehito
Published: October 2008

We designed and fabricated porous silicon-based broadband rugate filters by combining up to seven rugate structures. A near-infrared stop-band filter having a reflection band width of 1926 nm with no higher-order harmonics and very small sidelobes were realized. The suppression of higher-order harmonics and the reduction of sidelobes also allowed us to produce a high quality pass-band filter having three high transmittance regions consisting of broad stop-bands.
Deep Trench Etching in Macroporous Silicon - Application to Photonic Crystal Gas Sensors
Authors: Wehrspohn Ralf B. , Schweizer Stefan , Geppert Torsten , Lambrecht Armin
Published: October 2008

We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. The limits of this new process are simulated using electrostatic models and are verified experimentally. This new techniques enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics, as an example an photonic crystal gas sensor is shown.
Silicon/Metal Hybrid Nanosystem with Tailored Magnetic Properties in Two Characteristic Field Regions
Authors: Rumpf Klemens , Granitzer Petra , Poelt Peter , Krenn Heinz
Published: October 2008

Electrodeposition of ferromagnetic metal-nanostructures into a porous silicon (PS) matrix merges the electronic properties of a semiconductor and the ferromagnetic ones of the precipitated metal on one material level. The deposition is performed using a metal-salt solution as electrolyte and an applied pulsed current under cathodic conditions. The metal precipitation within a PS-template exhibiting unconnected mesopores with aspect ratios of about 1000 leads to nanostructures with a maximum elongation of a few microns (aspect ratio 100). The achieved hybrid system exhibits magnetic characteristics which drastically differ from the corresponding bulk materials. Magnetization measurements of this material show two characteristics, one at magnetic fields below the saturation magnetization MS of the deposited metals due to the spin-magnetism (e.g. MS (Ni)=0.62 T, MS (Co)=1.82 T) and another one at higher fields above MS which is assigned to a novel, recently intensively investigated magnetic contribution likely caused by spin-orbit interaction.
Novel Morphology Dependent Ferromagnetic Behaviour of Mesoporous Silicon
Authors: Granitzer Petra , Rumpf Klemens , Poelt Peter
Published: October 2008

Nanostructuring of a silicon wafer by etching in an HF-solution leads to a porous semiconductor which offers physical properties (e.g. optical, magnetic) drastically different from the ones of the according bulk material. A change of the magnetic behaviour from diamagnetic in case of bulk silicon to ferromagnetic has been observed in mesoporous samples. This ferromagnetism depends on the morphology (porosity) of the investigated samples, which can be modified by the electrochemical process parameters and/or the doping level of the used Si-substrate. The occurrence of this novel ferromagnetic behaviour is not completely clarified yet but has to be caused by surface-effects resulting in a new kind of interface-magnetism.
Formation Mechanism of Porous Silicon with Medium Pores: The Role of KMnO4
Authors: Fukami Kazuhiro , Kamakura Hiroki , Sakka Tetsuo , Ogata Y. H.
Published: October 2008

We investigated the medium pore formation in the presence of KMnO4, H2O2 or HNO3 in an HF solution. The time development of pore formation showed a crystallographically oriented etching with KMnO4, while a less-oriented etching in the presence of H2O2 or HNO3 or in the absence of the oxidants. In current vs. potential curves, the positive shift in the critical potential, above which uniform electropolishing occurs, was clearly observed in the presence of KMnO4, while the critical potential increased a bit with H2O2 or HNO3. The increase of the critical potential enabled to apply a higher current than that at the original critical potential, resulting in the formation of much wider pores.
In-Situ FFT Impedance Spectroscopy during the Growth of n-type InP "Crysto Pores"
Authors: Leisner Malte , Carstensen Jürgen , Cojocaru Ala , Föll Helmut
Published: October 2008

In this work the growth of crystallographically oriented pores in n type InP is studied. The evolution of the pore structure with time is outlined in detail. It is found that growth and branching of these pores in different crystallographic directions depend on the etching time. Besides an ex-situ evaluation of the pore structure by micros-copy, in-situ FFT impedance spectroscopy measurements have been performed. A model has been found which fits the data consistently. First steps towards a physico-chemical understanding of the processes underlying the pore growth have been made, yielding a qualitative view of pore growth.
Electric Field Effects on the Formation of Isolated Macro Porous Silicon
Authors: Vanga Lakshman Kumar , Oisten Michael K. , Ritzdorf T. , Bergstrom Paul L.
Published: October 2008

In this paper, we discuss some of the challenges involved in the formation of isolated vertical pores, thereby describing the electric field effects on the pore formation. The diameters of the pore features under investigation range from 5μm to 20μm. A variety of experiments have been conducted, which include exploration of features with large pyramidal pits, large patterned features with an array of pyramidal pits, and patterned features using a metal mask or a dielectrically isolated etch mask. Macroporous silicon is explored under these parameters for p-type (100) and p-type (111) silicon substrates using electrochemical anodization. Electric field effects on the pore profile and formation will be discussed using the experimental anodization results and electric field and process modeling analysis related to the formation of isolated pores.
Growth Modes of Macropores in n-Type Silicon
Authors: Cojocaru Ala , Carstensen Jürgen , Föll Helmut
Published: October 2008

The growth of macropores in Silicon under galvanostatic conditions always terminates at some maximum depth by some growth mode transition, e.g. from pore growth to cavity formation. It will be shown that macropore growth in lightly doped n-type Si under back side illumination may experience several different kinds of growth mode transitions, including some new ones; in particular if new and improved electrolytes are used. Existing models of macropore growth cannot account for these mode transitions and need to be augmented.
Are the Oscillations During the Anodic Dissolution of Si in Dilute Fluoride Electrolyte Damped or Sustained?
Authors: Chazalviel Jean-Noel , Ozanam Francois
Published: October 2008

The current oscillations observed under potentiostatic conditions during the anodic dissolution of silicon in a fluoride electrolyte have been reexamined. This phenomenon, originating from an oscillation of the oxide thickness on the local scale, can be observed as a macroscopic oscillation only if the phase of the local oscillators is synchronized over the whole electrode surface. In the absence of an external excitation, theoretical modeling indicates that such a synchronization can hardly be obtained from a short-range interaction between the local oscillators. Experimental analysis of the oscillation damping suggests that such an interaction is either absent or extremely weak. We conclude that the synchronization observed in some instances is most plausibly due to global coupling through the uncompensated series resistances of the electrode, its back-contacts, and the electrolyte.
Ellipsometric Porosimetry: Fast and Non Destructive Technique for Characterization of Porous Low-K; Highlights on Plasma Damage and Water Effect on Treated Materials
Authors: Bourgeois Alexis , Bondaz Alexis , Kitzinger Laurent , Defranoux Christophe
Published: October 2008

Ellipsometric porosimetry (EP) is a non contact, non destructive approach based on a spectroscopic ellipsometric measurement which allows the precise determination of the refractive indices and thicknesses of the porous films. EP combined spectroscopic ellipsometric technique with a suitably adapted adsorption chamber. EP accords the great advantage of performing an in situ fast spectroscopic ellipsometric measurement at each stabilized pressure interval. From this combination, we can obtain morphological information such as open and closed porosity, pore size distribution, etc for thin films with an excellent sensitivity. In this paper we will focus on a SiOCH porous low-K sample. Using EP we will demonstrate that it is a porous hydrophobic material.We will then study the effect of plasma treatment on the material. The damaged layer will be characterized. By using water as an absorptive, we will be able to demonstrate the water degradation effect on treated materials.
Formation of Porous Noble Metal Layer by Displacement Reactions with Porous Silicon
Authors: Hayase Masanori , Matsuzaka Taku , Brito-Neto Jose Geraldo Alves
Published: October 2008

Porous Pd layer was synthesized on a Si wafer using anodized porous Si as a starting material. In the immersion plating, Pd replaced Si and porous Pd layer was formed. Pt was deposited on the porous Pd layer by galvanic displacement reaction. It was demonstrated that fabrication process of our micro fuel cell electrode was applicable.
Dye-Sensitized TiO2 Nanotubes with Ag Nanoparticles
Authors: Shinkai Yuji , Tsuchiya Hiroaki , Fujimoto Shinji
Published: October 2008

The present work examines the deposition of Ag nanoparticles on anodic TiO2 nanotubes in order to improve solar energy conversion by increasing the optical absorption of dye. Ag nanoparticles are successfully deposited on TiO2 nanotube layers. The size of nanoparticles is increased when amorphous TiO2 nanotubes are crystallized and the tube diameter is increased. Photocurrent for dye-sensitized TiO2 nanotubes is increased by the deposition of Ag nanoparticles, but the increment is decreased during dye-sensitization. This may be ascribed to the dissolution of Ag nanoparticles during the sensitization and the decreased plasmon resonance effect by thickening the dye layer on Ag nanoparticles.
Resonant Energy Transfer from Porous Silicon to Iodine Molecules
Authors: Nakamura Toshihiro , Ogawa Tatsuya , Kubota Tomoo , Adachi Sadao , Fujii Minoru
Published: October 2008

The electronic excitation energy transfer between excitons in porous silicon and iodine molecules in an organic solution is studied. From the time-resolved photoluminescence the rate of the energy transfer is increased with approaching a wavelength region where the photoluminescence spectrum of porous silicon overlaps the absorption spectrum of iodine molecules, and with increasing the radiative recombination rate of porous silicon. We show that the dependence of the rate is well explained by Förster type dipole-dipole interaction mechanism in which the diffusion of the assemblies and molecules is taken into consideration. Furthermore, it is found that the efficiency of the energy transfer strongly depends on the emission wavelength at low iodine concentration.
Macropore Formation in p-type Silicon and Si/SiGe/Si/SiGe/p-type Silicon
Authors: Kim Jae Hyun , Seo Hong-Seok , Kim K Phil , Lyu Hong-Keun , Woo Sung-Ho , Lee Jung Ho
Published: October 2008

Random and ordered macropore formation in p-type silicon substrate (10 ~ 20 ohm•cm) by electrochemical anodization in various HF-containing electrolytes was investigated under different operating conditions. The effect of electrolyte composition controlling the macropore formation both for random and periodically arranged pores is reported. The role played by etch pit for ordered macropore formation was investigated. The results revealed that the nature of constituents of solution plays very important roles in determining pore formation and morphology and the stable ordered macropore growth is not possible without etch pit. By using Si/SiGe/Si/SiGe/p-type silicon structure, ordered pillar structures were fabricated without etch pit formation process. The possible role of two sets of Si/SiGe layer for pillar formation is proposed.
The Effect of N2 in Vapor Detectors Based on Porous Silicon Layers
Authors: Rucavado Esteban , Badilla Juan P. , Ramirez-Porras Arturo
Published: October 2008

Porous Silicon sensing devices have been developed and tested in air and pure nitrogen atmospheres containing organic vapors in order to study their electric response. It has been found differences in the electrical behavior of the sensors when subjected to both atmospheres. Possible explanations are proposed.
Stain Etching with Ferric Ion to Produce Thick Porous Silicon Films
Authors: Dudley Margaret E. , Kolasinski Kurt W.
Published: October 2008

Stain etching of silicon in aqueous solutions composed of FeCl3 + HF + concentrated (HCl, HClO4 or H2SO4) leads to brilliantly luminescent porous Si with a unique dual layer structure. The upper layer (~2 µm or more thick) exhibits bluer luminescence (peaked at 520-590 nm). The lower layer exhibits redder luminescence (peaked at 630-660 nm). The peak PL wavelength and the PL intensity both depend strongly on the excitation wavelength. Photoluminescence excitation (PLE) spectroscopy indicates that the upper and lower layers are distinct because the PLE spectra of the two layers are different. Additionally, we demonstrate that two completely new stain etchants can produce visibly luminescent microporous silicon: V2O5 dissolved in HF(aq) and CeF4 dissolved in H2SO4(aq). In all cases bubble formation is suppressed and layer homogeneity greatly exceeds that obtained with nitrate based stain etchants.
Photoexcited Silicon Nanocrystals as Multifunctional Spin-Flip Activator
Authors: Goller Bernhard , Polisski Sergej , Moskalenko Andriy , Loponov Konstantin , Kovalev Dmitry
Published: October 2008

Nano-sized silicon crystals have entirely new physical properties which do not occur in its bulk form. Investigation of its photoluminescence properties can explain the mechanism of transferring energy from photoexcited excitons confined in silicon nanocrystals to energy accepting substances via electron exchange mechanism. This excitation process changes the electronic spin structure of the acceptor molecule, which is forbidden in the dipole approximation, and therefore it requires the involvement of photosensitizers.
Growth of Porous Anodic Films on Niobium in Hot Phosphate-Glycerol Electrolyte
Authors: Oikawa Yuki , Fushimi Koji , Aoki Yoshitaka , Habazaki Hiroki
Published: October 2008

Porous anodic films have been developed on niobium at constant formation voltages between 5 and 50 V in glycerol electrolyte containing 0.8 mol dm-3 dibasic potassium phosphate at 433 K. Except at the formation voltage of 5 V, at which the current density is approximately constant during anodizing, the current shows the minimum and then maximum. After the current maximum, the current density decreases gradually, which follows the Cottrell equation. Thus, diffusion of some species in the pores should control the growth rate of the anodic films. The porous films developed are practically Nb2O5 with a small amount of carbon contamination. Incorporation of phosphorus species, which often occurs in aqueous electrolytes, is negligible at all the formation voltages in the present electrolyte. Based on the results obtained, the growth process of the porous anodic films on niobium in this hot organic electrolyte is discussed.
Fabrication of Self-Organized Nanoporous Oxide Semiconductors by Anodization
Authors: Ono Sachiko , Kobayashi Yuta , Kobayashi Ryohei , Asoh Hidetaka
Published: October 2008

Self-organized nanoporous semiconductors such as ZnO and SnO2 having high aspect ratio was prepared by a simple, high throughput and non-costly wet electrochemical process without use of catalyst. By using anodization of metal plate of zinc in sodium hydroxide solution, tubular oxide with a pore interval of 10-20 nm and the thickness up to several ten microns was obtained. Photocatalytic activity of anodic film on zinc was improved by increasing annealing temperature up to 400 oC associated with increasing crystallinity, although the specific surface area of the oxide film decreased as a result of decreasing grain size caused by sintering. Anodic film formed on tin in sodium hydroxide solution showed cellular structure with the size of 50 nm consisted of microcrystal and the thickness up to 60 μm in only 1 h. Photo catalytic activity of the anodic SnO2 was ascertained by a methylene blue degradation test under UV irradiation. If sulfuric acid was used as an anodizing electrolyte for tin, a peculiar tubular film composed of mixture of crystalline SnO, SnO2 and Sn3O(OH)2SO4 was found.
Anodic Porous and Tubular Oxide Layers on Ti Alloys
Authors: Tsuchiya Hiroaki , Nakata Junji , Fujimoto Shinji , Berger Steffen , Schmuki P.
Published: October 2008

The present work investigates anodic oxide layers on Ti-Zr, Ti-Ta and Ti-Al alloys, focusing on how chemical compositions of the alloys and metallurgical textures can affect the resulting morphology of anodic oxide layers. The formation of porous and tubular oxide layers is achieved on all alloys The homogeneity of anodic oxide layers strongly depends on metallurgical textures of the alloys - on binary a + b Ti-Ta alloys, anodic oxide layers are not uniform while on single phase alloys such as Ti-Zr and Ti-Al, uniform oxide layers are formed. On the other hand, pore (tube) diameter and length are varied with the chemical compositions of the alloys. Emphasis is that on Ti-Al alloy, the morphological transition from pore morphology to tubular morphology can be observed depending the chemical compositions of the alloy.
Self-organized Anodic TiO2-nanotubes in Fluoride Free Electrolytes
Authors: Hahn R. , Lee H. , Kim D. , Narayanan S. , Berger Steffen , Schmuki P.
Published: October 2008

The conventional approach for the formation of highly self-organized nanotube layers is based on anodization of titanium in fluoride containing electrolytes. In the present work we demonstrate that also chloride ions in a suitable organic electrolyte can be used to grow organized nanotube layers. The results show, that under specific electrochemical conditions the growth process can change from a previously reported rapid breakdown anodization mechanism (that leads to disordered nanotube bundles) to a self-organized nanotubular growth mechanism. Under these conditions the nanotubes exhibit the key characteristics of self-ordered tubes (closed tube bottoms, regular dimple structures on the metallic substrate and a linear dependence of the tube diameter on the applied potential).
Comments About the Mechanism of Porous Layer Growth: Case of InP
Authors: Santinacci Lionel , Gérard Isabelle , Bouttemy Muriel , Marques M. , Etcheberry Arnaud
Published: October 2008

Porous InP layer are obtained in HCl. Kinetic aspect associated to the growth are considered. XPS shows that specific Cl chemistry seems to be linked to the porous layer growth. Dosage of dissolution product by atomic spectroscopy demonstrated that a very interesting delay phenomenon for the observation of the final In concentration in solution is observed. This phenomenon can be understood as the consequence of the presence of a confined medium at the time of the porous layer inside the pore. This situation seems to generate a dissolution process with strong electron injection.
Bonding for 3-D Integration of Heterogeneous Technologies and Materials
Authors: Temple Dorota , Malta Dean , Lannon John M. , Lueck Matthew , Huffman Alan , Gregory Christopher , Robinson J. E. , Coffman P. R. , Welch T. B. , Skokan M. R.
Published: October 2008

Modern electronic applications demand more and more complex, multifunctional microsystems with performance characteristics which can only be achieved by using best-of-breed materials and device technologies. Three-dimensional (3-D) integration of separate, individually complete device layers provides a way to build complex heterogeneous microsystems without compromising the system performance and fabrication yield. In the 3-D integration approach, each device layer is fabricated separately using optimized materials and processes. The layers are bonded and interconnected through area array vertical interconnects with lengths on the order of microns. This paper will review bonding techniques for high density area array 3-D integration of integrated circuits, focusing on techniques suitable for die-to-die and die-to-wafer bonding configurations.
Aspects of Bonding Processed CMOS Wafers
Authors: Knechtel Roy
Published: October 2008

This paper will give an overview of special aspects and requirements of the back-end of line bonding of processed CMOS wafers. Due to the high complexity of this type of wafer, there are limitations in the bonding process, such as thermal budget or usable chemicals, which must be considered in the choice or development of bonding techniques. On the other hand, the bonding of extensively processed wafers is always challenging, due to the negative influences of wafer processing on the surfaces to be bonded, such as increased roughness and surface topology. These special aspects will be discussed, both generally and for some specific wafer bonding processes, in order to finally determine the general requirements of bonding processes suitable for CMOS wafers.
Enabling 3D Monolithic Integration
Authors: Batude Perrine , Vinet Maud , Pouydebasque Arnaud , Clavelier Laurent , LeRoyer Cyrille , Tabone Claude , Previtali Bernard , Sanchez Loic , Baud Laurence , Roman Antonio , Carron Véronique , Nemouchi Fabrice , Pocas Stéphane , Comboroure Corine , Mazzocchi Vincent , Grampeix Helen , Aussenac François , Deleonibus Simon
Published: October 2008

3D monolithic integration, thanks to its high vertical density of interconnections, is the only available option for applications requiring connections at the transistor scale. However to achieve 3D monolithic integration, some issues such as realization of high quality top film, high stability bottom FET, low thermal budget top FET still have to be solved. In this work, a 3D monolithic process flow relying on molecular wafer bonding is proposed and results in all critical steps are given. Significant breakthroughs have been obtained using a full wafer molecular bonding with thin interlayer dielectric and an original salicidation process stabilized up to 650oC enabling to reach high performance for the top and bottom transistor.
Smart Bumpless Bonding for MEMS - IC Vertical Integration
Authors: Shiozaki Masayoshi , Moriguchi Makoto , Sasaki Sho , Oba Masatoshi
Published: October 2008

In the future, it is desired that high performance sensing module in small volume is realized. However, conventional MEMS packaging technology is becoming difficult to meet its desire. Small and package-less sensing module, which consist of MEMS and IC chips bonded by SBB (Smart Bumpless Bonding), and is shown in Fig. 1 solves this problem. In the case of MEMS such as accelerometer needs vacuum package, vacuum sealing is accomplished by bonding IC wafers on both sides. This paper reports SBB technology which bond sealing parts for vacuum sealing and electrodes for electrical connection simultaneously. The plasma-CVD SiO2 is utilized to realize vacuum sealing as sealing material. Au projection is formed on the electrode and connected electrically by compressive plastic deformation and activation. Then, the experimental results to demonstrate its feasibility are reported. Enough bonding strength and electrical connection by Au compressive deformation were accomplished, therefore, its feasibility was confirmed.
Low Temperature Bonding for Optical Microsystems Applications
Authors: Higurashi Eiji
Published: October 2008

This paper focuses on the low temperature bonding technology and its application for optical microsystems in use in various fields. The integration is based on the hybrid integration approach achieving high performance, small size and weight, and better cost. First, we describe the key technologies used in hybrid integration, namely low temperature bonding technology and packaging technology for realizing 3D advanced microsystems. Then, we describe various integrated microsensors that can monitor displacement, rotation angle, or blood flow in human skin.
Clean and Conductive Wafer Bonding for MEMS
Authors: Yun Changhan H. , Martin Jack , Chen L , Frey T. J.
Published: October 2008

Various categories of bonding technologies were investigated for MEMS encapsulation applications. The bonding processes presented in this paper include Al to Al, Si to Si, and metal (Al or Au) to Si. Among the above different bonding schemes, the Al to Al bonding gave the highest process yield and bond strength. In addition, actual MEMS accelerometers were successfully integrated with Al to Al bonding with high yield all the way through plastic over-mold packaging and assembly.
Multilayer Au-Si Eutectic Wafer Bonding with Microstructured Sealing Rings
Authors: Lani Sebastien , Bosseboeuf Alain , Garel Olivier , Parrain Fabien , Isac Nathalie , Bouville David , Le Roux Xavier
Published: October 2008

Eutectic wafer bonding based on the use of deposited Au/Si (multi)layers has several advantages with respect to the classical Au-Si eutectic bonding process based on gold diffusion in the Si wafer(s). It allows a better control of the generation of the eutectic liquid phase and it can be applied to the bonding of various wafer pairs such as Si-Si, Si-Glass and Glass-Glass. A drawback of eutectic wafer bonding for wafer-level packaging is a possible large spilling of this liquid phase which is detrimental for encapsulated devices. In this work, it is shown that by a suitable choice of layer thicknesses and the use of microstructured sealing rings, a good control of the spilling of the liquid phase during bonding and a high bonding strength can be achieved.
Tuning the Electrostatic Properties of Silicon-on-Insulating Multilayer (SOIM) Structures
Authors: Kostrzewa Marek , Nguyen Tuan Quang , Mazellier Jean-Paul , Deguet Chrystel , Clavelier Laurent , Landry Karine , Cristoloveanu Sorin
Published: October 2008

We demonstrate the feasibility of SOI (Silicon-on-Insulator) substrates with silicon nitride Si3N4 and silicon dioxide SiO2 based buried composite stack. The SOI substrates with different oxide thicknesses were fabricated using the Smart Cut{trade mark, serif} technology. We provide the preliminary Pseudo-MOSFET characterization as well as an electrostatic model. The electrical charges present in the buried silicon nitride layer are responsible for threshold voltage, flat-band voltage and mobility variations. Numerical simulations and experimental results confirm that the electrostatic properties of SOI substrates can be easily tuned by varying the thickness of the oxide layer located above the buried nitride layer.
Integration of Compound Semiconductor Devices and CMOS (CoSMOS) with Die to Wafer Bonding
Authors: Patterson Pamela R. , Elliot Kenneth , Li James , Royter Yakov , Hussain Tahir
Published: October 2008

On the Compound Semiconductor Devices and CMOS (CoSMOS) program, HRL Laboratories, LLC is developing technology for intimate integration of silicon complementary metal-oxide- semiconductor (CMOS) devices with 400 GHz InP heterogeneous bipolar transistor (HBTs) to form complex integrated circuits. This research is investigating innovative microfabrication approaches, including adhesive bonding techniques, for transistor-scale integration of compound semiconductor and silicon-based transistors. We have successfully fabricated large area HBT's on thin (~1 µm) InP epitaxial layers transferred to silicon substrates with a die to wafer bonding process that preserves the growth orientation of the epitaxial layers bonded to the target substrate.
Engineering Substrates for 3D Integration of III-V and CMOS
Authors: Herrick Katherine J. , Kazior T. E. , LaRoche J. R. , Liu A W. , Lubyshev D. , Fastenau J. M. , Urteaga M. , Ha W. , Bergman J. , Brar B. , Bulsara M. T. , Fitzgerald Eugene A. , Clark D. , Smith D , Thompson R. F. , Daval N , Celler George K.
Published: October 2008

Our direct growth approach of integrating compound semiconductors (CS) and silicon CMOS is based on a unique silicon template wafer with an embedded CS template layer of Germanium (Ge). It enables selective placement of CS devices in arbitrary locations on a Silicon CMOS wafer for simple, high yield, monolithic integration and optimal circuit performance. HBTs demonstrate a peak current gain cutoff frequency ft over 200 GHz. To the best of our knowledge this represents the first demonstration of an InP-based HBT fabricated on a silicon wafer.
150 mm InP-to-Silicon Direct Wafer Bonding for Silicon Photonic Integrated Circuits
Authors: Liang Di , Fang Alexander , Oakley Douglas , Napoleone Antonio , Chapman David , Chen Chang-Lee , Juodawlkis Paul , Raday Omri , Bowers John E.
Published: October 2008

A low-temperature direct wafer bonding process was developed to realize the high-quality transfer of the largest (150 mm in diameter) available InP-based epitaxial structure onto the pre-patterned silicon-on-insulator (SOI) substrate. Over 95% bonding yield and a void free bonding interface was obtained. A InGaAsP multiple quantum-well (MQW) diode laser structure is well preserved after bonding, as indicated by the high-resolution X-ray diffraction (XRD) rocking curve measurement. XRD omega scans of the bonded wafers over a 9x9 matrix revealed a small bowing of only 64.12 micron, showing that the III-V epitaxial surface is relatively flat with low-strain. The first InGaAsP-based MQW hybrid Si evanescent racetrack ring lasers have been realized, showing comparable performance as previously InAlGaAs ring lasers.
3D Wafer-Scale Integration for RF and Digital Applications
Authors: Chang-Chien Patty , Gutierrez-Aitken Augusto , Sandhu Rajinder , Hennig Kelly , Scott Dennis , Zhou Joe , Nam Peter , Geiger Craig , Poust Ben , Parlee Mattew , Thai K. , Phan W. , Oyama B.
Published: October 2008

Northrop Grumman Space Technology has developed an integration technology that is capable of intimately integrating III-V semiconductor devices with Si CMOS under DARPA's COSMOS program. The integration approach is based on a direct face-to-face bonding between pre-fabricated III-V chiplets and CMOS wafers. It is capable of integrating CS (compound semiconductor) devices from smaller wafer substrates to a larger Si host wafer as well as integrating multiple CS technologies onto the same Si CMOS host wafer. This process can be applied to virtually any CS and Si technologies. Integrated differential amplifiers (DAs) have been demonstrated using this 3D AHI integration approach. This DA demonstration integrates the 0.18um Silicon CMOS technology with 6 layers of interconnections from Jazz Semiconductor and NGST's 0.4um emitter high speed HBT technology. Further integration details on AHI as well as demonstrated integrated circuit data will be presented in the full paper.
High Density Integration of Single Crystal Thin Film Devices by "Epifilm Bonding" Technology
Authors: Ogihara Mitsuhiko , Fujiwara Hiroyuki , Mutoh Masataka , Suzuki Takahito , Sagimori Tomohiko , Igari Tomoki , Furuta Hironori , Nakai Yusuke , Sakuta Masaaki
Published: October 2008

Bonding of single crystal thin film ("epifilm") by intermolecular-force ("epifilm bonding" (EFB)) has been investigated from view point of high-density integration of LEDs on dissimilar material substrates. Several bonding layers having different surface-roughness (Rpv) have been tested. Test result showed that EFB state on the bonding layer with Rpv~1nm was much better than those on bonding layers with Rpv >> 1nm; smooth surface of Rpv~1nm is preferable to achieve good EFB state. Diamond-like carbon (DLC) thin film with Rpv~1nm by chemical-vapor-deposition has been also tested as the bonding layer. Good EFB state on the DLC thin film has been achieved by optimizing of surface activation of the DLC thin film. EFB on the DLC thin film having higher thermal conductivities will be promising for high-density device-integration to obtain higher heat-dissipation and better device performance.