bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Formation of n- and p-Type Ohmic Contacts to 4H-SiC Using the Binary Ni/Al System
Authors: Ito Kazuhiro , Onishi Toshitake , Takeda Hidehisa , Tsukimoto Susumu , Konno Mitsuru , Suzuki Yuya , Murakami Masanori
Published: April 2011

Fabrication procedure for silicon carbide power metal oxide semiconductor field effect transistors can be improved through simultaneous formation of ohmic contacts on both the n-source and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n- and p-type SiC after annealing at 1000°C for 5 mins in an ultra-high vacuum. Ohmic contacts to n-type SiC were found when Al-layer thickness was less than about 5 nm while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with Al-layer thicknesses in the range of 5 to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with specific contact resistances of 1.8 × 10−4 Ωcm2 and 1.2 × 10−2 Ωcm2 for n- and p-type SiC, respectively. An about 100 nm-thick contact layer was uniformly formed on the SiC substrate and polycrystalline δ-Ni2Si(Al) grains were formed at the contact/SiC interface. The distribution in values for the Al/Ni ratio in the δ-Ni2Si(Al) grains which exhibited ohmic behavior to both n- and p-type SiC was the largest. The smallest average δ-Ni2Si(Al) grain size was also observed in these contacts. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the ohmic contacts to both n- and p-type SiC.
Influence of Shockley Stacking Fault Expansion and Contraction on the Electrical Behavior of 4H-SiC DMOSFETs and MPS diodes
Authors: Caldwell Joshua David , Stahlbush Robert E , Imhoff Eugene A. , Glembocki Orest J. , Hobart Karl D. , Tadjer Marko J. , Zhang Qingchun , Das Mrinal , Agarwal Anant
Published: April 2011

The forward voltage drop (Vf) increase observed in 4H-SiC bipolar devices such as pin diodes due to recombination-induced Shockley stacking fault (SSF) creation and expansion has been widely discussed in the literature. It was long believed that the deleterious affect of these defects was limited to bipolar devices. However, it was recently reported that forward biasing of the body diode of a 10kV 4H-SiC DMOSFET led to similar Vf increases in the body diode I-V curve as well as a corresponding degradation in the majority carrier conduction characteristics as well and this degradation was believed to be due to the creation and expansion of SSFs during the body diode forward biasing. Here we report measurements comparing the influence of similar stressing, along with annealing and current-induced recovery experiments in DMOSFETs and merged pin-Schottky diodes with the previously reported results of these experiments in 4H-SiC pin diodes. The results of these experiments provide sufficient support that the observed degradation in the majority carrier conduction characteristics is the result of SSF expansion.
Strengths and Limitations of the Vacancy Engineering Approach for the Control of Dopant Diffusion and Activation in Silicon
Authors: Claverie Alain , Cristiano Fuccio , Gavelle Mathieu , Sévérac Fabrice , Cayrel Frédéric , Alquier Daniel , Lerch Wilfried , Paul Silke , Rubin Leonard , Raineri Vito , Giannazzo Filippo , Jaouen Hervé , Pakfar Ardechir , Halimaoui Aomar , Armand Claude , Cherkashim Nikolay , Marcelot Olivier
Published: April 2011

The fabrication of highly doped and ultra-shallow junctions in silicon is a very challenging problem for the materials scientist. The activation levels which are targeted are well beyond the solubility limit of current dopants in Si and, ideally, they should not diffuse during the activation annealing. In practice, the situation is even worse and when boron is implanted into silicon excess Si interstitial atoms are generated which enhance boron diffusion and favor the formation of Boron-Silicon Interstitials Clusters (BICs). An elegant approach to overcome these difficulties is to enrich the Si layers where boron will be implanted with vacancies before or during the activation annealing. Spectacular results have been recently brought to the community showing both a significant control over dopant diffusion and an increased activation of boron in such layers. In general, the enrichment of the Si layers with vacancies is obtained by Si+ implantation at high energy. We have recently developed an alternative approach in which the vacancies are injected from populations of empty voids undergoing Ostwald ripening during annealing. While different, the effects are also spectacular. The goal of this work is to establish a fair evaluation of these different approaches under technologically relevant conditions. The application domains of both techniques are discussed and future directions for their development/improvement are indicated.
A Comparison of Intrinsic Point Defect Properties in Si and Ge
Authors: Vanhellemont Jan , Spiewak Piotr , Sueoka Koji , Simoen Eddy , Romandic Igor
Published: April 2011

Intrinsic point defects determine to a large extent the semiconductor crystal quality both mechanically and electrically not only during crystal growth or when tuning polished wafer properties by thermal treatments, but also and not the least during device processing. Point defects play e.g. a crucial role in dopant diffusion and activation, in gettering processes and in extended lattice defect formation.

Available experimental data and results of numerical calculation of the formation energy and diffusivity of the intrinsic point defects in Si and Ge are compared and discussed. Intrinsic point defect clustering is illustrated by defect formation during Czochralski crystal growth.
Theoretical Model of Crystal Nucleation in PCM Nano-Glasses
Authors: Karpov V. G. , Kryukov Y. A. , Mitra M. , Karpov I. V.
Published: April 2011

We propose a theoretical analysis of crystal nucleation in disordered nano-glass structure of chalcogenide phase change memory. Statistical fluctuations of microscopic structure parameters translate into statistical distribution of nucleation times determining the transition from the highly resistive (glassy) to the low resistive (crystalline) state. This distribution is shown to be log-normal with the peak time exponentially dependent on field strength, temperature, cell area and material parameters.
Sb bonding in GeSbTe compounds by NMR Measurements
Authors: Bobela David , Taylor P. Craig
Published: April 2011

We have measured the 121Sb NMR spectra, which are highly sensitive to the electric field gradients at the nuclear site, for crystalline Sb2Te3, Ge1Sb2Te4, Ge2Sb2Te4, and Ge2Sb2Te5. Estimates of the coupling constants, which are a measure of the field gradient, based on these spectra compare well with compounds containing Sb sites that are approximately 6-fold coordinated. The coupling constants of amorphous phase counterparts are roughly an order of magnitude larger and compare favorably with compounds where the Sb sites are 3-fold coordinated. We argue that the difference in the coupling constants arises primarily from a change in the local coordination, as opposed to the slight differences in the Sb-Te bond lengths and bond angles. The NMR data agree best with a structural model of amorphous phase based upon the “8-N” rule.
THERMAL EXPANSION OF PHASE-CHANGE RANDOM ACCESS MEMORY CELLS
Authors: Li Jianming , Shi L.P. , Yang H.X. , Lim K.G. , Miao X.S. , Lee H.K. , Chong T.C.
Published: April 2011

Three-dimensional finite element method (FEM) is used to solve the thermal strain-stress fields of phase-change random access memory (PCRAM) cells. Simulation results show that thermal stress concentrates at the interfaces between electrodes and phase change layer and it is significantly larger than that within the phase change layer. It has been found that the peak thermal stress is linearly related to the voltage of electrical pulse in the reset process but once amorphous state is produced in the cell, a nonlinear relationship between thermal stress and electrical power exists. This paper reported the change of thermal stress during set process. It was found that the stress decreases significantly due to the amorphous active region during set processes.
Thickness-dependent Crystallization Behavior of Phase Change Materials
Authors: Raoux Simone , Jordan-Sweet Jean L. , Kellock Andrew J.
Published: April 2011

We have investigated the crystallization behavior of phase change materials as a function of their thickness. Thin films of variable thickness between 1 and 50nm of the phase change materials Ge2Sb2Te5 (GST), N-doped GST (N-GST), Ge15Sb85 (GeSb), Sb2Te, and Ag and In doped Sb2Te (AIST) were deposited by magnetron sputtering, and capped in situ by a 10nm thick Al2O3 film to prevent oxidation. The crystallization behavior of the films was studied using time-resolved X-ray diffraction. For each material we observed a constant crystallization temperature Tx that was comparable to bulk values for films thicker than 10 nm, and an increased Tx when the film thickness was reduced below 10 nm. The thinnest films that showed XRD peaks were 2 nm for GST and N-GST, 1.5 nm for Sb2Te and AgIn-Sb2Te, and 1.3 nm for GeSb. The observed increase in the phase transition temperature with reduced film thickness and the fact that very thin films still show clear phase change properties are indications that Phase Change Random Access Memory technology can be scaled down to several future technology nodes.
Recent Advances on the Modeling of Phase Change Materials and Devices
Authors: Lacaita Andrea Leonardo , Russo Ugo , Ielmini Daniele
Published: April 2011

As non-volatile memory technology is approaching the 45nm generation node and in view of severe scaling limitations of conventional Flash, phase-change memory (PCM) is gaining momentum as a reference emerging memory. The high applicative interest in this new technologies asks not only for progress in the integration issues of the new storage concept, but, most importantly, for a significant improvement of the physical understanding of programming, reliability mechanisms and scalability of the new technology. This can only be possible by a detail study of microscopic processes in the chalcogenide material covering a wide range of physics, from electron transport in disordered media to self-heating effects, from solid-state nucleation and growth processes at the nanoscale.

The presentation will review the most recent advances in the understanding and modeling of the programming and reliability mechanisms in chalcogenide-based PCM devices. Electro-thermal simulations of the programming behavior allows to understand the impact of cell geometry and active/electrode materials on the programming current, and to benchmark different scaling rules for future technology nodes. Cell reliability will be discussed with emphasis on the spontaneous crystallization kinetics in the amorphous chalcogenide material, on the acceleration laws to predict retention time at low temperature, and on the possible scaling limitations due to fast phase transition in amorphous chalcogenide nanoclusters/nanowires. An analytical model for nucleation and growth in the amorphous phase will be shown, allowing to draw guidelines for material engineering and reliability improvement. Other scaling-related reliability issues, such as statistical spread of crystallization times and structural relaxation of the amorphous phase, will be discussed.
Physico-chemical Characterization of Thin Oxide Films: Difficulties and Solutions
Authors: Conard Thierry , Vandervorst Wilfried
Published: April 2011

Oxides have always been an integral part of semiconductor manufacturing both in front and back-end processing. With the necessary increase in performance, the demand on these oxides has been increasing leading to their (future) replacement by more complex materials, such as high-k's in gate oxide and metal gates. With the increasing material complexity, a thorough characterization of all aspects of these materials is necessary, covering, for instance, surfaces and interfaces, nucleation, growth, atomic structure, …

This article focuses on the characterization of front-end oxides and their interfaces. It shows that detailed information can be achieved by sophisticated experimental techniques such as synchrotron radiation, high energy ERD or AtomProbe but that adequate sample preparation and/or analysis by a combination of more routinely available techniques may achieve similar results. This is shown through the study of three different systems/problems in the gate stack analysis. We will first focus on the determination of substrate surface preparation conditions before deposition and their influence on growth mode and the growth characteristics by different growth techniques (ALD, MOCVD, …). Second, we present the possibilities of compositional depth profiling of thin layers both with nuclear techniques and Angle-Resolved XPS. Finally, we will show that using conventional XPS and a combination of front and back-side analysis, the interface between high-k oxide and metal gates can be investigated. More examples of gate stack characterization can be found elsewhere
Effect of GaAs Surface Treatments on Lanthanum Silicate High-K Dielectric Gate Stack Properties
Authors: Lichtenwalner Daniel J , Suri Rahul , Misra Veena
Published: April 2011

The properties of lanthanum silicate (LaSiOx) gate stacks on GaAs substrates have been examined, comparing different GaAs pretreatments; namely a) as-received, b) HCl-treated, and c) sulphur-treated. X-ray photoelectron spectroscopy of the As 3d, Ga 3d, and Ga 2p binding energy peaks were used to reveal the chemical nature of the stacks. After a 400 °C in situ anneal in 10−6 torr pO2, the LaSiOx chemically reduces the As oxides from the as-received GaAs, while Ga oxide species remain. HCl and S-treated GaAs similarly show no As oxides, and a much smaller degree of Ga oxides than the as-received case. The Ga-S bonding may be responsible for lowering the tendency towards Ga oxidation for the S-treated case. On p-type, Zn-doped GaAs, 3.0 nm lanthanum silicate films produce MOS device EOT values of 2.38 nm, 1.51 nm, and 1.37 nm, on as-received, HCl-treated, and S-treated substrates, respectively. The high EOT for the as-received GaAs corresponds to the thicker Ga oxide and elemental As at the interface. The decreases in both Ga oxide and elemental As at the interface of the S-treated stack appears to be related to it having the lowest EOT devices.
A-Site Distribution in La1−xSrxMnO3: a Computational Study
Authors: Jang Yun Hee , Gervais François , Lansac Yves
Published: April 2011

The possibility of an A-site (La3+/Sr2+) ordering in a colossal magnetoresistance manganite (CMR) La3/4Sr1/4MnO3 was explored using molecular dynamics (MD) simulations with a newly developed force field (FF) and quantum mechanics (QM) calculations on the structures obtained from MD. The calculated degrees of stabilization (enthalpy gain) of various patterns of A-site ordering are not significant enough to overcome the accompanying entropy loss, supporting the random A-site distribution in La3/4Sr1/4MnO3. This approach combining MD and QM as well as the versatile FF developed in this study should be useful to investigate the structures and functions of magnetic tunnel junction devices involving mixed-valence manganites.
Microstructural Investigations of Hafnium Aluminum Oxide Films
Authors: Craciun Doina , Socol Gabriel , Axente Emanuel , Galca Aurelian-Catalin , Singh Rajiv , Craciun Valentin
Published: April 2011

The crystalline structure, composition, chemical bonding and thermal stability of HfO2-Al2O3 mixtures deposited on Si using a combinatorial pulsed laser deposition technique were investigated. After deposition some films were annealed at temperatures from 850 to 950 °C for 6 or 12 minutes. Grazing incidence x-ray diffraction investigations were performed to asses the crystallinity and thermal stability of the annealed layers. Measurements of the Al to Hf ratios were performed using energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. From simulations of the x-ray reflectivity and spectroscopic ellipsometry spectra the phase composition and thickness of the films was calculated and then the Al to Hf ratios. Al/Hf values of 1 and 8 were found to be necessary to block the crystallization of the films after anneals at 850 and 950 °C, respectively.
A New Technique to Measure and Deliver Low Levels of Water Vapor into Atmospheric and Vacuum Processes
Authors: Spiegelman Jeffrey
Published: April 2011

As material processes move to the nanoscale, fine control of process chemistries becomes critical. Atomic Layer Deposition, Chemical Vacuum Deposition, and Selective Gate Oxidation, as well as fabrication of Carbon Nanotubes all need water vapor from 50 sccm (40mg/min) to below 1 sccm ( 0.8 mg/min). Water vapor can be used for oxidation, cleaning and annealing of the nanoscale devices and thin films.

At 0.8 mg/min, flow control of liquid water with a mechanical pump is difficult without pulsation. Because water is liquid at room temperature, a standard thermal mass flow controller for gas cannot be used. Instead bubblers are used. However, they do not provide consistent or repeatable delivery. They are affected by gas and liquid temperature, relative pressures as well as gas velocity, liquid height, thermal droop, and contamination build up.

RASIRC® has developed a new pervaporation device that selectively allows water to diffuse into a carrier gas stream. The liquid water never directly contacts the carrier gas, allowing for independent liquid and gas pressures. A nonporous, hydrophilic membrane provides very rapid diffusion of water vapor into the carrier gas stream. This allows for precise amounts of water vapor to be added to the carrier gas based solely on relative vapor pressures.

To validate the performance of the device at very low flow rates into both atmosphere and vacuum process pressures, a heated humidity probe was used. This device was able to measure flow rates of 1 to 200 sccm in both vacuum and atmospheric pressure. The experimental results were compared with the expected theoretical dew point to validate the procedure. The humidity probe was used to measure both long term stability of the device and the instantaneous response time. Experimental results were compared to the expected time needed to change the water vapor concentration in the test volume.
Numerical Simulation of the Growth of ZnO Nanostructures in a Tube Furnace by Physical Vapour Deposition
Authors: Dalal Sharvari , Gallo Federico , Flewitt Andrew J , Milne William I
Published: April 2011

Zinc oxide is a versatile II-VI naturally n-type semiconductor that exhibits piezoelectric properties. By controlling the growth kinetics during a simple carbothermal reduction process a wide range of 1D nanostructures such as nanowires, nanobelts, and nanotetrapods have been synthesized. The driving force for the nanostructure growth is the Zn vapour supersaturation and supply rate which, if known, can be used to predict and explain the type of crystal structure that results. A model which attempts to determine the Zn vapour concentration as a function of position in the growth furnace is described. A numerical simulation package, COMSOL, was used to simultaneously model the effects of fluid flow, diffusion and heat transfer in a tube furnace made specifically for ZnO nanostructure growth. Parameters such as the temperature, pressure, and flow rate are used as inputs to the model to show the effect that each one has on the Zn concentration profile. An experimental parametric study of ZnO nanostructure growth was also conducted and compared to the model predictions for the Zn concentration in the tube.
Effect of Inactivated Dopants Clusters and Processing Parameters on Electrical Properties of Indium Tin Oxide on Plastic Substrates
Authors: Han Hauk , Lewis Jay , Alford Terry
Published: April 2011

Indium tin oxide (ITO) thin films were deposited on polyethylene napthalate (PEN) by rf sputtering using different rf powers (60 and 120 W) and at different substrate temperatures (room temperature and 100 °C). Rutherford backscattering spectrometry was used to determine the oxygen content in the films. Hall effect measurements were used to evaluate the electrical properties. In this paper the influence of defect structure, sputtering conditions, and the effect of annealing on the electrical and optical properties of ITO on PEN have been investigated. Electrical properties such as carrier concentration, mobility, and resistivity of the ITO films varied with rf power and substrate temperature. The electricalproperties of the films changed after annealing in air. This study also describes how the as-deposited amorphous ITO changes from amorphous to crystalline as a result of heat treatment, and investigates the effects of Sn defect clustering on electrical and optical properties of the ITO films.
High-mobility Nanocrystalline Indium Oxide TFTs with Silicon Nitride Gate Dielectric
Authors: Wang Kai , Vygranenko Yuriy , Nathan Arokia
Published: April 2011

A variety of oxide semiconductors such as ZnO, SnO2, In2O3 and other multi-component oxide compounds have been successfully used as channel materials in thin-film transistors (TFTs). Compared with amorphous silicon and organic semiconductor counterparts, the unique features of these materials include good performance, stability, low temperature processing, and transparency. In this work, we report on room-temperature deposition of indium oxide thin films by reactive ion beam assisted evaporation (IBAE) and their application to TFTs. By modifying the deposition parameters, nanocrystalline indium oxide (nc-In2O3) with an average grain size of 12 nm was achieved. TFTs with IBAE nc-In2O3 channel and silicon nitride gate dielectric deposited by conventional plasma-enhanced chemical vapour deposition (PECVD), were fabricated. The n-channel TFT has a threshold voltage of ∼2.5 V, a field-effect mobility of ∼32 cm2/Vs, along with an ON/OFF current ratio of ∼108, and a sub-threshold slope of 2.5 V/decade. The TFT reported here has one of the best performance characteristics in terms of device mobility, ON/OFF current ratio, and OFF current, using conventional, and large area foundry-compatible PECVD gate dielectrics. The device performance coupled with its low-temperature processing makes IBAE-derived nc-In2O3 TFT a promising candidate for active matrix flat panel displays.
Ion Implantation Through Thin Silicon Dioxide Layers for Si-based Solid-State Quantum Computer Device Development
Authors: McCallum Jeffrey , Dunn Michael L. , Gauja Eric
Published: April 2011

Ion implantation doping of Si through an SiO2 overlayer is of interest for fabrication of a range of devices on the pathway to development of a solid–state quantum computer (SSQC). The fabrication requirements of devices based on the Kane architecture typically involve implantation through a pre-existing thin device–quality thermal oxide at low fluences ∼1011 cm−2 and ion energies in the range 10 – 20 keV. Here we present results from a deep level transient spectroscopy studies of ion–implanted MOS capacitors in which interface–trap densities have been measured in as–grown and H–passivated thermal oxides and in ion implanted and rapid–thermally processed devices. For thin oxides of 5nm or less and low ion fluences we find that implantation does not significantly increase interface trap densities and somewhat surprisingly that it can even be beneficial when the interface trap density is abnormally high, (∼ 1 × 1011cm−2.eV−1) in the as-grown oxide.
Microstrcutural Evolution of SiC Fibre Embedded AA6061 Matrix Induced by Ultrasonic Consolidation
Authors: Zhu Z. , Wynne B.P , Ghassemieh Elaheh
Published: April 2011

Ultrasonic consolidation (UC) uses high frequency (20-40KHz) mechanical vibrations to produce a solid-state metallurgical bond (weld) between metal foils. UC as a novel layered manufacturing technique is used in this research to embed reinforcing members such as silicon carbide fibers into the aluminium alloy 6061's matrices. It is known that UC induce volume and surface effect in the material it is acting on. Both effects are employed in embedding active/passive elements in the metal matrix. Whilst the process and the two effects are used and identified at macro level, what is happening at micro level is unknown and hardly studied. In this research we are investigating the phenomena occurring in the microstructure of the parts during UC process to obtain better understanding about how and why the process works.

In this research, high-resolution electron backscatter diffraction is used to study the effects of the UC process on the evolution of microstructure in AA6061 with and without fibre elements.

The inverse pole figures (IPF), pole figures (PF) and the correlated misorientation angle distribution of the mentioned samples are obtained. The characteristics of the crystallographic orientation, the grain structure and the grain boundary are analysed to find the effect of ultrasonic vibration and embedding fibre on the microstructure and texture of the bond. The ultrasonic vibration will lead to exceptional refinement of grains to a micron level along the bond area and affect the crystallographic orientation. Additional plastic flow occurs around the fibre which leads to the fibre embedding.
Efficient High Power ns Pulsed Fiber Laser for Lidar and Laser Communications
Authors: Liu Jian
Published: April 2011

Research results on high energy/power ns pulsed fiber lasers are discussed in this paper. Modulation schemes for a seed laser in getting various optical waveforms, high power operation of fiber amplifiers, nonlinearity mitigation in high power fiber lasers, and trade-offs have been addressed. It shows experimentally that ns pulses can be achieved by direct modulation of a semiconductor seed laser and an energy level of sub-mJ were demonstrated. 23 % wall plug efficiency was achieved for a compact laser module.
Simplified Homodyne Detection for Linear FM Lidar
Authors: Adany Peter , Allen Chris , Hui Rongqing
Published: April 2011

A fiber based lidar system is developed which simplifies the processing of linear FM pulses by using a modulated local oscillator power in the coherent detector. Experiments were conducted on lidar systems with direct, heterodyne and simplified homodyne detection to compare receiver sensitivity. A field experiment using the homodyne system verified the sensitivity estimation on a building target at 370-m range.
Surface Modification of ZrO2 Nanoparticles as Functional Component in Optical Nanocomposite Devices
Authors: Tsedev Ninjbadgar , Garnweitner Georg
Published: April 2011

We have recently shown the successful synthesis of zirconia nanoparticles that can be optimized for use in volume phase holography by a post-functionalization surface treatment. Here, we present further investigations on the surface modification treatment with the aim of providing tools to tailor the nanoparticle compatibility to the photocurable organic matrix. Highly crystalline ZrO2 nanoparticles with a mean diameter of 5nm are synthesized in multigram yield through a one-pot solvothermal reaction of zirconium (IV) n-propoxide in benzyl alcohol. It is shown that the yield of the ZrO2 nanoparticles and stability of the nanoparticle dispersions are strongly dependent on the synthesis temperature. Post-synthetic surface modification of ZrO2 nanoparticles using several aliphatic ligands with different surface binding groups such as carboxylate (-COO−), amine (−NH2), phosphate (−PO4) and methoxysilane (−SiOCH3) was performed in order to compare the binding ability of these functional groups to the nanoparticle surface and therefore provide a new rational approach for nanoparticle stabilization with organic ligands.
Fabrication of Nano-Structured Gold Arrays by Guided Self-assembly for Plasmonics
Authors: Li Xiaoli V. , Milhano Clelia A. , Cole Robin M. , Bartlett Phil N. , Baumberg Jeremy J. , de Groot Cornelis H.
Published: April 2011

Gold inverse spherical nanoscale voids have been fabricated in linear arrays for directional plasmon measurements in the visible spectral range. We show that by KOH anisotropic etching in Si, we are able to make V-grooves in which latex spheres of the order of 500 nm self-assemble with largely defect-free cubic symmetry. Both single layer and multilayer assembly in a face-centered close-packed (FCC) lattice can be achieved by varying the width of the trenches. This template is subsequently used for electrodeposition of gold to create the inverse spherical nanovoids.
Structural Dynamics of a Single Photoreceptor Protein Molecule Monitored With Surface-Enhanced Raman Scattering Substrates
Authors: Singhal Kushagra , Bhatt Karthik , Kang Zhouyang , Hoff Wouter , Xie Aihua , Kalkan A. Kaan
Published: April 2011

Photoactive yellow protein (PYP) is a small cytosolic photoreceptor that actuates the negative phototactic response in its host organism Halorhodospira halophila. It has an optical absorption maximum at 446 nm (blue light). We report an initial study of the photocycle of PYP at the single molecule level using “high enhancement factor” surface-enhanced Raman scattering (SERS)-active nanostructures with 514 nm laser excitation. The SERS-active “nanometal-on-semiconductor” structures are prepared employing a redox technique on thin germanium films, coated on glass slides. Single molecule spectra are observed in terms of sudden appearance of discernable Raman peaks with spectral fluctuations. The single molecule spectra capture protonation, photo-isomerization, and H-bond breaking - the steps that are instrumental in the photocycle of PYP. This is indicative of single PYP molecules diffusing to high-enhancement-factor SERS sites, and undergoing photo-cycle under 514 nm excitation.
Molecular-level Manipulation Technology for Low-k Dielectrics Controlling the Physical and Chemical Structures toward 32nm-node BEOLs
Authors: Hayashi Yoshihiro
Published: April 2011

Low-k materials in advanced interconnect modules are required not only to lower the parasitic capacitances, but also to have mechanical stability with damage-less interfaces. By plasma-polymerization (PP) process using ring-type siloxane precursor, a new self-organized porous SiOCH film is developed with preserving the original hexagonal silica-backbone structure, thus so called as a molecular-pore-stack (MPS) SiOCH film. The hydrocarbon-rich MPS film has high endurance to the process damages. A density-modulated MPS film is obtained with reinforced interfaces by plasma co-polymerization (PcP) process using not only the ring-type but also linear-type siloxane. Furthermore, an ultimate full low-k module with low-k silica-amorphous-carbon composite (SACC) cap, instead of high-k SiCN, is also obtained simply by the one-step deposition scheme. The modulated PcP process and the sophisticated molecular design of the precursor siloxane provides scaled-down interconnect modules with good mechanical strength and excellent dielectric reliability at a low manufacturing cost, applicable for 45/32/22nm-nodes ULSIs.
UV Curing Effects of Low-k Materials under Reactive Conditions
Authors: Moore Darren , Waldfried Carlo , Sakthivel Palani , Escorcia Orlando
Published: April 2011

This work describes the effect of addition of O2 and NH3 to the N2 ambient used during the UV cure process of low-k materials. The effects of O2 give an acceleration of the cure process, resulting in increased film modulus and shrinkage. The use of NH3 resulted in a retardation of UV cure, explained by the higher absorption cross section of NH3 at the wavelengths used.
Extendibility Study of a PVD Cu Seed Process with Ar+ Rf-Plasma Enhanced Coverage for 45nm Interconnects
Authors: Simon Andrew H. , Bolom Tibor , Tang Teck Jung , Baker Brett , Peters Carsten , Rhoads Bryan , Flaitz Philip L. , Sankaran Sujatha , Grunow Stephan
Published: April 2011

We present the results of a systematic benchmarking study, using 45nm-groundrule structures, of a commercially-available ionized PVD Cu technology which employs an in-situ Ar+ radio-frequency (Rf) plasma capability for enhanced coverage, and compare its performance and extendibility against the same seedlayer process operated in conventional low-pressure mode. Studies of single-damascene lines and dual-damascene via structures indicate that the PVD Cu seedlayer with Rf-Plasma enhancement enables a reduction of the PVD Cu seed thickness on the order of 35%, based on studies of Cu voiding, via-yield degradation, and transmission-electron microscopy (TEM). These results illustrate the critical importance of the Rf-plasma resputter capability in extending the PVD Cu process to advanced groundrules at 45nm and beyond.
TVS Measurements of Metal Ions in Low-k Dielectrics: Effect of H2O Uptake
Authors: Ciofi Ivan , Tökei Zsolt , Mangraviti Giovanni , Beyer Gerald
Published: April 2011

Drift of metal ions in low-k dielectrics was investigated by Triangular Voltage Sweep (TVS) measurements on planar capacitors with different gate materials: Al, Ta, Ru, Ti, Cu, Pt and a-Si.
Plasma Modification Of Si-O-Si Bond Structure in Porous Sioch Films
Authors: Dultsev Fedor N , Urbanowicz Adam M , Baklanov Mikhail R
Published: April 2011

Plasma modification of SiOCH low-k films is analyzed by means of Molecular Mechanics. It is shown that the most probable mechanism of SiOCH modification in He plasma is removal of hydrogen atoms from CH3 groups. The change of Si–O–Si bond angles depends on the amount of the formed –CH2* (CHx) groups. During the followed exposure in NH3 plasma, NH2* radicals bind CHx groups with Si forming a –CH2– Si–O–Si–O–Si–O–Si– chain. The end of this chain gets bound to its beginning through NH2. This process is the reason of pore sealing.
Using a Barrier Layer to Inhibit Ti/Oxide Reaction to Reduce RC Delay and Improve Electromigration in Al-Cu/Ti/W Interconnect for High Power Analog and Mixed Signal Applications
Authors: Murphy William , Lee Tom C , Chapple-Sokol Jonathan , Delibac Daniel A , He Z. X. , Luce Stephen E , Mongeon Stephen A , Thomas David C , Vanslette Daniel S , Sullivan Timothy D
Published: April 2011

In this paper, we report a novel method to improve aluminum interconnect electromigration performance, reduce metal line sheet resistance (Rs) and reduce via contact resistance (Rc) in a minimum pitch design. We report the effects of bottom redundancy layers on electrical line and via resistance and upstream electromigration performance. We studied 4 metallization stacks: (I) Ti/TiN/AlCu/Ti/TiN, (II) Ti/TiN/Ti/AlCu/Ti/TiN (annealed at 400°C for 20 minutes), (III) a flash process/stack I, (IV) stack III with aluminum deposition temperature of 250°C. Aluminum deposition temperature in stacks I, II, and III are 200°C. Bottom Ti/TiN, AlCu, and Top Ti/TiN layers have the same thickness for all these stacks. Metal line Rs and via contact resistances (Rc) of stack IV are 5% and 10% lower, respectively, than stack I. Stack II metal line sheet resistance is 15% higher than stack I, which is attributed to Al consumption in the TiAl3 formation during 400°C/20minutes annealing. Electromigration performance is best with stack IV followed by III, II, then I.
Degradation of ZnO nanowire devices under the ambient condition
Authors: Kim Dong-Wook , Choi Soo-Han , Ji Hyun-Jin , Kim Sang Woo , Moon Seung Eon , Park So Jung , Kim Gyu-Tae
Published: April 2011

Field effect transistors(FETs) made of ZnO nanowires are very sensitive to the gas environment, so that the passivation can be a good way to get reliable nanowire FETs with longer lifetime and the better mobility. The studies on the passivation effects with the positive electron-beam resist was investigated by selectively covering the part of nanowire devices between the electrodes. Reproducible electrical characteristics were recorded, reflecting the stable electrical properties by the passivation which deters the degradation of a device. Considering the defect states of oxide nanowires dominate the charge states, the pre-state just before the passivation process will be crucial to understand the reproducible and controllable device characteristics of nanowire devices.
CMOS Compatible Synthesis of Carbon Nanotubes
Authors: Uchino Takashi , Bourdakos Konstantinos N. , Ayre Gregory N. , de Groot Cornelis H. , Ashburn Peter , Smith David C.
Published: April 2011

A technique to synthesize high-quality single walled carbon nanotubes (SWNTs) using chemical vapour deposition (CVD) on Ge Stranski-Krastanow dots has been developed. From transmission electron microscopy and Raman measurements, the grown carbon nanotubes (CNTs) are identified as SWNTs with diameters ranging from 1.6 to 2.1 nm. Extensive scanning electron microscopy and atomic force characterisation of the effect of each stage in the growth process is presented. Our hypothesis is that pre-treatment stages lead to the formation of Ge nanoparticles, which act as seeds for CNT growth. This technique demonstrates the ability to synthesize high-quality SWNTs without the need for a metal catalyst, using processes and equipment standard to a silicon foundry.
Synthesis and Properties of Carbon Nanotube Yarns and Textiles
Authors: Schauer Mark , Lashmore David , White Brian
Published: April 2011

The strength of macroscopic materials made of carbon nanotubes depends on the quality of the nanotubes produced, as well as various methods of post-treatment. The average diameter and length of the nanotubes can be controlled through the various parameters of a specially designed injector system, in conjunction with the CVD furnace. Large non-woven textiles and yarns of pure nanotubes are created, and then post-processed in various ways to obtain the desired products. In this way textiles over 2 square meters, and yarns of over a half kilometer have been produced with strengths unprecedented in pure carbon nanotube materials.
Immobilization of CNT on Bamboo Charcoal by TEOS Vapor
Authors: Zhu Jiangtao , Kwong Fung Luen , Ng Dickon Hang Leung
Published: April 2011

Carbon nanotubes (CNTs) are successfully immobilized on a bamboo charcoal by chemical vapor deposition of gaseous tetraethyl orthosilicate (TEOS). Electron microscopies, Raman spectroscopy and electron energy loss spectroscopy are used to characterize the sample. The CNTs found on the bamboo charcoal support were several microns long, and their diameters ranged from 50nm to 300nm. From the high resolution transmission electron microscopic analysis, we found that the CNTs were composed of ∼30 layers of graphitic carbon sheets. Amorphous droplets were also found at the tips of the CNTs. This suggested that the growth of the CNT was via a vapor-liquid-solid mechanism. The amorphous droplets contained calcium, silicon and oxygen. The calcium impurity was originated from the bamboo while the silicon impurity was supplied by the TEOS. CNTs partially filled with calcium silicate were also found. It was evident that calcium silicate had played a critical role in the formation of these CNTs.
Use of Saccharides as Solid-state Precursors for the Synthesis of Carbon Nanotubes
Authors: Kucukayan Gokce , Kayacan Serim , Baykal Beril , Bengu Erman
Published: April 2011

Saccharides, ranging from simple table sugar (sucrose) to lactulose were successfully used as solid-state precursors for the synthesis of multi-walled carbon nanotubes (MWCNT). Dehydrated saccharide residues mixed with catalyst powders were subjected to pyrolysis at high temperatures (up to 1300°C) under flowing Argon atmosphere. Pyrolysis products were investigated using TEM, SEM, Raman spectroscopy and EDS. Images taken using the S/TEM and bright field mode of TEM showed the presence of helical multi-walled carbon nanotube (H-MWCNT) and regular MWCNT formation. More than two or three catalyst particles were observed to be present inside the hollow core of some of the nanotubes synthesized, suggesting a high level of capillary activity inside the tubes during synthesis.
Measurement of Ultrafast Carrier Dynamics in Epitaxial Graphene
Authors: Dawlaty Jahan M. , Shivaraman Shriram , Chandrashekhar Mvs , Spencer Michael G. , Rana Farhan
Published: April 2011

Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An initial fast relaxation transient in the 70-120 fs range is followed by a slower relaxation process in the 0.4-1.7 ps range. The slower relaxation time is found to be inversely proportional to the degree of crystalline disorder in the graphene layers as measured by Raman spectroscopy. We relate the measured fast and slow time constants to carrier-carrier and carrier-phonon intraband and interband scattering processes in graphene.
Evaluation of the Stiffness of Carbon Nanotube Probe by Force Curve Measurements
Authors: Hirooka Motoyuki , Okai Makoto , Tanaka Hiroki , Sekino Satoshi
Published: April 2011

Buckling of arc discharge made multi-walled carbon nanotubes with various lengths was studied by alternating the length of a multi-walled nanotube by intermittent cutting. Buckling stresses were determined by measuring force-distance curves employing an atomic force microscope and the values were compared with those expected from the Euler's theoretical model. As the length of a nanotube was shortened, its buckling mode changed from elastic compressive bending with Young's modulus of 1.2TPa, to inelastic compressive fracture. The inelastic behavior observed for short nanotubes can be attributed to the buckling mechanism, in which ripple-like distortions develop along the nanotube sidewalls.
Preliminary Measurements of Selective Sensing of DMMP and NH3 Using CNTFET Array Based Gas Sensors Fabricated Using Metal Diversified Electrodes for Electronic Fingerprinting
Authors: Bondavalli Paolo , Legagneux Pierre , Pribat Didier
Published: April 2011

This paper deals with preliminary measurements for prove-of-concept of a Carbon Nanotubes Field Effect Transistors (CNTFETs) based sensor array which could improve dramatically gas selectivity. CNTFET based sensors exploit the extremely sensitive change of the Schottky barrier heights between Single Wall Carbon NanoTubes (SWCNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the bending and the height of the Schottky barrier at the contacts [1,2]. Using CNTFET array fabricated using SWCNT mat as channel, we have achieved a sort of electronic fingerprinting of different gases. Actually, we want to demonstrate that the change of the metal electrode work function strictly depends on the metal/gas interaction : CNTFET transfer characteristics will change specifically as a function of this interaction. In this study we have fabricated different CNTFETs using three metal contacts (Au, Pd, Mo) and exposed them to two gases, DMMP and NH3, which have the same “electron-withdrawing” behavior. The CNTFETs array has been exposed to 1ppm of DMMP and 10ppm NH3 and we have identified two electronic fingerprinting. The totality of our measures have been performed at ambient conditions.
Nanotube Potential Future in Nuclear Power
Authors: Popa-Simil Liviu
Published: April 2011

The nanotubes presents high potential of applications in nuclear power, integrating them both in advanced fuels developments nano-breeding and in nano-shielding. The carbon nanotubes may be successfully used to create fuel wires used in high temperature applications and near perfect burning generating new procedures in nuclear reactor waste management while reducing the waste by two orders of magnitude. The modified nanowire may hold various other materials as conductors and insulators being useful in direct conversion of the nuclear energy into electricity, by including in the center a sequence of high and low electron density conductors. As direct conversion structures they can handle all the required functions into a nuclear reactor or energy harvesting blanket to assure high power density, high efficiency and minimal waste. Another very challenging application is the usage of nanotube to channel low energy nuclear radiation and guide it, similar to the GHz wave-guides or to hundreds of THz optic fibers. The operation domain of the nanotubes is placed mainly in the domain of UV to X rays, being the role of composite structures or nanowire channeling to cover the gamma ray domain. The carbon nanotubes may become useful cold neutrons transport devices with directive capabilities as short bending or focusing. The theoretical approaches and simulations predicted these new application capabilities of nanowires for nuclear materials with exceptional properties.
Ionic Liquid Based CO2 Capturing Fuel Cell for Greenhouse Gas Reduction
Authors: V. Wolkin Michal , Stumpp Raphael , Littau Karl
Published: April 2011

Room-temperature ionic liquids are utilized in a new CO2 capturing fuel cell. The cell is aimed at the efficient and cost effective removal of CO2 emitted from transportation related sources. The CO2 is captured from the atmosphere and is later converted into carbon free synthetic fuel such as methanol. In this study we optimized the operating conditions and the cell electrolytes. With ionic liquids such as 1-Butyl-1-methylpyrrolidinium dicyanamide, the extraction efficiencies increased to ∼20% while simultaneously making the capture process more robust. The ionic liquid approach is also compared to existing aqueous electrochemical CO2 concentration previously proposed by NASA for aerospace applications but with much lower efficiencies.
Compact Modelling of Electrical, Mechanical and Thermal Behaviour for MEMS with SPICE
Authors: Frank Andreas , Zoellner J.-P. , Sarov Y. , Ivanov Tz. , Kuhnholz I. , Klett St. , Rangelow I. W. , Swiatkowski M. , Gotszalk T. , Nikolov N.
Published: April 2011

In this paper we present a novel method of nonlinear macro model of a cantilever for mixed domain simulation only with SPICE. Based on lumped elements of equivalent circuits a model is developed, which realizes a coupled electro-thermal-mechanical simulation including crosstalk effects. The model is verified with measurement and helps to class and solve crosstalk. With SPICE as electrical circuit simulator the cantilever array could be simulate in conjunction with the excitations and analysis electronics more detailed like the system level models and faster like FEM-simulation.
Dielectric-barrier discharge plasma source and its application to synthesis of diamond like carbon films
Authors: Wang Xinpeng , Tang Xiaoliang , Feng Peter Xianping
Published: April 2011

Dielectric barrier discharge plasma sources have been studied and used for syntheses of diamond like carbon thin films. The plasma electrical properties under different gases concentrations and pressures were diagnosed. Based on the results of characterizations, dielectric barrier discharge plasma at different methane-hydrogen-argon gas ratios was used to synthesize large area of diamond like carbon films. Experimental data indicate that only at argon concentration equal to or less than 75% diamond like carbon film fabrication could be accomplished, which has been confirmed based on the Raman spectra and their hardness measurements, whereas high argon content during deposition would result in graphite type of thin films.