bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Beam Epitaxial Growth, Fabrication, and Characterization of High Efficiency InGaN/GaN Dot-in-a-Wire White Light Emitting Diodes on Si(111)
Authors: Nguyen Hieu P. , Zhang Shaofei , Cui Kai , Han Xueguang , Mi Zetian
Published: April 2011

We report on the molecular beam epitaxial growth, fabrication, and characterization of InGaN/GaN dot-in-a-wire white light emitting diodes (LEDs) grown on Si(111). By varying the In compositions in the dot layers, we have demonstrated strong white light emission. The dot-in-a-wire LEDs exhibit a relatively high internal quantum efficiency of ~ 36.7% and virtually zero efficiency droop for current densities up to ~ 200 A/cm2 at room temperature, which are attributed to the superior 3-dimensional carrier confinement provided by the dots and to the use of nearly defect and strain-free GaN nanowires.
Thick GaN Films Grown on Patterned Sapphire Substrates
Authors: Voronenkov Vladislav , Gorbunov Ruslan , Tsyuk Alexander , Latyshev Philippe , Lelikov Yuriy , Rebane Yuriy , Zubrilov Andrey , Bochkareva Natalia , Shreter Yuriy
Published: April 2011

GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower bowing and are less susceptible to fracture then ones, grown on unpatterned substrates under the same growth conditions. Numerical calculation shows good agreement with experiments. Such substrates could be an alternative to expensive GaN wafers sliced from GaN boules.
Growth Behavior of M-Plane ZnO Epilayer on (100) LiGaO2 by Chemical Vapor Deposition
Authors: Yu Jun-Yi , Huang Teng-Hsing , Chang Liuwen , Chou Mitch M. C. , Gan Dershin
Published: April 2011

The growth behavior of ZnO epilayer on (100) LiGaO2 (LGO) substrates by chemical vapor deposition was studied. At 650oC or above, (10 0)-oriented ZnO epilayers were obtained. The epitaxial deposition of ZnO is, however, in competition with the volatilization of Li from the substrate surface. A discrete layer composed of ZnGa2O4 spinel nanocrystals is formed on the substrate surface. The (10 0)-oriented ZnO grains, which nucleate epitaxially on the LGO substrate, have thus to grow laterally over the spinel nanocrystals to form a continuous epilayer.
Characteristics of 4H-SiC RF MOSFETs on a Semi-Insualting Substrate
Authors: Wu Tian-Li , Huang Chih-Fang , Cheng Chun-Hu
Published: April 2011

This study has provided considerable insight into the impact of device down scaling on the characteristics of RF devices. This type of RF devices, featuring a thin p-layer based on a semi-insulating substrate, is free from the unwanted parasitic effects resulting from traditional conducting substrates. We fabricated 4H-SiC RF MOSFETs with fT/fMAX of 0.7/1.5 GHz and, in so doing, identified the key issues associated with short channel effects, influencing device mobility and the RF characteristics of RF MOSFETs on a semi-insulating substrate.
Improved Model for Nanowire BioFETs on SOI Operating in Electrolyte
Authors: Denhoff Mike , Landheer D.
Published: April 2011

Using a readily available finite element code (Freefem++) the performance of nanowire (NW) field-effect transistors used as bio-affinity sensors has been simulated in 2D using realistic models for the semiconductor, gate insulator, Stern layer, and a layer of charged biomolecules (DNA) in electrolyte. The simulations are compared to those published previously for cylindrical NWs suspended in electrolyte. Calculations for Si NWs with circular and trapezoidal cross-section on SOI substrates are compared to assess the relative sensitivities for the devices made during the top-down (cylindrical) and bottom-up (trapezoidal) approach to device fabrication. It is shown that the performance of the trapezoidal structures could be superior, even when compared to cylinders with smaller dimensions. The simulations are compared to recent pH measurements with trapezoidal nanowires and pave the way to improved simulations for DNA and protein attachment.
Corrosion Properties of DLC-Coated Stainless Steel in Hanks Solution for Biomedical Applications
Authors: Kek Merl Darja , Panjan Peter , Čekada Miha , Kahn Markus , Waldhauser Wolfgang
Published: April 2011

Three-types of diamond-like carbon (DLC) coatings were prepared by employment of an anode layer source on stainless steel substrates (316L). The DLC films show an amorphous structure and their thickness ranges between 1.1 to 1.5 μm. An interlayer of sputtered Cr was used as buffer between the DLC and stainless steel substrate in order to enhance adhesion. The corrosion properties of DLC-coated stainless steel in Hank's solution (pH=7.2) were studied using electrochemical methods. Results show that all DLC-coated substrates have up to one order of magnitude better corrosion resistance than a bare substrate.
Growth and Morphology of Eumelanin Thin Films - A Future Bioelectronic Material
Authors: Wünsche Julia , Rosei Federico , Graeff Carlos F.O. , Santato Clara
Published: April 2011

We present a study on the thin film morphology and the optical properties of eumelanin resulting from different synthesis routes: the oxidation of tyrosine with hydrogen peroxide, the auto-oxidation of dihydroxyphenylanaline in water and its auto-oxidation in dimethyl sulfoxid. Atomic Force Microscopy images indicate that the presence of holes and particles depends on the eumelanin synthesis route and the substrate employed. Smooth films with very few defects could be obtained with eumelanin synthesized in dimethyl sulfoxide deposited on glass substrates. Our study shows that all eumelanin preparations are comparable in terms of thin film morphology on the submicrometer scale and UV-visible transmission properties.
An Electronic Nose for the Detection of Carbonyl Species
Authors: Deore Bhavana , Diaz-Quijada Gerardo A. , Wayner Danial D.M. , Stewart Duncan , Won D. , Waldron P.
Published: April 2011

Conjugated polymers are an important class of materials due to their luminescent and electrical properties which result from electronic charge delocalization. Consequently, these polymers provide a suitable platform for new sensors since electronic and conformational changes that arise from the interaction with analytes translate into measurable changes in electrical conductivity or luminescence. The main advantage of this platform is based on the ability to partially tune the response of the sensor by changing the chemical structure of the polymer. The present work illustrates proof-of-concept chemical sensors that incorporate a molecular recognition site for the detection of common indoor air polluting carbonyl species such as aldehydes and ketones. Emphasis is placed on the detection of formaldehyde which poses major concerns in Indoor Air Quality (IAQ). By taking advantage of the differential response of various polymers towards analytes in question, sensor elements can be implemented in an array format to give an electronic nose
Photonic Crystal Based Biosensor with Built-In Nanofluidics Channels
Authors: Nagare Gajanan , Mukherji Soumyo , Mitra Sushanta K.
Published: April 2011

A photonic crystal (PC-s) is essentially made of a periodic pattern of high and low refractive index materials on optically transparent substrate. Such a pattern acts as a waveguide as well as a grating layer and resonate the PC at a particular wavelength. The resonance wavelength depends on grating period, refractive indices of materials, grating thickness, and geometry of structure. A small change in the dimensions of the PC results in undesired behavior of the PC. Therefore, it is essential to fabricate such a device with minimal fabrication processes to minimize fabrication inaccuracy. In this paper, a systematic approach for the development of PC for biosensing application has been discussed. A novel approach has been proposed for the transportation of biomolecules using a built-in nanofluidic channel.
Electrochemical Studies of Morpholino-DNA Surface Hybridization
Authors: O'Connor Robert , Tercero Napoleon , Qiao Wanqiong , Levicky Rastislav
Published: April 2011

Surface hybridization, in which nucleic acids from solution bind to complementary "probe" strands immobilized on a solid support, is widely used to analyze composition of nucleic acid mixtures. Most often, detection is accomplished with fluorescent techniques whose sensitivity can be extended down to individual molecules. Applications, however, benefit as much if not more from convenience, accuracy, and affordability of the diagnostic test. By eliminating the need for fluorescent labeling and more complex sample workup, label-free electrochemical assays have significant advantages provided transduction remains sufficiently sensitive for applications. To this end, we have been exploring morpholinos, which are uncharged DNA analogues, as the immobilized probe species in surface hybridization assays based on measurement of interfacial capacitance. Through comparison of experimental trends with those predicted from basic physical models, the origins of diagnostic contrast in capacitive sensing are reviewed for assays based on morpholino as well as on DNA probes.
Tuning Fructosyl Peptidyl Oxidase into Dehydrogenase and Its Application for the Construction of an Enzyme Electrode
Authors: Ferri Stefano , Nibe Eri , Miyamoto Yusuke , Kim Seungsu , Tsugawa Wakako , Sode Koji
Published: April 2011

Fructosyl valyl-histidine, which is released from protease digestion of the major diabetes indicator HbA1c, is recognized as a target molecule for HbA1c sensors. The flavoenzyme fructosyl amino acid oxidase (FAOD) is an enzyme catalyzing the oxidative deglycation of fructosyl amino acids, with those also possessing high activity towards fructosyl dipeptides being referred to as fructosyl peptidyl oxidases (FPOXs). The high oxygen reactivity of FAODs and FPOXs limits their potential utility in amperometric enzyme sensors employing artificial electron mediators. We successfully modified the proton relay system of Pichia N1-1 FAOD, significantly decreasing its catalytic ability to employ oxygen as the electron acceptor, while having little effect on the dye-mediated dehydrogenase activity employing artificial electron acceptors instead of oxygen. We expect that similar engineering of a recently discovered FPOX will produce an enzyme that is ideally suited for HbA1c sensing.
Microsensor Arrays for Determination of Biomarkers of Oxidative Stress
Authors: Hepel Maria , Stobiecka Magdalena
Published: April 2011

Microsensors for the detection of biomarkers of oxidative stress have been investigated in view of the need for a wide scale testing of children for the development of autism which is partly associated with inadequate defenses against reactive oxidant species and radicals. Several sensor types for glutathione, which is the main peptide participating in the redox-potential homeostasis in eukaryotic cells, have been designed including anti-glutathione monoclonal antibody based sensor, molecularly-templated poly(orthophenylenediamine) sensors, and transition metal complex electrocatalyst based sensors. The microsensor arrays accommodating glutathione sensors with different responses to the matrix background and interferences have been constructed. For the analysis of sensor array outputs, specially designed artificial neural networks have been employed.
Fluctuations in Electronic Properties of MOS Interface in Nanoscale MOSFETs
Authors: Tsuchiya Toshiaki , Morimura Yuta , Mori Yuki
Published: April 2011

Fluctuations in the number, energy level, and carrier capture rate of Si/SiO2 interface traps in small-gate-area metal-oxide-semiconductor field-effect transistors (MOSFETs) containing only a few interface traps have been directly observed. This observation is based on an understanding of charge pumping phenomena and a newly observed phenomenon of on(off)-time-dependent charge pumping characteristics in their rising (falling) portion. It is directly shown from experimental results that the fluctuation in the number of interface traps contained in an individual MOSFET is fairly large, and that there are various interface traps with individual discrete energy levels and carrier capture rates. These fluctuations may have an impact on the variation in device performance of future digital metal-insulator-semiconductor (MIS) devices.
Electron States in MOS Systems
Authors: Engström Olof
Published: April 2011

The properties of charge carrier traps in the oxide bulk, at high-k/silicon transition regions, at the silicon interface and as dipoles are discussed from physical and electrical perspectives. In order to elucidate the charging properties of oxide traps the statistical mechanics for occupation is derived based on a constant pressure ensemble and used to interpret the influence of negative-U states. For the transition region close to the silicon interface, the existence of unstable traps in the shift of energy band between SiO2 and HfO2 with continuous modification is pointed out. The physical background for electrical measurements on interface states is examined and, finally, dipoles constituted by traps in high-k dielectrics for regulating threshold voltage of MOS transistors are considered.
Impact of Silicon Nitride Gate Dielectric Composition on the Stability of Low Temperature Nanocrystalline Silicon Thin Film Transistors
Authors: Esmaeili-Rad Mohammad , Chaji Gholamreza , Li Flora , Moradi Maryam , Sazonov Andrei , Nathan Arokia
Published: April 2011

We report on the stability of nanocrystalline silicon (nc-Si) bottom gate (BG) thin film transistors (TFTs) with various compositions ([N]/[Si]) of hydrogenated amorphous silicon nitride (a-SiNx:H) gate dielectric, formed at 280ºC. The shift in threshold voltage (ΔVT) is larger for gate dielectrics with lower [N]/[Si] content. For example, after 5 hours of stressing at 15 V, the ΔVT is 0.3 V, 1 V, and 12.4 V for [N]/[Si] of 1.3, 1.2, and 1, respectively. Relaxation tests on the stressed TFTs show that the charge trapping in the gate dielectric is the primary instability mechanism in nc-Si BG TFTs.
Development of a Fast Technique for Characterizing Interface States
Authors: Lin Lin , Ji Zhigang , Zhang J. , Zhang Weidong
Published: April 2011

Characterizing interface states is an important task for test engineers. The existing techniques typically have a measurement time in the order of seconds. Recent results, however, show that degradation can recover substantially within seconds and there is a need for improving the speed for measuring interface states. The central task of this work is to reduce the time for measuring interface states to the order of microseconds, so that the recovery during measurement can be minimized. An analysis of the existing techniques ruled out the popular techniques, such as conductance, various capacitance-voltage methods and the subthreshold swing, since they all require a gate voltage ramp that must be slow enough to maintain thermal equilibrium with interface states. Although conventional charge pumping (CCP) does not require such equilibrium, the DC recombination current used limits the speed. By replacing the DC current with transient currents, we will show that interface states can be extracted from a single pulse applied to the gate, allowing the measurement time being reduced to the order of microseconds. The results are calibrated against those from the well-established technique and accuracy in the order of 1010 cm-2 is achieved.
Impact of Twofold Coordinated Nitrogen on the Generation of Deep-Level Hole Traps under Negative-Bias Temperature Stressing
Authors: Gu Chenjie , Ang Diing Shenp , Teo Zhiqiang
Published: April 2011

In this paper, we discuss the generation of deep-level hole traps (DLHTs) during negative-bias temperature stressing. Because of their ability to trap positive charges for a long time, it is imperative to gain a sound understanding on the nature of the DLHT, especially in relation to nitrogen, which has been incorporated in increasing dose into the SiO2 gate oxide to solve boron penetration and gate tunneling leakage issues. Experimental evidence showing a correlation between the generation of DLHTs and nitrogen is first presented. This is followed by a discussion on the role nitrogen plays in influencing the generation of DLHT via first-principles simulation. We focus on the impact of a neighboring nitrogen atom on the structural and electronic properties of the oxygen-vacancy defect (VO), which is a major precursor for hole traps in the SiO2. Finally the charge transition levels (CTL) are discussed, which give us a more comprehensive understanding of DLHT.
Plasma-Assisted Atomic Layer Deposition of Low Temperature SiO2
Authors: Dingemans Gijs , Van Helvoirt Cristian , Van de Sanden M.C.M. , Kessels W. M.
Published: April 2011

Atomic layer deposition (ALD) was used to deposit SiO2 films in the temperature range of 50-400 oC. H2Si[N(C2H5)2]2 and an O2 plasma were used as Si precursor and oxidant, respectively. The growth process was characterized in detail, using various in situ diagnostics. Ultrashort precursor doses (~50 ms) were found to be sufficient to reach self-limiting ALD growth with a growth-per-cycle of ~1 Aå. The films exhibited a refractive index of 1.46 ± 0.02, a mass density of 2.0 ± 0.1 g/cm3, and an O/Si ratio of 2.1 ± 0.1, virtually independent of the substrate temperature. The results therefore demonstrate an efficient ALD process for the conformal and uniform deposition of SiO2 at low substrate temperatures. Also the surface chemistry during the plasma ALD process and surface passivation performance of the ALD SiO2 films on crystalline silicon surfaces are briefly addressed.
Nitric Acid Oxidation Method to Form a Gate Oxide Layer in Sub-Micrometer TFT
Authors: Matsumoto Taketoshi , Kubota Yasushi , Imai Shigeki , Kobayashi Hikaru
Published: April 2011

We have succeeded in fabrication of sub-micrometer TFT which can be operated at 1.5 V, having stack gate oxide structure formed by the nitric acid oxidation of Si (NAOS) method. The ultrathin NAOS SiO2 layer possesses a low leakage current density, and consequently, the gate oxide layer afterward deposited by the CVD method can be made as thin as 20 nm. Because of the thin gate oxide, miniaturization of TFT with the 0.6 µm gate length is achieved. The operation voltage of the TFTs can be set at as low as 1.5 V because of the low threshold voltages (i.e., −0.5 V for P-ch TFT and 0.5 V for N-ch TFT). The sub-threshold swing value is ~80 mV/decade and the on/off ratio is ~109 for both the P-ch and N-ch TFTs. The channel mobility is ~100 cm2/V•s for the P-ch TFT and ~200 cm2/V•s for the N-ch TFT.
Effects of Deposition Method of PECVD Silicon Nitride as MIM Capacitor Dielectric for GaAs HBT Technology
Authors: Yota Jiro
Published: April 2011

Thin silicon nitride (Si3N4) films deposited using plasma-enhanced chemical deposition (PECVD) method have been used as metal-insulator-metal (MIM) capacitor dielectric for GaAs hetero-junction bipolar transistor (HBT) technology. The characteristics of the films, which were deposited at 300oC, were found to be dependent on how the PECVD film was deposited. A silicon nitride film deposited as a multi-layer-layer film has different properties compared to a film deposited under the same processing conditions as a single layer film. When used as MIM capacitor dielectric, the multi-layer Si3N4 film is shown to have significantly superior and higher dielectric breakdown voltage and lower leakage current characteristics, as compared to the single layer film, while the capacitance density is found to be similar. Additionally, the multi-layer Si3N4 film is shown to have lower compressive stress and lower refractive index, indicating that the characteristics of the film are influenced by the additional interfaces present in a multi-layer film.
Low Temperature Processing of Si-Based Dielectric Thin Films
Authors: Joshi Pooran , Voutsas A. Tolis , Hartzell John
Published: April 2011

Low temperature processing of dielectric thin films is critical to realize high performance TFTs, solar cells, and sensors integrated on glass or plastic substrates. The plasma based deposition techniques have successfully met the dielectric performance requirements at process temperatures above 300 °C. However, the dielectric quality and reliability degrade severely at lower process temperatures indicating that the substrate surface reaction kinetics strongly dictate the thin film growth and properties. In the present work, we report on the low temperature processing (100-300 °C) of Si-based dielectric films by high-density PECVD technique which offers significant process and thin film property control. The microstructure and optical properties of the thin films, and the bulk and interfacial electrical quality and reliability of the MIS capacitors and TFTs as a function of process temperature are discussed in this report. The observed thin film and device performances at a low processing temperature of 100 °C show promise for low temperature electronic applications.
Physics-Based Hot-Carrier Degradation Modeling
Authors: Tyaginov Stanislav E. , Starkov Ivan , Enichlmair Hubert , Park Jong Mun , Jungemann Christoph , Grasser Tibor
Published: April 2011

We present a thorough analysis of physics-based hot-carrier degradation (HCD) models. We discuss the main features of HCD such as its strong localization at the drain side of the device, the weakening of the degradation at higher temperatures, and the change of the worst-case condition in small devices. The first feature is related to "hot" carriers, while the second is controlled by the fraction of "colder" particles. The latter feature is related to the change of the silicon-hydrogen bond-breakage mechanism from the single- to multiple-carrier process. All these findings suggest that the interface state creation process is controlled by the manner how the carriers are distributed over energy, that is, by the carrier energy distribution function. We distinguish between three main aspects of the physical picture behind hot-carrier degradation: carrier transport, microscopic mechanisms of defect creation and simulation of degraded devices. Therefore, we analyze and classify the existing HCD models in this context. Finally we present our hot-carrier degradation model based on a thorough evaluation of this distribution function by means of full-band Monte-Carlo device simulator. Our approach tries to address the whole hierarchy of physical phenomena in order to capture all the essential aspects of hot-carrier degradation.
Charge Trapping and Reliability Properties of MONOS Memory with High-k Blocking Layer
Authors: Yasuda Naoki , Fujii Shosuke , Fujiki Jun , Kusai Haruka
Published: April 2011

Carrier trapping and reliability characteristics during the cycling operation of metal-oxide-nitride-oxide-semiconductor (MONOS) devices with a high-k blocking layer (Al2O3) have been studied by measuring the injected charge during programming and erasing (P/E). The evaluated charge centroid during P/E indicates that the traps near the SiN/Al2O3 interface are filled at high electric field, while bulk traps in the SiN layer are also available at low electric field. The degradation of MONOS devices in cycling operation is found to be strongly correlated with injected charge during erasing. It is indispensable to suppress hole injection, as well as lowering the electric field to improve endurance of MONOS devices. The discussion of this paper also extends to the structure of the charge trapping layer to improve both cycling endurance and retention simultaneously. Finally, we report that a high-k blocking layer has significant impact on data readout and programming characteristics through its transient dielectric properties.
Dynamic Negative Bias Stress Instability Effects in Hafnium Silicon Oxynitride and Silicon Dioxide
Authors: Mee Jesse , Devine Roderick , Hjalmarson Harold , Kambour Ken
Published: April 2011

Negative bias temperature instability (NBTI) is an issue of critical importance as the space electronics industry evolves because it may dominate the reliability lifetime of space based assets. Understanding its physical origin is therefore essential in determining how best to search for methods of mitigation. It has been suggested ¬that the magnitude of the effect is strongly dependent on circuit operation conditions (static or dynamic modes). In the present work, we examine the time constants related to the charging and recovery of trapped charged induced by NBTI in HfSiON and SiO2 gate dielectric devices at room temperature.
High-k Integration and Interface Engineering for III-V MOSFETs
Authors: Oh H. J. , Sumarlina A. B. , Lee Sungjoo
Published: April 2011

We report the comprehensive study of performance enhancement of InGaAs n-MOSFET by plasma PH3 passivation. The calibrated plasma PH3 passivation of the InGaAs surface before CVD high-k dielectric deposition significantly improves interface quality, resulting in suppressed frequency dispersion in C-V, increase in drive-current with high electron mobility, and excellent thermal stability.
VT Stability Of High-K/Metal Gate Stacks with Device Scaling in 30nm FDSOI Technology
Authors: Garros Xavier , Brunet Laurent , Cassé Mikael , Weber Olivier , Andrieu Francois , Lafond Dominique , Gaumer Clément , Reimbold Gilles , Boulanger Fabien
Published: April 2011

The paper investigates the stability of the transistor threshold voltage VT with scaling in 30nm High-K/Metal Gate technology. For HfO2 and HfZrO oxides, large VT instability, up to 230mV, is seen when the device width (W) is scaled down to 80nm. It is explained by undesirable lateral oxygen diffusion through the spacers, which mainly modifies the metal workfunction in narrow transistors. HfSiO(N) oxides exhibit a much better immunity to this effect, attributed to a different crystallinity of the HK layer. Moreover, VT stability is not modified by Aluminum incorporation in the gate stack but can significantly be degraded by Lanthanum doping.
Universal Set/Reset Characteristics of Metal-Oxide Resistance Switching Memories
Authors: Ielmini Daniele
Published: April 2011

Resistance switching occurs in metal oxides after dielectric breakdown, as a result of localized thermally-activated ion migration and chemical reduction/oxidation. These phenomena form the fundamental basis for the resistive switching memory (RRAM), which is a novel memory device with high scaling potential for future non-volatile memories. The device is programmed/erased by the set/reset operations, consisting of the electrically-induced formation and dissolution of a conductive filament (CF) through the metal oxide layer. Understanding and modeling the set and reset processes is essential for developing device simulation tools and predicting the scalability and reliability of RRAM. This work studies set/reset characteristics for unipolar/bipolar RRAM devices. It is shown that the cell resistance after set and the reset current are universal functions of the compliance current, that is the maximum current flowing during the set operation for the formation of the CF. The universal reset characteristic is described in terms of a universal reset voltage, resulting from a weak dependence of the dissolution temperature on material parameters. Finally, the reliability of RRAM is reviewed focussing on data retention and discussing possible methods to improve resistance stability for non-volatile applications.
Electrical Characteristics Analysis at "Oxide Flat-Band Voltage" for Al-SiO2-Si Capacitor
Authors: Lu Han-Wei , Chen Tzu-Yu , Hwu Jenn-Gwo
Published: April 2011

In this paper, a new noun named "oxide flat-band voltage" is proposed meaningfully and further electrical characteristics study focused on non-uniformity in MOS capacitor will be demonstrated. Based on the rectangular barrier approximation, the slope of the ln[Jg@Vox,fb] versus oxide thickness plot of -12.18 is much closer to the theoretical slope of -12.42 than the slope of the ln[Jg@Vfb] versus oxide thickness plot of -11.09. It is because that there are some negative charges existing in the SiO2 dielectrics during the film-grown anodization system resulting in the non-uniformity phenomenon. Furthermore, various device areas of MOS capacitor were designed to do an advanced non-uniformity study. Both in the analysis of differential J-V curves and the slope of natural log of gate current density versus oxide thickness plot, it indicates evidently and identically that the larger the gate electrode area, the worse uniform the dielectric is.
Novel Hardmask for Sub-20nm Copper/Low K Backend Dual Damascene Integration
Authors: Xia Li-Qun , Cui Zhenjiang , Balseanu Mihaela , Nguyen Victor , Zhou Kevin , Pender Jeremiah , Naik Mehul
Published: April 2011

A new boron-based hardmask material was developed using a conventional CVD approach to address the integration challenges associated with the use of metal hardmask for low k dielectric patterning. Its low and tunable stress eliminates any patterning concerns due to line bending for device nodes below 20nm. Defectivity is also reduced because by-products from its F-based etch (BFx) are volatile unlike TiFx based defects, which dramatically widens the manufacturing process window. Extensive study concludes that boron content can be optimized to achieve good etch selectivity to the porous low k oxide. Preliminary electrical test using 45nm node 2-metal level structure showed good yield and 9% RC reduction compared to the conventional tri-layer integration scheme
Process Challenges for Integration of Copper Interconnects with Low-k Dielectrics
Authors: Gambino Jeff
Published: April 2011

Copper interconnects have gained wide acceptance in the microelectronics industry due to improved resistivity and reliability compared to Al interconnects. Initially SiO2 was used as the interlevel dielectric. To reduce interconnect capacitance, C-doped SiO2 or SiCOH was introduced at the 90 nm node, and porous SiCOH was introduced at the 45 nm node, to achieve a dielectric constant of 2.5 or less. However, there are many process problems with the integration of Cu interconnects and porous low-k dielectrics, including patterning, liner coverage, chemical mechanical polishing (CMP), and packaging. In this paper, some of the key integration challenges are discussed.
Patterning with Amorphous Carbon Thin Films
Authors: Antonelli George A. , Reddy Sirish , Subramonium Pramod , Henri Jon , Sims Jim , O'loughlin Jennifer , Shamma Nader , Schlosser Don , Mountsier Tom , Guo Wei , Sawin Herb
Published: April 2011

Amorphous carbon hard mask films grown with plasma enhanced chemical vapor deposition are an enabling technology for advanced front-end-of-line patterning technologies. These films must have a low etch rate and be weakly roughened in dielectric etch chemistries, high transparency at lithography alignment wavelengths, and the mechanical properties to mitigate elastic instabilities such as line bending. The deposition process affects all of these parameters through the resulting structure and composition. Highly graphitic films deposited at 550°C are common; however, other process spaces relying on ion bombardment rather than temperature can create less graphitic films with improved film properties like transparency, hardness, and etch selectivity.
Recent Findings in Electrical Behavior of CMOS High-K Dielectric/Metal Gate Stacks
Authors: Ghibaudo Gerard , Coignus Jean , Charbonnier Mathieu , Mitard Jerome , Leroux Charles , Garros Xavier , Clerc Raphael , Reimbold Gilles
Published: April 2011

We first review the kinetics of the trapping/detrapping process involved in hysteresis phenomena of HfO2 films on a large temperature range (20K-500K). We show that, up to 400K, trapping and detrapping processes are temperature independent after correction of threshold voltage variation with temperature. In most cases, the capture and emission into or from available traps are mainly controlled by tunneling. Then, we address the variations of the effective metal work function and its relation with the different fabrication processes. Based on C-V and internal photoemission measurements, we show the existence of an interfacial voltage drop (i.e. dipole) at the high-k SiO2 interface, as well as of variations in metal work function with metal gate process. Finally, we present a complete study of the transport mechanisms throughout the SiO2/HfO2 gate stacks combining C-V, I-V and Transmission Electron Microscopy measurements, on several nMOS transistors with different interfacial layer and HfO2 thicknesses, over a large temperature range (80K to 400K).
Physical and Electrical Effects of the Dep-Anneal-Dep-Anneal (DADA) Process for HfO2 in High K/Metal Gate Stacks
Authors: Clark Robert D. , Aoyama Shintaro , Consiglio Steve , Nakamura Genji , Leusink Gert
Published: April 2011

In this work we present physical and electrical characterization of HfO2 films deposited using the Dep-Anneal-Dep-Anneal (DADA) deposition scheme. Electrical results from MOSCAP devices fabricated using a low temperature (Gate Last-like) integration flow are presented. In addition we report detailed physical analyses of the films and changes in the films versus as-deposited ALD HfO2 and films undergoing a single post-deposition anneal and show the correlation between observed physical changes in the film and electrical results. Observed physical changes using HR-RBS, HR-TEM, SIMS, XPS and XRR include crystallization, densification, Si intermixing, reduction of in-film carbon and improved etch resistance leading to improved leakage vs. EOT and electrical non-uniformity. Dependence of these changes on the underlying interface layer (e.g. SiO2 vs SiON) is also described.
Global and Local Stress Characterization of SiN/Si(100) Wafers Using Optical Surface Profilometer and Multiwavelength Raman Spectroscopy
Authors: Yoo Woo Sik , Kajiwara Junya , Ueda Takeshi , Ishigaki Toshikazu , Kang Kitaek
Published: April 2011

Thin SiN films with various stress levels, from tensile +1.7 GPa to compressive -3.5 GPa, (as estimated by average curvature after SiN film deposition using Stoney's equation) were deposited on blanket Si(100) wafers by plasma enhanced chemical vapor deposition (PECVD). Global and local distortion and stress of SiN/Si(100) wafers were characterized using an optical surface profilometer and multiwavelength Raman spectroscopy. While wafers with tensile stress and compressive SiN films showed significant changes in wafer bowing (direction and curvature), negligible changes in Raman shift in the Si below the SiN film of all wafers were observed, as indicated by applying various excitation wavelengths. Periodic Raman shift fluctuations were observed from all SiN/Si(100) wafers, suggesting a self stress relaxation mechanism at the lattice level. The importance of global (wafer level), local (wafer level) and lattice level stress characterization and its contribution to proper understanding of the mechanisms involved in wafer bowing and stress build up, is discussed.
Mechanisms of Difficulty to Correlate the Leakage Current of High-k Capacitor Structures with Defect States Detected Spectroscopically by the Thermally Stimulated Current Technique
Authors: Lau Wai S.
Published: April 2011

Historically, it has been difficult to correlate the leakage current of capacitor structures involving high-k dielectric materials and defect states detected spectroscopically by the thermally stimulated current (TSC) technique. Four mechanisms are proposed and solutions are explained with tantalum oxide as an example. One of the mechanisms is the limitation of the TSC technique itself because of the presence of a parasitic current due to the bias voltage used. This can be solved by migrating to more advanced versions of TSC like zero-bias TSC.
Reliability Properties and Current Conduction Mechanisms of HfO2 MIS Capacitor with Dual Plasma Treatment
Authors: Chang Kow-Ming , Chang Ting-Chia , Chen Shou-Hsien , Deng I-Chung
Published: April 2011

The incorporation of nitrogen in HfO2 gate dielectrics has been reported to be beneficial for electrical performance. The improvement in the electrical characteristics of HfO2 thin film with plasma nitridation process or plasma fluorination process has also been examined. In this study, dual plasma, CF4 pre-treatment and nitrogen post-treatment, treatments were performed on HfO2 MIS capacitor for further improvement on reliability characteristic. We examine the reliability properties and the current conduction mechanism of HfO2 thin films. The frequency dispersion and constant voltage stress (CVS) characteristics of the samples were analyzed to estimate the improvement. According to the present study, dual plasma treatment could be better than single plasma treatment and would be an effective approach for HfO2 dielectric improvement.
Synthesis of Si Nanowire Arrays in AgO/HF Solution and Their Optical and Wettability Properties
Authors: Kato Yuki , Adachi Sadao
Published: April 2011

Silicon nanowire (SiNW) arrays are formed by Ag-assisted electroless etching at 25°C in 25% HF solution with AgO having concentration ranging from M = 0.003 to 0.2 mol/l. The maximum length of the SiNWs is ∼65 μm at an M of ∼0.045 mol/l. Optical absorption spectroscopy and Fourier-transform infrared spectroscopy show that the SiNWs have extremely large optical absorbability not only in the UV region but also in the far-infrared region. No photoluminescence is observed from the AgO/HF-formed SiNWs that are in direct contrast with the conventional AgNO3/HF-formed nanowires that generally emit orange light. Post-stain etching in the HF/HNO3 solution of the AgO/HF-formed nanowires enables light emission in the orange region. Passive HF etching of the SiNWs changes their wettability from highly hydrophilic (∼0°) to superhydrophobic (∼147°). This Ag-assisted electroless etching mechanism can be explained on the basis of an energy-band diagram of the Ag/p-Si interface in the AgO/HF solution.
One-Pot Synthesis of Platinum Nanoparticles Embedded on Reduced Graphene Oxide for Oxygen Reduction in Methanol Fuel Cells
Authors: Ha Hyung-Wook , Kim In Young , Hwang Seong-Ju , Ruoff Rodney S.
Published: April 2011

A simple approach has been developed for the synthesis of Pt nanoparticles with uniform diameters of approximately 2.9 nm supported on reduced graphene oxide (RG-O) platelets via a modified polyol method. Compared to Johnson Matthey (JM) Pt/C (75 wt % Pt) catalyst, the Pt/RG-O (70 wt % Pt) composite showed much higher electrochemical surface area, greater catalytic activity towards the oxygen reduction reaction (ORR), and significantly better single cell polarization performance. The maximum power density of the Pt/RG-O composite was about 128 mW cm−2, an 11% greater than the JM Pt/C commercial catalyst.
Liver X receptors regulate de novo lipogenesis in a tissue-specific manner in C57BL/6 female mice
Authors: Korach-André Marion , Archer Amena , Gabbi Chiara , Barros Rodrigo P. , Pedrelli Matteo , Steffensen Knut R. , Pettersson Amanda T. , Laurencikiene Jurga , Parini Paolo , Gustafsson Jan-Åke
Published: April 2011

The liver X receptors (LXRs) play a key role in cholesterol and bile acid metabolism but are also important regulators of glucose metabolism. Recently, LXRs have been proposed as a glucose sensor affecting LXR-dependent gene expression. We challenged wild-type (WT) and LXRαβ−/−mice with a normal diet (ND) or a high-carbohydrate diet (HCD). Magnetic resonance imaging showed different fat distribution between WT and LXRαβ−/−mice. Surprisingly, gonadal (GL) adipocyte volume decreased on HCD compared with ND in WT mice, whereas it slightly increased in LXRαβ−/−mice. Interestingly, insulin-stimulated lipogenesis of isolated GL fat cells was reduced on HCD compared with ND in LXRαβ−/−mice, whereas no changes were observed in WT mice. Net de novo lipogenesis (DNL) calculated from V̇o2and V̇co2was significantly higher in LXRαβ−/−than in WT mice on HCD. Histology of HCD-fed livers showed hepatic steatosis in WT mice but not in LXRαβ−/−mice. Glucose tolerance was not different between groups, but insulin sensitivity was decreased by the HCD in WT but not in LXRαβ−/−mice. Finally, gene expression analysis of adipose tissue showed induced expression of genes involved in DNL in LXRαβ−/−mice compared with WT animals as opposed to the liver, where expression of DNL genes was repressed in LXRαβ−/−mice. We thus conclude that absence of LXRs stimulates DNL in adipose tissue, but suppresses DNL in the liver, demonstrating opposite roles of LXR in DNL regulation in these two tissues. These results show tissue-specific regulation of LXR activity, a crucial finding for drug development.
Protection from diabetes development by single-chain antibody-mediated delivery of a NF-κB inhibitor specifically to β-cells in vivo
Authors: Ueberberg Sandra , Deutschbein Timo , Klein Harald H. , Dietrich Johannes W. , Akinturk Sara , Prochnow Nora , Schirrmacher Ralph , Schneider Stephan
Published: April 2011

Recently, we reported the generation of single-chain antibodies (SCAs) highly specific for rodent and human β-cells. Our current report describes the generation of a fusion protein of one of these SCAs (SCA B1) with a NF-κB essential modifier (NEMO)-binding domain (NBD) peptide, thereby creating a selective inhibitor of NF-κB activation in β-cells. The SCA B1-NBD fusion protein was cloned in the pIRES-EGFP, expressed in bacteria, and purified by metal affinity chromatography; the newly generated complex was then administered intravenously to rodents and evaluated for its ability to protect β-cells against cytokines in vitro and diabetogenic agents in vivo. First, it was shown clearly that our SCA B1-NBD fusion protein binds highly selective to CD rat β-cells in vivo. Second, we observed that SCA B1-mediated in vivo delivery of the NBD peptide completely blocked IL-1β + IFNγ- and TNFα + IFNγ-mediated induction of NF-κB as well as islet dysfunction in culture. Finally, repeated intravenous injection of SCA B1-NBD prior to multiple low-dose administration of streptozotocin in CD mice not only induced a striking resistance to diabetes development but also preserved β-cell mass. In conclusion, our data show for the first time that a SCA B1-NBD fusion peptide reliably protects β-cells against cytokines in vitro and allows protection from diabetes development in CD mice in vivo.
Premature aging with impaired oxidative stress defense in mice lacking TR4
Authors: Lee Yi-Fen , Liu Su , Liu Ning-Chun , Wang Ruey-Sheng , Chen Lu-Min , Lin Wen-Jye , Ting Huei-Ju , Ho Hsin-Chiu , Li Gonghui , Puzas Edward J. , Wu Qiao , Chang Chawnshang
Published: April 2011

Early studies suggest that TR4 nuclear receptor is a key transcriptional factor regulating various biological activities, including reproduction, cerebella development, and metabolism. Here we report that mice lacking TR4 ( TR4−/−) exhibited increasing genome instability and defective oxidative stress defense, which are associated with premature aging phenotypes. At the cellular level, we observed rapid cellular growth arrest and less resistance to oxidative stress and DNA damage in TR4−/− mouse embryonic fibroblasts (MEFs) in vitro. Restoring TR4 or supplying the antioxidant N-acetyl-l-cysteine (NAC) to TR4−/− MEFs reduced the DNA damage and slowed down cellular growth arrest. Focused qPCR array revealed alteration of gene profiles in the DNA damage response (DDR) and anti-reactive oxygen species (ROS) pathways in TR4−/− MEFs, which further supports the hypothesis that the premature aging in TR4−/− mice might stem from oxidative DNA damage caused by increased oxidative stress or compromised genome integrity. Together, our finding identifies a novel role of TR4 in mediating the interplay between oxidative stress defense and aging.
Gene expression variation between African Americans and whites is associated with coronary artery calcification: the multiethnic study of atherosclerosis
Authors: Huang Chiang-Ching , Lloyd-Jones Donald M. , Guo Xiuqing , Rajamannan Nalini M. , Lin Simon , Du Pan , Huang Qiquan , Hou Lifang , Liu Kiang
Published: April 2011

Coronary artery calcium (CAC) is a strong indicator of total atherosclerosis burden. Epidemiological data have shown substantial differences in CAC prevalence and severity between African Americans and whites. However, little is known about the molecular mechanisms underlying initiation and progression of CAC. Microarray gene expression profiling of peripheral blood leucocytes was performed from 119 healthy women aged 50 yr or above in the Multi-Ethnic Study of Atherosclerosis cohort; 48 women had CAC score >100 and carotid intima-media thickness (IMT) >1 mm, while 71 had CAC <10 and IMT <0.65 mm. When 17 African Americans were compared with 41 whites in the low-CAC group, 409 differentially expressed genes (false discovery rate <5%)were identified. In addition, 316 differentially expressed genes were identified between the high- and low-CAC groups. A substantial overlap between these two gene lists was observed (148 genes, P < 10−6). Furthermore, genes expressed lower in African Americans also tend to express lower in individuals with low CAC (correlation 0.69, P = 0.002). Ontology analysis of the 409 race-associated genes revealed significant enrichment in mobilization of calcium and immune/inflammatory response ( P < 10−9). Of note, 25 of 30 calcium mobilization genes were involved in immune/inflammatory response ( P < 10−10). Our data suggest a connection between immune response and vascular calcification and the result provides a potential mechanistic explanation for the lower prevalence and severity of CAC in African Americans compared with whites.
Genetically Modified Mouse Models Used for Studying the Role of the AT2 Receptor in Cardiac Hypertrophy and Heart Failure
Authors: Avila Maria D. , Morgan James P. , Yan Xinhua
Published: April 2011

The actions of Angiotensin II have been implicated in many cardiovascular conditions. It is widely accepted that the cardiovascular effects of Angiotensin II are mediated by different subtypes of receptors: AT1 and AT2. These membrane‐bound receptors share a part of their nucleic acid but seem to have different distribution and pathophysiological actions. AT1 mediates most of the Angiotensin II actions since it is ubiquitously expressed in the cardiovascular system of the normal adult. Moreover AT2 is highly expressed in the developing fetus but its expression in the cardiovascular system is low and declines after birth. However the expression of AT2 appears to be modulated by pathological states such as hypertension, myocardial infarction or any pathology associated to tissue remodeling or inflammation. The specific role of this receptor is still unclear and different studies involving in vivo and in vitro experiments have shown conflicting data. It is essential to clarify the role of the AT2 receptor in the different pathological states as it is a potential site for an effective therapeutic regimen that targets the Angiotensin II system. We will review the different genetically modified mouse models used to study the AT2 receptor and its association with cardiac hypertrophy and heart failure.
Behavioral Characterization ofGCLM-Knockout Mice, a Model for Enhanced Susceptibility to Oxidative Stress
Authors: Cole Toby B. , Giordano Gennaro , Co Aila L. , Mohar Isaac , Kavanagh Terrance J. , Costa Lucio G.
Published: April 2011

Glutathione (GSH) is a major player in cellular defense against oxidative stress. Deletion of the modifier subunit of glutamate cysteine ligase (GCLM), the first and the rate-limiting enzyme in the synthesis of GSH, leads to significantly lower GSH levels in all tissues including the brain.GCLM-knockout (Gclm−/−) mice may thus represent a model for compromised response to oxidative stress amenable toin vitroandin vivoinvestigations. In order to determine whether the diminished GSH content would by itself cause behavioral alterations, a series of behavioral tests were carried out comparing young adultGclm−/−with wild-type mice. Tests included the rotarod, acoustic startle reflex and prepulse inhibition of the startle reflex, open field behavior, and the platform reversal variant of the Morris Water Maze. Results showed no differences betweenGclm−/−and wild-type mice in any of the neurobehavioral tests. However, more subtle alterations, or changes which may appear as animals age, cannot be excluded.