bluuebunny/crossref_metadata_2025 huggingface dataset:
ZIB-EWMA CONTROL CHART FOR MONITORING RARE HEALTH EVENTS
Authors: NOOROSSANA RASSOUL , FATAHI AMIR AFSHIN , DOKOUHAKI PERSHANG , BABAKHANI MASSOUD
Published: April 2011

Monitoring rare health events, as a significant public health subject, has been considered recently by different authors. In this regard, different statistical methods such as g-type control chart, Poisson CUSUM control chart, sets-based methods, and Bernoulli CUSUM chart have been developed. Zero-inflated binomial (ZIB) distribution, due to its structure, can also be considered to develop methods for monitoring rare health-related events. If zero inflation is considered in the sampling data, and the sampling subgroup size is mandatory greater than 1, then the data best fits the ZIB distribution and the aforementioned control charts cannot be applied. ZIB distribution assumes that random shocks, corresponding to rare health events, occur and then number of failures in each subgroup fits a binomial distribution. In this paper, an exponentially weighted moving average (EWMA) control chart is applied for ZIB data to develop a ZIB-EWMA chart. Since ZIB-EWMA statistic values are not independent, Markov chain approach is considered to evaluate the performance of the proposed control chart in terms of average run length (ARL). According to the ARL measure, this ZIB-EWMA chart has a better performance in comparison with the methods available in the literature. In addition, a real case study related to rare infections in a hospital is investigated to show the applicability of the proposed control chart.
FRICTION OF STAINLESS STEEL, NICKEL-TITANIUM ALLOY, AND BETA-TITANIUM ALLOY ARCHWIRES IN TWO COMMONLY USED ORTHODONTIC BRACKETS
Authors: YU JIAN-HONG , HUANG HENG-LI , WU LI-CHUN , HSU JUI-TING , CHANG YIN-YU , HUANG HER-HSIUNG , TSAI MING-TZU
Published: April 2011

In orthodontic treatment, the efficiency of tooth movement is affected by the frictional force between the archwire and bracket slot. This study evaluated the static and kinetic frictional forces produced in different combinations of orthodontic archwires and brackets. Three types of archwires [stainless steel, nickel-titanium (NiTi) alloy, and beta-titanium (TMA) alloy] and two types of brackets (stainless steel and self-ligating) were tested. Both static and kinetic frictional forces of each archwire–bracket combination were measured 25 times using a custom-designed apparatus. The surface topography and hardness of the archwires were also evaluated. All data were statistically analyzed using two-way analysis of variance and Tukey's test. The experiments indicated that the static frictional force was significantly higher than the kinetic frictional force in all archwire–bracket combinations not involving TMA wire. TMA wire had the highest friction, followed by NiTi wire, and then stainless steel wire when using the stainless steel bracket. However, there was no difference between NiTi and stainless steel archwires when using the self-ligating bracket. For TMA wire, the friction was higher when using the stainless steel bracket than when using the self-ligating bracket. Scanning electron microscopy indicated that stainless steel wire exhibited the smoothest surface topography. The hardness decreased in the order of stainless steel wire > TMA wire > NiTi wire. This study demonstrates that the frictional forces of brackets are influenced by different combinations of bracket and archwire. The reported data will be useful to orthodontists.
FETAL HEART RATE VARIABILITY ANALYSIS FROM PHONOCARDIOGRAPHIC RECORDINGS
Authors: CHOURASIA VIJAY S. , TIWARI ANIL KUMAR
Published: April 2011

This paper presents an algorithm for classification of fetal health status using fetal heart rate variability (fHRV) analysis through phonocardiography. First, the fetal heart sound signals are acquired from the maternal abdominal surface using a specially developed Bluetooth-based wireless data recording system. Then, fetal heart rate (FHR) traces are derived from these signals. Ten numbers of linear and nonlinear features are extracted from each FHR trace. Finally, the multilayer perceptron (MLP) neural network is used to classify the health status of the fetus. Results show very promising performance toward the prediction of fetal wellbeing on the set of collected fetal heart sound signals. Finally, this work is likely to lead to an automatic screening device with additional potential of predicting fetal wellbeing.
INVESTIGATION OF THE ESSENTIALS FOR INTEGRATING OFF-THE-SHELF INDUSTRIAL ROBOTICS IN PRECISE COMPUTER-ASSISTED SURGERY
Authors: REN HONGLIANG , MENG MAX Q.-H.
Published: April 2011

Off-the-shelf industrial robotic technologies have achieved significant advancements in the past several decades in terms of mechanics and automation performances. We are expecting to take advantage of the industrial robots for assisting surgeons in surgeries and quick prototyping a robotic surgery system. In precise computer-assisted surgeries (CASs), such as pelvic-acetabular surgery, eye surgery, or neurosurgery, it is extremely important to position the tools accurately and precisely for surgical operations. Some of the industrial robotics arms are able to achieve good repeatability and dexterity while positioning the surgical tools. To enable the application of industrial robots in the surgical rooms, there are several other essential modules to be integrated to the robotic surgery systems, such as real-time navigation system, surgical planning system, and surgeon-guidance system. In this paper, we review the existing studies on the medical robots including the ones using industrial robots, and then investigate the essentials for using industrial robots in computer-integrated surgery.
THEORETICAL STUDIES ON BOND DISSOCIATION ENERGIES FOR SOME ALIPHATIC ALCOHOL COMPOUNDS BY DENSITY FUNCTIONAL THEORY AND CBS-Q METHOD
Authors: LI XIAO-HONG , YIN GENG-XIN , ZHANG XIAN-ZHOU
Published: April 2011

Quantum chemical calculations are used to estimate the bond dissociation energies (BDEs) for 20 aliphatic alcohol compounds. These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, and B3P86) methods with 6-311G** basis set and the complete basis set (CBS-Q) method together. It is demonstrated that B3P86 and CBS-Q methods are accurate to compute the reliable BDEs for aliphatic alcohol compounds. In order to test whether the non-local BLYP method suggested by Jursic18 is general for our study and whether B3P86 method has a low basis set sensitivity, the BDEs for 20 aliphatic alcohol compounds are also calculated using BLYP/6-31+G*, BLYP/6-31G*, and B3P86 methods with 6-31G*, 6-31+G*, and 6-31G** basis sets for comparison. The obtained results are compared with the available experimental results. It is noted that B3P86 method is sensitive to the basis sets. Considering the inevitably computational cost of CBS-Q method and the reliability of the B3P86 calculation, B3P86 method with 6-31G** basis set may be more suitable to calculate the BDEs of the C–O bond for aliphatic alcohol compounds.
A COMPARISON OF THE STEREOISOMERIC PENTA-COORDINATED PHOSPHORUS INTERMEDIATES FORMED FROM 19 DIMETHOXYL N-PHOSPHORYL AMINO ACIDS BY DFT CALCULATIONS
Authors: ZHAO LIJIAO , LIU TINGTING , ZHONG RUGANG
Published: April 2011

N-phosphoryl amino acids (PAAs) are important species in the origin of life that self-catalyze and self-assemble into polypeptides and polynucleotides under mild conditions. Both experimental and theoretical studies have shown that a penta-coordinated phosphorus intermolecular mixed carboxylic-phosphoric anhydride (IMCPA) is formed as the common intermediate in these reactions. In this work, the mechanism for the formation of stereoisomeric IMCPAs from PAAs is investigated using density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) theoretical level. The molecular structures of the cis- and the trans-IMCPAs, as well as the transition states of the two stereochemical reaction pathways, were characterized in detail. The results showed that the hydroxyl groups of PAAs were situated in favorable positions for attacking the phosphorus atom from two sides of the phosphoryl group, resulting in the formation of the cis-IMCPA and the trans-IMCPA, respectively. The trans-isomers were predicted to be more likely to undergo a further reaction involving an ester exchange on the phosphorus than the cis-isomers. By comparing the relative energies of the IMCPAs and the activation energies, the trans-IMCPAs were computed to be more stable than the cis-IMCPAs, but the energy barriers for the formation of the trans- and the cis-isomers were similar. This work is expected to shed light on the stereochemical effect involved in the chemical evolution of biomolecules.
SUPERALKALI MOLECULES CONTAINING HALOGENOIDS
Authors: ANUSIEWICZ IWONA
Published: April 2011

The structure and properties of hypermetalated Li 2X and Na 2X and their corresponding Li 2X+ and Na 2X+ cations utilizing halogenoids X (SCN, OCN, and CN) were investigated using ab initio methods at the CCSD(T)/6-311+G(3df)//MP2/6-311+G(d) level of theory. The vertical ionization potentials of Li 2X and Na 2X radicals were calculated at the outer valence Green function level (OVGF) with the 6-311+G(3df) basis sets. It was found that all Na 2X molecules studied possess the vertical ionization potentials (VIP) that are smaller than the IP of the Na atom (5.14 eV) and thus may be termed superalkali molecules, whereas the Li 2X radicals exhibit slightly larger IPs. The smallest VIP of 4.728 eV was calculated for the Na 2 CN system. The IP dependence on the structure and the singly occupied molecular orbital (SOMO) character is also discussed.
OPTIMIZATION OF THERAPEUTIC PROTEINS TO DELETE T-CELL EPITOPES WHILE MAINTAINING BENEFICIAL RESIDUE INTERACTIONS
Authors: PARKER ANDREW S. , GRISWOLD KARL E. , BAILEY-KELLOGG CHRIS
Published: April 2011

Exogenous enzymes, signaling peptides, and other classes of nonhuman proteins represent a potentially massive but largely untapped pool of biotherapeutic agents. Adapting a foreign protein for therapeutic use poses numerous design challenges. We focus here on one significant problem: modifying the protein to mitigate the immune response mounted against "non-self" proteins, while not adversely affecting the protein's stability or therapeutic activity. In order to propose such variants suitable for experimental evaluation, this paper develops a computational method to select sets of mutations predicted to delete immunogenic T-cell epitopes, as evaluated by a 9-mer potential, while simultaneously maintaining important residues and residue interactions, as evaluated by one- and two-body potentials. While this design problem is NP-hard, we develop an integer programming approach that works very well in practice. We demonstrate the effectiveness of our approach by developing plans for biotherapeutic proteins that, in previous studies, have been partially deimmunized via extensive experimental characterization and modification of limited segments. In contrast, our global optimization technique considers an entire protein and accounts for all residues, residue interactions, and epitopes in proposing candidates worth subjecting to experimental evaluation.
ncRNA CONSENSUS SECONDARY STRUCTURE DERIVATION USING GRAMMAR STRINGS
Authors: ACHAWANANTAKUN RUJIRA , SUN YANNI , TAKYAR SEYEDEH SHOHREH
Published: April 2011

Many noncoding RNAs (ncRNAs) function through both their sequences and secondary structures. Thus, secondary structure derivation is an important issue in today's RNA research. The state-of-the-art structure annotation tools are based on comparative analysis, which derives consensus structure of homologous ncRNAs. Despite promising results from existing ncRNA aligning and consensus structure derivation tools, there is a need for more efficient and accurate ncRNA secondary structure modeling and alignment methods. In this work, we introduce a consensus structure derivation approach based on grammar string, a novel ncRNA secondary structure representation that encodes an ncRNA's sequence and secondary structure in the parameter space of a context-free grammar (CFG) and a full RNA grammar including pseudoknots. Being a string defined on a special alphabet constructed from a grammar, grammar string converts ncRNA alignment into sequence alignment. We derive consensus secondary structures from hundreds of ncRNA families from BraliBase 2.1 and 25 families containing pseudoknots using grammar string alignment. Our experiments have shown that grammar string–based structure derivation competes favorably in consensus structure quality with Murlet and RNASampler. Source code and experimental data are available at .
INFERRING HAPLOTYPES FROM GENOTYPES ON A PEDIGREE WITH MUTATIONS, GENOTYPING ERRORS AND MISSING ALLELES
Authors: WANG WEI-BUNG , JIANG TAO
Published: April 2011

Inferring the haplotypes of the members of a pedigree from their genotypes has been extensively studied. However, most studies do not consider genotyping errors and de novo mutations. In this paper, we study how to infer haplotypes from genotype data that may contain genotyping errors, de novo mutations, and missing alleles. We assume that there are no recombinants in the genotype data, which is usually true for tightly linked markers. We introduce a combinatorial optimization problem, called haplotype configuration with mutations and errors (HCME), which calls for haplotype configurations consistent with the given genotypes that incur no recombinants and require the minimum number of mutations and errors. HCME is NP-hard. To solve the problem, we propose a heuristic algorithm, the core of which is an integer linear program (ILP) using the system of linear equations over Galois field GF(2). Our algorithm can detect and locate genotyping errors that cannot be detected by simply checking the Mendelian law of inheritance. The algorithm also offers error correction in genotypes/haplotypes rather than just detecting inconsistencies and deleting the involved loci. Our experimental results show that the algorithm can infer haplotypes with a very high accuracy and recover 65%–94% of genotyping errors depending on the pedigree topology.
Conformational distortions of π-cation radical (β-oxoporphyrin)copper(II) derivatives: [Cu(2,7,12-trioxoOEHP·)][SbCl6] and [Cu(2,7-dioxoOEiBC·)][SbCl6]
Authors: Turowska-Tyrk Ilona , Kang Seong-Joo , Scheidt W. Robert
Published: April 2011

The preparation and characterization of two π-cation radical derivatives of copper β-oxoporphyrins is described. [3,3,8,8,13,13,17,18-octaethyl-(3H,8H,13H)-porphine-2,7,12-trionato (2-)] copper π-cation radical, [ Cu (2,7,12-trioxoOEHP·)]+, and [3,3,8,8,12,13,17,18-octaethyl-(3H,8H)-porphine-2,7-dionato(2-)] copper π-cation radical, [ Cu (2,7-dioxoOEiBC·)]+, have been prepared and characterized by single-crystal X-ray determinations, UV/vis/NIR, and IR spectroscopies. Both molecules have modest distortion from the planarity and show monomeric units in the solid state. [ Cu (2,7-dioxoOEiBC·)]+ shows a concentration dependent near-IR band at 1410 nm.
Electrochemistry and spectroelectrochemistry of bismanganese biscorroles dyads
Authors: Chen Ping , Ojaimi Maya El , Gros Claude P. , Barbe Jean-Michel , Guilard Roger , Shen Jing , Kadish Karl M.
Published: April 2011

Three manganese biscorrole dyads were synthesized, physicochemically characterized and investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous media. Each dyad contained the same two corroles linked in a face-to-face arrangement via one of the three different linking groups, 9,9-dimethylxanthene, anthracene or diphenylether, the exact nature of which determined the distance and possible interaction between the two metallomacrocycles. The initial compounds contained Mn ( III ) in their air stable form and were shown to exhibit two major redox processes, one being a Mn (III)/ Mn (IV) conversion and the other being either Mn ( III )/ Mn ( II ) or reduction at the conjugated macrocycle to give a Mn ( III ) corrole π-anion radical when the solvent was pyridine. The potentials and reversibility of each electron transfer reaction were shown to depend upon the solvent (pyridine, CH2Cl2 , or PhCN ), type of spacer separating the two macrocycles and/or the presence or absence of axial ligation. The site of each electron transfer was assigned on the basis of spectroscopic and electrochemical data and by comparison with reactions and properties of the monocorrole ( Mes2PhCor)Mn which was characterized in a previous publication and also examined in the current study under the same solution conditions as the newly investigated dyads. Some electrode reactions of the dyads were followed by coupled chemical reactions and these were also elucidated in the present study.
Theoretical reconsideration on the hydrogen bonding and coordination interactions of chlorophyll a in aqueous solution
Authors: Liu Ji-Feng
Published: April 2011

In the present work, explicit water molecule and solvent-field effects on the absorption spectrum of chlorophyll a have been studied using time-dependent density functional theory (TDDFT) method. Calculated results show that the one complex and two water coordinated complexes formed by concerted coordination and hydrogen-bonding interactions would be the most preferable conformations of chlorophyll a in aqueous surroundings. Moreover, four obvious absorption bands are assigned by comparing the theoretically simulated absorption spectra with the experimental ones. The theoretical study shows that the explicit water molecule interactions slightly influence the first absorption band. However, the water coordination and hydrogen-bonding interactions can significantly affect the second absorption band which has a strong red-shift. The solvent-field effect due to the polarity of water on absorptions in Q-bands is relatively smaller than that on absorptions in B-bands. As a consequence, our theoretical study on the absorption spectra in the 350–400 nm region presents that the absorption strength in this region was influenced by the explicit coordination and hydrogen bonding interactions from water molecules, significantly.
Biomimetic models of nitric oxide synthase for the oxidation of oximes to carbonyl compounds catalyzed by water-soluble manganese porphyrins in aqueous solution
Authors: Ren Qing-Gang , Zhou Xian-Tai , Ji Hong-Bing
Published: April 2011

A mild green and efficient approach for hydrogen peroxide oxidative converting oximes to the corresponding carbonyl compounds with a water-soluble manganese porphyrin as catalyst in water/acetone mixture has been developed. The water-soluble manganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes under ambient conditions in the absence of any additive. The oxidative deoximation was through the formation of high valent oxo-manganese species, which was confirmed by in situ UV-vis spectroscopy.
REPRESENTATIONS OF ARITHMETIC PROGRESSIONS BY POSITIVE DEFINITE QUADRATIC FORMS
Authors: OH BYEONG-KWEON
Published: April 2011

For a positive integer d and a non-negative integer a, let Sd,a be the set of all integers of the form dn + a for any non-negative integer n. A (positive definite integral) quadratic form f is said to be Sd,a-universal if it represents all integers in the set Sd, a, and is said to be Sd,a-regular if it represents all integers in the non-empty set Sd,a ∩ Q((f)), where Q(gen(f)) is the set of all integers that are represented by the genus of f. In this paper, we prove that there is a polynomial U(x,y) ∈ ℚ[x,y] (R(x,y) ∈ ℚ[x,y]) such that the discriminant df for any Sd,a-universal (Sd,a-regular) ternary quadratic forms is bounded by U(d,a) (respectively, R(d,a)).
TUNING THE OPTICAL PROPERTIES OF MULTIWALL CARBON NANOTUBE THIN FILMS BY N+ ION BEAMS IRRADIATION
Authors: ISHAQ AHMAD , YAN LONG , HUSNAIN G. , LU BO , ARSHAD MAHMOOD , KHALID ALAMGIR
Published: April 2011

Measurements of optical transmission in the visible spectral range of N+ irradiated thin films of multiwall carbon nanotubes (MWCNTs) at various doses prepared by a vacuum filtration method are reported. An increase in optical transmission was observed corresponding to increase in N+ ion doses. Changes in Raman spectra at different ions doses ranging from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2 indicate that the structure of graphene evolves from a highly ordered layer to a disordered domains. These structural changes result in a dramatic increase in the optical transmission. Additionally, the increase of optical transmission of irradiated MWCNTs thin film as a function of electrical conductivity at various doses is also discussed. The optical transmission increases in irradiated MWCNT thin films is found to be a function of defects density in MWCNTs.
ENHANCEMENT OF FERROMAGNETISM IN NANOCRYSTALLINE Zn1-xCuxO(0.03 ≤ x ≤ 0.07)
Authors: MOHAPATRA JYOSHNARANI , MISHRA D. K. , MISHRA P. K. , BAG B. P. , SINGH S. K.
Published: April 2011

We report room temperature ferromagnetism (RTFM) in nanocrystalline Zn 1-x Cu x O (0.03 ≤ x ≤ 0.07) materials synthesized by autocombustion technique. The average particle sizes are in the range of 60 nm. The saturation magnetization and coercivity of 7% Cu -doped ZnO is enhanced significantly in comparison to 3% and 5% Cu -doped ZnO . There is not much variation in the optical band gap due to Cu doping, thus suggesting the uniform distribution of Cu in the ZnO matrix. Micro-Raman and photoluminescence analysis predict the presence of clusters of oxygen vacancies in Cu -doped system which improves with the increase in Cu concentration. This study provides further evidence that oxygen vacancies play an important role in the enhancement of room temperature ferromagnetic property in Cu -doped ZnO .
IN VITRO THROMBIN DOSE RESPONSE ON MADIN DARBY CANINE KIDNEY CELL MONOLAYER
Authors: AMIN RASHID , SHAKIR IMRAN , SULTANA ISHRAT , PARK SUNG HA , HUSSAIN RAFAQAT
Published: April 2011

Epithelial cells are known to play an important role in sustaining the airway barrier that may be impaired in certain inflammatory conditions. Recently, the use of thrombin has been reported to open the airway of patients with asthma as well as enhance the permeability of endothelial cell monolayers. We designed an in vitro model of Madin Darby Canine Kidney (MDCK) cells and the physiological functions of this model were evaluated by measuring the transepithelial resistance (TER). The epithelial cytoskeletal organization was observed by staining with Bisbenzimide and Rodamine-Phalloidin (BBZ-Phalloidin) and confirmed by fluorescence microscopy. Measurements of the TER generated values up to 2020 Ω/cm2. A dose response of thrombin was observed, showing the permeability changes in the MDCK monolayer and subsequent recovery. A relationship between TER values and cytoskeletal organization was also observed and discussed.
Isotope Tracing Study of GeO Desorption Mechanism from GeO2/Ge Stack Using 73Ge and 18O
Authors: Wang Sheng Kai , Kita Koji , Nishimura Tomonori , Nagashio Kosuke , Toriumi Akira
Published: April 2011

GeO desorption from a GeO2/Ge stack is a critical concern in Ge metal oxide semiconductor field effect transistors (MOSFETs). In this contribution, we focus on a uniform-desorption region and unveil the GeO desorption mechanism from a GeO2/Ge stack by 73Ge and 18O isotope tracing in thermal desorption spectroscopy (TDS) analysis, in which the Ge and O diffusion kinetics in GeO2 and the interfacial reaction kinetics have been investigated. Through 73Ge isotope tracing, we have clarified that Ge in the desorbed GeO dominantly comes from the GeO2 surface. Moreover, the self-diffusivity of oxygen was evaluated to be much larger than Ge in GeO2. Furthermore, owing to the difference among GeO desorptions from GeO2/Ge stacks with various substrate orientations, the reaction at the GeO2/Ge interface was attributed to the redox reaction kinetics. On the basis of our experimental findings, we have proposed an oxygen vacancy diffusion model of the GeO desorption mechanism.
Analytical Approach for Enhancement of n-Channel Metal–Oxide–Semiconductor Field-Effect Transistor Performance with Carbon-Doped Source/Drain Formed by Molecular Carbon Ion Implantation and Laser Annealing
Authors: Yamaguchi Tadashi , Kawasaki Yoji , Yamashita Tomohiro , Miura Noriko , Mizuo Mariko , Tsuchimoto Jun-ichi , Eikyu Katsumi , Maekawa Kazuyoshi , Fujisawa Masahiko , Asai Koyu
Published: April 2011

Enhancement of n-channel metal–oxide–semiconductor field-effect transistor (nMOSFET) performance with a carbon-doped source/drain (Si:C-S/D) was approached analytically for the first time. Si:C-S/D was formed by molecular carbon (C7H
x
) ion implantation and laser annealing. C7H
x
implantation forms a smooth interface between Si:C layers and Si substrates, and laser annealing also achieves a high carbon concentration of substitution. The channel strain with Si:C-S/D was successfully measured by UV Raman spectroscopy using a particular test pattern. The thick Si:C-S/D layer and the high carbon concentration of substitution produce a large strain at the channel region. It was confirmed that the performance of nMOSFETs is effectively improved by strained Si:C-S/D. These analytical approaches are quite valuable for promoting the development of strained nMOSFETs with Si:C-S/D.
Accurate Measurement of Silicide Specific Contact Resistivity by Cross Bridge Kelvin Resistor for 28 nm Complementary Metal–Oxide–Semiconductor Technology and Beyond
Authors: Ohuchi Kazuya , Kusunoki Naoki , Matsuoka Fumitomo
Published: April 2011

In scaling down the device feature size, a reduction in parasitic resistance is inevitable in realizing a high-performance complimentary metal–oxide–semiconductor field-effect transistor. In particular, a reduction in specific contact resistivity between silicide and silicon diffusion layers under silicide in source/drain electrodes becomes increasingly important. In this paper, we focus on the measurement accuracy of the specific contact resistivity and the experimental evaluation of the state-of-the-art 28 nm technology. The measurement accuracy of the specific contact resistivity was examined by three-dimensional technology computer-aided design simulation. The results confirmed that the specific contact resistivity measurement resolution obtained by using the proposed modified cross-bridge Kelvin resistor is extended to 10-9 Ω cm2. We also found experimentally that the 28 nm technology realizes 1.1×10-8 and 7.8×10-9 Ω cm2 for n+ and p+ silicon diffusion layers in source/drain electrodes, respectively, by utilizing the test structure of cross-bridge Kelvin resistors, which are fully applicable to the 28 nm technology.
Measurements of Electrostatic Potential Across p–n Junctions on Oxidized Si Surfaces by Scanning Multimode Tunneling Spectroscopy
Authors: Bolotov Leonid , Tada Tetsuya , Iitake Masanori , Nishizawa Masayasu , Kanayama Toshihiko
Published: April 2011

We investigated the variation in contact potential difference (CPD) voltage across p–n junctions on oxygen-passivated Si(110) surfaces by scanning multimode tunneling spectroscopy, which detects probe–sample interaction force simultaneously with tunneling current. The enhancement of sensitivity to electrostatic force was achieved with a small amplitude of probe vibration (0.3 nm) when the tip–sample gap was adjusted to reduce short-range interactions by maintaining the tunneling current at a specified bias voltage. At the optimal tip–sample gap, the CPD voltage, derived from force gradient spectra, agrees with the expected built-in potential across the p–n junction. The CPD voltage showed a standard deviation of ∼30 mV on atomically flat terraces. Larger fluctuations were ascribed to structural and charge variations on the oxidized surfaces.
Activation of As Atoms in Ultrashallow Junction during Milli- and Microsecond Annealing Induced by Thermal-Plasma-Jet Irradiation
Authors: Matsumoto Kazuya , Ohta Akio , Miyazaki Seiichi , Higashi Seiichiro
Published: April 2011

We irradiated a micro-thermal-plasma-jet (µ-TPJ) to an As-implanted Si wafer surface to form an ultrashallow junction (USJ). A high-power-density TPJ for microsecond rapid thermal annealing (RTA) was generated by using a small orifice of 0.8 mm diameter instead of 2.0 mm to concentrate the TPJ. The µ-TPJ could anneal the Si wafer surface at a temperature as high as 920 K for 340 µs. By reducing the annealing duration (t
a) from 1.2 ms to 340 µs, the sheet resistance (R
S) of the As2
+-implanted Si wafer decreased from 1520 to 1287 Ω/sq. In addition, the chemical bond states of As at the very surface were measured by X-ray photoelectron spectroscopy (XPS) and the fraction of activated As was estimated to be ∼15% larger than that in the case of millisecond annealing. Surface As atoms in Si wafers were more efficiently activated by a microsecond annealing than a millisecond annealing owing to the suppression of diffusion and clustering.
Analysis of Local Leakage Current of Pr-Oxide Thin Films with Conductive Atomic Force Microscopy
Authors: Adachi Masaki , Kato Yuzo , Kato Kimihiko , Sakashita Mitsuo , Kondo Hiroki , Takeuchi Wakana , Nakatsuka Osamu , Zaima Shigeaki
Published: April 2011

We have investigated the local leakage current in Pr-oxide thin films formed on Si(001) and Si(111) substrate by conductive atomic force microscopy. In Pr-oxide films formed on Si(111) substrates, many current leakage spots are observed in current images compared to that on Si(001) substrates. We found that the current conduction mechanism in Pr-oxide films is considered a Poole–Frenkel conduction. The X-ray photoelectron spectroscopy analysis revealed that cubic Pr2O3 is preferentially formed near the Pr-oxide/Si(111) interface compared with Si(001) samples. We also found that O2 annealing effectively reduces the leakage current in Pr-oxide films. It is considered that oxygen vacancies in Pr-oxide dominate the leakage current of oxide thin films.
Improvement in the Property of Field Effect Transistor Having the HfO2/Ge Structure Fabricated by Photoassisted Metal Organic Chemical Vapor Deposition with Fluorine Treatment
Authors: Lee DongHun , Imajo Hideto , Kanashima Takeshi , Okuyama Masanori
Published: April 2011

We have fabricated Ge-based p-channel metal–insulator–semiconductor field effect transistor (p-MISFET) devices using a hafnium oxide (HfO2) gate film prepared by photoassisted metal organic chemical vapor deposition (MOCVD). To reduce the interface state of a HfO2/Ge gate stack, we performed a new F2 treatment method on a Ge surface. Before the deposition of HfO2 insulation thin films on n-type Ge(100), Ge surfaces were treated in fluorine (F2) gas ambient under various conditions. Experimental results show that F is densely distributed at the interface of the HfO2/Ge gate stack with the F2 treatment of the HfO2 bottom layers. Poorly passivated dangling bonds and oxygen vacancies (Vo) near the interface between HfO2 and Ge were stabilized by chemically active F. Consequently, the interface state density (D
it) of the HfO2/Ge gate stack was reduced and the electrical characteristics of the HfO2/Ge p-MISFETs were improved. Therefore, the new F2 treatment method is very useful for fabricating a good HfO2/Ge p-MISFET device.
Many-Electron Multiplet Theory Applied to O-Atom Vacancies in High-κ Dielectrics
Authors: Lucovsky Gerald , Miotti Leonardo , Bastos Karen Paz
Published: April 2011

Two-electron multiplet theory has been used to develop a high-spin effective d2 model for O-vacancy spin-allowed and spin-forbidden dipole transitions, and for negative ion state traps. The transition and negative ion states have been detected by X-ray absorption spectroscopy in the O K pre-edge regime of transition metal (TM) elemental oxides and complex oxides. Occupied ground and excited states of the model satisfy Hund's rules by (i) including only high-spin state arrangements and (ii) using many electron state term symbols consistent with Russell–Saunders coupling. Qualitative and quantitative agreement between theory and experiment is demonstrated by using Tanabe–Sugano energy level diagrams for (i) identifying the symmetries and spin states, and (ii) determining the relative energies of intra-d-state transitions that are allowed in the presence of an intermediate strength ligand field. This includes removal of the spin degeneracy for the allowed transitions by a cooperative Jahn–Teller effect. The effective d2 model is applied to nanocrystalline thin films of ZrO2, HfO2, TiO2, and Lu2O3 and to illustrate the agreement between the new d2 model and the X-ray absorption spectroscopy data. The new model has also been applied with the same degree of success to complex TM oxides and SiO2.
Fabrication of Silicon Pillar with 25 nm Half Pitch Using New Multiple Double Patterning Technique
Authors: Kushibiki Masato , Hara Arisa , Nishimura Eiichi , Endoh Tetsuo
Published: April 2011

For the higher-density cells of next-generation semiconductor memories, many recent studies have focused on the vertical cell structure technology, which includes various performance merits such as small cell size, high drivability, and suitability for cell-stacked-type arrays. The authors developed a new method to fabricate 25 nm half pitch dense Si pillars that would be applicable to the fabrication of vertical cell devices. Using the proposed multiple double patterning techniques, 23.6 nm diameter, 114 nm height Si cylindrical pillars with a half pitch of 25 nm were fabricated. We confirmed the uniformity in a 300 mm wafer at 30 points, and its 3σ was only 1.7 nm. Moreover, we examined the presence of pillar collapse at arbitrarily selected chip dies for confirmation. Surprisingly, there was no pillar collapse within any of the inspected areas. From these verifications, we conclude that our proposed fabrication technique for slim Si pillars is now available.
Improvement of Uniformity and Reliability of Scaled-Down Cu Interconnects with Carbon-Rich Low-k Films
Authors: Kume Ippei , Ueki Makoto , Inoue Naoya , Kawahara Jun , Ikarashi Nobuyuki , Furutake Naoya , Saitoh Shinobu , Hayashi Yoshihiro
Published: April 2011

Highly selective dry-etching processes are developed for conventional via-first (VF) pattering sequences to fabricate reliable Cu dual-damascene interconnects (DDI) in carbon-rich low-k films, such as a molecular-pore-stack (MPS) SiOCH film (k = 2.55). The carbon-rich MPS film, which had excellent endurance against plasma-processes, acted as etching stopper during hard-mask (HM)-etching on it, and the high selectivity of trench-HM etching reduced variability of over-etching depth in the MPS film. This effect reduced variability in trench-depth in the MPS film, or interconnect characteristics such as capacitance–resistance (C–R) time delay. The via yield and reliability were influenced also by via-etch selectivity of MPS against SiCN cap underlain. We found that the SiCN thickness remained after the via etch should be greater than 10 nm to prevent Cu from oxidation by O2 ashing step followed. Chemical-reaction-enhanced gas chemistry in N2–CF
X
–Ar system, i.e., high N2/Ar ratio under limited CF
X
supply, increased the etching selectivity of MPS to keep enough thickness of SiCN. Early-failure-mode in electro-migration test was suppressed by the high selective via-etch. Precise selectivity control for robust carbon-rich low-k films was very important to achieve the low variability and high reliability of scaled-down Cu interconnects.
Analysis of the Low-Frequency Noise Reduction in Si(100) Metal–Oxide–Semiconductor Field-Effect Transistors
Authors: Gaubert Philippe , Teramoto Akinobu , Kuroda Rihito , Nakao Yukihisa , Tanaka Hiroaki , Sugawa Shigetoshi , Ohmi Tadahiro
Published: April 2011

The low-frequency noise was already a strong limiting factor for radio frequency/analog integrated circuits and was expected to become soon for the digital ones. However, a very significant and effective reduction of the 1/fnoise level has been realized for both n- and p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) by the means of two new fabrication processes, opening new horizons for the very large scale integration (VLSI) technology. Indeed, a significant reduction of more than two decades of the noise level has been achieved by implementing a new salicide structure for the source and drain contacts. Moreover, on account of a new process flow involving a newly developed plasma process for the realization of the gate oxide, one of the noise source, the induced mobility fluctuations, located in the channel and generating the 1/fnoise has been neutralized in the case of the p-MOSFETs. Furthermore, the implementation of an adapted salicide structure in addition to the plasma process will make the insulator charge fluctuations the sole noise source in these devices.
Abrupt Lateral-Source Heterostructures with Relaxed/Strained Layers for Ballistic Complementary Metal Oxide Semiconductor Transistors Fabricated by Local O+ Ion-Induced Relaxation Technique of Strained Substrates
Authors: Mizuno Tomohisa , Hasegawa Mitsuo , Ikeda Keiji , Nojiri Masashi , Horikawa Tsuyoshi
Published: April 2011

We have experimentally studied an abrupt lateral-relaxed/strained layer heterojunction for ballistic complementary metal oxide semiconductor (CMOS) transistors, which is fabricated by a local O+ ion-induced relaxation technique for strained semiconductors on a buried oxide layer. We have demonstrated that strained substrates in various conditions are suddenly relaxed at a critical recoil energy of O+ ions at the strained semiconductor/buried oxide layer interface. Moreover, after O+ ion implantation into strained substrates with a SiO2 mask as well as post-annealing processes, we have successfully formed lateral relaxed/strained Si layers with an abrupt strain distribution at the mask edge, according to Raman spectroscopy analysis of implanted strained substrates. In addition, strained Si layers even under the 50-nm length stripe SiO2 mask region can still keep over 60% of the strain value in strained Si layers with a large area.
Impact of Channel Direction Dependent Low Field Hole Mobility on (100) Orientation Silicon Surface
Authors: Kuroda Rihito , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: April 2011

An obvious channel direction dependency of the low field hole mobility on (100) oriented silicon surface is experimentally obtained for p-channel metal–oxide–silicon field-effect-transistor (MOSFET) fabricated on atomically flattened silicon wafer. The low electric field hole mobility measured at a low temperature takes the maximal at [001] directions and the minimal at [011] directions, respectively. The obtained channel direction dependency agrees very well with that of the heavy hole effective mass. The correlations between the magnitude of channel direction dependency of the hole mobility and some physical parameters such as channel length, temperature, and lateral electric field are evaluated. As a result, a universal relationship was found between the mobility increase from [011] to [001] direction and the channel length over the average relaxation time constant of carrier scattering.
Silicide Engineering to Boost Si Tunnel Transistor Drive Current
Authors: Leonelli Daniele , Vandooren Anne , Rooyackers Rita , Verhulst Anne S. , Gendt Stefan De , Heyns Marc M. , Groeseneken Guido
Published: April 2011

In this paper, we present for the first time a novel Si p-tunnel field effect transistor (pTFET) with high-k dielectric and metal gate fabricated in a multiple gate technology. The device exhibits an on-state current of 7 µA/µm at V
DD of 0.9 V and a high I
ON/I
OFF ratio of ∼106 with a fin width of 10 nm. The high on-current is believed to be due to an enhanced electric field caused by silicide encroachment and dopant segregation. Low variability of the device performance is reported for the different fin widths. Temperature measurements also show that the current is due to different transport mechanisms at different gate biases. Temperature measurements and TCAD simulations both confirm the presence of trap-assisted tunneling (TAT) as main responsible for the degradation of the subthreshold swing.
Dual-Material Gate Approach to Suppression of Random-Dopant-Induced Characteristic Fluctuation in 16 nm Metal–Oxide–Semiconductor Field-Effect-Transistor Devices
Authors: Li Yiming , Lee Kuo-Fu , Yiu Chun-Yen , Chiu Yung-Yueh , Chang Ru-Wei
Published: April 2011

In this work, we explore for the first time dual-material gate (DMG) and inverse DMG devices for suppressing the random-dopant (RD)-induced characteristic fluctuation in 16 nm metal–oxide–semiconductor field-effect-transistor (MOSFET) devices. The physical mechanism of suppressing the characteristic fluctuation of DMG devices is observed and discussed. The achieved improvement in suppressing the RD-induced threshold voltage, on-state current, and off-state current fluctuations are 28, 12.3, and 59%, respectively. To further suppress the fluctuations, an approach that combines the DMG method and channel-doping-profile engineering is also advanced and explored. The results of our study show that among the suppression techniques, the use of the DMG device with an inverse lateral asymmetric channel-doping-profile has good immunity to fluctuation.
Simulation Study of Intrinsic Parameter Fluctuations in Variable-Body-Factor Silicon-on-Thin-Box Metal Oxide Semiconductor Field Effect Transistors
Authors: Yang Yunxiang , Du Gang , Han Ruqi , Liu Xiaoyan
Published: April 2011

The effects of intrinsic parameter fluctuations, including line-edge-roughness (LER), silicon-body thickness variation (STV) and work-function variation (WFV), in 20-nm-gate variable-γ silicon-on-thin-box (SOTB) metal oxide semiconductor field effect transistors (MOSFETs) have been investigated and compared with those of the conventional SOTB. Results show that the variable-γ SOTB offers not only an enhancedIonbut also a reducedIonfluctuation with a small increase in the active-stateIofffluctuation. TheVth-roll-off value in the variable-γ SOTB can be reduced by adopting a reverse-biased side gate to optimize the short channel effect, but the variability of the DIBL effect is enlarged. It is expected that a thinner silicon body can be used to reduce the dominant variability sources.
Universal Relationship between Substrate Current and History Effect in Silicon-on-Insulator Metal–Oxide–Semiconductor Field-Effect Transistors
Authors: Amakawa Shuhei , Toda Asato , Ohyama Katsuroh , Higashiguchi Naoya , Hori Daisuke , Shintaku Yasuhiro , Miyake Masataka , Miura-Mattausch Mitiko
Published: April 2011

This paper presents an experimentally found device-size-independent universal relationship between the settling time of floating-body silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) and the substrate current in body-tied devices. Such a relationship could enable one to characterize dynamic properties of SOI MOSFETs through DC measurements and would be useful for physical compact modeling of history effects.
Advantage of Plasma Doping for Source/Drain Extension in Bulk Fin Field Effect Transistor
Authors: Izumida Takashi , Okano Kimitoshi , Kanemura Takahisa , Kondo Masaki , Inaba Satoshi , Itoh Sanae , Aoki Nobutoshi , Toyoshima Yoshiaki
Published: April 2011

The impact of plasma doping (PD) on the formation of source/drain extension (SDE) is demonstrated for a p-type bulk fin field effect transistor (FinFET). The impurity distribution in a narrow fin (15 nm) was analyzed with atom probe tomography (APT) and secondary ion mass spectroscopy (SIMS). The lateral distribution of boron in the Si fin by the PD is similar to the case with conventional beam-line ion implantation (BL). However, the vertical distribution of boron by the PD is much steeper than that by the conventional BL. TCAD simulations show that the driving current of the FinFET fabricated by the PD is 34% higher than that of the FinFET fabricated by the BL under the same off-leakage current. Therefore, the PD is a key technology for fabricating the SDE of narrow bulk-FinFETs in the future.
Multi-Gate Fin Field-Effect Transistors Junctions Optimization by Conventional Ion Implantation for (Sub-)22 nm Technology Nodes Circuit Applications
Authors: Veloso Anabela , Keersgieter An De , Brus Stephan , Horiguchi Naoto , Absil Philippe P. , Hoffmann Thomas
Published: April 2011

In this work we explore several doping schemes for aggressively scaled multi-gate field-effect transistor devices with the conduction channels wrapped around silicon fins (FinFETs) (H
Fin∼37 nm, W
Fin≥10 nm, L
g≥30 nm), using conventional ion implantation (I/I), and suitable for both logic and dense circuit applications. We demonstrate that low-energy and: 1) low-tilt, double-sided extension(-less) I/I, or 2) high-tilt, single-sided extension I/I schemes can enable pitch scaling without resist shadowing effects, with no penalty in device performance and yielding higher six transistors-static random access memory (6T-SRAM) static noise margin (SNM) values. Key advantages of the extension-less approach are: reduced cost and cycle time with 2 less critical I/I photos, enabling better quality, defect-free growth of Si-epitaxial raised source/drain (SEG), and up to 20× lower I
OFF. It, however, requires a tight spacer critical dimension (CD) control, a less critical parameter for the single-sided I/I scheme, which also allows wider overlay margins.
High Hole Mobility in 65 nm Strained Ge p-Channel Field Effect Transistors with HfO2 Gate Dielectric
Authors: Mitard Jerome , Jaeger Brice De , Eneman Geert , Dobbie Andrew , Myronov Maksym , Kobayashi Masaharu , Geypen Jef , Bender Hugo , Vincent Benjamin , Krom Raymond , Franco Jacopo , Winderickx Gillis , Vrancken Evi , Vanherle Wendy , Wang Wei-E. , Tseng Joshua , Loo Roger , Meyer Kristin De , Caymax Matty , Pantisano Luigi , Leadley David R. , Meuris Marc , Absil Philippe P. , Biesemans Serge , Hoffmann Thomas
Published: April 2011

Biaxially-strained Ge p-channel field effect transistors (pFETs) have been fabricated for the first time in a 65 nm technology. The devices are designed to have a reduced effective oxide thickness (EOT) while maintaining minimized short channel effects. Low and high field transport has been studied by in-depth electrical characterization, showing a high hole-mobility that is enhanced by up to 70% in the strained devices. The important role of pocket implants in degrading the drive current is highlighted. Using a judicious implantation scheme, we demonstrate a significant gain in on-current (up to 35%) for nanoscaled strained Ge pFETs. Simultaneous optimization of the gate metal and dielectric, together with the corresponding uniaxial stress engineering, is identified as a promising path for further performance enhancement.
Experimental Investigations on Ballistic Transport in Multi-Bridged Channel Field Effect Transistors
Authors: Jung Young Chai , Hong Byoung Hak , Choi Luryi , Hwang Sung Woo , Cho Keun Hwi , Lee Sung-Young , Kim Dong-Won , Park Donggun
Published: April 2011

Electrical characteristics of multi bridged channel field effect transistor (MBCFET) with various channel lengths (L) ranging from 500 to 48 nm have been investigated. The current–voltage characteristics do not show any sign of short channel effect due to surrounding gate structures. The gate bias power law of the drain saturation current, mobility, and ballistic efficiency as functions of L show mixed features of drift-diffusion and ballistic transport. The channel resistance shows anomalous decrease when L≤60 nm, which is related with the transconductance overshoot resulted in ballistic transport at small V
DS. Temperature (T) dependence of the 100 nm device shows another type of transport region when T < 40 K, which can be interpreted as the one-dimensional quantum ballistic regime.