bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of biomagnetic measurement system for mice with high spatial resolution
Authors: Ono Yumie , Ishiyama Atsushi , Kasai Naoko , Chinone Kazuo
Published: July 2004

We have been developing a mice biomagnetic measurement system using a dc superconducting quantum interference device magnetometer for a comparative magnetoencephalogram study of transgenic and wild mice. In this study, we adopted a magnetometer with a pickup coil of 1.0mm diameter and 0.7mm lift-off distance to improve spatial resolution and magnetic field sensitivity. The magnetocardiogram of a wild mouse was measured as the initial application of the system. The bipolar peak positions in a magnetic field map separated by 5.6mm were clearly detected with the maximum amplitude of 88pT.
Stable transistors in hydrogenated amorphous silicon
Authors: Shannon J. M.
Published: July 2004

Thin-film field-effect transistors in hydrogenated amorphous silicon are notoriously unstable due to the formation of silicon dangling bond trapping states in the accumulated channel region during operation. Here, we show that by using a source-gated transistor a major improvement in stability is obtained. This occurs because the electron quasi-Fermi level is pinned near the center of the band in the active source region of the device and strong accumulation of electrons is prevented. The use of source-gated transistors should enable stable analog circuits to be made in amorphous silicon.
Universal three-way few-electron switch using silicon single-electron transistors
Authors: He Jin , Durrani Zahid A. K. , Ahmed Haroon
Published: July 2004

A three-way few-electron switch is implemented using bidirectional electron pumps in silicon-on-insulator material. The switch consists of three branches defined by single-electron transistors, connected to a central node. Any combination of two single-electron transistors forms a bidirectional electron pump. At 4.2K, each cycle of an rf signal applied to the central node pumps electron packets approximately ten electrons in size through the circuit. It is possible to switch the electron packets in any direction through the branches. The switch may be used for the precise transfer of electrons, and as the basic element in few-electron logic applications.
Negative refraction of acoustic waves in two-dimensional phononic crystals
Authors: Zhang Xiangdong , Liu Zhengyou
Published: July 2004

Negative refraction of acoustic waves in two-dimensional phononic crystals has been demonstrated through both analysis and exact numerical simulation. The methods to achieve this behavior have been discussed. A microsuperlens for acoustic waves has also been designed. It is shown that refractive devices based on phononic crystals behave in a manner similar to that of optical systems. Therefore, a negative square root of the effective density or negative refraction index for acoustic waves can be introduced to describe this phenomena very well as the case of electromagnetic waves in the photonic crystals.
Quasisuperlattice storage: A concept of multilevel charge storage
Authors: Chang T. C. , Yan S. T. , Liu P. T. , Chen C. W. , Wu H. H. , Sze S. M.
Published: July 2004

A concept of the quasisuperlattice storage has been demonstrated in this study. Under suitably operated voltage, two apparent states of charge storage can be distinguished. The memory effects are due to the multilevel storage in the quasisuperlattice. Also, the a-Si quantum wells provide a feasible design for the 2 bit per cell nonvolatile memory devices. The operation of the 2 bit per cell needs to be performed by Fowler–Nordheim tunneling instead of conventional channel hot electron injection. Additionally, the dual read operation of the source and drain sides for conventional SONOS 2bit∕cell device is not necessary, which simplifies the circuit design engineering.
Microrubbing technique to produce high pretilt multidomain liquid crystal alignment
Authors: Varghese Soney , Crawford Gregory P. , Bastiaansen Cees W. M. , de Boer Dick K. G. , Broer Dirk J.
Published: July 2004

We disclose a microrubbing (μ-rubbing) technique to create multidomain alignment in liquid crystal displays. A small metallic sphere under sufficient load is used to directly rub a polyimide alignment layer that is known to enforce homeotropic boundary conditions of the liquid crystal. We demonstrate a 47μm linewidth and a 10° pretilt with respect to the substrate plane. We report on the electro-optic performance properties and viewing angle characteristics of four domain samples, where the midplane angle of the director is oriented in four different directions.
Mouse dyskerin mutations affect accumulation of telomerase RNA and small nucleolar RNA, telomerase activity, and ribosomal RNA processing
Authors: Mochizuki Yuko , He Jun , Kulkarni Shashikant , Bessler Monica , Mason Philip J.
Published: July 2004

Dyskerin is a nucleolar protein present in small nucleolar ribonucleoprotein particles that modify specific uridine residues of rRNA by converting them to pseudouridine. Dyskerin is also a component of the telomerase complex. Point mutations in the human gene encoding dyskerin cause the skin and bone marrow failure syndrome dyskeratosis congenita (DC). To test the extent to which disruption of pseudouridylation or telomerase activity may contribute to the pathogenesis of DC, we introduced two dyskerin mutations into murine embryonic stem cells. The A353V mutation is the most frequent mutation in patients with X-linked DC, whereas the G402E mutation was identified in a single family. The A353V, but not the G402E, mutation led to severe destabilization of telomerase RNA, a reduction in telomerase activity, and a significant continuous loss of telomere length with increasing numbers of cell divisions during
in vitro
culture. Both mutations caused a defect in overall pseudouridylation and a small but detectable decrease in the rate of pre-rRNA processing. In addition, both mutant embryonic stem cell lines showed a decrease in the accumulation of a subset of H/ACA small nucleolar RNAs, correlating with a significant decrease in site-specific pseudouridylation efficiency. Interestingly, the H/ACA snoRNAs decreased in the G402E mutant cell line differed from those affected in A353V mutant cells. Hence, our findings show that point mutations in dyskerin may affect both the telomerase and pseudouridylation pathways and the extent to which these functions are altered can vary for different mutations.
Signature quantization and representations of compact Lie groups
Authors: Guillemin Victor , Rassart Etienne
Published: July 2004

We discuss some applications of signature quantization to the representation theory of compact Lie groups. In particular, we prove signature analogues of the Kostant formula for weight multiplicities and the Steinberg formula for tensor product multiplicities. Using symmetric functions, we also find, for type
A
, analogues of the Weyl branching rule and the Gel'fand–Tsetlin theorem.
Rapid recent growth and divergence of rice nuclear genomes
Authors: Ma Jianxin , Bennetzen Jeffrey L.
Published: July 2004

By employing the nuclear DNA of the African rice
Oryza glaberrima
as a reference genome, the timing, natures, mechanisms, and specificities of recent sequence evolution in the
indica
and
japonica
subspecies of
Oryza sativa
were identified. The data indicate that the genome sizes of both
indica
and
japonica
have increased substantially, >2% and >6%, respectively, since their divergence from a common ancestor, mainly because of the amplification of LTR-retrotransposons. However, losses of all classes of DNA sequence through unequal homologous recombination and illegitimate recombination have attenuated the growth of the rice genome. Small deletions have been particularly frequent throughout the genome. In >1 Mb of orthologous regions that we analyzed, no cases of complete gene acquisition or loss from either
indica
or
japonica
were found, nor was any example of precise transposon excision detected. The sequences between genes were observed to have a very high rate of divergence, indicating a molecular clock for transposable elements that is at least 2-fold more rapid than synonymous base substitutions within genes. We found that regions prone to frequent insertions and deletions also exhibit higher levels of point mutation. These results indicate a highly dynamic rice genome with competing processes for the generation and removal of genetic variation.
In Vivo Reconstitution of the Negative Feedback in Nitric Oxide/cGMP Signaling: Role of Phosphodiesterase Type 5 Phosphorylation
Authors: Mullershausen Florian , Russwurm Michael , Koesling Doris , Friebe Andreas
Published: July 2004

Most effects of the messenger molecule nitric oxide (NO) are mediated by cGMP, which is formed by NO-sensitive guanylyl cyclase (GC) and degraded by phosphodiesterases (PDEs). In platelets, NO elicits a spike-like cGMP response and causes a sustained desensitization. Both characteristics have been attributed to PDE5 activation caused by cGMP binding to its regulatory GAF domain. Activation is paralleled by phosphorylation whose precise function remains unknown. Here, we report reconstitution of all features of the NO-induced cGMP response in human embryonic kidney cells by coexpressing NO-sensitive GC and PDE5. The spike-like cGMP response was blunted when PDE5 phosphorylation was enhanced by additional overexpression of cGMP-dependent protein kinase. Analysis of PDE5 activation in vitro revealed a discrepancy between the cGMP concentrations required for activation (micromolar) and reversal of activation (nanomolar), indicating the conversion of a low-affinity state to a high-affinity state upon binding of cGMP. Phosphorylation even increased the high apparent affinity enabling PDE5 activation to persist at extremely low cGMP concentrations. Our data suggest that the spike-like shape and the desensitization of the cGMP response are potentially inherent to every GC- and PDE5-expressing cell. Phosphorylation of PDE5 seems to act as memory switch for activation leading to long-term desensitization of the signaling pathway.
A laboratory of one's own: the life and works of Agnes Arber, F.R.S. (1879-1960)
Authors: Packer Kathryn
Published: July 2004

To many she was the ‘lady of botany’ and young biologists should think of an acute and powerful observer wrapt in penetrating and ever more powerful philosophy, who grasped the world without travel, and how they attract into the circle of discussion such another if they are fortunate.
Book reviews
Authors: Parkin Jon
Published: July 2004

Nine book reviews in the January 1997 edition of
Notes and Records
Nicholas Wolterstorff,
John Locke and the Ethics of Belief
. John Stoye,
Marsigli's Europe 1680–1730, the Life and Times of Luigi Ferdinando Marsigli, Soldier and Virtuoso
. Arthur Donovan,
Antoine Lavoisier: Science, Administration and Revolution
. James R. Hofmann,
André–Marie Ampére
. Patsy Gerstner,
Henry Darwin Rogers, 1808–1866––American Geologist
.
Charles Darwin's Letters. A selection 1825–1859
, Edited by Frederick Burkhardt.
Oliver Lodge and the Invention of Radio
, Edited by Peter Rowlands and J. Patrick. V.V. Krishna,
S.S. Bhatnagar on Science, Technology and Development 1938–54
. Jagdish Mehra,
The Beat of a Different Drum. The Life and Science of Richard Feynman
.
Confronting SARS: a view from Hong Kong
Authors: Peiris J. S. M. , Guan Y.
Published: July 2004

Severe acute respiratory syndrome (SARS) emerged as a new disease in Guangdong Province, People's Republic of China in late 2002. Within weeks it had spread to Hong Kong and thence globally to affect over 25 countries across five continents. The disease had the propensity to cause clusters of pneumonia, particularly in healthcare workers or close family contacts. A global effort coordinated by the World Health Organization successfully defined the aetiology, epidemiology and clinical characteristics of the disease, and the implementation of case identification, isolation and infection control measures led to the interruption of the global outbreak by July 2003. The pattern of disease emergence and strategies for control of SARS provides lessons for coping with future emerging infectious disease threats.
The international response to the outbreak of SARS in 2003
Authors: Heymann David L.
Published: July 2004

The sudden arrival of an internationally spreading outbreak of a newly identified infectious disease in early 2003, severe acute respiratory syndrome (SARS), provided an opportunity for a coordinated international response based on information and evidence obtained in real time through standard and electronic communications. Its containment represents a new way of working internationally, and demonstrates how intense collaboration in virology, clinical medicine and epidemiology can rapidly provide the information necessary to create and implement evidence–based control measures. The SARS outbreak serves as a reminder of the need for a strong national surveillance and response to infectious diseases, evidence–based international travel recommendations, and a global alert and response network to serve as a safety net when national surveillance fails.
An Analysis of the Distribution of Extreme Share Returns in the UK from 1975 to 2000
Authors: Gettinby G. D. , Sinclair C. D. , Power D. M. , Brown R. A.
Published: July 2004

This paper seeks to characterise the distribution of extreme returns for a UK share index over the years 1975 to 2000. In particular, the suitability of the following distributions is investigated: Gumbel, Frechet, Weibull, Generalised Extreme Value, Generalised Pareto, Log‐Normal and Generalised Logistic. Daily returns for the FT All Share index were obtained from Datastream, and the maxima and minima of these daily returns over a variety of selection intervals were calculated. Plots of summary statistics for the weekly maxima and minima on statistical distribution maps suggested that the best fitting distribution would be either the Generalised Extreme Value or the Generalised Logistic. The results from fitting each of these two distributions to extremes of a series of UK share returns support the conclusion that the Generalised Logistic distribution best fits the UK data for extremes over the period of the study. The Generalised Logistic distribution has fatter tails than either the log‐normal or the Generalised Extreme Value distribution, hence this finding is of importance to investors who are concerned with assessing the risk of a portfolio.
Replacement Investment: Optimal Economic Life Under Uncertainty
Authors: Dobbs Ian M.
Published: July 2004

Replacement investment is essentially a regenerative optimal stopping problem; that is, the key decision concerns when to terminate the life of existing plant – and hence when to start over again. This paper examines this optimisation problem within a continuous time framework and studies the qualitative and quantitative impact of uncertainty on the timing of new investment (and the criteria that should be used for terminating the life of existing plant).
Time‐Varying Volatility in the Foreign Exchange Market: New Evidence on its Persistence and on Currency Spillovers
Authors: Chowdhury Ibrahim , Sarno Lucio
Published: July 2004

We examine empirically the volatility of four major US dollar spot exchange rates using intraday data over 40 trading days. Using multivariate stochastic volatility models, we investigate the degree of persistence of exchange rate volatility for data sampled at different frequencies and the role of volatility spillovers across exchange rates. We find that the noise component of volatility ‘aggregates out’ very quickly, being dominated by the more persistent component of volatility for data sampled at 15–minute or lower frequencies. Our results also suggest that exchange rate volatility is very persistent and that cross–currency spillovers are small.
Regulation of Circuits and Excitability: Implications for Epileptogenesis
Authors: Hablitz John J.
Published: July 2004

Regulation of activity in neuronal circuits is poorly understood. Alterations in regulatory mechanisms may underlie the transition from interictal to ictal activity. Epileptogenesis is thought to arise from hyperexcitability in populations of neurons, resulting from alterations in connectivity and synaptic physiology. Recent studies suggest that excitability in local circuits of neurons also can be changed by short-term plasticity induced by repetitive stimulation and actions of neuromodulators. It is suggested that these factors could be elements underlying excitability changes that contribute to the periodic nature of seizures.
Characteristics of Heat Transfer During Machining With Rotary Tools
Authors: Kishawy and H. A. , Gerber A. G.
Published: July 2004

In this paper a model is developed to analyze heat transfer and temperature distribution resulting during machining with rotary tools. The presented model is based on a finite-volume discretization approach applied to a general conservation of energy statement for the rotary tool and chip during machining. The tool rotational speed is modeled and its effect on the heat partitioning between the tool and the chip is investigated. The model is also used to examine the influence of tool speed on the radial temperature distribution on the tool rake face. A comparison between the predicted and previously measured temperature data shows good agreement. In general the results show that the tool-chip partitioning is influenced dramatically by increasing the tool rotational speed at low to moderate levels of tool speed. Also, there is an optimum tool rotational speed at which further increase in the tool rotational speed increases the average tool temperature.
Monitoring Resistance Spot Nugget Size by Electrode Displacement
Authors: Farson, D. F. , Chen, J. Z. , Ely and K. , Frech T.
Published: July 2004

A high-speed video imaging system was employed to directly measure the electrode displacement of the small scale resistance spot welding (SSRSW) process. This measurement technique was chosen because it eliminates a number of potential error sources inherent in other electrode displacement measuring techniques. Careful observation of the heating and cooling portions of the electrode displacement curves revealed that each is comprised of two identifiable segments. Distinct high-velocity segments of the displacement curves were thought to correspond to solid-liquid phase transitions in the weld nugget, while lower-velocity portions corresponded to thermal expansion or contraction of solid material. It was found that the magnitudes of the high speed portions of the electrode displacement were more closely correlated with the weld nugget thickness than was the overall magnitude of the electrode displacement. Furthermore, all measures of electrode displacement were more closely correlated to weld nugget thickness than to nugget diameter.
Mechanics and Dynamics of Serrated Cylindrical and Tapered End Mills
Authors: Merdol S. D. , Altintas Y.
Published: July 2004

Serrated end mills are effectively used in suppressing chatter vibrations in roughing operations. Mechanics and dynamics of serrated cylindrical and tapered helical end mills are presented in the article. The serrated flute design knots are fitted to a cubic spline, which is then projected on helical flutes. Cutting edge geometry at any point along the serrated flute is represented by its immersion angle and tangent vectors in radial, tangential and helical directions. The chip thickness removed by each cutting edge point is determined by using exact kinematics of dynamic milling. The cutting forces are evaluated by orthogonal to oblique cutting mechanics transformation. The experimentally proven model is able to predict the cutting forces and chatter stability lobes in time domain. It is shown that the proposed model can be used in evaluating the performance of serrated end mills during their stage.
Production Line Calibration for Sensors on Actively Controlled Bullets
Authors: Erickson Mark , Costello Mark
Published: July 2004

A simple testing device is presented that simultaneously calibrates all dominant error sources for accelerometers and gyroscopes found in typical microelectromechanical inertial measurement units on smart projectiles, including bias, scale factor, cross axis sensitivity/misalignment, and misposition. The device consists of a table which rotates about a gimbal joint and is supported on the corners by elastic and damping elements. Using dynamic simulation it is shown that motion created by free vibration of the testing platform suitably excites sensors on projectiles so calibration can be performed. Calibration parameters are estimated using an extended Kalman filter. Platform support stiffness and damping characteristics significantly alter the time required to identify calibration parameters by shaping platform motion. A critical level of initial motion of the testing platform is required for adequate prediction of calibration parameters.
Experimental Characterization of Nonlinear Dynamics Underlying the Cylindrical Grinding Process
Authors: Bukkapatnam Satish T. S. , Palanna Rajkumar
Published: July 2004

This paper presents our characterization of dynamics underlying the cylindrical grinding of shafts using accelerometer signals gathered from a set of designed experiments. The results of our characterizations show that the dynamics, under steady state, evolves into a finite-dimensional, perhaps chaotic, attractor contaminated by noise, with fractal dimension values hovering between 3.1 and 3.8. The major implication of this finding is in the development of tractable models to control this industrially important shaft grinding process.
Machining Process Monitoring and Control: The State-of-the-Art
Authors: Liang Steven Y. , Hecker Rogelio L. , Landers Robert G.
Published: July 2004

Research in automating the process level of machining operations has been conducted, in both academia and industry, over the past few decades. This work is motivated by a strong belief that research in this area will provide increased productivity, improved part quality, reduced costs, and relaxed machine design constraints. The basis for this belief is two-fold. First, machining process automation can be applied to both large batch production environments and small batch jobs. Second, process automation can autonomously tune machine parameters (feed, speed, depth of cut, etc.) on-line and off-line to substantially increase the machine tool’s performance in terms of part tolerances and surface finish, operation cycle time, etc. Process automation holds the promise of bridging the gap between product design and process planning, while reaching beyond the capability of a human operator. The success of manufacturing process automation hinges primarily on the effectiveness of the process monitoring and control systems. This paper discusses the evolution of machining process monitoring and control technologies and conducts an in-depth review of the state-of-the-art of these technologies over the past decade. The research in each area is highlighted with experimental and simulation examples. Open architecture software platforms that provide the means to implement process monitoring and control systems are also reviewed. The impact, industrial realization, and future trends of machining process monitoring and control technologies are also discussed.
Process Design of Laser Forming for Three-Dimensional Thin Plates
Authors: Cheng Jin , Yao Y. Lawrence
Published: July 2004

Extensive efforts have been made in analyzing and predicting laser forming processes of sheet metal. Process design, on the other hand, is concerned with determination of laser scanning paths and laser heat condition given a desired shape. This paper presents an approach for process design of laser forming of thin plates with doubly curved shapes. The important feature of this method is that it first calculates the strain field required to form the shape. Scanning paths are decided based on the concept of in-plane strain, bending strain, principal minimal strain and temperature gradient mechanism of laser forming. Heating condition is determined by a lumped method. Effectiveness of the approach is numerically and experimentally validated through two different doubly curved shapes.
Decomposition of Thermal and Mechanical Effects on Microstructure and Hardness of Hard Turned Surfaces
Authors: Shi Jing , Liu C. Richard
Published: July 2004

Hard turning involves the mechanical deformation of materials, coupled with the heat generation from friction and dissipation of deformation energy. The mechanical and thermal effects on microstructure and hardness of hard turned surfaces are decomposed by a proposed method using X-Ray diffraction line profile analysis and hardness test. It is revealed that the structure could be represented by the diffraction profile and further by a parameter, Gaussian Curve Parameter (GCP), from fitting the diffraction line peak by a Gaussian curve. The thermal effect on structure can therefore be identified from the change in diffraction profiles. For heat treated parts, identical structures or profiles yield the same hardness. However, hard turned specimens with the same peak line profile often have higher measured hardness than the heat treated ones. Thus, the residual mechanical hardening effect, from strain and strain rate hardening, can be separated and reflected by the amount of hardness difference. The mechanical effects beneath the machined surfaces vary in depth, but little effect on the very surface is found. Larger tool wear and depth of cut usually give rise to deeper mechanical affected and thermal affected layers.
Continuous Optimal Infeed Control for Cylindrical Plunge Grinding, Part 2: Controller Design and Implementation
Authors: Dong Shaoqiang , Danai Kourosh , Malkin Stephen
Published: July 2004

This is the second of two papers concerned with on-line optimization of cylindrical plunge grinding cycles with continuously varying infeed control. In the first paper [1], dynamic programming was applied to a simulation of the cylindrical grinding process in order to explore the characteristics of optimal grinding cycles. Optimal cycles were found to consist of distinct segments each with predominant constraints. An optimal control policy was formulated with the infeed rate within each segment determined according to the prevailing constraint. The present paper is concerned with the design of the controller and its implementation. The control system to implement the optimization policy is described together with provisions to enhance robustness to modeling uncertainty and measurement noise. Robustness provisions include model adaptation by parameter estimation from on-line measurements of size and power, and incorporation of safety margins in the optimization process. Problems associated with practical implementation of the control system, stemming from power limitations and wheel wear, are also discussed. The controller performance is demonstrated on an instrumented internal cylindrical grinding machine.
Mechanical Reliability and Bump Degradation of ACF Flip Chip Packages Using BCB (Cyclotene™) Bumping Dielectrics Under Temperature Cycling
Authors: Kwon Woon-Seong , Kim Hyoung-Joon , Paik Kyung-Wook , Jang Se-Young , Hong Soon-Min
Published: July 2004

Interface degradation between dissimilar materials in the flip chip packages with anisotropic conductive adhesive joint is susceptible to mechanical and electrical failure upon temperature cycling. Particularly the mechanical reliability of flip chip using anisotropic conductive films (ACFs) often depends upon the interface characteristics between the bumping/passivation dielectrics and adjacent materials. This paper investigates the delamination and cracking in polymeric bumping/passivation dielectrics (Cyclotene™ 4024) and the damage mechanism of interconnect bump with BCB bumping dielectrics upon temperature cycling. Adhesion and fracture surface morphology after die shear testing show that the weakening and delamination of BCB passivation layer at the die corner is the main cause of the reduction of die adhesion strength after the thermal cycling. The sliding trace on fracture surface after three-point bending fracture reveals that cyclic shear displacement in a polymeric BCB layer fatigue the interface bonding or interconnect bump upon thermal cycling, leading to mechanical delamination and functional bump failure. Passivation cracks also develop around the circumference of BCB passivation over aluminum pad. A model is presented for the degradation of interconnect bump with surrounding BCB passivation.
Development of G-Helix Structure as Off-Chip Interconnect
Authors: Zhu Qi , Ma Lunyu , Sitaraman Suresh K.
Published: July 2004

Microsystem packages continue to demand lower cost, higher reliability, better performance and smaller size. Compliant wafer-level interconnects show great potential for next-generation packaging. G-Helix, an electroplated compliant wafer-level chip-to-substrate interconnect can facilitate wafer-level probing as well as wafer-level packaging without the need for an underfill. The fabrication of the G-Helix interconnect is similar to conventional IC fabrication process and is based on electroplating and photolithography. G-Helix interconnect has good mechanical compliance in the three orthogonal directions and can accommodate the differential displacement induced by the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate. In this paper, we report the wafer-level fabrication of an area-arrayed G-Helix interconnects. The geometry effect on the mechanical compliance and electrical parasitics of G-Helix interconnects have been studied. Thinner and narrower arcuate beams with larger radius and taller post are found to have better mechanical compliance. However, it is also found that structures with excellent mechanical compliance may not have good electrical performance. Therefore, a trade off is needed. Using response surface methodology (RSM), an optimization has been done. Furthermore, reliability of the optimized G-helix interconnects in a silicon-on-organic substrate assembly has been assessed, which includes the package weight and thermo-mechanical analysis. The pitch size effect on the electrical and mechanical performance of G-Helix interconnects has also been studied.
Accelerated Thermal Cycling Guidelines for Electronic Packages in Military Avionics Thermal Environment
Authors: Pucha Raghuram V. , Tunga Krishna , Pyland James , Sitaraman Suresh K.
Published: July 2004

A field-use induced damage mapping methodology is presented that can take into consideration the field-use thermal environment profile to develop accelerated thermal cycling guidelines for packages intended to be used in military avionics thermal environment. The board-level assembly process mechanics and critical geometric features with appropriate material models are taken into consideration while developing the methodology. The models developed are validated against in-house and published accelerated thermal cycling experimental data. The developed mapping methodology is employed to design alternate accelerated thermal cycles by matching the creep and plastic strain contributions to total inelastic strain accumulation in solder under military field-use and accelerated thermal cycling environments, while reducing the time for accelerated thermal cycling and qualification.
Relationship between field emission property and composition of carbon nanotube paste for large area cold cathode
Authors: Kang Sung Kee , Choi Jong Hyung , Park Jae Hong , Han Jae-Hee , Yoo Ji-Beom , Nam Joong-Woo , Lee Chun Kyu , Kim J. M.
Published: July 2004

Carbon nanotube (CNT) paste was prepared by a mixture of multi-walled carbon nanotubes powders synthesized by arc discharge, organic vehicles and inorganic binders. We investigated rheological properties of CNT paste using a rheometer. In order to obtain the fine dispersion of CNTs in paste, pass time of 3-roll mill was increased from 3–15. However, emission current density was decreased with an increase in pass time of 3-roll mill because of an increase in the interaction among CNT powders, organic vehicles and inorganic binder. It was found that emission property of a CNT paste depends mainly on the concentration of inorganic binder and firing time. We obtained good emission property by using a CNT paste with 30 wt% inorganic binders after treatment at 350 °C for 30 min.
Characteristics of nano electron source fabricated using beam assisted process
Authors: Murakami Katsuhisa , Takai Mikio
Published: July 2004

A nano electron source was fabricated using electron beam-induced deposition. Characteristics of a nano electron source fabricated using beam assisted processes were investigated by current–voltage measurement. The emission current was observed at a gate voltage of 25 V and showed a linear dependence in Fowler–Nordheim plots. An emission half-angle of about 9.8° was obtained.
Single-phase growth studies of GaP on Si by solid-source molecular beam epitaxy
Authors: Yu Xiaojun , Kuo Paulina S. , Ma Kai , Levi Ofer , Fejer Martin M. , Harris James S.
Published: July 2004

GaP/Si heterostructures were grown under different growth conditions by molecular beam epitaxy in order to obtain single-phase GaP on Si. The growth results were examined by reflective high-energy electron diffraction, anisotropic etching, atomic force microscopy, and x-ray diffraction. The results showed that high quality, single-phase GaP was grown on Si at a high growth temperature, about 500 °C, with a low P/Ga flux ratio of 2.5×, while at a lower temperature, a second phase with a 90° in-plane rotation was grown.
Temperature stabilized 1.55 μm photoluminescence in InAs quantum dots grown on InAlGaAs/InP
Authors: Zhang Z. H. , Cheng K. Y.
Published: July 2004

We report on temperature stabilized photoluminescence centered around 1.55 μm in InAs quantum dots grown by molecular beam epitaxy on InP substrate using InAlGaAs as the matrix layer. The photoluminescence emission peak wavelength of quantum dot samples with 5.5 monolayers of InAs deposition has a near zero shift between 300 and 77 K measurements. Decreasing the deposited InAs layer thickness or introducing a GaAs strain-balance layer leads to a regular redshift in the photoluminescence emission with increasing temperature. On the contrary, a blueshift is observed on samples with a thicker InAs layer thickness. These phenomena indicate the strain around quantum dots plays an important role in deciding the temperature-dependent properties of the quantum dot samples. This interesting temperature stabilization of photoluminescence in the quantum dot samples offers great potential for optical communication laser applications.
Effect of Ga-rich growth conditions on the optical properties of GaN films grown by plasma-assisted molecular beam epitaxy
Authors: Sampath A. V. , Garrett G. A. , Collins C. J. , Boyd P. , Choe J. , Newman P. G. , Shen H. , Wraback M. , Molnar R. J. , Caissie J.
Published: July 2004

While it is well known that high quality III–nitride material is deposited by plasma-assisted molecular beam epitaxy (PA-MBE) only under III-rich conditions, the extent of III-flux required for optimal film growth is unclear. In this article, we focus on the dependence of the optical properties of the material on the III/V flux ratio. Specifically, we report on the photoluminescence (PL) intensity and the lifetime of photogenerated carriers in homoepitaxially grown GaN films, deposited under Ga-rich conditions, as a function of the Ga flux employed during growth. The samples investigated consist of ∼1.2 μm thick GaN films deposited homoepitaxially on ∼85 μm thick GaN templates grown by the hydride vapor phase epitaxy method. The films were deposited under Ga-rich conditions but without the formation of metal droplets. The Ga flux was varied from 0.89 to 1.0×10−6 Torr while the N-plasma conditions (300 W, 0.6 sccm) were held constant. The intensity of the room temperature PL measured for films grown under intermediate flux (9.2×10−7 Torr) conditions is observed to be 3.5–4 times brighter than what is seen for films grown under the lower (8.9×10−7 Torr) and higher (1×10−6 Torr) flux conditions. Similarly, the lifetime of photogenerated carriers, as measured by pump–probe time-resolved reflectivity, in films grown at the higher Ga flux was found to be ∼2 times smaller than that observed for films grown at the intermediate flux. The dependence of the carrier lifetime on the density of photogenerated carriers in these films suggests that films grown under high flux conditions have a larger density of deep trap states than films grown under intermediate conditions. These results can be explained by the formation of defects under Ga-rich growth conditions that suppress band-to-band recombination in these materials, and are important for the development of PA-MBE-grown optoelectronic devices.
Theoretical analysis of the enhanced electric field at the triple junction
Authors: Chung Moon S. , Yoon Byung-G. , Cutler Paul H. , Miskovsky Nicholasky M.
Published: July 2004

The electric-field behavior at the triple junction of metal–dielectric–vacuum is theoretically investigated. For a two-dimensional junction in which the electric-field magnitude F behaves as rν−1, ν is obtained as a function of the configuration geometry and the dielectric constant. It is found that ν varies with the dielectric portion in the field-varying region, becoming as low as 0.25 in the extreme case. The enhancement of F due to the reduction of ν is responsible for the field emission enhancement as well as the vacuum insulation breakdown at the triple junction.
Solid-source molecular-beam epitaxy growth of GaInNAsSb/InGaAs single quantum well on InP with photoluminescence peak wavelength at 2.04 μm
Authors: Fu Jun-Xian , Bank Seth R. , Wistey Mark A. , Yuen Homan B. , Harris James S.
Published: July 2004

Single quantum wells In0.53Ga0.47As/Ga0.47In0.53N0.021As0.949Sb0.03/In0.53Ga0.47As with room-temperature photoluminescence peak wavelength at 2.04 μm were grown on InP substrate by solid-source molecular-beam epitaxy (MBE). In situ reflection high-energy electron diffraction was used to monitor the MBE growth. Double-crystal high-resolution x-ray diffraction and secondary ion mass spectrometry were utilized to characterize the samples and optimize the growth conditions. The roles of nitrogen and antimony atoms in the growth of quinary material, GaInNAsSb, were investigated.
In situ mass spectrometry in a 10 Torr W chemical vapor deposition process for film thickness metrology and real-time advanced process control
Authors: Cho Soon , Henn-Lecordier Laurent , Liu Yijun , Rubloff Gary W.
Published: July 2004

In situ mass spectrometric sensing has been implemented in a 10 Torr H2/WF6 W chemical vapor deposition process as a real-time process and wafer state metrology tool. Dynamic sensing through the process cycle reveals HF byproduct generation as well as H2 and WF6 reactant depletion as real-time quantitative indicators of deposition on the wafer. Thickness metrology is achieved by integrating the HF byproduct signal through the process cycle and comparing it to post-process measurements of film weight. To evaluate the quantitative precision of this metrology, multiwafer runs have been performed under different sets of conditions: (1) fixed process conditions, (2) intentionally introduced run-to-run process temperature drift, and (3) run-to-run deposition time variation. These results demonstrate that real-time thickness metrology is achievable at a level of 1% or better in two application settings: (1) when an essentially fixed process recipe is employed, as in high-volume manufacturing; and (2) when more substantial changes in process recipe are explored, as in a development environment. In situ mass spectrometry presents an attractive option for real-time advanced process control with the prognosis for real-time course correction demonstrated here and its already established benefit to fault detection and classification.
Size and site controlled Ga nanodots on GaAs seeded by focused ion beams
Authors: Lugstein A. , Basnar B. , Bertagnolli E.
Published: July 2004

We present an approach for the generation of uniform metallic nanodots which, in contrast to conventional bottom up or top down processes, is based on a subtractive self-organization process relying on material decomposition induced by focused ion beam exposure. Nearly pure gallium dots were fabricated on GaAs (100) using a 50 keV Ga focused ion beam at normal incidence and a subsequent rapid thermal annealing. A dose of 2.5×1016 ions/cm2 can be considered as a threshold dose for the development of dots on GaAs (100). The diameters of these dots range from 120 to 850 nm with an aspect ratio of about 0.4 and a dot density of up to 7.23×107/cm2. Two-dimensional ordered arrays of embedded as well as freestanding Ga dots were fabricated by a site control technique relying on pre-patterned holes and an irradiation mediated migration and agglomeration.
Dependences of bottom and sidewall etch rates on bias voltage and source power during the etching of poly-Si and fluorocarbon polymer using SF6, C4F8, and O2 plasmas
Authors: Min Jae-Ho , Lee Gyeo-Re , Lee Jin-kwan , Moon Sang Heup , Kim Chang-Koo
Published: July 2004

The dependences of bottom and sidewall etch rates on the bias voltage and source power in four plasma/substrate systems constituting the advanced Bosch process were investigated using a Faraday cage and a step-shaped substrate specially designed for the accurate observation of lateral and vertical etch rates. The four systems, established by combining discharge gases and substrates, were SF6/poly-Si, SF6/fluorocarbon polymer, O2/fluorocarbon polymer, and C4F8/Si. For etch systems using SF6/poly-Si, SF6/polymer, and O2/polymer, the degree of anisotropy showed a higher dependence on the bias voltage than on the source power. As the bias voltage was increased, the degree of anisotropy obtained in SF6/poly-Si decreased while that for the SF6/polymer and O2/polymer increased. The contribution of spontaneous etching by reactive radicals to the etch rates increased in the order of SF6/polymer<O2/polymer<SF6/poly-Si, while that of ion-enhanced chemical etching by ions to the degree of anisotropy increased in the inverse order. For C4F8/Si, the redeposition of bottom-emitted particles on the sidewall had a significant effect on the etch characteristics of the sidewall. The sidewall etch rate was dependent on the bottom etch rate and showed different trends with bias voltage and source power. Based on these findings, optimum conditions for bias voltage and source power for each step of the advanced Bosch process, which are required for improved anisotropy, are proposed.
Plasma silicon oxide–silica xerogel based planar optical waveguides
Authors: Ponoth Shom S. , Agarwal Navnit T. , Persans Peter D. , Plawsky Joel L.
Published: July 2004

In this study, silica xerogels are used as the cladding for high-refractive-index-contrast waveguide systems. Silicon oxide, due to its relatively low refractive index, is an extensively used cladding material. The lower-refractive-index silica xerogel films enable us, to report losses for planar-slab waveguide systems with silicon oxide as the core. A spin-on sol-gel process was used for the silica xerogel deposition. The silicon oxide core was deposited using plasma enhanced chemical vapor deposition (PECVD), with silane and nitrous oxide as the reactive gases. Slab waveguides systems with core thickness of 1 μm and refractive-index contrast (Δn) as high as 0.35 were fabricated. With regard to the PECVD process, a deposition temperature of 150 °C enabled a stable structure, however, unacceptably high optical losses of 7±1.01 dB/cm at a wavelength of 650 nm and 5.59±0.69 dB/cm at 830 nm were measured using a prism-coupler based setup. On increasing the deposition temperature of the silicon–oxide film to 225 °C, the losses decreased to 0.98±0.73 dB/cm at 650 nm and 0.69±0.46 dB/cm at 830 nm. The decrease in the losses resulting from increasing the deposition temperature provided the motivation to develop deposition conditions to reduce stress in the silicon–oxide films at higher deposition temperatures for improved stability on xerogel films. Reduction in the silicon–oxide film stress was achieved by varying the silane and nitrous oxide flow rates. The deposition stress in the film was reduced from ∼460 to ∼240 MPa, mainly by increasing the silane flow rate. The silicon oxide with the reduced stress was stable on xerogel film with porosities as high as 56%, even though a deposition temperature of 300 °C was used. However, the slab waveguide stack using the low-stress silicon oxide exhibited an optical loss of 1.81±0.18 dB/cm at 650 nm and 1.41±0.27 dB/cm at 830 nm. The higher loss, as compared to that obtained for the higher-stress film deposited at 225 °C, is attributed to scattering from the columnar structure of the lower-stress silicon–oxide film.
Fabrication of high-quality-factor photonic crystal microcavities in InAsP/InGaAsP membranes
Authors: Srinivasan Kartik , Barclay Paul E. , Painter Oskar , Chen Jianxin , Cho Alfred Y.
Published: July 2004

In recent work [K. Srinivasan, P. E. Barclay, O. Painter, J. Chen, A. Y. Cho, and C. Gmachl, Appl. Phys. Lett. 83, 1915 (2003)] resonant mode linewidths of 0.10 nm (corresponding to a quality factor ∼1.3×104) were measured in a photonic crystal defect microcavity fabricated in an InAsP/InGaAsP multi-quantum-well membrane. The quality of device fabrication is of critical importance in the performance of these devices. Here, we present the results of key processing steps, including inductively coupled plasma reactive ion etching of a SiO2 mask and the InAsP/InGaAsP membrane, and a selective undercut wet etch of an underlying sacrificial InP layer to create the freestanding membrane. The importance of etching through the membrane layer deeply into the sacrificial InP layer is highlighted, and discussed in the context of the crystallographic nature of the undercut wet etch process. The results of device processing are compared with previous work done using a chemically assisted ion-beam etch, and a discussion of the benefits of the current approach is given.
Scaling down of ultrathin HfO2 gate dielectrics by using a nitrided Si surface
Authors: Kang Chang Seok , Choi Rino , Cho Hag-Ju , Kim Y. H. , Lee Jack C.
Published: July 2004

A surface nitridation technique using NH3 anneal has been investigated to reduce interface reaction and consequently the equivalent oxide thickness (EOT) of TaN/HfO2/Si metal–oxide–semiconductor capacitor. For the same EOT, the nitrided samples showed 1–2 order of magnitude lower leakage current density compared to the non-nitrided ones. Furthermore, the nitrided samples showed better thermal stability. However, nitridation induced higher interface state density and larger hysteresis. The degraded interface quality due to the nitridation was improved by post-metal annealing (PMA). Using the optimized nitridation and PMA, EOT of the capacitor was scaled down to ∼10 Å with keeping leakage current below 0.1 mA/cm2 at −1.5 V. Interface state density and hysteresis were ∼8.4×1010 eV−1/cm2, and 45 mV, respectively.