bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Multiple Axial Erosions on a Three-Dimensional Crack in Determining the Fatigue Life of Autofrettaged Pressurized Cylinders
Authors: Levy C. , Perl M. , Ma Q.
Published: July 2002

Erosion geometry effects on the mode I stress intensity factor (SIF) for a crack emanating from an erosion’s deepest point in a multiply eroded, autofrettaged, pressurized, thick-walled cylinder are investigated. The problem is solved via the finite element method (FEM). Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and SIFs are determined by the nodal displacement method. SIFs are evaluated for a variety of relative crack depths, a0/t=0.01-0.40, and crack ellipticities, a0/c=0.5-1.5, emanating from the tip of erosions of different geometry, namely: (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t=0.05-0.4; and (c) semi-elliptical erosions with ellipticities of d/h=0.3-2.0. The erosion separation angle, α, is taken from 7 to 360 deg. Deep cracks are found to be almost unaffected by the erosion. The effective SIF for relatively short cracks is enhanced by the presence, separation distance and geometry of the erosion, as well as the crack geometry, and may result in a significant decrease in the vessel’s fatigue life of up to an order of magnitude.
Mechanical Behavior of a Branch Pipe Subjected to Out-of-Plane Bending Load
Authors: Chapuliot S. , Moulin D. , Plancq D.
Published: July 2002

A numerical and experimental study on the behavior of a branch pipe is presented in this article. The test is the first one of a series analyzing the behavior of the branch pipe under out-of-plane bending load in the presence of a crack near the junction, a weld or internal pressure. It is performed under bending alone, without weld and without internal pressure, so as to constitute a reference for the series, and thus to estimate each parameter influence. In complement to the experimental study, finite element calculations are performed and presented in this article, so as to analyze the elastic-plastic behavior of the branch pipe and its limit state.
Determination of Allowable Pushrod Angle Using a Three-Dimensional Valve Train Model
Authors: Cheng C. Y. , Lewandowski D. J. , David J. W.
Published: July 2002

Pushrod-type valve trains are still found in many engines. Since a vertical pushrod causes interference with the intake port, which reduces engine power, the pushrod is sometimes tilted to increase the available cross-sectional area of the intake port. In order to analyze this mechanism, a three-dimensional valve train model was developed. The model is then verified through experimention. Simulation and experimental results agree that valve train dynamic performance is not significantly affected by pushrod angles less than 20 degrees.
Some Algebraically Explicit Analytical Solutions of Unsteady Nonlinear Heat Conduction
Authors: Cai Ruixian , Zhang Na
Published: July 2002

The analytical solutions of nonlinear unsteady heat conduction equation are meaningful in theory. In addition, they are very useful to the computational heat conduction to check the numerical solutions and to develop numerical schemes, grid generation methods and so forth. However, very few explicit analytical solutions have been known for the unsteady nonlinear heat conduction. In order to develop the heat conduction theory, some algebraically explicit analytical solutions of nonlinear heat conduction equation have been derived in this paper, which include one-dimensional and two-dimensional unsteady heat conduction solutions with thermal conductivity, density and specific heat being functions of temperature.
Dispersion Relation and Stability Analysis of Flow-Induced Wave of a Flexible Circular Ring Subjected to Swirling Fluid Flow
Authors: Watanabe Masahiro , Kobayashi Nobuyuki
Published: July 2002

This paper deals with a theoretical stability analysis of unstable wave generated in a flexible circular ring subjected to swirling fluid flow. The flexible circular ring is set in a rotating circular outer casing with a narrow gap filled with fluid and is subjected to the swirling fluid flow caused by the rotation of the outer casing. In the stability analysis, a wave equation is derived from the equation of motion of the flexible circular ring coupled with the swirling fluid flow. The equation of motion of the flexible circular ring is based on the Kirchhoff-Love’s thin-shell model, and the equations of motion of the swirling fluid flow are based on the Navier-Stokes equations. Moreover, the dispersion relation of the wave generated in the flexible circular ring is derived from the wave equation as a function of the rotational speed of the outer casing. The analytical results show that an unstable wave occurs as a type of traveling forward wave due to the swirling fluid flow when the rotational speed of the outer casing becomes high, and that the most unstable wave mode, phase speed (traveling-wave speed), and growth rate of the wave vary greatly with increasing rotational speed of the outer casing.
A Computational Study of the Hemodynamics After “Edge-to-Edge” Mitral Valve Repair
Authors: Redaelli A. , Guadagni G. , Fumero R. , Maisano F. , Alfieri O.
Published: July 2002

Edge-to-edge mitral valve repair consists in suturing the free edge of the leaflets to re-establish coaptation in prolapsing valves. The leaflets are frequently sutured at the middle and a double orifice valve is created. In order to study the hemodynamic implications, a parametric model of the left heart has been developed. Different valve areas and shapes have been investigated. Results show that the simplified Bernoulli formula provides a good estimation of the pressure drop and that the pressure drop may be predicted on the basis of the pre-operative geometric and hemodynamics data by means of customized models.
Analysis of Cold Extrusion of Non Re-entry Product Shapes
Authors: Kumar Santosh , Shanker Kripa , Lal G. K.
Published: July 2002

The paper presents a feature-based analysis of cold extrusion process for non re-entry shapes. Part drawing of the shape to be extruded is drawn using line, arc, circle, polyline and ellipse entities of AutoCAD R-12 and corresponding DXF file is created. Treating shape as a feature, DXF file is processed and necessary data are separated for feature recognition. An upper-bound model for design of non re-entry cold extrudable shapes is proposed. The concept is then used to compare various die profiles based on the consideration of total extrusion power. It is found that third order stream-line and cosine dies are the best among various profiles considered. Parametric study for a square section using a third order polynomial die profile is carried out to study the effects of reduction ratio, friction factor and die length. Elliptical, trocoidal, rounded square and clover sections are examined for validating the proposed methodology.
Heat Transfer and Pressure Drop Characteristics of Laminar Flow
Through a Circular Tube With Longitudinal Strip Inserts Under Uniform Wall Heat
Flux
Authors: Saha S. K. , Langille P.
Published: July 2002

Heat transfer and pressure drop characteristics in a circular tube fitted with full-length strip, short-length strip, and regularly spaced strip elements connected by thin circular rods have been investigated experimentally. The strips have been rectangular, square and crossed in cross-section with different aspect ratio. Laminar flow of water and other viscous liquids was considered. The rod diameter and length of the strip-rod assembly and the length of the strips were varied. Isothermal friction factor data has been generated. The heat transfer test section was heated electrically imposing axially and circumferentially constant wall heat flux (UWHF) boundary condition. Reynolds number, Prandtl number, strip length, strip ratio, space ratio, and rod-diameter govern the characteristics. Smaller rod-diameter in the strip-rod assembly or “pinching” of the strips in place rather than connecting the strip elements by rods performs better thermohydraulically. Short-length strips (upto a limited fraction of the test section tube length) perform better than the full-length strip. The friction factor correlation and the correlation for Nusselt number under UWHF condition for full-length strip have been modified to make them suitable for short-length strip as well as regularly-spaced strip elements. Thermal entrance length in the correlations is represented by Graetz number. Friction factor and Nusselt number correlations for short-length strips as well as regularly-spaced strip elements, in the limit, reduce to their full-length counterparts.
Effective System Properties and Special Density in Random Vibration With Parametric Excitation
Authors: Krenk S. , Lin Y. K. , Ru¨dinger F.
Published: July 2002

The characteristic frequency and bandwidth of the random response to parametric excitation may be influenced by the excitation processes. It is demonstrated that the effective stiffness and damping properties can be expressed as conditional mean values for given displacement and energy levels, respectively. These properties are used to describe the response in terms of its probability density function and its spectral density function. An example demonstrates the accuracy in predicting change of frequency and damping of a parametrically excited oscillator, and another example extends the method to a self-excited oscillator with domains of negative damping.
Three-Dimensional Finite Element Analysis of the Cold Expansion of
Fastener Holes in Two Aluminum Alloys
Authors: Kang Jidong , Johnson W. Steven , Clark David A.
Published: July 2002

A three-dimensional finite element analysis is developed for the cold expansion process in two aluminum alloys, 2024-T351 and 7050-T7451. The entire cold working process including hole expansion, elastic recovery, and finish reaming is simulated. Both isotropic hardening and kinematic hardening models are considered in the numerical calculations. The results suggest that a three-dimensional nature exists in the residual stress fields surrounding the hole. There are significant differences in residual stresses at different sections through the thickness. However, residual stress at the surface is shown to remain the same for the different plastic hardening models after the hole has recovered and finish reaming has been performed. The reaming of the material around the hole has slight effect on the maximum value and distribution of residual stresses. A comparison has been drawn between the FEA of average through thickness strain and a previous experimental investigation of strain that utilized neutron diffraction and modified Sachs boring on a 7050 aluminum specimen containing a cold expanded hole. The different methods show very good agreement in the magnitude of strain as well as the general trend. The conclusions obtained here are beneficial to the understanding of the phenomenon of fatigue crack initiation and growth at the perimeter of cold worked holes.
A Deterministic Stress Model for Rotor-Stator Interactions in Simulations of Average-Passage Flow
Authors: Meneveau and Charles , Katz Joseph
Published: July 2002

A procedure for modeling deterministic stresses for average-passage simulations of flow in multiple blade-row turbomachines is proposed and tested. This method uses the results of several (two or more) steady Reynolds-averaged Navier-Stokes (RANS) simulations with boundary conditions that are representative of different inflow conditions encountered during the passage of a neighboring blade-row. The deterministic stresses are calculated by averaging the steady results while weighting them with the approximate duration of each inflow condition. This approach incorporates important rotor-stator interactions that are neglected in models based on a swept-wake approximation. The model is tested successfully by computing the deterministic stresses in the stator vane passage of a centrifugal pump, and comparing them with direct measurements using PIV data. Remaining discrepancies between model predictions and experimental data are probably linked to the inability of the turbulence models to account for flow phenomena at each phase, such as mid-vane separation.
The Influence of Indenter Tip Radius on the Micro-Indentation Hardness
Authors: Xue Z. , Huang Y. , Hwang K. C. , Li M.
Published: July 2002

The micro-indentation experiments have shown that the indentation hardness depends not only on the indentation depth but also on the indenter tip radius. In fact, the indentation hardness displays opposite dependence on the indentation depth h for a sharp, conical indenter and for a spherical indenter, decreasing and increasing, respectively, with increasing h. We have developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of indenter tip radius. The same indentation model captures this opposite depth dependence of indentation hardness, and shows the opposite depth dependence resulting from the different distributions of strain and strain gradient underneath a conical indenter and a spherical indenter. We have also used the finite element method to study the indentation hardness for a spherical indenter as well as for a conical indenter with a spherical tip. It is established that the effect of indenter tip radius disappears once the contact radius exceeds one half of the indenter tip radius.
Interfacial Stresses and Void Nucleation in Discontinuously Reinforced Composites
Authors: Tszeng T. C.
Published: July 2002

This paper presents the theoretical predictions of the stress state at the inclusion-matrix interface in discontinuous metal matrix composites by the generalized inclusion method. In the author’s previous works, this method had been extended to the elastoplastic deformation in the matrix material. The present analysis of the ellipsoidal inclusion problem indicates that the regions at the pole and the equator of the particle/matrix interface essentially remain elastic regardless of the level of deformation, although the size of the elastic region keeps decreasing as deformation becomes larger. It was also found that, when the composite is undergoing a relatively large plastic deformation (strain), the maximum interfacial normal stress is approximately linearly dependent upon the von Mises stress and the hydrostatic stress. Based on the stress criterion for void nucleation, the author determined the void nucleation loci and nucleation strain for a composite subjected to an axisymmetric macroscopic stress state. The influence of interfacial bonding strength, inclusion shape, and volume fraction on the occurrence of void nucleation have been determined. The interfacial bonding strength in a SiC-aluminum system was re-evaluated by using existing experimental evidence. [S0094-4289(00)01301-3]
Predictive Modeling of the Nonuniform Deformation of the Aluminum Alloy 5182
Authors: Bange M. E. , Beaudoin A. J. , Stout M. , Chen S. R. , MacEwen S. R.
Published: July 2002

We pose an experimental model for hot deformation that, in complexity, falls between a homogeneous laboratory test and an industrial process. Our objective is to document a transition between two distinct modes of thermally-activated deformation: diffusion controlled solute drag and hardening with concurrent recovery of dislocations. We demonstrate that constitutive equations for plasticity, describing different regimes of dislocation kinetics and calibrated with a minimum of adjustable constants, can be incorporated into finite element analysis and used reliably to predict the mechanical response of a nonuniform body. [S0094-4289(00)00302-9]
Effect of Cycle History on Thermomechanical Fatigue Response of Nickel-Base Superalloys
Authors: Arrell D. J. , Bressers J. , Timm J.
Published: July 2002

Thermo-mechanical fatigue of nickel-base superalloys has been carried out for more than twenty years, but a unified standard for such tests has yet to be fully formulated. As a consequence of this, even excluding differences in testing procedure from laboratory to laboratory, the range of testing conditions in use is very large. In this paper, the authors consider the effect of the different parameters in a TMF test such as hold-time and temperature-mechanical phase angle on the thermo-mechanical response of test samples. This is carried out in terms of both stress response and sample life, in order to identify the common trends in the sample damage during the evolution of the mechanical response. To date, no definitive test program systematically covering the different variables has been published in the scientific literature. As, even after a long span of time, the literature data for many alloys is sparse, the work presented here concentrates on analyzing TMF response data from test programs carried out by the authors on the single crystal nickel-base alloy SRR99. [S0094-4289(00)01003-3]
A Numerical Algorithm for Determining the Traction Between a Web and a Circumferentially Grooved Roller
Authors: Ducotey K. S. , Good J. K.
Published: July 2002

Air entrainment can become a significant problem in a web handling process line. The development of an air film between a roller and web can cause a reduction in traction. This can cause a velocity difference between the web and roller and may also cause guiding problems. Roller grooving is a common method to reduce the effects of the air entrainment to improve traction. A traction simulation model for circumferentially grooved rollers has been devised. The model is based on classical plate and shell theory, the Reynolds’ equation, and asperity contact theory. The governing equations are solved in an iterative scheme using a finite difference method with a variable mesh. Theoretical results are experimentally verified. [S0742-4787(00)02203-7]
Wear Characteristics of Padded Air Bearing Sliders During a Contact Take-Off Process
Authors: Hu Yong
Published: July 2002

The pressing and challenging demand for resolving the stiction/glide-height conflict, driven by today’s ever decreasing head/disk spacing, forces us to constantly search for new technologies. One of them is padding the slider’s air bearing surface. Although the padded air bearing sliders can significantly reduce the stiction, the wear of these landing pads becomes a central issue. This paper attempts to analytically predict the wear characteristics of the landing pads during a contact take-off process. A wear factor derived from the adhesive wear law is employed to measure the wear extent of the landing pads. The contact force profile and wear factor of each pad are calculated through the partial contact air bearing simulation of a slider’s take-off process. It is found that the rear pad wears an order magnitude more than the leading pads. The wear volume of the rear pad increases exponentially with pad height, interface roughness and altitude. Raising the leading pads alone slightly reduces the wear of the rear pad. Placing the rear pad away from the slider’s trailing edge, however, substantially alleviates the wear of the rear pad. Finally, a lightly textured pad/disk interface decreases the pads’ wear to a minimum value for a given padded air bearing design. [S0742-4787(00)01903-2]
The Effects of the Distance Between Two Defects on the Load-Carrying Capacity of a Pressure Vessel
Authors: Chen H. F. , Shu D. W.
Published: July 2002

A simplified numerical method for both lower and upper-bound limit analyses of 3-D structure has been developed in our previous work. The load-carrying capacities of 3-D pipelines with either one or two part-through defects of various geometrical configurations were calculated by the proposed method. In the present paper, the effects of the distance between two defects on the load-carrying capacity of pressure vessels are evaluated and discussed in details. Using curve-fitting schemes, an empirical formula for obtaining the load-carrying capacity of pressure vessels with double defects from that of pressure vessels with a single defect are proposed. Some engineering suggestions are presented simultaneously. All the numerical results confirm the applicability of the simplified numerical method. [S0094-9930(00)00102-5]
SrCO3 by XPS
Authors: Vasquez Richard P.
Published: July 2002

X-ray photoelectron spectroscopy measurements of the principal core levels of high purity strontium carbonate are presented.
Investigation of dilute SF6 discharges for application to SiC reactive ion etching
Authors: Scofield J. D. , Ganguly B. N. , Bletzinger P.
Published: July 2002

Impedance matching and power coupling efficiency optimization of SF6 gas discharges diluted with Ar and He have been compared in relation to reactive ion etch rates and etched feature anisotropy of hexagonal (6H) silicon carbide (SiC). In contrast to the measured radio frequency (rf) power coupling efficiency, He diluted mixtures resulted in greater etch rates by up to 50%, with superior anisotropy and surface morphology than comparable Ar:SF6 mixtures. The superior etched surface finish for the He diluted mixtures possibly arises from the less severe sputtering damage of SiC for He+ and SFX+, compared to Ar+ with the same energy. Etch rates over 3300 Å/min have been achieved with excellent surface morphologies and anisotropy. These results conflict with the notion that Ar+ ions are expected to enhance the ion assisted etch mechanism in technical gas mixtures. We observed superior, SiC etch performance for He:SF6 mixtures, compared to Ar:SF6, over the entire 10%–90% fractional ratios investigated. This result appears to be due to differing bulk discharge chemistries which control the flux of radicals and ions to the substrate, resulting in optimal surface polymerization conditions. This suggestion is based on our estimated bulk E/n values, known partial ionization cross sections, production rate coefficients for SF3+ and SF5+, and higher electron energy distributions for He dilution. In addition, we provide further evidence for the generic nature of utilizing the complex electrical characteristics of the rf discharge to optimize plasma etch conditions. On the other hand, we have demonstrated that understanding the details of gas phase kinetics is also necessary to fully exploit the power coupling optimization scheme for rf discharges, which are specific to the gas mixtures being utilized.
Influence of oxygen background pressure on the structure and properties of epitaxial SrTiO3/La0.35Nd0.35Sr0.3MnO3 heterostructures grown by pulsed laser deposition
Authors: Wu Wenbin , Wong K. H. , Mak C. L. , Pang Geoffrey , Choy C. L. , Zhang Yuheng
Published: July 2002

Epitaxial La0.35Nd0.35Sr0.3MnO3 (LNSMO) films and SrTiO3 (STO)/LNSMO heterostructures have been grown on LaAlO3 substrates by pulsed laser deposition. The effect of oxygen content on structure and properties of both the LNSMO and STO/LNSMO films was investigated through x-ray diffraction, atomic force microscopy, and resistivity-temperature measurements. It is found that the out-of-plane lattice constant and the metallic-semiconducting transition temperature of the LNSMO films are greatly influenced by the oxygen pressure during deposition, but, insensitive to the in situ annealing oxygen pressure ranging from 2×10−6 to 10 Torr after the deposition. For the STO/LNSMO heterostructures, oxygen out-diffusion from the LNSMO layer is evidenced when the top STO is deposited at an oxygen pressure of less than 5×10−4 Torr and temperatures higher than 500 °C. Our results strongly suggest that at the surface of as-grown LNSMO films a native passivation layer for oxygen diffusion may exist, and this layer could be damaged after depositing the STO film at reduced oxygen pressures.
Reactivity of heteropolyanions toward GaAs compound
Authors: Rothschild A. , Quennoy A. , Etcheberry A. , Debiemme-Chouvy C.
Published: July 2002

We studied the reactivity of GaAs in contact with acidic solutions of, respectively, four heteropolyanions (HPAs): SiW12O404−, SiMo12O404−, PW12O403−, and P2W18O626−. The results obtained by both x-ray photoelectron spectroscopy and etching rate and absorbance measurements showed that GaAs dipped into such solutions undergoes an oxidation/dissolution process while the HPAs are reduced. Indeed, after each immersion of GaAs into an heteropolyanionic solution, a deposit, which consists of As0 atoms with either partially reduced HPA or WO3 is observed. This study has given us the opportunity to determine the reactions which occur at the GaAs/“HPA solution” interface and to point out the importance of the semiconductor energy-band position with respect to the first redox potential of the HPA. Knowledge of the semiconductor/HPA energetic diagram allows one to predict the behavior of HPA species toward semiconductors.
Structural and electrical properties of chemical vapor deposited diamond films doped by B+ implantation
Authors: Wang S. B. , Zhang H. X. , Zhu P. , Feng K.
Published: July 2002

Chemical vapor deposited diamond films (DF) were prepared on p-type Si (100) substrates. The films were doped by 140 keV B+ implantation to doses between 1014–6×1016 cm−2. Structural changes were studied by scanning electron microscopy and Raman measurements. The DF become more and more seriously disordered versus dose. Surprisingly, the amorphization process is not as rapid as predicted. Secondary ion mass spectroscopy results show that the implanted B atoms have a strong tendency of outdiffusion during annealing. When experimental parameters are suitable, the B atoms’ profiles indicate perfect Gaussian-like shape and the electrical resistance of DF can be decreased ten orders of magnitude.
Photoemission spectroscopy of platinum overlayers on silicon dioxide films
Authors: Keister J. W. , Rowe J. E. , Kolodziej J. J. , Madey T. E.
Published: July 2002

Soft x-ray photoelectron spectroscopy (SXPS) has been used to study ultrathin Pt films on silicon dioxide as model supported-catalyst materials. Using monochromatic synchrotron radiation. Pt 4f and Si 2p core level photoelectron peaks were measured as a function of platinum coverage in the range 0–10 ML. The bulk silicon and silicon dioxide film Si 2p peaks each show a binding energy decrease within the first ML of dosing. However, the effect is stronger for the silicon dioxide Si 2p peak, indicating an increased screening of the 2p electrons by the metal overlayer. We also observe a monotonic increase of the work function of the ultrathin film Pt/SiO2 system with coverage from 4.52 initially to 5.58 eV at ∼10 ML. The Pt 4f7/2 core level binding energy decreased from ∼72.2 to ∼70.9 eV between 0 and ∼10 ML coverage. This binding energy shift at low dose (⩽1 ML), the coverage dependence of the Pt line shape and intensity, and the large saturation coverage for the work function are each consistent with two-dimensional cluster-island growth. The metallic nature of the Pt overlayer with dose is quantitatively verified by nonlinear, least-squares numerical fitting of the Pt 4f SXPS peak line shapes with Gaussian-broadened Doniach–Sunjic functions.
Epitaxial thin films of MgO on Si using metalorganic molecular beam epitaxy
Authors: Niu F. , Hoerman B. H. , Wessels B. W.
Published: July 2002

Epitaxial cubic MgO thin films have been deposited on single crystal Si(001) substrates by metalorganic molecular beam epitaxy. The Mg source was the solid precursor magnesium acetylacetonate and a rf excited oxygen plasma was the oxidant. The growth process involved initial formation of an epitaxial β-SiC interlayer followed by direct deposition of a MgO overlayer. The films were characterized by in situ reflection high energy electron diffraction, x-ray diffraction, conventional and high resolution transmission electron microscopy, atomic force microscopy, Auger electron spectroscopy, and Fourier transform infrared spectroscopy. The β-SiC interlayer had an epitaxial relationship such that SiC(001)∥Si(001) and SiC [110]∥Si [110]. The SiC interlayer showed a columnar grain structure with planar defects including twin bands and stacking faults. The MgO overlayer showed an epitaxial relationship given by MgO(001)∥Si(001) and MgO[110]∥Si[110]. No evidence of twins in the MgO layers was observed.
Growth and microstructure of self-assembled ErAs islands in GaAs
Authors: Kadow C. , Johnson J. A. , Kolstad K. , Ibbetson J. P. , Gossard A. C.
Published: July 2002

This article concerns the microstructure of self-assembled ErAs islands embedded in GaAs. The material is grown by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. A series of such samples were grown with different depositions of ErAs at a growth temperature of 535 °C. The microstructure of these samples was investigated by x-ray diffraction and transmission electron microscopy. We find that initially isolated ErAs islands with a diameter of 2 nm are nucleated. With increasing ErAs deposition, these islands branch out and form extended structures. The samples are coherent in growth directions for ErAs depositions up to 1.8 monolayers. At higher ErAs depositions defects are incorporated into the GaAs matrix.
Intrinsic limitations on ultimate device performance and reliability at (i) semiconductor–dielectric interfaces and (ii) internal interfaces in stacked dielectrics
Authors: Lucovsky G. , Yang H. , Niimi H. , Thorpe M. F. , Phillips J. C.
Published: July 2002

The scaling of electrical oxide thickness to 1.0 nm and below for advanced silicon devices requires a change from thermally grown oxides and nitrided oxides to deposited dielectrics which have dielectric constants, k, significantly greater than that of silicon dioxide, k0∼3.8. Implementation of the higher-k dielectrics into field effect transistor devices requires a processing protocol that provides separate and independent control over the properties of the Si–dielectric interface and the bulk dielectric film. Experiments to date have shown that plasma-grown nitrided oxides, ∼0.5–0.6 nm thick, satisfy this requirement. This paper addresses chemical bonding issues at the Si–dielectric interface and at the internal dielectric interface between the plasma-grown nitrided oxides and the high-k alternative dielectrics by applying constraint theory. Si–SiO2 is a prototypical interface between a “rigid” Si substrate and a “floppy” network dielectric, SiO2, and the interfacial properties are modified by a monolayer-scale transition region with excess suboxide bonding over what is required for an ideal interface. Additionally, the defect properties at the internal interface between a nitrided SiO2 interface layer and a bulk dielectric film reflect differences in the average number of bonds/atom, Nav, of the dielectrics on either side of that interface. Experimentally determined interfacial defect concentrations are shown to scale quadratically with increasing differences in Nav thereby establishing a fundamental basis for limitations on device performance and reliability.
Trench formation and filling technique for dielectric isolation of plasma display panel driver integrated circuits
Authors: Kim Sang-Gi , Kim Jongdae , Koo Jin Gun , Nam Kee Soo , Cho Kyoung-Ik , Bae In-Ho
Published: July 2002

Trench etching and filling technique for the isolation between the control (low voltage) and the power (high voltage) region in power integrated circuits was investigated. This technique consists of a deep trench formation (8.0 μm) with positive etching using 45% He–O2 of the HBr and SiF4 chemistries followed by filling and global planarization with the chemical mechanical polishing technique. The novel trench etching technique provides better surface quality of 3.1 Å roughness measured with atomic force microscopy. The filling and global planarization results in lower leakage current less than 1 nA at the supplying voltage of 400 V.
Planar integration of heterojunction bipolar transistors and resonant tunneling diodes
Authors: Thomas S. , Chow D. H. , Kiziloglu K. , Fields C. H. , Madhav M. , Arthur A.
Published: July 2002

A process is reported for monolithic integration of heterojunction bipolar transistors (HBTs) and resonant tunneling diodes (RTDs). The InGaAs/AlInAs HBT layers and the InGaAs/AlAs/InAs RTD layers are grown on an InP substrate in one molecular beam epitaxy growth run. The devices are separated by an InP etch stop layer grown between the two materials. The devices are planarized with polyimide and interconnected by second-level metal. Only minor modifications to the existing HBT process were required to incorporate the RTDs. Laser reflectometry was used to accurately control the polyimide etch depth for both etch steps. Process simulation was used prior to wafer fabrication to predict the required etch depths and reduce process development time. A two-step polyimide etch back allows both devices to be contacted directly by second-level metal. This allows both devices to be fabricated with the minimum design rule dimensions, thereby improving speed and reducing power consumption. An additional InP etch stop layer was included in one wafer between the emitter superlattice and the base spacer layer. The etch stop layer improved beta uniformity but decreased the unity current gain cutoff frequency (Ft) by 11% and the maximum frequency of oscillation (Fmax) by 18%.
Absolute Calibration of Apollo Lunar Orbital Mass Spectrometer
Authors: Yeager P. R. , Smith A. , Jackson J. J. , Hoffman J. H.
Published: July 2002

Recent experiments were conducted in Langley Research Center's molecular beam system to perform an absolute calibration of the lunar orbital mass spectrometer which was flown on the Apollo 15 and 16 missions. Tests were performed with several models of the instrument using two test gases, argon and neon, in the 10−13–10−9 Torr range. Sensitivity to argon at spacecraft orbital velocity was 2.8×10−4 A/Torr enabling partial pressures in the 10−14 Torr range to be measured at the spacecraft altitude. Neon sensitivity was nearly a factor of 5 less. The response of the instrument to off-axis beams shows a cosine-to-cosine dependence. Test data support the feasibility of using the lunar orbital mass spectrometer as a tool to gather information about the lunar atmosphere.
The Gamble I Pulsed Electron Beam Generator
Authors: Cooperstein G. , Condon J. J. , Boller J. R.
Published: July 2002

The Gamble I pulsed electron beam generator at NRL recently has undergone several major modifications. The modified generator has a nominal output into a matched 1.5-Ω load of 500 kA at 750 keV, with an 70-nsec (FWHM) pulse length and a 20-nsec (10%–90%) voltage risetime. The distinguishing characteristics of low prepulse (< 1%) and high reproducibility in output voltage and current (± 3%) result primarily from conversion from operation with self-breakdown water switches to operation with triggered high-pressure gas switches. Fast pulse risetime was maintained by using a low-inductance multichannel triggered output switch in conjunction with a new low-inductance vacuum diode with a radial insulator.
A conductance model (approach) for kinetic studies: The Ti–Ta–Si system
Authors: Pelleg Joshua , Rubinovich L.
Published: July 2002

Electrical resistance measurements provide a convenient way to study the kinetics of transformations in isothermally annealed thin films. The measured resistance and the amount of a new phase formed during some sort of reaction in a transformation process are often related by a linear function. This simple relationship between the measured resistance and the fraction of the new phase formed is not always valid and the reliability of the results might be questionable. In this communication, a different approach is suggested, which is based on conductance. The validity of the model is tested by experimental data for the Ti–Ta–Si system. The suggested and the linear resistance models are compared, and it seems that it is more appropriate in certain cases to use the conductance approach for kinetic purposes. An effective activation energy can be derived from the results by defining the time needed at each temperature to obtain either a constant resistance, or alternatively, a certain fraction of the new phase. The activation energy derived for the end phase, i. e. (Ti,Ta)Si2 formation from the experimental data in the example (Ti–Ta–Si) considered is ∼2.6 eV.
Thermal stability and adhesion improvement of Ag deposited on Pa-n by oxygen plasma treatment
Authors: Gadre Kaustubh S. , Alford T. L.
Published: July 2002

Parylene- n ( Pa- n) and silver are being studied for ultralarge scale integrated circuits because of their favorable properties. These include low dielectric constant (2.65), negligible water take-up, chemical inertness, low temperature deposition, as well as compatibility with current integrated circuits manufacturing for Pa-n and the low resistivity (1.6 μΩ cm), high electromigration resistance for silver. To meet integration requirements, Pa-n and Ag are studied to understand specific reliability issues, e.g., diffusion, delamination, or loss of adhesion, compatibility, etc. Initial measurements of silver and dielectric Pa-n were done using four-point probe. Thermal stability and texturing of Ag films on Pa-n were confirmed using x-ray diffraction analysis. The change associated with resistivity of Ag films on Pa-n sample supports the changes observed in x-ray spectra. Rutherford backscattering spectrometry and secondary ion mass spectroscopy analysis show insignificant diffusion of Ag in Pa-n. Adhesion analysis of Ag/Pa-n and Pa-n/Si was done using scratch and tape tests. Oxygen plasma surface treatment of Pa-n shows drastic improvement of adhesion between Ag and Pa-n without loss of thermal stability of the system. The improvement in adhesion is associated with increased roughness of Pa-n surface after plasma treatment.
Effects of contact barriers on Si-substrated GaN photodetectors
Authors: Zhao Z. M. , Jiang R. L. , Chen P. , Xi D. J. , Shen B. , Zhang R. , Zheng Y. D.
Published: July 2002

GaN photoconductive detectors were fabricated on Si (111) substrates. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at the wavelength from 360 to 250 nm. Both ohmic contact and non-ohmic contact detectors were studied in this article. The ohmic contact detectors exhibited a higher responsivity and a wider linear increase range in voltage-dependent responsivity than the non-ohmic contact detectors. Because the contact barriers can lower the photocurrent gain, and the built-in electric field caused by the contact barriers can increase the minority drift length at high applied voltage, the voltage-dependent responsivity of non-ohmic contact detectors increased slowly at low applied voltage and saturated earlier at high applied voltage than that of ohmic contact ones. Due to the persistent photoconductivity, effects of contact barriers on time response were negligible.
Novel technique to pattern silver using CF4 and CF4/O2 glow discharges
Authors: Nguyen Phucanh , Zeng Yuxiao , Alford T. L.
Published: July 2002

Silver is being studied as a potential metal for future interconnects in integrated circuits. Under appropriate conditions, Ag thin films can be removed at reasonable rates using a CF4 or CF4/O2 glow discharge followed by a conventional resist strip process. This is not a typical “dry-etch” process where the formation of volatile products is the main removal mechanism. Rather, it is novel in that the glow discharge is employed to form reactive byproducts of Ag. There are simultaneous sputtering and desorption of the byproducts during the plasma exposure; but the primary film removal mechanism is in the subsequent resist strip process. Two-level-factorial design, and one-factor-at-a-time experiments are employed to study the effects of process conditions on the etch rate, and postetch surface roughness. It is found that Ag removal rate in CF4 or CF4/O2 glow discharges depends strongly on applied power. Postetch surface roughness depends on both power and pressure.
Mechanism of the isotermic amorphous-to-crystalline phase transition in Ge:Sb:Te ternary alloys
Authors: González-Hernández J. , Prokhorov E. F. , Vorobiev Yu. V. , Morales-Sánchez E. , Mendoza-Galván A. , Kostylev S. A. , Gorobets Yu. I. , Zakharchenko V. N. , Zakharchenko R. V.
Published: July 2002

The kinetics of the amorphous-to-crystalline (fcc) phase transition under isothermal treatments has been investigated in alloys with the composition close to Ge22Sb22Te56, which is the most frequently used for the erasable optical memory devices. For monitoring the transformation, electrical, ellipsometric, optical transmission and electron microscopy measurements were employed. A procedure to determine the transformed volume fraction based on the electrical conductivity data is proposed. It is shown that the widely accepted assumption about the linear dependence between the conductivity variation and the transformed volume fraction is not correct. The use of this assumption could give an error in the determination of the crystalline volume fraction of up to one order of magnitude. The amorphous-to-crystalline transformation kinetics observed agrees with the Johnson–Mehl–Avrami formalism. The transformation exhibits two distinct stages that are attributed to the surface and bulk nucleation, and gives an average Avrami exponent around 2. The activation energy of the process is about 4 eV, which exceeds previous estimations.
Wet oxidation behaviors of polycrystalline Si1−xGex films
Authors: Kang S.-K. , Ko D.-H. , Lee K. C. , Lee T. W. , Lee Y. H. , Ahn T. H. , Yeo I. S. , Oh S. H. , Park C. G.
Published: July 2002

We investigated the oxidation behaviors of poly Si1−xGex films with a 15% and 42% Ge content. The films were deposited using ultrahigh vacuum chemical vapor deposition on a 1000 Å thick thermal SiO2 layer, and were oxidized using a conventional furnace in wet oxygen ambient at 700 and 800 °C. The physical and chemical properties of the oxide were analyzed by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy before and after the oxidation. We observed that the Ge content in the oxide layer and oxidation rate increased with the increase of Ge content in poly Si1−xGex films. We also observed that Ge content in the oxide layer decreased with the increase of oxidation temperature.
Relationship between work function and current fluctuation of field emitters: Use of SK chart for evaluation of work function
Authors: Gotoh Y. , Tsuji H. , Ishikawa J.
Published: July 2002

The relation between the work function and current fluctuation was investigated for various kinds of emitters: element metals, transition metal nitrides, and diamonds. Since these deposited emitters have no good standard, it is difficult to distinguish the effect of work function and the other physical parameters such as apex radius. In order to distinguish these effects, we propose a unique technique of the SK chart and plotting the Fowler–Nordheim characteristics in the SK chart in accordance with the magnitude of the noise power: SKN plot. The SKN plot clearly exhibits the relation between physical parameters and current fluctuation and it was found that the emitter with lower work function shows lower current fluctuation.
Critical dimension control optimization methodology on shallow trench isolation substrate for sub-0.25 μm technology gate patterning
Authors: Fan M. H. , Gerung H. , Yelehanka P. R. , Cheng A. , Zhou M. S. , Chi C. , Tan C. H. , Xie J.
Published: July 2002

The impact of shallow trench isolation (STI) chemical mechanical polishing on gate critical dimension (CD) control for submicron technology was studied. The CD depends on the STI process scheme, whether it is recessed or elevated STI. We investigated the surface topography for both STI schemes at different stages of patterning and how it affected the CD control. Surface topography affected organic bottom antireflective coating (BARC) and resist thickness uniformity, led to variation in the effective exposure dose and caused CD nonuniformity across the wafer [C. A. Mack, Appl. Opt. 25, 1958 (1986)]. We used an atomic force microscope surface scan to study substrate topographical variations. The solution is to optimize BARC and resist thickness by using simulations of topographical swing curves and CD error contour plot. Excellent agreement was found between simulation and experimental results.
Microtunneling sensors for vacuum level evaluation of field emission display devices
Authors: Park H. W. , Ju B. K. , Park Y. K. , Lee D. J. , Lee Y. H. , Kim C. J. , Park J. H. , Oh M. H.
Published: July 2002

In this article, the laterally tunneling diodes and triodes were fabricated with the general second polysilicon layer surface micromachining process. The thickness of each structural polysilicon and sacrificial phosphosilicate glass layer was 2 μm, respectively. By removing the sacrificial layer with the sublimation drying method, the stiction was avoided. Their emission characteristics were tested in a high vacuum chamber with probes. Current–voltage characteristics were tested under various vacuum environments and the simulation was done to know the electric field distribution near the tip end. They were then used as a vacuum level evaluation sensor. The sensor showed the emission current variation in the range of 1.20–2.42 μA for the vacuum range of 10−5–10−8 Torr.
A novel antistiction method using harmonic excitation on the microstructure
Authors: Lai Wen Pin , Fang Weileun
Published: July 2002

A novel antistiction method using harmonic excitation on the microstructure is presented. We exploit a simplified model consisting of a single-degree-of-freedom mass-damping-spring system to simulate the drying process of the microstructure. Based on this proposed method, we can predict the dynamic response of the microstructure including the resonant frequency and the damping characteristic of the drying system. And then adequate harmonic excitation is applied to release the microstructure during drying process. Silicon dioxide beams with 0.7-μm-thick, 16-μm-wide, 120-μm-long, 4 μm gap, were released successfully by this method. Theoretical predictions of the dynamic behavior of microstructures during the drying process agree well with experimental results. The proposed approach effectively improves the yield rate of the microstructure without additional masks and complicated process during the postetch release process.
Oxidation behavior of a patterned TiSi2/polysilicon stack
Authors: Kim Tae-Kyun , Jang Se-Aug , Yeo In-Seok , Yang Jun-Mo , Park Tae-Su , Park Jin Won
Published: July 2002

The oxidation behavior at the sidewall of patterned TiSi2/polysilicon gate stack has been studied at temperatures from 700 to 850 °C. Oxidation above 800 °C caused an abnormally enhanced oxidation of TiSi2 sidewall, which was not observed in unpatterned TiSi2/polysilicon stack, regardless of the oxidation atmosphere. High-resolution transmission electron microscopy study showed that a SiO2–TiO2 mixture was produced during the enhanced oxidation of TiSi2 film. Lightly doped drain structures with TiSi2/polysilicon gate and nitride spacer were fabricated using gate reoxidation at 750 °C without degradation of sheet resistance.
Edge transistor elimination in oxide trench isolated N-channel metal–oxide–semiconductor field effect transistors
Authors: Yang Jianan , Denton John P. , Neudeck Gerold W.
Published: July 2002

Bulk N-channel metal–oxide–semiconductor field effect transistors (MOSFETs) can suffer from parasitic edge transistor effects, unless several extra processing and masking steps are used. These edge devices increase the off-state current and degrade subthreshold slope of the N-MOSFETs. Parasitic edge transistors in oxide trench isolated N-MOSFETs, formed using selective epitaxial growth of silicon, were caused by the boron out-diffusion during high temperature process steps. Employing a simple ammonia nitridation of the field oxide before the epitaxial growth step, boron out-diffusion into the surrounding oxide was suppressed. The parasitic edge transistors in oxide trench isolated N-MOSFETs were eliminated.