Junction Design Research Articles

Hydraulic Jet Control for River Junction Design of Yuen Long Bypass Floodway, Hong Kong

The Yuen Long Bypass Floodway (YLBF) was designed to collect flows from the Sham Chung River (SCR) and the San Hui Nullah (SHN) and to serve as a diversion channel of the Yuen Long Main Nullah (YLMN). Under a 200-year return period design condition, the floodway was designed (1) to divert a flow of approximately 38 m3 ∕s from the supercritical YLMN flow and (2) to convey a total combined flow of 278 m3 ∕s to downstream within acceptable flood levels. The success of the design depends critically on complicated junction flow interactions that cannot be resolved by 1D unsteady flow models. These features include the supercritical-subcritical flow transition at the San Hui-Floodway (SHN-YLBF) junction and the diversion of part of the supercritical flow from the Main Nullah (YLMN). A laboratory Froude scale physical model was constructed to study water stages and flow characteristics in the floodway and to investigate optimal design arrangements at channel junctions and transitions. This paper summarizes the m...

A Novel Power MOSFET Structure with Shallow Junction Dual Well Design

Vertical Power MOSFETs are widely designed by deep structures for breakdown requirement. In this study, we proposed, simulated, and analyzed a dual well structure Power MOSFET, which utilize an n-well to cover the conventional p-well. The cell pitch can be reduced and results in an increased cell density. The reduced cell pitch and increased cell density improves the gate charge and on resistance performances about 66.5% and 15.8% without sacrificing the device breakdown owing to a shallow junction design. In addition, with the dual structure design, the breakdown point will occur at the center of the well. Therefore, the capability of avalanche energy can be improved about 1.9 times than the tradition structure.

Novel design of foam core junctions in sandwich panels

An improved design of core junctions in sandwich panels/beams is proposed. The improved/novel design consists of a specific geometrical shaping of the boundary of the adjoined core materials, which substantially diminishes the local stress concentrations at core junctions subjected to transverse shear loading. Two groups of the beams with conventional butt junctions and modified (spline shaped) junctions are manufactured and tested under fatigue loading conditions. A rigorous statistical treatment of the experimental data shows that sandwich beams with modified core junctions display significantly higher fatigue performance than sandwich beams with conventional “butt” core junctions.

Prevention of Wrong-Way Driving on Freeways

Traffic accidents that occur on freeways often end tragicallybecause of high driving speed. Wrong-way driving is also one ofthe causes of accidents on freeways. Research is based on theanalysis of traffic accident data caused by wrong-way drivingon freeways, and considering valid technical specifications forconnections and junctions design elements. Research is basedon the analysis of the data of traffic accidents that occurred becauseof wrong-way driving on freeways and on the considerationof valid technical specifications concerning connectionsand junction design elements. The thesis presents possiblecountermeasures for prevention of wrong-way driving and consequentialdecrease in the number of traffic accidents. The proposedprevention countermeasures of wrong-way driving onfreeways could greatly reduce incorrect traffic vehicle movementsthat are the consequence of wrong-way driving and thuspositively enhance the traffic safety level on freeways.

High current gain graded GaN/InGaN heterojunction bipolar transistors grown on sapphire and SiC substrates by metalorganic chemical vapor deposition

High-current-gain GaN/InGaN double heterojunction bipolar transistors having a graded-base and emitter design grown on sapphire and SiC substrates by metalorganic chemical vapor deposition are presented. Improved device performances result from the improvement of the InGaN graded layer material quality and the p-type doping enhancement as well as the improvement of device fabrication techniques. The devices show common-emitter incremental current gain values above 35. Device operation is demonstrated at temperatures as high as 300 °C. The results demonstrate the potential of the graded InGaN emitter-base junction design for high-performance III-nitride heterojunction bipolar transistors.

Device operation of InGaN heterojunction bipolar transistors with a graded emitter-base design

The device operation of InGaN heterojunction bipolar transistors with a graded InGaN emitter-base design grown by metal organic chemical vapor deposition on sapphire substrates is demonstrated. The Gummel plot, current gain, and common-emitter current-voltage characteristics of the device are presented. The dc common-emitter current gain of a 25×25μm2 (emitter size) device increases with collector current and the current gain reaches a high value of 13 at IC=10mA with a base width of 100nm and a hole concentration of p=2×1018cm−3. The improved device performance is attributed to the graded emitter-base design as well as the high quality of the material made possible by the indium composition grading that enables the epitaxial growth of InGaN layers with a low density of pits or defects. The results demonstrate the potential of the graded InGaN emitter-base junction design in nitride heterojunction bipolar transistors.

Electron transport and redox reactions in carbon-based molecular electronic junctions

A unique molecular junction design is described, consisting of a molecular mono- or multilayer oriented between a conducting carbon substrate and a metallic top contact. The sp2 hybridized graphitic carbon substrate (pyrolyzed photoresist film, PPF) is flat on the scale of the molecular dimensions, and the molecular layer is bonded to the substrate via diazonium ion reduction to yield a strong, conjugated C-C bond. Molecular junctions were completed by electron-beam deposition of copper, titanium oxide, or aluminium oxide followed by a final conducting layer of gold. Vibrational spectroscopy and XPS of completed junctions showed minimal damage to the molecular layer by metal deposition, although some electron transfer to the molecular layer resulted in partial reduction in some cases. Device yield was high (>80%), and the standard deviations of junction electronic properties such as low voltage resistance were typically in the range of 10-20%. The resistance of PPF/molecule/Cu/Au junctions exhibited a strong dependence on the structure and thickness of the molecular layer, ranging from 0.13 ohms cm2 for a nitrobiphenyl monolayer, to 4.46 ohms cm2 for a biphenyl monolayer, and 160 ohms cm2 for a 4.3 nm thick nitrobiphenyl multilayer. Junctions containing titanium or aluminium oxide had dramatically lower conductance than their PPF/molecule/Cu counterparts, with aluminium oxide junctions exhibiting essentially insulating behavior. However, in situ Raman spectroscopy of PPF/nitroazobenzene/AlO(x)/Au junctions with partially transparent metal contacts revealed that redox reactions occurred under bias, with nitroazobenzene (NAB) reduction occurring when the PPF was biased negative relative to the Au. Similar redox reactions were observed in PPF/NAB/TiO(x)/Au molecular junctions, but they were accompanied by major effects on electronic behavior, such as rectification and persistent conductance switching. Such switching was evident following polarization of PPF/molecule/TiO2/Au junctions by positive or negative potential pulses, and the resulting conductance changes persisted for several minutes at room temperature. The "memory" effect implied by these observations is attributed to a combination of the molecular layer and the TiO2 properties, namely metastable "trapping" of electrons in the TiO2 when the Au is negatively biased.

Corrosion of Modular Titanium Alloy Stems in Cementless Hip Replacement

Abstract Severe, localized corrosion of titanium-alloy femoral stems has been reported for specific designs of hip prostheses intended for fixation using acrylic cement. The purpose of the present study was to examine the possibility that corrosion might also occur when titanium-alloy stems are inserted without cement, but the body of the stem is modular in design. Fourteen (7 primary and 7 revision) cementless, modular-body, titanium-6% aluminum-4% vanadium alloy femoral stems of similar design were removed at revision surgery after 2 to 108 months in situ. The reason for removal was unexplained pain (4), femoral or acetabular loosening (4), infection (3), recurrent dislocation (2), or component malposition (1). The devices and, in selected cases, tissue from the joint psuedocapsule were studied with the use of light and scanning electron microscopy. Fretting corrosion products were characterized using energy dispersive x-ray analysis, selected area diffraction, and micro-Raman spectroscopy. Damage at the modular body connections was absent in 3 stems, mild in 6, moderate in 4, and severe in 1. The surface damage was characterized predominately by fretting scars and by pitting and etching. Thick deposits of mixed titanium oxides were found adherent to the stem at the sites of corrosion and as 0.01 to 200 micrometer particles within histiocytes and multinucleated giant cells in the joint pseudocapsule. Fretting corrosion at the modular-body junctions of titanium-alloy femoral stems can generate solid degradation products, adding to the particulate burden of the periprosthetic tissues and potentially accelerating bearing-surface wear by a third-body mechanism. Both of these features can potentiate the development and progression of osteolysis. In addition, fretting corrosion can increase the potential for structural failure of the device. These findings stress the importance of the design of modular junctions to minimize corrosion and the generation of corrosion products.

Structurally graded core junctions in sandwich elements

The paper addresses the problem of sandwich beams/panels with junctions between different core materials. The physics of the impairing local effects induced by a mismatch of the elastic material properties at core junctions is discussed, and the results of an experimental investigation concerning the failure behaviour of sandwich beams with conventional butt and ‘structurally graded’ core junctions subjected to quasi-static as well as fatigue loading conditions in a three-point bending scheme are discussed. The novel concept of structurally graded core junctions presents different geometrical shapes of the core interfaces (e.g. bias junctions) as well as core junctions with locally reinforced faces. The novel design of core junctions is shown to provide larger quasi-static failure loads, and more beneficial crack initiation and propagation patterns in sandwich beams. Furthermore, it is shown that structurally graded core junctions perform much better than conventional butt junctions under fatigue conditions. Thus, the fatigue life of the sandwich beams with structurally graded core junctions was up to 38% higher than the fatigue life of the sandwich beams with the conventional junction design.

Structurally graded core junctions in sandwich beams: fatigue loading conditions

Sandwich beams with inclusion of different core materials were the subject of the experimental study [Bozhevolnaya E, Thomsen OT. Structurally graded core junctions in sandwich beams: quasi-static analysis. Compos Struct, in press], which focused on the static performance of such sandwich elements. The concept of structurally graded core junctions, suggested in [Bozhevolnaya E, Thomsen OT. Structurally graded core junctions in sandwich beams: quasi-static analysis. Compos Struct, in press], presents different geometrical shapes of the core interfaces (e.g. bias junctions) as well as core junctions with locally reinforced faces. The novel design of core junctions was shown to provide larger critical static loads and more beneficial crack initiation and propagation patterns in sandwich beams. This paper is devoted to a comparative study of the performance of sandwich beams with conventional and structurally graded core junctions under fatigue loading conditions. An experimental investigation of the fatigue behaviour of the sandwich beams was performed using a three-point bending loading scheme. A rigorous statistical treatment of the experimental data has shown that structurally graded core junctions perform much better than conventional butt junctions. Thus, the fatigue life of the sandwich beams with structurally graded core junctions was up to 30% higher than the fatigue life of the sandwich beams with the conventional junction design.

Buckling experiments on steel silo transition junctions: II: Finite element modeling

This paper is concerned with the finite element modeling of the experiments on cone–cylinder–skirt–ring transition junctions in steel silos under simulated bulk solid loading presented in the companion paper. Before presenting the finite element results, the issue of modeling the interaction between the stored solid and the shell wall throughout the loading process is first examined. Results from nonlinear bifurcation analyses using the perfect shapes and nonlinear analyses using the measured imperfect shapes are then presented and compared with the experimental results. These comparisons show that despite the structural complexity of steel silo transition junctions, their behavior can be satisfactorily predicted by finite element analyses taking into account a number of important factors including geometric imperfections, effects of welding and the interaction between the junction and the stored solid. Next, the paper presents results of nonlinear analyses of these junctions with assumed eigenmode-affine imperfections. These results shed considerable light on the effect of ring buckling on the load-carrying capacity of transition junctions. Finally, the implications of the experimental and finite element results for the design of steel silo transition junctions are discussed.

GaN‐free transparent structure for ultraviolet light emitting diodes

AlGaN-based light emitting diodes (LEDs) are expected to be the next generation of ultraviolet light (UV) sources. With the aim of achieving AlGaN-based UV-LEDs comparable to those of conventional blue and red LEDs, we have investigated the regular epitaxial growth, the fabrication of uniform and abrupt heterointerfaces, the optical characteristics of AlGaN-based nitride quantum structures, the validity of the band engineering, the p-n junction designs, radiative recombination and light extraction. Efficient and transparent UV-LEDs grown on a high-quality AlN-template layer on a sapphire substrate are free from binary GaN, and have great potential for lighting equipment and other applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Technology Computer Aided Design of Ultra-shallow Junctions in Si Devices Formed by Laser Annealing Processes

ABSTRACTThe simulation of laser annealing, applied to the formation of ultra-shallow junctions in Si, is discussed. Our effort is developing tools capable to aid the process integration issue. The numerical approach deals with a double problem: 1) the interaction between the irradiated transistor structure and the laser light, 2) the non-equilibrium evolution of the thermal field, molten regions and dopant density. Here we present a complete methodology: the calculated heat source distribution, induced by the irradiation, is used as input of a phase-field approach for the simulation of the thermal phase and impurity fields. We solved numerically the phase field equations in two dimensional structures, considering as an initial status the generic material modification due to an ion implant process. We present various simulation results obtained in MOS structures with different geometry. With the support of the simulation results we discuss the problematic and the perspectives of the excimer laser annealing process application in the fabrication of MOS devices.

Prediction of boron transient enhanced diffusion through the atom-by-atom modeling of extended defects

The modeling of the atom-by-atom growth of extended defects is coupled to the diffusion equations of boron by transferring the free interstitial supersaturation calculated with a defect model into a process simulator. Two methods to achieve this coupling (equilibrium method and fully coupled method, respectively) are presented and tested against a variety of experimental conditions. They are first applied to a transient enhanced diffusion experiment carried out on a structure containing several B delta-doped layers, in which the amount of diffusion of the different layers is accurately predicted. The fully coupled method is then used to simulate the diffusion of ultrashallow B-implanted profiles. This work definitely demonstrates the relevance of accurate physical defect models for the successful design of ultrashallow junctions in future generations of integrated circuits.

Experimental study of playback giant magnetic resonance head nonlinearity in perpendicular recording

In this article, nonlinear distortions of the playback giant magnetic resonance (GMR) sensor in perpendicular recording are characterized in both time and frequency domains. We use three perpendicular media with different Mrt (0.46, 0.6, and 0.8 emu/cm2) and two groups of similar magnetic-read width (MRW) but different junction type [contiguous junction (CJ) and lead-over-lay (LOL)] GMR heads. Square-wave patterns at moderate densities are recorded to minimize NLTS, partial erasure, and transition broadening effects. Both time- and frequency-domain measurements indicate that the LOL-type GMR heads show playback nonlinearity (7%–23%), while the CJ-type GMR heads do not. Micromagnetic simulation is utilized to understand the hard bias field with different junction designs. The result indicates that the hard bias (HB) field in LOL type (HB field ∼6.9 Oe) at the air bearing surface (ABS) and stripe center is much lower than that in CJ type (HB field ∼54.0 Oe). Therefore, the free layer with large HB–HB distance will be more susceptible to saturation.

Planar intrinsic Josephson junctions fabricated on Bi-2212 LPE films

Planar design of intrinsic Josephson junctions (IJJs) is studied using Bi2Sr2CaCu2Ox (Bi-2212) films prepared by liquid phase epitaxy. Step-type IJJ stacks fabricated on step-patterned MgO substrates exhibit multibranched current–voltage characteristics inherent in Bi-2212 single crystals. This behavior is found to be limited to films on small-angle steps, suggesting the incorporation of defects near the steep steps of substrates.

Advances in elevated diode technologies for integrated circuits: progress towards monolithic instruments

Integrated circuit manufacturing capabilities have reached the stage where it is technically and economically feasible to create new components that may be monolithically combined with them to create unique devices. One of the most elementary yet reliable of such monolithic components is the elevated diode. These diodes may be used to detect or generate light for parallel photodetection or photogeneration applications, such as imaging, chemical detection, or displays. Because new materials are required for all implementations, various process flows and integration challenges are discussed. In particular, focus on interconnection to the top and bottom of the junction is considered. In addition, since the elevated diode concept gives the designer control of such parameters as junction thickness, semiconductor bandgap, and light emission spectrum, the issues that drive junction design are presented for both the elevated photodiode and elevated OLED. Finally, because of the decoupling of diode size and pixel size, and the presence of new materials, novel pixel circuits are considered to achieve novel or greater pixel-level functionality, and because material behaviour may dictate the method to drive the junction. The new possibilities that these junctions present create a new realm of applications and are initial examples of a new class of devices called monolithic instruments.

Magnetoresistance sensitivity mapping of the localized response of contiguous and lead-overlaid sensors

Magnetoresistance sensitivity mapping (MSM) was used to investigate the local response of magnetic recording sensors without convolution of the writer, magnetic media and data channel. From a 2D map of the local sensor response, the intrinsic pulse shape and magnetic track profile are readily obtained. Pulse-width is a concern for high data rate since if pulse-width is too broad, individual transitions become difficult to distinguish. Track profiles are important because due to the small difference between magnetic write-width and magnetic read-width, side reading will lead to an increase in noise. Three experiments are discussed: the dependence of the pulse-width (PW50) of the standard contiguous junction (CJ) design on shield-to-shield spacing; a comparison of the pulse shape of lead-overlaid (LOL) and CJ designs; and a comparison of the magnetic track profile (including track-width and skirt ratio) of LOL and CJ designs. The LOL design offers an increased sensitivity; however, as seen from MSM, the penalties are broadening of the track and pulse profiles. These are a direct result of the finite current in the lead overlay region and an increased shield-to-shield spacing in that region. The MSM image shows a curvature, which is associated with the topography of the top shield due to the lead overlay.

Supercritical flow in the 90° junction manhole

Based on previous observations of the 45° junction manhole for supercritical flow in the main and lateral branches, the hydraulics of the more common 90° junction manhole were explored. Using a selected manhole geometry involving: (1) a short straight piece in the lateral branch to inhibit full development of the bend wave, and (2) the addition of the junction extension as used in previous designs for the bend manhole, the present study gives results that are in basic agreement with those collected in the 45° junction manhole. This surprising result thus allows for a design basis independent of the junction angle.The present paper defines three waves that may occur in a junction manhole, i.e. bend wave, junction wave and the swell at the manhole outlet into the downstream pipe. In addition, the position of the determining junction wave was established. Important for the junction design is the discharge capacity for which supercritical flow can be maintained across the manhole. It was found that the lateral branch flow depth and the pipe diameter have an important effect on this capacity, for both branches or only one of the branches in operation.

Composition induced design considerations for InP/Ga xIn 1− xAs heterojunction bipolar transistors

Several design principles based on compositional grading and heavy doping of the base region of a heterojunction bipolar transistor (HBT) have been presented. Physical and technological advantages underlying composition induced design criteria of InP/Ga x In 1− x As HBTs have been discussed. A number of issues such as superlattice based grading in the base region, base resistance vs base region grading, the emitter–base junction design, tradeoffs between base region grading and the nonuniform doping of the base region, and the surface recombination at the external base region, have been articulated.