bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Integrity of Flexible Piping Systems Conveying Liquids
Authors: BastosFreitas Rachid Felipe
Published: August 2006

This work presents a structural integrity model for piping systems conveying liquids which takes the axial fluid-structure interaction into account. The model is used to numerically investigate the influence of pipe motion on the degradation of the piping when fast transients are generated by valve slam. The resulting mathematical problem is formed by a system of nonlinear partial differential equations which is solved by means of an operator splitting technique, combined with Glimm’s method. Numerical results obtained for an articulated piping system indicate that high piping flexibility may induce a substantial increase in damage growth along the pipes.
Ultimate Bending Capacity and Buckling of Pressurized 90 deg Steel Elbows
Authors: Karamanos S. A. , Tsouvalas D. , Gresnigt A. M.
Published: August 2006

The paper examines the nonlinear elastic-plastic response of internally pressurized 90 deg pipe elbows under in-plane and out-of-plane bending. Nonlinear shell elements from a general-purpose finite element program are employed to model the inelastic response of steel elbows and the adjacent straight parts. The numerical results are successfully compared with real-scale experimental measurements. The paper also presents a parametric study, aimed at investigating the effects of diameter-to-thickness ratio and moderate pressure levels on the ultimate bending capacity of 90 deg elbows, focusing on the failure mode (local buckling or cross-sectional flattening) and the maximum bending moment. Special attention is given to the response of 90 deg elbows under out-of-plane bending moments.
Control of Static Shape, Dynamic Oscillation, and Thermally Induced Vibration of Nozzles
Authors: Wang D. W. , Tzou H. S. , Arnold S. M. , Lee H.-J.
Published: August 2006

Static shape actuation and dynamic control of nozzles can improve their performance, accuracy, reliability, etc. A new curved laminated piezothermoelastic hexahedral finite element is formulated based on the layerwise constant shear angle theory and it is used for modeling and analysis of piezothermoelastic conical shell structures subjected to control voltages for static shape actuation and dynamically and thermally induced vibration controls. Free vibration characteristics of an elastic truncated conical shell nozzle with fixed-free boundary conditions are studied using the new finite element. Both frequencies and mode shapes are accurately computed and compared favorably with available experimental and other numerical data. This study is then extended to evaluate control effectiveness of the conical shell with laminated piezoelectric layers. Static shape control is achieved by an applied electric potential. Vibration sensing and control are carried out using the negative velocity control scheme. Control of thermal excitation is also investigated. Analysis data suggest that the dynamic behavior and control characteristics of conical shells are quite complicated due to the coupled membrane and bending effects participating in the responses. To improve control effectiveness, segmentation and/or shaping of sensor and actuator layers need to be further investigated.
Passive Control of Seismic Response of Piping Systems
Authors: Parulekar Y. M. , Reddy G. R. , Vaze K. K. , Muthumani K.
Published: August 2006

Passive energy dissipating devices, such as elastoplastic dampers (EPDs) can be used for eliminating snubbers and reducing the response of piping systems subjected to seismic loads. Cantilever and three-dimensional piping systems were tested with and without EPD on shaker table. Using a finite element model of the piping systems, linear and nonlinear time-history analysis is carried out using Newmark’s time integration technique. Equivalent linearization technique, such as Caughey method, is used to evaluate the equivalent damping of the piping systems supported on elastoplastic damper. An iterative response spectrum method is used for evaluating response of the piping system using this equivalent damping. The analytical maximum response displacement obtained at the elastoplastic damper support for the two piping systems is compared with experimental values and time history analysis values. It has been concluded that the iterative response spectrum technique using Caughey equivalent damping is simple and results in reasonably acceptable response of the piping systems supported on EPD.
Free Vibration Analysis of Spherical Caps Using a G.D.Q. Numerical Solution
Authors: Artioli E. , Viola E.
Published: August 2006

In this paper we present the frequency evaluation of spherical shells by means of the generalized differential quadrature method (G.D.Q.M.), an effective numerical procedure which pertains to the class of generalized collocation methods. The shell theory used in this study is a first-order shear deformation theory with transverse shearing deformations and rotatory inertia included. The shell governing equations in terms of mid-surface displacements are obtained and, after expansion in partial Fourier series of the circumferential coordinate, solved with the G.D.Q.M. Several comparisons are made with available results, showing the reliability and modeling capability of the numerical scheme in argument.
Clamp Load Loss due to Fastener Elongation Beyond its Elastic Limit
Authors: Nassar Sayed A. , Matin Payam H.
Published: August 2006

The amount of clamp load due to an externally applied separating force is determined for a boiled assembly in which the fastener is elongated past its proportional limit, while the clamped joint remained within its elastic range. After the initial tightening of the fastener, the joint is subsequently subjected to a tensile separating force, which further increases the fastener tensile stress into the nonlinear range. Such separating force will simultaneously reduce the clamping force in the bolted joint. Upon the removal of the separating service load, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the fastener tension is reduced from its value at initial assembly, due to the plastic elongation of the fastener. The reduction in fastener tension translates into a partial—yet permanent—loss of the clamping load that may lead to joint leakage, loosening, or fatigue failure. A nonlinear model is established in order to describe the fastener behavior past the proportional limit of its material, and to determine the clamp load loss due to the permanent set in the fastener after the separating force has been removed. Two fastener materials with significantly different rates of strain hardening are used for modeling the behavior of the bolted joint system. The effect of three nondimensional variables on the amount of clamp load loss is investigated. The first variable is the stiffness ratio of the joint and the fastener. The second is the ratio of initial fastener tension to the fastener elastic limit, and the third variable is the ratio of the separating force to the force that causes joint separation to start. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications. Experimental verification of the analytical results is presented.
An Experimental Investigation of the Effects of Clamped Length and Loading Direction on Self-Loosening of Bolted Joints
Authors: Zhang Ming , Jiang Yanyao , Lee Chu-Hwa
Published: August 2006

An experimental investigation was conducted to study the effects of clamped length and loading direction on the self-loosening behavior of bolted joints by using specially designed fixtures. The experiments mimicked two plates jointed by an M12×1.75 class 10.9 bolt and a nut. The joints were subjected to cyclic external loading. A constant preload of 25kN was used for all the experiments conducted. During an experiment, the relative displacement between the two clamped plates, δ, was a controlling parameter. The reduction in clamping force, the applied transverse load, and the nut rotation were measured cycle by cycle. The relationship between, Δδ∕2, the amplitude of the relative displacement between the two clamped plates, and, NL, the number of loading cycles to loosening is referred to as self-loosening curve and was obtained for different clamped lengths and applied load directions. Similar to a fatigue curve, an endurance limit can be identified from the self-loosening curve. It was found that increasing the clamped length can enhance the self-loosening endurance limits in terms of the controlled relative displacement of the two clamped plates. However, the load carrying capability was not influenced significantly due to the thickness of the clamped plates. For a given bolted jointed structure, an angle of the external load from the pure shearing direction resulted in an increase in self-loosening resistance.
Clamp Load Loss due to Elastic Interaction and Gasket Creep Relaxation in Bolted Joints
Authors: Nassar Sayed A. , Alkelani Ali A.
Published: August 2006

An experimental study is presented in order to determine the clamp load loss due to elastic interaction and gasket creep relaxation in bolted joints. Studied parameters include the gasket material and thickness, bolt spacing, tightening sequence, fastener grip length, and level of the fastener preload. The joint is composed of two steel flanges and a gasket made of styrene butadiene rubber or flexible graphite. The flanges are fastened together using M12x1.75 Class 10.9 fasteners. Force washers are used to monitor bolt tensions in real time. Four different gasket thicknesses of styrene butadiene rubber (1/16, 1/8, 3/16, and 1/4 in.) and two thicknesses of flexible graphite (1/16 and 1/8 in.) are considered. For the same bolt circle of the flange, the bolt spacing is varied by using a different number of bolts; spacing that corresponds to using three, five, or seven bolts is considered in this study. The effect of the tightening strategy is studied by using sequential, star, or simultaneous tightening patterns. Bolt tightening is accomplished by using either an electric digital torque wrench with various control options or by using a production-size multiple spindle fastening system that is capable of simultaneous tightening of all fasteners. Experimental data is presented and analyzed, in order to study the effect of the various parameters on the clamp load loss due to the combined effect of elastic interaction and gasket creep relaxation at room temperature.
Benchmark of Plate Forming and Weld Distortion Process
Authors: Gombas James
Published: August 2006

A circular flat plate with a perforated central region is to be formed by dies into a dome and then welded onto a cylindrical shell. After welding, the dome must be spherical within a narrow tolerance band. This plate forming and welding is simulated using large deflection theory elastic-plastic finite element analysis. The manufacturing assessment is performed so that the dies may be designed to compensate for plate distortions that occur during various stages of manufacturing, including the effects of weld distortion. The manufacturing simulation benchmarks against measurements taken at several manufacturing stages from existing hardware. The manufacturing simulation process can then be used for future applications of similar geometries.
Measurement of Residual Stresses in a Type 316H Stainless Steel Offset Repair in a Pipe Girth Weld
Authors: Hossain S. , Truman C. E. , Smith D. J. , Bouchard P. J.
Published: August 2006

This paper presents measurements of the in-plane residual stress components through the wall of a 218mm long, 26mm deep repair weld, offset by 7mm from the centerline of a girth weld joining two type 316H stainless steel pipes approximately 37mm thick. The measurements were obtained using the deep hole drilling technique. Two locations were examined: (i) mid-length of the repair weld and (ii) the stop-end of the repair. Both measurements were taken along the girth weld centerline. The distributions and magnitudes of the measured longitudinal and transverse stress components at the two locations were very similar over the outer half of the pipe wall. Over the inner half of the pipe wall both components of stress were found to be significantly more compressive at the stop-end of the repair than at mid-length. In general, the transverse residual stresses were found to be lower than the longitudinal residual stresses at both locations. The measured stress profiles are compared with predicted residual stresses from a three-dimensional finite element analysis.
Ultrasonic Control of Fastener Tightening Using Varying Wave Speed
Authors: Nassar Sayed A. , Veeram Aditya B.
Published: August 2006

A high precision ultrasonic technique and a test apparatus are developed for the real time control of the fastener elongation during the tightening process of bolted joints. This is accomplished by monitoring the propagation of longitudinal ultrasonic waves through the fastener material and the reflection of these waves at the end of the fastener. The round trip time of the longitudinal waves is continuously measured and monitored in real time. Using the wave speed in the fastener material, the change in the round trip time determines the fastener elongation, which creates fastener tension and joint clamp load. The wave speed through the bolt material is stress dependent; hence, it continuously changes as the fastener is being elongated during the tightening process. A varying wave speed algorithm is developed and utilized in order to compensate for wave speed variations. Because the torque-tension relationship in threaded fasteners is highly sensitive to friction variations, the scatter in such relationship is often unacceptable, especially in critical applications. By contrast, the automatic control of the fastener elongation during the tightening process would eliminate the dependence on the torque value as a predictor for the bolt tension. Hence, the new ultrasonic technique for the real-control of the fastener tension, by monitoring its elongation, would significantly enhance the reliability of bolted assemblies.
High Frequency Guided Wave Natural Focusing Pipe Inspection With Frequency and Angle Tuning
Authors: Zhang Li , Gavigan Brian J. , Rose Joseph L.
Published: August 2006

When ultrasonic guided wave nondestructive evaluation is used to inspect pipelines, partial loading of transducers around the circumference leads to a non-axisymmetric energy distribution. At particular axial distances and frequencies, the ultrasonic energy is naturally focused at some spots via constructive wave interference. This so-called “natural focusing” phenomenon can be used to improve guided wave sensitivity for a defect by impinging more energy onto it. However, defects located in other places can be missed, unless we can move the natural focusing points throughout the pipe. We have done this by frequency and circumferential angle tuning for specific circumferential loading lengths. In order to utilize the natural focusing phenomenon to enhance detection sensitivity, a frequency and angle tuning (FAT) technique is employed to extend the area that can be scanned by focal energy. It is observed that the natural focal points at a fixed axial distance move with frequency variation and circumferential excitation length change. In this paper, the natural focusing phenomenon with FAT is theoretically calculated and experimentally investigated. The results show that the natural focusing inspection technique can sufficiently inspect an entire pipe with FAT.
Modeling of Granular Flow and Combined Heat Transfer in Hoppers by the Discrete Element Method (DEM)
Authors: Kruggel-Emden Harald , Wirtz Siegmar , Simsek Erdem , Scherer Viktor
Published: August 2006

The discrete element method can be used for modeling moving granular media in which heat and mass transport takes place. In this paper the concept of discrete element modeling with special emphasis on applicable force laws is introduced and the necessary equations for heat transport within particle assemblies are derived. Possible flow regimes in moving granular media are discussed. The developed discrete element model is applied to a new staged reforming process for biomass and waste utilization which employs a solid heat carrier. Results are presented for the flow regime and heat transport in substantial vessels of the process.
Application of an Enhanced RBI Method for Petrochemical Equipments
Authors: Lee Sang-Min , Chang Yoon-Suk , Choi Jae-Boong , Kim Young-Jin
Published: August 2006

The American Petroleum Institute guideline provides a methodology for calculating the risks of equipments installed in refineries or petrochemical plants. However, especially in connection with consequence analysis, there are limitations of its direct application to petrochemical plant. As a principal cause, only representative material is recommended for the risk evaluation while the equipment contains numerous materials. The objectives of this paper are to propose an enhanced risk-based inspection (RBI) method to resolve above shortcomings and to assess the risks of typical petrochemical equipments. In this respect, a RBI program including a material management database is developed to fully incorporate the characteristics of different materials. The proposed program consists of qualitative, semi-quantitative, and quantitative evaluation modules in which representative material, as well as toxic materials, is selected automatically for comparison to those getting from the current guideline. It has been applied to assess the risks of major equipments in ethylene facility such as vessel and column. Thereby, realistic evaluation results were obtained and applicability of the proposed RBI program was proven.
On the Endurance Limit of Fiberglass Pipes Using Acoustic Emission
Authors: Ramirez Guillermo , Engelhardt Michael D. , Fowler Timothy J.
Published: August 2006

This paper proposes a method for determining endurance limits to leakage for fiberglass pipes under internal pressure using acoustic emission signals and static pressure tests. Results are presented from a series of cyclic internal pressure tests performed on fiberglass pipes fabricated according to ASME RTP-1 (1989) recommendations. The specimens were 8in.(20.32cm) internal diameter and 5ft(1.525m) long. The construction layup consisted of an internal corrosion barrier followed by several layers of continuous filament wound glass. A state of pure hoop stress was imposed via an internal pressure system that allowed free axial movement of the pipe. The purpose of the tests was to evaluate current design procedures and to assess the capabilities of acoustic emission (AE) monitoring to detect damage and to predict the leakage pressure for the pipes. Twenty-four specimens were tested to failure with AE monitoring. The results of these tests are presented, including data on the measured cyclic life of the specimens, comparisons to the static leakage capacity, and the effectiveness of AE in determining damage induced by cyclic loading.
The Effect of Pressure Relief Valve Blowdown and Fire Conditions on the Thermo-Hydraulics Within a Pressure Vessel
Authors: Birk A. M. , VanderSteen J. D. J.
Published: August 2006

In the summers of 2000 and 2001, a series of controlled fire tests were conducted on horizontal 1890liter (500 US gallon) propane pressure vessels. The test vessels were instrumented with pressure transducers, liquid space, vapor space, and wall thermocouples, and an instrumented flow nozzle in place of a pressure relief valve (PRV). A computer controlled PRV was used to control pressure. The vessels were heated using high momentum, liquid propane utility torches. Open pool fires were not used for the testing because they are strongly affected by wind. These wind effects make it almost impossible to have repeatable test conditions. The fire conditions used were calibrated to give heat inputs similar to a luminous hydrocarbon pool fire with an effective blackbody temperature in the range of 850°C±50°C. PRV blowdown (i.e., blowdown=poppressure−reclosepressure) and fire conditions were varied in this test series while all other input parameters were held constant. The fire conditions were varied by changing the number of burners applied to the vessel wall areas wetted by liquid and vapor. It was found that the vessel content’s response and energy storage varied according to the fire conditions and the PRV operation. The location and quantity of the burners affected the thermal stratification within the liquid, and the liquid swelling (due to vapor generation in the liquid) at the liquid∕vapor interface. The blowdown of the PRV affected the average vessel pressure, average liquid temperature, and time to temperature destratification in the liquid. Large blowdown also delayed thermal rupture.
Reliability Study of the Hydraulically Expanded Tube-to-Tubesheet Joint
Authors: Qian Caifu , Duan Chenghong , Yu Hongjie , Duan Hongwei , Tian Junli
Published: August 2006

A three-dimensional parametrized finite element model is established for the nonlinear analysis of the hydraulically expanded tube-to-tubesheet joint. Distribution of the residual contact pressure on the contact surface between the tube and the tubesheet is investigated. It is found that sealing circular bands exist on the contact surface which enhance the sealing of the joint since the residual contact pressures on the sealing circular bands are higher than on other positions. The sealing circular bands are located close to the two ends of the hole when it is not grooved, but they are located at the two brinks of the groove for a grooved hole and in the latter case, the residual contact pressures are even higher, reflecting that the joint with a grooved tube-sheet hole is more capable of sealing. Experiments and finite element calculations for the pull-out force of the joint are also performed for different expansion pressures and groove widths. Results show that with the increase of the groove width, the measured pull-out force increases significantly and becomes larger and larger than the calculated one, which is owing to the scratch on the contact surface between the tube and tubesheet.
Mixture Model Approach for Acoustic Emission Control of Cylindrical Pressure Equipment
Authors: Hamdan Hani , Govaert Gérard
Published: August 2006

In this paper, we present a new and original mixture model approach for acoustic emission (AE) data clustering. AE techniques have been used in a variety of applications in industrial plants. These techniques can provide the most sophisticated monitoring test and can generally be done with the plant/pressure equipment operating at several conditions. Since the AE clusters may present several constraints (different proportions, volumes, orientations, and shapes), we propose to base the AE cluster analysis on Gaussian mixture models, which will be, in such situations, a powerful approach. Furthermore, the diagonal Gaussian mixture model seems to be well adapted to the detection and monitoring of defect classes since the weldings of cylindrical pressure equipment are lengthened horizontally and vertically (cluster shapes lengthened along the axes). The EM (Expectation-Maximization) algorithm applied to a diagonal Gaussian mixture model provides a satisfactory solution but the real time constraints imposed in our problem make the application of this algorithm impossible if the number of points becomes too big. The solution that we propose is to use the CEM (Classification Expectation-Maximization) algorithm, which converges faster and generates comparable solutions in terms of resulting partition. The practical results on real data are very satisfactory from the experts point of view.
Synthesized processing techniques for monolithic integration of nanometer-scale hole type photonic band gap crystal with micrometer-scale microelectromechanical structures
Authors: Teo Selin H. G. , Liu A. Q. , Yu M. B. , Singh J.
Published: August 2006

This article reports the synthesized fabrication process design and module development that enabled the monolithic integration of deep submicrometer size, two dimensional hole-type photonic band gap crystals (PhCs) with microelectromechanical system (MEMS) actuators and optical testing structures (OTS). Techniques enabling sublithographic wavelength patterning using only conventional chrome-on-glass binary photomasks without phase shift features were achieved through the manipulation of mask bias designs and the partial coherence control of the lithographic exposure system. Together with the development of time multiplexed reactive ion etching and focus ion beam milling techniques, such design of the process allows the realization of highly dense PhC and MEMS actuators physically released from the buried oxide layer. Here, disparate pattern dimensions [with PhC critical dimensions (CDs) of only 175nm, MEMS typical dimensions of 2μm, and OTS openings more than 400μm wide], varied etch depth (3μm for the PhC and MEMS, 61μm for the OTS), and the requirement of a sufficient process latitude for exposure and etch processes are some of the key challenges that were overcome for a successful integration of air-bridge-type PhC CDs with movable MEMS actuators. Hence, the works described in this article enable MEMS tunable PhC properties with potential application in next generation dynamic optical communication networks and photonic integrated circuits.
Si nanowires sheathed with thin diamondlike carbon films
Authors: Qiu T. , Wu X. L. , Yang L. W. , Shen P. N. , Zhang Z. Y. , Siu G. G. , Chu Paul K.
Published: August 2006

Via electroless metal deposition and industrial plasma technology, we have successfully synthesized unique composite silicon nanowire structures with diamondlike carbon (DLC) sheaths acting as inorganic passivation layers. We have also discussed their growth mechanism in terms of a self-organization process. The thickness of the DLC sheaths were quantified with Raman spectroscopy. The Raman analytical result is in good agreement with direct microstructure observations.
Impact of extension implant energy purity and angle on the electrical characteristics of a 65nm device technology
Authors: Gossmann Hans-Joachim L. , Rubin Leonard , Parrill Tom , Agarwal Aditya
Published: August 2006

We show that a significant fraction of the overlap in advanced logic technologies originates in the as-implanted dopant profile. As a consequence, small changes in the as-implanted profile have a large impact on device characteristics. We have developed a virtual, high-performance, planar, bulk, 65nm technology that we use as a platform to investigate the impact of imperfections in the extension implant stemming from (1) contamination of the beam with higher energy ions and (2) angular alignment of the incident ion beam to the wafer. We find that a deceleration ratio of 7 and an energy contamination equal to 1% of the total dose double the off current. Small (of the order 1°) beam steering of the incident beam as seen by the wafer leads to large changes in on current (of the order of 20%) and speed. Steering that results in shadowing of the source has a far larger impact than drain-side shadowing. This can be alleviated significantly by a quad implant, provided the tilt angle is sufficiently large, on the order >5°. A quad implant twisted by 45° allows essentially complete recovery of the nominal device characteristics, even where beam steering leads to source-side shadowing.
Influence of silicon nitride passivation on transport properties in InAlAs∕InGaAs∕InP composite channel high electron mobility transistor structures
Authors: Liu Yuwei , Wang Hong
Published: August 2006

The influence of silicon nitride (SiN) passivation on the electron mobility of InGaAs∕InP composite channel high electron mobility transistor (HEMT) structures has been studied. Hall measurements were used to characterize the influence of SiN passivation on electrical properties. An increase in effective mobility μe with a negligible change of sheet carrier density ns after SiN deposition is clearly observed. This behavior is different from the previous report on the single InGaAs channel HEMT structure, in which the increase in sheet carrier density with a negligible change of electron mobility was found. Photoluminescence (PL) measurements were carried out to evaluate the effects of SiN passivation on electrical and optical properties. The variations of the PL peak position, the transition intensity, and the linewidth of different passivated samples were analyzed to clarify the mechanism for the change in electrical properties. Our results suggest that the enhancement of μe could be explained under the framework of electron transfer from the InP subchannel into the InGaAs channel region due to energy band bending at the surface region caused by the SiN passivation.
Chemical bonding and interdiffusion in scaled down SiO2∕Si3N4∕SiO2 stacks with top oxide formed by thermal ed copyoxidation
Authors: Saraf Meirav , Edrei Rachel , Akhvlediani Roza , Roizin Yakov , Shima-Edelstein Ruth , Hoffman Alon
Published: August 2006

The influence of thermal oxidation on the composition of silicon nitride films in SiO2∕Si3N4∕SiO2 stacks for advanced nonvolatile memories is reported. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses lead to the conclusion that wet thermal (pyrogenic) oxidation of silicon nitride enhances the incorporation of oxygen into the silicon nitride layer and creates a silicon oxynitride layer. In the oxynitride layer formed by wet oxidation, O is mostly bonded to N, whereas in the native oxynitride at the silicon nitride surface, O is preferentially bonded to Si. Dry oxidation (1200°C) results in an even higher amount of oxygen incorporation into the silicon nitride layer as compared with the pyrogenic process. After both pyrogenic and dry oxidation, hydrogen concentration decreases in the bulk of the silicon nitride layer. Following wet oxidation, hydrogen was found to accumulate at the surface layers of the grown oxynitride film. Oxygen penetration into the nitride layer was found to be higher in thinner nitride layers. The peculiarities of hydrogen distribution were not affected by the thickness of the nitride layer.
Soft mold and gasbag pressure mechanism for patterning submicron patterns onto a large concave substrate
Authors: Cheng Fang-Sung , Yang Sen-Yeu , Nian Shih-Chih , Wang Lon A.
Published: August 2006

A gasbag pressure (GBP) mechanism has been developed for patterning submicron patterns onto large concave substrate. The GBP mechanism consists of a pressure gasbag and a vacuum chamber system. It provides gradual contact, uniform pressure, and intact contact for imprinting patterns in the soft mold onto a concave substrate. The patterns on the soft mold can be successfully replicated over an entire photoresist-coated concave substrate. The accuracy of replication has been experimentally evaluated.
Performance of organic thin-film transistors
Authors: Marinov O. , Deen M. Jamal , Iñiguez B.
Published: August 2006

An investigation of the performance of organic and polymeric thin-film transistors (OTFTs) made of several organic semiconducting and insulating materials in the last two decades is presented, in an attempt to capture the state-of-the-art experimental values for effective mobility, threshold voltage, on/off ratio, and subthreshold slope in OTFTs made of different materials by different fabrication approaches. The analysis of published data demonstrates that the effective mobility decreases when the product of the semiconducting film thickness (tO) and gate capacitance per unit area (CI) increases. The decrease is given by a power-law function with parameters for several organic semiconductors, and examples are provided on how the deduced trend can be used in the practical design of organic circuits. The second observation is that the polarity of the OTFTs’ threshold voltage VT is random, but the spread in magnitudes of ∣VT∣ decreases, when CI increases. This trend, together with the third observation that the subthreshold slope tends to decrease when CI increases, is weak and no strong correlation between subthreshold slope and on/off ratio in the published data was found.
Structural and magnetic properties of (Ga,Mn)As∕AlAs multiple quantum wells grown by low-temperature molecular beam epitaxy
Authors: Kolovos-Vellianitis D. , Herrmann C. , Trampert A. , Däweritz L. , Ploog K. H.
Published: August 2006

Ga 1 − x Mn x As ∕ Al As multiple quantum wells (MQWs) with Mn concentrations of x=0.03 and x=0.043 are grown by low-temperature molecular beam epitaxy on GaAs(100) surfaces. We establish the optimum growth conditions by carefully determining the corresponding As partial pressure and growth temperature. The samples are characterized by x-ray diffraction in conjunction with simulations based on the dynamical diffraction theory to determine the structural and compositional parameters of the MQWs. High resolution transmission electron microscopy is used to analyze the microstructure of the MQWs and, in particular, to measure the interface roughness. Magnetic measurements reveal that the grown samples show ferromagnetic behavior.
On microscopic compositional and electrostatic properties of grain boundaries in polycrystalline CuIn1−xGaxSe2
Authors: Hetzer M. J. , Strzhemechny Y. M. , Gao M. , Goss S. , Contreras M. A. , Zunger A. , Brillson L. J.
Published: August 2006

We report on the microscopic characteristics of polycrystalline CuIn1−xGaxSe2 thin films probed with Auger electron spectroscopy, cathodoluminescence spectroscopy, secondary ion mass spectrometry, and work function measurements. Confirming theory, we find a substantial reduction in Cu content from grain interior to boundary and a p-type potential barrier that acts to reduce hole recombination. Such compositional and electrostatic variations between grain boundaries and grain interiors in CuIn1−xGaxSe2 solar cell absorber layers may improve the overall photovoltaic efficiency. The high degree of intergranular inhomogeneity emphasizes the importance of detailed grain-by-grain analysis. These results show that careful specimen preparation and ultrahigh vacuum conditions, coupled with nanoscale instrumental resolution, are pivotal for such analysis.
Interactive relationships between sidewall and bottom etch rates, as-affected by sidewall angle, during SiO2 etching in a CHF3 plasma
Authors: Min Jae-Ho , Lee Jin-Kwan , Moon Sang Heup , Kim Chang-Koo
Published: August 2006

Relationships between sidewall and bottom etch rates during SiO2 etching in a CHF3 plasma were studied using a Faraday cage system, which permitted the sidewall angle to be controlled with respect to ions incident on the surface and the sidewall and bottom surfaces to be examined on a scale larger than in actual microfeatures. The etch rates for the sidewall were significantly decreased at sidewall angles near 75° and the resulting angular dependence of the etch rates decreased monotonously following an “inversely S-shaped” curve. On the other hand, the degree of sidewall effect (DSE), which represents changes in the bottom etch rates due to the presence of the sidewall, showed a characteristic “W-shaped” curve with respect to sidewall angle, due to a decrease in the bottom etch rates at sidewall angles near 75°. The relationship between the sidewall etch rate and the DSE was affected by a thick, rough steady-state fluorocarbon film formed on the sidewall surface. The thickness, roughness, and F∕C ratio of the fluorocarbon film were examined for cases of different sidewall angles, and their contributions to the sidewall etch yield and the bottom etch rate are discussed with respect to energy transferred to the sidewall surface by bombarding ions.
Modification of polymethylmethacrylate by deep ultraviolet radiation and bromination for photonic applications
Authors: Henzi P. , Bade K. , Rabus D. G. , Mohr J.
Published: August 2006

Deep UV-induced modification of the refractive index of polymers is a useful technique for realizing integrated optical circuits for telecommunication and sensor applications. The combination with replication techniques such as hot embossing opens up a variety of possibilities such as a monolithic integration in optical or fluidic microsystems. In this article the fundamental understanding of the deep UV process is given including examples of fabricated waveguide based devices.
Efficacy of ECR-CVD silicon nitride passivation in InGaP∕GaAs HBTs
Authors: Zoccal L. B. , Diniz J. A. , Doi I. , Swart J. W. , Daltrini A. M. , Moshkalyov S. A.
Published: August 2006

High quality passivation silicon nitride films have been obtained requiring no surface pretreatment and being fully compatible with monolithic microwave integrated circuits. The nitride film is deposited by electron cyclotron resonance—chemical vapor deposition directly over GaAs-n substrate and over InGaP∕GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Metal∕nitride∕GaAs-n capacitors were fabricated for all the samples. Effective charge densities of 3×1011cm−2 and leakage current densities of 1μA∕cm2 were determined. Plasma analysis showed a reduced formation of molecules such as NH in the gas phase at low pressures, allowing the deposition of higher quality films. The process was used for InGaP∕GaAs HBT fabrication with excellent results, such as higher current gain of passivated device comparing to unpassivated HBTs.
Focused ion beam sculpting curved shape cavities in crystalline and amorphous targets
Authors: Adams D. P. , Vasile M. J. , Mayer T. M.
Published: August 2006

This work demonstrates accurate sculpting of predetermined micron-scale, curved shapes in initially planar solids. Using a 20keV focused Ga+ ion beam, various features are sputtered including hemispheres, parabolas, and sinusoidal wave forms having dimensions from 1to30μm. Ion sculpting is accomplished by varying the dose at different points within individual scans. The doses calculated per point account for the material-specific, angle-dependent sputter yield, Y(θ), the beam current, and the ion beam spatial distribution. Several target materials are sculpted using this technique. These include semiconductors that are made amorphous or disordered by the high-energy beam and metals that remain crystalline with ion exposure. For several target materials, curved feature shapes closely match desired geometries with milled depths within 5% of intended values. Deposition of sputtered material and reflection of ions from sloped surfaces are important factors in feature depth and profile evolution. Materials that are subject to severe effects of redeposition (e.g., C and Si) require additional dose in certain regions in order to achieve desired geometries. The angle-dependent sputter yields of Si, C, Au, Al, W, SiC, and Al2O3 are reported. This includes normal incidence values, Y(0°), and Yamamura parameters f and Σ.
Gate etch process model for static random access memory bit cell and FinFET construction
Authors: Stout Phillip J. , Rauf Shahid , Peters Richard D. , Ventzek Peter L. G.
Published: August 2006

A reactor/feature/lithography modeling suite has been developed to study the gate etch process. The gate etch process study consists of an eight step process designed to etch through a hard mask (HM)/antireflective coating/polysilicon gate stack and a 22+ step modeled process for FinFET (field effect transistor) manufacture. Coupling to a lithography model allows for a study of how a static random access memory (SRAM) bit cell layout transfers into the gate stack during the gate etch process. The lithography model calculates a three-dimensional (3D) photoresist (PR) profile using the photomask, illumination conditions, and a PR development model. The 3D PR profile is fed into the feature model, Papaya, as the initial PR etch mask condition. The study of the cumulative effect of the gate etch process required to transfer a photomask layout into a gate stack allows for a better understanding of the impact one step in the gate etch process can have on subsequent steps in the process. Studies of pattern transfer of a SRAM bit cell into a gate stack have shown that more edge movement occurs at line ends than at line sides. The line ends are more exposed to incoming etchants and have less opportunity for passivant buildup from the etching wafer than along line sides. An increase in sidewall slope at line ends during the trim and HM etch is observed experimentally and predicted by the model. The slope at line ends during trim and HM etch is more prevalent for narrow ends versus the wider “contact” ends. The lower the PR etch mask height after the HM etch step, the larger the angle seen at line ends which increases the line end pullback. So, a correlation exists between higher wafer power during the HM etch and line end pullback. Passivant formation at the polysilicon sidewall during the main etch/soft landing/overetch polysilicon etch sequence can straighten the profile as well as cause hourglassing and trapezoidal profiles. Passivant thickness, passivant deposition rate, as well as the passivant to polysilicon etch ratio all control this profile behavior. Increased passivation levels also have the tendency to increase linewidth roughness. In FinFET manufacture the gate etch needs to account for the increased topography introduced by the fins.
Comparison of high resolution negative electron beam resists
Authors: Bilenberg B. , Schøler M. , Shi P. , Schmidt M. S. , Bøggild P. , Fink M. , Schuster C. , Reuther F. , Gruetzner C. , Kristensen A.
Published: August 2006

Four high resolution negative electron beam resists are compared: TEBN-1 from Tokuyama Corp. Japan, ma-N 2401XP and mr-L 6000.1XP from microresist technology GmbH Germany, and SU-8 2000 series from MicroChem Corp., USA. Narrow linewidth high density patterns are defined by 100kV electron beam lithography, and the pattern is transferred into silicon by a highly anisotropic SF6∕O2∕CHF3 based reactive ion etch process with a selectivity between silicon and the investigated resists of approximately 2. 20nm half-pitch lines and 10nm lines with a pitch down to 60nm are written and transferred into silicon.
Microfabrication of ultrahigh density wafer-level thin film compliant interconnects for through-silicon-via based chip stacks
Authors: Arunasalam Parthiban , Ackler Harold D. , Sammakia Bahgat G.
Published: August 2006

The current trend in wafer-level three-dimensional integration is by copper-filled through-silicon vias (TSVs) which considerably minimize signal transmission time due to the short wiring length required to integrate vertically stacked chips. However, the present wire bonding technology widely used in peripheral integration of stacked chips cannot integrate TSV based chip stacks. This article describes the fabrication methodology of a thin film compliant interconnect referred to as Smart Three Axis Compliant (STAC) interconnects which can be directly integrated onto TSV based chip stacks. These batch processed compliant interconnects are successfully fabricated utilizing microelectromechanical systems technology at the wafer level by magnetron sputtering oppositely stressed layers of TiW films. Once patterned and released, STAC interconnects easily achieve input/output counts of 104∕cm2 or greater, making it suitable to be directly integrated onto through-silicon-via based chip stacks.
Characterization of defects in the drift region of 4H-SiC pin diodes via optical beam induced current
Authors: Caldwell Joshua D. , Stahlbush Robert E. , Glembocki Orest J. , Liu Kendrick X. , Hobart Karl D.
Published: August 2006

SiC based electronic devices are extremely promising candidates for high power, temperature, and radiation applications. However, a variety of defects created during the substrate and subsequent epitaxial growth persists. Many of these defects are electrically active and adversely affect the electrical characteristics of these devices. Determining which defects are the most damaging, how they are created, their structure, and methods for removing them are four basic steps paramount to the creation of reliable SiC based power devices. Here we present optical beam induced current (OBIC) imaging of various dislocations, stacking faults, and defects, which along with electroluminescence (EL) imaging reveals the electrical activity and the identifying features of the various defects. A strong correlation is established between the features observed via EL and those seen using OBIC imaging.
Ballistic electron transport properties of Fe-based films on Si(001)
Authors: Stollenwerk A. J. , Krause M. R. , Idell D. H. , Moore R. , LaBella V. P.
Published: August 2006

Thickness dependent ballistic electron emission microscopy (BEEM) studies have been performed on Au∕Fe81C19∕Si(001) and Au∕Si(001) Schottky diodes at 80K. The Schottky height was measured to be 0.70±0.02eV for the Fe81C19∕Si(001) interface. Electron attenuation lengths were extracted from the slope of the semilog BEEM current versus the thickness of the Fe81C19 layers for electron energies ranging from 1.0to1.5eV. In this range the attenuation length was found to decrease with increasing energy from 4.1±0.9to2.5±0.6nm, which indicates that some electron-electron scattering is occurring in the metal overlayer. This decrease is slightly greater than predicted for a free electron gas system, resulting from the complex structure of the Fe81C19 film.
Spectroscopic ellipsometry characterization of ultrathin silicon-on-insulator films
Authors: Price J. , Diebold A. C.
Published: August 2006

Spectroscopic ellipsometry is used to characterize the optical response of a series of ultrathin silicon-on-insulator (SOI) films with thickness ranging from 50to2nm. Due to the potential barrier formed by the buried oxide layer and the interface with air, the electrons in the top silicon layer of the thinner samples experience dimensional confinement effects. Transition energies were extracted for the E1 and E2 critical points using reciprocal space analysis. This method offers improved accuracy over conventional regression-based techniques, such as line shape fitting, by eliminating error due to correlation among multiple fit parameters. It is shown that dimensional confinement increases the E1 transition energy of ∼3.375eV for bulk silicon to 3.38, 3.393, 3.42, and 3.45eV for the ∼10, ∼7, ∼4, and ∼2nm SOI films, respectively. This trend resembles the 1∕L2 law predicted by quantum mechanical considerations for a confined particle. The dependence of these critical point transitions is investigated as a function of film thickness L. Additionally, the E2 critical point transition energy is found to be much less affected by quantum confinement, contrary with theoretical predictions.
Fabrication of single-crystalline insulator∕Si∕insulator nanostructures
Authors: Fissel A. , Kühne D. , Bugiel E. , Osten H. J.
Published: August 2006

We study the growth of double-barrier insulator∕Si∕insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of nanostructures with continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. The approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. As an example, we demonstrate the growth of epitaxial silicon buried in epitaxial Gd2O3. The incorporation of epitaxial Si islands into single-crystalline Gd2O3 is also demonstrated.