bluuebunny/crossref_metadata_2025 huggingface dataset:
The Bouncing Ball Apparatus as an Experimental Tool
Authors: Kini Ananth , Vincent Thomas L. , Paden Brad
Published: June 2006

The bouncing ball on a sinusoidally vibrating plate exhibits a rich variety of nonlinear dynamical behavior and is one of the simplest mechanical systems to produce chaotic behavior. A computer control system is designed for output calibration, state determination, system identification, and control of a new bouncing ball apparatus designed in collaboration with Magnetic Moments. The experiments described here constitute the first research performed with the apparatus. Experimental methods are used to determine the coefficient of restitution of the ball, an extremely sensitive parameter needed for modeling and control. The coefficient of restitution is estimated using data from a stable one-cycle orbit both with and without using corresponding data from a ball map. For control purposes, two methods are used to construct linear maps. The first map is determined by collecting data directly from the apparatus. The second map is derived analytically using a high bounce approximation. The maps are used to estimate the domains of attraction to a stable one-cycle orbit. These domains of attraction are used to construct a chaotic control algorithm for driving the ball to a stable one-cycle from any initial state. Experimental results based on the chaotic control algorithm are compared and it is found that the linear map obtained directly from the data not only gives a more accurate representation of the domain of attraction, but also results in more robust control of the ball to the stable one-cycle.
The Extended Variable Structure Filter
Authors: Habibi Saeid
Published: June 2006

In this paper, a new method for state estimation, referred to as the variable structure filter (VSF), is briefly reviewed. The VSF method is model based and has been formulated for its application to linear systems. It provides a means of explicitly defining the level of uncertainty in the dynamic model used by the filter, thus allowing for tradeoff between the performance indicators of the filter. This trade-off feature is not generally explicitly available in some of the more established concepts used for state estimation. In this paper, an extension to the VSF method for its application to nonlinear systems is proposed and referred to as the extended variable structure filter (EVSF). The derivation of EVSF and its application to a nonlinear robotic example is provided.
Controlling Chaos by Hybrid System Based on FREN and Sliding Mode Control
Authors: Treesatayapun C. , Uatrongjit S.
Published: June 2006

This paper presents a direct adaptive controller for chaotic systems. The proposed adaptive controller is constructed using the network called fuzzy rules emulated network (FREN). FREN’s structure is based on human knowledge in the form of fuzzy rules. Parameter adaptation algorithm based on the steepest descent method is presented to fine tune the controller’s performance. To improve the system stability, the modified sliding mode algorithm is applied to estimate the upper and lower bounds of the control effort. The suitable control effort is generated by FREN and kept within these bounds. Some computer simulations of using the controller to control the Hénon map have been performed to demonstrate the performance of the proposed controller.
State Feedback Gain Scheduling for Linear Systems With Time-Varying Parameters
Authors: Montagner Vinícius F. , Peres Pedro L. D.
Published: June 2006

This paper addresses the problem of parameter dependent state feedback control (i.e. gain scheduling) for linear systems with parameters that are assumed to be available (measured or estimated) in real time and are allowed to vary in a compact polytopic set with bounded variation rates. A new sufficient condition given in terms of linear matrix inequalities permits to determine the controller gain as an analytical function of the time-varying parameters and of a set of constant matrices. The closed-loop stability is assured by means of a parameter dependent Lyapunov function. The condition proposed encompasses the well-known quadratic stabilizability condition and allows to impose structural constraints such as decentralization to the feedback gains. Numerical examples illustrate the efficiency of the technique.
SISO Continuous-System Reduction via Impulse Response Gramian by Iterative Formulae
Authors: Choo Younseok , Kim Dongmin
Published: June 2006

This paper concerns the order reduction of single-input single-output (SISO) linear time-invariant continuous systems based on the impulse response Gramian. From the recursive relationship among the Gramians, a new formula is derived for computing the system matrix in controllability canonical form. The result is applied to the model reduction problem. Reduced models obtained approximate the reduced-order Gramians while preserving some initial time moments and Markov parameters of the original system.
Stable Reconfigurable Generalized Predictive Control With Application to Flight Control
Authors: Shi Jianjun , Kelkar Atul G. , Soloway Don
Published: June 2006

This paper presents the development of a multiinput multioutput generalized predictive control (GPC) law and its application to reconfigurable control design in the event of actuator saturation. The stability of the GPC control law without reconfiguration is first established using an end-point state weighting. Based on the constrained nonlinear optimization, an end-point state weighting matrix synthesis method is derived. A novel reconfiguration strategy is developed for systems that have actuator redundancy and are faced with actuator saturation type failure. An elegant reconfigurable control design is presented with stability proof. A numerical simulation using a short-period approximation model of a civil transport aircraft is presented to demonstrate the reconfigurable control architecture.
A Generalized Time-Optimal Bidirectional Scan Algorithm for Constrained Feed-Rate Optimization
Authors: Dong J. , Stori J. A.
Published: June 2006

The problem of generating an optimal feed-rate trajectory has received a significant amount of attention in both the robotics and machining literature. The typical objective is to generate a minimum-time trajectory subject to constraints such as system limitations on actuator torques and accelerations. However, developing a computationally efficient solution to this problem while simultaneously guaranteeing optimality has proven challenging. The common constructive methods and optimal control approaches are computationally intensive. Heuristic methods have been proposed that reduce the computational burden but produce only near-optimal solutions with no guarantees. A two-pass feedrate optimization algorithm has been proposed previously in the literature by multiple researchers. However, no proof of optimality of the resulting solution has been provided. In this paper, the two-pass feed-rate optimization algorithm is generalized and a proof of global optimality is provided. The generalized algorithm maintains computational efficiency, and supports the incorporation of a variety of state-dependent constraints. By carefully arranging the local search steps, a globally optimal solution is achieved. Singularities, or critical points on the trajectory, which are difficult to deal with in optimal control approaches, are treated in a natural way in the generalized algorithm. A detailed proof is provided to show that the algorithm does generate a globally optimal solution under various types of constraints. Several examples are presented to illustrate the application of the algorithm.
Robust Repetitive Controller Design in Parameter Space
Authors: Güvenç Bilin Aksun , Güvenç Levent
Published: June 2006

A new and simple robust repetitive controller design procedure in controller parameter space is presented here. The structure of the repetitive controller filters are fixed, thus, simplifying the design procedure to tuning of the fixed structure filters’ parameters. This approach results in simple and physically meaningful robust controllers that are easily implementable. The design method is based on mapping frequency domain performance specifications into a chosen controller parameter plane. Weighted sensitivity (nominal performance) and weighted complementary sensitivity (robust stability) function magnitude bounds are chosen as the frequency domain specifications to be mapped into controller parameter space here. The design method is illustrated numerically in the context of a servohydraulic material testing machine application available in the literature.
A Robustly Stable Multiestimation-Based Adaptive Control Scheme for Robotic Manipulators
Authors: Ibeas A. , de la Sen M.
Published: June 2006

A multiestimation-based robust adaptive controller is designed for robotic manipulators. The control scheme is composed of a set of estimation algorithms running in parallel along with a supervisory index proposed with the aim of evaluating the identification performance of each one. Then, a higher-order level supervision algorithm decides in real time the estimator that will parametrize the adaptive controller at each time instant according to the values of the above supervisory indexes. There exists a minimum residence time between switches in such a way that the closed-loop system stability is guaranteed. It is verified through simulations that multiestimation-based schemes can improve the transient response of adaptive systems as well as the closed-loop behavior when a sudden change in the parameters or in the reference input occurs by appropriate switching between the various estimation schemes running in parallel. The closed-loop system is proved to be robustly stable under the influence of uncertainties due to a poor modeling of the robotic manipulator. Finally, the usefulness of the proposed scheme is highlighted by some simulation examples.
A Problem With the LQ Control of Overhead Cranes
Authors: Wang Zhonghua , Surgenor Brian W.
Published: June 2006

The control of an overhead crane is a classic optimum control problem, and its solution can be found in most textbooks on the subject of automatic controls. However, there is a design issue with respect to the relative mass of the cart and the suspended payload. If this problem is ignored, then the results of an analysis can be misleading and the response can be unstable. Based on a stability analysis, a design recommendation for optimal asymptotic linear quadratic (LQ) controllers with fixed gains is presented to avoid this problem. The results are validated by both simulation and experiment.
Reliable Decentralized Servomechanism Problem for Large-Scale Systems
Authors: Chang Timothy , Chen Zhengfang
Published: June 2006

In this paper, the reliable control problem for decentralized systems is considered. It concerns the ability of closed-loop system to maintain stability and disturbance rejection properties during arbitrary sensor, controller, and actuator failure without being retuned. The notion of block decentralized robust servomechanism problem with complete reliability is first introduced to address systems with a block diagonal feedback structure. This is followed by establishing two conditions for reliability: (i) systems satisfying certain steady-state interaction characteristics or (ii) systems possessing minimum phase “block” transmission zeros. Accordingly, two types of decentralized controllers are applied to achieve reliable control for these two categories of systems. Simulation examples are also included to illustrate the properties of the reliable control system.
Pushing Manipulation for Multiple Objects
Authors: Harada Kensuke , Nishiyama Jun , Murakami Yoshihiro , Kaneko Makoto
Published: June 2006

This paper discusses the manipulation of multiple objects by pushing. When multiple objects are placed on the flat floor and manipulated simultaneously by pushing, relative motion between two objects such as sliding and rotation may occur. The set of the pusher motion manipulating objects stably is obtained as an intersection of multiple sets of pusher motion where each set prevents the relative motion at one of the contact areas. Experimental results are also included to show the effectiveness of our idea.
Adaptive Threshold Based Diagnostics for Steer-By-Wire Systems
Authors: Pisu Pierluigi , Serrani Andrea , You Song , Jalics Laci
Published: June 2006

In the process of implementing modular fault diagnostics for X-by-Wire systems (Pisu et al., 2000), it was discovered that distinguishing between the model uncertainties and occurrence of faults is a real challenge. It is imperative to solve the problems that exist in using fixed observer and threshold, including the observer model mismatch, generated threshold misfit, diagnostic parameter uncertainties, and incorrect diagnostic output during high stress but normal vehicle operation. Compared to the fixed observer and threshold strategy, the improved adaptive threshold-based diagnostics described in this report are more robust and applicable because of the addition of adaptation into the diagnostic observer and threshold generator. The report also describes an approach to fault detection and isolation in the presence of model and parameter uncertainties. This approach has been successfully implemented in the NAVDyn (Non-Linear Analysis of Vehicle Dynamics) simulation model using Matlab/Simulink, and simulation results are provided to verify that the strategy and implementation are viable.
Output Feedback Neural Network Adaptive Robust Control With
Application to Linear Motor Drive System
Authors: Gong J. Q. , Yao Bin
Published: June 2006

In this paper, neural networks (NNs) and adaptive robust control design method are integrated to design a performance oriented control law with only output feedback for a class of single-input-single-output nth order nonlinear systems in a normal form. The nonlinearities in the system include repeatable unknown nonlinearities and nonrepeatable unknown nonlinearities such as external disturbances. In addition, unknown nonlinearities can exist in the control input channel as well. A high-gain observer is employed to estimate the states of system. All unknown but repeatable nonlinear functions are approximated by the outputs of multilayer neural networks with the estimated states as inputs to achieve a better model compensation. All NN weights are tuned on-line. In order to avoid possible divergence of on-line tuning, discontinuous projections with fictitious bounds are used in the weight adjusting law to make sure that all the weights are adapted within a prescribed range. Theoretically, the resulting controller achieves a guaranteed output tracking transient performance and a guaranteed final tracking accuracy in general. Certain robust control terms is then constructed to effectively attenuate various model uncertainties and estimate errors. Furthermore, if all the states are available and the unknown nonlinear functions are in the functional ranges of the neural networks, an asymptotic output tracking is also achieved to retain the perfect learning capability of NNs in the ideal situation provided that the ideal NN weights fall within the prescribed range. The output feedback neural network adaptive robust control is then applied to the control of a linear motor drive system. Experiments are carried out to show the effectiveness of the proposed algorithm and the excellent output tracking performance.
Fabrication of ultrathin (∼100nm), low-index nanoporous silica films for photonic devices: Role of substrate adhesion on the film thickness
Authors: Ojha M. , Gill W. N. , Plawsky J. L. , Cho W.
Published: June 2006

Low refractive index, nanoporous silica films can enhance the reflectivity of multilayer omnidirectional reflectors by decreasing the refractive index of the low-index layer below that of dense silicon dioxide (∼1.458) or even of magnesium fluoride (∼1.4). Precise thickness and refractive index control of the low-index dielectric layer are required to achieve maximum benefit. In this article, we demonstrate successful processing and integration of quarter wavelength nanoporous silica films (105nm thick, refractive index ∼1.24 at 632.8nm) for applications in omnidirectional reflectors. The low-index film’s thickness was found to depend strongly on the choice of underlying substrate and for identical processing conditions, the film thickness decreased in the order Si>GaAs>GaSb. The thickness variation on these substrates was related to liquid-solid adhesion during spin coating and final film thicknesses were well correlated with the contact angle and spreading coefficient for the sol on the substrate. Two different models were evaluated to simulate the dependence of film thickness on the underlying substrate. The spin coating model proposed by Yanagisawa [J. Appl. Phys. 61, 1035 (1987)] introduces liquid slip at the solid-liquid interface and the model of [Adrienko et al., J. Chem. Phys. 119, 13106 (2000)] proposes the formation of an interfacial vapor layer that provides an effective slip at the interface. Calculated film thickness values using both models agree well with those obtained from the experiments.
Characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition using O2 plasma and N2O plasma
Authors: Kim Seokhoon , Kim Jinwoo , Choi Jihoon , Kang Hyunseok , Jeon Hyeongtag , Bae Choelhwyi
Published: June 2006

The characteristics of HfO2 dielectrics deposited by the plasma-enhanced atomic layer deposition (PEALD) method using O2 and N2O plasmas were investigated. The deposited HfO2 films had a randomly oriented polycrystalline phase while the interfacial layers of the films were amorphous. During the PEALD process with N2O plasma, nitrogen was mainly incorporated into the interfacial region between the HfO2 film and the Si substrate. The nitrogen content of 2–3at.% in the interface was analyzed by Auger electron spectroscopy. The incorporated nitrogen at the interface effectively suppressed residual oxygen diffusion during subsequent annealing at 800°C in a N2 atmosphere. A thicker interfacial layer was observed in the as-deposited and annealed HfO2 film with O2 plasma than with N2O plasma. For HfO2 films prepared with the N2O plasma, where equivalent oxide thickness (EOT) increased from 1.43to1.56nm after annealing, the leakage current densities, measured at a gate bias voltage of ∣VG−VFB∣=2, increased from 3.5×10−8to4.8×10−8A∕cm2. For HfO2 films prepared with the O2 plasma, where EOT increased from 1.60to2.01nm after annealing, the leakage current densities decreased from 1.1×10−6to1.3×10−7A∕cm2. The film with O2 plasma had a higher amount of negative fixed oxide charges than the film with N2O plasma. N2O plasma improved the leakage current properties by allowing nitrogen incorporation at the interfacial region and less crystallization of HfO2 film.
Band structures of double-walled carbon nanotubes
Authors: Ho Y. H. , Ho G. W. , Wu S. J. , Lin M. F.
Published: June 2006

The tight-binding model is used to investigate band structures of zigzag double-walled carbon nanotubes. The intertube interactions significantly change symmetry of energy bands, energy dispersions, Fermi energy, energy gap, and wave functions. Electronic properties are also affected by the magnetic flux and the Zeeman effect. The main features of band structures are directly reflected in optical absorption spectra, such as the blueshift of absorption frequency, the increase of absorption peaks, and the enhancement of spectral intensity. There are certain important differences between zigzag and armchair double-walled systems.
X-ray diffraction analysis of interdiffusion in AlxIn1−xAsySb1−y∕GaSb multilayers
Authors: Forrest R. L. , Stokes D. W. , Li J. H. , Lukic R. , Golding T. D.
Published: June 2006

We report the results of a detailed x-ray diffraction analysis of two AlxIn1−xAsySb1−y∕GaSb multilayer samples grown by molecular beam epitaxy on GaSb (100). The kinematical scattering theory was used to fit the x-ray diffraction intensity profiles to determine the lattice spacing, composition, and strain of the multilayers, allowing for interdiffusion between the layers and variation in the multilayer wavelength. It has been determined that the quaternary alloy composition varies throughout the layer and that there is an interfacial quaternary layer that differs in composition from that of the bulk AlxIn1−xAsySb1−y layer. A rationale for this graded composition and interfacial layer will be discussed based on the growth dynamics for this system.
Thermal annealing effects on the structure and electrical properties of Al2O3 gate dielectrics on fully depleted SiGe on insulator
Authors: Di Zengfeng , Zhang Miao , Liu Weili , Shen Qinwo , Luo Suhua , Song Zhitang , Lin Chenglu , Chu Paul K.
Published: June 2006

The interfacial characteristics and electrical properties of as-deposited and annealed Al2O3 gate dielectric films fabricated on fully depleted SiGe on insulator are investigated. The surface morphology of the gate dielectric is observed by atomic force microscopy, and its physical thickness and structure are determined by high-resolution transmission electron microscopy. Assessment of the energy shifts of the interfacial components observed by high-resolution x-ray photoelectron spectroscopy shows that oxidation of Ge occurs readily at the growth temperature, leading to a mixture of Si and Ge oxides at the Al2O3∕SiGe interface. After annealing, the relative intensity of GeOx diminishes significantly, whereas the relative intensity of the Si suboxides or SiO2 increases, and especially, the formation of silicate is observed. The chemical state changes in the interfacial layer affect the flatband voltage (Vfb) and the density of the interfacial states.
Integrated model for chemically enhanced physical vapor deposition of tantalum nitride-based films
Authors: Li Ning , Brenner P. W. , Ruzic D. N.
Published: June 2006

A zero-order semiempirical model has been developed for chemically enhanced physical vapor deposition (CEPVD), a recently developed hybrid approach to film deposition offering the step coverage of chemical vapor deposition while maintaining film quality similar to films produced by ionized physical vapor deposition (IPVD). CEPVD is done by introducing a chemical precursor to the substrate during IPVD. A synergistic effect between the two processes results in which the high energy ions from IPVD aid in the decomposition of the precursor. The precursor then provides film deposition on surfaces that are not easily impacted by IPVD’s directional ions. The model stems from knowledge of reactive sputtering and plasma-enhanced chemical-vapor deposition processes as well as results acquired from CEPVD experiment. It focuses on the Ta–N material system since Ta∕TaN is widely used as a diffusion barrier in Cu damascene processing. Processing parameters are correlated with the target and film surface coverage by Ta, TaN, and organic sites, from which one can predict the operation mode, either metallic or poison, and the film elemental composition. The organic by-products accounting for the detection of carbon on the substrate by Auger electron spectroscopy analysis and poisoning of the target during the processing are categorized into nonvolatile products (OR1) and volatile products (OR2) in a lump-sum assumption. Electron impact, H reduction and ion bombardment are considered as the enhancing mechanisms between the physical and chemical components and included as the reactants of the chemical reactions. Simulation results compare favorably with the experimental data.
Fabrication of organic light-emitting devices on flexible substrates using a combined roller imprinting and photolithography-patterning technique
Authors: Kao Po-Ching , Chu Sheng-Yuan , Zhan Chuan-Yi , Hsu Lien-Chung , Liao Wen-Chang
Published: June 2006

A patterning method has been developed to fabricate patterned organic light-emitting devices (OLEDs) (60×80mm2) with a pixel size of 500×300μm2 on flexible polyethylene terephthalate substrates. The patterns of the pixel array were defined in crossed-strip style with indium tin oxide anode and patterned using a combination of roller-type imprinting lithography and photolithography (CRIP) followed by wet etching. Compared with conventional imprint lithography or photolithography, the CRIP technique has the advantages of better uniformity, less force, consuming less time, lower cost, and higher aspect ratio. The performance of the CRIP OLEDs was the following: the turn-on voltage at 1cd∕m2 was 7.5V and the maximum luminance was 13530cd∕m2 at 17.5V. The highest luminous efficiency reached 1.27lm∕W (3.23cd∕A) at a luminance of 4.8cd∕m2 and kept the values stable from 5to15V. The performance was comparable to that of devices patterned by conventional photolithography.
Thin-capping-and-regrowth molecular beam epitaxial technique for quantum dots and quantum-dot molecules
Authors: Suraprapapich S. , Thainoi S. , Kanjanachuchai S. , Panyakeow S.
Published: June 2006

A thin-capping-and-regrowth molecular beam epitaxial technique is proposed and demonstrated to be a suitable approach for the growth of lateral quantum-dot molecules (QDMs). By regrowing on top of nanoholes, previously formed from as-grown quantum dots (QDs) via a thin-capping process, nanopropeller QDs are formed. By repeating the thin-capping-and-regrowth process for several cycles at the regrown thickness of 0.6 ML, nanopropeller QDs are linked along the [11¯0] crystallographic direction, leading to the alignment of QDs. The thin-capping-and-regrowth process is repeated for 1, 3, 5, 7, and 10cycles on different samples for comparison purposes. It is found from ex situ atomic force microscopy that at 7cycles of thin capping and regrowth of QDs, the best alignment of QDs is achieved. This is due to the strain having an optimum condition. The samples that undergo three and five thin-capping-and-regrowth cycles show some randomness of QD formation. When the process is repeated for 10cycles, QDs become randomly distributed, but with a higher dot density than the as-grown sample. The high dot density results in a strong photoluminescence at room temperature. It is also shown that when self-aligned QDs are used as templates, aligned QDMs can be obtained at a regrowth thickness of 1.2 ML.
Formation and property of InSb self-assembled quantum dots on GaAsSb lattice matched to InP
Authors: Wu Bing-Ruey , Cheng K. Y. , Xu Chaofeng , Hsieh Kuang-Chien
Published: June 2006

InSb was deposited on GaAsSb lattice matched to InP matrices using gas-source molecular beam epitaxy to form self-assembled quantum dots (SAQDs). The InSb critical thickness of the two-dimensional to three-dimensional growth was determined to be about 1 monolayer (ML). The off-normal streak angle analysis of the reflection high-energy electron diffraction patterns indicated that the facets of InSb SAQDs are of the {111} family. Transmission electron microscopy further confirmed that the InSb quantum dot has a truncated pyramid structure with {111} facets. The relationship between the dot density and indium deposition rates was analyzed using atomic force microscopy. The 80K photoluminescence spectrum of a multiple-layer InSb∕GaAsSb SAQD array with 1 ML nominal InSb thickness shows an emission peak wavelength of ∼1.72μm.
Molecular beam epitaxy and morphological studies of homoepitaxial layers on chemical mechanical polished InSb(100) and InSb(111)B substrates
Authors: Vangala S. R. , Qian X. , Grzesik M. , Santeufemio C. , Goodhue W. D. , Allen L. P. , Dallas G. , Dauplaise H. , Vaccaro K. , Wang S. Q. , Bliss D.
Published: June 2006

Noncontact atomic force microscopy (AFM) has been used to assess the surface morphology and structure of InSb homoepitaxial layers grown on chemical mechanical polished (CMP) InSb(100) and InSb(111)B surfaces. Although it is difficult to grow epilayers on highly conducting InSb substrates, this work demonstrates the ability to grow layers with an average roughness (Ra) of 5.7Å on 2×1018 n-type InSb(100) surfaces. Furthermore on 7×1014 n-type InSb(111)B surfaces, extremely flat layers with Ra’s of approximately 1.7Å were grown. Thermal x-ray photoelectron spectroscopy was implemented to analyze surface oxide desorption on the CMP prepared “epiready” wafers. Sb to In flux ratio and substrate deposition temperature are critical in obtaining high quality epitaxial material. For the InSb(100) surfaces, an Sb∕In flux ratio of 1.5:1, a substrate temperature of 380°C, and a background pressure of 1×10−10Torr produced smooth surfaces. For InSb(111)B surfaces, a ratio of 7:1 and a substrate temperature of 380°C at a similar background pressure produced smooth surfaces. Higher flux ratios resulted in atomically rough surfaces. The homoepitaxy formation of an ordered step terrace surface was confirmed with AFM on both epiready CMP prepared InSb crystal surfaces.
Influence of Si doping on the performance of quantum dots-in-well photodetectors
Authors: Attaluri R. S. , Annamalai S. , Posani K. T. , Stintz A. , Krishna S.
Published: June 2006

The effects of doping on InAs∕In0.15Ga0.85As quantum dots-in-well infrared photodetectors have been investigated by measuring the dark current, photocurrent, spectral response, responsivity, and detectivity. The dark current increased monotonically as a function of the doping level in the dots. The photocurrent too increased with the increase in the doping level. By measuring the background limited infrared photodetector temperature, we find that the optimum sheet doping concentration in these detectors is n=3×1010cm−2 (corresponding to about 1e∕dot). These results were corroborated by measurement of responsivity and generation-recombination noise limited detectivity of these detectors.
Tunneling through MnAs particles at a GaAs p+n+ junction
Authors: Bloom F. L. , Young A. C. , Myers R. C. , Brown E. R. , Gossard A. C. , Gwinn E. G.
Published: June 2006

In this article we examine tunneling through MnAs particles at a GaAs p+n+ junction. We grew the device structures by molecular beam epitaxy on semi-insulating GaAs (001) substrates, with the n+(5×1018cm−3Si) and p+(2×1019cm−3Be) layers grown at 580°C. At the p+n+ junction, we grew a 30nm layer of random alloy Ga1−xMnxAs at 250°C. In situ annealing the Ga1−xMnxAs transforms to thermodynamically stable MnAs particles in a GaAs matrix. Magnetization measurements show that the MnAs particles are superparamagnetic with a distribution of blocking temperatures that depends on the annealing protocol. The MnAs particles at the interface are imaged using atomic force microscopy of selectively etched, MnAs-topped nanocolumns. Current-voltage (IV) scans show that the presence of particles increases the forward bias current density. Low-temperature current-voltage (IV) scans confirm an increase in the forward bias current density due to tunneling through MnAs particles.
Structural and magnetic behavior of transition metal doped InN grown by molecular beam epitaxy
Authors: Rajaram R. , Ney A. , Farrow R. F. C. , Parkin S. S. P. , Solomon G. S. , Harris J. S.
Published: June 2006

We present growth and characterization of Cr- and Mn-doped InN films grown by plasma-assisted molecular beam epitaxy. The films were deposited on c-plane sapphire substrates, employing GaN intermediate layers to accommodate the lattice mismatch between InN and sapphire. Preliminary studies were also made on growth of Cr-doped InN over (111) GaAs substrates. X-ray diffraction and Hall measurements were used for structural and electrical characterization of the films. The magnetic properties of these materials were measured using superconducting quantum interference device magnetometry. While InN:Mn showed signs of phase segregation and paramagnetism, InN:Cr displayed ferromagnetic properties.
Growth of GaN films on GaAs substrates in an As-free environment
Authors: Maksimov O. , Fisher P. , Du H. , Acord J. D. , Weng X. , Skowronski M. , Heydemann V. D.
Published: June 2006

We investigated growth of GaN films on [001] GaAs substrates by plasma-assisted molecular beam epitaxy in an As-free chamber. The crystalline quality and the surface morphology of the films were studied with x-ray diffraction and transmission electron, scanning electron, and atomic force microscopes. We determined that direct GaN deposition on the thermally desorbed substrate resulted in the growth of a polycrystalline film containing misoriented grains and inclusions. We achieved a significant improvement of the film quality by adopting a procedure consisting of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth.
Effects of plasma conditions on properties of ZnO films grown by plasma-assisted molecular beam epitaxy
Authors: Lee W. C. T. , Miller P. , Reeves R. J. , Durbin S. M.
Published: June 2006

The influence of rf power and aperture plate configuration on the growth of ZnO thin films using plasma-assisted molecular beam epitaxy was investigated. It was found that by changing the aperture plate geometry from 276 to 25 holes, an increase of growth rate was observed, suggesting that the latter is more efficient for ZnO growth. The structural, electrical, and optical properties were also improved as measured by in situ electron diffraction, single field Hall effect, and photoluminescence. A background carrier concentration of 1×1018cm−3 and a mobility of 52cm2∕Vs were measured, and a room-temperature band edge peak 200 times the defect band intensity was observed. Optical emission spectroscopy shows significantly different behavior in plasma generated using the two plates and suggests that more than increased atomic oxygen production is occurring.
Sub-10-nm high aspect ratio patterning of ZnO in a 500μm main field
Authors: Saifullah M. S. M. , Subramanian K. R. V. , Anderson D. , Kang Dae-Joon , Huck W. T. S. , Jones G. A. C. , Welland M. E.
Published: June 2006

We demonstrate the fabrication of sub-10-nm high aspect ratio electron beam patterning of ZnO at the center as well as corners of the 500μm square main deflection field using a negative tone zinc naphthenate resist. After electron beam exposure, the resist was developed in toluene, resulting in high-resolution patterns as small as 7nm with an aspect ratio of ∼10 in the center as well as at the corners of the main field. The line edge roughness (3σ) of these lines shows roughness with fluctuations of about 2.8nm; thus making it the smallest value of the line edge roughness measured so far for any electron beam resist. Heating the structures at 500°C resulted in reduction of feature sizes to ∼5nm and in the formation of crystalline ZnO. Such sub-10-nm high aspect ratio patterning within the main deflection field is an important step to enable full-wafer-level nanofabrication.
Spin-polarized vertical-cavity surface-emitting laser: Epitaxial growth issues and device properties
Authors: Holub M. , Shin J. , Chakrabarti S. , Bhattacharya P.
Published: June 2006

Epitaxial growth issues and device properties of an electrically injected, spin-polarized, vertical-cavity surface-emitting laser are discussed. Using the ferromagnetic semiconductor (Ga,Mn)As to introduce spin anisotropy via hole spin injection into an In0.2Ga0.8As quantum well active region, polarization control is achieved in a vertical-cavity surface-emitting laser with a maximum degree of circular polarization of 4.6% measured at 80K. Spin transport across a distance of ∼0.25μm for temperatures ranging from 80to105K is demonstrated.
Damage of ultralow k materials during photoresist mask stripping process
Authors: Hua Xuefeng , Kuo Ming-shu , Oehrlein G. S. , Lazzeri P. , Iacob E. , Anderle M. , Inoki C. K. , Kuan T. S. , Jiang P. , Wu Wen-li
Published: June 2006

Plasma-based ashing of photoresist masks after pattern transfer is a common processing step in the fabrication of integrated circuits. In this work we investigated damage mechanisms of nanoporous ultra low k (ULK) materials with different overall porosities due to the ashing process. Oxygen-, nitrogen- and hydrogen-based photoresiststripping using direct and remote plasma processes were examined. Ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and transmission electron microscopy were utilized to study the damage layer thickness, physical (pore morphology), and chemical modifications of the nanoporous silica thin films after exposure to the O2-, N2- or H2-based ashing processes. As a result of the plasma exposure, carbon groups in nanoporous silica can be removed from the ULK layers which is also accompanied by material densification. We find severe ashing damage of ULK materials after O2-based ashing using both direct and remote discharges. N2 and H2 discharges also damage ultralow k materials for direct plasma ashing processes which are accompanied by low energy ion bombardment of the substrates. The introduction rate and degree of the ULK materials modifications correlates with the overall porosity. We show that the pore interconnectivity is one of the key parameters that determine ashing damage. ULK damage is greatly reduced for remote N2 or H2 discharges, but the resist removal rates are impractically low if the substrate is at room temperature. We show that both acceptable photoresist stripping rates and ULK damage levels can be achieved for remote H2 plasma ashing processes if the substrate temperature is 250°C and higher.
Implementation of an imprint damascene process for interconnect fabrication
Authors: Schmid Gerard M. , Stewart Michael D. , Wetzel Jeffrey , Palmieri Frank , Hao Jianjun , Nishimura Yukio , Jen Kane , Kim Eui Kyoon , Resnick Douglas J. , Liddle J. Alexander , Willson C. Grant
Published: June 2006

Advanced integrated circuits require eight or more levels of wiring to transmit electrical signal and power among devices and to external circuitry. Each wiring level connects to the levels above and below it through via layers. The dual damascene approach to fabricating these interconnected structures creates a wiring level and a via level simultaneously, thereby reducing the total number of processing steps. However, the dual damascene strategy (of which there are several variations) still requires around 20 process steps per wiring layer. In this work, an approach to damascene processing that is based on step-and-flash imprint lithography (SFIL) is discussed. This imprint damascene process requires fewer than half as many steps as the standard photolithographic dual damascene approach. Through use of a template with two tiers of patterning, a single imprint lithography step can replace two photolithography steps. Further improvements in efficiency are possible if the imprint material is itself a functional dielectric material. This work is a demonstration of the compatibility of imprint lithography (specifically SFIL) with back-end-of-line processing using a dual damascene approach with functional materials.
Analysis of atomic diffusion mechanism of interconnect voiding failure caused by stress-induced migration
Authors: Aoyagi Minoru
Published: June 2006

Interconnect voiding failures caused by stress-induced migration were investigated by analysis of atomic diffusion mechanisms using simple numerical computations for aluminum and copper interconnects. The activation energy for the voiding failure of aluminum interconnects, assuming that the lattice diffusion of atoms is the primary diffusion mechanism of stress-induced migration, was calculated to be approximately 0.8eV, which was close to the activation energy obtained from actual high-temperature storage tests (i.e., 0.5–0.6eV). This agreement implies that for aluminum interconnects the assumption is correct, and the lattice diffusion is the primary diffusion mechanism for stress-induced migration. The computed activation energy for voiding failure of copper interconnects was less than 1.5eV and did not agree with the activation energy obtained from high-temperature storage tests (0.74eV). The calculated interconnect lifetime was approximately six orders of magnitude larger than that obtained from the high-temperature storage tests. These results suggest that lattice diffusion is not the primary diffusion mechanism for stress-induced migration in copper interconnects.
Long-wavelength semiconductor saturable absorber mirrors using metamorphic InP grown on GaAs by molecular beam epitaxy
Authors: Suomalainen S. , Vainionpää A. , Tengvall O. , Hakulinen T. , Herda R. , Karirinne S. , Guina M. , Okhotnikov O. G.
Published: June 2006

Metamorphic growth of InP on GaAs has been used to tailor the recovery time of 1.55μm semiconductor saturable absorber mirrors. By decreasing the thickness of the InP “lattice reformation layer” grown between a GaAs-based distributed Bragg reflector and the active region, we were able to purposely reduce the recovery time. For thickness of the reformation layer below 200nm, the semiconductor saturable absorber mirrors exhibited a short absorption recovery time enabling a robust, self-starting passive mode-locked operation of an erbium-doped fiber laser. We are also reporting preliminary results on the stability of the saturable absorbing mirrors parameters after rapid thermal annealing.
Gate dielectric on compound semiconductors by molecular beam epitaxy
Authors: Droopad Ravi , Rajagopalan K. , Abrokwah J. , Passlack M.
Published: June 2006

An oxide-based high-κ gate dielectric stack for GaAs has been developed using molecular beam epitaxy. A template layer of Ga2O3, initially deposited on a GaAs(001) surface, serves to unpin the GaAs Fermi level while the deposition of a bulk ternary (GdxGa1−x)2O3 layer forms the highly resistive layer to reduce leakage current through the dielectric stack. The use of molecular beam epitaxy allows for the control and uniformity of the oxide layers along the growth direction and deposition conditions were optimized for oxide surface morphology and interface quality. The midgap interface state density for the high-κ stack on GaAs of ≅2×1011cm−2eV−1 and a dielectric constant of k≅20 are determined using electrical measurements. Metal oxide semiconductor field effect transistor layer structures were produced by replacing the GaAs cap layer in a pseudomorphic high electron mobility transistor-type layer structure with the high-κ gate dielectric stack.
Bias-enhanced lateral photoelectrochemical etching of GaN for the fabrication of undercut micromachined system structures
Authors: Yang Bo , Fay Patrick
Published: June 2006

Voltage bias-enhanced photoelectrochemical (PEC) etching of GaN is demonstrated for fabrication of undercut III-V microelectromechanical system (MEMS) structures. The use of voltage bias was found to enhance lateral etching of GaN under opaque Ti etch masks, resulting in a regular and uniform undercut. The etch profiles obtained using bias-enhanced PEC etching are dramatically different from those obtained with either conventional unbiased PEC etching or through-wafer illuminated etching. Bias-enhanced etching was observed to result in improved morphology for typical MEMS applications. Bias-enhanced etching is demonstrated for the formation of fully released Ti cantilevers on GaN, as well as undercut structures.
Modeling dual inlaid feature construction
Authors: Stout Phillip J. , Rauf Shahid , Nagy Andrew , Ventzek Peter L. G.
Published: June 2006

Dual inlaid construction of copper interconnect structures involves a sequence of tightly coupled plasma processes with subtle variations in one process impacting subsequent processes. An integrated plasma reactor/feature physics based modeling suite has been applied to three-dimensional (3D) dual inlaid (DI) feature construction. Specifically, the goal of this article is to understand process interdependencies during DI construction. The DI feature is used in inlaid copper interconnects to define metal lines and their connection to the metal layer below. One advantage of the DI feature is only one metallization step (barrier deposition/seed deposition/electroplating/chemical mechanical polish) is required to deposit metal into both the metal lines and the via connections to the metal layer below. Discussed will be the 3D feature modeling of fluorocarbon plasma etching of vias and trenches in SiO2 to construct dual inlaid features. The model includes 11 steps in the dual inlaid construction process. Papaya, the feature model, applies the many mask, etch, and deposition process steps as characterized by reactor models onto an evolving feature. The model thus allows for an integrated study of the dual inlaid feature construction including the cumulative effect of prior etch steps on subsequent etch steps. Polymer build up can shield a surface from enchants and plays a role in etch selectivity. The amount of polymer in the via and trench etch is shown to affect the amount of bowing in the feature as decreased passivation from less polymer leads to more chemical etching on the via and trench sidewalls. The height of the “slug” used to protect the via in a via first trench last (VFTL) DI integration controls the fencing or notching seen at the via opening. As the slug to dielectric etch ratio is increased the etching at the via opening is enhanced leading to notching at the via opening as well as widened and sloped vias. A larger trench width versus via diameter leads to larger via openings and more flared vias. Also, bilayer resist VFTL and trench first via last (TFVL) DI integration schemes have been modeled. TFVL DI integration is shown not to suffer issues at the via opening (fencing, notching, and flare) as seen in the VFTL DI integration scheme.
Nanoscale selective area epitaxy of C60 crystals on GaAs by molecular beam epitaxy
Authors: Nishinaga Jiro , Aihara Tomoyuki , Toda Takeshi , Matsutani Fumio , Horikoshi Yoshiji
Published: June 2006

Fabrications of nanoscale structures of C60 crystals on GaAs substrates are successfully achieved by selective area molecular beam epitaxy. The grown structures are examined by scanning electron and atomic force microscopies. The {100} and {110} facets appear at the side boundaries of the C60 crystals. The surface morphology of C60 crystals grown on GaAs (111)B is much smoother than that grown on GaAs (001). Good crystalline properties of C60 films grown on GaAs (111)B are also confirmed by x-ray diffraction φ (phi) scan measurement. During C60 deposition, C60 molecules landing on SiO2 mask either evaporate or migrate to the open area enhancing the growth rate at the edges of the area. The mean diffusion length of C60 molecules on SiO2 mask at 200°C is evaluated to be 200–300nm. The C60 crystals grown on GaAs (001) with narrow open area (100–200nm) have a fourfold symmetry, indicating that the epitaxial orientation of these C60 crystals is [001]. This result should be compared with the [111] orientation observed in planar or wide area growth.
Influence of hydrogen plasma surface treatment of Si substrate on nickel silicide formation
Authors: Vengurlekar Aniruddha , Balasubramanian Satheesh , Ashok S. , Theodore David , Chi Dongzhi
Published: June 2006

Nickel silicide (NiSi) offers the advantages of lower processing temperature, reduced silicon consumption in silicide formation, and absence of bridging failures and is hence expected to replace Ti and Co silicides as contact material in Si microelectronics. In this article, we report on our work involving the study of hydrogen plasma pretreatment of the Si substrate on the properties of subsequently formed NiSi. We observe the sheet resistance of the silicide film to decrease with hydrogenation at the expected lower processing temperatures of 400 and 500°C. Transmission electron microscopy studies do reveal that defects are introduced near the silicide-silicon interface in the hydrogenated wafers at lower processing temperatures. But these defects are annealed out at higher processing temperatures. Secondary ion mass spectroscopy profiles show an enhanced diffusion of Ni into the Si substrate at 500 and 600°C, apparently due to the defects introduced in the substrate by the hydrogen treatment.