The integration of multiple digitally driven processes is seen as the solution to many of the current limitations arising from standalone Additive Manufacturing (AM) techniques. A technique has been developed to digitally fabricate fully functioning electronics using a unique combination of AM technologies. This has been achieved by interleaving bottom-up Stereolithography (SL) with Direct Writing (DW) of conductor materials alongside mid-process development (optimising the substrate surface quality), dispensing of interconnects, component placement and thermal curing stages. The resulting process enables the low-temperature production of bespoke three-dimensional, fully packaged and assembled multi-layer embedded electronic circuitry. Two different Digital Light Processing (DLP) Stereolithography systems were developed applying different projection orientations to fabricate electronic substrates by selective photopolymerisation. The bottom up projection orientation produced higher quality more planar surfaces and demonstrated both a theoretical and practical feature resolution of 110 μm. A top down projection method was also developed however a uniform exposure of UV light and planar substrate surface of high quality could not be achieved. The most advantageous combination of three post processing techniques to optimise the substrate surface quality for subsequent conductor deposition was determined and defined as a mid-processing procedure. These techniques included ultrasonic agitation in solvent, thermal baking and additional ultraviolet exposure. SEM and surface analysis showed that a sequence including ultrasonic agitation in D-Limonene with additional UV exposure was optimal. DW of a silver conductive epoxy was used to print conductors on the photopolymer surface using a Musashi dispensing system that applies a pneumatic pressure to a loaded syringe mounted on a 3-axis print head and is controlled through CAD generated machine code. The dispensing behaviour of two isotropic conductive adhesives was characterised through three different nozzle sizes for the production of conductor traces as small as 170 μm wide and 40 μm high. Additionally, the high resolution dispensing of a viscous isotropic conductive adhesive (ICA) also led to a novel deposition approach for producing three dimensional, z-axis connections in the form of high freestanding pillars with an aspect ratio of 3.68 (height of 2mm and diameter of 550μm). Three conductive adhesive curing regimes were applied to printed samples to determine the effect of curing temperature and time on the resulting material resistivity. A temperature of 80 °C for 3 hours resulted in the lowest resistivity while displaying no substrate degradation. ii Compatibility with surface mount technology enabled components including resistors, capacitors and chip packages to be placed directly onto the silver adhesive contact pads before low-temperature thermal curing and embedding within additional layers of photopolymer. Packaging of components as small as 0603 surface mount devices (SMDs) was demonstrated via this process. After embedding of the circuitry in a thick layer of photopolymer using the bottom up Stereolithography apparatus, analysis of the adhesive strength at the boundary between the base substrate and embedding layer was conducted showing that loads up to 1500 N could be applied perpendicular to the embedding plane. A high degree of planarization was also found during evaluation of the embedding stage that resulted in an excellent surface finish on which to deposit subsequent layers. This complete procedure could be repeated numerous times to fabricate multilayer electronic devices. This hybrid process was also adapted to conduct flip-chip packaging of bare die with 195 μm wide bond pads. The SL/DW process combination was used to create conductive trenches in the substrate surface that were filled with isotropic conductive adhesive (ICA) to create conductive pathways. Additional experimentation with the dispensing parameters led to consistent 150 μm ICA bumps at a 457 μm pitch. A flip-chip bonding force of 0.08 N resulted in a contact resistance of 2.3 Ω at a standoff height of ~80 μm. Flip-chips with greater standoff heights of 160 μm were also successfully underfilled with liquid photopolymer using the SL embedding technique, while the same process on chips with 80 μm standoff height was unsuccessful. Finally the approaches were combined to fabricate single, double and triple layer circuit demonstrators; pyramid shaped electronic packages with internal multilayer electronics; fully packaged and underfilled flip-chip bare die and; a microfluidic device facilitating UV catalysis. This new paradigm in manufacturing supports rapid iterative product development and mass customisation of electronics for a specific application and, allows the generation of more dimensionally complex products with increased functionality.

Emerging transparent conducting and semiconducting oxide (TCO) and (TSO) materials have achieved success in display markets. Due to their excellent electrical performance, TSOs have been chosen to enhance the performance of traditional displays and to evaluate their application in future transparent and flexible displays. This dissertation is devoted to the study ZnO-based thin film transistors (TFTs) using multilayer dielectrics and channel layers. Using multilayers to engineer transistor parameters is a new approach. By changing the thickness, composition, and sequence of the layers, transistor performance can be optimized. In one example, Al2O3/Ta2O5 bilayer gate dielectrics, grown by atomic layer deposition at low temperature were developed. The approach combined high dielectric constant of Ta2O5 and the excellent interface quality of Al2O3/ZnO, resulting in enhanced device performance. Using zinc oxide (ZnO)/hafnium oxide (HfO2) multilayer stack as a TFT channel with tunable layer thicknesses resulted in significant improvement in TFT stability. Atomic layer deposited SnO2 was developed as a gate electrode to replace ITO in thin film transistors and circuits. The SnO2 films deposited at 200 °C show low electrical resistivity of ~3.1×10-3 Ohm-cm with the high transparency of ~93%. TFT fabricated with SnO2 gate show excellent transistor properties. Using results from the above experiments, we have developed a novel process in which thin film transistors (TFTs) are fabricated using one binary oxide for all transistor layers (gate, source/drain, semiconductor channel, and dielectric). In our new process, by simply changing the flow ratio of two chemical precursors, C8H24HfN4 and (C2H5)2Zn, in an ALD system, the electronic properties of the binary oxide HZO were controlled from conducting, to semiconducting, to insulating. A complete study of HZO thin films deposited by (ALD) was performed. The use of the multi-layer (HfO2/ZnO) channel layer plays a key role in improving the bias stability of the devices. The low processing temperature of all materials at 160 °C is an advantage for the fabrication of fully transparent and flexible devices. After precise device engineering, including growth temperature, gate dielectric, electrodes (S/D&G) and semiconductor thickness, TFT with excellent device performance are obtained.

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No description available.

Computer modeling using finite element analysis (FEA) was performed to examine the effects of constructing multilayered thick film inductors using an artificially modulated magnetic composite structure. It was found that selectively introducing regions of low permeability material increased both the inductance and the current carrying capacity compared to thick film inductors made with single material magnetic cores. Permeabilities of the composite cores ranged from 1 to 220. The frequency for the models ranged from 0 to 5.0 MHz. Experimental devices were constructed using thick film screen printing techniques and characterized to validate the models and to determine the effectiveness of the design modifications. Quantitative comparisons were made between inductors of single permeability cores with inductors produced with magnetic composite cores. It was found that significant (> 130%) increases could be gained in saturation current with only a 12% decrease in inductance. It was found that the key parameters affecting performance were 1) the placement of low permeability regions, 2) the extent of non-uniform flux distribution within the structure, and 3) the volume fraction of low permeability material. / Master of Science

Made available in DSpace on 2014-12-17T14:56:07Z (GMT). No. of bitstreams: 1 FranciscoAAS_DISSERT.pdf: 1526658 bytes, checksum: 7ba5b80f03a10eaf25a4f9e6a4c91372 (MD5) Previous issue date: 2012-08-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Artificial neural networks are usually applied to solve complex problems. In problems with more complexity, by increasing the number of layers and neurons, it is possible to achieve greater functional efficiency. Nevertheless, this leads to a greater computational effort. The response time is an important factor in the decision to use neural networks in some systems. Many argue that the computational cost is higher in the training period. However, this phase is held only once. Once the network trained, it is necessary to use the existing computational resources efficiently. In the multicore era, the problem boils down to efficient use of all available processing cores. However, it is necessary to consider the overhead of parallel computing. In this sense, this paper proposes a modular structure that proved to be more suitable for parallel implementations. It is proposed to parallelize the feedforward process of an RNA-type MLP, implemented with OpenMP on a shared memory computer architecture. The research consistes on testing and analizing execution times. Speedup, efficiency and parallel scalability are analyzed. In the proposed approach, by reducing the number of connections between remote neurons, the response time of the network decreases and, consequently, so does the total execution time. The time required for communication and synchronization is directly linked to the number of remote neurons in the network, and so it is necessary to investigate which one is the best distribution of remote connections / As redes neurais artificiais geralmente s?o aplicadas ? solu??o de problemas comple- xos. Em problemas com maior complexidade, ao aumentar o n?mero de camadas e de neur?nios, ? poss?vel conseguir uma maior efici?ncia funcional, por?m, isto acarreta em um maior esfor?o computacional. O tempo de resposta ? um fator importante na decis?o de us?-las em determinados sistemas. Muitos defendem que o maior custo computacional est? na fase de treinamento. Por?m, esta fase ? realizada apenas uma ?nica vez. J? trei- nada, ? necess?rio usar os recursos computacionais existentes de forma eficiente. Diante da era multicore esse problema se resume ? utiliza??o eficiente de todos os n?cleos de processamento dispon?veis. No entanto, ? necess?rio considerar a sobrecarga existente na computa??o paralela. Neste sentido, este trabalho prop?e uma estrutura modular que ? mais adequada para as implementa??es paralelas. Prop?e-se paralelizar o processo feed- forward (passo para frente) de uma RNA do tipo MLP, implementada com o OpenMP em uma arquitetura computacional de mem?ria compartilhada. A investiga??o dar-se-? com a realiza??o de testes e an?lises dos tempos de execu??o. A acelera??o, a efici?ncia e a es- calabilidade s?o analisados. Na proposta apresentada ? poss?vel perceber que, ao diminuir o n?mero de conex?es entre os neur?nios remotos, o tempo de resposta da rede diminui e por consequ?ncia diminui tamb?m o tempo total de execu??o. O tempo necess?rio para comunica??o e sincronismo est? diretamente ligado ao n?mero de neur?nios remotos da rede, sendo ent?o, necess?rio observar sua melhor distribui??o

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With the amalgamation of hard coating in cutting tools industries for three decades now, a stage with proven performance has been reached. Today, nearly 40% of all cutting tools used in machining applications are sheltered with coatings. Coatings have proven to dramatically improve wear resistance, increase tool life and enable use at higher speed. Over the years TiN, TiAlN and TiC have emerged as potential materials to coat machining tools. Chemical vapor deposition was the first technology to be used to deposit these coatings followed by physical vapor deposition. Currently, extensive use is being made of cathodic arc evaporation and sputtering for coatings components. The principal limiting factor in the performance of these cutting tools lies in their failure due to the brittleness of these coatings. These hard coatings, usually coated on soft steel substrates, are subjected to contact damage during service. This contact damage is driven by mismatch strain between the elastically deforming film on a plastically deforming substrate. Understanding of the contact damage is the key parameter for improvement in the coating design. Contact damage involves initiation of cracks and subsequent propagation within coating. Multiple cracking modes are seen in nitride coatings on soft substrate and mutual interaction of cracks may lead to spallation of the coating, exposing the substrate to extreme service conditions. Hence visualization of subsurface crack trajectories facilitates the classification of benign and catastrophic modes of failure, which consequently allows us to tailor the coating architecture to eliminate catastrophic failure. Multilayers have shown to perform better then monolayer coatings. In multilayer coatings, application specific particular properties can be engineered by alternately stack-ing suitable layers. The multilayer utilizes benefits of interfaces by crack deflection, crack blunting and desirable transition in residual stress across the interface. Hence, designing interfaces is the key parameter in the multilayer coating. However, very few studies exist that describe experimental visualization of deformation modes in multilayer coatings with different types of interfaces, e.g. nitride/nitride and nitride/metal. Thus the prime objective of the present study is to comprehend the influence of different interface structures as well as its architecture on the various contact damage modes in these coatings. TiAlN/TiN has shown better tribological properties compared to its constituent monolayers. There is an order of magnitude augmentation in loads for cracking without any hardness enhancement relative to monolayers of constituents, with the additional feature that both constituents exhibit similar hardness and modulus. The resistance to cracking is seen to increase with increase in number of interfaces. Hence this uniqueness in toughening without drastic reduction in mechanical properties provides the motivation for understanding the fundamental mechanisms of toughening provided by the interfaces in these hard/hard coatings. Another combination for the present study is with interfaces between hard-soft phases ZrN/Zr, a composite that seeks to compromise hardness in order to achieve greater toughness. The selected combination has potential of providing a model system without any substoichiometric nitrides influencing the interfacial structure. There is a great need to optimize the metal fraction/thickness for exploiting the benefits of toughening without much compromise on hardness and stiffness, since the principal applications of these coatings lies in preventing erosive and corrosive wear. As all the deformation modes in theses coatings are stress driven, the influence of different variables on stress field would dictate the emerging damage. To understand the role of stress fields on contact damage, finite element method and an analytical model was used to predict the stress field within the coating. The TiAlN/TiN coatings were deposited by cathodic arc evaporation, while sputtering was employed to procure the ZrN/Zr multilayer coatings with much finer layer spacing. Microstructural characterization of the as received coatings was done by XRD, scanning electron microscopy, focused ion beam cross section machining and transmission electron microscopy. Mechanical properties like hardness and modulus were evaluated by nanoindentation with restricted penetration depths to allow measurements that were not influenced by the substrate. Contact damage was induced by micro indentation at high loads. Indentations were examined from plan view as well as cross section for getting details of crack nucleation as well as propagation trajectories. Focused ion beam was used to examine cross sections of indents as well as to prepare electron transparent thin foils for transmission electron microscopy examination of subsurface damage induced by indentation. To emphasize specific issues in detail, the present work is divided into four sections: 1 Microstructure and mechanical characterization of the as deposited coatings of ZrN/Zr multilayer (while that of TiAlN/TiN has been reported elsewhere) 2 Details of contact damage in ZrN/Zr coating 3 Resolution of micro mechanistic issues in TiAlN/TiN coating utilizing detailed microscopy 4 The effect of change in architecture through heat-treatment of ZrN/Zr multilayer coatings on the mechanical behavior and contact damage Detailed microstructural, compositional and mechanical characterization was done on ZrN/Zr as received multilayer coatings. Thickness of metal layer was seen to influence the texture in the nitride, thick metal acquiring basal texture in turn inducing (111) texture in the nitride to reduce interfacial energy. Microstructure revealed that the nitride grows with interrupted columnar grains, renucleating at each metal/nitride interface. Presence of both phases was confirmed at even very low bilayer spacing, with slight changes in multilayers architecture, from planar interfaces to curved interfaces. The chosen system proved to be an ideal system for multilayer study without formation of secondary nitrides. Residual stress and hardness reduced with increase in metal layer thickness, whereas modulus was seen to follow the rule of mixture value. Detailed contact damage study of ZrN/Zr is reported in section two with influence of volume fraction and metal layer thickness. All the experimental results were corroborated with finite element methods. A comparative study of contact damage of multilayer with monolayer was carried out with cross section as well as plan view of indents. Metal plasticity was able to distribute damage laterally as well as vertically, hence reducing the stress concentration. There lies an optimum thickness of the metal providing maximum toughening by increasing the threshold load required for edge cracking. The sliding of columns is resisted by the metal. However, thick metal layers promote microcracking in individual nitride layers. Cracking is restricted to within individual nitride layers, eliminating through thickness cracking. The intermediate metal thickness was able to provide a mechanism of laterally distributing sliding and hence a higher tolerance level of the indentation strain that can be accommodated without cracking. Thin metal multilayers were seen to show delamination, strongly influenced by the multilayer architecture. We use the finite element method to understand the influence of stress fields in driving these various modes of damage for varying volume fraction and metal layer thicknesses. It is demonstrated how metal plasticity results in stress enhancement in the nitride layer compared to a monolayer and reduces the shear stress, which is the driving force for columnar sliding. The micro cracking to columnar shearing transition with metal thickness was explained with the help of average shear and normal stress across the multilayer which could explain the transition from cracking and sliding to interfacial delamination in thin metal layer multilayers with enhancement in interfacial shear stress. TiAlN/TiN multilayer allowed to exploit a form of compositional contrast to measure the strain with respect to depth. Layers acting as strain markers quantify the amount of sliding in terms of the offset in layers with respect to depth within the coating. We illustrate with transmission electron micrographs, the flaw generation that occurs as a result of sliding of misaligned column boundaries. These boundary kinks,upon further loading, may lead to cracks running at an angle to the indentation axis in an otherwise dense, defect free, as deposited coating. A previous study illustrates the increase in resistance of multilayers to multiple modes of cracking that are seen in the monolayer nitride coatings on steel substrates. We provide evidence of the enhanced plasticity, seen as macroscopic bending, which in reality is column sliding in a series of distributed small steps. We discuss the role of misfit dislocations in spreading the material laterally to accommodate the constraints during indentation and lattice bending. Interfacial sliding is seen to reduce the stress concentration by distributing the vertical column sliding and accommodating the flaws generated by the sliding of misaligned column boundaries. Some preferred boundaries with special orientation relations do slide, while near the substrate, the sliding is facilitated by the relaxation in intrinsic residual stresses. An analytical model which was formulated earlier is used to support our experimental findings. Investigations of the plausible reasons for the naturally occurring multilayer mollusc sea shells to reach stiffnesses equal to the upper bound of the rule of mixture value have concluded that its brick and mortar organization is responsible for its exceptional mechanical properties. Inspired by the same model, heat treatment was used to change the architecture of the soft-hard metal/nitride combination from that of the planar interface of the as deposited multilayer to a brick and mortar arrangement. Such an interconnected ZrN microstructure was successfully achieved and the stiffness and hardness were both seen to increase relative to the as received coatings. The possible reasons for this enhancement are discussed in term of this newly emerged architecture ,change in residual stress as well as changes in stoichiometry after heat treatment. The contact damage, though, was found to be more catastrophic relative to the as deposited coating with increased propensities for edge and lateral cracking. This was attributed to the interconnected nitrides formed in the brick and mortar architecture as well as residual stress changes due to the dissolution of Zr in ZrN to form off-stoichiometric nitrides. The cracks feel the presence of the metal and deviate from the otherwise smooth trajectory and take a path along the interface of the metal packet and the interconnected nitride. Summarizing, the present study clearly illustrates the fact that interfaces play an important role in damage control under contact loading. Fracture and deformation are either controlled by metal plasticity, distributing the column sliding in metal/nitride multilayers or by interfacial sliding mediated by interfacial misfit dislocations in case of the nitride/nitride multilayer coatings. The effective role of interfaces is to distribute damage laterally as well as horizontally to relieve stresses and hence enhance the damage tolerance under indentation. Optimum metal layer thickness has been proposed for maximum toughening in the metal/nitride multilayer coating and the role of interfaces in providing modes of plasticity is presented for the nitride/nitride multilayer coatings by use of extensive transmission electron microscopic investigations. A new interconnected architecture coatings provides a unique way of combining stiffness and toughness along with scope for further developing such configurations with improved mechanical properties.

Student Number : 0006036T - MSc(Eng) project report - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment / Demographic and medical history information obtained from annual South African antenatal surveys is used to estimate the risk of acquiring HIV. The estimation system consists of a classifier: a neural network trained to perform binary classification, using supervised learning with the survey data. The survey information contains discrete variables such as age, gravidity and parity, as well as the quantitative variables race and location, making up the input to the neural network. HIV status is the output. A multilayer perceptron with a logistic function is trained with a cross entropy error function, providing a probabilistic interpretation of the output. Predictive and classification performance is measured, and the sensitivity and specificity are illustrated on the Receiver Operating Characteristic. An auto-associative neural network is trained on complete datasets, and when presented with partial data, global optimisation methods are used to approximate the missing entries. The effect of the imputed data on the network prediction is investigated.

New restrictions and regulations regarding internal combustion engines introduced severe mechanical and thermo-mechanical loads on engine parts, mostly on piston rings, leading to high wear and premature damage, thus causing oil leakage into the combustion chamber and increasing emissions. One of the most viable solutions to overcome these issues is the use of coatings to change surface properties. Coatings produced by High Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (dcMS) have shown promising results to form dense coatings with high hardness and high wear resistance. Those properties can be further enhanced by using a periodic structure in the form of multilayers of different materials. In this study, we proposed a hybrid process with HiPIMS and dcMS to produce multilayer coatings of CrN and CrAlN. Different target combinations and negative substrate bias were studied. Furthermore, the base layer influence and an evaluation of the periodicity effects were presented. Structure and morphology of the coatings were characterized with X-Ray Diffraction, Scanning Electron Microscopy and Atomic Force Microscopy. Meanwhile, instrumented nanohardness, corrosion and wear tests were performed to characterize mechanical, electrochemical and tribological properties. Results showed that the choice of target combination and bias values are fundamental for enhancing mechanical and tribological properties. On the other hand, we found no evidence of superlattice hardening when changing periodicity but an increase in corrosion resistance when reducing periodicity was found. The combination of targets, substrate bias, base layer and periodicity presented here showed promising results on wear tests, especially when compared with the current coating under the same engine conditions. / Novas restrições e regulamentações de motores de combustão interna introduziram severas cargas mecânicas e termomecânicas no motor, principalmente nos anéis de pistão, o que leva a um alto desgaste e ao dano prematuro dos mesmos e causa vazamentos de óleo na câmara, aumentando as emissões de poluentes. Uma das soluções mais viáveis para solucionar este problema é o uso de recobrimentos para alterar as propriedades da superfície. Recobrimentos produzidos pelas técnicas High Power Impulse Magnetron Sputtering (HiPIMS) e Direct Current Magnetron Sputtering (dcMS) mostraram resultados promissores na formação de filmes densos com elevada dureza e resistência ao desgaste. Essas propriedades podem ser melhoradas com a utilização de estruturas periódicas na forma de multicamadas. Nesse estudo, foi proposto um processo híbrido de HiPIMS e dcMS para produzir recobrimentos multicamadas de CrN/CrAlN. Diferentes combinações de alvos e de valores de polarização negativa do substrato (bias) foram estudadas. Além disso, foram apresentadas a influência da camada base e a avaliação dos efeitos da mudança de periodicidade. Estrutura e morfologia dos recobrimentos foram caracterizadas por Difração de Raios-X, Microscopia Eletrônica de Varredura e Microscopia de Força Atômica. As caracterizações mecânica, eletroquímica e tribológica foram realizadas com ensaios de Nanodureza Instrumentada, Corrosão e Desgaste. Os resultados mostram que a escolha da combinação de alvos e de valores de bias são fundamentais para a melhoria das propriedades mecânicas e tribológicas. Por outro lado, não foram encontradas evidências de endurecimento devido ao efeito de super-redes com a variação de periodicidade, mas um aumento da resistência à corrosão foi evidenciado. A combinação de alvos, bias, camada base e periodicidade apresentadas aqui mostraram resultados promissores em testes de desgaste, principalmente quando comparadas com os recobrimentos utilizados comercialmente nas mesmas condições de trabalho do motor.