Дисертації з теми "Advance Device Applications"

Magnetocaloric and magnetoelastic materials can be utilised in various device applications and have a potential to increase their efficiency by a considerable amount. In this thesis, Gd5(SixGei_x)4 is extensively researched on its magnetic properties such as magnetic phase transition temperature, magnetostriction, magnetoresistance and anisotropy. Field induced phase transition in Gd5(SixGei_x)4 was observed in several compositions and the rate of change of the first order phase transition temperature was determined to be approximately 5 K/Tesla. Various methods of transition temperature measurements were compared and the Arrott plot technique was determined to be accurate method for magnetocaloric materials. An advanced technique based on Arrott plots was developed to estimate the second order phase transition temperature when it is suppressed by the first order phase transition. This technique was also extended to estimate the transition temperature of mixed phase alloys. Field induced phase transition at high temperature using high magnetic field measurements up to 9 Tesla were carried out on two compositions of Gd5(SixGei-x)4 for x=0.5 and x=0.475 to validate the Arrott plot technique. Magnetostriction measurements were carried out on Gd5(SixGei_x)4 for various compositions. Fine structure was observed in the magnetostriction measurement in single crystal and polycrystalline Gd5Si1.95Ge2.05 samples but not on other compositions, which might be due to the presence of a secondary phase. It was demonstrated that a giant magnetostriction of the order of 1813 ppm could be obtained by varying the temperature using a Peltier cell and removing the requirement of bulky equipment such as Physical Properties Measurement System (PPMS). Magnetoresistance was measured for various compositions and an irreversible increase in resistivity was observed which depended linearly on the number of thermal cycles passing through the first order phase transition temperature. The irreversibly increased resistivity was recovered by holding the samples at high temperature for a long period of time of up to 3 days. A theoretical model was developed to explain the recovery in the resistance and was experimentally verified. First order magnetocrystalline anisotropy constant Kj, easy and hard axes of the single crystal Gd5Si2.7Gei j sample were determined using magnetic moment as a function of angle of rotation of the sample at room temperature. Dependence of the first order phase transition temperature on the angle of rotation of the single crystal Gd5Si2Ge2 sample was determined to be negligible. Additionally polycrystalline samples of Gd5Sii.8Ge2.2 and Gd5Sii.9Ge2.i were prepared by arc- melting and heat treatment was carried out on these samples in accordance with the literature to remove residual secondary phases in the sample at the Materials and Metallurgy Department of the Birmingham University. XRD measurements were carried out on these samples to confirm the crystal structure.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Tomografia por coerência óptica (OCT) é uma técnica de imageamento não invasiva que usa radiação infravermelho para sondar alguns milímetros the profundidade de um alvo com um resolução de poucos micrômetros. Aqui, nós expomos a base teórica para entender a técnica. O texto cobre as duas variedades de OCT domínio temporal e domínio da frequência e descreve três aplicações da técnica em odontologia: a) Um na avalição the propagação rachaduras em polímeros reforçado com fibra usado em restauração dental; b) O imageamento da sobra de dentina e cavidade pulpar após excavação da dentina, com o propósito de medir a espessura da dentina, e c) uma avaliação clínica da integridade de restaurações dentais. Em todas essa aplicações, OCT gerou imagens marcantes e forneceu informações semiquatitativas sobre a estrura dentária. Com o objetivo de desenvolver um sistema de tomografia óptica integrada em um chip. Nós expomos a base teórica da plataforma de fotônica integrada. Após uma revisão literária, nós descobrimos que não existe espectrômetro integrado com a especificações necessárias para uso em OCT. Nós, então, desenvolvemos um espectrômetro com a características necessárias. Isso foi possível devido a uma nova arquitetura de espectrômetro baseada na combinação de um ressoador em anel e um espectrômetro de grade de difração

The main objective of this work is to investigate advanced applications of fibre gratings with the combination of nonlinear fibre optical effects, including the stimulated Raman scattering (SRS), Kerr effects, four-wave mixing (FWM) and second-harmonic generation. A Raman distributed-feedback (R-DFB) fibre laser formed in a passive optical fibre by using Raman gain is considered as the most promising route to generate a single-frequency and narrow-linewidth laser source at any wavelength given a proper pump source. In this thesis, the R-DFB fibre laser has been intensively studied both numerically and experimentally. Simulation results of centre π phase-shifted R-DFB fibre lasers show that the longer length of the DFB grating, the higher Raman gain coefficient and the lower background loss of the host fibre are always beneficial for achieving low threshold R-DFB fibre lasers. 30-cm long centre π phase-shifted R-DFB fibre lasers have been respectively demonstrated in two types of commercially available Ge/Si fibres of PS980 and UHNA4. Both un-polarised and linearly polarised CW Yb-doped fibre lasers at ~1.06 μm were used as the pump sources. The R-DFB fibre lasers are single-frequency operation at around 1.11 μm and have 3 dB linewidth less than 2.5 kHz; lasing thresholds down to sub-watt power levels; total output powers up to ~2 W; and total conversion efficiencies against incident pump power around 13%. Ultra-wide range (>110 nm) wavelength conversion by using FWM in these 30 cm-long R-DFB fibre lasers have been observed and up to ~-25 dB FWM conversion efficiency has been obtained. The nonlinearities and photosensitivity of several high-index non-silica glasses and fibres are also studied in order to incorporate fibre Bragg gratings (FBGs) with the highly nonlinear fibres to form R-DFB fibre lasers with lower thresholds. In particular, the Raman gain coefficient of a house-made tellurite glass fibre has been found to be ~35 times higher than the silica fibre and a SRS-assisted supercontinuum from ~1.1-1.7 μm has been observed in the fibre with a length of ~1.35 m by pumping at ~1.06 μm in the normal dispersion region of the fibre. Preliminary investigations into concatenating periodic poled silica fibres (PPSFs) to improve the frequency-doubling conversion efficiency are also presented.

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed July 9, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 155-161).

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
Neste trabalho, desenvolveram-se dois tipos de substratos flexíveis para dispositivos orgânicos. Para tal, usou-se o termoplástico comercial de alto desempenho, poli(éter imida) (PEI), e a celulose bacteriana (CB), um polímero natural e biocompatível comumente utilizado como pele artificial. Os filmes de PEI foram fabricados com boa transparência óptica no visível, flexibilidade e ausência de poros, enquanto os filmes de CB foram utilizados como recebidos. Filmes finos de óxido de índio dopado com estanho (ITO) foram depositados sobre os filmes, utilizando a técnica de rf-sputtering, a fim de torná-los condutores elétricos para serem utilizados em dispositivos. Os valores de resistividade elétrica dos substratos modificados foram aprimorados através da variação dos parâmetros de deposiçãoo dos filmes de ITO. Os menores valores de resistividade alcançados foram 3, 27 × 10(-4) omega· cm para os substratos de PEI e 3, 70×10(-4) omega· cm para os de CB, comparáveis ao valor alcançado para os substratos de vidro [3, 66×10(-4) omega·cm], utilizados como referência. Além disso, devido às ótimas propriedades térmicas da PEI, os filmes de ITO sobre este material e sobre vidro passaram por um tratamento térmico a fim de baixar ainda mais o valor da resistividade. Após este tratamento, os valores de resistividade baixaram para 2, 88×10(-4) omega·cm e 3, 41 × 10(-4) omega· cm, para a PEI e o vidro, respectivamente. Os resultados obtidos são comparáveis ou melhores àqueles obtidos por outros autores em diferentes substratos, com e sem tratamento térmico, e mostraram-se promissores para o desenvolvimento de dispositivos orgânicos flexíveis.
In this work, it has developed two types of flexible substrates for organic devices. For this purpose, it was used the commercial high-performance thermoplastic, poly(ether imide) (PEI), and a natural and biocompatible polymer commonly used as artificial skin, bacterial cellulose (BC). PEI films were fabricated with good optical transparency in the visible range of spectra, flexibility and absence of pores, while the CB films were used as received. Thin films of indium tin oxide (ITO) were deposited on those films using rf magnetron sputtering in order to turn them electrical conductors for using in organic devices. The electrical resistivity of the modified substrates was improved by varying the ITO films deposition parameters. The lowest achieved resistivity was 3.27 × 10(-4) omega· cm for PEI substrates and 3.70×10(-4) omega·cm for CB substrates, comparable to the reference substrate (glass) 3.66 × 10(-4) omega· cm. In addition, due to the excellent thermal properties of PEI, ITO films on this material and on glass substrates were thermally treated to further improvement of its electrical properties. After this treatment, the resistivity values decreased to 2.88 × 10-4 ! · cm and 3.41× 10(-4) omega· cm for PEI and glass substrates, respectively. The obtained results are comparable or better than those obtained by other authors on different substrates, with and without heat treatment, establishing these materials as outstanding substrates for the development of flexible organic devices.

Ruthenium and ruthenium dioxide thin films have shown great promise in various applications, such as thick film resistors, buffer layers for yttrium barium copper oxide (YBCO) superconducting thin films, and as electrodes in ferroelectric memories. Other potential applications in Si based complementary metal oxide semiconductor (CMOS) devices are currently being studied. The search for alternative metal-based gate electrodes as a replacement of poly-Si gates has intensified during the last few years. Metal gates are required to maintain scaling and performance of future CMOS devices. Ru based materials have many desirable properties and are good gate electrode candidates for future metal-oxide-semiconductor (MOS) device applications. Moreover, Ru and RuO2 are promising candidates as diffusion barriers for copper interconnects. In this thesis, the thermal stability and interfacial diffusion and reaction of both Ru and RuO2 thin films on HfO2 gate dielectrics were investigated using Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). An overview of Ru and RuO2/HfO2 interface integrity issues will be presented. In addition, the effects of C ion modification of RuO2 thin films on the physico-chemical and electrical properties are evaluated.

Due to an ever-increasing global population and limited resource availability, there is a constant need for detection of both natural and anthropogenic hazards in water, air, food, and material goods. Traditionally a different instrument would be used to detect each class of contaminant, often after a concentration or separation protocol to extract the analyte from its matrix. Raman spectroscopy is unique in its ability to detect organic or inorganic, airborne or waterborne, and embedded or adsorbed analytes within environmental systems. This ability comes from the inherent abilities of the Raman spectrometer combined with concentration, separation, and signal enhancement provided by drop coating deposition Raman (DCDR) and surface-enhanced Raman spectroscopy (SERS). Herein the capacity of DCDR to differentiate between cyanotoxin variants in aqueous solutions was demonstrated using principal component analysis (PCA) to statistically demonstrate spectral differentiation. A set of rules was outlined based on Raman peak ratios to allow an inexperienced user to determine the toxin variant identity from its Raman spectrum. DCDR was also employed for microcystin-LR (MC-LR) detection in environmental waters at environmentally relevant concentrations, after pre-concentration with solid-phase extraction (SPE). In a cellulose matrix, SERS and normal Raman spectral imaging revealed nanoparticle transport and deposition patterns, illustrating that nanoparticle surface coating dictated the observed transport properties. Both SERS spectral imaging and insight into analyte transport in wax-printed paper microfluidic channels will ultimately be useful for microfluidic paper-based analytical device (𝜇PAD) development. Within algal cells, SERS produced 3D cellular images in the presence of intracellularly biosynthesized gold nanoparticles (AuNP), documenting in detail the molecular vibrations of biomolecules at the AuNP surfaces. Molecules involved in nanoparticle biosynthesis were identified at AuNP surfaces within algal cells, thus aiding in mechanism elucidation. The capabilities of Raman spectroscopy are endless, especially in light of SERS tag design, coordinating detection of analytes that do not inherently produce strong Raman vibrations. The increase in portable Raman spectrometer availability will only facilitate cheaper, more frequent application of Raman spectrometry both in the field and the lab. The tremendous detection power of the Raman spectrometer cannot be ignored.
Ph. D.

This thesis studies lead suphide (PbS) colloidal quantum dots and their photovoltaic applications. Different sizes of PbS QDs were synthesised and characterised using absorption spectroscopy and transmission electron microscopes. PbS QD Schottky junction devices were fabricated with AM1.5 power conversion efficiency up to 1.8 %. The Schottky junction geometry limits the device performance. A semiconductor heterojunction using ZnO as an electron acceptor was built and the device efficiency increased to 3%. By studying the light absorption and charge extraction profile of the bilayer device, the absorber layer has a charge extraction dead zone which is beyond the reach of the built-in electric field. Therefore, strategies to create a QD bulk heterojunction were considered to address this issue by distributing the junction interface throughout the absorber layer. However, the charge separation mechanism of the QD heterojunction is not clearly understood: whether it operates as an excitonic or a depleted p-n junction, as the junction operating mechanism determines the scale of phase separation in the bulk morphology. This study shows a transitional behaviour of the PbS/ZnO heterojunction from excitonic to depletion by increasing the doping density of ZnO. To utilise the excitonic mechanism, a PbS/ZnO nanocrystal bulk heterojunction was created by blending the two nanocrystals in solution such that a large interface between the two materials could facilitate fast exciton dissociation. However, the devices show poor performance due to a coarse morphology and formation of germinate pairs. To create a bulk heterojunction where a built-in electric field could assist the charge separation, a TiO₂ porous structure with the pore size matching with the depletion width was fabricated and successfully in-filled by PbS QDs. The porous device produces 5.7% power conversion efficiency, among one of the highest in literature. The enhancement comes from increased light absorption and suppression of charge recombination.

InP-based InAlAs/InGaAs pseudomorphic High Electron Mobility Transistors (pHEMTs) have shown outstanding performance; this makes them prominent in high frequency mm-wave and submillimeter-wave applications. However, conventional InGaAs/InAlAs pHEMTs have major drawbacks, i.e., very low breakdown voltage and high gate leakage current. These disadvantages degrade device performance, especially in Monolithic Microwave Integrated Circuit (MMIC) low noise amplifiers (LNAs). The optimisation of InAlAs/InGaAs epilayer structures through advanced bandgap engineering offers a key solution to the problem. Concurrently, device modelling plays a vital role in the design and analysis of pHEMT devices and circuit performance. In this research, two-dimensional (2D) physical modelling of 1 m and sub-micro metre gate length strained channel InAlAs/InGaAs/InP pHEMTs has been developed, in ATLAS Silvaco. All modelled devices were optimised and validated by experimental devices, which were fabricated at the University of Manchester. An underlying device physics insight is gained, i.e., the effect of changes to the device's physical structure, theoretical concepts and its general operation, and a reliable pHEMT model is obtained. The kink anomalies in the I-V characteristics were reproduced. The 2D simulation results demonstrate an outstanding agreement with measured DC and RF characteristics. The aim of developing linear and non-linear models for sub-micro metre transistors and their implementation in MMIC LNA design is achieved with the 0.25 m In0.7Ga0.3As/In0.52Al0.48As/InP pHEMT. An accurate method for the extraction of empirical models for the fabricated active devices has been developed, and optimised using the Advance Design System (ADS) software. The results demonstrate excellent agreement between experimental and modelled DC and RF data. Precise models for MMIC passive devices are also obtained, and incorporated in the proposed design for a single- and double-stage MMIC LNAs at C- and X-band frequencies. The single-stage LNA is designed to achieve a maximum gain ranging from 9 to 13 dB over the band of operation, while the gain is increased to between 20 dB and 26 dB for the double-stage LNA designs. A noise figure of less than 1.2 dB and 2 dB is expected, for the C- and X-band LNAs respectively, while retaining stability across all frequency bands. Although the RF performance of pHEMT is being vigorously pushed towards the terahertz (THz) region, novel devices such as the Resonant Tunnelling Diode (RTD) are needed to support future ultra-high-speed, high-frequency applications. Hence, the study of physical modelling is extended to quantum modelling of an advanced In0.8Ga0.2As/AlAs RTD device. The aim is to effectively model both large-size and submicron RTDs, using Silvaco's ATLAS software to reproduce the peak current density, peak-to-valley-current ratio (PVCR), and negative differential resistance (NDR) voltage range. The physical modelling for the RTD devices is optimised to achieve an excellent match with the fabricated RTD devices; variations in the spacer thickness, barrier thickness, quantum well thickness and doping concentration are included.

This work is primarily comprised of five self-contained papers. Three papers are applications oriented. A common element in the first three papers is that micro-perforated panels (MPP), the permeable membranes in diesel particulate filters, and a source impedance are all modeled as a transfer impedance. The first paper deals with enhancing the performance of micro-perforated panels by partitioning the backing cavity. Several different backing schemes are considered which enhance the performance without increasing the total volume of the MPP and backing. In the second paper, a finite element modeling approach is used to model diesel particulate filters below and above the plane wave cutoff frequency. The filter itself is modeled using a symmetric finite element model and results are compared to plane wave theory. After the transfer matrix of the filters is known, it is used in three-dimensional finite and boundary element models. The third paper is a tutorial that shows how a source impedance can be modeled using transfer impedance approaches in finite element analysis. The approach used is useful for better understanding the resonance effects caused by pipes upstream and downstream of the exhaust. The fourth paper examines the best practice for the two-load transmission loss measurement. This method was integral to obtaining the measurements for validating the diesel particulate filter models. The fifth paper proposes transmission and insertion loss metrics for multi-inlet mufflers. It is shown that the transmission loss depends on the amplitude and phase relationship between sources (at the inlets) whereas insertion loss depends on both the source strength and impedance for each inlet.

Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.

Gallium Nitride is a promising wide-bandgap material for electronics. With GaN based devices it is possible to achieve higher operative frequencies and power densities in comparison to Silicon. The first GaN-based High Electron Mobility Transistor (HEMT) has been designed in the 1995, and after twenty years this technology start to be ready to compete in the market with Silicon-based devices. There are several reason why it was necessary all this time to obtain a stable technology. Unlike Silicon, it is still not possible to grow a gallium nitride crystal starting from a seed, with reasonable quality dimensions and costs. Thus, itis necessary to grow it on different substrates, like Silicon Carbide, Sapphire or Silicon. Therefore, the obtained crystals have a high defects concentration that limits the device performances. With the optimization of the process and the introduction suitable nucleation layer on the substrate it is now possible to grow GaN wafers with a tolerable defectivity. The main problems induced by the defects are trap states and reliability issues. The trap states generate problems during dynamic operation, inducing a drop in the output characteristics. In addition to this recoverable phenomena, the GaN-HEMTs can even present problem of reliability, that have been widely explored in the past. Nowadays, the estimated device life time of the last technologies allow to start the production of electronics both for consumer market than for the more demanding space applications. Within this work it will be presented a summary of the research activity performed during my PhD. In the first part is presented a short summary of the state of the art of GaN-HEMT technology. In the last two years a lot of new results have been demonstrated in literature, showing the last technological improvements. Then, a short summary on the trapping phenomena and reliability issue is presented, that is fundamental to understand all the obtained results. The research activities involved the two main GaN-based HEMTs applications: the RF devices and the power switching transistors. For the RF applications the transistor is used as an amplifier, in a frequency range from 1 GHz to 100 GHz. The main applications are radar and telecommunications for mobile phone, radio and satellites. I collaborated in a project of the European Space Agency, with subject “Preliminary Validation of Space Compatible Foundry Processes”. They will be presented all the results of the reliability assessment carried out within this project. The purpose was to validate a GaN-HEMT technology for space applications, trying to estimate the device lifetime and the failure mechanisms. We will see that the two analysed technologies are very stable, and the estimated life time exceed the twenty years. Nevertheless, not all the failure mechanisms are clear, but we found some degradation signatures that can be related to the gate metallization. On the side of power switching transistors I will report first the results obtained in a collaboration with ON Semiconductor on the development of d-mode MIS-HEMTs. Our role was to give a feedback on the device performance improvement, mainly focused on the on-resistance. It represents indeed one of the main problems of GaN-HEMT working in switching conditions and it is mainly related to trapping phenomena. Then, we developed a new original measurement procedure that allows to test the devices in a condition closer to the operative one. This new setup helps us to demonstrate the impressive stability of the last device generations. Now this technology is ready to work at 600 V in switching operation, with performances better than Silicon. The second part about the power devices will report the work carried out during the period by the Ferdinand-Braun-Institut, Leibniz-Institut für Hochfrequenztechnik (FBH), in Berlin. The target was to investigate the reliability of the p-GaN devices developed by the research center by means of long term on-state life test. The gate leakage current is suspected to be one of the main problem for the reliability of this kind of device in on-state operation. However, there are not many works in literature that analyse this issue, and we will see how our test helps to consolidate one of the proposed degradation modes. Within this analysis it was fundamental the role of physical based simulations, for which is devoted a separated chapter. The simulations were very helpful for the understanding of the degradation mechanism. They allowed us to have a complete vision of the conduction mechanisms and of the device weakness. In this way we can give fundamental information to the device developers, in particular which device regions need to be improved.
Il nitruro di gallio è un promettente materiale a semiconduttore con ampio energy gap. Tramite dispositivi bastai su GaN è possibile raggiungere frequenze operative e densità di potenza maggiori in confronto al silicio. Il primo transistor HEMT (High Electron Mobility Transistor) basato su GaN è stato sviluppato nel 1995, e dopo vent'anni questa tecnologia inizia ad essere pronta a competere sul mercato con dispositivi basati su silicio. Ci sono diversi motivi per cui è servito del tempo per ottenere una tecnologia stabile. A differenza del silicio, non è possibile crescere cristalli di nitruro di gallio partendo da un seme, non almeno con costi, qualità e dimensioni ragionevoli. Perciò è necessario crescere il nitruro di gallio su substrati diversi, come il carburo di silicio, lo zaffiro o il silicio. Perciò, i cristalli ottenuti hanno una concentrazione di difetti che limita le prestazioni dei dispositivi. Con l'ottimizzazione del processo e l'introduzione di un adeguato strato di transizione, detto nucleation layer, è possibile ottenere dei wafer con una difettività tollerabile. Il problema principale introdotto dai difetti sono gli stati trappola e questioni di affidabilità. Gli stati trappola danno problemi durante il funzionamento dei transistor, creando un calo temporaneo della caratteristica di uscita. Oltre a questo fenomeno temporaneo gli HEMT basati su GaN presentano problemi di affidabilità, ampiamente studiati in passato. Al giorno d'oggi il tempo di vita medio stimato delle ultime generazioni di transistor permette la produzione di dispositivi elettronici sia per il settore commerciale che per applicazioni spaziali. In questo lavoro sarà presentato un riassunto delle attività di ricerca svolte durante il dottorato. Nella prima parte è presentato un riepilogo dello stato dell'arte della tecnologia GaN-HEMT. Negli ultimi due anni in letteratura sono stati dimostrati nuovi risultati, rivelando un notevole miglioramento tecnologico. Verrà poi presentato un breve riassunto sui fenomeni di trapping e sull'affidabilità, che risulterà fondamentale per comprendere al meglio i risultati ottenuti. Le attività di ricerca hanno coinvolto le due applicazioni principali dei transistor GaN-HEMT: i dispositivi RF e i transistor di potenza. Per applicazioni RF il transistor è usato come amplificatore, in un range di frequenze tra 1 GHz e 100 GHz. Le applicazioni principali sono radar e telecomunicazioni per telefonia mobile, radio e satellitare. Ho collaborato in un progetto dell'Agenzia Spaziale Europea dal titolo: “Preliminary Validation of Space Compatible Foundry Processes”. Verranno presentati i risultati della valutazione dell'affidabilità svolta in questo progetto. Lo scopo era di validare la tecnologia GaN-HEMT per applicazioni spaziali, provando a stimare il tempo di vita dei dispositivi e i meccanismi di guasto. Vedremo come la tecnologia analizzata sia stabile, con un tempo di vita stimato che oltrepassa i vent'anni. Ciò nonostante, non sono ancora chiari tutti i meccanismi di guasto, ma è stata trovata qualche caratteristica tipica del degrado legata alla metallizzazione di gate. Dal lato dei transistor di potenza verranno riportati prima i risultati ottenuti nella collaborazione con ON Semiconductor, nello sviluppo di dispositivi MISHEMT normally-on. Il nostro ruolo era di dare un feedback all'azienda riguardo alle performance dei dispositivi, in particolare in termini di resistenza in on-state. Questo rappresenta infatti uno dei problemi maggiori dei transistor GaNHEMT che lavorano in condizioni switching ed è dovuto a fenomeni di trapping. Poi, è stato sviluppata una nuova procedura di misura che permette di testare i dispositivi in condizione vicine a quelle operative. Questo nuovo setup è stato d'aiuto per dimostrare l'eccezionale stabilità delle ultime generazioni di transistor. Ora questa tecnologia è pronta per lavorare a 600 V con prestazioni migliori di quelle del silicio. La seconda parte relativa ai dispositivi di potenza parlerà del lavoro svolto presso il Ferdinand-Braun-Institut, Leibniz-Institut für Hochfrequenztechnik (FBH), a Berlino. L'obiettivo principale era quello di investigare l'affidabilità dei dispositivi p-GaN sviluppati presso il centro di ricerca, tramite stress in on-state a lungo termine. La corrente di leakage di gate è sospettata di essere uno dei problemi principali per l'affidabilità di questo tipo di dispositivi in on-state. Tuttavia, non ci sono tanti lavori in letteratura che analizzano il problema, e si vedrà come i test svolti aiutano a consolidare uno dei modelli proposti. In questa analisi è stato fondamentale il ruolo delle simulazioni, a cui è stato riservato un capitolo a parte. Le simulazioni sono state di grande aiuto nella comprensione dei meccanismi di guasto e hanno permesso di avere una visione completa dei meccanismi di conduzione e dei punti deboli del dispositivo. In questo modo possono essere date informazioni essenziali a chi sviluppa i transistor, in particolare quali sono le regioni del dispositivo che andrebbero migliorate.

Nanomaterials have attracted great interest due to the unique physical properties and great potential in the applications of nanoscale devices. Two dimensional atomic crystals, which are atomic thickness, especially graphene, have triggered the gold rush recently due to the fascinating high mobility at room temperature for future electronics. The crystal structure of nanomaterials will have great influence on their physical properties. Thus, this thesis is focused on developing the methods to control the crystal structure of nanomaterials, namely quantum dots as semiconductor, boron nitride (BN) as insulator, graphene as semimetal, with low cost for their applications in photonics, structural support and electronics. In this thesis, firstly, Mn doped ZnSe quantum dots have been synthesized using colloidal synthesis. The shape control of Mn doped ZnSe quantum dots has been achieved from branched to spherical by switching the injection temperature from kinetics to thermodynamics region. Injection rates have been found to have effect on controlling the crystal phase from zinc blende to wurtzite. The structural-property relationship has been investigated. It is found that the spherical wurtzite Mn doped ZnSe quantum dots have the highest quantum yield comparing with other shape or crystal phase of the dots. Then, the Mn doped ZnSe quantum dots were deposited onto the BN sheets, which were micron-sized and fabricated by chemical exfoliation, for high resolution imaging. It is the first demonstration of utilizing ultrathin carbon free 2D atomic crystal as support for high resolution imaging. Phase contrast images reveal moiré interference patterns between nanocrystals and BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes using a newly developed equation method. Double diffraction is observed and has been analyzed using a vector method. As only a few microns sized 2D atomic crystal, like BN, can be fabricated by the chemical exfoliation. Chemical vapour deposition (CVD) is as used as an alternative to fabricate large area graphene. The mechanism and growth dynamics of graphene domains have been investigated using Cu catalyzed atmospheric pressure CVD. Rectangular few layer graphene domains were synthesized for the first time. It only grows on the Cu grains with (111) orientation due to the interplay between atomic structure of Cu lattice and graphene domains. Hexagonal graphene domains can form on nearly all non-(111) Cu surfaces. The few layer hexagonal single crystal graphene domains were aligned in their crystallographic orientation over millimetre scale. In order to improve the alignment and reduce the layer of graphene domains, a novel method is invented to perform the CVD reaction above the melting point of copper (1090 ºC) and using molybdenum or tungsten to prevent the balling of the copper from dewetting. By controlling the amount of hydrogen during the growth, individual single crystal domains of monolayer over 200 µm are produced determined by electron diffraction mapping. Raman mapping shows the monolayer nature of graphene grown by this method. This graphene exhibits a linear dispersion relationship and no sign of doping. The large scale alignment of monolayer hexagonal graphene domains with epitaxial relationship on Cu is the key to get wafer-sized single crystal monolayer graphene films. This paves the way for industry scale production of 2D single crystal graphene.

碩士
中州科技大學
工程技術研究所
101
With the development of technology, human’s reliability on a growing technology convenience has increase. Technology not only bring in convenience buy also brings enormous benefits worth. As the development of high-tech industry companies, the incoming disasters are more serious and dangerous compare to traditional industry plant. This research is focusing on the safety device in these high-tech plants. The multi directions research will suggest the safety device for these high tech plants. In this study, are surveys base on people who related to these high-tech facility. After analysis the result, suggesting high-tech plants by focusing on the safety device operator training when they purchase these safety device. Increase the safety device usage efficiency, and economical cost. In the future research, the researchers are able to increase the research area throughout the country with similar high-tech plants. This research can be the basic data for the future research, and able to focus on research analysis on other influence effect, or difference between each background effect.

Magnetic sensors are deployed in many applications such as automotive, consumer electronics, navigation and data storage devices. Their market’s growth is driven by demands of higher performance; primarily to assist in the advancement of the Internet of Things (IoT) and smart systems. Challenging obstacles of miniaturization and power consumptions must be overcome. A leading sensor that has the potential to accelerate the development is the magnetic tunnel junction (MTJ) devices. Corrosion causes catastrophic consequences for industries. Preventive measures could save up to 35% of annual corrosion-related costs. An advanced corrosion sensing technique is developed based on iron nanowires. The iron nanowires are magnets which lose their magnetization when corroded. Their magnetization loss is monitored using sensitive MTJ sensor. Combined, the nanowires and the MTJ sensor realize a highly integrated sensor concept that enables corrosion sensing with an ultra-low power consumption of less than 1 nW, a sensitivity of 0.1 %/min, a response time of 30 minutes and an area of 128 μm2. Surgical tool development is accelerating in the healthcare sector. Cardiac catheterization specifically is a minimally invasive surgery that relies heavily on x-ray imaging and contrast dyes. A flexible tri-axis MTJ sensor is developed to help minimizing the need for x-ray imaging during the procedure. The flexible sensor can bend to a diameter of 500 μm without compromising the performance and can endure over 1000 bending cycles without fatigue. Three flexible sensors are mounted onto the tip of a 3 mm cardiac catheter, realizing a novel sensor-on-tube (SOT) tri-axis sensor concept. The sensor has a high sensitivity of 9 Ω/° and an MR ratio of 29%. It weighs 16 μg only, adds 5 μm to the catheter’s diameter and a total size 300 μm2. The prototype system estimated the heading angle with an RMS error value of 7° and tracked the orientation of the sensor with an acceptable accuracy. However, the sensor has a misalignment issue caused by the manual placement of the sensors. A high precision tool is needed for the assembly, and any further misplacement -within a reasonable margin of error- could be corrected by calibration algorithms.

碩士
國立中山大學
光電工程研究所
95
Recently, memory-cells employing discrete traps as the charge storage media have been attracting a lot of attention as a promising candidate to replace conventional DRAM or Flash memories. Conventional floating gate (FG) non-volatile memories (NVMs) present critical issues on device scalability beyond the sub-50nm node. In achieving non-volatility in conventional FG memories, thicker control and tunnel oxide (~8nm) are required to guarantee longer retention time. Relatively, nano-dots memories causes more resistant leakage charges by localized storage sites, thus improving the device retention characteristics. Hence, nano-dots memories allow more aggressive scaling of the tunnel oxide and exhibit superior characteristics compared to Flash memories in term of operation voltage, write / erase speed, retention time and endurance. The advantages of metal nano-dots compared with other material counterparts include higher density of states , stronger coupling with the channel, better size scalability, and the design freedom of engineering the work function to optimize device characteristics. However, tungsten nano-dots are the most interested in all of metal dots is that tungsten metal has more extra attractive advantages, such as ultra high melting point make high process temperature caused superior thermal stability of device and wide application in VLSI technology nowadays caused real possibility of tungsten nano-dots NVMs fabricated in industry in practice. This dissertation is divided into four sections: (1) discussion of basic properties for tungsten nano-dots memory devices; (2) Tunneling Oxide Engineering,; (3) Improvement by novel processes; and (4) The influence with supercritical CO2 (SCCO2) and vapor treatment. Initially, formative mechanism of tungsten nano-dots and electrical characteristics of devices was investigated in the first section. Tungsten nano-dots were formed by oxidizing tungsten silicide / amorphous silicon double stack film at high temperature condition. From electrical measurement, the better characteristics have been achieved for oxidation condition at 1050°C / 120 sec. Secondly, the rapid thermal anneal (RTA) oxidation is used to grow tunnel oxide by two different forming gas (O2/N2O). Comparison of electrical characteristics, program characteristics of the device using tunnel oxide with N2O process is inferior than the common device. However, endurance is a important electrical characteristics in the semiconductor device especially apply on the non-volatile memory. Thirdly, novel processes were employed into fabrication of tungsten nano-dots memory devices, include the N2O oxidation and NH3 plasma treatment. The purpose of novel processes is production additional trapping states in nonvolatile memories, which is considerably as combination nano-dots with SONOS structure. In the final section, the application of supercritical CO2 with vapor on tungsten nano-dots memoery devices have been studying. It is found that the device treated by SCCO2 which electrical characteristics is improved obviously. Furthermore, this technology also can fabricate the nano-dots memory which is like the device used high temperature oxidation process. It suggests that the SCCO2 with vapor treatment could oxidize silicide film under a low temperature environment. This novel oxidation process has some advantages and could be noticed in the semiconductor industry.

碩士
清雲科技大學
電機工程所
99
The aim of this study is to create a self sufficient, environmentally friendly, and sustainable energy source by using solar fuel cells and advanced energy storage devices as the primary energy source for a distributed power system. Solar energy is affected by time of the day and climate changes. As a result, fuel concentration is inconsistent and the power is unstable. The advanced energy storage system stores electricity generated from solar panels, fuel cells in batteries. The charging and discharging system controls the energy storage to keep the power system stable. This is especially important when solar energy and fuel cell are in low voltage. To achieve a stable power system the digital signal processor (TMS320LF2407) of digital power conversion solar changing system is the main control centre in the system. It''s energy conversion efficiency is 84.5%. Using the advanced energy storage devices and distributed power generation systems, we can reduce electricity usage during peak hours, thus reducing cost. The results reinforces the current ideas of environmental preservation and sustainability.

碩士
臺灣大學
材料科學與工程學研究所
98
Advanced lithography has been widely applied on the field of optoelectroincs. Because of the advantages of fast manufacturing and convenience, advanced lithography is competive againest tranditional photolithography and e-beam lithography. In this article, we successfully fabricated one-dimensional corrugated structure and two-dimensional hexagonal hole array on gold films. Because these subwavelength periodical metal structures are capable to induce surface plasmon resonance, they have the potential to be chemical sensors. We fabricate a chemical sensor based on one-dimensional corragted gold film and demonstrate that this chemical sensor possesses extremely high sensitivity. Moreover, the comparison between the chemical sensors based on one-dimensional and two dimensional strucuture is also carried out in this article. Besides, we used the dual side nanoimprint lithography to fabricate a high aspect ratio gratings strucuture on PC substrate. This subwavlength gratings structure has demonstrated the form birefringence, and thus has the potential to be optical wave plate. With contolling the filling factor and trench depth of the gratings structure, we successfully fabricate a 1/8 wave plate that works at 633nm. Moreover, with stacking numerical wave plate together, we can obtain any amount of phase retardation. This stacking-wave plate method is suitable for any working wavelength if we presicely control the trench depth of each gratings-based wave plate. In the last, we use the colloidal lithography to fabricate a transparent electrode based on metal nanomesh structure. For applying on photovoltaic devices, the nanomesh metal electrode has the advantages of highly optical transmittance and excellent conductivity. The period and diameter of the hexagonal hole array on nanomesh can be tuned by the fabricating parameters of colloidal lithography. The organic solar cells associated with the transparent nanomesh electrode demonstrate a high power conversion efficiency, and we conclude that the metal nanomesh electrode is a promising candidate for replacing traditional conductive oxide such as ITO.

碩士
逢甲大學
土木工程所
94
In recent year, the cost of conventional design is raised with promoting the earthquake-resist standard and economic benefits has not been found as before. Government and academia are actively to encourage and investigate how to promote the earthquake-resist capability of structure. Passive control technology has been proved as the efficient method in seismic mitigation by analysis, experiment and real application. Among earthquake proof devices, reinforced added damping and stiffness (RADAS) with sufficient ductility and stable behavior is acknowledged as the efficient energy dissipation device, and this device possess some advantages such as low cost in fabrication, convenient for installation and maintenance. Therefore, RADAS is widely used to absorb the energy induced by earthquake on the real life practice. In this thesis, the transform method which replaces the properties of RADAS is used to construct the capacity spectrum of structure with RADAS, and expect to simplify the nonlinear analysis process for structure with RADAS.

博士
國立清華大學
工程與系統科學系
103
This thesis focuses on the advanced devices based on the metal-insulator-metal (MIM) structure, the first one is MIM capacitor, and another one is resistive random access memory (RRAM). The first part is MIM capacitor, our works revolve around how to suppress the quadratic voltage coefficient of capacitance, so called, VCC-α. However, VCC-α will become larger as the dielectric constant of oxide increases that brings out our main goal, how to increase the capacitance density but suppress VCC-α at the same time. In this part, we adopted amorphous TiO2 and Y2O3 stack as dielectric of MIM capacitor, the main reason is that yttrium has larger atom radius would let TiO2 maintain in amorphous phase. Hence, after annealed TiO2/Y2O3 shows higher capacitance density but TiO2 stays in amorphous state at the same time. Due to capacitance density and VCC-α has an inverse relationship, so we need to utilize another way called “canceling effect” of VCC-α. Canceling effect is achieved by two different oxide films, one has positive VCC-α and another one has negative VCC-α. Compare to adopt only one oxide film, once stack these two oxide films the effective VCC-α will become smaller due to positive VCC-α and negative VCC-α compensates each other. Furthermore, by utilizing the crystalline TiO2 to get higher capacitance density, but the VCC-α will become larger rapidly at the same time. To reduce the VCC-α, nitrogen plasma treatment on the surface of crystalline TiO2 was adopted; moreover, to further suppress the VCC-α, SiO2 is stacked on the crystalline TiO2 because of SiO2 has negative VCC-α that can compensate the positive VCC-α introduced by crystalline TiO2. In this work, MIM capacitor shows 30 ppm/V2 of VCC-α, 11.2 fF/μm2 of capacitance density, these results fit the requirements of MIM capacitor in 2018 by ITRS. But compare to novel metal oxide, SiO2 has much lower dielectric constant (κ) value, so the next part is replacing SiO2 to ZrTiOx. It is worth to mention that ZrTiOx demonstrates negative VCC-α characteristic like SiO2, but has much higher κ value, 22.5. Thus, the results of this work we got a much higher capacitance density of 14.38 fF/μm2 and 68 ppm/V2 of VCC-α. In the RRAM topic, we spent lots of effort to discuss how the property of ZrTiOx affects the electrical characteristics of RRAM. First, we explored the influence of crystalline ZrTiOx compared to amorphous one. Second, we examined how the position of IL effects switching mechanism, based on this, we planned three experiments each has different IL position, one has no IL, another has an IL on the bottom electrode and the last one has IL on the both top and bottom electrode. In this series experiments, we found that amorphous ZrTiOx demonstrates better uniformity, lower switching voltage, faster switching speed and larger sense margin; on the other hand, the position of IL is a critical factor that affects switching voltage, thus, IL could be modulated to achieve higher switching speed and better power consumption. In summary, one-sided IL shows better electrical characteristics. In addition, if we want to achieve higher storage capacity, 3D stack structure is an inevitable solution; however, to avoid the misread situation due to unexpected current flow, for one RRAM device we need another diode to form a 1D1R structure. In this work, we combined a simple metal-semiconductor diode and a RRAM to a TaN/ZrTiOx/Ni/n+-Si structure, the advantages are following, first, this structure is compatible with the incumbent ULSI technology; second, reduced the cost due to discard the expensive and hardly processing metal, such as W and Pt. Additionally, this structure is combined the one-sided IL formation that will further improve the electrical characteristics of RRAM.

博士
國立臺灣大學
電子工程學研究所
99
SiGe epitaxial growth by ultra-high vacuum chemical vapor deposition has been investigated in this dissertation. The SiGe quantum dots (QDs) and nanorings were fabricated for the applications of the photodetectors, while the SiGe quantum wells (QWs) and the SiGe graded buffer layers (GBLs) were fabricated for the applications of the metal-oxide-semiconductor field effect transistors (MOSFETs) and the insulator-gate field effect transistors (IGFETs). In the first part of this thesis, the growth mechanisms of the SiGe QWs and SiGe QDs have been discussed. The carrier gas effects on the growth of the QWs and QDs are also discussed. The hydrogen passivation, which can influence the Ge concentration and the strain in the SiGe nanostructures, plays a crucial role in the SiGe QWs and SiGe QDs growth. Moreover, the device applications are also introduced. The MOSFETs fabricated from the SiGe QWs grown on Si(100), Si(110), and Si(111) have been discussed. The higher mobility in the <110> direction of Si and SiGe is due to the smaller conductive effective mass. The quantum dot infrared photodetectors (QDIPs) made by the multi-layer SiGe QDs substrate have also been demonstrated. After the discussion on the growth of the SiGe QWs and QDs, the SiGe nanorings have also been investigated. The Si surface diffusion mechanism and the Ge out-diffusion mechanism were proposed for nanorings formation at 600oC and 500oC, respectively. The SiGe nanorings created by Ge out-diffusion show controllable depth and well-defined Ge content at edges. The novel nanoring structures can be used in new optoelectronic devices. Moreover, the surface orientation effects on SiGe QDs and nanorings formation are investigated. The base shapes of SiGe QDs and nanorings can be controlled by different surface orientation. In the third part of this thesis, the two dimensional electron gas (2DEG) devices with the world record high 2DEG mobility have been investigated. The 2DEG in a Si QW on SiGe GBLs with the world record high mobility of 1.6×106 cm2/Vs at carrier densities n~1.5×1011 /cm2. On the other hand, the complementary devices on an undoped Si/SiGe substrate where both 2D electrons and holes have also been investigated. A p-channel FET is characterized and the operation of an inverter is demonstrated. Moreover, the limitations of the two dimensional electron densities and 2DEG mobility have been discussed. The scattering from remote dopants, background impurities, interface roughness, and threading dislocations can all degrade the mobility in SiGe heterostructures. Based on the knowledge above, we have successfully improved the 2DEG mobility to 2×106 cm2/Vs by changing the substrate structures. Finally, the growth mechanism of the Si on Ge growth was investigated. The transition from 3-dimensional (3D) to 2-dimensional (2D) growth for Si on Ge, which is different from the Ge on Si case, was observed for the first time. The Si quantum dots can be observed in the initial Si growth on Ge. With the increasing Si deposition, the ring-like structures appeared. Finally, the flat surface without any nanostructures above can be observed. The tensile strain to enhance surface mobility of Si atoms favors proposedly the lateral growth, and leads to the three to two dimensional growth. The flatter Si layer growth directly on Ge can be used for the application of novel nanoelectronics and optoelectronics devices.

Carbon nanotubes (CNTs) have recently emerged as promising candidates for electron field emission (FE) cathodes in integrated FE devices. These nanostructured carbon materials possess exceptional properties and their synthesis can be thoroughly controlled. Their integration into advanced electronic devices, including not only FE cathodes, but sensors, energy storage devices, and circuit components, has seen rapid growth in recent years. The results of the studies presented here demonstrate that the CNT field emitter is an excellent candidate for next generation vacuum microelectronics and related electron emission devices in several advanced applications.

The work presented in this study addresses determining factors that currently confine the performance and application of CNT-FE devices. Characterization studies and improvements to the FE properties of CNTs, along with Micro-Electro-Mechanical Systems (MEMS) design and fabrication, were utilized in achieving these goals. Important performance limiting parameters, including emitter lifetime and failure from poor substrate adhesion, are examined. The compatibility and integration of CNT emitters with the governing MEMS substrate (i.e., polycrystalline silicon), and its impact on these performance limiting parameters, are reported. CNT growth mechanisms and kinetics were investigated and compared to silicon (100) to improve the design of CNT emitter integrated MEMS based electronic devices, specifically in vacuum microelectronic device (VMD) applications.

Improved growth allowed for design and development of novel cold-cathode FE devices utilizing CNT field emitters. A chemical ionization (CI) source based on a CNT-FE electron source was developed and evaluated in a commercial desktop mass spectrometer for explosives trace detection. This work demonstrated the first reported use of a CNT-based ion source capable of collecting CI mass spectra. The CNT-FE source demonstrated low power requirements, pulsing capabilities, and average lifetimes of over 320 hours when operated in constant emission mode under elevated pressures, without sacrificing performance. Additionally, a novel packaged ion source for miniature mass spectrometer applications using CNT emitters, a MEMS based Nier-type geometry, and a Low Temperature Cofired Ceramic (LTCC) 3D scaffold with integrated ion optics were developed and characterized. While previous research has shown other devices capable of collecting ion currents on chip, this LTCC packaged MEMS micro-ion source demonstrated improvements in energy and angular dispersion as well as the ability to direct the ions out of the packaged source and towards a mass analyzer. Simulations and experimental design, fabrication, and characterization were used to make these improvements.

Finally, novel CNT-FE devices were developed to investigate their potential to perform as active circuit elements in VMD circuits. Difficulty integrating devices at micron-scales has hindered the use of vacuum electronic devices in integrated circuits, despite the unique advantages they offer in select applications. Using a combination of particle trajectory simulation and experimental characterization, device performance in an integrated platform was investigated. Solutions to the difficulties in operating multiple devices in close proximity and enhancing electron transmission (i.e., reducing grid loss) are explored in detail. A systematic and iterative process was used to develop isolation structures that reduced crosstalk between neighboring devices from 15% on average, to nearly zero. Innovative geometries and a new operational mode reduced grid loss by nearly threefold, thereby improving transmission of the emitted cathode current to the anode from 25% in initial designs to 70% on average. These performance enhancements are important enablers for larger scale integration and for the realization of complex vacuum microelectronic circuits.

Dissertation

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
O objetivo desta dissertação consiste na descrição do projeto desenvolvido com o propósito de criar uma interface completamente nova, que implementa tecnologias de Realidade Mista para a programação e monitorização de robôs manipuladores. Esta interface tem como intuito principal expandir o número de pessoas com capacidades para programar e monitorizar robôs manipuladores, ao tornar o conhecimento avançado de linguagens de programação um requerimento opcional e não fundamental. A motivação para este projeto começa pela vontade de proporcionar avanços em interfaces de comunicação Homem-Máquina (IHM), e na demonstração das vantagens proporcionadas pelas tecnologias de Realidade Mista na monitorização e programação de processos robóticos avançados (Produção aditiva, robôs colaborativos, entre outros). Ter acesso direto a informação como conteúdo visual aplicado no espaço e em tempo real, antecipar trajetórias, ou até modificar o movimento de um robô através de som ou gestos manuais, são algumas das grandes vantagens proporcionadas por esta tecnologia.O projeto desenvolvido durante a realização desta tese de mestrado resultou na criação de duas aplicações para um Microsoft HoloLens, ambas com propósitos diferentes. A primeira aplicação (Path Visualization) consiste numa interface de realidade mista que permite aos utilizadores o total controlo sobre um robô manipulador e ao mesmo tempo uma completa monitorização das trajetórias realizadas pelo mesmo. A segunda aplicação (Graphical Path Manipulation) consiste num novo ambiente de realidade mista que permite que os utilizadores criem uma trajetória nova para o robô, facilmente ajustável sempre que necessário, e também proporciona a possibilidade de alterar os parâmetros inerentes ao movimento do robô. Todas as trajetórias são depois enviadas pela aplicação para o robô real que as executa como definido. Esta dissertação apenas terá foco no desenvolvimento realizado pelo escritor, que consiste nas aplicações de realidade mista para o Microsoft HoloLens. As aplicações foram realizadas utilizando os softwares Unity3D, Vuforia e Visual Studio.Apesar do projeto não ser direcionado para uma tarefa especifica, pode ser facilmente adaptado para uma, estando o conceito disponível para avanços futuros.
The main goal of this Master Thesis’ dissertation consists in describing a new project developed with the purpose to create a completely new interface, which provides a generic implementation of Mixed Reality to monitor, optimize and program robot manipulators’ tasks. This interface will hopefully expand the range of people with capabilities to program industrial robots, since the advanced knowledge of programming languages will be an optional requirement. The motivation for this project begins with the will to improve Human-Machine Interfaces (HMI) and to demonstrate that an approach with Mixed Reality can lead to huge improvements in monitoring and programming advanced robotic tasks, such as Additive-manufacturing, collaborative robots, amongst others. Perceiving information as direct visual content, in real time, anticipate trajectories, or even apply modifications to a robot motion with gesture or sound inputs, are some of the great advantages of this technology. The project developed in this master thesis resulted in two apps for a Microsoft HoloLens each with different purposes. The first (Path Visualization) is a Mixed Reality interface that allows users to control a robotic manipulator, visualize its movement and fully monitor the task assigned to the robot. The second app (Graphical Path Manipulation) is a new Mixed Reality environment that allows users to create a completely new path or adjust one, as well as enabling the possibility to change motion parameters and teach the new/adjusted path trajectory to the robot. This Master Thesis will focus on all the development, made by the writer, to create the Mixed Reality applications for the Microsoft HoloLens. This was possible using the Unity3D, Vuforia and Visual Studio software interfaces.Although this project’s purpose is not to focus on a specific industrial task, it can be easily adapted posteriorly to any kind of robotic task desired. The concept however is open for further studies.

abstract: Group IV alloy films exhibit the ability to tune both band structure and lattice parameters and have recently attracted attention for their potential applications in Si-photonics and photovoltaics. In this work, several new approaches to produce these alloys directly on Si(100) and Ge(100) wafers are developed. For photovoltaics, use of Ge-buffered Si(100) wafers as a low cost platform for epitaxy of In1-xGaxAs layers was explored. The results indicate that this approach has promise for transitioning from bulk Ge platforms to virtual substrates for a significant cost reduction. The electrical and optical properties of Ge and Ge1-ySny layers produced using several different techniques were explored via fabrication of high performance heterostructure photodiodes. First, a new CVD approach to Ge-like materials was developed in which germanium is alloyed with very small amounts of tin. These alloys exhibited no significant difference in their structural properties or band gap compared to pure Ge, however superior photo response and reduced dark currents were observed from fabricated devices relative to pure Ge on Si reference diodes. Additionally, pure Ge/Si(100) photodiodes were fabricated using layers grown via reactions of Ge4H10 on Si(100) and found to exhibit low dark current densities with high collection efficiencies. Ge1-x-ySixSny materials represent the newest member of group IV alloy family. The ability to decouple the lattice constant and the band gap in this system has led to strong interest both for strain/confinement layers in quantum well structures, and as the possible "missing" 1 eV junction in multijunction photovoltaics. Recent progress in this field has allowed for the first time growth, fabrication and measurement of novel photodiodes based on Ge1-x-ySixSny. This work presents the material, electrical and optical properties of Ge1-x-ySixSny layers and photodiodes grown directly on Ge and Si wafers using two different synthetic approaches. A series of photodiodes containing Sn concentrations from 1-5%, all lattice matched to Ge, was fabricated. The devices exhibited low dark current densities with high collection efficiencies as required for photovoltaics. By measuring the photoresponse, tunable band gaps ranging from 0.85 eV to 1.02 eV were observed.
Dissertation/Thesis
Ph.D. Chemistry 2012

La Realtà Aumentata (AR) promette di creare collegamenti diretti, automatici e azionabili tra il mondo fisico e le informazioni elettroniche. Fornisce un'interfaccia utente immediata e diretta ad un mondo fisico potenziato elettronicamente. In particolare, la AR industriale permette l'integrazione tra le informazioni basate sulla conoscenza, tradizionalmente utilizzate dagli operatori e fornite principalmente sotto forma di documentazione cartacea e di dati disponibili dai sensori sulle attrezzature. Questo approccio è suggerito dalle aziende, soprattutto dalle piccole e medie imprese, che desiderano un'introduzione graduale delle tecnologie di Industria 4.0 all'interno delle loro pratiche consolidate. Lo scopo di questo lavoro è quello di sviluppare un sistema avanzato di documentazione tecnica in AR per un impianto di macinazione di farina. Il lavoro discusso in questa tesi mira a portare un valore aggiunto alla letteratura esistente nel campo dell'AR industriale e della documentazione tecnica avanzata. Inoltre, si cercherà di far luce sul ruolo dell'AR come tecnologia abilitante per l'industria del futuro. In primo luogo, ci siamo concentrati su diverse interfacce AR industriali al fine di comprendere le pratiche consolidate per guidare la progettazione dell'interfaccia IAR. Poi, indaghiamo la tecnologia chiave AR con un nuovo approccio basato sulla ricerca sui brevetti. Infine, il risultato principale di questo lavoro è la progettazione e lo sviluppo di due sistemi AR per un impianto di macinazione della farina che seguono due diversi approcci di progettazione.
Augmented Reality (AR) promises to create direct, automatic, and actionable links between the physical world and electronic information. It provides an immediate and straightforward user interface to an electronically enhanced physical world. In particular, Industrial AR allows the integration between knowledge-based information, traditionally used by operators and provided mainly in paper documentation and data available from sensors on equipment. This approach is suggested by companies, especially small and medium-sized enterprises, who want a gradual introduction of Industry 4.0 technologies within their established practices. The scope of this work is to develop an advanced technical documentation system in AR for a flour milling plant. The work discussed in this dissertation aims to bring added value to the existing literature in the field of industrial AR and advanced technical documentation. Besides, an attempt will be made to shed light on the role of AR as an enabling technology for the industry of the future. First, we focused on different industrial AR interfaces in order to understand established practices to guide IAR interface design. Then, we investigate the AR key technology with a novel approach based on patent research. Finally, the main result of this work is the design and development of two AR systems for a flour milling plant that following two different design approaches.