Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 235-239).

<p>The objective of this thesis is to evaluate a generic process for fabrication and characterization of the Superconductive coplanar waveguide (CPW) resonators. Superconductive CPW resonators with various lengths and shapes are designed to investigate their electrical and magnetic properties as well as resonance properties and sensitivities. In the first part of thesis, two different models are introduced in order to estimate the nonlinear kinetic inductance of a superconducting CPW resonator. The first model is based on Bean critical-state model and the second one is based on current dependence of London penetration depth. The existence of a shift in resonant frequency  of Superconductive CPW resonator caused by a non-linear kinetic inductance is also shown experimentally. Simulations were carried out to estimate the nonlinear kinetic inductance due to the self- induced magnetic field penetration.</p><p>The rest of the thesis is concerned with development of very smooth Aluminum (Al) thin films with RMS (Root Mean Square) roughness 1~nm and CAD (Computer Aid Design) of superconductive CPW resonators. Experimental investigation of a generic fabrication technique for superconductive CPW resonator is carried out. Many resonators are fabricated with different design parameters, such as centerline or gap width, film thickness and gap capacitors length. The fabrication process is described in detail. Electron Beam Lithography is used to fabricate Nb and Al CPW resonators which are coupled to outer conductors via gap capacitors. We have fabricated GHz frequency CPW resonators with quality factors, Q up 5X10^5.</p>

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Orientadores: Edson Moschim, Oscar Ferreira de Lima / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-10T22:58:29Z (GMT). No. of bitstreams: 1 Vieira_KleberBetini_M.pdf: 5146160 bytes, checksum: 696a41837ed744dda41722755ffb45c3 (MD5) Previous issue date: 2008 / Resumo: Desde a descoberta do fenômeno da supercondutividade no diboreto de magnésio (MgB2) no ano 2001, a dinâmica dos vórtices neste material tem sido muito estudada, pois este fenômeno pode causar a destruição do estado supercondutor. Este trabalho tem o objetivo de avaliar o impacto no aprisionamento dos vórtices e analisar o comportamento da densidade de corrente crítica (Jc) em amostras de MgB2 misturadas com nanopartículas de níquel (Ni) em várias proporções. As amostras foram preparadas no National Physical Laboratory (Índia). Os pós de Mg e B foram misturados em proporções estequiométricas e mantidos em uma atmosfera de argônio (Ar) por 5h a 800 ºC. Em seguida, foram misturadas as nanopartículas de Ni com 0,5%, 1%, 2%, 3% e 5% em relação à massa da amostra de MgB2. A seguir elas foram homogeneizadas, prensadas e sinterizadas. Foram realizadas medições, em um sistema PPMS (Physical Property Measurement System) da Quantum Design, do: a) momento magnético em função da temperatura, para a determinação da temperatura crítica Tc das amostras; e b) momento magnético DC em função do campo magnético aplicado, para determinar o laço de histerese magnética das amostras. Com auxilio do Modelo de Bean foi determinada a corrente crítica Jc. Através de técnicas de mapeamento por imagem foram analisados: a) os domínios magnéticos presentes na amostra, através das técnicas de Microscopia de Força Atômica e de Força Magnética (AFM/MFM); e b) a granulometria média e homogeneidade, pela técnica de Microscopia Eletrônica de Varredura com detecção de Energias dos Raios-X Dispersos (MEV-EDX). Com o auxílio da Difração de Raios-X (DRX) foi analisada a formação da matriz de MgB2 e sua alteração com as adições do Ni, a formação de novos compostos e a presença de contaminantes. Através do nosso estudo podemos observar que as nanopartículas de Ni causaram o aprisionamento dos vórtices de Abrikosov, gerando um aumento na densidade de corrente crítica do MgB2. Apesar de uma pequena fração de Ni ter sido dissolvido na estrutura cristalina do MgB2, a degradação da temperatura crítica causada não é relevante frente ao aumento de Jc / Abstract: Since the discovery of the phenomenon of superconductivity in magnesium diboride (MgB2) in the year 2001, the vortex dynamics in this material has been widely studied, because this phenomenon can cause the destruction of the superconducting state. This study intends to assess the impact on the pinning of vortex and the behavior of the critical current density (Jc) in samples of MgB2, mixed with nickel nanoparticles in many proportions. Samples were prepared at the National Physical Laboratory (India). The Mg and B powders were mixed in stoichiometric proportion and maintained in an atmosphere of argon (Ar) for 5h at 800 °C. Then, they were mixed with the Ni nanoparticles in fractions of 0.5%, 1%, 2%, 3% and 5% of the mass of the sample. After they were homogenized, pressed and sintered. The following measurements were performed in a PPMS (Physical Property Measurement System) of Quantum Design: a) magnetic moment as a function of temperature, for determining the critical temperature Tc of the samples, and b) DC magnetic moment as a function of applied magnetic field, to determine the magnetic hysteresis loop of the samples. Using the Bean Model the critical current (Jc) was determined. Through techniques of image mapping there were analyzed: a) the magnetic domains present in the sample, through the techniques of Atomic Force Microscopy, and Magnetic Force (AFM / MFM), and b) the average grain size and uniformity by the technique of Scanning Electron Microscopy with the detection of dispersive X-ray energies (SEM-EDX). With the aid of X-Rays Diffraction (DRX) there has been examined the formation of the matrix MgB2 and the effects of Ni additions, the formation of new compounds and the presence of contaminants. Through our study we could observe that the Ni nanoparticles of lead to the pinning of Abrikosov vortices, generating an increase in the critical current density of the MgB2. Despite a small fraction of Ni that was dissolved in the crystal structure of MgB2, the degradation of the critical temperature is not relevant in face of the Jc increase / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Les études concernent le développement de dispositifs supraconducteurs de détection de photon unique. Le nitrure niobium (NbN) est un matériau adapté à l’élaboration de fils supraconducteurs de la cible du détecteur. Ces travaux ouvrent des perspectives sur l’élaboration de films de nitrure de niobium épitaxié sur saphir par la méthode de dépôt chimique en phase vapeur (CVD). L’élaboration des films minces (5-100 nm) est effectuée à haute température (1000°C à 1300°C) à partir de chlorure de niobium et d'ammoniaque dilués dans l'hydrogène (H2-NH3-NbCl5). Les substrats sont du saphir monocristallin (Al2O3) orienté (0002), du nitrure d'aluminium (AlN) orienté (0002) et de 'oxyde de magnésium (MgO) orienté (100).L'étude des relations d’épitaxie au cours de la croissance du nitrure de niobium sur le substrat de saphir a tout d'abord été effectuée. L’observation des microstructures et des orientations cristallines des différents films élaborés a permis de mettre en évidence les relations existant entre l'état de surface du substrat et le mode de croissance du NbN. Les perspectives d'utilisation de substrats monocristallins de type MgO et AlN sont présentées en conclusion.L’étude du procédé de croissance et les relations existant entre les conditions d'élaboration et la "qualité" des films minces a permis de dégager les fenêtres expérimentales conduisant à une croissance épitaxiale. L’énergie d’activation des réactions de croissance et les conditions de sursaturation propices à la croissance épitaxiale ont été calculées.L'étude des relations entre les propriétés structurales et les caractéristiques supraconductrices des films a permis de relier la température de transition supraconductrice à la densité de défauts atomiques, aux défauts microstructuraux, à l’épaisseur des films élaborés et à leur état de contrainte. Il existe une relation linéaire entre l’espace interréticulaire des plans parallèles au substrat et la température de transition supraconductrice.Enfin, l'étude de la durabilité des films ultraminces (5 – 8 nm) de nitrure de niobium a été menée. Dans cette étude les propriétés électriques et supraconductrices de films élaborés à 1000°C et 1200°C sur des substrats de saphir et de couches épitaxiales d'AlN ont été analysées sur une durée de six mois. Les propriétés des films évoluent surtout au cours du premier mois. Le dépôt effectué à haute température permet de limiter la dégradation rapide des films et de conserver leurs propriétés supraconductrices. / The studies concern the development of superconducting devices for single photon detection. Niobium nitride (NbN) is a material suitable for the production of superconducting wires for the detector target. This work is opening up perspectives on the development of epitaxial niobium nitride films on sapphire by the chemical vapor deposition (CVD) method. The production of thin films (5-100 nm) is carried out at high temperature (1000°C to 1300°C) from niobium chloride and ammonia diluted in hydrogen (H2-NH3-NbCl5). The substrate is oriented single crystalline sapphire (Al2O3) (0002), aluminum nitride (AlN) (0002) or magnesium oxide (MgO) (100).The study of epitaxial relationships during the growth of niobium nitride on the sapphire substrate was first performed. Observation of the microstructures and crystalline orientations of the various films processed made it possible to highlight the relationships between the surface state of the substrate and the growth mode of NbN. The potential for using single crystal substrates such as MgO and AlN is discussed in the conclusion.The study of the growth process and the relationships between the working conditions and the "quality" of thin films made it possible to identify the experimental windows leading to epitaxial growth. The activation energy of the growth reactions and the supersaturation conditions favorable to epitaxial growth were calculated.The study of the interactions between the structural properties and superconducting properties of films has allowed the superconducting transition temperature to be linked to the density of atomic defects, microstructural defects, the thickness of the films and their stress state. There is a linear relationship between the interplanar space of planes parallel to the substrate and the superconducting transition temperature.Finally, the durability of ultra-thin films (5 - 8 nm) of niobium nitride was studied. The electrical and superconducting properties of films processed at 1000°C and 1200°C on sapphire substrates and epitaxial layers of AlN were analyzed over a period of six months. The properties of films change most notably during the first month. High temperature deposition limits the rapid degradation of the films and preserves their superconducting properties.

The objective of this thesis is to evaluate a generic process for fabrication and characterization of the Superconductive coplanar waveguide (CPW) resonators. Superconductive CPW resonators with various lengths and shapes are designed to investigate their electrical and magnetic properties as well as resonance properties and sensitivities. In the first part of thesis, two different models are introduced in order to estimate the nonlinear kinetic inductance of a superconducting CPW resonator. The first model is based on Bean critical-state model and the second one is based on current dependence of London penetration depth. The existence of a shift in resonant frequency  of Superconductive CPW resonator caused by a non-linear kinetic inductance is also shown experimentally. Simulations were carried out to estimate the nonlinear kinetic inductance due to the self- induced magnetic field penetration. The rest of the thesis is concerned with development of very smooth Aluminum (Al) thin films with RMS (Root Mean Square) roughness 1~nm and CAD (Computer Aid Design) of superconductive CPW resonators. Experimental investigation of a generic fabrication technique for superconductive CPW resonator is carried out. Many resonators are fabricated with different design parameters, such as centerline or gap width, film thickness and gap capacitors length. The fabrication process is described in detail. Electron Beam Lithography is used to fabricate Nb and Al CPW resonators which are coupled to outer conductors via gap capacitors. We have fabricated GHz frequency CPW resonators with quality factors, Q up 5X10^5.

This dissertation is the result of research and development of a power conditioning system for Superconductive Magnetic Energy Storage System. The dominant challenge of this research was to develop the power conditioning system that can match slowly varying dc voltage and dc current on the super conductive magnet side with the ac voltages and ac currents on the utility side. At the same time the power conditioning system was required to provide a bi-directional power flow to the superconductive magnet. The focus of this dissertation is a three-level diode clamped dc-ac converter which is a principle part of the power conditioning system. Accordingly, this dissertation deals with the space vector modulation of three-level converters and introduces a computationally very efficient three-level space vector modulation algorithm that is experimentally verified. Furthermore, the proposed space vector modulation algorithm is successfully generalized to allow equally efficient, real time implementation of space vector modulation to dc-ac converters with virtually any number of levels. The most important advantage of the proposed concept is in the fact that the number of instructions required to implement the algorithm is almost independent from the number of levels in a multilevel converter. More on the side of the control of multilevel converters, the particular attention in this dissertation is paid to the problem of charge balance in the split dc-link capacitors of three-level neutral-point-clamped converters. It is a known fact that although the charge balance in the neutral point can be maintained on a line cycle level, a significant third harmonic current flows into the neutral point for certain loading conditions, causing the neutral point voltage ripple. The logical consequence of that ripple is the deteriorated quality of the output voltage waveforms as well as the increased voltage stress on the switching devices. This was the motivation to more carefully explore the loading conditions that cause the unbalance, as well as to study the fundamental limitations of dc-link capacitor charge balancing algorithms. As a part of that work, a new model of the neutral point current in the rotating coordinate frame is developed as a tool in investigation of theoretical limitations and in providing some intuitive insight into the problem. Additionally, the low frequency ripple is quantified and guidelines are offered that can help size the dc-link capacitors. Because the study of the neutral point balance identified the loading conditions, that under some possible system constraints, cause an unavoidable neutral point voltage ripple, a feed forward type of control method is developed next. The proposed feed forward algorithm can effectively prevent the neutral point voltage ripple from creating distortions in the converter output voltage under all loading conditions and without causing additional disturbance in the neutral point voltage. The feed forward method is developed for a sine triangle as well as for the space vector type PWM algorithm. The simulation results that include the full dynamic model of the converter and load system validate the feed forward approach and prove that the feed forward algorithm can effectively compensate the effect of the neutral point voltage ripple. The simulation results are than experimentally verified. / Ph. D.