Global ETD Search

1	Development of single wall carbon nanotube transparent conductive electrodes for organic electronics Jackson, Roderick Kinte' 22 June 2009 (has links) Organic electronic devices are receiving growing interest because of their potential to employ lightweight, low-cost materials in a flexible architecture. Typically, indium tin oxide (ITO) is utilized as the transparent positive electrode in these devices due to its combination of high transmission in the visible spectrum and high electrical conductivity. However, ITO may ultimately hinder the full market integration of organic electronics due to its increasing cost, the limited availability of indium, lack of mechanical flexibility, and sustainability with regards to the environment and material utilization. Therefore, alternatives for ITO in organic electronics are currently being pursued. Transparent electrodes comprised of single wall carbon nanotubes (SWNTs) are an appealing choice as a surrogate because of the extraordinary electrical and mechanical properties these 1-D structures posses. As such, the research presented in this dissertation has been conducted to advance the goal of manufacturing SWNT networks with transparent electrode properties that meet or exceed those of ITO. To this end, SWNT films were characterized with regard to the collective and individual optoelectronic properties of the SWNTs that comprise the network. Specifically, corroborative theoretical and experimental observations were employed to expand the understanding of how the optoelectronic properties of polydisperse and monodisperse SWNT networks are enhanced and sustained through chemical treatment and subsequent processing. In addition, the impact of interfacial electrical contact resistance between SWNT electrodes and metallic fingers often used in photovoltaic system applications was elucidated. In summary, the research presented in this dissertation can be leveraged with present state of the art in SWNT films to facilitate future SWNT electrode development. Carbon nanotubes SWNT film Specific contact resistance Transparent electrodes Contact resistance SWNTs Organic electronics Nanotubes Electrodes, Carbon Light emitting diodes
2	Diagnostic de l'asthme chez l'enfant par la réversibilité de l'obstruction bronchique / Diagnosis of asthma in children by reversibility of bronchial obstruction Balan Ioan, Iulia-Cristina 05 November 2014 (has links) Des techniques d’exploration de la fonction respiratoire nécessitant une coopération minimale, réalisables en ventilation spontanée, sans anesthésie, sont nécessaires chez les jeunes enfants asthmatiques. De telles méthodes sont la mesure de l’impédance respiratoire par la technique des oscillations forcées, la mesure de la résistance spécifique des voies aériennes par pléthysmographie ou la capnographie qui mesure la concentration de CO2 dans le gaz expiré. L’objectif principal de travail a été l’amélioration du diagnostic de l’asthme infantile en utilisant des études cliniques et fondamentales. Une étude clinique incluant des enfants asthmatiques et témoins a montré que la spécificité de la résistance est améliorée en expiration par rapport à l’inspiration du au fait que la fermeture de la glotte à l’expiration est proportionnelle au degré de l’obstruction bronchique. Une autre étude a démontré que le diagnostic de l’asthme est amélioré par le calcul des variations d’admittance respiratoire à un bronchodilatateur, ce calcul n’étant pas influencé par l’artefact des voies aériennes supérieures. Une étude a montré que la mesure de la résistance spécifique des voies aériennes en ventilation spontanée est surestimée par rapport à la mesure en halètement. La capnographie est une méthode noninvasive qui donne des renseignements sur l’inhomogénéité de la ventilation pendant une obstruction bronchique aigue. Toutefois, elle peut être limitée chez le jeune enfant par une fréquence ventilatoire élevée. Une étude expérimentale a été menée chez le lapin pour valider les indices capnographiques à différentes fréquences ventilatoires pour identifier la présence d’une obstruction aigue / Shorter lung function testing methods are needed in young asthmatic children, requiring minimal cooperation, performed in spontaneous breathing, without anaesthesia. Such methods are measurement of respiratory impedance by forced oscillations technique, measurement of specific airway resistance by plethysmography or capnography, measurement of CO2 concentration in expired air. The main objective of this work was to improve pediatric asthma diagnosis by using clinical and experimental studies. A study including asthmatic and control children showed that the specificity of resistance was improved in expiration compared to inspiration due to the fact that the glottis closure during expiration was proportional to the degree of airway obstruction. Another clinical study demonstrated that asthma diagnosis was improved by computation of respiratory admittance response to a bronchodilator because this computation is not affected by upper airways artifact. A study showed that specific airway resistance measured during spontaneous breathing was overestimated compared to panting metthod. Capnography is a non invasive technique. The shape of the expired CO2 time course is altered by the non homogenous distribution of ventilation resulting from bronchoconstriction. But its clinical usefulness in young children may be limited by the relatively high respiratory rate. An experimental study was conducted in rabbits to validate capnogram shape indices at different rates of breathing during airway constriction by methacholine. The indices have detected the acute airway obstruction even at high frequencies, frequencies usually presented by infants during an acute bronchoconstriction Asthme Enfant Réversibilité Oscillations forcées Capnographie Asthma Child Reversibility Forced oscillations Capnography Specific airway resistance 618.922 38
3	Fabrication and Characterization of Silicon Carbide Power Bipolar Junction Transistors Lee, Hyung-Seok January 2008 (has links) Silicon carbide bipolar junction transistors (BJTs) are attractive power switching devices because of the unique material properties of SiC with high breakdown electric field, high thermal conductivity and high saturated drift velocity of electrons. The SiC BJT has potential for very low specific on-resistances and this together with high temperature operation makes it very suitable for applications with high power densities. For SiC BJTs the common emitter current gain (β), the specific on-resistance (RSP_ON), and the breakdown voltage are important to optimize for competition with silicon based power devices. In this thesis, power SiC BJTs with high current gain β ≈ 60 , low on-resistance RSP_ON ≈ 5 mΩcm2, and high breakdown voltage BVCEO ≈ 1200 V have been demonstrated. The 1200 V SiC BJT that has been demonstrated has about 80 % lower on-state power losses compared to a typical 1200 V Si IGBT chip. A continuous epitaxial growth of the base-emitter layers has been used to reduce interface defects and thus improve the current gain. A significant influence of surface recombination on the current gain was identified by comparing the experiments with device simulations. In order to reduce the surface recombination, different passivation layers were investigated in SiC BJTs, and thermal oxidation in N2O ambient was identified as an efficient passivation method to increase the current gain. To obtain a low contact resistance, especially to the p-type base contact, is one critical issue to fabricate SiC power BJTs with low on-resistance. Low temperature anneal (~ 800 oC) of a p-type Ni/Ti/Al contact on 4H-SiC has been demonstrated. The contact resistivity on the ion implanted base region of the BJT was 1.3 × 10-4 Ωcm2 after annealing. The Ni/Ti/Al p-type ohmic contact was adapted to 4H-SiC BJTs fabrication indicating that the base contact plays a role for achieving a low on-resistance of SiC BJTs. To achieve a high breakdown voltage, optimized junction termination is important in a power device. A guard ring assisted Junction Termination Extension (JTE) structure was used to improve the breakdown voltage of the SiC BJTs. The highest breakdown voltage of the fabricated SiC BJTs was obtained for devices with guard ring assisted JTE using the base contact implant step for a simultaneous formation of guard rings. As a new approach to fabricate SiC BJTs, epitaxial regrowth of an extrinsic base layer was demonstrated. SiC BJTs without any ion implantation were successfully demonstrated using epitaxial regrowth of a highly doped p-type region and an etched JTE using the epitaxial base. A maximum current gain of 42 was measured for a 1.8 mm × 1.8 mm BJT with a stable and reproducible open base breakdown voltage of 1800 V. / QC 20100819 silicon carbide power device BJT current gain specific on resistance (RSP_ON) breakdown voltage forward voltage drop surface recombination ohmic contact. Elektroteknik, elektronik och fotonik
4	Biological And Chemical Sludge Filtration Yukseler, Hande 01 July 2007 (has links) (PDF) Up to date, sludge filterability has been characterized by the Ruth&rsquo / s classical filtration theory and quantified by the well-known parameter specific cake resistance (SCR). However, the complexity of the actual phenomenon is clearly underestimated by the classical filtration theory and SCR is often not satisfactory in describing filterability. Although many scientific studies were conducted for a better analysis and understanding of the filtration theory, still a practically applicable solution to replace the classical theory for a better description of filterability has not been proposed yet. In the present study, blocking filtration laws proposed by Hermans and Bred&eacute / e, dating back to 1936, which have been extensively used in the membrane literature for the analysis of fouling phenomenon and the multiphase filtration theory developed by Willis and Tosun (1980) highlighting the importance of the cake-septum interface in determining the overall filtration rate have been adopted for the analysis of filterability of sludge systems. Firstly, the inadequacy of the classical filtration theory in characterizing the filterability of real sludge systems and also the lack of the currently used methodology in simulating filtration operation was highlighted. Secondly, to better understand the effect of slurry characteristics and operational conditions on filtration, model slurries of spherical and incompressible Meliodent particles were formed. Finally, a methodology was developed with the gathered filtration data to assess the filterability of the sludge systems by both theories. The results clearly show that both approaches were superior to the classical approach in terms of characterizing the filterability of sludge systems. While blocking laws yielded a slurry specific characterization parameter to replace the commonly used SCR, the multiphase theory provided a better understanding of the physical reality of the overall process.
5	The Design, Fabrication, and Characterization of Waffle-substrate-based n-channel IGBTs in 4H-SiC Md monzurul Alam (11184600) 27 July 2021 (has links) <div>Power semiconductor devices play an important role in many areas, including household</div><div>appliances, electric vehicles, high speed trains, electric power stations, and renewable energy</div><div>conversion. In the modern era, silicon based devices have dominated the semiconductor</div><div>market, including power electronics, because of their low cost and high performance. The</div><div>applications of devices rated 600 V - 6.5 kV are still dominated by silicon devices, but they</div><div>are nearly reaching fundamental material limits. New wide band gap materials such as silicon</div><div>carbide (SiC) offer significant performance improvements due to superior material properties</div><div>for such applications in and beyond this voltage range. 4H-SiC is a strong candidate</div><div>among other wide band gap materials because of its high critical electric field, high thermal</div><div>conductivity, compatibility with silicon processing techniques, and the availability of high</div><div>quality conductive substrates.</div><div>Vertical DMOSFETs and insulated gate bipolar transistors (IGBT) are key devices for</div><div>high voltage applications. High blocking voltages require thick drift regions with very light</div><div>doping, leading to specific on-resistance (R<sub>ON,SP</sub> ) that increases with the square of blocking</div><div>voltage (V<sub>BR</sub>). In theory, superjunction drift regions could provide a solution because of a</div><div>linear dependence of R<sub>ON,SP</sub> on V<sub>BR</sub> when charge balance between the pillars is achieved</div><div>through extremely tight process control. In this thesis, we have concluded that superjunction</div><div>devices inevitably have at least some level of charge imbalance which leads to a quadratic</div><div>relationship between V<sub>BR</sub> and R<sub>ON,SP</sub> . We then proposed an optimization methodology to</div><div>achieve improved performance in the presence of this inevitable imbalance.</div><div>On the other hand, an IGBT combines the benefits of a conductivity modulated drift</div><div>region for significantly reduced specific on-resistance with the voltage controlled input of a</div><div>MOSFET. Silicon carbide n-channel IGBTs would have lower conduction losses than equivalent</div><div>DMOSFETs beyond 6.5 kV, but traditionally have not been feasible below 15 kV. This</div><div>is due to the fact that the n+ substrate must be removed to access the p+ collector of the</div><div>IGBT, and devices below 15 kV have drift layers too thin to be mechanically self-supporting.</div><div>In this thesis, we have demonstrated the world’s first functional 10 kV class n-IGBT with</div><div>a waffle substrate through simulation, process development, fabrication and characterization.</div><div><div>The waffle substrate would provide the required mechanical support for this class of devices.</div><div>The fabricated IGBT has exhibited a differential R<sub>ON,SP</sub> of 160 mohm</div><div>.cm<sup>2</sup>, less than half of</div><div>what would be expected without conductivity modulation. An extensive fabrication process</div><div>development for integrating a waffle substrate into an active IGBT structure is described</div><div>in this thesis. This process enables an entirely new class of moderate voltage SiC IGBTs,</div><div>opening up new applications for SiC power devices.</div></div> IGBT power semiconductor devices semiconductor device characteristics TCAD simulation device characterizations Breakdown voltage (VBR) Superjunction MOSFET 10 kV IGBT Semiconductor device fabrication Specific-on resistance 4H-SiC
6	Lung function by plethysmography : a new method in Vietnam for asthma diagnosis / La pléthysmographic : une nouvelle méthode d’exploration fonctionnelle au Vietnam pour le diagnostic de l’asthme Lê Tuan, Thành 22 September 2015 (has links) La fréquence de l’asthme augmente au Vietnam, mais les moyens de diagnostic et d’évaluation fonctionnelle sont limités. Une étude précédente utilisant la technique des oscillations forcées a montré une différence de résistance des voies aériennes entre enfants français et vietnamiens à l’âge de 10 ans mais pas à 6 ans. Si l’hypothèse d’une différence ethnique significative est correcte, alors des différences semblables devraient aussi exister à l’âge adulte. Pour tester l’hypothèse, une étude par pléthysmographie a été mise en place pour mesurer la résistance des voies aériennes et la résistance spécifique des voies aériennes chez de jeunes adultes sains en France et au Vietnam. Nous avons profité de l’étude pour établir des valeurs de référence pour les volumes pulmonaires dans ces populations. La résistance des voies aériennes est significativement plus grande chez les sujets vietnamiens que chez les caucasiens, mais il n’y a aucune différence de résistance spécifique des voies aériennes. Au final, l’étude ne montre pas de différence de calibre des voies aériennes normalisé pour le volume pulmonaire liée l’ethnie, à l’âge adulte. La taille debout est le facteur prédictif le plus important pour la capacité pulmonaire totale, tandis que l’ethnicité est un facteur important pour la capacité vitale et le rapport du volume résiduel à la capacité pulmonaire totale. Cette étude est la première qui fournit des valeurs de référence pour la résistance des voies aériennes, la résistance spécifique des voies aériennes et les volumes pulmonaires par pléthysmographie chez l’adulte vietnamien. La pléthysmographie a été validée à Hanoi et l’étude a permis la formation d’un nouveau groupe de travail sur le diagnostic et la prise en charge de l’asthme au Vietnam / Despite the increasing prevalence of asthma in Viet Nam, the country has limited means for respiratory function testing. A previous study using the forced oscillation technique suggested lower respiratory resistance between French and Vietnamese children at 10 years but not 6 years of age. If the hypothesis of a significant ethnic difference in airway caliber is correct, then similar differences should exist at adult age. To test the hypothesis, a plethysmographic study was set up to measure airway resistance and specific airway resistance in healthy young adults in France and Viet Nam. We took advantage of the study to provide reference values for lung volume in these populations. Airway resistance is significantly larger in Vietnamese than in Caucasians but there is no difference in specific airway resistance. Altogether the study does not support the consequence of a putative ethnic difference in childhood airway caliber on airway resistance normalized for lung volume at adult age. The standing height is the best predictor of the total lung capacity, while ethnicity is an important predictor of vital capacity and of the residual volume to total lung capacity ratio. This is the first study which provides reference values for airway resistance, specific airway resistance and lung volumes by plethysmography in healthy young Vietnamese adults. Plethysmography was validated in the north of Viet Nam, and the study allowed initiating a young working group on asthma diagnosis in Vietnam Asthme Pléthysmographie Résistance des voies aériennes Volume gazeux thoracique Appartenance ethnique Halètement Écoulement laminaire Écoulement turbulent Sujets sains Effet thermique Enfant Asthma Plethysmography Specific Airway Resistance Airway Resistance Thoracic Gas Volume Ethnicity Panting Turbulent, Laminar airflow Healthy subjects Thermal effect Child 616.238
7	Elektrische Charakterisierung PLD-gewachsener Zinkoxid-Nanodrähte Zimmermann, Gregor 14 October 2010 (has links) (PDF) Die vorliegende Arbeit beschäftigt sich mit der elektrischen Charakterisierung von Zinkoxid-Nanodrähten, die mittels gepulster Laserablation (PLD) hergestellt wurden. Ausgehend von den so generierten ZnO-Nanodraht-Ensembles werden Methoden zu deren elektrischer Untersuchung diskutiert und auf praktische Anwendbarkeit hin verglichen. Die entwickelten Methoden werden auf Ensembles von auf n-leitenden ZnO- und ZnO:Ga-Dünnschichten aufgewachsenen Phosphor-dotierten ZnO-Nanodrähten angewendet. Deren reproduzierbares, in Strom–Spannungs- (I–U-) Kennlinien beobachtetes diodenartiges Verhalten wird genauer beleuchtet. Im Zusammenhang mit der elektrischen Charakterisierung einzelner ZnO-Nano-drähte werden experimentelle Methoden zur Vereinzelung und zur Kontaktierung der vereinzelten ZnO-Nanodrähte diskutiert. Dabei werden sowohl etablierte Methoden wie Elektronenstrahllithographie (EBL) als auch neue Techniken wie elektronen- und ionenstrahlinduzierte Deposition (EBID/IBID) und Strom–Spannungs-Rastersondenmikroskopie (I-AFM) behandelt und ihre Eignung für eingehende elektrische Untersuchungen und reproduzierbare Messungen analysiert. Die geeignetsten Methoden werden schließlich eingesetzt, um spezifischen Widerstand sowie Ladungsträgermobilität und -dichte sowohl in nominell undotierten als auch in Aluminium-dotierten ZnO-Nanodrähten zu untersuchen und zu vergleichen. In der Ableitung der physikalischen Materialparameter aus den Messdaten wird dabei besonderes Augenmerk auf die Einbeziehung der geometrischen Besonderheiten der Nanodrähte gegenüber Volumenmaterial- und Dünnschichtproben gelegt. Im Zuge dessen wird unter anderem ein Modell für den elektrischen Widerstand in Nanodrähten mit ihrer Länge nach veränderlichem Querschnitt abgeleitet. Zinkoxid ZnO Nanodraht PLD Dotierung Phosphor Aluminium elektrische Charakterisierung spezifischer Widerstand Transferlänge Kontaktierung Lithographie EBID IBID EBL SPM EDX IU Ensemble Polystyren einbetten stabilisieren zinc oxide ZnO nanowire PLD doping phosphorus aluminium electric charakterisation specific electrical resistance resistivity transfer length contacts lithography EBID IBID EBL SPM EDX IU ensemble Polystyrene embedding stabilization ddc:537 ddc:539 Zinkoxid Nanostruktur Nanodraht Impulslaserbeschichten Dotierung Aluminium Phosphor Strommessung Elektrischer Strom Spezifischer Widerstand Ladungsträgerbeweglichkeit Freier Ladungsträger Elektronenstrahllithographie Rasterelektronenmikroskop Rasterkraftmikroskop
8	Elektrische Charakterisierung PLD-gewachsener Zinkoxid-Nanodrähte Zimmermann, Gregor 17 August 2010 (has links) Die vorliegende Arbeit beschäftigt sich mit der elektrischen Charakterisierung von Zinkoxid-Nanodrähten, die mittels gepulster Laserablation (PLD) hergestellt wurden. Ausgehend von den so generierten ZnO-Nanodraht-Ensembles werden Methoden zu deren elektrischer Untersuchung diskutiert und auf praktische Anwendbarkeit hin verglichen. Die entwickelten Methoden werden auf Ensembles von auf n-leitenden ZnO- und ZnO:Ga-Dünnschichten aufgewachsenen Phosphor-dotierten ZnO-Nanodrähten angewendet. Deren reproduzierbares, in Strom–Spannungs- (I–U-) Kennlinien beobachtetes diodenartiges Verhalten wird genauer beleuchtet. Im Zusammenhang mit der elektrischen Charakterisierung einzelner ZnO-Nano-drähte werden experimentelle Methoden zur Vereinzelung und zur Kontaktierung der vereinzelten ZnO-Nanodrähte diskutiert. Dabei werden sowohl etablierte Methoden wie Elektronenstrahllithographie (EBL) als auch neue Techniken wie elektronen- und ionenstrahlinduzierte Deposition (EBID/IBID) und Strom–Spannungs-Rastersondenmikroskopie (I-AFM) behandelt und ihre Eignung für eingehende elektrische Untersuchungen und reproduzierbare Messungen analysiert. Die geeignetsten Methoden werden schließlich eingesetzt, um spezifischen Widerstand sowie Ladungsträgermobilität und -dichte sowohl in nominell undotierten als auch in Aluminium-dotierten ZnO-Nanodrähten zu untersuchen und zu vergleichen. In der Ableitung der physikalischen Materialparameter aus den Messdaten wird dabei besonderes Augenmerk auf die Einbeziehung der geometrischen Besonderheiten der Nanodrähte gegenüber Volumenmaterial- und Dünnschichtproben gelegt. Im Zuge dessen wird unter anderem ein Modell für den elektrischen Widerstand in Nanodrähten mit ihrer Länge nach veränderlichem Querschnitt abgeleitet. info:eu-repo/classification/ddc/537 ddc:537 info:eu-repo/classification/ddc/539 ddc:539

Search results