<p>This thesis discusses non-linearities associated with a sampling switch and compares transmission gate, bootstrapping and bulk-effect compensation architectures at circuit level from linearity point of view for 0.35 um CMOS process. All switch architectures have been discussed and designed with an additional constraint of switch reliability.</p><p>Results indicate that for a specified supply of 3.3 Volts, bulk-effect compensation does not improve third-order harmonic distortion significantly which defines the upper most limit on linearity for a differential topology. However, for low-voltage operations bulk-effect compensation improves third-order harmonic noticeably.</p>

This thesis discusses non-linearities associated with a sampling switch and compares transmission gate, bootstrapping and bulk-effect compensation architectures at circuit level from linearity point of view for 0.35 um CMOS process. All switch architectures have been discussed and designed with an additional constraint of switch reliability. Results indicate that for a specified supply of 3.3 Volts, bulk-effect compensation does not improve third-order harmonic distortion significantly which defines the upper most limit on linearity for a differential topology. However, for low-voltage operations bulk-effect compensation improves third-order harmonic noticeably.

No presente trabalho, três tipos de fotocatalisadores híbridos nanométricos, CdS, CdS/TiO2, e CdS/TiO2/SiO2, foram preparados e utilizados em três aplicações fotoquímicas: fotodegradação macro e microscópica de um corante, fotólise da água para geração de H2 com acompanhamento via espectrometria de massas in situ e estudo de uma reação redox via microscopia de fluorescência de campo largo. As análises por microscopia eletrônica de varredura (MEV) e de transmissão (MET) apresentaram esferas de sílica com diâmetro em torno de 300 nm e nanopartículas de CdS e TiO2 com diâmetro da ordem de 5 nm e com alta aglomeração. O recobrimento da sílica com TiO2 e CdS não foi uniforme, resultando em \"ilhas\" preferencialmente isoladas. Apesar da morfologia heterogênea, os fotocatalisadores foram eficientes na degradação da safranina O, apresentando cinética de 1ª ordem em relação à concentração do corante. No que se refere à fotólise da água, o sistema ternário (CdS/TiO2/SiO2) apresentou a maior taxa de produção de H2 (0,79 mmol h-1 g-1), o que indica maior eficiência na transferência ou injeção de carga entre CdS e TiO2, devido ao melhor contato entre os dois semicondutores na superfície das nanopartículas (NPs) de sílica. Esse sistema também foi o mais eficiente na fotorredução do corante não fluorescente resazurina no corante fluorescente resorufina, acompanhada através de medidas de intermitência de fluorescência utilizando microscopia de fluorescência de campo largo. Em geral, os sistemas após adição do corante apresentaram intermitência de fluorescência mais lenta, com maiores tempos de relaxação de off. A fotorredução do corante estabeleceu um método interessante para o mapeamento das regiões de injeção de carga CdS/TiO2, inicialmente escuras e a seguir com alta intensidade de emissão. / In the present work, three types of nanosized hybrid photocatalysts, CdS, CdS/TiO2 and CdS/TiO2/SiO2, were synthesized and used in three photochemical applications: macro and microscopic photodegradation of a dye, photolysis of water to generate H2 monitored by in situ mass spectrometry and study of a redox reaction by wide-field fluorescence microscopy. Scanning (SEM) and transmission (TEM) electronic microscopies showed quasi-monodispersed silica spheres with a diameter of about 300 nm and CdS and TiO2 nanoparticles with a diameter of approximately 5 nm highly agglomerated. The coating of the silica with CdS and TiO2 was not uniform, resulting in \"islands\" preferentially isolated. Despite the heterogeneous morphology of the photocatalysts, they were efficient in the degradation of a safranine O solution, showing kinetics of first order with respect to dye concentration. With regard to water photolysis, the ternary system (CdS/TiO2/SiO2) showed the highest rate of H2 production (0.79 mmol g-1 h-1) , which indicates more efficient charge transfer or injection between CdS and TiO2 due to better contact between the two semiconductors on the surface of the silica nanoparticles (NPs). This system also was the most efficient photocatalyst in the photorreduction of the nonfluorescent dye resazurin into the fluorescent dye resorufin, monitored by fluorescence intermittency measurements using wide-field microscopy. In general, the systems after adding the dye presented slower fluorescence intermittency, with higher times of off relaxation. The photoreduction of the dye provided an interesting method for mapping the regions of CdS/TiO2 charge injection, initially dark and then with high emission intensity.

Fabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the interface. Therefore, having a favorable contact at electrode/semiconductor is highly desirable for high-performance devices fabrication. In this dissertation, the fabrication of nanoelectronic devices and investigation of their transport properties using carbon nanotubes (CNTs) and graphene as electrode materials will be shown. I investigated two types of devices using (i) semiconducting CNTs, and (ii) organic semiconductors (OSC). In the first part of this thesis, I will demonstrate the fabrication of high-performance solution-processed highly enriched (99%) semiconducting CNT thin film transistors (s-CNT TFTs) using densely aligned arrays of metallic CNTs (m-CNTs) for source/drain electrodes. From the electronic transport measurements at room temperature, significant improvements of field-effect mobility, on-conductance, transconductance and current on/off ratio for m-CNT/s-CNT devices were found compared to control palladium (Pd contacted s-CNT devices. From the temperature dependent transport investigation, a lower Schottky barrier height for the m-CNT/s-CNT devices was found compared to the devices with control metal electrodes. The enhanced device performance can be attributed to the unique device geometry as well as strong ?- ? interaction at m-CNT/s-CNT interfaces. In addition, I also investigated s-CNT TFTs using reduced graphene oxide (RGO) electrodes. In the second part of my thesis, I will demonstrate high-performance organic field-effect transistors (OFETs) using different types of graphene electrodes. I show that the performance of OFETs with pentacene as OSC and RGO as electrode can be continuously improved by increasing the carbon sp2 fraction of RGO. The carbon sp2 fractions of RGO were varied by controlling the reduction time. When compared to control Pd electrodes, the mobility of the OFETs shows an improvement of ?200% for 61% sp2 fraction RGO, which further improves to ?500% for 80% RGO electrode. Similarly, I show that when the chemical vapor deposition (CVD) graphene film is used as electrodes in fabricating OFET, the better performance is observed in comparison to RGO electrodes. Our study suggests that, in addition to ?-? interaction at graphene/pentacene interface, the tunable electronic properties of graphene as electrode have a significant role in OFETs performance. For a fundamental understanding of the interface, we fabricated short-channel OFETs with sub-100nm channel length using graphene electrode. From the low temperature electronic transport measurements, a lower charge injection barrier was found compared to control metal electrode. The detailed investigations reported in this thesis clearly indicated that the use of CNT and graphene as electrodes can improve the performance of future nanoelectronic devices.

Organic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating highperformance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising electrode material which can address this challenge. In this dissertation, we demonstrate fabrication of high-performance OFETs using aligned array CNT electrodes and investigate the detailed electronic transport properties of the fabricated devices. The OFETs with CNT electrodes show a remarkable enhancement in the device performance such as high mobility, high current on-off ratio, higher cutoff frequency, absence of short channel effect and better charge carrier injection than those OFETs with metal electrodes. From the low temperature transport measurements, we show that the charge injection barrier at CNT/OSC interface is smaller than that of the metal/OSC interface. A transition from direct tunneling to Fowler-Nordheim tunneling observed in CNT/OSC system shows further evidence of low injection barrier. A lower activation energy measured for the OFETs with CNT electrodes gives evidence of lower interfacial trap states. Finally, OFETs are demonstrated by directly growing crystalline organic nanowires on aligned array CNT electrodes. In addition to investigating the interfacial barrier at CNT/OSC interface, we also studied photoconduction mechanism of the CNT and CNT/OSC nanocomposite thin film devices. We found that the photoconduction is due to the exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode/CNT interface and diffusion of the charge iv carrier through percolating CNT networks. In addition, it is found that photoresponse of the CNT/organic semiconductor can be tuned by changing the weight percentage of CNT into the organic semiconductors.

No description available.

We present fabrication of n-type organic field effect transistors (OFETs) using densely aligned array carbon nanotube (CNT) electrodes. The CNTs were aligned with a high linear density via dielectrophoresis (DEP) from an aqueous solution. In order to fabricate the CNT electrodes, aligned CNTs were cut by using electron beam lithography (EBL) and precise oxygen plasma etching. The n-type OFETs were fabricated in a bottom-contact configuration by depositing a thin film of C60 molecules between the CNT source and drain electrodes, and compared against a controlled C60 OFET with gold electrodes. The electron transport measurements of the OFETs using CNT electrodes show better transistor characteristics compared to OFETs using gold electrodes due to improved charge injection from densely aligned and open-ended nanotube tips.

Ce travail est une analyse de la structure des panaches Électrohydrodynamiques plans également appelés jets Électrohydrodynamiques en géométrie plane. Il a pour objectif de proposer une description la plus précise possible de l'écoulement, d'apporter une meilleure compréhension des phénomènes physiques notamment à l'aide de modèles simples et de quantifier la force électrique. Le chapitre I est une étude bibliographique qui propose un résumé des principales connaissances sur la structure de deux écoulements très similaires aux jets EHD : les jets classiques et les panaches thermiques. Le chapitre II est consacré à la présentation du montage expérimental, ainsi qu'à la méthodologie expérimentale utilisée dans cette étude. La qualité des mesures obtenues grâce à la méthode de vélocimétrie par images de particule y est discutée ; les problèmes de non corrélation, de convergence statistique des résultats y sont par exemple abordés. L'analyse des champs de vitesse permet de mettre en évidence la structure des panaches et de proposer une classification des jets EHD. Le chapitre III est consacré à l'étude de la force électrique dans les panaches EHD. L'actionneur utilisé pour produire le jet plan est de type lame-plan. Trois méthodes indirectes ont été utilisées pour estimer la force à partir du champ de vitesse. La première méthode appelée méthode intégrale classique calcule la force par intégration volumique de l'équation de Navier-Stokes. La deuxième méthode appelée méthode RANS intégrale estime la force à partir de chacun des termes de l'équation RANS en utilisant une décomposition de la vitesse en valeur moyenne et fluctuation. Enfin, la force est également calculée selon une troisième méthode basée sur une modélisation simplifiée de l'écoulement inspirée des travaux de Malraison et Atten. Dans le dernier chapitre, l'étude est étendue à un écoulement électroconvectif de type jet de paroi électrique. Il est généré par un actionneur à barrière diélectrique. L'étude est faite avec deux types des liquides diélectriques différents. Comme pour le jet plan, l'analyse des champs de vitesse permet de définir les structures de l'écoulement mais également de calculer l'intensité de la force produite. / This work is related to the analysis of the structure of electrohydrodynamic plane plumes also called electrohydrodynamic jets in plane geometry. The aim of this work is to provide a more precise description and a better understanding of its physical phenomenon and to quantify the electric force using the simple models. Chapter I is a literature review which provides a summary of two flows with the structure very similar to EHD jets: classic jets and thermal plumes. Chapter II is devoted to the presentation of the experimental setup and method used in this study. The quality of the measurements obtained by the method of Particle Image Velocimetry is discussed; problems of non correlation and statistical convergence of the results are also discussed. The analysis of velocity fields allows us to identify the structure and propose a classification of the EHD plumes. Chapter III is devoted to the study of the electric force in the EHD plumes. The actuator used to produce the plane jet is a blade plane device. Three indirect methods were used to estimate the force from the velocity field. The first classical method called integral method calculates the force by volumetric integration of Navier-Stokes equations. The second method called RANS integral method estimates the force from each term of RANS equation using the average and fluctuating velocity components. Finally, the force is also calculated using a third approach with a simplified flow model based on the work of Malraison and Atten. In the last chapter, the study is extended to one type of électroconvectif flow: the electrical wall jet. It is generated by a dielectric barrier actuator. The study is carried out with two different dielectric liquids. As is the case with plane jet, the analysis of velocity fields is used to define the flow structures and calculate the force produced.

A bipolar charge transport (BCT) model is used to simulate charge injection and transportdynamics inside insulation material which are used in a high voltage direct current (HVDC)cable. Gaining knowledge about space charge density and electric field distribution in theinsulation material enables minimising charge injection at the metal-insulator interface andavoiding unnecessary energy loss. Simulation methods using the numerical Finite ElementMethod (FEM) are implemented in COMSOL multiphysics in order to investigate the effect ofchemical structure such as dipoles, physical defects such as interface roughness and impurityconcentration leading to ions, on the potential barrier and charge injection at the interface.Interface dipoles such as surface dipoles or chemical dipoles can increase or decrease thepotential barrier at the interface depending on direction/orientation of the dipole. Moreover,using a field enhancement factor to include the effect of interface roughness at the interfaceyields increased charge injection when higher values of the field enhancement factor wereused. The barrier height becomes therefore locally lower where the degree of roughness ishigher. Including the effect of ions, the electric field was observed to be enhanced near theelectodes, where it was weakened in the middle of the insulation, depending on the amount ofthe impurity concentration inside the insulation. Improvement on the charge injection lows isalso done using a combination of both Richardson-Schottky and Fowler-Nordheim chargeinjection laws to include both a classical and a quantum mechanical description in the BCTmodel. Solving for the transmission coefficient from Schrödinger equation could improve theaccuracy of Fowler-Nordheim as well. Including potentials due to image effect or chemicalcompositions such as water dipoles will affect the charge injection barrier and the transmission coefficient.

No description available.