Dissertations / Theses on the topic 'High refractive thin film'

Thin film planar waveguides were originally introduced in microwave engineering. The spectroscopist began to use such waveguides as tools to solve chemical characterization problems since Harrick and Fahrenfort introduced the Attenuated Total'Reflection (ATR) in the early 1960's. Today, planar waveguides are playing an important and ever-increasing role in modem chemistry. In this thesis, a novel design for a refractometer involving the application of a thin film planar waveguide and coupling prism was demonstrated. This device shows the feasibility of refractive index measurements in a flowing stream. Therefore, an online detector for High Performance Liquid Chromatography (HPLC) was chosen as the vehicle to test out the concepts. The research works were devoted to studies of waveguide properties and flow dynamics in a chromatographic situation. It was found that microscale detection is possible. The sensitivity can be enhanced by using the highest propagation mode as the probe, and by selecting a proper refractive index liquid as the solvent carrier. A description of the investigation and the various factors involved in designing and optimizing a planar waveguide for refractive index detection is included. The results provide guidelines for the device as a realistic analytical detector.
Ph. D.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007.
Committee Chair: A. Rahman Zaghloul ; Committee Members: W. Russell Callen and Doug Yoder. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Research in High Voltage Thin Film Transistors (HVTFTs) has been driven by the need for devices with reduced on-state resistance and high blocking capability to improve the performance of large area electronic applications. Conventional HVTFTs give unsatisfactory performance because of the high on-state resistance, low breakdown voltage (Offset Drain HVTFT), high possibility of oxide failure and requirement for extra external bias line (Metal Field Plate HVTFT) etc. This thesis presents a novel high voltage thin film transistor structure - Semi-Insulating Field Plate HVTFT (SIFP HVTFT) which utilises a semi-insulating layer as the field plate to modify the conductivity in the offset region. The new structure has demonstrated and enhanced on-state performance relative to conventional offset drain device and a much improved blocking capability compared with all existing high voltage thin film transistor structures. Unlike conventional offset drain TFTs, during the "on-state", the channel formed under the gate can be extended into the offset region by the potential on the semi-insulating field plate which is controlled by the bias on the gate and the drain. Equivalent circuit models for the SIFP HVTFT have been developed for the device analysis. New concepts such as "extended channel" have been proposed for the first time to illustrate the device physics underlying the improvement in performance of the new device. The superior blocking capability is attributed to a very small leakage current flowing through the semi-insulating field plate which increases the radius of potential curvature near the drain. This leakage current, however, does not significantly contribute to the main current flowing through the device. It is concluded that the SIFP HVTFT presents a new concept to the high voltage thin film transistor family and has clearly shown many advantages over conventional HVTFTs.

Since the recent discovery of a new class of high critical temperature superconductors (HTS), much interest has been shown in their potential use as optical detectors. The purpose of this research was to test thin film samples of the HTS Y1Ba2Cu3O7-delta as detectors and investigate any response to optical radiation. A laboratory test facility was designed and built for this purpose. The experimental results exhibit a variety of optical responses that are dependent upon the physical characteristics of each HTS thin film. Polycrystalline films exhibited a different detection mode than did epitaxial films. This research demonstrates that HTS thin films are viable optical detectors and have the potential to become competitive high-performance detectors as the new technology continues to emerge.

The thermocouple systems used for the measurement of surface temperature in high temperature applications such as advanced aerospace propulsion systems and diesel engine systems are expected to perform in rapidly fluctuating and extremely high heat fluxes corresponding to high temperatures (in excess of 1400 K) and high speed flows. Traditionally, Pt/Pt-Rh based thin film thermocouples have been used for surface temperature measurements. However, recent studies indicated several problems associated with these thermocouples at temperatures exceeding 1000 K, some of which include poor adhesion to the substrate, rhodium oxidation and reaction with the substrate at high temperatures. Therefore, there is an impending demand for thermoelectric materials that can withstand severe environments in terms of temperature and heat fluxes. In this study, thin films of titanium carbide and tantalum carbide as well as two families of conducting perovskite oxides viz., cobaltites and manganates (La(1-x)SrxCoO3, M(1-x)Cax MnO3 where, M=La,Y) were investigated for high temperature thin film thermocouple applications as alternate candidate materials. Thin films of the carbides were deposited by r.f. sputtering while the oxide thin films were deposited using pulsed laser ablation. Sapphire (1102) was used as substrate for all the thin film depositions. All the thin films were characterized for high temperature stability in terms of phase, microstructure and chemical composition using x-ray diffraction, atomic force microscopy and electron spectroscopy for chemical analysis respectively. Electrical conductivity and seebeck coefficients were measured in-situ using a custom made device. It was observed that TiC/TaC thin film thermocouples were stable up to 1373 K in vacuum and yield high and fairly stable thermocouple output. The conducting oxides were tested in air and were found to be stable up to at least 1273 K. The manganates were stable up to 1373 K. It was observed that all the oxides studied crystallize in a single phase perovskite structure. This phase is stable up to annealing temperatures of 1373 K. The predominant electrical conduction mechanism was found to be small polaron hopping. Stable and fairly high electrical conductivities as well as seebeck coefficients accompanied with phase, structure, composition and microstructure stability indicate that these materials hold excellent promise for high temperature thin film thermocouple applications.
Master of Science

There has always been an increasing demand for high density data storage. However, the increased areal storage densities of hard disk drives require a level of miniturisation of the recording heads where the micromagnetic details and switching mechanisms can no longer be ignored. Furthermore, theoretical and numerical studies on thin-film recording heads tend to separate the micromagnetics from the electromagnetic aspects of the head during switching and hence ignore the lossy nature of head materials. This project was aimed to develop a numerical simulation approach that simultaneously incorporates the fundamental micromagnetic and electromagnetic details of magnetic materials to study the fast switching process in soft magnetic materials in general, and in thin-film inductive writers in particular. The project also was aimed at establishing an impedance measurement system to characterise losses in magnetic recording heads, and to allow comparison with the simulations. This project successfully met all its original objectives. A numerical technique to simulate the dynamic behaviour of magnetic materials and devices has been developed, and applied to study the switching process in thin-film recording heads. Two-dimensional simulations of complete commercial head structures including the coils and pole regions were carried out and parameters such as gap field rise times, gap field distributions, and core inductances, which are important for head designers, were predicted. Moreover, the role of eddy currents delaying the magnetisation switching was elucidated. Furthermore, it was found that the gradient of the recording fields were sharper near the conrner regions of the poles when considering magnetic details. A high precision, high bandwidth impedance measurement system was established to characterise losses in magnetic heads. Fittings of measured core inductances to a proposed equivalent circuit model of the core’s relaxation processes revealed the switching times of heads (of the order 0.1 to 1.0ns).

Thesis (M.S.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 17, 2009) Includes bibliographical references.

Glow discharge sputtering has been used for many years to produce thin films but its commercial applications are severely limited by low deposit ion rates. The DC planar magnetron, developed a decade ago, allows much higher deposition rates and its commercial use has expanded rapidly. Non-reactive magnetron sputtering of metallic thin films is well understood and utilized. However when a reactive gas is introduced the process becomes harder to control and can switch between two stable modes. Often films are produced simply by using one of these stable modes even though this does not lead to optimum film properties or high deposition rates. This work gives a model of reactive magnetron sputtering and verifies experimentally its predictions. A 0.5 m long magnetron was designed and built specifically to allow reactive sputtering onto A4 rigid substrates. This magnetron has a variable magnetic field distribution which allows plasma bombardment of the substrate during film growth. This was shown to activate reactions at the substrate. The target lifetime was extended in our design by broadening the erosion zone and increasing the target thickness. The reactive sputtering process was shown to be inherently unstable and a control system was designed to maintain the magnetron in an unstable state. Light emission by the plasma at metal line emission wavelengths changes across the instability and so with this control signal a feedback system was built. The accuracy of control was shown experimentally and theoretically to depend on the delay time between measurement, action and effect. In practice this delay was limited by the time constant of the gas distribution manifold. The time constant of such manifolds was measured and calculated. Using our controller high quality films were produced at high rates in normally unstable deposition systems. Conducting indium oxide was produced at 6 nm/s with a resistivity of 6 x 10-6 ohm. metres onto A4 glass sheets. Tin oxide was produced at increased rates onto 2.5 m by 3 m substrates.

The main objective of this thesis was to develop high efficiency thin film solar cells based on low-toxic and earth-abundant kesterite Cu2ZnSnSe4 (CZTSe) absorbers through the implementation of innovative doping strategies. Special focus is put on the optimization of reactive thermal processes, followed by the screening of possible doping elements and further analysis of the most promising ones. Additionally, deeper investigations were carried out in order to improve understanding of main loss mechanisms that can degrade device performance and the use of small amounts of Ge to mitigate some of them, including the possible interactions with alkali elements and the effect of post-deposition annealing treatments on devices properties. Most of the results obtained in this thesis have been published as articles in high impact peer-reviewed journals, included in text. In the first part of the thesis, previous study and optimization of the thermal processes were presented, identifying and varying the most critical parameters in a conventional tubular furnace selenization, in order to establish the best performing treatment for our particular precursors and set-up. Following this, after a preliminary screening of possible doping elements in the CZTSe system (including Ag, In, Si, Ge and Pb), In and Ge were both selected as the most promising/interesting ones to further analyze their doping properties. Although In doping did not show any performance improvement, it was demonstrated that CZTSe absorbers can tolerate rather high quantities of this element without significant modifications of their properties, confirming the possibility of using In-containing layers in kesterite CZTSe-based devices. On the other hand, with regard to Ge, a remarkable improvement of solar cells performance (from about 7% efficiency for Ge-free reference samples to more than 10% efficiency for Ge-doped ones) was presented, based on the introduction of nanometric Ge layers into the metallic stack precursors. Several reasons were proposed to explain the great efficiency improvement in spite of the observed Ge loss. In the following optimization, we determined the optimum Ge thickness range, achieving a 10.6% efficiency and open-circuit voltage values around 490 mV for pure selenide CZTSe, leading to voltage deficits around 0.56 V, which are among the best values reported for kesterites. Furthermore, a detailed microstructural analysis of high efficiency Ge-doped CZTSe solar cells was presented, revealing the presence of two distinct types of grain boundaries: one type is meandering in nature and grows largely parallel to the substrate, and denotes the boundary between two CZTSe layers with differing Cu/Zn ratios; and the second type is Cu-enriched and more straight, and predominates in the upper layer. After that, a new approach for obtaining high quality CZTSe layer was presented, by introducing extremely thin Ge nanolayers below and above metallic stack precursors. This strategy led to eliminate the previously characterized meandering horizontal grain boundaries and to obtain huge CZTSe grains. In addition, a deep study of the effect of Ge on the selenization process revealed that Ge strongly affects the in-depth elemental distribution and the phases formation, ultimately, modifying the reaction pathways of CZTSe. Through the optimization of the quantity and location of Ge, a record efficiency of 11.8% was achieved. In the last part of the thesis, the complex Ge-Na interaction was investigated, and a detailed analysis of low temperature post-deposition annealings by multi-wavelength Raman spectroscopy was also presented. On the whole, the work presented in this thesis provides meaningful results and innovative strategies to boost the efficiency of kesterite solar cells, by tackling some limiting factors of this promising material.
El objetivo principal de esta tesis es el desarrollo de células solares de capa fina de alta eficiencia basadas en absorbedores compuestos de elementos de baja toxicidad y abundantes en la corteza terrestre (kesterita, Cu2ZnSnSe4 (CZTSe)), mediante la implementación de estrategias innovadoras de dopaje. En particular, se ha desarrollado un método secuencial basado en el depósito por sputtering de capas metálicas seguido por un proceso térmico reactivo. A través de la optimización de los procesos y la implementación y análisis de diferentes elementos dopantes, se han investigado los mecanismos de pérdida de eficiencia más relevantes en kesteritas, contribuyendo a desarrollar soluciones alternativas. Los resultados obtenidos han sido publicados como artículos en revistas internacionales de alto factor de impacto. En la primera parte de la Tesis, se han estudiado profundamente los procesos térmicos reactivos, variando los parámetros más críticos para adaptarlos a las características particulares de los precursores metálicos. Seguidamente, se ha realizado un análisis de diferentes elementos dopantes (Ag, Si, Ge, Pb e In); In y Ge se han seleccionado como los más prometedores. De estos, Ge ha mostrado excelentes propiedades como dopante, incrementando la eficiencia de los dispositivos desde 7% hasta más de 10%, mediante la introducción de capas nanométricas (10 nm aprox.) en el precursor metálico. A través de una optimización profunda del proceso de dopado con Ge, se ha obtenido una eficiencia de conversión máxima de 11.8% y un déficit de voltaje de alrededor de 0.56 V, que representa uno de los mejores valores reportados para esta tecnología. Estos progresos se han acompañado de una profunda caracterización micro-estructural, que ha facilitado la identificación de importantes características de las kesteritas, como por ejemplo la presencia de dos tipos diferentes de fronteras de grano con distinta composición. Adicionalmente, Ge induce una modificación en los mecanismos de formación de kesteritas, que ha sido clave para mejorar las propiedades de los dispositivos fotovoltaicos basados en estas tecnologías. En resumen, los resultados obtenidos en la presente Tesis han servido para comprender, implementar y demostrar soluciones innovadoras para conseguir avances significativos en el desarrollo de tecnologías fotovoltaicas sostenibles basadas en kesteritas.

Magnetismus ist ein Phänomen, das eine wichtige Rolle in einer Vielfalt technischer Anwendungen spielt. Ohne den Einsatz magnetischer Effekte und Materialen wäre der heutzutage erreichte technische Fortschritt unmöglich, da viele grundlegende Techniken wie Stromerzeugung, elektrischer Antrieb, Informationsübertragung und viele andere auf magnetische bzw. elektromagnetische Phänomene zurückzuführen sind. Dabei haben die ferromagnetischen Materialen stets zur Effizienz von elektrischen und elektronischen Anwendungen beigetragen, weswegen an diesen Materialen auch entsprechend viel geforscht worden ist. Moderne Technologien, insb. Massenspeicher basieren oft auf Ferromagneten und erfordern daher die weitere Erforschung und Anpassung ihrer Eigenschaften. Für die Funktionalität von Hochgeschwindigkeitsgeräten spielt das dynamische Verhalten dünner magnetischer Schichten eine kritische Rolle. In dieser Arbeit wird die Magnetisierungsdynamik dünner Schichtelemente mittels zeitaufgelöster Weitfeld- Kerrmikroskopie untersucht. Dies ist ein aktuelles Thema, an dem in den letzten Jahren sehr intensiv gearbeitet wird. Allerdings sind viele für die Anwendungen sehr wichtige Details des magnetischen Schaltens wegen ihre Vielfältigkeit und Komplexität doch nicht vollständig untersucht und verstanden. In dieser Arbeit werden überwiegend experimentelle Ergebnisse vorgestellt, die einen zusätzlichen Beitrag zum aktuellen Wissenstand leisten. In einem ferromagnetischen Körper bilden sich Bereiche mit spontaner Magnetisierung, die man als Domänen bezeichnet. Die spontane Magnetisierung entsteht aufgrund der Spin-Spin Wechselwirkung, und die Domänen bilden sich aufgrund der Energieminimierung des magnetisierten Körpers. Langsame Magnetisierungsprozesse werden im Wesentlichen getragen von Domänenumordnungen und Domänengrenzenverschiebungen. Solche Prozesse bezeichnet man als quasistatisch, da sich der Körper durch deren Langsamkeit immer im Gleichgewicht oder zumindest sehr nahe daran befindet. Mit zunehmender Anregungsgeschwindigkeit gilt diese Annahme nicht mehr, da die Präzessionsbewegung der magnetischen Momente das Schaltverhalten in diesem Fall definiert. Die Untersuchung der Magnetisierungsdynamik setzt die Möglichkeit voraus, nicht-unterbrochene Prozesse beobachten zu können. Dieses Ziel kann mittels stroboskopischer Abbildung erreicht werden. Dabei wird derselbe Prozess kontinuierlich wiederholt (vorausgesetzt, dass die Prozesse sich reproduzierbar wiederholen lassen), und zu definierten Zeitpunkten werden die entsprechenden Kerraufnahmen gemacht. Dafür wird eine CCD Kamera mit einem Photoverstärker benutzt, welcher als optischer Schalter fungiert. Die Zeitauflösung dieses Systems und damit auch das Vermögen, die Hochfrequenzvorgänge abzubilden, beträgt 250 ps. Die Eigenschaften des magnetischen Umschaltens hängen stark von der Elementgeometrie ab. Diese Unterschiede sind auf unterschiedliche Entmagnetisierungsfaktoren, und damit auf Unterschiede in den effektiven Feldern zurückzuführen. Solche Unterschiede werden auf zwei Weisen initiiert: ein quadratisches Element wird entlang unterschiedlicher Richtungen (entlang der Seite und der Diagonalen) angeregt; die Form des Elementes wird zwischen Quadrat und Rechteck mit unterschiedlichen Seitenverhältnissen variiert. Die beobachteten Schaltvorgänge werden miteinander verglichen und die Ergebnisse dargestellt. Dabei werden auch die dynamischen Vorgänge immer mit den quasistatischen verglichen. Aus dem Vergleich folgt, dass ein steigendes Seitenverhältnis zur geringeren Schaltgeschwindigkeit führt, und dass die dabei entstehenden Domänen zunehmend komplexer werden. Dabei gibt es wesentliche Unterschiede zwischen den dynamischen und quasistatischen Domänen, vor allem in der Domänenwandstruktur. Das Schalten an sich unterscheidet sich auch sehr stark. Quasistatisches Schalten erfolgt überwiegend durch Domänenwandbewegung, während das dynamische Schalten durch inkohärente Rotation der Magnetisierung im ganzen Element erfolgt. Das Hochfrequenzverhalten am Prototypen eines Mikroinduktors wird untersucht. Der Induktor besteht aus vielen magnetischen Elementen, die eine induzierte uniaxiale Anisotropie besitzen. Diese ist bei der Hälfte der Elemente entlang des Magnetfeldes, und bei der anderen Hälfte senkrecht zum Magnetfeld der Spule ausgerichtet. Das dynamische Verhalten der beiden Elementtypen unterscheidet sich stark, vor allem die Ummagnetisierungsgeschwindigkeit. Diese Unterschiede können zu einer Phasenverschiebung im elektrischen Signal führen, was die Effizienz des Induktors senkt. Durch die Untersuchung der Magnetisierungsdynamik in Wechselfeldern unterschiedlicher Frequenz ist auch festgestellt worden, dass bis 100 MHz die Magnetisierungsvorgänge überwiegend durch Domänenwandbewegung erfolgen, während ab 200 MHz- Rotationsprozesse stattfinden.

As technologies continue advancing, semiconductor devices with dimensions in nanometers have entered all spheres of human life. This research deals with both the statistical aspect of reliability and some electrical aspect of reliability characterization. As an example of nano devices, TaO_x-based high k dielectric thin films are studied on the failure mode identification, accelerated life testing, lifetime projection, and failure rate estimation. Experiment and analysis on dielectric relaxation and transient current show that the relaxation current of high k dielectrics is distinctive to the trapping/detrapping current of SiO₂; high k films have a lower leakage current but a higher relaxation current than SiO₂. Based on the connection between polarization-relaxation and film integrity demonstrated in ramped voltage stress tests, a new method of breakdown detection is proposed. It monitors relaxation during the test, and uses the disappearing of relaxation current as the signal of a breakdown event. This research develops a Bayesian approach which is suitable to reliability estimation and prediction of current and future generations of nano devices. It combines the Weibull lifetime distribution with the empirical acceleration relationship, and put the model parameters into a hierarchical Bayesian structure. The value of the Bayesian approach lies in that it can fully utilize available information in modeling uncertainty and provide cogent prediction with limited resources in a reasonable period of time. Markov chain Monte Carlo simulation is used for posterior inference of the reliability projection and for sensitivity analysis over a variety of vague priors. Time-to-breakdown data collected in the accelerated life tests also are modeled with a bathtub failure rate curve. The decreasing failure rate is estimated with a non-parametric Bayesian approach, and the constant failure rate is estimated with a regular parametric Bayesian approach. This method can provide a fast and reliable estimation of failure rate for burn-in optimization when only a small sample of data is available.

Magnetismus ist ein Phänomen, das eine wichtige Rolle in einer Vielfalt technischer Anwendungen spielt. Ohne den Einsatz magnetischer Effekte und Materialen wäre der heutzutage erreichte technische Fortschritt unmöglich, da viele grundlegende Techniken wie Stromerzeugung, elektrischer Antrieb, Informationsübertragung und viele andere auf magnetische bzw. elektromagnetische Phänomene zurückzuführen sind. Dabei haben die ferromagnetischen Materialen stets zur Effizienz von elektrischen und elektronischen Anwendungen beigetragen, weswegen an diesen Materialen auch entsprechend viel geforscht worden ist. Moderne Technologien, insb. Massenspeicher basieren oft auf Ferromagneten und erfordern daher die weitere Erforschung und Anpassung ihrer Eigenschaften. Für die Funktionalität von Hochgeschwindigkeitsgeräten spielt das dynamische Verhalten dünner magnetischer Schichten eine kritische Rolle. In dieser Arbeit wird die Magnetisierungsdynamik dünner Schichtelemente mittels zeitaufgelöster Weitfeld- Kerrmikroskopie untersucht. Dies ist ein aktuelles Thema, an dem in den letzten Jahren sehr intensiv gearbeitet wird. Allerdings sind viele für die Anwendungen sehr wichtige Details des magnetischen Schaltens wegen ihre Vielfältigkeit und Komplexität doch nicht vollständig untersucht und verstanden. In dieser Arbeit werden überwiegend experimentelle Ergebnisse vorgestellt, die einen zusätzlichen Beitrag zum aktuellen Wissenstand leisten. In einem ferromagnetischen Körper bilden sich Bereiche mit spontaner Magnetisierung, die man als Domänen bezeichnet. Die spontane Magnetisierung entsteht aufgrund der Spin-Spin Wechselwirkung, und die Domänen bilden sich aufgrund der Energieminimierung des magnetisierten Körpers. Langsame Magnetisierungsprozesse werden im Wesentlichen getragen von Domänenumordnungen und Domänengrenzenverschiebungen. Solche Prozesse bezeichnet man als quasistatisch, da sich der Körper durch deren Langsamkeit immer im Gleichgewicht oder zumindest sehr nahe daran befindet. Mit zunehmender Anregungsgeschwindigkeit gilt diese Annahme nicht mehr, da die Präzessionsbewegung der magnetischen Momente das Schaltverhalten in diesem Fall definiert. Die Untersuchung der Magnetisierungsdynamik setzt die Möglichkeit voraus, nicht-unterbrochene Prozesse beobachten zu können. Dieses Ziel kann mittels stroboskopischer Abbildung erreicht werden. Dabei wird derselbe Prozess kontinuierlich wiederholt (vorausgesetzt, dass die Prozesse sich reproduzierbar wiederholen lassen), und zu definierten Zeitpunkten werden die entsprechenden Kerraufnahmen gemacht. Dafür wird eine CCD Kamera mit einem Photoverstärker benutzt, welcher als optischer Schalter fungiert. Die Zeitauflösung dieses Systems und damit auch das Vermögen, die Hochfrequenzvorgänge abzubilden, beträgt 250 ps. Die Eigenschaften des magnetischen Umschaltens hängen stark von der Elementgeometrie ab. Diese Unterschiede sind auf unterschiedliche Entmagnetisierungsfaktoren, und damit auf Unterschiede in den effektiven Feldern zurückzuführen. Solche Unterschiede werden auf zwei Weisen initiiert: ein quadratisches Element wird entlang unterschiedlicher Richtungen (entlang der Seite und der Diagonalen) angeregt; die Form des Elementes wird zwischen Quadrat und Rechteck mit unterschiedlichen Seitenverhältnissen variiert. Die beobachteten Schaltvorgänge werden miteinander verglichen und die Ergebnisse dargestellt. Dabei werden auch die dynamischen Vorgänge immer mit den quasistatischen verglichen. Aus dem Vergleich folgt, dass ein steigendes Seitenverhältnis zur geringeren Schaltgeschwindigkeit führt, und dass die dabei entstehenden Domänen zunehmend komplexer werden. Dabei gibt es wesentliche Unterschiede zwischen den dynamischen und quasistatischen Domänen, vor allem in der Domänenwandstruktur. Das Schalten an sich unterscheidet sich auch sehr stark. Quasistatisches Schalten erfolgt überwiegend durch Domänenwandbewegung, während das dynamische Schalten durch inkohärente Rotation der Magnetisierung im ganzen Element erfolgt. Das Hochfrequenzverhalten am Prototypen eines Mikroinduktors wird untersucht. Der Induktor besteht aus vielen magnetischen Elementen, die eine induzierte uniaxiale Anisotropie besitzen. Diese ist bei der Hälfte der Elemente entlang des Magnetfeldes, und bei der anderen Hälfte senkrecht zum Magnetfeld der Spule ausgerichtet. Das dynamische Verhalten der beiden Elementtypen unterscheidet sich stark, vor allem die Ummagnetisierungsgeschwindigkeit. Diese Unterschiede können zu einer Phasenverschiebung im elektrischen Signal führen, was die Effizienz des Induktors senkt. Durch die Untersuchung der Magnetisierungsdynamik in Wechselfeldern unterschiedlicher Frequenz ist auch festgestellt worden, dass bis 100 MHz die Magnetisierungsvorgänge überwiegend durch Domänenwandbewegung erfolgen, während ab 200 MHz- Rotationsprozesse stattfinden.

[ES] Las energía solar fotovoltaica ha emergido como una fuente de energía nueva y sostenible, que es ecológica y rentable si la producción es a gran escala. En el escenario actual, los dispositivos fotovoltaicos económicos y de alta eficiencia de conversión sin que se degraden sus componentes están bien posicionados para la generación de electricidad. Las células solares basadas en silicio dominan este mercado desde hace muchos años. Para la fabricación y producción de células solares basadas en silicio, se requieren sofisticadas técnicas de fabricación que hacen que el panel solar sea costoso. Por otra parte estan las células solares de película delgada, las cuales, debido a la intensificación de las capacidades de fabricación están ganando importancia. La tecnología de película delgada es una de las tecnologías más rentables y eficientes para la fabricación de células solares, y es un tema de intensa investigación en la industria fotovoltaica. La tecnología de película delgada es más económica que otras tecnologías porque los dispositivos utilizan menos material y están basados en varios tipos de materiales semiconductores que absorben la luz. Entre estos materiales, las células solares de kesterita que utilizan CZTS, CZTSe y sus aleaciones CZTSSe pueden convertirse en el reemplazo óptimo a los absorbentes de calcopirita. Estos materiales presentan unas características ópticas y eléctricas sobresalientes y tienen un gap óptico directo con una banda prohibida que oscila entre 1,4\ eV\ y 1,5\ eV y un coeficiente de absorción, \alpha>{10}^4{cm}^{-1}. Estas características han propiciado que las kesteritas esten siendo muy investigadas por la comunidad fotovoltaica de películas delgadas. De acuerdo con el límite de Shockley-Queisser, la eficiencia de conversión para una célula solar basada en CZTS\ es alrededor del 28%. Esta eficiencia es teóricamente posible mediante el ajuste de la banda prohibida, pero aún así, todavia no se ha podido alcanzar experimentalmente, probablemente debido a la falta de comprensión de las características de los dispositivos.Para una mejor comprensión de las características de los dispositivos, la modelación numérica puede jugar un papel importante al perimitir estudiar diferentes estructuras de dispositivos que pueden ahorrar tiempo y costos a la comunidad científico-técnica. En este trabajo, se ha llevado a cabo una modelazación numérica para estimar y analizar el efecto de parámetros físicos como el espesor y la concentración de dopado de la capa absorbente, la capa tampón y las capas ventana, además de estudiar el efecto de la temperatura y el efecto de la potencia de iluminación del sol en el rendimiento del dispositivo. El análisis numérico de los dispositivos se realizó con el software de simulación denominado "Solar Cell Capacitance Simulator" (SCAPS-1D). Para ello se analizó una estructura simple p-n-n^+ usando molibdeno como contacto posterior y FTO como ventana óptica y contacto frontal y siguiendo la secuencia de materiales Mo/CZTS/CdS/ZnO/FTO. A través del análisis, se estudió el rendimiento de las células solares con la variación en el espesor del absorbente para encontrar el espesor óptimo de la capa absorbente. También se estudió el efecto de la concentración del dopado y de la función de trabajo del metal. Después de la visualización de una estructura de dispositivo básica en SCAPS-1D, se modelo una célula solar experimental basada en CZTS. Los resultados de las células solares CZTS diseñados experimentalmente se simularon por primera vez en el entorno SCAPS-1D. Los resultados simulados de SCAPS-1D se compararon con los resultados experimentales. Después de la optimización de los parámetros de la celda, se incrementó la eficiencia de conversión de un dispositivo optimizado y, a partir del modelado, se descubrió que el rendimiento del dispositivo mejora al aumentar el tiempo de vida de los porta
[CAT] L'energia solar fotovoltaica ha emergit com una font d'energia nova i sostenible, que és ecològica i rendible si la producció és a gran escala. En l'escenari actual, els dispositius fotovoltaics econòmics i de gran eficiència de conversió estan ben posicionats per a la generació d'electricitat neta i sostenible. Les cèl·lules solars basades en silici dominen aquest mercat des de fa molts anys. Per a la fabricació i producció de cèl·lules solars basades en silici, es requereixen tècniques de fabricació sofisticades que fan que el panell solar sigui costós. Per altra banda estan les cel·les solars de capa fina, que estan guanyant importància a causa de l'intensificació de les capacitats de fabricació. La tecnologia de capa fina és una de les tecnologies més rentables i eficients per a la fabricació de cel solars, i és un tema d'intensa investigació en la fotovoltaica industrial. La tecnologia de capa fina és més econòmica que altres tecnologies perquè els dispositius utilitzen menys material i estan basats en diversos tipus de materials semiconductors que absorbeixen la llum. Entre aquests materials, les cèl·lules solars de kesterita que utilitzen CZTS, CZTSe i les seves aleacions CZTSSe poden convertir-se en el reemplaçament òptim als absorbents de calcopirita. Aquests materials presenten unes característiques òptiques i elèctriques sobresalientes i tenen un gap òptic directe amb una banda prohibida que oscil·la entre 1,4eV i 1,5eV i un coeficient d'absorció, \alpha>{10}^4{cm}^{-1}. Aquestes característiques han propiciat que les Les kesteritas estan sent molt investigades per la comunitat fotovoltaica de capes primes. D'acord amb el límit de Shockley-Queisser, l'eficiència de conversió per a una cel·la solar basada en CZTS és d'aproximadament 28%. Aquesta eficiència és teòricament possible a través de l'ajust de la banda prohibida, però tot i així, encara no s'ha pogut assolir experimentalment, probablement a causa de la incomprensió del funcionament dels dispositius. Per a una millor comprensió de les característiques i funcionament dels dispositius, la modelització numèrica pot jugar un paper important al permetre estudiar diferents estructures de sistemes que poden estalviar temps i costos a la comunitat científica-tècnica. En aquest treball, s'ha dut a terme una modelització numèrica per estimar i analitzar l'efecte de paràmetres físics com l'espessor i la concentració de dopatge de la capa absorbent, la capa tampó i la capa finestra, a més d'estudiar l'efecte de la temperatura i l'efecte de la potència d'il·luminació del sol en el rendiment del dispositiu. L'anàlisi numèrica dels dispositius es va realitzar amb el programari de simulació denominat "Solar Cell Capacitance Simulator" (SCAPS-1D). Per això es va analitzar una estructura senzilla p-n-n^+ utilitzant molibdé com contacte posterior i FTO com a finestra òptica i contacte frontal i seguint la seqüència de materials Mo/CZTS/CdS/ZnO/FTO. A través de l'anàlisi, es va estudiar el rendiment de les cel·les solars amb la variació en l'espessor de l'absorbent per trobar l'espessor òptim de la capa absorbent. També es va estudiar l'efecte de la concentració del dopatge i de la funció de treball del metall. Després de la visualització d'una estructura de dispositiu bàsic en SCAPS-1D, es model una cel·la solar experimental basada en CZTS. Els resultats de les cel·les solars CZTS dissenyats experimentalment es simularen per primera vegada en l'entorn SCAPS-1D. Els resultats simulats de SCAPS-1D es van comparar amb els resultats experimentals. Després de l'optimització dels paràmetres de la celda, es va incrementar l'eficiència de conversió d'un dispositiu optimitzat i, a partir del modelatge, es va descobrir que el rendiment del dispositiu es millora a l'augmentar la vida útil dels minoritaris, cosa que es aconsegueix amb la incorporació d'un camp elèctric a la superfície del con
[EN] The solar cell has emerged as a newer and a relatively sustainable energy source, that is eco-friendly and cost-effective if the production is on a larger scale. In the current scenario, the economic and high-power conversion efficiency photovoltaic devices without degradation of materials are designed for the generation of electricity. The silicon-based solar cells dominated the market for many years. For the manufacturing and production of silicon-based solar cells, sophisticated fabrication techniques are required that make the solar panel costly. Due to intensification in manufacturing capabilities, thin film solar cells are gaining significance. Thin film technology is one of the most cost-effective and efficient technologies for the manufacturing of solar cells, and it is an excellent subject of intense research in the photovoltaic industry. Thin film technology is economical than other technologies because devices have relatively less material and are based on various types of light absorbing semiconductor materials. Among these materials, kesterite solar cells utilizing CZTS, CZTSe and their alloys CZTSSe are emerging as the most auspicious replacement for the chalcopyrite absorbers. The outstanding electrical and optical features having direct optical band gap ranges among 1.4eV to 1.5eV and large absorption coefficient \alpha\ >{10}^4{cm}^{-1} of CZTS have made it very interesting in the thin film community. According to the Shockley-Queisser limit, the optimum conversion efficiency of around 28\ % is theoretically possible from a CZTS based solar cell by tuning the band gap, but still, it is not experimentally possible to achieve 28% conversion efficiency from a solar cell due to lack of understanding of device characteristics. For a better understanding of device characteristics, numerical modeling can play a significant role by modeling different device structures that can save time and cost of the research community. In this work, numerical modeling was carried out for estimating and analyzing the effect of physical parameters such as thickness and doping concentration of absorber, buffer and window layers, temperature effect and effect of illumination power of the sun on device performance. Device modeling had performed on the dedicated simulation software "Solar Cell Capacitance Simulator" (SCAPS-1D). To achieve this task first, a simple {p-n-n}^+ structure for Mo/CZTS/CdS/ZnO/FTO had been analyzed with molybdenum as back contact and FTO as a front contact. Through analysis, it had been found that solar cell performance was affected by variation in absorber thickness, doping concentration, and metal work function. After visualization of a basic device structure in SCAPS-1D, CZTS based experimental solar cell had been modeled. Experimentally designed CZTS solar cell results were first simulated in SCAPS-1D environment. The SCAPS-1D simulated results were then compared with experimental results. After optimization of cell parameters, the conversion efficiency of an optimized device was increased and from modeling, it had been found that device performance was improved by improving minority carrier lifetime and integration of back surface field at the back contact. Based on the results presented, it was found that recombination in a solar cell can greatly affect the performance of a solar cell. Therefore, a new structure (Back\ contact/CFTS/ZnS/Zn(O,S)/FTO) was modeled and analyzed in which interface recombination is reduced by optimizing the band gap of Zn(O,S) layer. Based on different device structure modeling, it was found that solar cell with structure CFTS/ZnS/Zn(O,S)/FTO can exhibit an efficiency of 26.11% with optimized physical parameters like absorber thickness layer of 4\mu m and acceptor concentration density of 2\times{10}^{18}\ {cm}^{-3}. The proposed results will give a valuable guideline for the feasible fabrication and designing of high-power conversion efficiency solar cells.
Khattak, YH. (2019). Modeling of High Power Conversion Efficiency Thin Film Solar Cells [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/118802
TESIS

This thesis describes the development of a fast rate method for the deposition of high quality CdS and CdTe thin films. The technique uses Pulsed DC Magnetron Sputtering (PDCMS). Surprisingly, the technique produces highly stable process conditions. CREST is the first laboratory worldwide to show that pulsed DC power may be used to deposit CdS and CdTe thin films. This is a very promising process technology with potential for eventual industrial deployment. The major advantage is that the process produces high deposition rates suitable for use in solar module manufacturing. These rates are over an order of magnitude faster than those obtained by RF sputtering. In common with other applications it has also been found that the energetics of the pulsed DC process produce excellent thin film properties and the power supply configuration avoids the need for complex matching circuits. Conventional deposition methodologies for CdS, Chemical Bath Deposition (CBD) and CdTe thin films, Electrodeposition (ED), have been chosen as baselines to compare film properties with Pulsed DC Magnetron Sputtering (PDCMS). One of the issues encountered with the deposition of CdS thin films (window layers) was the presence of pinholes. A Plasma cleaning process of FTO-coated glass prior to the deposition of the CdS/CdTe solar cell has been developed. It strongly modifies and activates the TCO surface, and improves the density and compactness of the deposited CdS thin film. This, in turn, improves the optical and morphological properties of the deposited CdS thin films, resulting in a higher refractive index. The pinhole removal and the increased density allows the use of a much thinner CdS layer, and this reduces absorption of blue spectrum photons and thereby increases the photocurrent and the efficiency of the thin film CdTe cell. Replacing the conventional magnetic stirrer with an ultrasonic probe in the chemical bath (sonoCBD) was found to result in CdS films with higher optical density, higher refractive index, pinhole and void-free, more compact and uniform along the surface and through the thickness of the deposited material. PDCMS at 150 kHz, 500 W, 2.5 μs, 2 s, results in a highly stable process with no plasma arcing. It allows close control of film thickness using time only. The CdS films exhibited a high level of texture in the <001> direction. The grain size was typically ~50 nm. Pinholes and voids could be avoided by reducing the working gas pressure using gas flows ii below 20 sccm. The deposition rate was measured to be 1.33 nm/s on a rotating substrate holder. The equivalent deposition rate for a static substrate is 8.66 nm/s, which is high and much faster than can be achieved using a chemical bath deposition or RF magnetron sputtering. The transmission of CdS can be improved by engineering the band gap of the CdS layer. It has been shown that by adding oxygen to the working gas pressure in an RF sputtering deposition process it is possible to deposit an oxygenated CdS (CdS:O) layer with an improved band gap. In this thesis, oxygenated CdS films for CdTe TF-PV applications have been successfully deposited by using pulsed DC magnetron sputtering. The process is highly stable using a pulse frequency of 150 kHz and a 2.5 μs pulse reverse time. No plasma arcing was detected. A range of CdS:O films were deposited by using O2 flows from 1 sccm to 10 sccm during the deposition process. The deposition rates achieved using pulsed DC magnetron sputtering with only 500 W of power to the magnetron target were in the range ~1.49 nm/s ~2.44 nm/s, depending on the oxygen flow rate used. The properties of CdS thin films deposited by pulsed DC magnetron sputtering and chemical bath deposition have been studied and compared. The pulsed DC magnetron sputtering process produced CdS thin films with the preferred hexagonal <001> oriented crystalline structure with a columnar grain growth, while sonoCBD deposited films were polycrystalline with a cubic structure and small grainy crystallites throughout the thickness of the films. Examination of the PDCMS deposited CdS films confirmed the increased grain size, increased density, and higher crystallinity compared to the sonoCBD CdS films. The deposition rate for CdS obtained using pulsed DC magnetron sputtering was 2.86 nm/s using only 500 W power on a six inch circular target compared to the much slower (0.027 nm/s) for the sonoChemical bath deposited layers. CdTe thin films were grown on CdS films prepared by sonoCBD and Pulsed DC magnetron sputtering. The results showed that the deposition technique used for the CdS layer affected the growth and properties of the CdTe film and also determined the deposition rate of CdTe, being 3 times faster on the sputtered CdS. PDCMS CdTe layers were deposited at ambient temperature, 500 W, 2.9 μs, 10 s, 150 kHz, with a thickness of approximately 2 μm on CdS/TEC10 coated glass. The layers appear iii uniform and smooth with a grain size less than 100 nm, highly compact with the morphology dominated by columnar grain growth. Stress analysis was performed on the CdTe layers deposited at room temperature using different gas flows. Magnetron sputtered thin films deposited under low gas pressure are often subject to compressive stress due to the high mobility of the atoms during the deposition process. A possible way to reduce the stress in the film is the post-deposition annealing treatment. As the lattice parameter increased; the stress in the film is relieved. Also, a changing the deposition substrate temperature had an effect on the microstructure of CdTe thin films. Increasing the deposition temperature increased the grain size, up to ~600 nm. CdTe thin films with low stress have been deposited on CdS/TEC10 coated glass by setting the deposition substrate temperature at ~200°C and using high argon flows ~ 70 sccm Ar. Finally, broadband multilayer ARCs using alternate high and low refractive index dielectric thin films have been developed to improve the light transmission into solar cell devices by reducing the reflection of the glass in the extended wavelength range utilised by thin-film CdTe devices. A four-layer multilayer stack has been designed and tested, which operates across the wavelength range used by thin-film CdTe PV devices (400 850 nm). Optical modelling predicts that the MAR coating reduces the WAR (400-850 nm) from the glass surface from 4.22% down to 1.22%. The application of the MAR coating on a thin-film CdTe solar cell increased the efficiency from 10.55% to 10.93% or by 0.38% in absolute terms. This is a useful 3.6% relative increase in efficiency. The increased light transmission leads to improvement of the short-circuit current density produced by the cell by 0.65 mA/cm2. The MAR sputtering process developed in this work is capable of scaling to an industrial level.

Thesis (M.S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Tummala Rao; Committee Member: Pulugurtha Raj; Committee Member: Wong C P. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis presents the results of research into the performance of advanced polymer dielectrics for the realization of high-power electronic circuits in a miniature form. These polymeric materials must satisfy a number of critical thermal, environmental, and electrical requirements to meet the required performance criteria for microelectronics applications. These desired attributes include thermal stability, low moisture uptake, high breakdown voltage (low leakage current), low dielectric constant, low loss tangent, high glass transition temperature, and low surface roughness. The use of these polymers allows for advanced electronic packaging techniques, resulting in improved system performance and reliability. Research was performed using a commercially available polymer dielectric and evaluated the feasibility of utilizing these materials as interlayer dielectrics in multilayer power electronic circuits. Historically, efforts to develop advanced interlayer dielectric materials have concentrated on promoting their use in high speed digital circuits. However, dielectrics used in power electronics must meet requirements not commonly stressed in designs for digital circuits. Multilayer circuits used in power electronics place a particular emphasis on the material properties of high dielectric strength or breakdown voltage and small values for loss tangent or dissipation factor. The focus of this research has been to characterize these particular properties for a commercially available polymer dielectric.
Master of Science

The possibility of using heavy rare earth metals and some of their alloys as pole piece materials for nanoscale electromagnets as in magnetic recording devices (hard drive disks) at cryogenic temperatures was evaluated. To set the frame an extensive literature review on high-moment materials and concepts is presented. Thin films of Permendur (Fe6%Co35 alloys), gadolinium (Gd), dysprosium (Dy), Dy50Gd50 binary alloys, terbium (Tb), holmium (Ho), DyRh binary alloys, and DyRhX (X = Fe, Ni, Co, Gd) ternary alloys were magnetron-sputtered and characterised for their chemical and crystal structure. In-plane magnetic properties were investigated over a temperature range of T = 3 -300 K by SQUID magnetometry, with an emphasis on the saturation magnetisation, i.e. the magnetic moment per unit volume, and points of magnetic transition such as Curie temperature. All heavy rare earth metals (Gd, Dy, DyGd, Tb, Ho) were found to be suitable write-pole candidates, for their saturation magnetisation exceeds that of Fe65Co35 in the cryogenic temperature regime. In terms of reasonably high magnetisation at moderate temperatures, DyGd and Tb are deemed the best materials. However, other write-pole relevant magnetic properties such as softness and initial permeability were unfavourable for all heavy rare earth metals. The DyRh binary and DyRhX ternary alloy system were found to be completely unsuitable, since they had very low saturation magnetisation, due to antiparallel coupling of the rare earth and the transition metals, as well as very low Curie points, i.e. operating temperatures of T -0 K. All thin films had saturation magnetisations slightly reduced, and transition temperatures slightly lower, than that of their bulk counterparts as a result of finite size effects.

The increasing demand for high performance electronics that can be fabricated onto large area substrates employing low manufacturing cost techniques in recent years has fuelled the development of novel semiconductor materials such as organics and metal oxides, with tailored physical characteristics that are absent in their traditional inorganic counterparts such as silicon. Metal oxide semiconductors, in particular, are highly attractive for implementation into thin-film transistors because of their high charge carrier mobility, optical transparency, excellent chemical stability, mechanical stress tolerance and processing versatility. This thesis focuses on the development of high performance transistors based on zinc oxide (ZnO) semiconducting films grown by spray pyrolysis (SP), a low cost and highly scalable method that has never been used before for the manufacturing of oxide-based thin-film transistors. The physical properties of as-grown ZnO films have been studied using a range of techniques. Despite the simplicity of SP, as-fabricated transistors exhibit electrical characteristics comparable to those obtained from ZnO devices produced using highly sophisticated deposition processes. In particular, electron mobility up to 25 cm2/Vs has been achieved in transistors based on pristine ZnO films grown at 400 °C onto Si/SiO2 substrates utilising aluminium source-drain (S-D) electrodes. A strong dependence of the saturation mobility on the work function of S-D electrodes and the transistor channel length (L) has been established. Short channel transistors are found to exhibit improved performance as compared to long channel ones. This was attributed to grain boundary effects that tend to dominate charge transport in devices with L < 40 μm. High mobility, low operating voltage (<1.5 V) ZnO transistors have also been developed and characterised. This was achieved through the combination of SP, for the deposition of ZnO, and thermally stable solution-processed self-assembling monolayer gate dielectrics. Detailed study of the temperature dependence of the operating characteristics of ZnO transistors revealed a thermally activated electron transport process that was described by invoking the multiple trapping and release model. Importantly, ZnO transistors fabricated by SP are found to exhibit highly stable operating characteristics with a shelf lifetime of several months. The simple SPbased fabrication paradigm demonstrated in this thesis expands the possibilities for the development of advanced simple as well as multi-component oxide semiconductors far beyond those accessible by traditional deposition methods such as sputtering. Furthermore, it offers unprecedented processing scalability hence making it attractive for the manufacturing of future ubiquitous oxide electronics.

Gli ossidi amorfi semiconduttori (AOS) sono nuovi candidati per l’elettronica flessibile e su grandi aree: grazie ai loro legami prevalentemente ionici hanno una mobilità relativamente alta (µ > 10cm^2/Vs) anche nella fase amorfa. Transistor a film sottile (TFT) basati sugli AOS saranno quindi più performanti di tecnologie a base di a-Si e più economici di quelle a base di silicio policristallino. Essendo amorfi, possono essere depositati a basse temperature e su substrati polimerici, caratteristica chiave per l’elettronica flessibile e su grandi aree. Per questa tesi, diversi TFT sono stati fabbricati e caratterizzati nei laboratori del CENIMAT all’Università Nova di Lisbona sotto la supervisione del Prof. P. Barquinha. Questi dispositivi sono composti di contatti in molibdeno, un canale semiconduttivo di ossido di zinco, gallio e indio (IGZO) e un dielettrico composto da 7 strati alternati di SiO2 e SiO2+Ta2O5. Tutti i dispositivi sono stati depositati mediante sputtering su sostrati flessibili (fogli di PEN). Le misure tensione-corrente mostrano che i dispositivi mantengono alte mobilità (decine di 10cm^2/Vs) anche quando fabbricati a temperature inferiori a 200°C. Si è analizzato il funzionamento dei dispositivi come fototransistor rilevando la risposta alla luce ultravioletta e in particolare la loro responsività e spostamento della tensione di soglia in funzione della lunghezza d’onda incidente. Questi risultati consentono di formulare ipotesi sul comportamento dei dispositivi alla scala microscopica. In particolare, indicano che i) la mobilità del canale non è influenzata dall’illuminazione, ii) sia l'IGZO sia il Ta2O5 contribuiscono al processo di fotoconduttività e iii) il processo di fotogenerazione non è adiabatico. La tesi contiene inoltre una descrizione del processo di ricombinazione e presenta un’applicazione pratica di tali dispositivi in un circuito per RFID. Infine, esplora la possibilità di migliorarne la flessibilità e le prestazioni.

Three high speed thin film patterning applications have been investigated using a high average power, high peak power laser system. Throughout this work the spatial intensity profile of the laser output was tailored to produce more efficient results. The first application involved the development of rapid laser patterning of an indium tin oxide layer on a glass substrate in order to generate transparent electrodes for a flat panel display. This work showed that the stitch line that occurs in-between adjacent laser pulses was formed by redeposition of material via the plume generated by the second, slightly overlapping pulse which is deposited within the region of overlap, an area which has an increased surface temperature at that time. The second application, laser edge deletion for thin film solar photo-voltaic panels, was an investigation of whether dual wavelength processing was able to avoid introducing micro-cracks into the soda-lime glass substrate. The third application was an examination of high speed removal of an aluminium coating from a stainless steel substrate which demonstrated that the layer could be adequately removed but required a series of highly overlapped pulses.

Hydrogenated amorphous silicon (a-Si:H) is increasingly being used in applications that require large-area, thin-film semiconductor. It can be deposited easily, at low temperature and low cost, on inexpensive substrates of almost any size by chemical vapour deposition methods. One of these applications of a-Si:H is the fabrication of thin-film transistors (TFTs) that are most often used in liquid crystal displays (LCDs). Plasma enhanced chemical vapour deposition (PECVD) is also called glow discharge deposition because of its visible luminosity of the plasma glow region, which is mainly the result of the de-excitation of emitting molecular and atomic species contained in the plasma. The field can be direct current (DC), radio frequency (RF), very high frequency (VHF), and microwave frequency. Deposition of a-Si:H employing the VHF-PECVD technique (typical frequency range 20-110 MHz) has been reported to yield an increase in deposition rate by one order of magnitude with respect to the conventional used frequency of 13.56 MHz, without adversely affecting material quality. The various electrical and optical properties of the VHF films were investigated as a function of main factors involved in the a-Si:H, SiN_x, and n⁺ µc-Si layers deposition processes. The effects of the total pressure, the gases flow ratio, and the influence of VHF power have been intensively investigated to gain device-quality materials. Finally, a number of fabrication techniques and electrical testing were employed in order to realise high-performance thin film transistors with the optimised materials.

In general, La-based high-k gate dielectric owns superior properties to offer transistor excellent characteristics. Thus, amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric has been investigated in this thesis. Different approaches have been adopted to improve the device performance. First of all, the influence of gate-dielectric annealing in oxygen for different times on the device characteristics of the amorphous InGaZnO thin-film transistor with HfLaO gate dielectric has been investigated. It is demonstrated that this annealing treatment can effectively suppress the negative oxide charges. Moreover, it is discovered that this annealing treatment can suppress the acceptor-like border and interface traps. Accordingly, a high saturation carrier mobility of 35.2 〖cm〗^2/V∙s is achieved for the 30’-annealed device. Then, the effects of dielectric-annealing gas (O2, N2 and NH3) for a fixed annealing time of 10 min on the device characteristics are studied, and improvements by the dielectric annealing are observed for each gas. Among the samples, the N2-annealed sample has a high saturation carrier mobility of 35.1 〖cm〗^2/V∙s, the lowest subthreshold swing of 0.206 V/dec and a negligible hysteresis. On the contrary, the O2-annealed sample shows poorer performance due to a decrease of electron concentration in InGaZnO. Furthermore, the NH3-annealed sample displays the lowest threshold voltage (1.95 V) due to increased gate-oxide capacitance and generated positive oxide charges. Next, the effects of fluorine incorporation in amorphous InGaZnO by ion implant on the characteristics of InGaZnO thin-film transistor have been investigated. The electrical characteristics can be improved by this treatment due to increase of carrier concentration and passivation of defects in the InGaZnO film. Consequently, the saturation carrier mobility can be increased to 34.0 〖cm〗^2/V∙s, and the output current can be nearly doubled. However, device degradation is observed for very high fluorine dose above 1.0×1015 /〖cm〗^2. Then, another method for fluorine incorporation has been studied by treating the amorphous InGaZnO film in a CHF3/O2 plasma. The saturation carrier mobility can be improved to as high as 39.8 〖cm〗^2/V∙s. Then, a new high-k material is proposed by investigating the effects of Ta incorporation in the La2O3 gate dielectric of amorphous InGaZnO thin-film transistor. Since the Ta incorporation is found to effectively enhance the moisture resistance of the La2O3 film, both the dielectric roughness and trap density at/near the InGaZnO/dielectric interface can be reduced, resulting in a significant improvement in the electrical characteristics of the device. Nevertheless, excessive incorporation of Ta can degrade the device characteristics due to newly-generated Ta-related traps. Finally, the proposed TaLaO is compared with Ta2O5 as the gate dielectric of amorphous InGaZnO thin-film transistor. It is found that the electrical characteristics of the device can be effectively improved by the incorporation of La in the Ta2O5 gate dielectric, which is ascribed to the fact that La incorporation can enlarge the band gap of Ta oxide and its conduction-band offset with InGaZnO, and also reduce the trap densities in the Ta2O5 gate dielectric and at the InGaZnO/gate-dielectric interface.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy

碩士
淡江大學
化學工程與材料工程學系碩士班
100
In this study, TiO2 sols with very small particle sizes (~5 nm) were synthesized in an aprotic solvent, N,N-dimethylacetamide (DMAc) and N,N- dimethylformamide (DMF), via sol-gel reaction at room temperature. The TiO2 sol showed long-term storage stability (30 days) and can provide operating control for the preparation of high–refractive–index polyimide-TiO2 hybrid thin films. By means of spin coating and multistep baking (up to 300 oC), the hybrid thin films were prepared from the solutions composed of soluble polyimide and TiO2 sol. The FE-SEM images showed a smooth and uniform morphology of the hybrid thin films. TiO2 domains were in the nanometer range, thus avoiding the light scattering. The refractive indices at 633 nm of the prepared hybrid thin films increase from 1.63 to 2.16 with increasing TiO2 content, which suggested the potential application to anti-reflective coatings and optical waveguides.

TeO2-based glasses have attracted growing attention due to their unique combination of properties (e.g., high refractive index, visible-to-infrared transparency window, high rare-earth solubility), which are promising for a wide range of applications. This thesis presents a mechanistic study on the relationship between glass-structure and properties of TeO2-based glasses with the aim of (i) enhancing visible transparency of TeO2-ZnO-Na2O (TZN) glass film and (ii) understanding ionic conductivity of TeO2-Na2O-NaX (TNN) glass system with X=Cl, Br, I. The first focus of this thesis is driven by the notorious issue that metallic-Te formed in TZN solgel films deteriorates the transparency. Previous research has revealed that metallic-Te is formed due to the chemical reduction of Te4+ to Te0 during the synthesis process. Applying O2 rich atmosphere during the thermal treatment (for converting organic sol to inorganic TZN glass) can suppress the formation of metallic-Te. However, the complete prevention of metallic-Te formation has not been achieved to date. In this thesis, the research on non-hydrolytic sol-gel (NHSG) process of making TZN transparent glass film elucidates the mechanism of metallic-Te formation, which reveals the use of O2 combined with a longer sol aging time (30~60 days) and an optimized sol heating temperature (150 oC) can completely prevent the formation of metallic-Te. The TZN glass film prepared via this optimized protocol has a transmission close to the theoretical limit. The achievement of high-transparent TeO2-based glass film paves the way to develop hybrid optoelectronic films by incorporating diverse nanoparticles with unique functionalities. The second part of this thesis focuses on ionic conductive glasses that rely on the migration of mobile alkali (sodium or lithium) ions. The conductivity of such glasses is determined by the concentration and mobility of mobile alkali ions. The research on traditional oxide glasses (SiO2- , B2O3, P2O5-based) has revealed that the incorporation of halides enhances the conductivity. This thesis investigates the impact of halides on the conductivity of the less-explored glass system, which is TNN glasses with varied (type and concentration) NaX. The conductivity depends on the mobility and concentration of the mobile ions. This research reveals the increase of free volume with increasing NaX concentration, which suggests an increase of space for ion migration thus mobile ion mobility. The Raman spectra confirm the expansion of glass network caused by the introduced NaX. The conductivities of NaCl and NaBr containing glasses remain constant while the mobile ion mobility increases with increasing NaCl or NaBr concentration, which infers a decrease of mobile Na+ ion concentration. The conductivity of NaI containing glasses significantly increases with increasing NaI concentration, which suggests an increase of mobile Na+ ion concentration in addition to the increase of the mobility. This research achieved the enhancement of conductivity while maintaining a good transparency of TeO2-based glasses. In addition, the mechanistic understanding of the relationship of halides, glass-structure and conductivity is a valuable guidance to the future research on ionic conductive glasses.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2022

碩士
淡江大學
化學工程與材料工程學系碩士班
99
In this study, UV-cured hybrid optical thin films were successfully prepared on PMMA substrates using TiO2 sols and acrylic monomers. TiO2 nanoparticles were synthesized via a sol-gel route at room temperature. Through the heat reflux process, the TiO2 nanoparticles became partial crystalline. The prepared TiO2 sols can provide operating control for the preparation of hybrid thin films by spin coating. Transparent high-refractive-index thin films were obtained with high TiO2 content. Photocatalytic ability of synthesized TiO2 nanoparticles was poor while some crystal structure existed. This may resulted from limited crystallinity of TiO2, and avoided a distinct degradation of organic moieties in the hybrids. TiO2 sols were characterized by DLS, TEM, XRD, and UV-Vis absorption, while TiO2 hybrid thin films were analyzed by UV-Vis absorption, FTIR, N&K, TGA, SEM, AFM, and contact angle. All hybrid thin films showed good adhesion to the PMMA substrate with refractive index falling over the range 1.66-1.82. These results suggested the potential application of present TiO2 hybrid films in optical devices, such as anti-reflective coatings.

Impressive examples of the generation of hierarchically-patterned, three-dimensional (3-D) structures for the control of light can be found throughout nature. Morpho rhetenor butterflies, for example, possess scales with periodic parallel ridges, each of which consists of a stack of thin (nanoscale) layers (lamellae). The bright blue color of Morpho butterflies has been attributed to controlled scattering of the incident light by the lamellae of the wing scales. Another stunning example is the frustule (microshell) of the Coscinodiscus wailesii diatom, which is capable of focusing red light without possessing a traditional lens morphology. The photonic structures and the optical behaviors of Morpho butterflies and Coscinodiscus wailesii diatoms have been extensively studied. However, no work has been conducted to shift such light manipulation from the visible to the infrared (IR) range via shape-preserving conversion of such biogenic structures. Controlling IR radiation (i.e., heat) utilizing biogenic or biomimetic structures can be of significant utility for the development of energy-harvesting devices. In order to enhance the optical interaction in the IR range, inorganic replicas of biogenic structures comprised of high-refractive-index materials have been generated in this work. Such replicas of Morpho rhetenor scales were fabricated via a combination of sol-gel solution coating, organic pyrolysis, and gas/solid reaction methods. Diatomimetic structures have also been generated via sol-gel coating, gas/solid reaction, and then patterning of pore arrays using focused ion beam (FIB) milling.

Throughout the sol-gel solution coating and chemical conversion steps of the processes developed in this study, attention was paid to preserve the starting shapes of the nanopatterned, microscale biogenic or biomimetic structures. Factors affecting such shape preservation included the thicknesses and uniformities of coatings applied to the biogenic or biomimetic templates, nano/microstructural evolution during thermal treatment, and reaction-induced volume changes. A conformal surface sol-gel (SSG) coating process was developed in this work to generate oxide replicas of Morpho rhetenor butterfly scales with precisely-controlled coating thicknesses. The adsorption kinetics and relevant adsorption isotherm of the SSG process were investigated utilizing a quartz crystal microbalance. Analyses of thermodynamic driving forces, rate-limiting kinetic steps, and volume changes associated with various chemical reactions were used to tailor processing parameters for optimized shape preservation.

碩士
國立中正大學
機械工程所
94
With the progress of micro-component and micro-system technology in recent years, micro-optics has already become a hot research field. The optics can roughly be divided into a diffracting type and refracting type, the main of this text is that the new method of refracting optic-component was developed. Using spin coating, Excimar laser forming and soft replica molding fabricate a variety of the optic components. The main characteristic of this study is Excimer laser forming technology to utilize, and break through traditional person who is expose way that develop produce. Using physical method fabricate micro-curved surface. Utilize PDMS mold to form convex and concave two kinds of soft mold of shape of the microlens at the same time. It is common characteristic to be simple to make step in that make these develop with chemistry etching, it is low to mostly reach the purpose and cost for the physics way, the good stability of quality, so that can be suitable forming amount is produced.

碩士
國立成功大學
機械工程學系碩博士班
93
In this article, the main purpose is that using multiple beam interferometry to produce the Fringe of Equal Chromatic Order (FECO) and then using FECO to determine the thickness and refractive index of the thin film. There are two methods to determine the thickness and refractive index of the thin film: one is symmetrical three-layer formula from Israelachvili, the other is multilayer matrix method and fast spectral correlation interferometry. In this article, I used the two methods respectively to analysis the FECO from the simulation or from the experiment and then to determine the thickness and refractive index of the thin film. And I compared the two methods and analysis the property of FECO. Finally, I developed a completed program. Let the results in this article to aid our experiments in surface force apparatus.

碩士
國立中央大學
化學工程與材料工程研究所
97
The purpose of this research is the preparation of transparent thick film or monolith with high refractive index. Titanium oxide, with a reported refractive index of 2.5 for anatase, can be a suitable inorganic additive in improving the refractive index of organic-inorganic hybrid materials. Epoxy resin, which is in common use of LED’s encapsulation. If titanium oxide and epoxy could be composited into a transparent material, the resulting product would have wide applications. To achieve such hybrid material with high refractive index and good transparency, the particle size of titanium dioxide must be below 10 nm, for otherwise light scattering effect would dominate. 　　For the synthesis of nano-sized titanium dioxide, tetrachloride (TiCl4) was used as a precursor, followed by hydrolysis and condensation reactions. After washed the white titanium hydroxide gel by water, peptization and crystallization took place in acidic condition. Since peptize size is strongly dependent on the solution concentration, pH and peptizing temperature, the first part of this research was finding the optimum experimental parameters to produce the smallest nano particles dispersible in water. 　　To disperse titanium dioxide in organic solvent and resin, surface modification of the particles is pivotal. Two aliphatic amines, for instance, n-hexlamine and dodecylamine were modifying agents used in this study. After surface modification with these agents, titanium dioxide can be dispersed in chloroform. 　　Concurrently, surface modification was done with functional silane, 3-(Trimethoxysilyl) propyl methacrylate (MPS) and 3-Glycidoxypropyl trimethoxysilane(GPS), allowing titanium dioxide to be dispersible in ethylacetate. Having successfully dissolved titanium dioxide, epoxy resin 4221 and EP828 were added. 　　The as-synthesized TiO2/epoxy thick film is formed from MPS&GPS modified TiO2 and then dispersed in ethylacetate/epoxy 4221 mixture. From thermal gravimetric analysis (TGA), the 8 micron thick film contains up to 50 wt% inorganic material (approximately 45 wt% TiO2 estimated). In addition, the refractive index is measured to be up to 1.70, and it has over 96% transmittance at 600nm wavelength. Nonetheless, such tranparent thick film has a very low glass transition temperature (~70oC), resulting in limited applications.

碩士
國立成功大學
機械工程學系碩博士班
94
The material will show remarkable different characteristic and phenomenon in the nano scale. It has become unlackable to build and use precise measuring technology and system to understand and control the material characteristic. The surface force apparatus not only be used in the measurement of thin film thickness and refractive index but also in the analysis of mechanics. For example: surface adsorbability ,friction.Therefore,the surface force apparatus can be used as one of the important tools to research nano science and technology. In this article,the main purpose is to build model system of surface force apparatus that applied to measure the thickness and refractive index of thin film. The main method to analyze the Fringe of Equal Chromatic Order(FECO) produced from multiple beam interferometry is by using symmetrical three-layer formula from Israelachvili. In this article, I used multilayer matrix method to simulate FECO and comparing it with the FECO from the experiment. And I researched the factors that influencing the definition of FECO. Finally, let the results in this article to aid development in the surface force apparatus.

碩士
國立成功大學
機械工程學系碩博士班
101
A surface-plasmon resonance(SPR) method based on a metal film deposited on anisotropic thin film is proposed. A polarization scanning ellipsometry is applied to achieve higher sensitivity and precision of measurement. An anisotropic thin film has been deposited in TIRE(Total Internal Reflection Ellipsometry) setup. By six anisotropic effective ellipsometric parameters based upon the amplitude ratio and phase difference of two orthogonal waves in an arbitrary coordinate system with a rotation angle θ relative to the X-Y coordinate frame, the higher sensitivity and precision of measurement can be achieved. In simulation, two different models (4-layer and 5-layer) are set to simulate solid and bio-fluidic samples. In an fixing incident angle at 72.5° of polarization scanning ellipsometry with scanning the input light’s polarization status from 0° to 180°, the resolution on 4 x 10-8 RIU can be achieved by extracting in theoritcal analysis, with refractive index varying. (1.33~1.37). And experimental confirmation in Stoke’s method has done. It has the accuracy is 2 x 10-7 which considered the instrumental error. The new method has achieved about 4 times sensitivity more than traditional spectrum-based SPR method. An polarization scanning ellipsometry only scans the linear input polarization status to excite the SPR phenomenon with an incident angle and dual-EO modulator can be applied to achieve the scanning fuction. Thus, the proposed method can reduce the risk of vibration and positioning errors from the mechanical scanning stage used in traditional ellipsometry.

碩士
國立臺灣大學
光電工程學研究所
96
This thesis focuses on two aspects of ZnO thin film transistors, the post oxygen passivation on ZnO thin film and a delta structure of ZnO TFTs. The first part demonstrates a high-performance enhancement-mode ZnO TFT on a glass substrate. A post deposition oxygen passivation technique is proposed with the purpose to fill up oxygen vacancies in the upper part of the ZnO channel layer. Before realizing the TFT device, the characteristics of ZnO thin film are examined to find out the optimal deposition conditions. The ZnO thin film is deposited by RF magnetron sputtering with the presence of O2 at low deposition rate and low temperature. The optimum duration of oxygen passivation in this work yields a device with a drain-source current level 0.87mA under a bias condition VGS=5V and VDS=15V, Ion/Ioff ratio 1.4×106. In the second part, we insert a delta doped layer into the conventional channel layer, and proposed a delta doped ZnO TFT. This structure can improve the stability and the operating current. Before realizing the TFT device, we need to find an optimal condition to growth GZO and combine the two films (ZnO and GZO) as a good channel layer. The optimum structure of a delta doped ZnO TFTs in this work yields a device with a drain-source current level 3.4mA under a bias condition VGS=5V and VDS=14V.