by Poon Sai Keung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1978. / Includes bibliographical references (leaves 92-94).

L’objectif de cette thèse est de développer la caractérisation et le diagnostic non destructif de microbatteries « tout solide » par spectroscopie d’impédance électrochimique. Ces travaux s’appuient sur des microbatteries commerciales EnFilmTM EFL700A39, basées sur une architecture lithium métal Li/LiPON/LiCoO2. La caractérisation unitaire des couches actives, constituant ces microbatteries, a permis d’une part, d’identifier les principales propriétés de transport des ions Li+ dans l’électrolyte solide, et d’autre part, a permis de mettre en avant la présence de zones plus ou moins conductrices dans la couche active LiCoO2, pouvant engendrer des limitations électroniques et/ou ioniques lors du fonctionnement de la microbatterie. L’étude des microsystèmes complets par spectroscopie d’impédance électrochimique a ensuite été effectuée en fonction du taux de lithiation de l’électrode positive, du nombre de cycles, et du vieillissement calendaire de la microbatterie. Les résultats obtenus ont donné naissance à un circuit électrique équivalent permettant de modéliser le comportement (souvent indépendant) des différentes couches actives durant l’utilisation d’une microbatterie. Cette modélisation permet en outre de cibler les origines éventuelles de défaillances, soit après la fabrication, soit au cours du vieillissement d’une microbatterie. Les travaux additionnels effectués sur des systèmes lithium free (LiCoO2/LiPON/Cu) révèlent, quant à eux, une forte interaction électrochimique entre le lithium et le collecteur de cuivre (partiellement oxydé) et mettent en évidence l’importance capitale des premiers cycles de la cellule pour ses performances ultérieures / The goal of this work is to develop characterization and non-destructive diagnosis of all-solid-state lithium microbatteries, essentially by means of electrochemical impedance spectroscopy. This work is based on commercial microbatteries EnFilmTM EFL700A39, built with the lithium metal architecture Li/LiPON/LiCoO2. Firstly, the elemental characterization of active layers allowed us to identify the main properties of the ionic motion in the solid electrolyte layer. Secondly, characterization of the positive electrode (LiCoO2) revealed the existence of more or less conductive areas inside the layer. Theses areas can cause ionics or electronics limitations during battery operation. The study of the entire microsystems by electrochemical impedance spectroscopy was then performed according to lithiation rate (SOC), number of cycles, and battery aging. The results obtained allowed the building of an electrical equivalent circuit for modeling the behaviour of the different active layers of a microbattery in use. This model also allows targeting the origins of any failures after manufacturing or upon microbattery aging. Additional works on lithium free systems (LiCoO2/LiPON/Cu) reveals a strong electrochemical interaction between in situ deposited lithium and copper current collector (partially oxidized) and highlight the critical importance of the very first cycles of the cell for subsequent performance

No description available.

Xia, Daxue. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The rapid progress of n-type metal oxide thin film transistors (TFTs) has motivated research on p-type metal oxide TFTs in order to realise metal oxide-based CMOS circuits which enable low power consumption large-area electronics. Cuprous oxide (Cu2O) has previously been proposed as a suitable active layer for p-type metal oxide TFTs. The two most significant challenges for achieving good quality Cu2O TFTs are to overcome the low field-effect mobility and an unacceptably high off-state current that are a feature of devices that have been reported to date. This dissertation focuses on improving the carrier mobility, and identifying the main origins of the low field-effect mobility and high off-state current in Cu2O TFTs. This work has three major findings. The first major outcome is a demonstration that vacuum annealing can be used to improve the carrier mobility in Cu2O without phase conversion, such as oxidation (CuO) or oxide reduction (Cu). In order to allow an in-depth discussion on the main origins of the very low carrier mobility in as-deposited films and the mobility enhancement by annealing, a quantitative analysis of the relative dominance of the main conduction mechanisms (i.e. trap-limited and grain-boundary-limited conduction) is performed. This shows that the low carrier mobility of as-deposited Cu2O is due to significant grain-boundary-limited conduction. In contrast, after annealing, grain-boundary-limited conduction becomes insignificant due to a considerable reduction in the energy barrier height at grain boundaries, and therefore trap-limited conduction dominates. A further mobility improvement by an increase in annealing temperature is explained by a reduction in the effect of trap-limited conduction resulting from a decrease in tail state density. The second major outcome of this work is the observation that grain orientation ([111] or [100] direction) of sputter-deposited Cu2O can be varied by control of the incident ion-to-Cu flux ratio. Using this technique, a systematic investigation on the effect of grain orientation on carrier mobility in Cu2O thin films is presented, which shows that the [100] Cu2O grain orientation is more favourable for realising a high carrier mobility. In the third and final outcome of this thesis, the temperature dependence of the drain current as a function of gate voltage along with the C-V characteristics reveals that minority carriers (electrons) cause the high off-state current in Cu2O TFTs. In addition, it is observed that an abrupt lowering of the activation energy and pinning of the Fermi energy occur in the off-state, which is attributed to subgap states at 0.38 eV below the conduction band minimum. These findings provide readers with the understanding of the main origins of the low carrier mobility and high off-state current in Cu2O TFTs, and the future research direction for resolving these problems.

Zhao, Wei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Acknowledgements --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2. --- H-bonded Acenes- An Approach to Self- assembled Organic Semiconductors --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Result and discussion --- p.17 / Chapter 2.3 --- Experiment --- p.23 / Chapter Chapter 3. --- Transistors from a Conjugated Macrocycle Molecule: Field and Photo Effects --- p.30 / Chapter 3.1 --- Introduction --- p.30 / Chapter 3.2 --- Result and discussion --- p.31 / Chapter 3.3 --- Conclusion --- p.37 / Chapter 3.4 --- Experiment --- p.37 / Chapter Chapter 4 --- Synthesis of Soluble and liquid crystalline Conjugated Macrocylces --- p.48 / Chapter 4.1 --- Introduction --- p.48 / Chapter 4.2 --- Result and Discussion --- p.49 / Chapter 4.3 --- Conclusion --- p.54 / Chapter 4.4 --- Experiment --- p.55 / Appendix --- p.65

The body of work in this dissertation focuses on the properties of an environmental thin film system, including the roughness and composition of the surface. The deposition of particles, such as airborne soil and plant pollen, from the atmosphere creates a thin film known as “environmental film” or “urban film” that covers virtually all of Earth’s solid surfaces. Environmental films have been shown to accumulate a variety of chemicals, including toxic pollutants. To investigate the means by which environmental films uptake chemicals, model films are made in the lab and real films are collected outside. Model films serve to mimic the properties of native films and allow for a simple analysis of a complex system. Native films serve to provide real field samples to analyze. The properties of model and native films are characterized using reflected light to determine what the film is made of and microscopes capable of imaging small particles. The results of the model film study indicate a model capable of reproducing the surface roughness and other properties of native films. This study serves as a platform with the goal of making model films that better mimic native films. The results of the native film study indicate successful imaging using microscopes capable of revealing the structure and chemical composition of the films. This imaging adds an important contribution to the field that has not previously been performed.

Due to the size of the nano-scale and micro-scale materials, traditional method for measuring the thermal properties of the bulk materials cannot be applied. The 3 OmegaMethod was developed by D. G. Cahill in the early 90s. It was used extensively to measure the thermal properties of thin film dielectric materials. Compare with other simulations or experimental methods, the 3 Omega Method has many advantages. Previous research has indicate that the 3 Omega method is capable of measuring the cross-plane thermal conductivity of thin film materials. In extension, an alternative improvement for measurement of the in-plane thermal conductivity and calculating the difference between the in-plane thermal property and the cross-plane thermal property (anisotropy) are developed based on the concept of the 3 Omega Method.

Pressure measurement using a strain gauge bonded with epoxy adhesive to a metallic mechanical support has been, and still is, extensively employed, however, for some applications the use of an epoxy is inadequate, especially when temperatures exceed 120C. There is therefore particular interest in the use of thin film techniques to vacuum deposit strain gauges directly on metallic substrates. Such devices are highly cost effective when produced in large quantities due to the manufacturing techniques involved. This makes them ideally suited for use in large-volume products such as electronic weighing scales and pressure transducers. In this thesis, new techniques for fabricating thin film vapour deposited strain gauge transducers on metal substrates for application as novel pressure sensors in the fastener industry are developed. Clearly, for a vapour deposited strain gauge to function correctly, it is essential that it be deposited on a defect free, high quality electrically insulating film. This was a significant challenge in the present study since all available physical vapour deposition (PVD) equipment was direct current (DC) and insulators of around 4 um thick were needed to electrically isolate the strain gauges from metal. As a result, several methods of depositing insulators using DC were developed. The first involved the use of DC magnetron sputtering from an aluminium target to reactively deposit up to 4 um thick AlN. DC magnetron discharges suffer arc instability as the AlN forms on the target and this limits the maximum thickness that can be deposited. Consequently, the arc instability was suppressed manually by increasing argon gas flow at the onset of arcing. Although the deposited AlN showed a high insulating resistance, it was found that the breakdown voltage could significantly increase by (a) utilising a metallic interlayer between the thin film insulator and the metallic substrate and (b) annealing in air at 300C. A second deposition method involved the use of DC magnetron sputtering to deposit modulated thin film insulators in which an aluminium target was used to reactively deposit alternating layers of aluminium nitride and aluminium oxide. These films showed significant increases in average breakdown voltage when the number of layers within the composite film was increased. The third method involved the deposition of AlN thin film insulators using partially filtered cathodic arc evaporation with shielding. Initially, AlN was deposited under partially filtered conditions to obtain a relatively thick (~ 4 um) coating then, while still depositing under partially filtered conditions, a smooth top coating was deposited by using a shielding technique. The deposition of metal macroparticles is an inherent problem with cathodic arc deposition and shielding is one form of macroparticle filtering. Such particles are highly undesirable in this study as they are electrically conductive. A fourth coating technique for depositing insulators on steel was based on thermal spray technology. Insulating films of Al2O3 were plasma sprayed and then polished to thereby fabricate viable electrical insulators for vapour deposited strain gauges. With respect to depositing strain gauges two methods were employed. The first involved the sputter deposition of chromium through a shadow mask to form a strain gauge with gauge factor sensitivity of around 2. The second used cathodic arc evaporation to fabricate a multi-layered strain gauge composed of alternating CrN and TiAlN layers that yielded a gauge factor of around 3.5. The technique achieves better compatibility between gauge and insulator by allowing a wider selection of materials to form the gauge composition. Finally, a novel pressure sensor in the form of a load cell was developed that consisted of a chromium strain gauge on a steel washer electrically insulated with AlN thin film. The load cell showed good performance when tested under compressive load.

Metallised polypropylene (MPP) capacitors, the dominant capacitor type used in a wide range of power and electronic circuit applications, offer high volumetric capacitor density, low cost, excellent frequency characteristics and a unique ability to recover from point failures in the dielectric film. However MPP capacitors have a generic weakness that is not well understood, failure of the self-healing process leading to ongoing catastrophic failure. The work described in this thesis includes the derivation of an improved electrical model of a capacitor and the uncovering of a mechanism for the catastrophic failure mode. Corrosion of the thin metallic field is firmly linked to drastic increases in metal film current densities and generation of hot spots in capacitors. In the work, novel formulae were derived relating capacitor parameters such as equivalent series resistance and equivalent series capacitance to frequency and physical characteristics such as metal film resistivity and physical dimensions of multiple layer capacitors. Modelling using numerical methods and diffusion equation showed that capacitors with double-end connection topology have more uniform voltage and power distribution than single-end connected capacitors. External characteristics of both connection topologies were shown to be virtually identical up to frequencies well above typical self-resonance. The aggregate spatial distribution of power from both layers and the voltage across the dielectric were found to be fundamentally different in the two circuit connection topologies. In this work it was shown that above singularity frequencies defined by distributed capacitance and metal film spreading resistance, equivalent series resistance and capacitance both fall with the square root of frequency Analysis of the inductance of typical MPP capacitors for single-end and double-end connected topologies and for circumferentially connected capacitor metallization showed that the magnitude and effect of distributed inductance in typical MPP power capacitors was insignificant compared to packaging inductance. Thermal and electrical modelling and experimental measurements showed that corrosion effects could readily account for the generic catastrophic failure mode of metallised polypropylene capacitors. Modelling showed that remnant vestiges of metal bridging corrosion gaps between the schooping and the metallic film could also pose serious thermal danger to the affected capacitor. Fusing current modelling and experimental measurement showed that fusing in metallic films typically occurred for current densities of several hundred thousand amperes per square centimetre. The partial disconnection of the metallic layers from the schooping edge by corrosion for example, was shown to result in large increases in dissipation factor and power loss in a capacitor readily explaining how capacitors