Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>Tantalum diffusion barrier coatings were investigated as a way to improve the conversion efficiency of CIGS (copper indium gallium diselenide) solar cells.  Tantalum coatings were deposited upon silicon and stainless steel foil substrates using direct current magnetron sputtering (DcMS) and high power impulse magnetron sputtering (HiPIMS).  The coatings were characterized using scanning electron microscopy (SEM).  Cross-sectional scanning electron micrographs revealed that the HiPIMS coatings appeared denser than the DcMS coatings.</p>

The long-term goal of this research project is the development of solution-based inorganic dielectric and semiconductor materials for inkjet printed electronics. The main focus of this thesis involves testing of the materials and devices under development. A new solution-based inorganic dielectric material (HfOSO₄), given the name hafsox, is developed and shows excellent dielectric properties. Hafsox with the addition of lanthanum, to improve film dehydration, has successfully been demonstrated as a gate dielectric. Metal-insulator-metal (MIM) capacitance testing of hafsox with lanthanum, has resulted in a low loss tangent of 0.30% at 1 kHz, a relative permittivity of 11.47 at 1 kHz, a breakdown voltage of 6.30 MV cm⁻¹, and a leakage current density of 4.38 nA cm⁻² at 1 MV cm⁻¹. Progress has also been achieved in the development of solution-based semiconductor materials. To date the most successful of these materials is zinc indium oxide (ZIO), which has been demonstrated as a thin-film-transistor (TFT) channel material. This ZIO TFT is a depletion-mode device with a turn-on-voltage of V[subscript on]~ -19 V, a threshold voltage of V[subscript T] ~-16 V, and a drain current on-to-off ratio of ~10³. Mobilities extracted from this ZIO TFT include an incremental mobility of μ[subscript inc] ~0.05 cm² V⁻' sec⁻', an effective mobility of μ[subscript eff] ~0.02 cm² V⁻' sec⁻', and an average mobility of μ[subscript avg] ~0.02 cm² V⁻' sec⁻' at V[subscript GS]=20 V. The development of metal-semiconductor field-effect transistors (MESFET) TFTs is also investigated as a means of eliminating the need for a dielectric material in order to reduce the complexity of fabricating circuits. MESFETs are attempted with semiconductor materials such as CdS that is deposited by chemical bath deposition (CBD) and SnO₂ that is deposited by RF magnetron sputtering, but with little success. The most successful MESFET-like device fabricated, employing SnO₂ as the channel material, is a strong depletion-mode device with a small amount of gate voltage modulation. / Graduation date: 2006

Graduation date: 1998

TiNi films were prepared by co-sputtering TiNi target and a separate Ti target. Crystalline structure and phase transformation behaviors of TiNi films were investigated. Results showed that TiNi films had fine grain size of about 500 nm and fully martensitic structure at room temperature. X-ray photoelectron spectroscopy (XPS) results indicated that there is adherent and natural TiO₂ film, which is beneficial to its corrosion resistance and biocompatibillity. Results from differential scanning calorimeter (DSC), in-situ X-ray diffraction (XRD) and curvature measurement revealed clearly martensitic transformation upon heating and cooling. The TiNi films were further deposited on micromachined silicon cantilever and membrane structures in order to form micro-gripper or microvalve with large deformation due to shape-memory effect. / Singapore-MIT Alliance (SMA)

Part I - We have designed a binary metallic alloy for nanoscale resonator applications. We used magnetron sputtering to deposit films with different stoichiometries of aluminum and molybdenum and then characterized the microstructure and physical properties of each film. A structure zone map is proposed to describe the dependence of surface and bulk structure on composition. We then fabricated proof of principle resonators from the Al-32 at%Mo composition, selected for its optimized physical properties. An optical interferometer was used to characterize the frequency response of our resonators. Part II - We investigate the growth of faceted polycrystalline thin films with modeling and simulations. A new analytic model is derived for the case of orientation dependent facet growth velocity and the dependence of growth on initial grain orientations is explicitly calculated. Level set simulations were used to both confirm this analytic model and extend it to include various angular flux distributions, corresponding to different deposition methods. From these simulations, the effects of self-shadowing on polycrystalline film growth are quantitatively evaluated. / Materials Engineering

Advanced optical technologies profoundly impact countless aspects of modern life. At the heart of these technologies is the manipulation of light using optical materials. Currently, optical technologies are created using naturally occurring materials. However, a new and exciting approach is to use nanomaterials for technology development. Nanomaterials are artificially constructed material systems with precisely engineered nanostructures. Many technological revolutions await the development of new nanoscale fabrication methods that must provide the ability to control, enhance, and engineer the optical properties of these artificial constructs. This thesis responds to the challenges of nanofabrication by examining glancing angle deposition (GLAD) and improving its optical-nanomaterial fabrication capabilities. GLAD is a bottom-up nanotechnology fabrication method, recognized for its flexibility and precision. The GLAD technique provides the ability to controllably fabricate high-surface-area porous materials, to create structurally induced optical-anisotropy in isotropic materials, and to tailor the refractive index of a single material. These three advantages allow GLAD to assemble optical nanomaterials into a range of complex one-dimensional photonic crystals (PCs). This thesis improves upon previous GLAD optical results in a number of important areas. Multiple optical measurement and modeling techniques were developed for GLAD-fabricated TiO2 nanomaterials. The successful characterization of these nanomaterials was extended to engineer PC structures with great precision and a superior degree of control. The high surface area of basic PC structures was exploited to fabricate an optimized colourimetric sensor with excellent performance. This colourimetric sensor required no power source and no read-out system other than the human eye, making it a highly attractive sensing approach. Incorporating engineered defects into GLAD-fabricated PCs established a new level of design sophistication. Several PC defect structures were examined in detail, including spacing layers and index profile phase-shifts. Remarkable control over defect properties was achieved and intriguing polarization-sensitive optical effects were investigated in anisotropic defect layers. The success of these results demonstrates the precision and flexibilty of the GLAD technique in fabricating optical nanomaterials and advanced photonic devices. / Micro-Electro-Mechanical Systems (MEMS) and Nanosystems

We use different methods to deposit Ti thin film on the ITO glass substrate. Under the circumstances of using fixed concentration of electrolyte, changing anodic time, and applying voltage, we are able to use anodic method to make ordered nano TiO2 thin film,of which the smallest pore size is 18nm and the thickness is 4500

¡@¡@Because of the poly-si thin film transistor have the advantage of high mobility, it can improve the analysis for the flat plan display. Using the above advantage can combine the integrated circuit as control IC and memory on the small panel to reduce the number between the switch circuits and the outside contacts. These precise circuits must be considering the photo current¡Bthermal effects and the parasitical capacitance more due to the influence of these precise circuits is more serious than the switch circuits. In my thesis, the research of the electrical characteristics of the newest excimer laser crystallize coplane poly-si thin film transistors ,and using the device length with width is 128um/6um and 128um/16um can be extracted that the environment of the facing illumination have the photo-leakage current than none illumination about four orders, and the photo-leakage current is not consider with any gate voltage. ¡@¡@With the discussion of the capacitance, the main point of my researches is to change different conditions to extract the gate to source capacitance (Cgs). In addition, the slight carriers may effect the devices with the high mobility system on panel (SOP) technology error, the temperature must be considered. ¡@¡@We find the mobility is bigger at the environment of the temperature is 300K than the environment of the temperature is 100K when the device work in the linear region and the on current is lower at the environment of the temperature is 300K than the environment of the temperature is 100K when the device work in the saturation region. Using some references and some models as the concepts can analysis some phenomenons I refer to above.

The objective of this investigation was to develop micro/nano-scale temperature sensors for measuring surface temperature transients in multi-phase flows and heat transfer. Surface temperature fluctuations were measured on substrates exposed to phase change processes. Prior reports in the literature indicate that these miniature scale surface temperature fluctuations can result in 60-90 percent of the total heat flux during phase change heat transfer. In this study, DTS (Diode Temperature Sensors) were fabricated with a doping depth of ~100 nm on n-type silicon to measure the surface temperature transients on a substrate exposed to droplet impingement cooling. DTS are expected to have better sensor characteristics compared to TFTs (Thin Film Thermocouples), due to their small size and faster response (which comes at the expense of the smaller operating temperature range). Additional advantages of DTS include the availability of robust commercial micro fabrication processes (with diode and transistor node sizes currently in the size range of ~ 30 nm), and that only 2N wire leads can be used to interrogate a set of N x N array of sensors (in contrast thermocouples require 2 N x N wire leads for N x N sensor array). The DTS array was fabricated using conventional semi-conductor processes. The temperature response of the TFT and DTS was also calibrated using NIST standards. Transient temperature response of the DTS was recorded using droplet impingement cooling experiments. The droplet impingement cooling experiments were performed for two different test fluids (acetone and ethanol). An infrared camera was used to verify the surface temperature of the substrate and compare these measurements with the temperature values recorded by individual DTS. PVD (Physical Vapor Deposition) was used for obtaining the catalyst coatings for subsequent CNT synthesis using CVD (Chemical Vapor Deposition) as well as for fabricating the thin film thermocouple (TFT) arrays using the "lift-off" process. Flow boiling experiments were conducted for three different substrates. Flow boiling experiments on bare silicon wafer surface were treated as the control experiment, and the results were compared with that of CNT (Carbon Nano-Tube) coated silicon wafer surfaces. Similar experiments were also performed on a pure copper surface. In addition, experiments were performed using compact condensers. Micro-scale patterns fabricated on the refrigerant side of the compact heat exchanger were observed to cause significant enhancement of the condensation heat transfer coefficient.