n-channel and p-channel amorphous-silicon thin-film transistors (a-Si:H TFTs) with copper electrodes prepared by a novel plasma etching process have been fabricated and studied. Their characteristics are similar to those of TFTs with molybdenum electrodes. The reliability was examined by extended high-temperature annealing and gate-bias stress. High-performance CMOS-type a-Si:H TFTs can be fabricated with this plasma etching method. Electrical characteristics of a-Si:H TFTs after Co-60 irradiation and at different experimental stages have been measured. The gamma-ray irradiation damaged bulk films and interfaces and caused the shift of the transfer characteristics to the positive voltage direction. The field effect mobility, on/off current ratio, and interface state density of the TFTs were deteriorated by the irradiation process. Thermal annealing almost restored the original state's characteristics. Floating gate n-channel a-Si:H TFT nonvolatile memory device with a thin a- Si:H layer embedded in the SiNx gate dielectric layer has been prepared and studied. The hysteresis of the TFT's transfer characteristics has been used to demonstrate its memory function. A steady threshold voltage change between the "0" and "1" states and a large charge retention time of > 3600 s with the "write" and "erase" gap of 0.5 V have been detected. Charge storage is related to properties of the embedded a-Si:H layer and its interfaces in the gate dielectric structure. Discharge efficiencies with various methods, i.e., thermal annealing, negative gate bias, and light exposure, separately, were investigated. The charge storage and discharge efficiency decrease with the increase of the drain voltage under a dynamic operation condition. Optimum operating temperatures are low temperature for storage and higher temperature for discharge. a-Si:H metal insulator semiconductor (MIS) capacitor with a thin a-Si:H film embedded in the silicon nitride gate dielectric stack has been characterized for memory functions. The hysteresis of the capacitor's current-voltage and capacitance-voltage curves showed strong charge trapping and detrapping phenomena. The 9 nm embedded a-Si:H layer had a charge storage capacity six times that of the capacitor without the embedded layer. The nonvolatile memory device has potential for low temperature circuit applications.

Hydrogenated amorphous silicon films subjected to KrF excimer laser irradiation with a profiled beam in air leads to the formation of microstructures. The main objective of this research was to perform a comprehensive study in understanding this material in three different aspects: thermal, electrical, and optical properties by experiment, SEM analysis and modelling. For the thermal interactions, analysis was carried out to investigate factors relating to the formation of the microstructures in a range of applied laser fluences from 93.8 to 443.8 mJ/cm2. The tallest microstructures were formed with average height from 1 to 3 ?m at laser fluence of 312.5 mJ/cm2. Investigation also include the effect of different applied laser fluence, different scanning schemes, the effect of the presence of 300 nm metal layer, and irradiation environment. Thermal modelling using COMSOL simulation software was used to simulate heat transfer during laser-material interaction and the results suggest a fair agreement with experimental findings. SEM and TEM reveal that the material formed was an oxynitride with embedded particles of crystalline silicon. In the electrical part, conductivity and field emission were the main tools to help elucidate the internal structure. Arrhenius plots acquired from conductivity measurements demonstrates a decrease in activation energy from 0.8957 eV from original sample to 0.3955 and 0.1727 eV for HE and LE sample respectively. Analysis also showed an agreement with Meyer Neldel rule for both samples. Observation made on the ratio of dark current to photogenerated current revealed the decrease from 59600 in original sample to 1.77 and 1.40 for HE and LE samples respectively. For the field emission properties, IE plots from samples were analysed using 170 ?m fixed gap structure, and lowest emission thresholds were achieved at 3 and 2.4 V/?m for HE and LE samples respectively. The results were fitted to a model of conducting particles in an insulating matrix offering a transport route to the surface. In the optical part, FTIR measurements were carried and analysis in IR absorbance profile within range of 550 to 2200 cm-1 demonstrates SiHx absorbance peaks at 640 cm-1, between 1980 to 2100 cm-1, and at 2095 cm-1. Hydrogen content was found to be decreased with the increase in applied laser fluence from 12 % in original sample to 4.2 and 1.5 % for HE and LE sample respectively. Measurements using UV-Vis between wavelengths of 200 to 1100 nm shows high absorbance up to 98% for laser process sample from 218.8 to 312.5 mJ/cm2. TR analysis demonstrated increasing absorbance properties at increasing incident angle. Raman spectroscopy showed an increase in the crystal fraction with laser fluence. The final analysis work in this thesis examines the material as a potential disordered photonic crystal and studies the propagation and localisation of light in ordered and disordered photonic crystal, modelled using COMSOL simulation software. This shows the transition from diffusive to localised propagation. A number of applications are suggested for this structured material. This is the first report of a new large area ‘black silicon’ material that has a number of interesting applications.

Rapid progress over the last decade on thin film transistor (TFT) active matrix organic light emitting (AMOLED) displays led to the emergence of high-performance, low-power, low-cost flat panel displays. Despite the shortcomings of the active matrix that are associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the AMOLED backplane. To take advantage of this technology, it is crucial to develop driving schemes and circuit techniques to compensate for the limitations of the TFTs. The driving schemes proposed in this thesis address these challenges, in which, the sensitivity of the OLED current to the transistor variations is reduced significantly. This is achieved by comparing the data signal with a feedback signal associated with the pixel current by means of an external driving circuit through a column feedback line. Depending on the nature of the feedback signal, (i.e. current or voltage) several pixel circuits and external drivers are proposed. New AMOLED pixel circuits with voltage and current feedback are designed, simulated, fabricated, and tested. The performance of these circuits is analyzed in terms of their stability, settling time, power efficiency, noise, and temperature-dependence. For the pixel circuits with current feedback, an operational transresistance amplifier is designed and implemented in a high-voltage CMOS process. Measurement results for both voltage and current feedback driving schemes indicate less than a 2%/V sensitivity to shifts in the threshold voltage of the TFTs. By using current feedback and an accelerating pulse, programming times less than 50 s are achieved.

Rapid progress over the last decade on thin film transistor (TFT) active matrix organic light emitting (AMOLED) displays led to the emergence of high-performance, low-power, low-cost flat panel displays. Despite the shortcomings of the active matrix that are associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the AMOLED backplane. To take advantage of this technology, it is crucial to develop driving schemes and circuit techniques to compensate for the limitations of the TFTs. The driving schemes proposed in this thesis address these challenges, in which, the sensitivity of the OLED current to the transistor variations is reduced significantly. This is achieved by comparing the data signal with a feedback signal associated with the pixel current by means of an external driving circuit through a column feedback line. Depending on the nature of the feedback signal, (i.e. current or voltage) several pixel circuits and external drivers are proposed. New AMOLED pixel circuits with voltage and current feedback are designed, simulated, fabricated, and tested. The performance of these circuits is analyzed in terms of their stability, settling time, power efficiency, noise, and temperature-dependence. For the pixel circuits with current feedback, an operational transresistance amplifier is designed and implemented in a high-voltage CMOS process. Measurement results for both voltage and current feedback driving schemes indicate less than a 2%/V sensitivity to shifts in the threshold voltage of the TFTs. By using current feedback and an accelerating pulse, programming times less than 50 s are achieved.

The traditional displayer ¡V CRT has already been substituted by liquid crystal displayer (LCD).The a-Si TFT is used to be a switch, while the size of the displayer increases, the require of the performance and quality of TFTs is more and more better. Therefore, it is very important subject to study the stability and to improve the performance of a-Si TFTs. In this thesis, we fabricate another new structure (asymmetry dual-gate TFTs).For asymmetry dual-gate TFTs, the ITO back gate is extended to the middle of the channel and only covered on the drain contact. The new structure has the advantages of dual-gate TFTs. With dual-channel conduction, it exhibit higher Ion and lower photo leakage current performance than the conventional inverted staggered TFTs. In addition, we use the asymmetry dual-gate structure to investigate how the parasitic capacitance influences the feed-through voltage by C-V measurement. We also to investigate the influences of electrical characteristics with the ITO back gate whether or not overlap the source contact. The asymmetry in on current with source-drain swapping can be attributed to the difference in the ITO back gate whether overlaps the source contact. Finally, it simulated the process of the degradation on the TFTs to find the stability mechanism of the TFTs.

In this thesis study, fabrication and characterization of silicon thin films prepared by magnetron sputtering and electron beam evaporation for solar cell applications have been investigated. In the first part of the study, magnetron sputtering method was used to fabricate thin hydrogenated amorphous silicon (a-Si:H) film on a Si substrate. Some samples were prepared on glass substrate for the basic characterizations like transmission and resistivity. Dark and illuminated I-V characteristics of the silicon heterojunction (SHJ) solar cells were studied as a function of material type and process parameters. It was observed that devices show diode characteristics, however their response to the illumination was quite weak. Low performance of the devices was discussed in terms of the resistivity and dopability of the sputtered film. The second part of the thesis deals with the fabrication and characterization of thin polysilicon films fabricated by e-beam evaporation. In order to dope the deposited Si films, a very thin boron film v was deposited by e-beam evaporation on SiO2 surface thermally grown on a Si wafer. Then an a-Si was evaporated by the same technique. Samples were annealed for polysilicon formation by using the technique called solid phase crystallization (SPC). The annealing was performed in two steps. The first step was the nucleation part, carried out at 475&deg / C for 8 hours and the second step was the diffusion and crystallization parts that are accomplished at 900&deg / C for several minutes. The Raman measurements revealed out the crystallinity and grain size. The crystallinity of the polysilicon thin films was also identified by X-Ray diffraction measurements. Finally, the Secondary Ion Mass Spectroscopy (SIMS) analysis was carried out to find out the amount of boron that diffuses into Si film. It was found that a graded boron profile, which is desirable for the solar cell applications, was achieved.

No description available.

Silicon based materials, including silicon oxides and silicon oxynitrides, have found use in a number of areas in photonics including waveguides, antireflection and highly reflective coatings for laser facets, and detectors. For effective use of these materials in photonics it is necessary to characterize their optical properties as a function of their composition and structure. Since these characteristics are often dependent on the method used to deposit the films it is necessary to also determine the effect of deposition type and conditions on the film's properties. Recently, silicon based materials have been seen to display luminescence due to quantum confinement effects when nanocrystals are formed. This opens up the possibility of a silicon based emitter, something that has not had previous success due to the indirect bandgap of bulk silicon. The development of a silicon based emitter in turn would open up the possibility for monolithically integrated photonic circuits that could take advantage of CMOS processing technology. This thesis presents the results of research into the characterization of amorphous silicon and silicon oxide thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition. Optical properties of the films have been determined through the use of ellipsometry and correlated with the results from compositional analysis, done using Rutherford backscattering and elastic recoil detection, and bonding structure analysis, done using Fourier transform infrared spectroscopy. Nanocrystals were formed within the films by subjecting them to post-deposition thermal annealing, which induces a phase separation in silicon rich silicon oxide films. The effects of different annealing conditions on composition, structure and optical properties have also been analyzed. Finally, photoluminescence experiments were conducted on the films and correlated with the results from other characterization techniques. / Thesis / Master of Applied Science (MASc)

Hydrated amorphous silicon dioxide (Si02.nH-,O), or opal-A, is deposited naturally from seepage and runoff water as white or brown rock surface coatings, called 'skins', that often partly obscure rock paintings and engravings, but occasionally, a thin translucent silica skin can form a protective film over rock art. White lustrous silica skins, less than 1 mm thick, occur where seepage water regularly flows from bedding and joint planes, whereas much thinner brown skins form on the sides of boulders and cliffs where runoff water periodically flows. To find the degree of silica skin variability and to determine how climate and rock type affect the properties of silica skins I collected samples at seven Australian and two Canadian rock painting sites that were located in temperate, tropical and sub-arctic regions. The skins had developed on sandstone, quartzite, schist, gneiss and migmatite. I studied the effects of the skins on rock art stability, documented their compositions, textures and structures to establish their common properties, and searched for a way to date the silica which would provide an indication of the minimum age of the underlying art. 1 also made replication experiments to determine factors that influence the properties of artificial silica skins and the rates of their precipitation so that I could propose a mechanism for natural silica skin formation, and ascertain whether an artificial silica skin could act as a protective rock art conservation measure. I was able to subdivide the analysed samples into silica skin Types I, II and III on the basis of their colour (translucent, white or brown), composition (SiO2, Al2O3 and absorbed water contents) and texture (smooth vitreous or vermiform). I propose that silica skins initially begin to form on stable rock surfaces by a process involving a combination of evaporation- and ionic-induced polymerisation of silicic acid in seepage and runoff water. Condensation reactions, random clustering of small silica spheres and deposition of the resulting aggregates eventually produce a thin surficial silica film. Deposition of silica often traps micro-organisms that live in the damp seepage and runoff water zones, and these fossils in finely laminated skins enable the radiocarbon dating of silica deposition, and therefore the dating of rock paintings enclosed by silica. Micro-excavation of silica layers associated with rock art combined with accelerator mass spectrometry gave preliminary radiocarbon determinations that were either consistent with, or contradicted, prevailing opinions about the antiquity of the rock art at selected sites. Experiments using a laser technique for combusting fossilised microorganisms in finely laminated skins were unable to generate sufficient carbon for dating. Catalysis of a mixture of equal proportions of methyl-trimethoxy silane and water produces a translucent stable film that may be suitable as a consolidant, whereas other artificial silica skins made from silica glass and tetra-ethoxy silane develop microfractures on drying, and these are unsuitable as rock art consolidants.

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are used as charge switches in flat-panel X-ray detectors. The inherent noise in the TFTs contributes to the overall noise figure of the detectors and degrades the image quality. Measurements of the noise provide an important parameter for modeling the performance of the detectors and are a sensitive diagnostic tool for device quality. Furthermore, understanding the origins of the noise could lead to change a method of a-Si:H deposition resulting in a reduction of the noise level. This thesis contains measurements of the low-frequency noise in a-Si:H TFTs with an inverted staggered structure. The noise power density spectrum fits well to a power law with Ñ near one. The normalized noise power is inversely proportional to gate voltage and also inversely proportional to channel length in both the linear and saturation regions. The noise is nearly independent of the drain-source voltage and drain-source current. The noise is unaffected by degrading the amorphous silicon through gate-biasing stress. Hooge¡¦s parameter is in the range 1-2*E-3 or 2-4*E-4 depending on whether the parameter is calculated using the total number of charge carriers in the accumulation layer or just the number of free carriers. As an example, the signal to noise ratio is calculated for photodiode detector gated by a TFT using the results from the noise measurements.