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The a. c. thin film electroluminescent (ACTFEL) devices are of scientific interest due to their applications in large area, flat panel displays. Of particular interest to the research community is the mechanism of electron transport and luminance in these devices. Toward this end, a physical model and a mathematical model for SrS:Cu ACTFEL Devices were developed and published earlier by our group. The purpose of this thesis is to obtain a qualitative and quantitative match between experiment and theory. A brief summary of the model can be found here [1]. Effects of variation in drive parameters in experimental steady state measurements, and analysis of VIL (Voltage-Current-Luminance) plots for different simulated device and drive parameters are performed. The effects of voltage amplitude, activator concentration, interface energy levels, and critical field for dipole collapse were studied. The plots matched qualitatively in that all major experimental features were produced in the simulated waveforms. The measured and the simulated peak currents are 72.5 mA/cm2 and 66.42 mA/cm2 for VA = 123 V. Experimental and theoretical charge transferred per pulse were 2.75 C/cm2 and 2.26 C/cm2. Peak experimental and simulated luminance values for VA = 123 V were 531 cd/m2 and 49150 cd/m2. Total experimental and simulated luminance values for VA = 123 V case were 6.2 cd/m2 and 561.2 cd/m2 respectively. The large difference is attributed to the loss factors such as optical losses (due to total internal reflection), scattering of electrons by impurities in the bulk phosphor layer, and concentration quenching; these have not been incorporated in the model yet.

The purpose of this thesis is to contribute to the understanding of SrS based ACTFEL devices. Better understanding of the processes in the host phosphor will give us the possibility to design more efficient blue emitting ACTFEL devices. Towards this aim, a physical model, that describes the optoelectronic processes taking place in the phosphor, was developed and analytical equations were written. The analytical model was numerically simulated and the plots of flux flowing through the device and luminance output by the device were obtained. Experiments were performed to obtain the plots of current flowing through the device and luminance output by the device. These plots were then qualitatively compared and the results of comparisons are presented. The numerical simulations qualitatively verify the accuracy of the model. The drive parameters were varied in order to study its effect on the VIL characteristics of the device. On varying the voltage applied to the device and its rise and fall times, a good insight was obtained into device behavior. Simulations were also performed to obtain responses to qualitatively match the experimentally obtained responses. Various What-If scenarios have been studied by varying the device parameters. These studies have indicated the importance of these parameters in determining device performance.

<p> Thin silicon based films were produced using low temperature (less than 60° C) electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR PECVD). These films were examined for suitability in flat panel display applications. SiOxNy films were tested for use as insulating films in thin film electroluminescent (TFEL) devices. The ECR PECVD method was found to be suitable when the plasma was created using pure nitrogen (as opposed to argon) in high ratios to the silane precursor.</p> <p> Hydrogenated silicon films were also produced and evaluated for their suitability as semiconductor layers in thin film transistors (TFTs). The silicon films were subject to nickel induced crystallization. The silicon films were found to crystallize at low temperatures, (<950° C) in the presence of nickel. These films were used to produce prototype metal insulator semiconductor (MIS) capacitors and TFTs.</p> / Thesis / Master of Applied Science (MASc)

Transparent oxide semiconductors (TOSs) are materials that exhibit electrical conduction and optical transparency. The traditional applications of these materials are transparent conducting oxides in flat-panel displays, light-emitting diodes, solar cells, and imaging sensors. Recently, significant research has been driven to extend state-of-the-art applications such as thin-film transistors (TFTs). A new and rapidly developing field is emerging, called transparent electronics. This thesis advances transparent electronics through developing a new technique to fabricate TOSs and demonstrating their applications to active semiconductor devices such as diodes and TFTs. Ion beam assisted evaporation (IBAE) is used to deposit two common TOSs: zinc oxide (ZnO) and indium oxide (In2O3). The detailed material study is carried out through various characterization of their electrical properties, chemical composition, optical properties, crystal structure, intrinsic stress, topology, and morphology, as well as an investigation of thin-film property as a function of the deposition parameters: ion flux and energy, and deposition rate. The study proves that IBAE technique provides the capability for fabricating TOSs with controllable properties. By utilizing the newly developed semiconducting ZnO, p-NiO/i-ZnO/n-ITO and n-ITO/i-ZnO/p-NiO heterostructure photodiodes with a low leakage are proposed and assessed. Analysis of their current-voltage characteristics and current transient behaviour reveals that the dominant source of leakage current stems from the deep defect states in the intrinsic zinc oxide layer, where its dynamic response at low signal levels is limited by the charge trapping. The exploration of the photoconduction mechanism and spectral response confirms that such photodiodes are potentially applicable for ultraviolet (UV) sensors. The comparative study of both device structures provides further insights into the leakage current mechanisms, p-i interface properties, and quantum efficiency. Secondly, with the novel semiconducting In2O3, TFTs are fabricated and evaluated. The device performance is optimized by addressing the source/drain contact issue, lowering the intrinsic channel resistance, and improving the dielectric/channel interface. The best n-channel TFT has a high field-effect mobility of ~30 cm^2/Vs, a high current ON/OFF ratio of ~10^8, and a sub-threshold slope of 2.0 V/decade. More important, high-performance indium oxide TFTs here are integrated with the silicon dioxide and silicon nitride gate dielectrics by conventional plasma-enhanced chemical vapour deposition, which makes indium oxide TFT a competitive alternative for next generation TFTs to meet the technical requirements for flat-panel displays, large area imager arrays, and radio frequency identification tags. The stability study shows that indium oxide TFTs are highly stable with a very small threshold voltage shift under both a long-term constant voltage and long-term current stress. The dynamic behaviour indicates factors that affect the operation speed of such TFTs. A descriptive model is proposed to link the material properties and the processing issues with the device performance to facilitate further research and development of TOS TFTs. The research described in this thesis is one of the first investigations of the fabrication of TOSs by the IBAE and their applications to a variety of thin-film devices, particularly UV sensors and TFTs.

Transparent oxide semiconductors (TOSs) are materials that exhibit electrical conduction and optical transparency. The traditional applications of these materials are transparent conducting oxides in flat-panel displays, light-emitting diodes, solar cells, and imaging sensors. Recently, significant research has been driven to extend state-of-the-art applications such as thin-film transistors (TFTs). A new and rapidly developing field is emerging, called transparent electronics. This thesis advances transparent electronics through developing a new technique to fabricate TOSs and demonstrating their applications to active semiconductor devices such as diodes and TFTs. Ion beam assisted evaporation (IBAE) is used to deposit two common TOSs: zinc oxide (ZnO) and indium oxide (In2O3). The detailed material study is carried out through various characterization of their electrical properties, chemical composition, optical properties, crystal structure, intrinsic stress, topology, and morphology, as well as an investigation of thin-film property as a function of the deposition parameters: ion flux and energy, and deposition rate. The study proves that IBAE technique provides the capability for fabricating TOSs with controllable properties. By utilizing the newly developed semiconducting ZnO, p-NiO/i-ZnO/n-ITO and n-ITO/i-ZnO/p-NiO heterostructure photodiodes with a low leakage are proposed and assessed. Analysis of their current-voltage characteristics and current transient behaviour reveals that the dominant source of leakage current stems from the deep defect states in the intrinsic zinc oxide layer, where its dynamic response at low signal levels is limited by the charge trapping. The exploration of the photoconduction mechanism and spectral response confirms that such photodiodes are potentially applicable for ultraviolet (UV) sensors. The comparative study of both device structures provides further insights into the leakage current mechanisms, p-i interface properties, and quantum efficiency. Secondly, with the novel semiconducting In2O3, TFTs are fabricated and evaluated. The device performance is optimized by addressing the source/drain contact issue, lowering the intrinsic channel resistance, and improving the dielectric/channel interface. The best n-channel TFT has a high field-effect mobility of ~30 cm^2/Vs, a high current ON/OFF ratio of ~10^8, and a sub-threshold slope of 2.0 V/decade. More important, high-performance indium oxide TFTs here are integrated with the silicon dioxide and silicon nitride gate dielectrics by conventional plasma-enhanced chemical vapour deposition, which makes indium oxide TFT a competitive alternative for next generation TFTs to meet the technical requirements for flat-panel displays, large area imager arrays, and radio frequency identification tags. The stability study shows that indium oxide TFTs are highly stable with a very small threshold voltage shift under both a long-term constant voltage and long-term current stress. The dynamic behaviour indicates factors that affect the operation speed of such TFTs. A descriptive model is proposed to link the material properties and the processing issues with the device performance to facilitate further research and development of TOS TFTs. The research described in this thesis is one of the first investigations of the fabrication of TOSs by the IBAE and their applications to a variety of thin-film devices, particularly UV sensors and TFTs.

Recently, active matrix flat-panel displays are widely used in consumer electronic products. With increasing popularity of flat-panel displays, market competition becomes more intense and demands for high performance flat-panel displays are increasing. Low-temperature polysilicon (LTPS) with higher mobility, as well as drive current can integrate electric circuit, such as controllers and memory on glass substrate of display to achieve the purpose of system on panel (SOP). Thus, flat-panel displays can be more compact, while reducing reliability issues and lowering production costs. In this dissertation, we studied the nonvolatile memory for system on panel applications and reducing cost of memory by increasing the memory density or reducing the processing steps. Therefore, we proposed several modes of operation in nonvolatile memory. First, we use channel hot-electron (CHE) to inject electrons into the nitride layer that¡¦s above source or drain sides of SONOS thin film transistor (TFT). Thus, we can increase the memory density by storing two-bit state in a memory cell. In this study, the two-bit memory effect is clearly observed for devices with a shorter gate length after CHE programming; however, the two-bit memory effect is absent in devices with a longer gate length. The gate-length-dependent two-bit memory effect is related to the location of injected electrons in the nitride layer. When electrons are injected into the nitride layer above the channel, they can create an additional energy barrier in the channel thus increasing the threshold voltage of the device to perform the programming operations. However, if electrons are injected into the depletion region at the P-N junction between the drain and the channel, the energy barrier induced by electrons is not significant when exchanging the source and drain electrodes to measure the memory status, and the program effect is not as significant. When the channel length is shorten, the built-in potential between the source and the channel can be decreased, the energy barrier caused by programmed electrons can affect electrons in the channel and increase the threshold voltage. Therefore, the two-bit memory effect can be seen in devices with the shorter gate length after CHE programming. Secondly, we stored charges in the body of the thin film transistor to make the conventional thin-film transistors become a non-volatile memory. This method does not need a floating gate or a tunneling oxide in the memory cell; therefore the memory cost can be reduced. In this study, we used trap-assisted band-to-band thermionic field emission enhanced by self-heating in TFT to produce electron-hole pairs. The hole will be separated by a vertical field under the gate and be injected into the body of TFT to complete the programming operation. The erasing operation is performed by applying a lateral electric field between the source/drain to remove holes in the body of TFT. Thirdly, we proposed an edge-FN tunneling method to allow SONOS TFT possess not only a pixel switch but also a two-bit nonvolatile memory function in a display panel, thus causing the memory density to increase. In this study, we used a channel FN tunneling to program the SONOS TFT. Because the electric field in the gate-to-drain overlap region is larger than that in the channel region, it will cause a smoother electron injection into the nitride layer inside of the gate-to-drain overlap region, which also increases the gate-induced drain leakage (GIDL) current. The edge-FN tunneling method is used to erase electrons in the gate-to-drain overlap region, by doing so, the GIDL current has decreased. The memory status at the source/drain side is determined by the corresponding GIDL current of the SONOS TFT. Fourthly, we stored electrons in the nitride layer at source, channel, and drain regions of SONOS TFT to make sure that TFT possess a three-bit memory effect in a unitary cell, which also allows the memory density to increase significantly. In this study, programming and erasing operations in the source/drain region are performed by channel hot-electron injection and edge-FN tunneling method, while that in the channel region are accomplished by channel FN tunneling. The memory status in the source/drain is determined by the corresponding GIDL current, while that in the channel region by threshold voltage of the device The memory density for the device operated by proposed method can be further increased. In addition, if we store a number of N different types of electrons in those three regions mentioned above, there are N3 status can be stored in a memory cell. The memory density can beyond conventional multi-level-cell (MLC) flash memory. Two-bit memory effect per cell in a MLC flash memory can be achieved by storing four quantitative electrons in the floating gate of the memory device. If we store four quantitative electrons in the nitride layer at source, channel, and drain regions of SONOS TFT, we can obtain 64 memory states or 6-bit memory effect in a memory cell. Thus, the proposed concept is promising to storage the messages in a memory cell beyond four-bit.

The electronics industry today is one that stands as a multi-billion dollar industry that is increasingly incorporating more and more products that have ever escalating applications in our everyday life. One of the main sectors of this industry, and one that is likely to continue expanding for a considerable number of years are flat-panel displays. Traditionally, the displays market has been dominated by cathode ray tube (CRT) and liquid crystal displays (LCDs) display types. The drawback of such display displays is that they can be bulky, heavy and/or expensive and so there is considerable room for an alternative and superior technology. One possibility is organic semiconductor displays where light-emitting molecules can be dissolved in common solvents before being inkjet printed, spin-coated or even painted onto any surface giving the benefits of simple and cost effective processing. Organic light-emitting diodes (OLEDs) have recently become ever more evident as a major display type. This thesis focuses on the advancement of light-emitting dendrimers towards flat-panel display applications. The particular interest in dendrimers arises because it has been found they are capable of giving solution-processed phosphorescent devices with high efficiency. Throughout the thesis the benefits of the dendrimer concept are repeatedly shown revealing why this could become the ideal organic material for display applications. The thesis introduces various techniques of electroluminescence and photoluminescence measurements before applying such methods to study a large number of light-emitting dendrimers in order to explore the role of intermolecular interactions, how they are related to molecular structure, and how this determines photophysical and charge transporting properties of the dendrimers. By such studies a number of highly efficient solution-processed phosphorescent light-emitting dendrimers have been identified while the efficiency of devices made from these dendrimers has been improved. This has been demonstrated in each of the three primary display colours of red, green and blue. The work detailed thus brings closer the prospect of dendrimer light-emitting diodes being the future flat-panel display type of choice.