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Emerging transparent conducting and semiconducting oxide (TCO) and (TSO) materials have achieved success in display markets. Due to their excellent electrical performance, TSOs have been chosen to enhance the performance of traditional displays and to evaluate their application in future transparent and flexible displays. This dissertation is devoted to the study ZnO-based thin film transistors (TFTs) using multilayer dielectrics and channel layers. Using multilayers to engineer transistor parameters is a new approach. By changing the thickness, composition, and sequence of the layers, transistor performance can be optimized. In one example, Al2O3/Ta2O5 bilayer gate dielectrics, grown by atomic layer deposition at low temperature were developed. The approach combined high dielectric constant of Ta2O5 and the excellent interface quality of Al2O3/ZnO, resulting in enhanced device performance. Using zinc oxide (ZnO)/hafnium oxide (HfO2) multilayer stack as a TFT channel with tunable layer thicknesses resulted in significant improvement in TFT stability. Atomic layer deposited SnO2 was developed as a gate electrode to replace ITO in thin film transistors and circuits. The SnO2 films deposited at 200 °C show low electrical resistivity of ~3.1×10-3 Ohm-cm with the high transparency of ~93%. TFT fabricated with SnO2 gate show excellent transistor properties. Using results from the above experiments, we have developed a novel process in which thin film transistors (TFTs) are fabricated using one binary oxide for all transistor layers (gate, source/drain, semiconductor channel, and dielectric). In our new process, by simply changing the flow ratio of two chemical precursors, C8H24HfN4 and (C2H5)2Zn, in an ALD system, the electronic properties of the binary oxide HZO were controlled from conducting, to semiconducting, to insulating. A complete study of HZO thin films deposited by (ALD) was performed. The use of the multi-layer (HfO2/ZnO) channel layer plays a key role in improving the bias stability of the devices. The low processing temperature of all materials at 160 °C is an advantage for the fabrication of fully transparent and flexible devices. After precise device engineering, including growth temperature, gate dielectric, electrodes (S/D&G) and semiconductor thickness, TFT with excellent device performance are obtained.

Since the discovery of organic semiconductors (OSCs) over four decades ago, the field of organic electronics has broken our misconceptions regarding the possibilities of modern electronics. The synthetic toolkit of organic chemistry enables the creation of a limitless number of unique OSCs that can be specifically tailored and engineered with the specific and desired properties for unique applications. The rapid adoption of modern information systems, “Internet of Things,” in which smart devices and sensors ubiquitously collect and exchange data has resulted in a need for low-cost sensors to be deployed everywhere from the monitoring of food supply chains, environmental conditions, to human health. Organic thin-film transistors (OTFTs) are a necessary component to support these technologies. However, their mass adoption will require reduction in cost and improved compatibility with low voltage generating printed batteries or flexible and ultrathin photovoltaics. This thesis is focused on the development of high performing solid state polymer electrolytes to be employed as the gating medium in OTFTs. The choice of conventional gating materials often leads to a tradeoff between high capacitance, operating speed and material softness. For example liquid electrolyte gating materials have high capacitance but low operating speed and are liquid at room temperature which is unacceptable for many electronics application. Polymer gating materials often have lower capacitance but fast operating conditions and solid at room temperature. In this thesis we establish structure property relationships which aid in the design of novel block copolymer-based gating materials which simultaneously enable the increase in capacitance and switching speed while remaining solid at room temperature. In the first study I established a styrene-based ionic liquid monomer can be using as a controlling monomer in the nitroxide mediated copolymerization of methacrylates. The second study then focuses on the integration of these materials into OTFT devices; the morphology (block vs random copolymers) effect on device performance is assessed. The last study builds on the findings of the previous study and further explores the structural elements of block copolymers on device performance. The work presented here outlines the development of advanced poly(ionic liquid) based solid electrolyte materials that enables both reduced operating voltages and fast switching. Finally, we establish structure-property relationships that relate the molecular architecture to OTFT device performance paving the way for the adoption of a new generation of high performing, printable and flexible electronics.

Graduation date: 2006 / A discrete trap model is developed and employed for elucidation of thin-film transistor (TFT) device physics trends. An attractive feature of this model is that only two model parameters are required, the trap energy depth, E[subscript T], and the trap density, N[subscript T]. The most relevant trends occur when E[subscript T] is above the Fermi level. For this case drain current – drain voltage simulations indicate that the drain current decreases with an increase in N[subscript T] and E[subscript T]. The threshold voltage, V[subscript T], extracted from drain current – gate voltage (I[subscript D] – V[[subscript GS]) simulations, is found to be composed of two parts, V[subscript TRAP], the voltage required to fill all the traps and V[subscript ELECTRON], the voltage associated with electrons populating the conduction band. V[subscript T] moves toward a more positive voltage as N[subscript T] and E[subscript T] increase. The inverse subthreshold voltage swing, S, extracted from a log(I[subscript D]) – V[subscript GS] curve, increases as N[subscript T] and E[subscript T] increase. Finally, incremental mobility and average mobility versus gate voltage simulations indicate that the channel mobility decreases with increasing N[subscript T] and E[subscript T].

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 119-133). Also available on the World Wide Web.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 89-91).

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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