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The characteristic polarization response of a ferroelectric material to an applied electric field enables a binary state device in the form of a thin film ferroelectric capacitor that can be used to store digital information. In a high density memory the capacitor is placed on the top of a poly-silicon plug which is connected to the drain of a transistor. Such a configuration poses constraints on the processing conditions of the ferroelectric capacitor in addition to the already existing reliability issues of a ferroelectric capacitor. The current research is an attempt to integrate the ferroelectric capacitor directly into a high density memory structure. Pb_1.1Zr_0.53Ti_0.47O₃ (PZT) and SrBi₂Ta₂O₉ (SBT) are two most promising materials for ferroelectric memory applications. PZT has excellent ferroelectric properties with wide operating temperature range. However, PZT exhibits a considerable loss of switchable polarization with cumulative switching cycles. This phenomenon is known as fatigue and is one of the critical problems affecting the life time of ferroelectric memories. In this research, Ir based electrodes are shown to improve fatigue characteristics of PZT based capacitors not only by enhancing a homogenous growth of perovskite phase of PZT but also by lowering the entrapment of oxygen vacancies at the interface. These Ir electrodes also acted as diffusion barriers for silicon, oxygen and lead. Additionally, Ir electrodes were found to be chemically stable at the processing temperatures of PZT capacitors. These features of Ir based electrodes could help in realization of a practical PZT based high density non volatile random access memories. SBT is an another promising ferroelectric material for ferroelectric memory applications. While SBT has a fatigue free nature, it has a very high processing temperature (>800 °C). Such a high processing temperature limits the choice of electrodes that could be used to integrate the ferroelectric capacitor into the high density memory structure. In this research, an attempt is made to lower the processing temperature and suitable electrodes are chosen accordingly, to enable the integration of SBT based capacitors into high density memories. Lowering the processing temperature was obtained by growing a-b oriented SBT crystallites rather than c-axis oriented crystallites. Additionally, reliability (degradation) and yield of SBT thin film capacitors was found to be correlated to the amount of segregated bismuth oxide in the films. Elimination of secondary phase bismuth oxide was found to result in dramatic improvement in the reproducibility of SBT thin films with a processing temperature close to 750 °C. PtRh based electrodes were found to be quite suitable for integrating SBT capacitors into high density memory structures. These electrodes could withstand a processing temperature of 750 °C while preventing the interdiffusion of silicon, oxygen and bismuth. A solid solution of SBT and Bi₃TiNbO₉ (BTN) is made which reduced the processing temperature of the capacitor material from 750 °C to 650 °C while retaining the excellent fatigue and retention characteristics of SBT. / Ph. D.

Research on pi-conjugated organic materials in the recent past has produced enormous developments in the field of organic electronics and it is mainly due to their applications in electronic devices such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic photovoltaic cells (OPVs). The primary goal of this research work is to design and synthesize high performing charge transport organic semiconductors. One of the criteria for better performance of the organic thin film transistor (OTFT) is to have high uniform thin film morphology of the organic semiconductor layer on the substrate. The first project in this dissertation has been directed towards improving the thin film morphology of the functionalized pentacenes through liquid crystalline behaviour. The results have suggested the possibility of thermotropic liquid crystalline phases in 6,13-bis(diisopropylhexylsilylethynyl) pentacene which has no pi-stacking in its solid state and the presence of silyl group at the peri-position is crucial for the stability of the functionalized pentacenes. In the second project, i have investigated the effect of alkyl groups with varying chain length on the anthradithiophene chromophore on the performance of the charge transporting devices. Organic blend cell based on solution processable 2,8-diethyl-5,12-bis(triethylsilylethynyl) anthradithiophene has showed 1% power conversion efficiency and the performance is mainly attributed to the large crystalline phase segregation of the functionalized anthradithiophene from the amorphous soluble fullerene derivative matrix. OTFT study on alkyl substituted functionalized anthradithiophenes suggested the need of delegate balance between thin film morphology and the crystal packing. Third project has been directed towards synthesizing halogen substituted functionalized anthradithiophenes and their influence in the performance of OFETs. OTFT made of 2,8-difluoro-5,12-bis(triethylsilylethynyl) anthradithiophene produced devices with thin film hole mobilities greater than 1 cm2/Vs. The result suggested that the device is not contact limited rather this high performance OTFTs are due to the contact induced crystallinity of the organic semiconductor.

In first part, the supercritical CO2 (SCCO2) fluid technology is employed to improve the device properties of ZnO TFT. The SCCO2 fluid exhibits liquid-like property, which has excellent transport ability. Furthermore, the SCCO2 fluid has gas-like and high-pressure properties to diffuse into the nanoscale structures without damage. Hence, the SCCO2 fluid can carry the H2O molecule effectively into the ZnO films at low temperature and passivate traps by H2O molecule at low temperature. The experimental results show that the on current, sub-threshold slope, and threshold voltage of the device were improved significantly. Next, the electrical degradation behaviors and mechanisms under drain bias stress of a-IGZO TFTs were investigated. A current crowding effect and an obvious capacitance-voltage stretch-out were observed after stress. During the drain-bias stress, the oxygen would be absorbed on the back channel near the drain region of IGZO film. Therefore, the carrier transport is impeded by the additional energy barrier near drain region induced by the adsorbed oxygen, which forms a depletion layer to generate the parasitism resistance. We also investigated the RRAM device based on IGZO film, and proposed the related physical mechanism models. The IGZO RRAM will be very promising for integration with IGZO TFTs for advanced system-on-panel display applications to be a transparent embedded system. In this part, the transparent RRAM device with ITO/IGZO/ITO structure was fabricated. The proposed device presents an excellent bipolar resistive switching characteristic and good reliability. The bipolar switching mechanism of our device is dominated by the formation and rupture of the oxygen vacancies in a conduction path. The influence of electrode material on resistance switching characteristic is investigated through Pt/IGZO/TiN and Ti/IGZO/TiN structure. As the bias applied on the Ti or TiN, the Ti or TiN electrode can play the role of oxygen reservoir to absorb/discharge oxygen ions. Therefore, the device presents a bipolar resistive switching characteristic. However, as the bias applied on the Pt electrode, the device presents a unipolar resistive switching characteristic. Because the Pt electrode can¡¦t store the oxygen ion, the device should use the joule heating mode to rupture the conduction path and present the unipolar resistive switching characteristic. Finally, the resistive switching properties of IGZO film deposited at different oxygen content were investigated, since the resistance switching behaviors are related to the formation and rupture of filaments composed of oxygen vacancies in the IGZO matrix. Experiment results show that the HRS current decreases when the oxygen partial pressure gradually increases. Based on the XPS analysis, these phenomena are related to the non-lattice oxygen concentration. With increasing oxygen ratio, the filaments will rupture completely through the abundant non-lattice oxygen inducing oxidation, which leads to HRS current decrease and an increase in the memory window.

We deposited CuInSe2 or CuIn1-xGaxSe2 on the substrate of bi-layer Mo by electrodeposition. Besides, we deposited bi-layer Mo by RF sputtering on soda-lime glass. First, we discussed the characteristic of Mo metal, and how can we have a good adhesion and a low resistivity simultaneously. Then, we deposited CuInSe2 and CuIn1-xGaxSe2 thin film by electrodeposition, and discussed the effect of depositing time, pH value in depositing solution, depositing current and different concentration ions respectively.

EDS is a tool for quantitative and qualitative analysis of the materials. In electron microscopy, the energy of the electrons determines the depth of the region where the X-rays come from. By varying the energy of the electrons, the depth of the region where the X-rays come from can be changed. If a thin film is used as a specimen, different quantitative ratios of the elements for different electron energies can be obtained. Unique thickness of a specific film on a specific substrate gives unique energy-ratio diagram so the thickness of a thin film can be calculated by analyzing the fingerprints of the energy-ratio diagram of the EDS data obtained from the film.

Since the traditional CRT(Cathode Ray Tube) replaced by FPD(Flat Panel Display), e.g. LCD¡BOLED¡BPDP, FPD industry is regarded as the important one of global industry following Semi-conductor industry. The main stream of Large-Area Displays is TFT-LCD(Thin Film Transistor-Liquid Crystal Display) and it¡¦s applied a-Si:H TFT (the hydrogenated Amorphous Silicon Thin Film Transistor) as pixel-switch device on LCD. In a-Si:H TFT Cell process, the active region material(a-Si:H) with higher Photoconductivity results into higher off-state current under light illumination and that causes color performance discrepancy as incomplete On/Off operation of pixel-switch devices. As long as the introduction of F into a-Si:H modify the density of states in the gap of a-Si:H(:F), that may result the shift of the Fermi level toward the valence band edge and The density-of-states increasing. It¡¦s effective to decrease the photo leakage current. Due to electro-optical properties of liquid crystal(LC), to drive Pixel-switch device in TFT-LCD shall force On/Off voltage to change Twist Angle of LC is corresponding to have Stress on TFT device. According to DC Stress experiment results, it¡¦s found TFT device with SiF4 dopant can reach better reliability. This issue is aimed to research the photo leakage current variation of a-Si:H TFT at low temperature and ON/Off state effect by stress on TFT device.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 75-79). Also available on the World Wide Web.

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