Thin Film Transistors For High Resolution Liquid Crystal Displays

In this dissertation, thin film transistor (TFT) for high-resolution liquid crystal displays(LCDs) was studied focusing on the optimization of main materials preparation and device design to make it applicable to the large-size and high content LCDs.The main device materials such as amorphous silicon and poly-crystalline silicon were characterized based on our complete understanding of their micro structures and a rational energy band structure and the conduction mechanism were lucubrated. The correlation between the key factors such as the dangling bonds, the concentration of bonded hydrogen, the grain boundary defects, etc and the material electric characterizations was investigated and that was an instructive conference for the material preparations. High quality hydrogenated amorphous silicon and poly-crystalline silicon films were obtained by plasma enhanced chemical vapor deposition and laser annealing respectively. The material characterizations were optimized by rational choosing the preparation parameters and measured by IR, SEM, XRD and AFM etc.Amorphous thin film transistor (a-Si TFT) electric model was developed with the conference of MOSFET and its I-V characterization was deduced based on that model. The TFT device was designed by synthesizing both the requisitions of TFT and LCD pixel, and as high as six decade On to Off state current ratio TFT was fabricated. A 3 inch diagonal a-Si TFT liquid crystal display panel was manufactured successfully.The characteristics of laser recrystallised polycrystalline silicon (p-Si) TFT were analyzed especially the thoroughly clarification of the anomalous leakage current, which was the main impediment in the application of p-Si TFT. Under high Yds, the Off-state leakage current was due to the field emissions via grain boundary traps in the surface depletion region at the drain. In order to restrain the horizontal electric fieldbetween drain and source electrodes, the lightly doped source and drain (LDD) model was introduced and analyzed by solving Poisson equation. The model predictions were consistent with measured current- voltage characteristics. With optimizing the parameters such as the lightly doping concentration and the length of LDD region, the leakage current was effectively depressed as lower as three decade comparing with the simple structure p-Si TFT.Large size and high resolution displays have been the main development tendency of TFT -AMLCDs in recent several years. The electrical signals would be deformed by the transition delay of the complex circuitry on the TFT matrix panel. An analytical model for signal delay simulation was established and display panel parameters such as screen diagonal, display resolution and signal electrode resistivity were simulated with the distribution contour of the maximum charge on the two dimensional LC pixel capacity matrix.In order to decrease the RC(resistance and capacity) delay, Al-alloy and double layer electrode films were prepared by magnetized sputtering system. The hillock on pure Al film phenomena was physically explained. High thermal stability and low resistivity Al-Cr and Al-Ta alloys and Al-Mo double layer films for large size and high resolution TFT-AMLCDs were obtained supported by SEM and four probes resistivity measurements.