Fast Switching, High Optical Contrast, and Slim Form Factor Nematic Liquid Crystal Display Devices
Autor: | Bo-Ru Yang, 楊柏儒 |
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Rok vydání: | 2008 |
Druh dokumentu: | 學位論文 ; thesis |
Popis: | 97 The main objective of this dissertation is to explore the ultimate features of a liquid crystal display (LCD) device. Particular attention is spent on the nematic type LCD device with the attributes of fast-switching, high-optical-contrast, and slim-form-factor. Fast-switching is a demanding requirement of an LCD device for realizing the novel display systems such as field sequential color LCD and temporally multiplexing 3D display. Regarding this requirement, pi-cell (also know as optically compensated bend, OCB) is the most promising LCD mode whose fast-switching results from its symmetric LC profile and parallel backflow. However, the issue of undesirable recovery hinders the pi-cell from commercial applications. In this thesis, we propose to use the symmetric H (Hs) state and the polymerized bend state to overcome this unwanted recovery. The difficulty of utilizing the Hs state results from its short lifetime. To resolve this issue, we propose a stroboscopic illumination assisted conoscopy to verify its transient LC profile. According to this result, we further design a polymer wall structure to extend its lifetime. With the verification of LCD simulation, the lifetime can be elongated by a factor of more than 10. High-optical-contrast is a critical attribute for an LCD device to show a vivid image. Here, we propose two methods for enhancing the optical contrast in the polymerized OCB-LCD and the organic light emitting diode (OLED) embedded LCD. In the polymerized OCB-LCD, we stabilize the relaxed bend state which has the highest brightness among the bend states. The optical contrast is enhanced by a factor of 1.5 compared with that of the conventionally polymerized OCB-LCD. In the OLED embedded LCD, after adopting the volumetric scattering layer (VSL), the optical contrast in the reflective mode is increased by a factor of 12. Slim-form-factor is the most important factor as considering the mobile display applications. We propose and successfully accomplish the experiment of embedding an OLED directly into an LCD device, which thus eliminate the bulky backlight module. Meanwhile, the contrast ratio can be significantly increased compared with the case of trans-flective display. Because the OLED section can be turned off, whereas the conventional trans-flective display should sustain the backlight to be turned on even in the dark state. Referring to the neology of “trans-flective” display, we therefore term this OLED embedded LCD as “emi-flective” display, which is a combination of “emissive” and “reflective.” Considering the scientific achievements, this dissertation demonstrates a stroboscopic illumination method, which opens a new era in observing and further stabilizing the transient states in an LCD device. As for the technical achievements, the realization of embedding the OLED into an LCD and the optical optimization with VSL have demonstrated a tremendous progress in OLED area. Combing these results, the integrated device is able to be low power consumption, high image quality, slim form factor, and fully flexible. |
Databáze: | Networked Digital Library of Theses & Dissertations |
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