Control of disclinations and walls in new types of display devices.

摘要

Owing to its advantage of fast switching and intrinsic wide viewing angle characteristics over other LCD modes, Pi-cell mode (also known as OCB mode) is thought to have a big potential for the application of direct-view type of large screen LCD-TV. With addition of chiral dopent, the Pi-cell configuration can also applied as in bistable displays, which is an effective way of reducing power consumption. In both applications, the transition between the two topologically distinct states from splay to bend is involved. It has been shown this transition could occur through the movement of disclination lines near the surface of the cell or through an anchoring breaking. Recently, an alternative mechanism was proposed that the transition was explained as a bulk biaxial melting and then an order reconstruction in a two-dimensional sheet near the center of the cell. This explained the phenomenon that previously could not be understood with the surface transition models. However, this new mechanism is based on a one-dimensional director field study, which does not allow the existence of a modulation of the director field in the plane of the cell, or for a disclination line. In this dissertation, we study the phenomenon of a fast bulk transition through a two-dimensional dynamic model based on the Q tensor method. By adding a small perturbation to the system, the defect nucleation and the motion of disclination lines is observed during the transition. This gives a lower energy alternative to the simultaneous order parameter change over a sheet in the center of the cell.; Among the microdisplay technologies, LCoS is thought to be capable of providing large, high quality, high-resolution displays with a very small and hence, relatively inexpensive LCD device based on silicon technology. Due to the small electrode size (about 10-20 mum) and interpixel gap (in the order of sub-micro meter), fringe field effect becomes a problem that can not be neglected in LCoS. How to control or eliminate the wall or disclination line problem resulted from the fringe field in LCoS is therefore important for improving the device performance. In this dissertation, a new type of diffractive LCoS display is proposed that is polarization independent and immune to the fringe field problem.