Alignment defects of actual devices

Neel walls, twist- and tilt-reverses are the three major disclinations in actual LCDs. A Neel wall disclination may be caused by weak azimuthal anchoring. A twist-reverse is a defect in which the twist direction is opposite to the chirality of the added chiral agent. A tilt-reverse is a defect in which the inclination direction induced by applying a voltage is the opposite of the intended direction. These tilt-reverse defects may be caused by the lateral electric field generated by the fringe field of the pixel electrodes. 

Tilt-reverse occurs when the pretilt angle is not large enough to prevent inclination opposite to the intended direction caused by the lateral electric field coming from the edges of the pixel electrodes. The alignment in a tilt-reverse defect is shown in Fig. 2.31. Recently, the pixel size has become smaller as the resolution increases. 

To fix the twist direction of the twisted nematic (TN) display mode, several methods are used. One is to add a small amount of a chiral agent. A typical chiral pitch for the 5 pm gap TN mode is 100 pm. The other method involves the rubbing direction. The rubbing direction determines the inclination direction of the LC, and it is selected so as to avoid a splay alignment as shown in Fig. 2.32. If the pretilt 

Spacer beads are sprayed on the substrate to make the cell gap uniform, and they C in cause alignment defects in the LC because of their surface alignment strength and movement. Recently, the density of spacer beads has tended to increase in order to produce lightweight panels with thinner glass substrates. 

Light reflection from disclination line around spacer 

5 2005 Kohki Takatoh, Masaki Hasegawa, Mitsuhiro Koden, Nobujodd Itoh, Ray Hasegawa and Masanori Sakamoto 

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