ABSTRACT
CHAPTER 5 Twisted-Nematic Cell The electro-optical effect in a twisted nematic (TN) liquid-crystal cell described in 1971 1 is now widely used in active-matrix liquid-crystal displays. As shown in Figure 5.1, a thin (5 um) layer of nematic liquid-crystal is placed between two glass plates provided with a transparent and conductive coating. On both plates the orientation of liquidcrystal molecules or director, is aligned to be nearly parallel to the surface of the glass plate (planer or homogeneous alignment), and as shown schematically in Figure 5.2 (a), on each plate this orientation is twisted 90° with respect to that of the other plate, so that the orientation is continuously twisted from the bottom to the top glass plate by 90°. The homogeneous alignment of liquid-crystal molecules on each plate is produced by rubbing the surface of a polyimide thin film in the proper direction with
Figure 5.1 Fundamental configuration of the TN cell. A thin ( 5 um) layer of liquid crystal is placed between two glass plates. The cell is driven by an ac voltage applied to the transparent electrodes of ITO. The planar or homogeneous molecular alignment is achieved by the rubbed surface of the polyimide film, and the alignment orientations on the two glass plates are perpendicular to each other.
