The inside of the glass in the liquid crystal box the whole display area is covered with a layer of the directional layer. Directional layer's role is to make the liquid crystal molecules are arranged in a particular direction, the directional layer is usually a thin layers of organic material, and the friction process; Also can pass on the glass surface with a certain Angle by vacuum evaporation silicon oxide thin film preparation.
In the type TN LCD filled with positive nematic liquid crystal. The orientation of liquid crystal molecules is to make the long rod type liquid crystal molecules parallel to the surface of glass arranged along a fixed direction, the direction of the molecular long axis along the direction of the directional treatment. Orientation on the surface of the glass up and down direction is perpendicular to that, in the direction perpendicular to the surface of the glass, the orientation of liquid crystal molecules became distorted inside the box, from glass to glass distorts the 90 ° (see below), which is the origin of the name of twisted nematic liquid crystal displays.