Twisted Nematic (TN) LCDs

TN displays have a 90° or less twist (the rotation of the molecules from one plane of the display to the other). All passive direct drive, active matrix, and most passive low level (x2 to x32) multiplexed LCDs have a 90° twist. 

The basic Twisted Nematic (TN) LCD consists of a layer of liquid crystal material supported by two glass plates. The liquid crystal material is a mixture of long, cylindrically shaped molecules with different electrical and optical properties, depending on direction.

On the inner surfaces of the glass plates are transparent electrodes, which are patterned to form the desired visual image. The inner surfaces are coated with a polymer, which is rubbed so that the liquid crystal material at one surface lies perpendicular to the other. Across the film of liquid crystal, the molecules form a 90° twist.

On the outer surface of the glass plates, polarizers are placed so they are parallel to the liquid crystal orientation and perpendicular to each other. In the "off" state, light entering the first polarizer is guided by the liquid crystal layer twist to the second polarizer, through which it is transmitted. When the cell is energized, the LC material is aligned with the electric field; light transmitted through the first polarizer is blocked by the second polarizer, forming a dark image. The effect may be reversed if the polarizers are placed parallel to each other, and a light image on a dark background is formed.

The TN technology comes in a single coloration; it is Black characters on a gray background. It is the least expensive, but has the lowest visual quality, primarily in viewing angle.