Principles of LCD technology

Principles of LCD technology

TN type liquid crystal display technology can be said to be the most basic of liquid crystal displays, and other types of liquid crystal displays can also be said to be improved based on TN type as the origin.

The structure of the TN type liquid crystal display includes vertical and horizontal polarizing plates, alignment films with fine grooves, liquid crystal materials and conductive glass substrates. Without an electric field, the incident light passes through the polarizer and passes through the liquid crystal layer. The polarized light is rotated by 90 degrees by the liquid crystal layer whose molecules are twisted. When it leaves the liquid crystal layer, its polarization direction is exactly the same as the direction of the other polarizer, so the light can After passing smoothly, the entire electrode surface is bright. When an electric field is added, the optical axis of each liquid crystal molecule turns to be consistent with the direction of the electric field, and the liquid crystal layer loses its optical rotation ability. As a result, the polarization direction from the incident polarizer is perpendicular to the polarization direction of the other polarizer. The relationship cannot pass, so the electrode surface is dark. The imaging principle is to place the liquid crystal material between two pieces of transparent conductive glass attached to the vertical polarizing plate of the optical axis. The liquid crystal molecules will rotate in order according to the direction of the fine grooves of the alignment film. If the electric field is not formed, the light will be smooth Inject from the polarizer, rotate the direction of travel according to the liquid crystal molecules, and then exit from the other side. If the two pieces of conductive glass are energized, an electric field will be created between the two pieces of glass, which will affect the arrangement of the liquid crystal molecules between them, so that the molecular rods will be twisted, and the light will not be able to penetrate, thereby shielding the light source. The phenomenon of light-dark contrast obtained in this way is called twisted nematic field effect, or TNFE (twisted nematic field effect) for short. The liquid crystal displays used in electronic products are almost all made by the twisted nematic field effect principle.

TFT-type liquid crystal displays are more complicated, and the main components include fluorescent tubes, light guide plates, polarizing plates, filter plates, glass substrates, alignment films, liquid crystal materials, thin-mode transistors, and so on. First of all, the liquid crystal display must first use a backlight, that is, a fluorescent tube to project a light source. These light sources pass through a polarizing plate and then through the liquid crystal. At this time, the arrangement of the liquid crystal molecules changes the angle of light penetrating the liquid crystal. Then the light must pass through the colored filter film and another polarizing plate in the front. Therefore, we can control the final light intensity and color by changing the voltage value that stimulates the liquid crystal, and then can change the color combination of different shades on the LCD panel.