At present, most of the liquid crystal display technologies are based on TN, STN and TFT technologies, so we will explore their operating principles from these three technologies. TN type liquid crystal display technology can be said to be the most basic among liquid crystal displays, and other types of liquid crystal displays can be said to be improved based on TN type. Similarly, its operating principle is simpler than other technologies. Please refer to the picture below. Figure 1 shows a simple structural diagram of a TN type liquid crystal display, including vertical and horizontal polarizing plates, an alignment film with fine grooves, a liquid crystal material and a conductive glass substrate. The imaging principle is to place the liquid crystal material between two transparent conductive glasses attached to the optical axis perpendicular to the polarizing plate. The liquid crystal molecules will rotate and arrange in sequence according to the direction of the fine grooves of the alignment film. If the electric field is not formed, the light will smoothly enter from the polarizing plate, rotate its direction of travel according to the liquid crystal molecules, and then emit from the other side. If two pieces of conductive glass are electrified, an electric field will be created between the two pieces of glass, which will affect the arrangement of the liquid crystal molecules between them, causing the molecular rods to twist, so that light cannot penetrate and the light source is blocked. The phenomenon of light-dark contrast obtained in this way is called twisted nematic field effect, or TNFE (twisted nematic field effect). Almost all liquid crystal displays used in electronic products are made using the twisted nematic field effect principle.
The display principle of the STN type is similar, except that the liquid crystal molecules of the TN twisted nematic field effect rotate the incident light by 90 degrees, while the STN super twisted nematic field effect rotates the incident light by 180~270 degrees. It should be explained here that a simple TN liquid crystal display has only two conditions of light and dark (or black and white), and there is no way to change the color. STN liquid crystal displays involve the relationship between liquid crystal materials and the interference of light, so the displayed tones are mainly light green and orange. However, if a color filter is added to the traditional monochrome STN liquid crystal display, and any pixel of the monochrome display matrix is divided into three sub-pixels, the three primary colors of red, green and blue are displayed through the color filter respectively, and then the three primary colors are adjusted in proportion, the full color mode can also be displayed. In addition, if the display screen of the TN type liquid crystal display is made larger, its screen contrast will appear poor, but the improvement technology of STN can make up for the lack of contrast.
