LCD Technology and Industrialization Development
11.13.2023
LCD technology and development: Liquid crystal is a kind of organic compound between solid and liquid. It will become a transparent liquid when heated, and will become a crystalline turbid solid after cooling. Under the action of an electric field, the liquid crystal The arrangement of molecules will change, which will cause the incident light to change in intensity. People can control the light and dark changes by controlling the liquid crystal electric field, and finally achieve the purpose of displaying information. Using liquid crystal materials to make display devices, from the perspective of technological development, it has mainly experienced 4 development stages:
1.The era of dynamic scattering liquid crystal display devices (1968-1970): In 1968, Radio Corporation Of America (RCA) personnel discovered the dynamic scattering (DS) effect of liquid crystals and made static image liquid crystals for the first time The display marked the birth of the liquid crystal display. The main structure of the static image liquid crystal display device is a liquid crystal cell. The liquid crystal cell is composed of two glass substrates with transparent conductive electrode patterns. The liquid crystal material is mixed with a certain proportion of ionic organic electrolyte materials. When not energized, the liquid crystal cell is transparent; when a certain frequency of alternating current is passed, it will cause turbulence and agitation in the liquid crystal layer, and then produce a strong light scattering effect on the light, showing a specific static image. The static image liquid crystal display device has no polarizer structure, and the back is generally lined with a black substrate to achieve black and white display. The large current is likely to cause the deterioration of the liquid crystal, and it is not widely used.
2.The era of twisted nematic liquid crystal display devices (1971-1984): In 1971, twisted nematic liquid crystal display devices (Twisted Nematic, TN-LCD) appeared, the technology is to coat a layer of orientation film on the glass substrate of the liquid crystal panel , The liquid crystal molecules can be arranged in parallel along the glass surface. Since the orientation processing directions of the orientation film on the two glass substrates are perpendicular to each other, the liquid crystal molecules can be twisted at 90 degrees between the two pieces of glass, thereby realizing the change of light and the image show.
This technology was extended to the fields of electronic watches and calculators. Japanese manufacturers gradually improved the twisted nematic liquid crystal display technology. Because of its low manufacturing cost, it was mass-produced in the 1970s and 1980s. In 1971, Gruen Teletime, the first watch with a liquid crystal display, came out; in 1973, the first calculator SharpEL-805 with a liquid crystal display came out; in 1981, the first portable computer EPSONHX-20 with a liquid crystal display came out. However, this technology displays a small amount of information, and can only be used for pen-segment digital display and simple character display driven by a low number of channels, and its application fields are limited.
3.The era of super-twisted nematic liquid crystal display devices (1985-1990): In the 1980s, theoretical analysis and experiments found that when the twist angle of liquid crystal molecules is increased, the photoelectric effect speed can be greatly improved, and the market has Super Twisted Nematic (STN-LCD). The display principle of the super twisted nematic liquid crystal display and the twisted nematic liquid crystal display are the same, but the twist angle of the liquid crystal molecules is different, and the twist angle is increased from 90 degrees to 180 degrees to 270 degrees from the previous twisted nematic liquid crystal display. Moreover, the pure twisted nematic liquid crystal display itself has only two changes of light and dark, while the super twisted nematic liquid crystal is mainly light green and orange, and can display colors by adding color filters.
This technology has been developed and applied in the fields of portable calculators and LCD TVs. At the same time, it has been widely used in notebook computers, graphics processors, and other office and communication equipment with large information capacity, and it has become the mainstream product at that time.
4.The era of thin film transistor liquid crystal display devices (from 1991 to present): Super-twisted nematic liquid crystal display mode will have non-selected state color problems, multi-color display is more difficult, and the display of moving images is difficult to meet the requirements. As a result, thin film transistor liquid crystal display technology (TFT-LCD) has emerged on the market. TFT-LCD utilizes the transistor array on the glass substrate of the liquid crystal panel to make each pixel of the LCD have an independent semiconductor switch. Each pixel can control the liquid crystal between the two glass substrates through dot pulses, that is, through active switches to achieve independent, precise and continuous control of each pixel "point-to-point". Such a design helps to improve the response speed of the LCD screen and control the gray scale of the display, thereby ensuring that the image color is more realistic and the picture quality is more pleasing to the eye.
Due to the advantages of TFT-LCD, such as small size, light weight, low power consumption, easy drive, no radiation, and long working life, TFT-LCD is gradually applied to notebook computers, desktop monitors, TVs and other fields. During this period, new display technologies such as OLED and laser TV appeared and continued to develop. LCD manufacturers continue to increase investment, improve product production technology, continuously increase the size of glass substrates, reduce production costs, and increase product output. With the popularization of large-size LCD TVs and smart phones, TFT-LCD has become the mainstream display technology.
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