TFT (Thin Film Transistor) LCD i.e. thin film field effect transistor LCD, an active matrix type liquid crystal display one kind of device (AM-LCD) in.

  Different from the TN technology, the TFT display adopts the "back-through" illumination mode-the imaginary light source path is not from top to bottom like TN liquid crystal, but from bottom to top. This approach is to install a special light pipe on the back of the liquid crystal, and the light source will penetrate upward through the lower polarizer when illuminated. Since the upper and lower interlayer electrodes are changed to FET electrodes and common electrodes, when the FET electrodes are turned on, the performance of the liquid crystal molecules will also change. The purpose of display can be achieved through light shielding and light transmission, and the response time is greatly increased to about 80ms. Because it has a higher contrast ratio and richer colors than TN-LCD, the screen update frequency is also faster, so TFT is commonly called "true color".

  Compared with DSTN, the main feature of TFT-LCD is to configure a semiconductor switching device for each pixel . Because each pixel can be directly controlled by dot pulse. Therefore, each node is relatively independent and can be continuously controlled. This design method not only improves the response speed of the display screen, but also can accurately control the display gray level, which is why the TFT color is more realistic than DSTN.

  At present, most notebook computer manufacturers use TFT-LCD in their products. Early TFT-LCDs were mainly used in the manufacture of notebook computers . Although TFT had great advantages over DSTN at that time, due to technical reasons, TFT-LCD still had a big gap with traditional CRT displays in response time, brightness and viewing angle . In addition, the extremely low yield has led to its high price, making the desktop TFT-LCD an unattainable stunner.

  However, with the continuous development of technology, the continuous improvement of the yield rate, and the emergence of some new technologies, the TFT-LCD has made great progress in response time, contrast, brightness, and viewing angle, bringing it closer to the traditional CRT monitor gap. Nowadays, the response time of most mainstream LCD displays has been improved to below 50ms, which has paved the way for LCD to become mainstream.

  The LCD application market should be said to have huge potential. But in terms of LCD panel production capacity, the world's LCDs are mainly concentrated in the three main production bases in Taiwan, South Korea and Japan. Asia is the center of LCD panel R&D and manufacturing, while the development of Taiwan, Japan, and South Korea is different.

  The current mainstream TFT panel a-Si (amorphous silicon thin-film crystaltube), TFT and LTPS TFT technology (low temperature polysilicon) TFT technology.

  In terms of a-Si, the technologies of the three production bases have their own merits. Japanese manufacturers have developed LCD products with a resolution of up to 2560×2048. Therefore, some people believe that a-Si TFT technology can fully meet the needs of high-resolution products. However, due to the immaturity of the technology, it cannot meet the needs of high-speed video images or animations. LTPS TFT can save costs relatively, which is of great significance for the promotion of TFT LCD. At present, Japanese manufacturers have the capacity to mass produce 12.1-inch LTPS TFT LCD. Taiwan, China has developed LTPS component manufacturing technology and LTPS SXGA panel technology. South Korea lacks specialized designers and R&D experts in this regard, but major companies such as Samsung have launched LTPS products, showing the strength of Korean manufacturers. However, the current LTPS technology is still immature, the products are concentrated in small screens, and the yield is low, and the cost advantage is not yet discussed.

  Compared with LTPS, a-Si is undoubtedly the mainstream of TFT LCD at present. Almost all Japanese companies’ a-SiTFT investment strategies focus on the third-generation LCD products, and improve production technology and yield rates to increase production and reduce costs. Japan has been taking the high-end route, and its technology is undoubtedly the most advanced. Due to limited R&D capabilities, Taiwan’s a-Si TFT technology mainly comes from the transfer of Japanese manufacturers, but because Taiwanese companies are generally labor-intensive and have low technical content and prices, they mainly produce low-end products. South Korea has a strong R&D strength in a-Si. For example, Samsung has mass-produced the world’s first 24-inch a-Si TFT LCD—240T. Its response time is less than 25ms, which can meet general application needs; Reached 160 degrees, so that LCD does not lose to CRT in the traditional weakness. Samsung 240T marks the maturity of large-screen TFT LCD technology, and also shows the world that the strength of Korean manufacturers is beyond doubt.

Market analysis of TFT-LCD

  TFT-LCD is a typical representative of active matrix liquid crystal display (AM LCD). Its research is the most active, the fastest growing, and the application grows the fastest. It is the leader in applications such as notebook computers, video cameras and digital camera monitors. In addition, it has been well used in geographic information systems, aircraft cockpits, portable DVDs, desktop computers and multimedia displays. The idea of color TFT-LCD was first proposed by the American (Westinghouse) in 1972, and Toshiba of Japan took the lead in realizing mass production of this technology in 1982, but the production technology was not mature at that time. Since Japan mastered the TFT-LCD production technology in 1993, the resolution has evolved from CGA (320 * 200) to today's UXGA (1600 * 1200), and the substrate size has also been the first generation 240 * 270-32O * 400mm2 developed to the seventh generation of 1350*1700 mm2 which was launched in 2001 by Sharp of Japan, Samsung Electronics of South Korea and LG-Philips. At present, the application of TFT-LCD is mainly in five areas: the small-size mobile phone market, the medium-size palmtop and notebook computer market, the large-size LCD monitor and the LCD TV market. In 2005, TFT-LCD will be mainly used in the five fields of monitors (39%), notebook computers (25%), mobile phones (16%), LCD TVs (10%), PDAs (6%), and the market sales amount will exceed 250 Billion US dollars, accounting for more than 90% of the LCD market, becoming the leading technology in the field of liquid crystal and even the entire flat panel display technology.

Industrial characteristics of TFT-LCD technology

  Capital-intensive, large-scale operation: the investment in establishing a production line is about 1 billion US dollars. Technology-intensive: involving semiconductor technology, precision machinery , precision optics , automatic control, large-scale integrated circuit design and manufacturing technology, optoelectronics, microelectronics, fine chemicals, Light sources, materials, communications, computer software, etc.

  Fast development speed and stable core technology: The production line of TFT-LCD has undergone 7 major developments in the past ten years of industrialization, and the production line has to be updated every one and a half years on average. But the core technology of TFT-LCD is relatively stable.

  The industries that are driven are broad and have overall significance to the national economy: upstream raw materials, production equipment, and production technologies involve dozens of fields of modern industrial production. The development of new materials, the manufacture of large-scale production equipment, and the application of advanced production technologies will drive upstream industry groups. The TFT-LCD module is the core device of the information industry, involving almost all fields such as communications, transportation, home appliances, computers, education, industry, medical treatment, and national defense.

Research status of a-Si TFT-LCD technology

  Resolution: The resolution of TFT-LCD has passed CGA (320 * 200), VGA (640 * 4 80), SVGA (1280 * 1024) in recent years. XGA (1024 * 768). SXGA (1280 * 1024) has developed to the current level of UXGA (1600 * 1200) and QXGA (2560 * 2048).

  Contrast ratio: PPMuhoray and others in the United States introduced waveguide-based LCD technology and used this technology to achieve a high contrast ratio of 174:1, while the current TFT-LCD contrast ratio can reach up to 500:1.

  Viewing angle: Since the liquid crystal material is anisotropic, the orientation of its molecular arrangement and the rearrangement under the action of an electric field uniformly affect the widening of the viewing angle of the LCD device, which causes the shortcomings of the viewing angle of the LCD device. A variety of widening has been proposed. Viewing angle technology, like plane switching mode, symmetrical micro unit mode, domain vertical mode, etc., the viewing angle can reach 170 degrees.

  Response speed: When the frame rate is 60%, the frame period is about 16ms. The response time of ordinary TFT-LCD devices using TN LCD can be less than 20ms. Recently, a planar switch method using elastic continuous polymer stabilization has been introduced, which can shorten the response time to 10ms. The use of optical compensation tape can shorten the response time to 2~3ms. At present, the response time of 8ms has been developed using this technology. Color LCD TV.

  Life: Due to the development of manufacturing technology, the life of TFT-LCD can reach more than 30,000 hours.

  Large screens and reflective types have appeared: 38in TFT-LCTV has been successfully developed, ending the splicing era of large-screen LC, and reflective TFT-LCD color displays have also begun to commercialize.

  Due to the development of TFT manufacturing technology, the improvement of liquid crystal material performance, the adoption of wide viewing angle technology, the improvement of response speed and the improvement of yield, TFT-LCD display performance is no less than CRT.


What is the structure and principle of TFT LCD?