TFT-LCD is a thin film transistor LCD English Thin Film Transistor-Liquid Crystal Display abbreviation of the head of the word.
TFT (Thin Film Transistor) LCD that is thin film field effect transistor LCD, is the active matrix type liquid crystal display (AM-LCD) in a kind.
And TN technology is different, the TFT display using "back-transparent" irradiation mode - the hypothetical path of the light source is not like the TN liquid crystal from the top to the bottom, but from the bottom up. This is done by setting up a special light pipe on the back of the liquid crystal, and the light source is transmitted upward through the lower polarizing plate. Since the electrodes of the upper and lower layers have been changed to FET electrodes and *** pass electrodes, the performance of liquid crystal molecules changes when the FET electrodes are energized, and it is possible to achieve the purpose of displaying by shading and transmitting light, and the response time is greatly improved to about 80ms. Because it has a higher contrast ratio than TN-LCD and richer colors, the screen update frequency is also faster, so TFT is commonly known as "true color".
Relative to DSTN, the main feature of TFT-LCD is a semiconductor switching device for each pixel. Since each pixel can be directly controlled by point pulses. As a result, each node is relatively independent and can be continuously controlled. This design method not only improves the response speed of the display, but also allows precise control of the display gray scale, which is the reason why TFT colors are more realistic than DSTN.
Currently, the vast majority of notebook computer manufacturers use TFT-LCDs in their products. early TFT-LCDs were mainly used in the manufacture of notebook computers. Although at that time TFT had a great advantage over DSTN, due to technical reasons, TFT-LCDs still have a big gap with traditional CRT displays in terms of response time, brightness and viewing angle. Coupled with the extremely low yield rate resulting in its high price, making the desktop TFT-LCD become unattainable.
However, with the continuous development of technology, yield rate continues to improve, coupled with the emergence of a number of new technologies, so that the TFT-LCD in the response time, contrast, brightness, viewing angle has made great progress, and to close the gap with the traditional CRT monitors. Today, the response time of most mainstream LCD monitors have been improved to below 50ms, all of which pave the way for LCD to go mainstream.
The LCD application market should be said to have great potential. However, in terms of LCD panel production capacity, the world's LCD is mainly concentrated in China, Taiwan, South Korea and Japan three major production bases. Asia is the center of LCD panel R & D and production and manufacturing, and Taiwan, Japan, South Korea, the three major origins of the development of different situations.
The current mainstream TFT panels are a-Si (amorphous silicon thin film transistor), TFT technology and LTPS TFT (low temperature polycrystalline silicon) TFT technology.
In terms of a-Si, the three production bases have their own technologies. Japanese manufacturers once developed LCD products with resolutions as high as 2560×2048. Therefore, some people believe that a-Si TFT technology can fully meet the needs of high-resolution products, but because of the immaturity of the technology, it can not meet the needs of high-speed video images or animation, etc. LTPS TFT relative cost savings, which is important for the promotion of TFT LCD. At present, Japanese manufacturers have mass production of 12.1 inches LTPS TFT LCD capacity. And China Taiwan has developed LTPS component manufacturing technology and LTPS SXGA panel technology. South Korea in this regard lacks specialized designers and R & D experts, but major companies like Samsung has launched LTPS products, showing the strength of Korean manufacturers. However, the current LTPS technology is still immature, the product is concentrated in the small screen, and low yield, cost advantage is not yet available.
Compared with LTPS, a-Si is undoubtedly the mainstream of the current TFT LCD. Japanese companies a-SiTFT investment strategy is almost always the third generation of LCD products, through the manufacturing technology and yield improvement to improve production and reduce costs. Japan has been taking the high-end route, its technology is undoubtedly the most advanced. Due to the limited R & D strength, Taiwan's a-Si TFT technology mainly comes from the transfer of Japanese manufacturers, but due to the fact that Taiwan enterprises are generally labor-intensive, low technology content, to produce low-end products. South Korea in a-Si has a strong R & D strength, such as Samsung mass production of the world's first 24-inch a-Si TFT LCD-240T, its response time is less than 25ms, can meet the general application needs; and the viewing angle of 160 degrees, so that the LCD in the traditional weaknesses of the CRT does not lose out. samsung 240T mark the Large screen TFT LCD technology to maturity, but also to the world to show the strength of Korean manufacturers can not be doubted.
TFT-LCD market analysis
TFT-LCD is a typical representative of the active matrix liquid crystal display (AM LCD), the most active research, the fastest development, the application of the most rapid growth in notebook computers, video cameras and digital camera monitors and other aspects of the application of the unique trend, in addition, it is in the geographic information system and aircraft cockpit, portable DVD, desktop computers and multimedia monitors. DVD, desktop computers and multimedia displays are well used. The idea of color TFT-LCD was initially proposed by the Americans (Westinghouse) in 1972, Japan's Toshiba took the lead in 1982 to achieve the scale of production of this technology, but at that time the production technology is still immature. Since 1993, Japan has mastered the TFT-LCD production technology, the resolution has been developed from CGA (320 * 200) to today's UXGA (1600 * 1200), the substrate size has been the first generation of 240 * 270-32O * 400mm2 development to the 2001 Sharp, South Korea's Samsung Electronics and LG-Philips companies were launched on the Currently, the application of TFT-LCD is mainly in the small size of the cell phone market, medium-sized PDA and laptop market, large size of the LCD monitor and LCD TV market and other five aspects. 2005 TFT-LCD will be mainly used in monitors (39%), laptop computers (25%), cell phones ( 16%), TFT-LCD will be mainly used in the market for the first time. 16%), LCD TV (10%), PDA (6%) five major areas, the market sales will exceed $ 25 billion, accounting for more than 90% of the LCD market, becoming the dominant technology in the field of liquid crystal and even the entire flat panel display technology.
TFT-LCD technology industry characteristics
Capital-intensive, large-scale operation: the establishment of a production line investment of about $ 1 billion. 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 and so on.
Development speed, stable core technology: TFT-LCD industrialization ten years production line has experienced seven major developments, an average of one and a half years production line to be updated. But the core technology of TFT-LCD is relatively stable.
Driven by a wide range of industries, the national economy has a global significance: upstream raw materials, production equipment, production technology involves dozens of areas of modern industrial production. The development of new materials, the manufacture of mass production equipment, the application of advanced production technology will drive the upstream industrial clusters.TFT-LCD module is the core device of the information industry, involving communications, transportation, home appliances, computers, education, industry, health care, national defense, and so on, almost all the fields.
Research Status of a-Si TFT-LCD Technology
Resolution: TFT-LCD resolution in recent years by CGA ( 320 * 2 00), VGA ( 640 * 4 80), SVGA (1280 * 1024). xGA (1024 * 768). SXGA (1280 * 1024) to the current level of UXGA (1600 * 1200), QXGA (2560 * 2048).
Contrast ratio: the United States P.P. Muhoray and others introduced the waveguide-based LCD technology, and the use of this technology to achieve a high contrast ratio of 174:1, and now the TFT-LCD contrast ratio up to 500:1.
Viewing Angle: Because the liquid crystal material is anisotropic, its molecular arrangement of the orientation and rearrangement under the action of the electric field to obtain a uniform influence on the viewing angle of the LCD device. Uniform impact on the LCD device view angle broadening, which causes the LCD device view angle shortcomings, has been proposed a variety of wide viewing angle technology, such as plane switching mode, symmetric micro-unit mode, domain vertical mode, etc., the viewing angle can reach 170 degrees.
Response speed: when the frame rate of 60%, the frame period of about 16ms, the use of TN-type LCD common TFT-LCD device response time can be less than 20ms. recently introduced a use of elastic continuous polymer stabilized planar switching method, which can shorten the response time to 10ms, the use of optical compensation band can be shortened to the response time of 2 ~ 3ms, the current A color LCD TV with a response time of 8ms has been developed using this technology.
Life: Due to the development of manufacturing technology, the life of TFT-LCD can reach more than 30,000 hours.
Large screen and reflective type has appeared:38in TFT-LCTV has been successfully developed, ending the era of large-screen LC splicing, reflective TFT-LCD color monitors have also begun to commercialize.
Because of the development of TFT production technology, liquid crystal material performance improvement, wide viewing angle technology, the adoption of the response speed and finished product rate increase, TFT-LCD display performance is no less than CRT.
TFT-type LCD structure
The usual a-Si TFT is mainly composed of a glass substrate, gate electrodes, the gate insulating layer, the semiconductor, the active layer a-Si, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor, the semiconductor. active layer a-Si, ohmic contact layer n + a-Si, source and drain electrodes and protective film and other components, of which the gate insulating layer and the protective film is generally used SiN.
a-SiTFT structure can be divided into four typical structures: source, drain, gate electrode is located in the semiconductor active layer of the same side of the plane structure of the a-Si, of which the source, drain, gate electrodes are located in the upper side of the layer of the a-Si, the gate is said to be positive! planar structure, the source, drain, gate three electrodes are located in the a-Si layer on the lower side of the inverted gate planar structure; source, drain, electrodes and gate electrodes are located in the a-Si layer on both sides of the staggered structure, where the gate electrode in the a-Si layer on the upper side, the source, drain electrode in the a-Si layer on the lower side of the positive gate staggered structure or the top gate structure, the gate electrode in the a-Si on the lower side, the source, drain electrode in the a-Si layer on the upper side of the inverted gate staggered structure or the bottom gate structure. The inverted gate staggered structure or bottom gate structure.
From the manufacturing process, the staggered structure of SiN, a-Si and n + a-Si three-layer (or two of them) can be continuously deposited, suitable for assembly line operation, and can reduce cross-contamination. Now, the interleaved structure has become the mainstream, it is not only for a-Si, SiN., n + a-Si can be continuous operation, and the inverted gate can also be used as a shading layer (no need to set up a separate shading layer), which is important for the a-Si TFT is important, because the a-Si is sensitive to light, once there is a light inflow caused by the leakage current increases, will lead to deterioration of image quality.