Technical characteristics of TFT

TFT technology was developed in the 1990s. It adopts new materials and new processes for large-scale semiconductor all-integrated circuit manufacturing technology. It is used for liquid crystal (LC), inorganic and organic thin-film electroluminescence (EL and OEL) flat panel displays. basis. TFT is a non-single wafer such as a glass or plastic substrate (of course, it can also be on a wafer) through sputtering and chemical deposition processes to form various films necessary for manufacturing circuits, and large-scale semiconductor integrated circuits (LSIC) are manufactured by processing the films. . The use of non-single crystal substrates can greatly reduce costs, and is an extension of traditional large-scale integrated circuits to large-area, multi-function, and low-cost directions. It is more technically difficult to manufacture TFTs that control the switching performance of pixels (LC or OLED) on large-area glass or plastic substrates than to manufacture large-scale ICs on silicon wafers. The requirements for the production environment (purification degree is 100), the requirements for the purity of raw materials (the purity of electronic special gas is 99.999985%), and the requirements for production equipment and production technology exceed the large-scale integration of semiconductors. It is the top of modern large-scale production. technology. Its main features are:

(1) Large area: The first generation of large-area glass substrate (300mm×400mm) TFT-LCD production line was put into production in the early 1990s. By the first half of 2000, the area of the glass substrate had been expanded to 680mm×880mm). Recently, 950mm×1200mm The glass substrate will also be put into operation. In principle, there is no area limitation.

(2) High integration: The 1.3-inch TFT chip used for liquid crystal projection has a resolution of XGA containing millions of pixels. The 16.1-inch TFT array amorphous silicon with a resolution of SXGA (1280×1024) has a film thickness of only 50nm, and TAB ON GLASS and SYSTEM ON GLASS technologies, the integration of its IC, the requirements for equipment and supply technology, and the technical difficulty All exceed the traditional LSI.

(3) Powerful functions: TFT was first used as a matrix location circuit to improve the light valve characteristics of liquid crystals. For high-resolution displays, through voltage adjustment in the range of 0-6V (typically 0.2 to 4V), precise control of the object is achieved, making it possible for the LCD to achieve high-quality and high-resolution displays. TFT-LCD is the first flat panel display in human history that exceeds CRT in display quality. People begin to integrate the driver IC on the glass substrate, and the function of the entire TFT will be more powerful, which is unmatched by traditional large-scale semiconductor integrated circuits.

(4) Low cost: The glass substrate and plastic substrate fundamentally solve the cost problem of large-scale semiconductor integrated circuits, and open up a broad application space for the application of large-scale semiconductor integrated circuits.

(5) Flexible process: In addition to sputtering, CVD (Chemical Vapor Deposition) MCVD (Molecular Chemical Vapor Deposition) and other traditional processes for film formation, laser annealing technology has also begun to be applied, which can produce amorphous films, polycrystalline films, and Single crystal films can be manufactured. It can not only make silicon film, but also make other Ⅱ-VI group and Ⅲ-V group semiconductor thin films.

(6) The application field is wide. The LCD flat panel display based on TFT technology is the pillar industry of the information society, and the technology can also be applied to the rapidly growing thin film transistor organic electroluminescence (TFT-OLED) flat panel display. Growing.

3. Main features of TFT-LCD:

With the maturity of TFT technology in the early 1990s, color LCD flat-panel displays developed rapidly. In less than 10 years, TFT-LCD has rapidly grown into a mainstream display, which is inseparable from its advantages. The main features are:

(1) Good use characteristics: low-voltage applications, low driving voltage, and improved safety and reliability of solid use; flat panel, light and thin, saving a lot of raw materials and use space; low power consumption, its power consumption is about CRT display One-tenth of that, reflective TFT-LCD is even only about one-hundredth of CRT, saving a lot of energy; TFT-LCD products also have specifications, models, and sizes in series, with various varieties, convenient and flexible use, maintenance, and update , Easy to upgrade, long service life and many other features. The display range covers the application range of all displays from 1 inch to 40 inches and large projection planes. It is a full-size display terminal; the display quality ranges from the simplest monochrome character graphics to high resolution and high color fidelity. Various specifications and models of video displays with high brightness, high contrast and high response speed; display methods include direct view, projection, see-through, and reflective.

(2) Good environmental protection characteristics: no radiation, no flicker, no harm to the user's health. In particular, the emergence of TFT-LCD e-books will bring mankind into the era of paperless office and paperless printing, triggering a revolution in the way that mankind learns, spreads, and remembers civilization.

(3) The application range is wide, and it can be used normally in the temperature range from -20°C to +50°C. The low temperature working temperature of the TFT-LCD after temperature reinforcement can reach minus 80°C. It can be used as a mobile terminal display, a desktop terminal display, and a large-screen projection TV. It is a full-size video display terminal with excellent performance.

(4) The degree of automation of manufacturing technology is high, and the characteristics of large-scale industrial production are good. The TFT-LCD industry technology is mature, and the mass production yield rate has reached more than 90%.

(5) TFT-LCD is easy to be integrated and updated. It is a perfect combination of large-scale semiconductor integrated circuit technology and light source technology, and has great potential for continued development. There are amorphous, polycrystalline and monocrystalline silicon TFT-LCDs. In the future, there will be TFTs of other materials, including glass substrates and plastic substrates.