惠州市清洋实业有限公司

In today's rapidly developing smartphone era, I believe many netizens are already familiar with the term TFT, having seen it in mobile phone specifications. TFT stands for Thin Film Transistor, which means that each liquid crystal pixel on the display is driven by a thin film transistor integrated behind it, allowing for high-speed, high-brightness, and high-contrast display of screen information. TFT belongs to active matrix liquid crystal displays, and TFT-LCD is a type of liquid crystal display.

TFT sets up special light tubes at the back of the liquid crystal, allowing for "active" control of each independent pixel on the screen, which is the origin of the term active matrix TFT. This greatly improves the response time, with typical TFT response times being around 80ms, while STN is about 200ms. If you want to improve it further, flickering may occur. Additionally, because TFT is an active matrix LCD, it allows the arrangement of liquid crystals to have memory, meaning they do not immediately return to their original state after the current disappears.

TFT displays use a "back-transmission" illumination method—where the hypothetical light source path is not from top to bottom like TN liquid crystals, but from bottom to top. This method involves setting up special light tubes at the back of the liquid crystal, where the light source shines through the lower polarizer. Due to the change of the electrodes in the upper and lower layers to FET electrodes and common electrodes, when the FET electrode is turned on, the behavior of the liquid crystal molecules also changes, allowing for display through light blocking and transmission. The response time is greatly improved to around 80ms, and because it has higher contrast and richer colors than TN-LCD, the refresh rate of the screen is also faster, hence TFT is commonly referred to as "true color."

Compared to DSTN, the main feature of TFT-LCD is that each pixel is equipped with a semiconductor switching device. Since each pixel can be directly controlled by pulse signals, 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 for precise control of display grayscale, which is why TFT colors are more realistic than DSTN.

TFT also improves the flickering (water ripple) blur phenomenon of STN, effectively enhancing the ability to play dynamic images. Compared to STN, TFT has excellent color saturation, restoration capability, and higher contrast, but the downside is that it consumes more power and is more expensive.

TFT Technology Features

TFT technology was developed in the 1990s and is a large-scale semiconductor integrated circuit manufacturing technology that uses new materials and processes. It is the foundation for liquid crystal (LC), inorganic and organic thin-film electroluminescent (EL and OEL) flat panel displays. TFT is formed on non-monocrystalline substrates such as glass or plastic substrates (it can also be on chips) through sputtering and chemical deposition processes to create various films necessary for circuit manufacturing. By processing these films, large-scale semiconductor integrated circuits (LSIC) can be produced. Using non-monocrystalline substrates can significantly reduce costs, extending traditional large-scale integrated circuits towards large area, multifunctional, and low-cost directions. Manufacturing control pixels (LC or OLED) on large-area glass or plastic substrates is technically more challenging than manufacturing large-scale ICs on silicon wafers. The requirements for the production environment (purity level of 100), the purity of raw materials (purity of electronic special gases at 99.999985%), and the requirements for production equipment and technology exceed those of semiconductor large-scale integration, making it a top technology in modern mass production. Its main features include:

Large Area

In the early 1990s, the first generation of large-area glass substrate (300mm×400mm) TFT-LCD production lines was put into operation. By the first half of 2000, the area of glass substrates had expanded to 680mm×880mm, and recently, 950mm×1200mm glass substrates will also be put into operation. In principle, there is no area limitation.

High Integration

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

Powerful Functionality

TFT was initially used as a matrix addressing circuit to improve the optical valve characteristics of liquid crystals. For high-resolution displays, precise control of object pixels is achieved through voltage adjustment in the range of 0-6V (with a typical value of 0.2 to 4V), making high-quality high-resolution display of LCD possible. TFT-LCD is the first flat panel display in human history to surpass CRT in display quality. Now, people are beginning to integrate driving ICs into glass substrates, making the overall functionality of TFT even more powerful, which is unmatched by traditional large-scale semiconductor integrated circuits.

Low Cost

Glass substrates and plastic substrates fundamentally solve the cost issue of large-scale semiconductor integrated circuits, opening up vast application space for large-scale semiconductor integrated circuits.

Flexible Process

In addition to using traditional film-forming processes such as sputtering, CVD (Chemical Vapor Deposition), and MCVD (Molecular Chemical Vapor Deposition), laser annealing technology has also begun to be applied, which can produce amorphous films, polycrystalline films, and single-crystal films. It can produce not only silicon films but also other II-VI and III-V semiconductor thin films.

Wide Application Fields

Liquid crystal flat panel displays based on TFT technology are a pillar industry of the information society, and the technology can also be applied to the rapidly growing thin-film transistor organic electroluminescent (TFT-OLED) flat panel displays.