Thin film transistor liquid crystal display, often referred to as TFT LCD , is one of most used liquid crystal displays. It uses thin film transistor technology to improve image quality. Although TFT-LCD is collectively referred to as LCD, it is an active matrix LCD, which is used in TVs, flat panel displays and projectors.
In short, TFT LCD skin can be seen as two glass substrates with a layer of liquid crystal sandwiched between them. The glass substrate on the upper layer is connected with the color filter, while the glass on the lower layer is embedded with transistors. When the current passes through the transistor, the electric field changes, causing the deflection of liquid crystal molecules, so as to change the polarization of light, and then use the polarizer to determine the light and dark state of the pixel. In addition, because the upper glass fits with the color filter, each pixel contains three colors of red, blue and green. These pixels emitting red, blue and green colors constitute the image on the skin.
Ordinary liquid crystal display is like the display panel of calculator, whose image elements are directly driven by voltage; When one unit is controlled, it will not affect other units. When the number of pixels increases to a maximum, such as timing in millions, this method becomes impractical. Note that each pixel’s red, green and blue colors must have individual connecting lines. To avoid this dilemma, arranging pixels in rows and columns can reduce the number of connecting lines to thousands. If all pixels in a column are driven by a positive potential and all pixels in a row are driven by a negative potential, the pixels at the intersection of rows and columns will have the maximum voltage and be switched. However, there are still some problems in this method, that is, although the voltage received by other pixels in the same row or column is only part of the value, this partial switching can still darken the pixels (for liquid crystal displays that do not switch to bright) The solution is to add a transistor switch to each pixel, so that each pixel can be controlled independently. The significance of the low leakage current characteristic of the transistor is that the voltage applied to the pixel will not be lost arbitrarily before the picture is updated. Each pixel is a small capacitor, with a transparent indium tin oxide (ITO) layer in front and a transparent layer in the back, and an insulating liquid crystal in it.
This circuit arrangement is very similar to dynamic access memory, except that the whole architecture is not built on silicon wafer, but on glass. Many silicon wafer processes require temperatures that exceed the melting point of the glass. The silicon matrix of ordinary semiconductors uses liquid silicon to grow large single crystals, which has the good characteristics of transistors. The silicon layer used in thin film transistor liquid crystal display uses silicide gas to produce amorphous silicon layer or polycrystalline silicon layer. This manufacturing method is not suitable for making high-grade transistors.
TN
TN + film (twisted nematic + film) is the most common type, mainly due to the low price and diversity of products. On the modern TN panel, the reaction time of pixels is fast enough to greatly reduce the residual shadow problem, and even the reaction time is fast in the specification. However, this traditional reaction time is a standard formulated by ISO, which only defines the conversion time from all black to all white, but it does not mean the conversion time between gray scales. The conversion time between gray scales (which is actually more frequent in ordinary liquid crystals) is longer than that defined by ISO. The rtc-od (response time compensation overdrive) technology now used allows manufacturers to effectively reduce the conversion time between different gray scales (G2G). However, the reaction time defined by ISO has not actually changed. The reaction time is now represented by the number of G2G (gray to gray), such as 4ms and 2ms, which is common in TN + film products. This market strategy, with TN panel with lower cost than VA panel, has dominated the trend of TN in the consumer market.
TN displays suffer from the limitation of viewing angle, especially in the vertical direction, and most of them cannot display 16.7 million colors (24 bit real color) output by the current drawing card. In a special way, RGB tricolor uses 6 bits as 8 bits. It uses the reduction method combined with adjacent pixels to approach the 24 bits color, so as to simulate the required gray scale. Some people also use FRC (frame rate control)
For liquid crystal displays, the actual penetration rate of pixels generally does not change linearly with the applied voltage.
In addition, b-tn (best TN) was developed by Samsung Electronics. Improve TN color and reaction time.
STN
STN display (super twisted nematic display) is the abbreviation of super twisted nematic liquid crystal. After the invention of TN Display, people naturally thought of using TN liquid crystal matrix to display complex graphics. The torsion of STN liquid crystal is 180 to 270 degrees relative to that of TN liquid crystal. In the early 1990s, color STN liquid crystal came out. A pixel of this liquid crystal is composed of three liquid crystal units, covered with a layer of color filter, and the color can be generated by controlling the brightness of the liquid crystal unit with voltage.
VA
CPA (continuous pinwheel alignment) is developed by sharp. High color reproduction, low output and high price.
MVA (multi domain vertical alignment) was developed by Fujitsu in 1998 as a compromise between TN and IPS. At that time, it had fast pixel response, wide viewing angle and high contrast, but relatively sacrificed brightness and color reproducibility. Analysts predict that MVA technology will dominate the whole mainstream market, but TN has this advantage. This is mainly due to the high cost of MVA and the slow pixel response (it will increase significantly when the brightness changes).
P-mva (premium MVA) is developed by Youda optoelectronics to improve the visual angle and reaction time of MVA.
A-mva (Advanced MVA) is developed by Youda optoelectronics.
S-mva (super MVA) was developed by Qimei electronics.
PVA (patterned vertical alignment) is developed by Samsung Electronics. Although the company calls it the technology with the best comparison at present, it also has the same problems as MVA.
S-PVA (super PVA) is developed by Samsung Electronics to improve the visual angle and reaction time of PVA.
C-PVA was developed by Samsung Electronics.
IPS
IPS (in plane switching) was developed by Hitachi in 1996 to change the poor viewing angle and color reproducibility of TN panel. This improvement increases the reaction time. Its initial level is 50ms, and the cost of IPS panel is also very expensive.
S-IPS (super IPS) not only has the advantages of iPS technology, but also improves the update time of pixels. The color reproducibility is closer to CRTs and the price is also reduced. However, the comparison is still very poor. At present, S-IPS is only applied to larger displays for professional purposes.
Super PLS
PLS (plane to line switching) is developed by Samsung Electronics. In addition to its amazing perspective, it can also improve the brightness of the display screen by 10%, and the manufacturing cost is 15% less than that of IPS. At present, the resolution provided can reach WXGA (1280) × 800), and some MacBook Pro with retina display also adopts this kind of display produced by Samsung (resolution up to 2880) × 1800), and the rest still use IPS display. The main objects will be smart phones and tablets, which have been mass produced in 2011.
ASV
Sharp has developed ASV (advanced super-v) technology to improve the visual angle of TFT.
FFS
Modern electronics adopts FFS (fringe field switching) technology, which is an advanced extension of IPS (in plane switching) wide viewing angle technology and has the characteristics of low power consumption, high brightness and so on. FFS can extend AFFS + (Advanced FFS +) and HFFs (high aperture FFS) technology. AFFS + has visual function in the sun.
OCB
OCB (optical compensated birefringence) is the technology of Panasonic electric in Japan.
Industry introduction
Due to the huge cost of building TFT factories, there may not be more than four or five major skin OEM manufacturers. Several well-known are sharp, Youda, Qimei, Samsung, LG Philips, etc.
Before the system and ID assembly, the skin module is usually divided into three categories in the factory, which are the number of bright and dark spots, the gray scale and color uniformity displayed by the skin and the general product quality. In addition, there is still a difference in + / – 2ms reaction time between different pieces of skin of the same batch number. The skin with the worst quality will be sold to white brand manufacturers later.
Poor quality skin or sizes below 15 inches usually do not contain digital signal compatible interface DVI, so their future applicability may be limited. For the higher 17 inch or 19 inch models, the screens used by players and offices may have dual display slots: analog D-sub and digital DVI; Almost all professional screens will have DVI and turn 90 degrees for letter mode. In any case, even if the video signal of DVI is used, there is no guarantee that it will have better image quality: a good image card RAMDAC and a suitable and protected analog VGA cable can also provide the same display quality.
development history
Thin film transistor liquid crystal display technology was first proposed by European and American countries. However, due to the immature technology and manufacturing process, until the late 1980s, Japanese manufacturers fully mastered the main production technology and began large-scale production, forming the current huge industrial year. In 1992, with the demand for liquid crystal display products of notebook computers, Thin film transistor liquid crystal display has established its mainstream status as liquid crystal display. With the further development of technology, the production cost of thin film transistor liquid crystal display has decreased significantly, which has prompted people’s demand for display devices to shift from bulky cathode ray tube to light thin film transistor, and finally exceeded the market share of cathode ray tube. Around 2000, it opened a new industry of liquid crystal TV, according to China electronic news, At present, the manufacturing technology of thin film transistor liquid crystal display has developed to the 8th generation line, and the construction of 10th generation line, 11th generation line and 12th generation line is also under planning. China’s thin film transistor liquid crystal display has fallen behind in the display field, but experts suggest that we should not bypass the thin film transistor liquid crystal display and look for other breakthroughs to develop China’s flat panel display industry, We should quickly carry out the construction of TFC: LCD production line and related technological innovation capacity to improve the international competitiveness of China’s thin film transistor LCD device industry.
Development prospect
In the current rapid development of liquid crystal display technology, thin film transistor liquid crystal display is widely favored by people for its large capacity, high definition and high quality full true color. The display quality and overall performance of thin film transistor liquid crystal display largely depend on the performance of thin film transistor. Thin film transistor (787) is an amorphous silicon among many field effect transistors (897). With the maturity of the technology used to make thin film transistor liquid crystal display, amorphous thin film transistor liquid crystal display occupies a dominant position in the market of thin film transistor liquid crystal display, However, amorphous silicon thin film transistor seriously restricts the development of thin film transistor LCD due to its low mobility and conductivity. Looking for suitable substitutes and pursuing high mobility and high conductivity has always been the focus of researchers. On this basis, polycrystalline silicon and microcrystalline silicon have developed one after another. Although the problem of low mobility and conductivity has been temporarily solved to a certain extent, due to the high price of polycrystalline silicon and microcrystalline silicon The shortage of materials failed to shake the dominant position of amorphous silicon. The subsequent nano silicon thin film transistor liquid crystal display has become a new highlight due to its advantages of high conductivity and high mobility and the progress of nanotechnology.
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