Generally, LCD display is divided into four major categories according to product application, including: Twistwd nematic lcd (TN-LCD), super twisted nematic lcd(STN-LCD), thin film transistor-LCD (TFT-LCD) and low-temperature polycrystalline silicon-liquid crystal display (LTPS-LCD), wherein TN and STN are in fact the type of LCD, while TFT and LTPS are the different switch components, Since the early black-and-white LCD panels are passive matrices, both TN and STN will appear, and we are now introducing their differences.
The torsional nematic liquid crystal (TN) molecule divides into layers between two conductive glasses, each layer of liquid crystal molecules rotate one angle, and the first layer and the last layer of liquid crystal molecules rotate the angle "less than 90 °". Torsion to the column-type liquid crystal (tn) of each layer of molecular rotation of the angle is small, in the chemical viewpoint we call this liquid crystal molecule "energy is lower, comparatively stable", when we applied voltage, LCD will stand on the glass, the relatively stable TN molecules as if "lying on the glass molecules, very stable and comfortable", so by the external voltage reaction is slower, it takes a long time to stand on the glass, this LCD display of black-and-white reaction speed is slower.
Advantages: Low drive voltage, low power consumption, low production cost.
Disadvantage: The reaction speed is slow, has the residual shadow occurrence, only suits to make the black-and-white display.
Application: Electronic meter, electronic calculator, electronic dictionary.
Super twisted nematic liquid crystal (STN) molecules will be divided into a number of layers between two pieces of glass, the liquid crystal molecules of each layer will rotate an angle, and the first layer and the last layer of liquid crystal molecules "rotation angle greater than 90 degrees (180 degrees to 240 degrees), as shown in Figure five (b) shown. Super twisted nematic liquid crystal (STN) of each layer of the molecular rotation angle is relatively large, in the point of view of chemistry on the liquid crystal molecules we call this "high energy, less stability", when we applied voltage, the LCD will stand on the glass, the STN molecule unstable like molecular "squat in the glass, is very unstable and uncomfortable, so by the applied voltage when compared with the reaction quickly, immediately stood on the glass, and the liquid crystal display reaction speed is faster.
Advantages: The reaction rate is faster than TN, making the TFT easy.
Disadvantages: The reaction speed is still not fast enough, only suitable for gray scale or high color display.
Application: Color mobile phone, color personal digital assistant (PDA), digital camera.
Thin film transistor (TFT) control of each pixel is fabricated directly on the glass, we use chemical vapor deposition (CVD) growth of a layer of amorphous silicon on glass above the thin film transistor (TFT) fabricated on the amorphous silicon above, because the glass substrate is "amorphous" so making the switch in the above is the "amorphous". The glass transition temperature "(Trnasition temperature)" about 300 DEG C, the transformation temperature is actually "softening temperature", which is heating up to 300 DEG C glass will begin to soften, so the process temperature can not exceed 300 DEG C, or soft off glass. In the process of temperature lower than 300 DEG C under the condition of using chemical vapor deposition (CVD) in thin film transistor above the glass making "amorphous silicon" (TFT), known as the "low temperature of amorphous silicon (Low temperature amorphous silicon)", is what we call a "thin film transistor liquid crystal display (TFT LCD)" is the use of low temperature amorphous silicon process.
Advantages: The reaction speed is faster than the STN, can make full color display.
Disadvantages: Thin Film transistor production difficulty, cost more than the STN high conductivity, amorphous silicon, so driving voltage is higher, amorphous silicon conductivity is not good so high power consumption, amorphous silicon thin film transistors larger, lower opening rate.
pplication: Full-color LCD, notebook computer, LCD TV,gps car.
Common size:lcd 3.2,lcd 3.5,2.4 lcd.
In fact, the use of polysilicon production monitors can be divided into "high temperature poly silicon (HTPS)" and "Low temperature poly silicon (LTPS)" Two kinds:
High temperature poly silicon
Because of the thin film transistor fabricated using amorphous silicon (TFT), poor conductivity, slow working speed, if we want to increase the speed of work, you must use the "Silicon" best, unfortunately, because the glass is amorphous, it is not possible to grow on the glass base plate on the amorphous silicon, scientists thought a good idea, is to use "annealing (Anneal)", the solid material temperature, then cooling slowly forming polycrystalline. we will be "glass and amorphous silicon thin film" into a high temperature furnace, heating to 600 DEG C, and then slowly cooled to room temperature, you can become a "process" of the polycrystalline silicon thin film, called "high temperature polysilicon (HTPS)".
The glass transition temperature of about 300 DEG C, the glass heating up to 600 DEG C glass will begin to soften, so in the high temperature polysilicon (HTPS) process can not use glass as substrate must be conductive glass glass "(Glass)" replaced "quartz (Quartz)" for quartz (Quartz "the crystal") is silica, high melting temperature up to 1200 DEG C, but the price is high, and the size of the larger quartz, price is a geometric series increase (and diamond like), so the high temperature polysilicon (HTPS) cannot be used in large size LCD display is low, early are used in liquid crystal "projection display in high resolution, small size LCD panel, usually less than 3 inches. On the LCD projection display will be described in detail later.
Low temperature poly silicon
By the introduction of the above is not difficult to find, in fact, we want to "annealing (Anneal)" is only part of the thin film transistor (TFT), the glass substrate and thin film transistor into the whole heated high temperature furnace is foolish, you may wish to think and see, what method can only heat the thin film transistor can keep the glass substrate at low temperature? Clever scientists have invented a new technology called laser annealing (Laser anneal) ", glass and amorphous silicon thin film" into the laser annealing furnace, using high energy laser incident to the lens, and then focus on amorphous silicon film heating, heating to 600 DEG C, and then slowly cooled to room temperature, you can become a "polysilicon film", below the laser annealing furnace cooling water, can the glass substrate is maintained at a temperature below 300 DEG C, how such a simple method of you is not thought?
Advantages: The fastest reaction speed, the conductivity of polycrystalline silicon is better so the driving voltage is lower, polycrystalline silicon thin film transistors are smaller, so the opening rate is high.
Disadvantages: Laser annealing technology is not mature, product yield is low.
Application: Full-color LCD, notebook computer, LCD TV.