The difference between TFT and LCD

- May 21, 2018-


TFT is a variant of LCD, TFT, Thin Film Transistor is a kind of active matrix type liquid crystal display AM-LCD, TFT sets a special light tube on the back of the liquid crystal, can be "active" on the screen Independent pixels control, which is the origin of the so-called active matrix TFT (AcTIve Matrix TFT), which can greatly improve the reaction time, the general TFT response time is faster, about 80ms, while the STN is 200ms, if you want to improve There will be flickering. Moreover, since the TFT is an active matrix LCD, the arrangement of the liquid crystals can have a memory and cannot be restored immediately after the current disappears. The TFT also improves the STN flicker (blur)-blur phenomenon effectively improving the ability to play dynamic pictures. Compared with STN, TFT has excellent color saturation, reduction ability and higher contrast, but the disadvantage is that it consumes more power and costs more.

???????LCD: Liquid Crystal Display, liquid crystal display, is divided into: monochrome, pseudo-color, true color and so on. TFT is a kind of LCD, also called true color screen. The brightness and viewing angle are stronger than the other two!

LCD refers to a liquid crystal display, TFT is a kind of LCD

The common liquid crystal display is divided into four types according to the physical structure:

(1) Twisted nematics (TN-Twisted NemaTIc);

(2) Super Twisted Nematic (STN-Super TN);

(3) DSTN-Dual Scan Tortuosity Nomograph;

(4) TFT-Thin Film Transistor.

The basic display principles of TN-LCD, STN-LCD, and DSYN-LCD are the same, except that the twist angles of the liquid crystal molecules are different. The liquid crystal molecules of the STN-LCD have a twist angle of 180 degrees or even 270 degrees. The TFT-LCD adopts a completely different display mode than the TN series LCD.

TFT-LCD technology is a technology that combines microelectronic technology and liquid crystal display technology. People took advantage of the micro-electronics fine processing technology on Si, transplanted to the processing of TFT arrays on large-area glass, and then used this array substrate with another substrate with a color filter film and matured LCD technology. A liquid crystal cell is combined to form a liquid crystal display (screen) after undergoing processes such as polarizer pasting.

In TFT-LCD, the function of TFT is equivalent to a switch tube. The commonly used TFT is a three-terminal device. A semiconductor layer is generally formed on a glass substrate with source and drain connected to both ends. And through the gate insulating film, opposite to the semiconductor, with a grid. The voltage applied to the gate controls the current between the source and drain electrodes.

For a display screen, each pixel can be simplified in structure as a layer of liquid crystal sandwiched between a pixel electrode and a common electrode. More importantly, it can be seen as a capacitor from the electrical point of view. The equivalent circuit is shown in Figure 1. To charge the pixel P(i,j) in the j row i column, the switch T(i,j) is turned on to apply a target voltage to the signal line D(i). When the pixel electrode is fully charged, even if the switch is turned off, the charge in the capacitor is preserved, and the liquid crystal layer molecules between the electrodes continue to have a voltage application field. The role of the data (column) driver is to apply a target voltage to the signal line, and the gate (row) driver functions to turn the switch on and off. Since the display voltage applied to the liquid crystal layer can be stored in the storage capacitance of each pixel, the liquid crystal layer can be stably operated. This display voltage can also be rewritten in a short time through the TFT, so even in a high-definition LCD, it can meet the requirement of not reducing image quality.

The key to displaying an image is also the molecular orientation of the liquid crystal under the action of an electric field. In general, different display modes are realized by aligning the alignment of liquid crystal molecules by aligning the inside of the substrate. Selecting a certain display mode, under the action of the electric field, the liquid crystal molecules produce an orientation change, and through the cooperation with the polarizer, the intensity of the incident light after passing through the liquid crystal layer changes accordingly. In order to achieve image display. All in all, TFT-LCD is different from the simple matrix of passive TN-LCD and STN-LCD. It has a thin film transistor (TFT) on each pixel of the liquid crystal display, which can effectively overcome the non-selection time. Crosstalk makes the static characteristics of the display screen independent of the number of scan lines, thus greatly improving the image quality. The characteristics of the switching element (ie, TFT) must meet the requirement that the on-state resistance be low and the on-state resistance be very large.