Unlike TN technology, the TFT display uses a "back-penetrating" approach-the imaginary light path is not from top to bottom like the TN liquid crystal, but from the bottom up. This approach is to set up a special light tube on the back of the liquid crystal, the light source irradiation through the lower side of the plate. As the electrodes of the upper and lower layers are changed into FET electrodes and a common ohmic electrode, the performance of the liquid crystal molecule will also change when the FET electrode is conductive, and the display can be achieved by shading and light transmission, and the response time is greatly increased to about 80ms. Because of its higher contrast than TN-LCD and richer color, screen update frequency is also faster, so the TFT commonly known as "True Color." Compared to DSTN, the main feature of TFT-LCD is to configure a semiconductor switch device for each pixel. Because each pixel can be directly controlled by a point pulse. Thus each node is relatively independent and can be continuously controlled. This design method not only enhances the display screen's reaction speed, but also can precisely control the display gray level, this is the TFT color is more lifelike than the dstn reason.
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 fabricated on a glass substrate, at both ends of which the source and drain are connected. And the gate insulation film is connected with the semiconductor, and the gate is arranged. The current between the source and the leakage electrode is controlled by the voltage applied to the gate. For a display, each pixel can be structurally simplified to look at a liquid crystal between a pixel electrode and a common electrode. It is more important to think of it as a capacitor from the angle of electricity. The equivalent circuit is shown in Figure 1. To charge the pixel p (i,j) of the J Row I column, the Switch T (I,J) is directed and the target voltage is applied to the signal line D (i). When the pixel electrode is fully charged, even if the switch is disconnected, the electrical charge in the capacitor is preserved, and the liquid crystal layer between the electrodes continues to have a voltage field effect. The function of the data (column) drive is to exert a target voltage on the signal line, while the gate (row) drive is the conduction and disconnect of the switch. Because the display voltage on the liquid crystal layer can be stored in the storage capacitance of each pixel, the liquid crystal layer can work stably. This display voltage through the TFT can also be rewritten in a short period of time, so even in the high-definition LCD, it can not reduce the image quality requirements. The key of the display image is the molecular orientation of the liquid crystal in the electric field. In general, the orientation of the inside of the substrate is treated so that the arrangement of the liquid crystal molecule produces the desired structural deformation to achieve different display modes. Select a certain display mode, in the electric field action, the liquid crystal molecule produces the orientation change, and through with the Polarizer's match, causes the incident light to pass through the liquid crystal layer the strength to change. So as to realize the image display. In a word, TFT-LCD and passive TN-LCD, STN-LCD simple matrix, it is in each pixel of the LCD screen has a thin film transistor (TFT), can effectively overcome the crosstalk when not selected, so that the static characteristics of the display LCD screen and the number of scan lines, Therefore, the image quality is greatly improved. and switch unit (that is, TFT) characteristics, it is required to meet the low state resistance, the closed-state resistance is very large.