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What is TFT-LCD

Fig. 1a  Display principle and structure of TFT-LCD Fig. 1b Full engineering of TFT-LCD module

As shown in Fig.1a, a liquid crystal of 3~4um is injected between the top and bottom transparent electrodes of LCDs. When there is no external electric field, the liquid crystal molecules will rotate by 90 degrees in the layer and cause the incident light polarization to rotate by 90 degrees along the long axis of liquid crystals by the waveguide phenomenon, which will transmit through the orthogonal polarizer and produce a bright screen. On the contrary, when there is a non-zero external electric field, the long axis of liquid crystals will be parallel to the field direction to maintain the minimum static potential. In this case, the light polarization stays unchanged and won’t be able to pass through the polarizer, leading to a dark state screen. In addition, the strength of the electric field across the liquid crystal layer can be controlled by changing the voltages applied to the pixel electrode, which can further modulate the strength of the incident light and produce a gray level screen between fully bright and completely dark. The current mainstream LCD design and manufacturer technique is the Active matrix (AM) LCD, which consists of Color filter (CF), TFT Array substrate, Backlight module, as shown in Fig. a. Each individual pixel of a TFT-LCD needs one set of TFT to control its voltage. To produce different colors in the lights generated by the backlight module and passing the liquid crystal, red, blue, and green color resists need to be coated on the CF glass to produce the full color effect combined with the gray level. When the TFT array and CF substrate are completely separated, liquid crystal is injected between the CF top plate and TFT bottom plate, followed by paired adhesion and completed by attaching the polarizer. This part of the process is called the LCD process. The final LCM process involves connection of the driver IC and PCBA to the glass substrate (JI process), followed by assembling with the backlight module (MA process) and is completed with the illumination test (Fig.1b).