What is TFT-LCD
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| 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).
Advantages of AUO TFT-LCD Process and Technology
Continual Investment of New Generation Plants
Fig. 2 Dimensions of G8.5 glass substrate
AUO has developed processes for G8.5 plant, which produces the panels used in large size LCD TVs (Fig. 7). In December of 2008, AUO successfully illuminated the first 46” LCD TV panel produced in its G8.5 plant, demonstrating its leading process technology in Taiwan. This achievement marked a brand new page and reached another milestone of the new generation plant and also established the example of green plant for TFT-LCDs. The size of G8.5 glass substrate is about that of a pool table, with its glass less than 1mm thick. As a result, the new generation plant requires more advanced process technology. As the technology of large size panels matures, AUO will remain focused on developing new generation plant in the future and move forward to increase production capacity, improve process quality, and target customer service.
Vigorously Implement Green Production Technology
The development of the next generation process includes simplified process, utilizing optimized raw materials, component method, improvement of process yield and capacity, and reduction of production costs. The investment cost of the equipment for the front-end TFT array and CF processes consists of over 60% of the entire expense of TFT-LCD. Therefore, the front-end process development focuses primarily on process simplification and increasing percentage usage of raw materials. One example is the simplified four-mask technology (Fig. 8 (a)) and pattern definition that requires no exposure or etching. In addition, using thinner glass substrates can reduce the glass material consumption and has the advantages of lightweight and slim body. Meanwhile, it can reduce the use of packaging materials, improve transportation efficiency, and save more energy by reducing the generated wastes. As for LCM, with significant improvements of gate driver on array (GOA) as shown in Fig. 3 (b) and half source driving (HSD) technologies, they’re not only minimize the material dependence on a large amount of driver ICs as conventional panels, but also assist in improving the LCM production capacity. For the backlight module, replacing conventional cold cathode fluorescent lamps (CCFL) with light-emitting diodes (LED) not only avoids the environmental hazard posed by mercury vapors, the final products conserve more energy by having better emission efficiency.
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Rooted on TFT-LCD process technology and brave the panel blue sea
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Fig. 4 Emergence of new panel applications such as 3D and touch control
The existing LCD industry has experienced fundamental changes, where the focus shifted from pursuing production scale to increasing business core competitiveness and developing added values of products. Facing the new trend, with its experience in the front-end production flow of large size TFT-LCDs and excellent performance in back-end driver electrical control, opto-mechanical design and assembling, AUO is drafting the plan for the next ten years in the panel industry based on its current TFT-LCD process technology. This wave of panel revolution has new applications in the areas of 3D (Fig. 9(a)), touch panel (Fig. 9(b)), etc. The layout of the new technology involves new display technologies such as OLED.