Introduction
The full phrase of TFT-LCD is thin film transistor liquid crystal display. Recently, it grows rapidly and it is applied in the large size for television to small-medium size display such as mobile phone and PDA. In comparison with STN-LCD, its resolution is much sharpness and brightness as well as faster response time. On the contrary, it bears higher cost and has higher power consumption.

Principle
The infrastructure of TFT-LCD: With silicon etching technology, it spreads film so called a-Si transistor on the ITO glass as well as pours the liquid crystal in between two pieces of glass corresponds with two pieces of polarizer. The basic infrastructure of TFT-LCD is represented as the figure 1.
　

Figure 1

Operating Theorem
The transistor included semiconductor, gate, source and drain function is alike the electricity breaker. The source connects to data line, the gate is joint with scan line as well as the drain is link to pixel electrode. Its infrastructure of transistor is represented as the figure 2.
　

Figure 2

The active matrix operating theorem is to process the semiconductor by the gate voltage in order to link to the source and drain as well as to dominate the display signal current from the source to the drain. When voltage that is applied in the liquid crystal layer and remains in the load capacitor for pixels, this drives the liquid crystal steadily to be activated till renew the display data by the next frame in the microseconds. We clearly distinguish the darkness or the lightness of red, green and blue with our eyes when incident light from backlight passes through polarizer, liquid crystal layer and color filter.