1. Product Overview

Thin-film transistor liquid crystal display (TFT-LCD) is the most important kind of liquid crystal display, and its output value and influence have an important position in the liquid crystal display family. Widely used in TV, laptop, monitor, mobile phone and other aspects. TFT-LCD is divided into amorphous silicon TFT (a-Si TFT), polycrystalline silicon (p-Si TFT) and single crystal silicon MOSFET (c-Si MOSFET) according to the different thin film transistor materials In LCOS (Liquid Crystal on Silcon) technology.

TFT-LCD technology is a technology that combines microelectronics and liquid crystal display ingeniously. People will transfer the technology of microelectronics fine processing on Si to the processing of TFT arrays on large-area glass, and then combine it with the mature LCD technology in order to continuously improve product quality and enhance automated large-scale production capacity. Improve the pass rate, reduce costs, and make its performance / price ratio continue to approach CRT.

The concept of active matrix drive should be traced back to 1971. Lechner et al. Of RCA proposed to overcome the disadvantages of passive LCD devices (such as TN-LCD, STN-LCD), such as low contrast and small display capacity. But the real TFT development work is carried out at Dundee University in the UK. In 1981, Snell and others successfully trial-produced a 5X7 dot matrix TFT-LCD in the world. Subsequently, Japan and other countries quickly carried out research work, successively launched TFT-LCD products and began commercialization. Starting in 1993, TFT-LCD began to enter the heyday of mass production.

2. Working principle

In TFT-LCD, the function of TFT is a switch tube. Commonly used TFTs are three-terminal devices. A semiconductor layer is formed on a glass substrate, and a source electrode and a drain electrode are connected at both ends. The gate insulating film is opposed to the semiconductor, and the current between the source and drain electrodes is controlled by the voltage applied to the gate.

For the display screen, each pixel can be viewed as a layer of liquid crystal sandwiched between the pixel electrode and the common electrode. More importantly, it can be regarded as a capacitor from an electrical point of view. The equivalent circuit is shown in Figure 1. To charge the pixel P (i, j) in row j and column i, the switch T (i, j) is turned on, and the target voltage is applied 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 molecules between the electrodes continue to have an electric field. The role of the data (column) driver is to apply a target voltage to the signal line, while the role of the gate (row) driver is to turn on and off the switch. Since the voltage applied to the liquid crystal layer can be stored, the liquid crystal layer can work stably. This display voltage can be rewritten in a short time through the TFT, so even high-definition LCDs can meet image quality requirements.

The key to displaying images is also the molecular orientation of the liquid crystal under the action of an electric field. Generally, different display modes are realized by orienting the inside of the substrate to produce a desired deformation of the arrangement of liquid crystal molecules. Under the action of the electric field, the orientation of the liquid crystal molecules changes, and through cooperation with the polarizer, the intensity of incident light changes after passing through the liquid crystal layer. In order to achieve image display.