Research Status of TFT-LCD Technology

Contrast: P.P. Muhoray et al. of the United States introduced the waveguide-based LCD technology, and used this technology to achieve a high contrast of 174:1. Now the true contrast of TFT-LCD can reach up to 500:1. If software modulation is added, the contrast can be driven dozens of times on this basis.

The angle of view: because the liquid crystal material is anisotropic, the orientation of its molecular arrangement and its rearrangement under the effect of an electric field has a uniform effect on the broadening of the angle of view of the LCD device, which results in the shortcomings of the angle of view of the LCD device, a variety of wide viewing angle technologies have been proposed, such as plane switching mode, relative micro unit mode, domain vertical mode, etc. The viewing angle can reach 170 degrees, the viewing angle can reach 176 degrees after the angle enlargement of the glass substrate and optical film.

Response speed: when the frame rate is 60%, the frame period is about 16ms, and the response time of ordinary TFT-LCD devices using TN LCD can be less than 20ms.recently, a planar switching method stabilized by elastic continuous polymer was introduced, which can reduce the response time to 10ms, the response time can be shortened to 2-3 ms by using optical compensation tape, If the length of liquid crystal molecular chain and the thickness of liquid crystal layer is further reduced, the response speed can be further shortened.

Service life: Due to the development of manufacturing technology, the service life of TFT-LCD can reach more than 30000 hours. With the addition of a stabilizer, the actual service life of liquid crystal materials has exceeded 100000 hours.

◆TFT LCD Structure

The common a-Si TFT is mainly composed of the glass substrate, gate electrode, gate insulation layer, semiconductor active layer a-Si, ohmic contact layer n+a-Si, source-drain electrode, and protective film, among which the gate insulation layer and protective film generally use SiN.

The structure of a-Si TFT can be divided into four typical structures: the source, drain, and gate three electrodes are located on the same side of the semiconductor active layer a-Si, where the source, drain, and gate three electrodes are located on the upper side of the a-Si layer, which is called the positive gate plane structure; the source, drain, and gate three electrodes are located on the lower side of the a-Si layer, which is called the inverted gate plane structure; The staggered structure where the source, drain, electrode and gate electrode are located on both sides of the a-Si layer, wherein the gate electrode is on the upper side of the a-Si layer, the so-called positive grid staggered structure or top grid structure where the source and drain electrode are on the lower side of the a-Si layer, the so-called inverted grid staggered structure or bottom grid structure where the grid electrode is on the lower side of the a-Si layer, and the source and drain electrode are on the upper side of the a-Si layer.

From the perspective of the manufacturing process, three layers (or two of them) of interlaced SiN, a-Si, and n+a-Si can be deposited continuously, which is suitable for the flow process and can reduce cross-contamination. Now, the staggered structure has become the mainstream, not only for a-Si, SiN. N+a-Si can operate continuously, and the inverted grid can also be used as a light shielding layer (no need to set another light shielding layer), which is important for a-Si TFTs, because a-Si is sensitive to light, and once light flows in, causing an increase in leakage current, it will lead to deterioration of image quality.

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