Thin film transistor liquid crystal display, often abbreviated as TFT-LCD) is a type of most liquid crystal displays that use thin film transistor technology to improve image quality. Although TFT-LCD is collectively referred to as LCD, it is an active matrix LCD that is used in televisions, flat-panel displays and projectors.

1. Overview

Simply put, the TFT-LCD screen can be regarded as a layer of liquid crystal sandwiched between two glass substrates, the upper glass substrate is a color filter (ColorFilter), and the lower glass has transistors inlaid on it. When the current passes through the transistor, the electric field changes, causing the liquid crystal molecules to deflect, thereby changing the polarization of the light, and then using the polarizer to determine the light and dark state of the pixel. In addition, the upper layer of glass is attached to the color filter, so that each pixel (Pixel) contains three colors of red, blue and green, and these red, blue and green pixels constitute the image on the skin.

The English name of thin film transistor liquid crystal display is Thin Film Transistor-Liquid Crystal Display, TFT-LCD is the abbreviation of English prefix. Thin film transistor liquid crystal display technology is a technology that combines microelectronics technology and liquid crystal display technology ingeniously. The technology of microelectronic fine processing on single crystal is transplanted to the processing of thin film transistor (TFT) array on large-area glass, and then the array substrate and another substrate with color filter film are used and matured. Liquid crystal display (LCD) technology, forms a liquid crystal cell, and then goes through post-processes such as polarizer sticking and other processes, and finally forms a liquid crystal display device.

2. Principle

TFT-LCD (Thin film transistor liquid crystal display, Thin film transistor liquid crystal display) is a type of most liquid crystal displays that uses thin film transistor technology to improve image quality. Although TFT-LCD is collectively referred to as LCD, it is an active matrix LCD. It is used in televisions, flat-panel displays and projectors.

Simply put, the TFT-LCD skin can be regarded as a layer of liquid crystal sandwiched between two glass substrates, the upper glass substrate is a color filter (Color Filter), and the lower glass has transistors inlaid on it. When the current passes through the transistor, the electric field changes, causing the liquid crystal molecules to deflect, thereby changing the polarization of the light, and then using the polarizer to determine the light and dark state of the pixel. In addition, the upper layer of glass is attached to the color filter, so that each pixel (Pixel) contains three colors of red, blue and green, and these red, blue and green pixels constitute the image on the skin.

3. Architecture

A common LCD is like the display panel of a calculator, whose picture elements are directly driven by voltage; when one unit is controlled, it does not affect other units. This approach becomes impractical as the number of pixels increases as large as millions of clocks, noting that each pixel has individual connecting lines for the red, green, and blue colors. To avoid this dilemma, arranging pixels in rows and columns reduces the number of connecting lines to thousands. If all pixels in a column are driven by a positive potential and all pixels in a row are driven by a negative potential, then the pixel at the intersection of the row and column will have the maximum voltage and be switched states. However, there are still some problems with this method, that is, although other pixels in the same row or in the same column receive only a partial voltage, this partial switching can still make the pixels darker (for a liquid crystal display that does not switch to bright). ) The solution is to add a transistor switch to each pixel so that each pixel can be controlled independently. The meaning of the low leakage current characteristic of the transistor is that the voltage applied to the pixel will not be arbitrarily lost before the picture is updated. Each pixel is a small capacitor with a transparent indium tin oxide (ITO) layer in front and a transparent layer in the back with an insulating liquid crystal in it.

This circuit arrangement is similar to dynamic access memory, except that the entire architecture is not built on silicon wafers, but on glass. Many silicon wafer process technologies require temperatures that exceed the melting point of glass. The silicon substrate of ordinary semiconductors is made of liquid silicon to grow large single crystals, which have the good characteristics of transistors. The silicon layer used in the thin film transistor liquid crystal display uses silicide gas to manufacture an amorphous silicon layer or a polysilicon layer, which is not suitable for making high-level transistors.

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