TFT-LCD color filter

TFT-LCD color filter

The white light emitted by the backlight of the liquid crystal display, and in order to obtain a color display, we must rely on the key display material-color filters. A color filter is an optical filter that expresses colors. It can accurately select the small range of light waves to be passed, and reflect other undesired wavelengths. Color filters are usually installed in front of the light source so that the human eye can receive saturated light of a certain color. The structure of the color filter includes a glass substrate, a black matrix, a color layer, a protective film, and an ITO conductive film. The structure of different types of Color Filters is also slightly different.

Glass substrate: Glass is the carrier of the color filter, which can be different from the TFT glass substrate. However, considering the yield of the image, the same type of glass is generally selected. The color filter used in TFT-LCD must use alkali-free glass. Alkali glass accounts for more than half of the cost of color filters.

Black matrix: mainly to prevent light leakage between pixels and increase color contrast. The materials used can be divided into metal film and black photoresist film. The metal film is an oxide film resin type. The black photoresist film uses carbon black as the main material. The metal film is the most common, because the circuit is easy to etch and the shading effect is good.

Color filter layer: The color photoresist is mainly used as the filter film layer. The two major components are binder and colorant. The binder is a polymer resin with high transparency and high heat resistance, which can provide an overall formulation. The material of film characteristics is currently acrylic resin as the mainstream. Colorants can be dyes or pigments to make the specific color of the transparent polymer resin. Generally, it needs to have light resistance, good heat resistance, high color saturation and good penetration. And other characteristics, pigments are currently the mainstream.

Protective film: The main function is to protect the color filter layer and increase the smoothness of the surface, act as an insulator with both black matrix and transparent electrode layer, and isolate the liquid crystal and prevent pollution. The materials are epoxy resin and acrylic Polymer materials such as resins.

ITO transparent conductive film: ITO electrodes and liquid crystal pattern electrodes form positive and negative electrodes to drive the rotation of liquid crystal molecules. They have conductivity and light transmittance, and require low resistance and light transmittance. TFT CF does not need to make an OC flattening layer, and The use of materials made by BM is also slightly different, STN CF can be plated with resin or Cr TFT CF can only be plated with Cr.

Color filter display principle

The R, G, and B primary colors of the Color Filter are arranged in a certain pattern and correspond to the TFT sub-pixels on the TFT substrate one-to-one. The white light emitted by the backlight becomes the corresponding R, G, and B color light after passing through the filter film. Adjust the voltage value added to each sub-pixel through the TFT array subject, thereby changing the transmission intensity of each color light, and mixing RGB color lights of different intensities to achieve color display. The process of Color Filter is to make an anti-reflective light-shielding layer-Black matrix on a transparent glass substrate, and then make color filter films with the three primary colors of red, green and blue in order, and then filter the light A smooth protective layer (Over Coat) is coated on the layer, and finally a transparent ITO conductive film is sputtered.