According to different technologies and functions, monochrome LCD (Liquid Crystal Display) products can be divided into seven categories: twisted nematic (TN), high twisted nematic (HTN), super twisted nematic (STN), and compensation film super twisted nematic (FSTN), wide viewing angle double compensation film super twisted nematic (FFSTN), ultra-wide viewing angle liquid crystal compensation film super twisted nematic (ASTN), vertical orientation type (VA).
The technical characteristics and application fields are as follows:
1. TN technology
TN technology, it is short of Twisted Nematic technology. The structure and practical principle of the TN mode LCD screen are shown in the figure below. There are transparent electrode ITO (Indium-Tin-Oxide) films on the upper and lower glass substrates and alignment films with a thickness of hundreds of angstroms on the surface. After the alignment film is rubbed, the alignment directions of the liquid crystal molecules on the upper and lower substrates are perpendicular to each other, that is, the director of the liquid crystal molecules is continuously rotated by 90° from the upper substrate to the lower substrate. Polarizing plates are attached to the outer sides of the upper and lower substrates, and the optical axis directions of the polarizing plates are respectively the same as the alignment directions of the liquid crystals on the adjacent substrates. As shown in the figure below, light enters from the upper substrate and passes through the liquid crystal layer. The polarization plane of the light rotates along the twisting direction of the liquid crystal molecules. After reaching the lower substrate, it passes through the lower polarizer, so the liquid crystal panel is in a bright state. When the voltage applied to the liquid crystal cell is much greater than the threshold voltage Vth, the directors of the liquid crystal are aligned along the electric field direction, and the liquid crystal layer does not have a birefringence effect. After the lower substrate, since the polarization plane of the light is perpendicular to the polarization axis direction of the lower polarizer, the light cannot pass through the lower polarizer, so the liquid crystal panel is in a dark state.
The TN technology is widely applied to low-duty drive products, the temperature range is -40°C~80°C, the left and right viewing angles are -30°~30°, the up and down viewing angles are -30°~ 15° (12-point viewing angle), the response time is about 100 milliseconds, and the contrast ratio is about 30. Comparing to other LCD panel technologies, TN type has the merit of lower cost and quick response time, which is mostly used for customized segment pattern displays.
Below shows different display mode of TN technology.
1) Positive, reflective mode.
Black fonts on a white background, used under visible light conditions, mainly used in electronic consumer products and meters used under strong natural light, such as game consoles, calculators, remote controls, counters and other products.
2) Positive, transmissive/translative mode.
White fonts on a black background, equipped with a backlight, can be used with and without natural light. It is mainly used in various industrial and electronic consumer products, such as instruments, vehicles, industrial controllers, counters and other products.
3) Negative, transmissive mode and backlight is needed.
White fonts on a black background, equipped with a backlight, can be used in the presence and absence of natural light. The response time is about 100-150 milliseconds, and the contrast is 30-100. Mainly used in various industrial and electronic consumer products, such as instruments and meters, vehicles, industrial controllers, counters and other products.
2. HTN technology
HTN, high twisted nematic technology is basically the same as that of TN, except that the twist angle is changed to 110°~130°.
The viewing angle is wider than that of TN products. It is used in low-duty drive products. The temperature range is -40°C~80°C, the left and right viewing angles are -35°~35°, the upper and lower viewing angles are -35°-20° (12-point viewing angle), and the response time is 150. About milliseconds, the contrast is about 30.
Two common display modes of HTN display.
1) Positive, reflective mode.
Black font on a white background, use under visible light. Mainly used in electronic consumer products used under natural light, such as game consoles, blood pressure monitors and other products.
2) Positive, transimissive/transflective
Black fonts on a white background indicates that the product can be applied to electronic consumer products with or without natural light, such as rice cookers, refrigerators, sphygmomanometers, instruments and other products.
3. STN technology.
STN (Super Twisted Nematic) technology, the twist angle of the liquid crystal molecules from the upper surface to the lower surface reaches 180°~270°, with the upper and lower two ordinary polarizers, the super twisted birefringence effect of the liquid crystal is realized. With wide viewing angle and multi-channel driving, the image quality of STN is higher than that of TN under the same driving conditions. Comparing STN to TN, the viewing angle of STN is wider than TN under the same driving condition. The main advantage of STN technology is it can support high resolution graphic display up to 320*240 dots.
The retardation of the liquid crystal is 830~890nm, the twist angle is 180~270 degrees, the viewing angle is -30~50 degrees up and down, the left and right viewing angles can reach -40~50 degrees, and the response time is about 230~300 milliseconds. The contrast is around 5. It can be applied to the diving duty below 240, and can realize the display of dot matrix and segment code. Products can be applied to various industrial and consumer electronics categories, such as digital display modules, numerical control equipment, communication equipment, instrumentation, medical equipment, elevators, white goods, small household appliances and other products.
STN technology can achieve different display mode though different design configuration (Polarizer and liquid crystal parameter).
1) Positive mode
a. STN Y/G: Due to the dispersion, it is displayed with black font on a yellow-green background, which is called a yellow-green mode.
b. STN Gay: With a purple dye polarizer and a normal polarizer, the background is gray while the fonts are blue, which is called a gray mode.
2.) Negative mode, backlight is needed.
STN Blue: Due to the dispersion, the white font on a blue background is displayed, which is called a blue mode.