One, what is a liquid crystal
Physics in junior middle school has three states: solid, liquid and gas. In fact, the so-called three state is only a general distinction, some of the material can be subdivided into different nature of the state of the state. Similarly, the liquid can also have different "states", where the molecular arrangement of the liquid we have to say "liquid crystal", referred to as "liquid crystal".
Solid crystals are in general direction, so many of their physical properties are also in the direction of the. Liquid crystal in the same direction of the crystal with the liquid flow. To change the direction of a solid crystal must rotate the whole crystal, and the liquid crystal is different, and its direction can be controlled by electric or magnetic field.
Both STN and TFT are the material which is called "nematic" liquid crystal (Nematic), which is a kind of material which is used to control the direction of "the wire". A component that is made of liquid crystal, usually in the two piece of glass. In the surface of the glass, a layer of a layer of glass is called a distribution of the material, which is controlled by the arrangement of liquid crystal in the absence of an external electric field.
Two, STN liquid crystal principle
The world's first liquid crystal display in the beginning of the seventy's, known as the TN Twisted (Nematic), twisted nematic. In the eighty's, the STN Nematic (Twisted Super Thin) is presented, and the technology of Film Transistor TFT (thin film transistor) is proposed.
We first come to talk about the principle of TN type liquid crystal, LCD STN and LCD TN display principle, but the liquid crystal molecules of different angle.
The nematic liquid crystal is sandwiched between two pieces of glass, and the surface of the glass is coated with a layer of transparent and conductive film which is used for the electrode and the surface of the film is coated with the surface of the film, so that the liquid crystal is arranged along a specific and parallel to the glass surface. The natural state of the liquid crystal has 90 degrees of distortion, the liquid crystal is rotated by the electric field, the refractive index of liquid crystal changes with the direction of the liquid crystal. The result is that the polarity of the liquid crystal is changed after TN liquid crystal. As long as the proper thickness of the light is changed to 90 degrees, it can be used to make the light of two parallel polarized light. And enough of the voltage can make the liquid crystal direction parallel to the electric field direction, so that the polarity of the light will not change, light can pass through second polarizing plates. So you can control the light and dark. In the front, the STN type liquid crystal and TN type liquid crystal display principle same, but it will light the incident light 180 ~ 270 degrees, but not 90 degrees. Moreover, the pure TN type liquid crystal display itself only has two kinds of light and shade change. And STN liquid crystal is based on light green and orange. But if in the traditional color STN LCD display and a color filter, and monochrome display matrix, each pixel is divided into three sub pixels, respectively by color filters to display red, green and blue three primary colors, can show color.
Three, TFT liquid crystal principle
Because of the principle of TN and STN type of liquid crystal display, if it is shown that the larger the more, then the central part of the electrode reaction time may be relatively long. In fact, this is not a big problem for the mobile phone, because the current mobile phone display is relatively small, the impact of the time of the liquid crystal reaction is relatively small. But for the notebook and other large screen liquid crystal display device, too slow of liquid crystal reaction time will seriously affect the display effect, so TFT LCD technology has caused the attention of manufacturers. And color in the mobile phone used more and more, in a new generation of products many support 65536 color displays, and some even support 16 million color display, then TFT high contrast, colorful advantage is more important.
STN type liquid crystal belongs to reflective LCD device, its advantage is small power consumption, but in a relatively dark environment, the definition is very poor, so it has to be equipped with external light source. The TFT liquid crystal using the "back" and "reflection" in a way, the back of the LCD set up special light tube. This is why we see some of the mobile phone is like a "light", and some of the phone's light is like the screen itself is made out of the reasons. Moreover, the LCD backlight technology is also in constant progress, from monochrome to color, from thick to thin, from the side of the fluorescent lamp type to flat panel fluorescent lamp.
By the way, reflective LCD devices have black bottom white characters (NB) and white bottom black character (NN) two, we see the V70 display is a NB type, of course, this is definitely the integration of the latest technology enhanced NB. Well, we still continue to show the principle hark back to the subject, TFT LCD screen. TFT liquid crystal display technology uses the "active matrix" approach to drive. Method is by thin film technology made the transistor electrode, using scanning method "active" control arbitrary a display of the opening and closing. When the light source is illuminated, the light source is passed through the lower polarizing plate, and the light source is conducted with the liquid crystal molecules. When the electrode is on, the liquid crystal molecules are like the arrangement of TN liquid crystal, which can be changed, and the display can be achieved by shading and light transmission. It sounds like this and the TN - type liquid crystal display principle is the same, it is true. But the difference is that, because the FET transistor has a capacitive effect, to maintain the potential state, has been transparent to the liquid crystal molecules will remain this state