Basic knowledge of LCM

1. The origin of liquid crystal:

In 1888, the Austrian botanist F. Reintzer discovered liquid crystal. After long-term research by scientists, in 1968, Radio Corporation of America (RCA) G.H. Heilmeiler discovered nematic liquid crystal.

The turbidity phenomenon (ie electro-optical effect) of the transparent thin layer when energized, people's understanding of the structure, characteristics and applications of liquid crystals has been developed by leaps and bounds. Now liquid crystals have been widely used in many new technical fields, becoming a new field for physicists, chemists, biologists, and electronics scientists.

2. What is LCD

Liquid crystals are usually solid, and become transparent liquids when the temperature rises to a clearing point. It is a combination of liquid fluidity and crystal birefringence in a certain temperature range. Liquid crystals are different from the usual solid, liquid and gaseous states. It is also called liquid crystal phase, mesophase, and intermediary phase. English is liquid

crystals. The birefringence of the crystal refers to the difference in the direction through which light passes, and the refractive index is different.

3. Types of LCD

With the gradual understanding of liquid crystals, it has been discovered that liquid crystal substances are basically organic compounds, and every 200 kinds of existing organic compounds

One of them has a liquid crystal phase. From the perspective of the composition and the physical conditions for the appearance of the liquid crystal phase, liquid crystals can be divided into two categories: thermotropic liquid crystals and lyotropic liquid crystals. The liquid crystals formed by rod-shaped molecules have three types of liquid crystal phases: smectic phase (Smectic

Liquid crystals refers to clay-like), nematic phase (Nematic liquid crystals refers to filamentous

And cholesteric phase (Cholesteric liquid crystals refers to cholesterol).

4. What is thermotropic liquid crystal

The liquid crystal formed by heating and dissolving certain organic substances and destroying the crystalline lattice by heating is called thermotropic liquid crystal. It is a liquid crystal phase that appears due to temperature changes. The liquid crystal materials currently used for displays are basically thermotropic liquid crystals.

5. What is lyotropic liquid crystal

Put some organics in a certain solvent, and the liquid crystal formed by the solvent destroying the crystal lattice is called lyotropic liquid crystal. It is a liquid crystal phase that appears due to changes in the concentration of the solution, the most common being soapy water and so on.

6. Characteristics of smectic liquid crystals

Smectic phase liquid crystals are composed of rod-shaped or strip-shaped molecules. The molecules are arranged in layers. The long axes of the molecules in the layer are parallel to each other, and the direction can be perpendicular to the plane or arranged obliquely to the plane. Because the molecules are arranged neatly, their regularity is close to that of crystals, and it has two-dimensional order. The position of the molecular center of mass is disordered in the layer and can be translated freely, so that it has fluidity, but the viscosity coefficient is very large. The molecule can slide back and forth, left and right, but cannot move between the upper and lower layers. Because of its high degree of order, the smectic phase often appears in the lower temperature range.

7. Features of nematic liquid crystal

The rod-shaped molecules of nematic liquid crystals also remain aligned parallel to the molecular axis direction, but they do not have the layered structure of smectic liquid crystals. The center of mass of the molecules is chaotic and disordered, but the orientation of the molecules (rods) is roughly the same, so that the optical and electrical properties of nematic substances, namely the refractive index and dielectric constant, are different along and perpendicular to this orderly arrangement direction. It is precisely because the nematic liquid crystals optically display positive birefringence, uniaxiality and electrical dielectric constant anisotropy, it is possible to use electricity to control optical performance or liquid crystal display. Compared with the smectic phase, the nematic liquid crystal has a low viscosity and is rich in fluidity. The reason for this fluidity is mainly due to the fact that each molecule of the nematic liquid crystal is easy to move freely along the long axis direction. The arrangement and movement of molecules are relatively free, and they are quite sensitive to external effects, so they are widely used. At present, the liquid crystal materials used in liquid crystal displays, such as TN, STN, etc., are all nematic liquid crystal materials.

8. The characteristics of cholesteric liquid crystals

After being esterified or substituted by halogen, cholesterol presents a liquid crystal phase, which is called cholesteric liquid crystal. This type of liquid crystal molecules are in a flat shape, arranged in layers, and the molecules in the layer are parallel to each other. The direction of the long axis of the molecules of different layers changes slightly, and they are arranged in a spiral structure along the normal direction of the layer. When the long axis of different molecules are arranged along the spiral direction, it goes through 360. After the change, it returns to the original orientation. Cholesteric liquid crystals are very sensitive to temperature. When the temperature changes, the cholesteric liquid crystals show different colors. In practice, the principle of liquid crystal temperature display is to use a series of cholesteric liquid crystals.

9. What is a liquid crystal display

First introduce the definition of electro-optic effect. Because liquid crystal molecules have a fixed dipole moment, the application of an electric field can cause the axis of the liquid crystal molecules to move, so the arrangement of the liquid crystal molecules changes. In a certain display mode, the liquid crystal molecules may flow unstable, and this unstable state changes depending on the strength of the electric field. As a result, the transmission function of the polarized light inside the liquid crystal cell will change, the birefringence change, and the phenomenon of light scattering, etc., that is, the optical properties in the liquid crystal cell will change. This phenomenon is called the electro-optic effect of the liquid crystal.

For the use of various electro-optical effects of liquid crystals, the changes in external conditions such as electric field, magnetic field, light and temperature of the liquid crystal can be converted into visible signals under certain conditions to make a display. This is a liquid crystal display.

10. LCD monitors have gone through three generations

The first generation is used in calculators and watches; the second generation is used in electronic translation machines, game consoles, home appliances, and testing equipment; the third generation is used in various office automation equipment and new information transmission equipment in the advanced information society, namely personal computers , Word processors, mobile phones, portable color televisions, etc.

11. Advantages of LCD

Flat display, small size, light weight, easy to carry, low power consumption, low driving voltage, for example, the working voltage of the calculator is 2~5V, the power consumption is about 0.01mw, a silver oxide battery can be used for two to three years; long life , Generally more than 50,000 hours; it does not contain harmful rays, so it is harmless to the human body and does not easily cause eye fatigue; passive display, not easy to be washed by strong light, and can be displayed in a bright environment; simple structure, no complicated machinery Part and so on.

12. Basic structure of liquid crystal display

Different liquid crystal displays have different structures, but their basic structure is to inject liquid crystal between two glass substrates and seal them with sealing materials to form a liquid crystal cell. The cell thickness of the liquid crystal cell is generally a few microns (the diameter of a human hair). Tens of micrometers), the upper and lower glass are pasted with polarizers, and a thin layer of organic polyimide orientation is covered on the inside of the glass substrate in the liquid crystal cell, and rubbed in a certain direction. Then assemble the connectors, integrated circuits, control and drive circuits, PCB circuit boards, backlight sources, and structural parts together.

13. The principle of LCD display

Take TN

The LCD is taken as an example to illustrate the display principle of the liquid crystal display. When the polarizer is pasted on the upper and lower glass substrates of the liquid crystal cell in which the liquid crystal is injected, and the optical axes of the upper and lower polarizers are orthogonal (the characteristic of the polarizer is that only light that is allowed to pass through a certain aspect), when no voltage is applied, it is injected into The liquid crystal molecules of the liquid crystal cell are arranged along the friction grooves of the upper and lower glass PI (polyimide film) respectively at the interface, so that the liquid crystal molecules on the surface of the upper and lower glass substrates of the liquid crystal cell are arranged in a state of being twisted by 90 degrees as shown in the figure below. When the light emitted by the backlight passes through the upper polarizer, only light that vibrates in one direction can pass. Then, the liquid crystal molecules are twisted 90 degrees to reach the lower polarizer, and pass parallel to the axis of the lower polarizer, which is a "white" state. When a voltage is applied, the liquid crystal molecules are not affected by the small PI grooves on the upper and lower glass substrates, and they stand up in the same direction along the electric field and are twisted 90 degrees with the direction of the polarizer below, and the light cannot pass through, and the light is blocked. For the "black" state. With or without an external voltage, the arrangement of the liquid crystal molecules in the liquid crystal cell will change. If the axis direction of the upper and lower polarizers is 90. Whether the light that only vibrates in one direction can pass through the liquid crystal cell depends on whether there is an external voltage. Whether it passes determines the "white" and "black", and the image is displayed on the LCD. Of course, the intermediate colors of "white" and "black" are determined by the intermediate potential of the applied voltage.

14. What is normally white LCD and normally black LCD

When the axis direction of the upper and lower polarizers is 90. When there is no applied voltage, the irradiated light can pass through, and it is "white". When there is an applied voltage, the irradiated light is blocked and it is "black". This type of liquid crystal display is called a normally white LCD. When the upper and lower polarizer axis

When it is in the same direction and no applied voltage, the illuminating light is blocked, and it is "black" at this time, and when there is an applied voltage, the illuminating light can pass through, and it is "white" at this time. This type of LCD is called normally black LCD.

The structure in which active elements such as thin film transistors or diodes are injected with liquid crystal material is called active matrix LCD. Therefore, in terms of whether it contains active components, liquid crystal displays can be divided into two categories, passive matrix LCD and active matrix LCD. Passive matrix LCD and active matrix LCD have different driving methods and different uses.

Then according to the display mechanism:

Passive matrix LCD and active matrix LCD can be divided into many types.

Commonly used liquid crystal displays made by electro-optical effect are roughly as follows: TN-LCD, STN-LCD, HTN-LCD, FSTN-LCD, TFT-LCD, etc.

16. Features and applications of TN-LCD

TN-LCD is Twist Nematic Liquid Crystal

The abbreviation of Display, that is, twisted nematic liquid crystal display. The characteristic of this display mode is that the liquid crystal molecules are arranged substantially parallel to the substrate, but the upper and lower liquid crystal molecules are aligned in a twisted arrangement, and the overall twist angle is 90°. TN-LCD is the liquid crystal display that people discovered earlier, and is also the most widely used, most numerous, and cheapest liquid crystal display. The display screens of electronic watches, calculators, game consoles, etc. that we see daily are mostly TN-LCD.

17. Features and applications of STN-LCD

STN-LCD is Super Twist Nematic

Liquid Crystal

The abbreviation of Display, that is, super twisted nematic liquid crystal display. It is similar in structure to TN-LCD, except that the twist angle is not 90°, but between 180° and 270°. Although only the twist angle is different, its working principle is completely different from that of TN-LCD. STN-LCD is currently a mid-range product produced by LCD. It has the characteristics of displaying more information than TN-LCD. It is mainly used in various instruments, Chinese displays, notebooks, notebook computers, etc.

18. Features and applications of HTN-LCD

HTN-LCD is High Twist Nematic Liquid Crystal

Display short for high-twist nematic liquid crystal display. It is similar in structure to TN-LCD and STN-LCD, except that the twist angle is between 100° and 120°, which is between TN-LCD and STN-LCD. There are not many HTN-LCDs at present, and their performance is between TN-LCD and STN-LCD.

19. Features and applications of FSTN-LCD

STN-LCD is Film Super Twist Nematic Liquid Crystal

The abbreviation of Display, that is, the compensation film super twisted nematic liquid crystal display. Film refers to compensation film or retardation film. Through a layer of specially processed compensation film, it can overcome the shortcomings of STN-LCD, and it can overcome the background color of STN-LCD to become black and white, so some people call FSTN-LCD as STN-LCD in black and white mode.

20. Features and applications of TFT-LCD

TFT-LCD is Thin Film Transistor Liquid Crystal

Display is short for thin film transistor active matrix liquid crystal display. Each pixel of it is controlled by one (or more) thin film transistor switches. In fact, each pixel is a small TN-type liquid crystal display. The image displayed by this type of display is clear, flicker-free, wide viewing angle (0.5), fast response speed, and can display almost any gray scale, and can achieve full-color display after adding a color filter. Compared with other displays such as STN and ferroelectric liquid crystals, TFT-LCD is still the best in terms of large area, multiple display content, color and gray scale. It has the advantages of using transparent substrates such as glass, capable of transmissive display, good signal transmission performance, uniform display of halftones, and large-capacity display. The highest quality image can be obtained in the active matrix method. It is currently the most high-end product in the LCD market. It is mainly used in notebook computers, LCD color TVs, etc. The manufacturing process of TFT-LCD is relatively complicated and the price is relatively high.

21. Features and applications of ECB-LCD

ECB-LCD is ElectricallyControlled Birefringence Liquid Crystal

Display is short for electronically controlled birefringent liquid crystal display. This type of display applies voltage to the liquid crystal cell. Due to the dielectric anisotropy of the liquid crystal, the arrangement of the liquid crystal molecules changes, resulting in a change in the birefringence in the liquid crystal cell. If the liquid crystal cell is placed in two polarizers, the change in refractive index is manifested as a change in light transmittance. This electro-optical effect is to control the birefringence of the liquid crystal cell (ECB:

Electrically Controlled

Birefringence), so it is called the ECB effect. The ECB effect is very important as the working principle of a multi-color liquid crystal display element. It is suitable for large-screen multi-color display with magnified projection.

22. Features and applications of ferroelectric liquid crystal displays

The ferroelectric liquid crystal display currently under development adopts ferroelectric smectic liquid crystal, which is characterized by extremely fast response speed (microsecond level) and image storage function. After the applied voltage signal is removed, the original displayed image remains Can be maintained.

23. Basic characteristics of liquid crystal display devices

The display performance of the liquid crystal display stipulates various items. The basic characteristics are the color display of the LCD, the number of pixels (ie, the resolution) and the screen size, pixel pitch, display size (display range), aspect ratio, brightness, aperture ratio, gray Degree and color number, contrast, response speed, normally white, normally black, LCD transmittance, LCD glass substrate size. Introduce them separately.

24. LCD color display

TFT LCD realizes color display by using color film to irradiate and color by fluorescent lamp. When the light passing through the array substrate passes through the color film (CF), it will be colored. TFT LCD

A pixel is divided into RGB3 primary colors (red, green, blue), and each is colored by the corresponding RGB color film. It is an additive mixing method that uses color film to mix RGB light to obtain various colors. The light of the backlight is divided into 3 colors by the RGB color film. The LCD, which acts as a light valve, balances and adjusts the amount of light of the 3 colors to obtain the desired color.

25. Pixels and screen size

The LCD displays images by arranging many dots (the smallest unit for displaying text and images) to form a screen. The smallest unit of point is called pixel. In the color display, the pixels are divided into red (R), green (G), and blue (B), and the three colors together are called pixels, and dividing this pixel into 1/3 of the RBG points is called sub-pixels. According to how many pixels are arranged on a screen, the name of the LCD is also different.