This chapter will explain the structure and basic working principle of the screen. The screen is basically divided into LCD screen and OLED screen. The two have different lighting principles, but they have certain similarities in structure.
Before talking about the structure of the screen, we must first understand the light. Light is an electromagnetic wave. In the direction of propagation along a straight line, light waves oscillate vertically and oscillate in a random and evenly distributed direction on the vibration plane.
If the direction of vibration of the light wave is fixed, then such light is called linearly polarized light, the direction of vibration is called the direction of polarization, and the positive direction of polarization is in front of the propagation direction of light waves. A liquid crystal display (LCD) controls the polarization state of light passing through a liquid crystal cell, thereby controlling the transmitted light and the state to achieve a display effect.
Therefore, the structure of the LCD can be simply divided into a front-back polarizer, a front-back glass, a liquid crystal layer, and a backlight system, as shown in the following figure. The front and rear polarizers are used to select the incoming and outgoing light waves. The front and rear glass slides are used to carry various types of materials. The liquid crystal layer is used for color toning. Since the liquid crystal itself cannot emit light, the backlight is needed to irradiate the light. Finally, the colorful light is displayed. Now.
OLEDs, on the other hand, have self-luminous properties and therefore do not require a backlight source. On the TFT substrate, an RGB three-color organic film layer capable of self-luminous under power-on is deposited. By controlling the size of the current through the TFT substrate, the brightness and darkness of the RGB organic film layer can be controlled so that the desired color of the display can be mixed.
LCD panel
The composition of an LCD screen can be divided into two parts: the LCD panel and the backlight. The liquid crystal panel (liquid crystal cell) includes a polarizer, a glass substrate, a color filter film, an electrode, a liquid crystal, and an alignment layer. The backlight module consists of a cold cathode fluorescent lamp (CCFL), a light guide plate (optical waveguide), a diffuser plate, and a prism sheet, and its role is that the light source is uniformly transmitted to the liquid crystal panel.
The full name of the polarizer is the polarizer, and the imaging of the liquid crystal display must rely on polarized light. All the liquid crystals have two polarizers in close proximity to the liquid crystal glass, which constitute a liquid crystal panel with a total thickness of about 1 mm. The polarizer in the LCD screen is divided into an upper polarizer and a lower polarizer, and the upper polarizer and the lower polarizer are perpendicular to each other. It acts like a fence and blocks the light component perpendicular to the fence, allowing only light components parallel to the fence to pass through.
The liquid crystal glass substrate is an important part of the liquid crystal flat panel display, its thickness is mainly 0.7 mm and 0.5 mm, and it is about to step into a thinner (for example, 0.4 mm) thickness process. This is a very smooth surface of the production of thin glass float glass, the surface deposited with a layer of In2O3 or SnO2 transparent conductive layer ITO film, lithographic processing made of transparent conductive patterns. These graphics consist of pixel graphics and outer lead graphics. Therefore, the outer leads cannot be conventionally soldered and can only be connected by conductive rubber strips or conductive tapes. If scratched, cut or corroded, the device will be scrapped.
The glass substrate is divided into a glass substrate and a lower glass substrate and is mainly used for sandwiching the liquid crystal. For the TFT-LCD, the lower glass has a thin film transistor (TFT), and the upper glass is attached with a color filter film. Color filter: Generates three primary colors of red, green, and blue.
The liquid crystal material is a small molecule organic compound, which is the main body of the liquid crystal display. The liquid crystal material is generally composed of several to a dozen kinds of monomer liquid crystal materials, each of which has its own fixed cooling point TL and crystallization point Ts. Therefore, it is also required that each liquid crystal display device must be used and stored within a certain temperature range between Ts-TL. Through the voltage control, the liquid crystal molecules will turn, and then change the polarization direction after the light is injected. The liquid crystal material is the most upstream in the entire LCD screen, and the technical difficulty is greatest.
In simple terms, the basic structure of the TFT LCD panel is a layer of liquid crystal sandwiched between two glass substrates. A front-end LCD panel is attached with a color filter, and a thin-film transistor (TFT) is fabricated on the back-end TFT panel. When a voltage is applied to the transistor, the liquid crystal turns and the light passes through the liquid crystal to create a pixel on the front panel. The backlight module is located behind the TFT-Array panel and is responsible for providing the light source. Color filters give each pixel a specific color. Combining the colors of each color pixel presents the front panel image.
The OLED has less hierarchical structure, and the backlight panel, the enhancement sheet, and some of the polarizer structures are eliminated from the LCD; the organic light-emitting materials used by the OLED have higher plasticity than the multi-layer light-emitting structure of the LCD, and the substrate serving as the supporting function of the OLED device can be selected more. Flexible plastic material, the overall flexibility of the device.
Backlight module's "gain and loss"
The backlight is a form of lighting and is often used on LCD displays. The difference between the backlight mode and the front light mode is that the backlight is irradiated from the side or the back, and the light source may be an incandescent light bulb, an electro-optic panel (ELP), a light-emitting diode (LED), a cold cathode fluorescent tube (CCFL), or the like. Electro-optical panels provide uniform light throughout the surface, while other backlight modules use diffusers to provide uniform light from uneven light sources.
The liquid crystal molecule itself does not emit light, and the human eye can see the object because the eyeball receives the light emitted by the light source. Currently, the mainstream LCD backlight technology in the industry includes a light emitting diode (LED) or a cold cathode lamp (CCFL), which is also referred to as a light source.
There are mainly three types of LED backlights, a top view, a side view, and a quantum dot backlight. The direct type is characterized by the delicate picture quality, backlight can be set area, that is, the so-called "local control" technology, so as to achieve separate processing for different colors, the thickness of the direct type backlight is from the bottom of the light box and the distance from the scattering plate The decision, generally the thicker the thickness, the better the light uniformity of the backlight.
Side-entry backlight is installed around the LCD panel LED light bulbs, after the light guide plate to achieve LCD screen lighting. The back is thinner and can not achieve local light control. The color performance is not as good as the direct type. Quantum dot backlighting is characterized by the use of nanocrystalline materials instead of LED light sources, to achieve a more pure, color reproduction more realistic backlight color, the effect is close to OLED.
The OLED is a current-injection type light-emitting display device that emits light when power is applied. OLED is a solid-state semiconductor device with a thickness of 100-500 nanometers. It is composed of a base layer, an anode, an organic layer, a conductive layer, an emissive layer, and a cathode, wherein the base layer (transparent plastic, glass, metal foil) is used as the base layer. Support the entire OLED.
The anode eliminates electrons (increases electron "holes") when current flows through the device, and the cathode (which may be transparent or opaque, depending on the OLED type). When current flows in the device, the cathode will inject electrons into the circuit. The conductive layer consists of organic plastic molecules that transport "holes" from the anode. Polyaniline can be used as the conductive polymer of the OLED. The emissive layer consists of organic plastic molecules (different from the conductive layer) that transport electrons from the cathode; the luminescence process takes place in this layer. Polyfluorene can be used as the emission layer polymer.
Because of this, OLEDs do not require a backlight layer, and due to pixel-level control, OLED screens have a high degree of collapsibility and a higher resolution display.
Active/Passive Matrix Drive
With the above two technologies, the liquid crystal display is still a poor driver. The display is composed of thousands of pixels, and in order to realize the color effect, each pixel needs three primary colors of red, blue, and green to reconcile.
By controlling the brightness of three pixels of RGB, each pixel displays a color, and then a single pixel is controlled to refresh at a certain frequency in real time, and finally a continuous dynamic picture can be displayed. To complete these tasks, you have to rely on driver ICs and control ICs.
TFT (Thin Film Transistor) is a thin film transistor (matrix) - it can "actively" control the individual pixels on the screen, which is the so-called source of the active matrix TFT.
It has the dual characteristics of "active (switching, amplification)" and "thin" of "thin film" of a transistor, and is combined with a flat panel display (such as LCD, OLED, etc.) to constitute a current flat panel TV (TFT-LCD, TFT). -OLED), TFT is one of the key core components.
The two most commonly used LCD drive methods are active matrix and passive matrix. The driving method of the image signal is continuously given to all the pixels, and is called a static driving method or a direct driving method.
For the grouping of pixels into several groups (width time), each group sequentially gives the driving mode of the signal, which is a dynamic driving mode or a multiple driving mode. In a display with a small number of pixels, although static driving is possible, if the number of pixels is too large, the electrodes of all pixels must be wired independently, and the static driving method cannot.
TFT-LCDs are active (active) drive displays, while traditional TN/S TN-LCDs are passive drives. Passive (passive) drive display OLED or LCD can usually only display 200 lines at the same time, so to display more lines to achieve high-definition, we must use active (active) drive display, that is, TFT-LCD, AMOLED. Active (active) drive display methods include TFT fabrication technology.
According to the driving mode of the organic light emitting display, the OLED is classified into a passive type (PMOLED) and an active type (AMOLED), and the active type also utilizes a TFT and a capacitor to control brightness grayscale performance.
In the active driving mode, the OLED does not need to drive to a very high brightness, so it can achieve better life performance and can also achieve high resolution requirements. The technology of OLED combined with TFT can realize active driving of OLED, which can meet the requirements for fluency of screen playback and higher and higher resolution in the current display market, and fully demonstrate the above superior characteristics of OLED.
The above is the basic composition and working principle of the screen. In the entire structure of the screen, the technical barrier grades are liquid crystals, glass substrates, drive ICs, etc., and in particular, the glass substrates also involve technological difficulties. "Advanced Engineering Smart Car" will continue to analyze.
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