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    What is the difference between OLED and LCD

    2021-11-06 11:56:55  News

     LCD (short for Liquid Crystal Display) liquid crystal display. The LCD structure is to place a liquid crystal cell between two parallel glass substrates. The lower substrate glass is equipped with TFT (thin film transistor), and the upper substrate glass is equipped with color filters. The signal and voltage on the TFT are changed to control the liquid crystal molecules. Rotate the direction, so as to control whether the polarized light of each pixel point is emitted or not to achieve the purpose of display. LCD has replaced CRT as the mainstream, and the price has dropped a lot, and it has become fully popular.

    LCD is the acronym for Liquid Crystal Display, which means "liquid crystal display", that is, liquid crystal display. The LED display refers to a type of liquid crystal display (LCD), that is, a liquid crystal display (LCD) with LED (light emitting diode) as the backlight source. It can be seen that LCD includes LEDs. Corresponding to the LED display is actually a CCFL display.

    (1) CCFL

    Refers to a liquid crystal display (LCD) with CCFL (cold cathode fluorescent lamp) as the backlight source.

    The advantage of CCFL display is good color performance, but the disadvantage is higher power consumption.

    (2) LED

    Refers to a liquid crystal display (LCD) that uses LEDs (light emitting diodes) as a backlight source, and generally refers to WLEDs (white light LEDs).

    The advantages of LED displays are small size and low power consumption. Therefore, using LEDs as a backlight source can achieve high brightness while taking into account lightness and thinness. The main disadvantage is that the color performance is worse than that of CCFL monitors, so most professional graphics LCDs still use traditional CCFL as the backlight source.

    technical parameter

    (1) Low cost

    Generally speaking, reducing costs has become an important rule for companies to survive. Throughout the development history of TFT-LCD, it is not difficult to find that increasing the size of glass substrates, reducing the number of masks, increasing base station productivity and product yield, and purchasing raw materials nearby are the continuous efforts of many TFT-LCD manufacturers. .

    Glass substrate is an important raw material for the production of TFT-LCD, and its cost accounts for about 15% to 18% of the total cost of TFT-LCD. mm), it has only gone through a short period of twenty years. However, due to the extremely high requirements for the chemical composition, performance and production process conditions of the glass substrate for TFT-LCD, the global production technology and market for the glass substrate for TFT-LCD have long been used by Corning,It is monopolized by a few companies such as Asahi Glass and Electric Glass. Under the strong promotion of market development, my country's mainland also began to actively participate in the research and development and production of TFT-LCD glass substrates in 2007. In China, many TFT-LCD glass substrate production lines of the fifth generation and above have been built and planned In the second half of 2011, two 8.5-generation high-generation liquid crystal glass substrate production line projects were launched. This provides an important guarantee for the localization of upstream raw materials for TFT-LCD manufacturers in mainland my country and a significant reduction in manufacturing costs.

    The most core part of TFT production technology is the photolithography process, which is not only an important part of determining product quality, but also a key part that affects product cost. In the photolithography process, the most attention is paid to the mask. Its quality determines the quality of TFT-LCD to a large extent, and the reduction of its use can effectively reduce equipment investment and shorten the production cycle. With the change of TFT structure and the improvement of production process, the number of masks used in the manufacturing process is correspondingly reduced. It can be seen that the TFT production process has evolved from the early 8-mask or 7-mask lithography process to the commonly used 5-mask or 4-mask lithography process, which greatly reduces the TFT-LCD production cycle and production costs.55a

    4 Mask lithography process has become the mainstream in the industry. In order to continuously reduce production costs, people have been trying to explore how to further reduce the number of masks used in the photolithography process. In recent years, some Korean companies have made breakthroughs in the development of the 3-mask lithography process, and have announced mass production. However, due to the difficulty of the 3-mask process and the low yield rate, it is still in further development. And improving. From a long-term development perspective, if Inkjet (inkjet) printing technology makes a breakthrough, the realization of maskless manufacturing is the ultimate goal that people pursue.

    OLED (Organic Light-Emitting Diode), also known as organic electric laser display, organic light-emitting semiconductor (Organic Electroluminescence Display, OLED). OLED is a kind of current-type organic light-emitting device, which is a phenomenon of luminescence through the injection and recombination of carriers, and the luminous intensity is proportional to the injected current. Under the action of an electric field, the holes generated by the anode and the electrons generated by the cathode will move in the OLED, and are injected into the hole transport layer and the electron transport layer respectively, and then migrate to the light emitting layer. When the two meet in the light-emitting layer, energy excitons are generated, which excites the light-emitting molecules and finally produces visible light.

    (2) High resolution

    In order to realize a large-area high-resolution liquid crystal display, it is usually necessary to use low-impedance metal materials, high-performance switching elements, and high-precision processing techniques. Aluminum is the most researched and used material for making TFT buses with low-impedance metals. By solving the problems of easy formation of hillocks, chemical corrosion and oxidation of aluminum, alloy methods (such as Al-Cu, Al-Si, Al-Nd and Al-Ti, etc.) and interlayer methods (such as Mo/Al/Mo) have been reported successively. , Cr/Al/Cr and Ti/Al/Ti, etc.), the alloy method is relatively simple in process, but the material has a higher resistivity. In May 1998, IBM developed a 16.3-inch ultra-high resolution (200ppi) a-Si TFT display using Al-Nd alloy as the gate electrode, and mass production has been achieved. In April 1999, Toshiba introduced the 20.8-inch 16-SVGA (3, 200 × 2, 400) a-Si TFT-LCD, which can be said to represent the highest level of a-Si TFT-LCD in terms of high resolution and high capacity. .

    OLED (Organic Light-Emitting Diode), also known as organic electric laser display, organic light-emitting semiconductor (Organic Electroluminescence Display, OLED).

    (2) High resolution

    In order to realize a large-area high-resolution liquid crystal display, it is usually necessary to use low-impedance metal materials, high-performance switching elements, and high-precision processing techniques. Aluminum is the most researched and used material for making TFT buses with low-impedance metals. By solving the problems of easy formation of hillocks, chemical corrosion and oxidation of aluminum, alloy methods (such as Al-Cu, Al-Si, Al-Nd and Al-Ti, etc.) and interlayer methods (such as Mo/Al/Mo) have been reported successively. , Cr/Al/Cr and Ti/Al/Ti, etc.), the alloy method is relatively simple in process, but the resistivity of the material is higher. In May 1998, IBM developed a 16.3-inch ultra-high resolution (200ppi) a-Si TFT display using Al-Nd alloy as the gate electrode, and mass production has been achieved. In April 1999, Toshiba introduced the 20.8-inch 16-SVGA (3, 200 × 2, 400) a-Si TFT-LCD, which can be said to represent the highest level of a-Si TFT-LCD in terms of high resolution and high capacity. 

    Principle of luminescence

    OLED display

    The light-emitting process of OLED devices can be divided into: injection of electrons and holes, transport of electrons and holes, recombination of electrons and holes, and de-excitation light of excitons. Specifically:

    Injection of electrons and holes. The electrons in the cathode and the holes in the anode will move to the light-emitting layer of the device under the drive of an external driving voltage. During the process of moving to the light-emitting layer of the device, if the device contains an electron injection layer and a hole injection layer, then The electrons and holes first need to overcome the energy barrier between the cathode and the electron injection layer and the anode and the hole injection layer, and then move to the electron transport layer and hole transport layer of the device through the electron injection layer and the hole injection layer; The electron injection layer and the hole injection layer can increase the efficiency and lifetime of the device. The mechanism of electron injection in OLED devices is still under constant research. The most commonly used mechanisms are tunneling and interface dipole mechanisms.


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