With the rapid development of smart phones, smart bracelets, TVs, computers and other consumer electronics products in the direction of lightness, portability, and intelligence, their display screens are also undergoing rapid evolution and iteration of "spherical screens-flat screens-flexible screens". In the era of spherical screens, CRT is the only choice; in the era of flat screens, LCD has become a well-deserved king; in the era of flexible screens in the future, OLEDs have simple structure, ultra-light and thin, high color saturation and contrast, low power consumption, and easy The realization of flexible display and other advantages has become the focus of investment and research in the industry and academia.
Flexible OLED panels will grow rapidly in the next 5 years
In recent years, smart phones, smart bracelets, smart watches, TVs and other products that use OLEDs as screens have shown rapid growth. In the main battlefield of smart phones, more and more high-end phones use OLED displays, especially flexible OLED screens. According to statistics, my country's vivo, Meizu, OPPO and other brands have begun to adopt OLED screens on a large scale. In 2016, the penetration rate of OLED screens in smartphones of these brands reached over 12%. As Apple plans to upgrade its LCD screens to OLED screens in 2017~2018, the upstream and downstream industrial chains at home and abroad are also actively carrying out related industrial layouts, and the entire OLED market is showing a trend of vigorous development. Flexible OLED display panels will maintain a rapid growth momentum in the next 5 years, with a compound annual growth rate of more than 30%, and its market size will reach more than US$40 billion in 2020. The penetration rate of OLED screens in the smartphone market will be More than 50%.
Facing huge market demand and bright market prospects, my country’s BOE, Tianma, Visionox, Hehui Optoelectronics, Huaxing Optoelectronics, Truly and other companies have invested heavily in the construction of multiple G4.5～G6 generation OLED production lines in recent years. In 2016, glass-based OLED displays began to gain small-scale applications in smart phones. However, due to my country's immature technical mastery of OLED products and late investment, the full release of production capacity needs to be around 2018. At present, Korean companies are in an absolute market monopoly. Among them, Samsung occupies more than 95% of the small and medium-sized OLED panel market share, while LG monopolizes the entire large-size OLED TV panel market.
There are two mainstream OLED production technology routes
From a technical point of view, mainstream OLED production technology routes can be divided into two: low-temperature polysilicon thin film transistors (LTPS-TFT) driving red, green and blue (RGB) OLED light-emitting pixels, and oxide thin film transistors (Oxide-TFT) driving white light OLED pixels Glow and pass through the Color Filter to obtain RGB pixels. The former is mainly used for small-size displays, and the representative company is Samsung; the latter is mainly used for large-size displays, and the representative company is LG.
Samsung adopts LTPS technology, mainly focusing on the small-size OLED screen technology used in smart phones. From Galaxy S to Galaxy S7, the screen resolution has been increased from 218ppi to 2K (577ppi). It is expected that the resolution of OLED mobile phones may reach in the future. Around 800ppi.
The advantages of LTPS technology are its high mobility and low power consumption, which is beneficial to mobile terminal devices such as battery-powered smartphones; but LTPS itself is a polycrystalline structure with poor uniformity, and laser annealing and ion implantation must be used. The high-cost process causes the product cost to remain high, and it is difficult to apply to the production of large-size panels.
LG uses Oxide technology, mainly because Oxide is an amorphous structure, which is easy to realize large-area and low-cost preparation, and can be used in the field of large-size OLED TVs; however, the mobility of IGZO (Oxide material) technology TFT backplanes currently adopted by LG is biased. Low (~10cm2/Vs) leads to higher power consumption. If the mobility of Oxide TFT can be greatly improved, the disadvantage of high power consumption can be reversed, and it is expected to gain a competitive advantage in small-size markets such as smart phones. Especially in the field of flexible OLED display, the production temperature of LTPS is as high as 450℃, which is a strict test for flexible substrate materials and manufacturing processes, and the cost remains high; while the production temperature of Oxide can be as low as 350℃. Simple, low cost, and greatly reduced requirements for raw materials are conducive to expanding the localization rate of raw materials and key equipment. It is an effective idea for my country to catch up.
Packaging and bending resistance reliability issues need to be solved
In the field of high-mobility Oxide TFT technology, some Chinese universities/research institutions (South China University of Technology, Shanghai University, Fudan University, Peking University, Suzhou Institute of Nanotechnology, Chinese Academy of Sciences, etc.) and enterprises are actively exploring. Guangzhou New Vision Optoelectronics Technology Co., Ltd. (hereinafter referred to as: New Vision) is committed to breaking through the foreign restrictions on IGZO Oxide materials, and is committed to developing new Oxide semiconductor materials based on lanthanide rare earth doped In-Zn-O (Ln-IZO) , Combined with the self-developed Nano-Barrier BCE structure process route (5 times photolithography, compatible with s-Si TFT production line), realizes the high mobility Oxide TFT technology with an electron mobility close to 40cm2/Vs, which can effectively reduce the OLED display The overall power consumption. Currently, New Vision is actively cooperating with domestic panel manufacturers to explore the possibility of large-scale application of high-mobility Ln-IZO TFT technology in the field of small-size OLED displays such as smart phones.
In the future development of the flexible OLED display industry, in addition to the low-cost replacement of TFT technology, it is also necessary to consider issues such as packaging, bending resistance and reliability.
From the perspective of the packaging of flexible OLED devices, the organic materials and electrodes in OLED devices are sensitive to water vapor and oxygen in the environment. Therefore, OLED devices must be packaged in-situ after the production is completed to achieve the effect of water and oxygen resistance. The packaging film The water vapor barrier capacity of the device needs to reach 10-6g/m2/day to ensure the life of the device. At present, the most effective packaging method is to use thin film packaging technology. The so-called thin-film encapsulation is not to prepare the encapsulation film in advance and then attach it to the OLED device, but after the OLED electrode is made, PECVD, ALD and other methods need to be grown in situ on the OLED electrode in a vacuum state. In order to achieve the purpose of packaging, the nano-scale film with water and oxygen barrier properties has very high technical requirements. Especially for flexible OLEDs, since it needs to face multiple free bending, more stringent requirements are inevitably put on the packaging performance.
From the perspective of the bending resistance of flexible OLED displays, all flexible OLEDs on the market now have fixed curved surfaces, and users cannot bend freely according to their own preferences, mainly because of the number of bending or bending of the flexible OLED display. If the radius of curvature exceeds a certain limit, device aging problems will occur, resulting in a decrease in brightness, black spots, dark lines and other damages, and a rapid decline in service life. This needs to be solved continuously through systematic research from the perspective of "materials-thin films-devices-processes".
In short, the flexible OLED display industry is in a period of rapid development, and the industry prospects are bright. However, my country's industrial development is still facing problems such as insufficient technology accumulation, late start of production line construction, and dependence on imports of equipment and materials. This requires close collaboration between domestic upstream and downstream industries, striving to take the initiative in the new round of flexible OLED industry competition.
