Lim Jung-Han, Director of the High-Performance Display Division of Corning, said, "We started mass production of ‘Astra’, a new glass substrate, in March of this year. In the second half of the year, TVs made with the display panel containing the substrate glass will be available." Director Lim also added, "Currently, we supply our substrate to only one panel company, but we are also conducting sample and qualification tests with other display companies."
US glass maker Corning has exhibited Astra for the first time at the International Information Display Society (SID) Display Week 2019 held this month. Astra is a glass substrate brand specialized in the oxidation process. Oxide TFT is a technology commercialized in the early 2010s. Corning's existing substrate glass brand, Eagle XG, can also be used to make oxide TFT. Corning said, "By differentiating glass compositions, there is less change in high-temperature processes and the sagging phenomenon at larger sizes has been improved."
Director Lim said, "There is not a significant difference between the methods for extracting glass and those for cotton, only the raw material composition differs. It is possible to produce various sizes in any existing production site with only a little tuning (modification) of a facility. The width of Astra currently being mass produced is at the level of the 8th generation." He did not reveal the mass production site and supply target of Astra. The price comparison with the Eagle XG has also not been disclosed due to various factors.
For panel makers, the "appeal points" of Astra are process efficiency and cost savings. Director Lim said, "Oxide TFT manufacturing process is classified into a general process and high-temperature process. When the general process is applied, ESL is required," he said. "If you use Astra, It will be easier. "
Subtracting the etch stopper layer (ESL) reduces the number of mask process steps, which can lead to increased production and cost savings based on decreased takt time. Moreover, Corning explains that the physical changes in the high-temperature process are small and stable, helping to improve the production yield of high-resolution panels.
Currently, major TFT-LCD displays are categorized into amorphous silicon (a-Si), polycrystalline silicon (LTPS), and Oxide according to the active layer material. The active layer acts as a channel between the source and the drain in the transistor. When an electrical current is applied to a gate, a carrier in the active layer creates a 'bridge' between the source and the drain.
In the case of a switch transistor, it turns on when a crosslink is formed and turns off when the bridge is removed. The active layer material dictates the flicker rate of crosslinking. It must be quickly created when needed and disappear quickly when not needed. The speed difference is also related to the required drive power. The faster it is, the lower power requirement is necessary.
LTPS is the fastest, followed by oxide, then amorphous silicon. As the display resolution increases to 4K or 8K, the number of TFTs goes up. In addition, a high refresh rate is required, which needs improved electrical characteristics over conventional amorphous silicon. Thus, in the advanced panel area, small size panels select LTPS and large size panels select oxide basically. The two are in competition for small and medium-size panels such as laptops and tablet PCs.
LTPS is applied to production lines with a substrate area of the only 6G (1500mm x 1850mm) or less. To make amorphous silicon into polycrystalline silicon, the surface must be instantaneously melted with a laser, which is because the maximum size of ELA equipment is the 6th generation. A commercially available length is 1,500 mm, which is obtained by dispersing a laser beam that advances in a point shape with an optical lens and by drawing it as a long line.
Oxide is a method designed in consideration of the electrical properties better than amorphous silicon on substrates over 8G (2200mmx2500mm). It is made by oxidizing alloy that mixed indium (In), gallium (Ga), and zinc (Zn). The heat treatment process is essential. All Large OLED TVs are made of oxide TFT. LCD TVs apply oxides for high-resolution products.
Corning has recently introduced Astra in places where the production bases of major display panel manufacturers are located such as China, Japan, and Taiwan. In Korea, Director Lim, who was promoted last November, personally interviewed the media. Director Lim is leading the overall operation of Corning's high-performance display business.