UPDATED. 2019-09-16 06:32 (월)
Ultra-large OLED formation technology, challenges and tasks
Ultra-large OLED formation technology, challenges and tasks
  • Researcher Chang Hyun-jun
  • 승인 2018.12.18 16:04
  • 댓글 0
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Bottom-up deposition, vertical surface deposition, inkjet technology are in competition

In the premium TV market, sales of 65-inch products are on the rise. The 70 to 80-inch or larger TV class is also being released. 

The display panel industry is also investing in the 10th generation line optimized for 65-inch panels, after discontinuing investment in the 8th generation class mass-production line optimized for 55-inch panels. The liquid crystal display (LCD) franchise opened the 10th generation first, but organic light emitting diode (OLED) is also preparing to invest in the 10th generation. However, there are a lot of issues to solve in order to operate the 10th generation OLED mass production line. The biggest challenge is the thin film formation technology.

Currently, the technology with the highest potential is the bottom-up evaporation method, which is being mass-produced in the existing 8th generation. In the bottom-up deposition method, the deposition source is located at the bottom of the deposition chamber, and the open mask and the substrate are placed on the chamber, thereby evaporating the organic material from the bottom to form the OLED on the substrate. However, because the substrate is placed on the upper part, the problem of warping occurs as the substrate area becomes wider, and the accuracy of deposition is lowered and the substrate is difficult to control. Currently, large-scale deposition equipment has been developed from the 8th generation half-size to the 8th generation full-size and is being applied to the mass production line, while the 10.5th generation full-size deposition equipment is under development.

Bottom-up deposition and WOLED structure.
Bottom-up deposition and WOLED structure.

Another technology that is attracting attention as the 10th generation OLED forming equipment is inkjet printing.

The ink-jet printing technique forms OLED pixels by using a nozzle of an ink-jet head to drop a soluble OLED material containing solvent into each of R, G, and B pixels, and then drying in an oven.

Currently, it is being developed mainly for the 8th generation line. Development for the 10th generation is under consideration because it is easy to increase the area for forming the OLED pixel by adding an ink jet head and there is no substrate deflection problem because the substrate is placed on the floor and ink is dropped.

In addition, the use efficiency of the light emitting material is theoretically 90% or more, which is advantageous in that the use of material cost is reduced and the overall OLED panel cost can be reduced. However, the fact that the efficiency and lifetime of soluble OLED light emitting materials are lower than that of conventional evaporation materials is the biggest problem now.

Inkjet printing concept, LG Display blog.
Inkjet printing concept, LG Display blog.

In recent years, vertical surface deposition technology has attracted attention as a large-area OLED deposition technology. In the vertical surface deposition technology, the OLED light emitting material is evaporated by a conventional bottom-up deposition technique on a metal plate to form a donor film, then the metal plate and the TFT substrate are changed in the vertical direction, and the metal plate is uniformly heated. It is a technique for depositing an OLED light emitting material onto a TFT substrate.

The vertical process can eliminate the problem of substrate deflection which is the biggest problem of equipment enlargement. It is possible to uniformly deposit across a large area because there is no movement of substrate unlike the deposition technique applying a linear source when the face source is applied, which is another advantage. 

Therefore, it is expected that it will be applicable, even if it is expanded to the mass production line for the 10th generation or more, according to future large-sized display development direction as well as the 10th generation currently undergoing investment. However, vertical surface deposition technology is still in the development stage, and it is expected that investment and time for development will be needed to apply to the mass production line.

Vertical surface deposition concept.
Vertical surface deposition concept.

As such, OLED large-area pixel formation technologies such as bottom-up deposition, ink-jet printing, and vertical surface deposition are being developed in earnest. Up to now, bottom-up deposition has been dominated by the experience of the 8th generation class mass production. In the future, it is expected that the large-scale OLED pixel-forming line will continue to be used in the 10th generation and above, and it is expected that OLED pixel makers will be able to select a large-area OLED pixel forming technology.

Comparison of each pixel formation method.
Comparison of each pixel formation method.

 


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