China Star wants to print your display
China Star recently ordered an unusual tool that it will use as part of a pilot line at its Gen 6 fab in Wuhan. The tool, which is used to deposit ITO[1], an important material that acts as an electrode in OLED displays, uses a pulsed laser to deposit ITO at room temperature, different from typical ITO process tools that operate at higher temperatures. This will help to avoid the issues that occur when using plastic substrates with high temperature processes, and is expected to also increase the transparency of the ITO layer, which is essential for getting light from the OLED stack. The tool, which is being provided by Solmates (pvt), a spin-off of the University of Twente in the Netherlands, is able to produce 8” x 8” R&D displays, but is said to be able to be scaled to larger sizes.
This tool is part of the China Star pilot line, which is trying to develop an ink-jet process for printing large panel OLED displays, which are currently produced through a vacuum deposition process. The vacuum deposition process has some very specific limitations that make it unable to be scaled to large size OLED displays, and the discovery of a process, either ink-jet or roll-to-roll, that would enable the direct deposition of patterned OLED materials on large size displays would be a very significant achievement for the OLED display space.
Current OLED TVs are produced by depositing a number of layers of OLED materials across the entire substrate without patterning, and using a color filter to create the individual sub-pixels that are necessary to display images. Unfortunately this increases the cost of the device and reduces the light output of the screen, as light levels are lowered by the color filter. Small panel OLED displays however are not produced with a color filter and the OLED materials are patterned by using a fine metal mask to position the sub-pixels directly, however there are two problems to this process. One, it is very inefficient, with materials also being deposited on the FMM and the evaporation chamber itself. The efficiency of such systems are between 20% and 30%, and waste expensive OLED materials and need to be cleaned and the masks replaced regularly. Further, as the masks must remain very thin but rigid so the OLED materials are precisely deposited, they cannot be made large, as they would not lay flat in the deposition chamber and pixels would be misaligned.
Ink-jet printing would allow the OLED materials to be deposited directly on the substrate without a mask, which would theoretically remove any display size limitations, and research continues through a variety of companies such as Kateeva (pvt), Dainippon Printing (7912.JP), Konica Minolta (4902.JP), and Tokyo Electron (8035.JP), but as yet the problems associated with ink-jet printing have not been solved. The materials used in OLED displays have to be made soluble in order to pass through the high-speed print heads, which also means they have to dry quickly (panel process time is 90 seconds or less) and stay in shape and place while drying, and all must be done in an inert atmosphere to avoid degradation of the OLED materials, not an easy task. That said, the Kateeva ink-jet tool has already been adopted for the deposition of encapsulation materials by Samsung Display, and research continues to refine the process and materials for the key deposition steps. We note that ink-jet deposition systems, at least in the R&D stage, have a material efficiency of ~95%, which would yield significant savings in OLED material costs if proven viable
China Star seems to have a particular interest in developing an ink-jet process for large panel OLED displays and has joined forces with a number of equipment and material suppliers to that end and has shown a 31” printed OLED TV display a number of times recently. As China Star knows it must compete directly with LG Display for share in the OLED TV market, they have taken a longer-term view, and hope to create what would be a very significant edge in the OLED TV space if they are able to move such a process from R&D to mass production. Many have tried and many continue to try, so it will be interesting to see if China Star can come up with a workable solution that can be applied to a cost-effective mass production process.
[1] Indium tin oxide
This tool is part of the China Star pilot line, which is trying to develop an ink-jet process for printing large panel OLED displays, which are currently produced through a vacuum deposition process. The vacuum deposition process has some very specific limitations that make it unable to be scaled to large size OLED displays, and the discovery of a process, either ink-jet or roll-to-roll, that would enable the direct deposition of patterned OLED materials on large size displays would be a very significant achievement for the OLED display space.
Current OLED TVs are produced by depositing a number of layers of OLED materials across the entire substrate without patterning, and using a color filter to create the individual sub-pixels that are necessary to display images. Unfortunately this increases the cost of the device and reduces the light output of the screen, as light levels are lowered by the color filter. Small panel OLED displays however are not produced with a color filter and the OLED materials are patterned by using a fine metal mask to position the sub-pixels directly, however there are two problems to this process. One, it is very inefficient, with materials also being deposited on the FMM and the evaporation chamber itself. The efficiency of such systems are between 20% and 30%, and waste expensive OLED materials and need to be cleaned and the masks replaced regularly. Further, as the masks must remain very thin but rigid so the OLED materials are precisely deposited, they cannot be made large, as they would not lay flat in the deposition chamber and pixels would be misaligned.
Ink-jet printing would allow the OLED materials to be deposited directly on the substrate without a mask, which would theoretically remove any display size limitations, and research continues through a variety of companies such as Kateeva (pvt), Dainippon Printing (7912.JP), Konica Minolta (4902.JP), and Tokyo Electron (8035.JP), but as yet the problems associated with ink-jet printing have not been solved. The materials used in OLED displays have to be made soluble in order to pass through the high-speed print heads, which also means they have to dry quickly (panel process time is 90 seconds or less) and stay in shape and place while drying, and all must be done in an inert atmosphere to avoid degradation of the OLED materials, not an easy task. That said, the Kateeva ink-jet tool has already been adopted for the deposition of encapsulation materials by Samsung Display, and research continues to refine the process and materials for the key deposition steps. We note that ink-jet deposition systems, at least in the R&D stage, have a material efficiency of ~95%, which would yield significant savings in OLED material costs if proven viable
China Star seems to have a particular interest in developing an ink-jet process for large panel OLED displays and has joined forces with a number of equipment and material suppliers to that end and has shown a 31” printed OLED TV display a number of times recently. As China Star knows it must compete directly with LG Display for share in the OLED TV market, they have taken a longer-term view, and hope to create what would be a very significant edge in the OLED TV space if they are able to move such a process from R&D to mass production. Many have tried and many continue to try, so it will be interesting to see if China Star can come up with a workable solution that can be applied to a cost-effective mass production process.
[1] Indium tin oxide
China Star 31" Printed OLED demo - Source: ofWeek
Kateeva Yieldjet Gen 8 ink-jet tool - Source: OLED-news blogspot
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