From the Samsung article posted yesterday:
"When several nozzles are arranged side by side in a thin rectangular shape and heat is applied, organic matter evaporates and sticks to the upper substrate. This technology is the most stable, but it is not applicable to 4K resolution in small and medium size flexible OLED. QHD + has the highest resolution of commercial small and medium size flexible OLED currently available. In addition to the evaporator source method, upgrading several related parts technologies such as Fine Metal Mask (FMM) can achieve 4K resolution. In the FMM market, the 4K implementation has been researched and developed for a long time, but the technical difficulty has not yet surpassed the wall."
I have posted before that FMM is the limitation for Samsung's Gen 6 and above. The "cotton" deposition mentioned in the article is likely about using metal plate to turn the line vapor source into a surface vapor source for VTE deposition. VTE is a line-of-sight deposition. Any angle between the mask and the vapor source blocks the deposition on the substrate and distorts the patterning of the pixels. It is called the shadowing effect. As the pixels get smaller while the mask wall cannot be reduced further, it becomes very challenging for patterning using VTE. That is another reason that the distance between the vapor source and the substrate increases with substrate size as is described in the Capital Market Day presentation.
OVPD deposits the films top down as opposed to VTE's bottom up, The FMM sits on the substrate so there is no sagging of the mask and the substrate in OVPD. That in my opinion is a huge advantage. In addition, OVPD is a non line-of-sight deposition since the carrier gas molecules carries the organic vapor through the shower head everywhere to the substrate surface, so there is no shadowing effect. However, that creates a problem too. There should be no gap between the mask and the substrate or the deposition would go everywhere across the whole substrate and destroy patterning. Aixtron has a patent providing the solution by using magnets under the substrate support to pull the FMM down to close that gap. There may also be thermal mismatch issues such as the substrate is actively cooled to enhance deposition while the FMM is warm to avoid deposition on the mask wall, etc.
None of these things are easy, long and hard R&D is required, among other things such as developing new composition and OLED structure to fully take advantage of OVPD. That is what I believe Samsung and Aixtron are working on, or it wouldn't make sense to spend $ and time on OVPD. The "cotton deposition source" could be just a transitory approach that Samsung is contemplating taking since I do not think it could solve the inherent VTE limitations. The key takeaway from the Samsung article to me is that Samsung has a problem in its hands and it is actively pursuing a solution. It has a small/medium size OLED business to protect so it needs to go 4K, If it could make OVPD work, it is a no brainier IMO. Mass production of cost-effective micro LED display is 3-5 years away, or never.
All are my personal opinions. Only time will tell how much of it is fantasy and how much might turn out to be factual.
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