OLED Breakthroughs

By Super User
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Unusually, we lead this week with a technical story. However, the breakthrough in blue lifetime could be significant indeed. It was 2003 when we reported two talks by David Fyfe of CDT, one of the pioneering companies in OLED (and later acquired by Sumitomo). One was at the DisplaySearch event in the March and the second in the autumn at Meko’s DisplayForum. In those speeches, Fyfe set out in surprisingly frank terms, the challenges for OLED. There were four big technical challenges. One of them was the lack of blue phosphorescent materials. Phosphorescent materials were clearly a big advantage in efficiency, but blue was proving a problem. Blue fluorescent materials were getting better – at that time, Fyfe was claiming 10,000 hours lifetime (although he didn’t define the starting brightness), but this was a long way short of red and green. However, phosphorescent materials, which are much more efficient, were elusive.

The other three problems were the quality of silicon needed and the related complexity of the active matrix substrate made of that silicon, the lack of an accepted industry standard for manufacturing and encapsulation. In February of 2003, Vitex (who we had been reporting on since 2001) and Samsung announced that they were going to work together on OLED encapsulation. Given that products have been in the market now for some time with no real issues of lifetime that we have heard about, we can reasonably assume that the encapsulation issues are solved, even though it may be that the cost and complexity is higher than desired. OLED materials are incredibly sensitive to oxygen and water, so encapsulation to shield the materials was always tricky. (I had a pair of OLED electronic “dice” given to me by CDT, but sadly, the glass got cracked in transit and in a matter of a few weeks, the display was useless).

That leaves two problems to crack. Manufacturing remains an issue for large RGB patterning because of inaccuracies in the shadow masks used in vapour deposition. In May 2003, we reported from SID that Kodak in an interview, answered a straight question with a straight answer, amazing for a US public corporation! We said that we had heard that shadow mask techniques were tricky beyond 15″. “Yes”, they said! We understand that remains one of the barriers for larger OLEDs using deposition. LG, with its white OLED and colour filter approach doesn’t suffer from this problem as it doesn’t have to deposit the different colour materials in different places. This highlights that there isn’t a single manufacturing technology for OLEDs at the moment.

LCD makers didn’t have this problem, they shared common manufacturing techniques and materials and that allowed equipment development cost to be spread across multiple vendors and factories and that helped to keep costs and capex down. Unfortunately, that meant, as I’ve written about before, that there was little edge that any one company could get, so profits in LCD have been hard to find. When it came to OLED, there was a determination to keep things secret and, so far, that has allowed Samsung to dominate the OLED market. However, for mass adoption, the lack of a single manufacturing technology has kept OLEDs out of the large display mainstream.

Which brings us to the final problem, that of complex substrates made of high quality silicon. Because the transistors that are in OLEDs have to provide the current as well as control the pixel, the electron mobility has to be a lot higher than for LCDs, where the energy for the display comes from the backlight. That means that LTPS or some other material such as IGZO has to be used. LTPS has proved just too difficult for large sizes, which is one of the reasons that Samsung has delayed its plans to ship OLEDs for TVs. Oxide is also tricky, but the complexity and quality needs of the substrates is always going to be a disadvantage of OLED technology.

In 2003, it didn’t look as though we would still have only solved, maybe, two of the four problems that Fyfe identified (assuming the blues that UDC are talking about are usable) by 2014. The manufacturing question might take a bit longer. A number of Chinese companies want to get into OLEDs. Could they combine for a common manufacturing approach? That might help with the shared manufacturing, at least. You can be assured that we’ll continue to watch to see!

Bob