OLED Manufacturing Makes a Breakthrough
Back at the SID/DSCC Display Week Business Conference, one of the more significant slides that was shown highlighted how many opportunities there are to boost the performance of OLED displays. Among the numerous technology developments that are expected in the next year or two was the development of new methods of patterning OLED displays.
How OLED Displays are Made
There are three currently used ways to mass produce OLED displays. For its WOLED TV panels, LG Display uses multiple layers of unpatterned OLED materials with different colors to create white light (hence the W in WOLED). It then passes that white light through a color filter to create the RGB subpixels. The method avoids patterning the OLED materials but is also inefficient as much of the light is lost in the filter. To compensate for this and to boost the brightness, white subpixels are included but this reduces the saturation of the brightest colours.
For its TV use QD-OLED panels, Samsung Display creates blue layers that are overlaid with Quantum dots to downconvert some of the blue light to red and green. This is more efficient than using filters and also avoids white sub-pixels so the reduction in saturation at high brightness is avoided. QD-OLEDs provide high color volume and great image quality.
For smartphones, tablets and notebooks, Samsung uses RGB patterning of the OLED materials. That has the same high color volume as QD-OLED, and good efficiency but has some manufacturing challenges.
FMM Processing
Up to now, RGB OLED manufacturing has used a process of evaporating the OLED materials through a kind of stencil, known as a fine metal mask (FMM). Other concepts have been researched and tried but none has been able to improve on the process, so FMM is used both for the small OLEDs in smartphones and tablets and the larger OLEDs used in IT applications.
Unfortunately, FMMs tend to suffer from issues that cause them to be less accurate than makers might hope. In turn, those inaccuracies mean that the RGB OLED materials have to have gaps between them to account for errors. As a result, less of the surface of the display is covered with material than is ideal. The sag also gets worse as the displays get bigger, so TV panels are not made this way (although Samsung Display tried very hard some years ago, but gave up).
An Alternative Method
One of the approaches that has been suggested over the years (and the idea goes back a long way) is to use a photolithographic process to create the RGB dots. That’s not dissimilar to the way that semiconductor chips are made and the process that is used to create the active matrix of transistors that controls the OLED materials on the back of the display. Unfortunately, a practical solution to make this work in mass production could not be found partly because OLED materials are so sensitive. Until now.
Over the last couple of years, display makers JDI (using the name eLeap) and Visionox (using the VIP name) have promoted the idea of photolithography and now the technology to mass produce panels has been announced by Applied Materials. While JDI has been struggling in recent years and Visionox, based in China, is a smaller player, Applied Materials is the second largest supplier of semiconductor equipment in the world based on revenue and has the clout to bring the technology to market. The company announced its patented MAX OLED manufacturing technology in November.
MAX OLED
The MAX OLED technology allows the photo lithography process to be used for much larger glass substrates – up to Gen 8, the firm said. That’s important to allow the efficient manufacture of TV scale displays. However, a feature of this way of making OLEDs is that it can also be used to make very small pixels, down to 2,000 ppi. (The press release says 2000 pixels per sq inch, but this is incorrect). That makes the technology suitable for pretty well all current OLED applications.
Ross Young of Display Supply Chain Consultants, and an expert on FPD manufacture, said that
“The MAX OLED technology has the potential to enable OLED manufacturers to target all applications from a single fab for the first time with the best performance and quality, ensuring maximum utilization”.
Applied Materials also said that
“Many of the core technologies used by the MAX OLED solution have already been proven by Applied in making large-area LCD screens at panel sizes up to Gen 10.5”.
Again, that would help the competitiveness of OLED TVs compared to LCD. Applied also reported that Samsung Display is testing the technology. Samsung leads the small OLED panel market and is the world’s biggest TV set brand, so that the adoption of the technology could indicate that it has real competitive advantage.
Applied claims that the ‘more than doubling’ of the amount of material that can be deposited means that display brightness can be increased by ‘as much as 3X’, ‘reduce power consumption by 30%’ and ‘increase display lifetime by up to 5X’. It’s not completely clear whether the power consumption saving can be made at the same time as the other factors (although that seems to be the case) but that will, no doubt, become clearer as real panels emerge that have been made using the process.
What Does it Mean for 8K?
On the one hand, better patterning and efficiency with smaller pixels has to be a real advantage for the development of more 8K OLED panels. However, as we have previously discussed, OLEDs are much harder to drive in the TFT structure than LCDs and the Applied Materials development doesn’t really help in the backplane.
On the other hand, in the making of really small displays for near-to-eye displays, the MAX OLED approach should be a real help and that will mean real advances in the kind of 4K per eye displays like the Apple Vision Pro. In turn, demand for that level of quality of content will reinforce the development of more and better 8K and beyond capture for immersive applications (like the 8K x 8K sensor that NHK is developing)
