This week, we’ve seen rumours from Korea that Samsung may be getting back into the OLED TV business by adopting the “White OLED with colour filter” approach that was developed by Kodak and is being used by LG in its OLED TVs.
Up to now, in making OLEDs for TVs Samsung has been trying using a “purist” approach, based on the same technology that it uses in its small OLEDs, that is to say by using separate RGB pixels*. This should give the best efficiency and colour performance. However, it has some drawbacks in production and Samsung dropped out of the OLED TV business after a brief production period.
In particular, the approach means that there are multiple patterning processes to deposit the OLED materials and the transport layers. Samsung has investigated a number of different patterning methods – for example, the company talked for some time about Laser Induced Thermal Imaging or “LITI”, where OLED materials were transferred from a carrier sheet to the display using lasers. This turned out to be difficult without reducing the efficacy and lifetime of the materials. (we first reported on it in March 2003 from the DisplaySearch US FPD event).OLED Structures – Image source – UDC – SID Business Conference 2014 – note that the right hand structure is not the one used by LG, but illustrates the use of filters
The fall back position was to use shadow mask techniques (also known as Fine Metal Mask [FMM]) where the OLED material is deposited through holes in a metal mask. However, this is difficult to do on large areas because of the accuracy needed. In fact, at the SID conference in 2003, we spoke to Kodak about rumours that we had heard of problems scaling beyond 15″. I remember the meeting when the company confirmed this – it is very rare for large US corporations to clearly and openly admit to problems like this! We reported on the issue at the time.
I didn’t think that LITI ever made it into production, although the Korean Daily said in 2012 that the firm was working on a hybrid LITI for red and green/FMM for blue strategy.
When Samsung said that it planned to use patterned RGB, we wondered if it would solve the patterning problem for large sizes. It would seem that it hasn’t, if the rumours are true.
In the LG approach, the technology for which it acquired when it first licensed the Kodak OLED technology in 2008 and then bought the business at the end of 2009, the materials (Blue and Yellow/Green) are deposited in layers that are not patterned, which means that the patterning issue simply doesn’t arrive – the surface emits white light. That light is then passed through a colour filter in the same way that the backlight of an LCD is filtered.
The disadvantage of this approach is that lots of the light is lost in the filters and the filters add cost. At CES this year, the HDR OLED shown by LG had great contrast, but the peak brightness was nowhere near the peak brightness of LCDs. Getting rid of the filter would help with this.
Back at the Latin Display 2014 conference, OLED pioneer Dr. Gopalan Rajeswaran (Raj) told delegates (OLED Basics From a Pioneer – subscription required) in a fascinating talk that the two approaches of FMM and White OLED with colour filter were both seen as “temporary work arounds” when they were developed back at Kodak. It is testament to the engineering teams of LG and Samsung that they have managed to build businesses around them, but his view is that there should be a better way of doing things.
Back when Samsung made its big committment to the development of the OLED TV market, I wondered in an editorial, why they would do something so difficult, but of course the reason the firm was trying to do it was precisely because it was so difficult. LCD has been characterised by much shared know how, technology and materials, which led to rapid growth, but little profit. With Chinese LCD makers ramping up, the future for profits looks, at the very best, challenging for LCD makers (and as Barry Young has pointed out, the Chinese are also ramping up OLEDs).
The hope for OLED was that it would allow companies to develop their own unique technologies and make better profits. So far, that hasn’t worked out and it seems that Samsung might have to look at developing something very close to LG, ideally without infringing the patents that LG now owns.
Bob
* Samsung also used polysilicon in its backplane for OLED TV, compared to Oxide TFT from LG. That’s another barrier that Samsung had to climb and possibly a good subject for another Display Daily!
