MicroLEDs and Sliced Bread
February 28, 2017
 
Here comes another market researcher without research claiming that μLEDs are the best invention since sliced bread and have a good chance of replacing OLEDs. Norbert Hildebrand says he loves writing about new technologies, because they offer so much opportunity and so little is known about the real challenges the technology faces. Meaning he can say anything he wants and no one can prove him wrong. He now positions himself as an expert on MicroLED displays citing Sony’s Cledis wall display and Apple purchase of LuxVue. Based on these datapoints he argues; “MicroLED Could be a Challenger”
 
He starts with key properties including power demand (luminous efficacy), pixel density, brightness, color space, lifetime, and cost. Norbert Hildebrand equivocates by saying, “I don’t need to be right, I just need to define the space so that I can explain why I am not sure at all how this will end.” He argues, “assume that you can use a display panel that uses 20% less energy at the same brightness, with the other display properties being similar. This could be a very important factor for the success of a brand. Just look at the success of Samsung that could arguably be seen as the consequence of the superior display technology used in its OLED panels. As a matter of fact, semiconductor based LEDs are beating OLEDs typically by some good margin and should have some advantage in mobile applications. This includes not only smartphones but all forms of wearable devices and even tablets.” He goes on, “From a perspective of brightness LEDs are still ahead, as their main adoption is in general lighting applications where high brightness is the most important aspect. Then he shows an old luminous efficacy chart that already has been displaced by DOE’s SSL program.  His chart shows the Luminous Efficacy History only to 2012
 
He further argues that “Since OLEDs are matrix displays, the smaller the pixel the harder I have to drive the OLED pixel to reach my desired brightness. This does have an effect on the lifetime and power consumption as well. Micro LED displays are different in this perspective as the actual LED chip is always very small and does not fill the entire pixel area anyway.”  Some might argue that physical handling anything is more expensive than simply patterning during a near lithographic deposition step. (Roger Stewart formally of Alien Technology)
 
 
Norbert Hildebrand claims color space is little trickier. The emission spectrum of the OLED or LED is mostly defined by the material choices made. A certain emitter type will have a wavelength that can only shift a little. For example a blue emitter cannot be shifted to become a red or green emitter. This is true for OLED as well as LED. This characteristic is a question of material development. One day, LED is ahead and then OLED is ahead again to provide the best emitter wavelength. He believes that both technologies will be able to achieve their desired emitter characteristics. However, OLED, being based on organic chemistry, may have it easier to find the optimal material, as there are just many more organic compounds than semiconductor materials available. The inorganic LED wins the lifetime question, even though OLEDs may be just becoming 'good enough'. If OLEDs really are getting good enough in this perspective, it may become a moot point. He doesn’t believe that OLEDs will ever beat an LED semiconductor in lifetime, under the same conditions. Which brings up the question of cost and this is where he says,' the rubber meets the road'. Whoever wins in this category may be taking home the whole prize. When looking at the numbers of units that use each technology it seems that the number game is slowly shifting in favor of OLED. However from a perspective of single LED manufacturing we have to include general lighting and that makes it clear that the number of single LEDs produced outnumbers OLED manufacturing by a wide margin. He knows this is an unfair comparison, as OLEDs have many single pixels per display, nevertheless LED makers are still cranking out these insane numbers of single LEDs that all have to function and still contribute to the learning curve of making LEDs cheaper and better. Since the current μLED displays are still more or less a dream (with the exception of LED walls of course), Nobert looks at other applications to predict a winner in the race between OLED and LED. At the end Norbert equivocates and just says that there are challenges in both (OLED and μLED) technologies.
 
I am obviously biased towards OLEDs and as the CEO of the OLED Association my role is clear. However, I will try to take a fact-based approach to comparing OLEDs and MicroLEDs. 

• First, I concede that OLEDs and μLEDs offer similar benefits in terms of
  • Contrast Ratio
  • Viewing Angle
  • Response Time
  • Color Gamut – OLEDs may have a lead here in that Green and Red LEDs do not have the high efficacy of blue, sort of the opposite for OLEDs
  • Form Factor – except for folding, which is unlikely for MicroLEDs and not yet available for OLEDs
  • Black Levels
• Second, there is no argument that μLED will be more efficient and offer higher luminance than OLEDs.  Case closed and it’s a waste of time to dwell on the subject. Although the availability of wireless charging could make power consumption a mute point.
• Third, the case for μLEDs having lower cost than OLEDs has not been made. More realistically, it looks like the μLED, could be cost prohibitive. Bob Raikes recently reported that ASPs for LEDs from 0.1 mm to 1.0 mm ranged from US$0.001 to US$0.01, with the lowest cost at around 0.5 mm. Jed Dorsheimer quoted μLED costs at 10x standard LEDs. Looking at the next table, there are 6.2m sub pixels in a FHD display and 24.9m sub-pixels in a 4K display. Given that the current price of a 5.5” FHD panel is ~ US$15.00, according to IHS, LED pricing would have to come down by 4 orders of magnitude without redundancy, from today’s costs to achieve parity with OLEDs today. At last years SID, researchers from UC Santa Barbara, the home of advanced LED studies, scientists claimed that under current conditions, it would likely take three levels of redundancy to meet the demands of a modern display. Current LEDs fail catastrophically and the display watcher will notice a single sub pixel not performing. In backlights, this phenomenon is not a problem as the failure of a single LED is averaged with all the other LEDs and is not generally noticed. Designers may get clever and reduce the number of LEDs per pixel; UDC has shown that it could be a reduction as much as 1 in every three.  Nonetheless, the number of LEDs would be staggering and potentially expensive.

 

Table 1 Theoretical Cost of μLEDs for Smartphones

Source: OLED-A

​

• Fourth, there is also the problem of moving millions of LEDs from a sapphire wafer to a glass or flexible substrate. So-called pick and place (P&P) systems or even advanced stamping approaches are being proposed.  Again, let’s look at the data; according to Charles Li of Playnitride, the state of the art in P&P is 64K μLED  per operation. It would take between 100 and 800 P&P steps depending on resolution and redundancy.  In the most likely case, when μLEDs are ready and 4K is common, perhaps 200 steps w/o redundancy or 400 steps w/redundancy would be required. Assuming 20 seconds to do the operation, a full display would take 4000 to 8000 seconds.  Given the need to optimize the other equipment around a 60 sec TACT, the number of P&P tools would be 70 to 140.  We don’t know the cost of P&P, but assuming US$5m, the capex would be US$3.5b to US$7.0b for 15,000 substartes/month. This amount s more than an entire 6th Gen OLED fab.

​
 
Table 2 Theoretical P&P Steps for Moving μLEDs from Wafer to Glass Substrate

Source: OLED-A


Clearly, the high cost argues for applications such as TVs that can be more expensive with the same resolution or for lower resolution applications, such as smart watches.  Another example would be microdisplays, where the LEDs would not have to be moved individually and a portion of the entire wafer could be transferred in bulk to a single crystal silicon wafer.  The microdisplay would then need a color filter that might block as much as 80% of the luminance according to eMagin. 
 
So what can we conclude about Norbert’s thesis? If he likes new technology so much, take the challenge, don’t buy the Kool Aid.  Do some basic research.  Where can this new technology be used and why?  And how will existing technologies compete? Displays have been a graveyard for new technologies, remember Plasma, Field Emission, MEMS dead and buried and at a very high cost. 
 
Figure 1 MicroLED Display Shipment Forecast

Source: Company


Many are taking up the cry and Norbert is not alone in his assessment of the future of μLEDs. Yole just released a report showing 250m μLEDs shipped in 2023, of which 200m were for smartphones. Yole said they did a thorough patent search and analysis finding many leading display makers, LED makers, start-ups and a flurry of electronic OEMs and semiconductor manufacturers including Intel with patents and applications. LuxVue has one of the most comprehensive portfolios. But many smaller companies have also developed very smart technology bricks, including Lumiode, VueReal, Mikro-Mesa, Playnitride, and mLED. One also must not forget Sony, which has been pioneering the field since its first TV demo in 2012.

Vertical Divider