Excitement about microLED display technology has been palpable since 2014, when Apple acquired MicroLED display startup Luxvue. Since then, many large consumer electronics and semiconductor companies have committed to the technology, including Facebook-Oculus, Google, Intel, Sharp, Samsung and LG. In total, a thorough analysis conducted by Yole Developpement and Knowmade shows that more than 120 companies or research organizations have already filed about 1,500 patents in more than 500 families. Yole Développement therefore asked analyst Eric Virey, author of the report MicroLED Displays 2018, to explain what’s been happening in this promising area.
(Source: MicroLED Displays 2018 – Yole Développement, July 2018)
Yole Développement: Could you please tell us what a microLED display is and what is unique about the technology?
Eric Virey: Most people will hopefully know all about light-emitting diodes (LEDs), whose important applications include providing backlighting for liquid-crystal displays (LCDs). Variants on this technology, like organic LEDs (OLEDs) and microLEDs can produce self-emissive display technologies, where each subpixel is an independently controllable light source. MicroLEDs and OLEDs therefore both offer high contrast, wide viewing angles and fast refresh rates. However, microLEDs could potentially exceed OLED performance in term of energy efficiency, brightness, which could be up to a thousand times higher, color gamut, ruggedness and durability. Inorganic LED materials are extremely stable over time and relatively insensitive to oxygen and moisture. They can also operate in a wide range of temperatures, up to 100°C.
YD: So what are the major technological challenges?
EV: Unlike OLEDs, there are no technologies to deposit microLED blanket layers over large surfaces. OLED displays are manufactured on substrates up to 5.5m2 in a Generation 8.5 fab, and soon 9.9m2 in the upcoming Generation 10.5, which is being set up by LG.
LED emitters are grown by traditional semiconductor technologies on 4”-8” wafers. The art of making a microLED display is patterning and singulating tiny LED emitters that are often less than 10µm or even 5µm per side. Manufacturers then must assemble them on a backplane substrate, which incorporates the individual subpixels driving circuitry. To put things in perspective, manufacturing a 4K resolution display implies assembling and connecting 25 million microLED chips the size of large bacteria without a single error, with placement accuracy of 1µm or less.
Beside this daunting challenge, engineers face many other problems. For example, while the efficiency of traditional LED can exceed 70%, this number decreases when the chip size falls under 10-15µm per side and can drop below 5% for the smallest chips. Yield and defect management are also major challenges. Nowadays, displays are essentially defect free. Even a 99.99% overall pixel manufacturing and assembly yield means hundreds or thousands of defective pixels on a display. Repairing a pixel is challenging and costly, so there are a lot of benefits of managing yields upstream via testing and binning. However, efficiently testing and binning LED die on a wafer that can hold hundreds of millions of microLED chips is quite a challenge!
YD: So how is the industry progressing and addressing those issues?
EV: Actually, surprisingly well! We’re not saying it’s a slam dunk but there’s been remarkable progress on all front over the last 18-24 months. New transfer technologies are emerging and the more mature companies now claim yields close to 99.99% or even 99.999%. Small die efficiency is approaching or exceeding that of OLEDs, although there is still some work needed for red and green die. Epitaxy reactor suppliers also have credible roadmaps to deliver tools with the capabilities and cost ownership that the industry needs. Color conversion and other aspects are also progressing.
That is not to say all challenges have been resolved. As a matter of fact, new ones are emerging that might have been overlooked as most of the energy was focused on die manufacturing and assembly. For example there’s a debate regarding whether traditional Thin Film Transistors such as Low-Temperature Polysilicon (LTPS) or oxide, which are both used for OLEDs, can be used for microLEDs. There might be some complications here since microLEDs are more difficult to drive than OLEDs, which are already more complex than LCDs!
YD: So, can we still expect to see microLED displays hit the market in consumer applications one day?
EV: Recent progress and the increasing amount of resources poured into the technology are encouraging. That said, there are still no guarantees that microLEDs will ever be a mainstream success.
Our cost analyses show that technology advances pave the way for credible cost reduction paths toward volume manufacturing, but none are straightforward. We can see how microLEDs could compete in the high-end segment of various applications such as TV, augmented reality (AR) and wearables. For AR the unique performance of microLEDs in terms of brightness could make it the best, or even the only display technology for the application. For TV, differentiation is not as obvious and OLED is a moving target. The development of efficient Thermally Activated Delayed Fluorescent or phosphorescent blue material could significantly improve efficacy and brightness and new manufacturing technologies such as inkjet printing could reduce cost. For smartphones, approaching OLED cost implies pushing microLEDs toward what is likely to be the limits of the technology in term of die size. To succeed, microLEDs will have to count on some level of price elasticity. It must deliver performance and features that no other display technology can offer and that are perceived by the consumer as highly differentiating.
YD: Which companies are the best positioned to bring microLED to mass market?
EV: There are two aspects to the question. The first one is “Who has the technology?” The second is “Who has sufficient financial resources and leverage in the industry to set up the supply chain?”
Many companies have developed clusters of technologies, focusing on one or a few aspects of microLED displays. Few have a broad intellectual property (IP) portfolio covering all the critical technology blocks. Apple is very well positioned with a comprehensive portfolio, although this doesn’t necessarily mean that its technology choices are the right ones. Time will tell. Recent leaks and rumors confirmed that the company still has hundreds of people working on the project and is spending hundreds of millions annually to keep advancing the technology. Apple also obviously has the financial scale required to set up the supply chain, but it also faces some unique challenges. It has built its reputation and a devoted following on the quality of its products and the experience they deliver. If Apple was to adopt microLED displays, it would be with the purpose of introducing a highly differencing technology, and it would have to deliver a product that is essential. In addition, it requires high volumes, which makes setting up the supply chain more challenging than for any other company.
On the other hand, we could imagine one of the fast growing Chinese handset manufacturers such as Huawei or Xiaomi introducing microLED displays in a limited edition flagship model and initially using it only to herald its technical superiority. In that case, cost doesn’t matter as much and the supply chains only need to support the manufacturing of a few tens of thousands of units initially.
The situation also varies from one application to another. AR doesn’t require mass transfer technologies and volumes are rather small so setting a supply chain is easier. One can even imagine a well-funded start up partnering with an established display maker or even setting up a supply chain by outsourcing most of the manufacturing blocks.
YD: So when are we going to see microLED displays in consumer applications?
EV: There are arguably some products already in the market. Sony’s Cledis large videowall can qualify as a microLED display and Lumens has introduced a microLED microdisplay for head up displays, although it is not clear if it is actually available in volume yet.
Lumens’ microLED Had Up Display system
(Courtesy of Lumens)
For larger volume, we don’t expect anything significant for at least two to three years for AR microdisplays, and more like three to five years for smartphones and TVs. However, in the meantime, we will see a variety of high-end, low-volume “test products” sporadically enter the market.
For example, Samsung is planning to introduce a “microLED” TV by the end of 2018. It will likely be very expensive and only sell a few hundreds of thousands of units and the product will initially be assembled in a “quasi-artisanal” fashion.
Samsung’s 146″ microLED TV unveiled at CES 2018
(Courtesy of Samsung)
In any case, observing the evolution of the technologies, the positioning and the strategy of the different players is going to be a fascinating journey!
Dr. Eric Virey serves as a Senior Market and Technology Analyst at Yole Développement (Yole), within the Photonic & Sensing & Display division. Eric is a daily contributor to the development of LED, OLED, and Displays activities, with a large collection of market and technology reports as well as multiple custom consulting projects. Thanks to its deep technical knowledge and industrial expertise, Eric has spoken in more than 30 industry conferences worldwide over the last 5 years. He has been interviewed and quoted by leading media over the world.
Previously Eric has held various R&D, engineering, manufacturing and business development positions with Fortune 500 Company Saint-Gobain in France and the United States.
Dr. Eric Virey holds a Ph-D in Optoelectronics from the National Polytechnic Institute of Grenoble.
MicroLED Displays 2018
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