Coming Soon to a Wrist Near You: MicroLED Displays

Apple and others expect bright and efficient, microLEDs to extend the life of your smart-watch battery

3 min read

Samuel K. Moore is IEEE Spectrum’s semiconductor editor.

Photo: Plessey
Bright Light: This transparent microLED display from Plessey Semiconductors appears bright even against ambient light.
Photo: Plessey

The race for the next great display technology may be nearing the finish line. British chipmaker Plessey Semiconductors claims it will be the first to market with a microLED display—a screen in which each pixel is made from bright, efficient gallium nitride–based LEDs. The company plans to begin selling a monochrome display in the first half of 2018. But Plessey is, in fact, a latecomer to a crowded field that includes big names like Apple, Facebook, and cash-caffeinated startups around the world.

They’re all chasing a display that offers orders of magnitude more brightness and double or triple the efficiency of today’s technologies. Though it’s difficult to see microLEDs being practical for screens much bigger than smartphones, there are plenty of smaller displays that desperately need brightness and efficiency, especially for smart watches and augmented-reality systems.

“This is going to be a generational shift in technology,” says Giorgio Anania, CEO of Aledia, a French startup, based in Grenoble, that’s developing a nanowire-based microLED display. Investors seem to agree. In January, Aledia took in US $37 million, adding Intel Capital to its investors. Its Swedish nanowire competitor, Glo, got $15 million, with Google leading the investment in August.

But it was Apple that saw the value of this technology early on. It acquired microLED display startup LuxVue back in 2014. Judging by its patent portfolio, Apple has been growing its investment, according to Eric Virey, an analyst at Yole Développement. ­Facebook, through its Oculus VR division, is also among the early spenders, having acquired ­InfiniLED, of Cork, Ireland, in 2016.

The main advantages of using gallium nitride LEDs as pixels are brightness and efficiency. OLED displays, such as what you find on Samsung smartphones, typically throw off about 1,000 candelas per square meter, or nits, Virey explains. MicroLEDs should give you 100,000 nits or even 1 million. “Clearly that’s overkill for a smartphone,” he says, “but it’s valuable for augmented reality and head-up displays,” where the image is competing with the brightness of daylight.

/image/MzAzMzYwMQ.jpegClose Up: Lumiode employees examine a wafer containing microLEDs and thin-film transistors.Photo: Lumiode

Indeed, text was nearly invisible against anything but a black tablecloth when I tried a 1,000-nit LCD-based head-up display kit at the New York City offices of the startup Lumiode. But replacing the LCD with the company’s 100,000-nit microLED unit produced clear-blue lettering even against the blue sky.

The other draw, efficiency, is no less impressive. LCDs and OLED displays are only around 5 to 7 percent efficient. But the efficiency of gallium nitride LEDs for lighting is closer to 70 percent. Efficiency degrades as you make the LEDs tinier and tinier, Anania points out, but even a 15-percent-efficient display “would be a revolution” because it would free VR systems from power cords and hugely extend smart-watch and smartphone battery life.

Right now, the revolution seems to be coming in two general flavors. Plessey and startups such as Lumiode and JB Displays are chasing what are called monolithic displays. In these, the ­gallium nitride LED pixels are produced in place on a chip and then connected as a unit to an array of silicon transistors that switch them on and off. The problem here is that it doesn’t make sense to build displays much bigger than a centimeter or two. It’d be a waste of silicon, which is expensive, and of ­gallium nitride, which is even more expensive.

So these firms are targeting the high-density displays needed for things like AR. Each has its own take on the technology, and much of that uniqueness has to do with dodging the fundamental thermal and crystalline mismatch between the silicon control matrix and the ­gallium nitride LEDs. This mismatch can cause stress-related dislocations in the LED crystal that can kill such a tiny device. Plessey’s claim that it will be first is backed up by its considerable commercial experience growing gallium nitride LEDs on ­silicon substrate and making silicon backplanes, according to Myles Blake, marketing director at Plessey.

The second approach to microLED displays seems absurd on the face of it, yet it has the potential to work in smart-watch screens and larger displays. It involves dicing up wafers into individual microLEDs, making sure they’re all working perfectly, and transferring each one to its proper place on the display (not necessarily in that order). A 42-mm Apple Watch has roughly 120,000 pixels, each one of three colors, so that might mean some 360,000 microLEDs. “You need a technology that can transfer 30,000 LEDs per second for a consumer application,” says Virey.

Yet that’s exactly the technology Apple is pursuing, and the company is thought to be nearing its goal. Apple did not respond to requests for comment. Virey estimates that Apple’s and possibly other microLED displays will debut in products in 2019. Watch for signals in the supply chain about six months prior, he says.

This article appears in the April 2018 print issue as “The Next-Gen Display: MicroLEDs.”

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