Is The MicroLED The Next Display Revolution?
Displays based on microLEDs combine exceptional contrast with a vast colour gamut, tremendous brightness and a great deal of ruggedness, but will production be held back by their complexity?
BY ERIC VIREY FROM YOLE DÉVELOPPEMENT
Despite the rapid growth in solid-state lighting, the backlighting of displays remains a substantial market for the LED. For more than a decade, screens have been illuminated with these devices – initially housed in a traditional package, and more recently the chip-scale package – and they are now the omnipotent lighting source in LCDs.
A related success story for the packaged LEDs is as the illumination source in large video billboards, which are a common sight in stadiums, malls and video facades. Here, discrete-packaged LEDs containing red, green and blue chips form individual pixels, with pitches typically ranging from 1 mm to 40 mm, depending on the size of the display and its resolution.
As of today, LEDs have never been used as the direct emissive element – that is the pixel – in small-pitch consumer displays. Many issues prevent this from happening, including concerns related to cost and manufacturability. However, the idea of building a display with microLEDs and sub-millimetre pixel pitches can be traced back to the time when the LED was in its infancy.
During the last five years, interest in developing microLED-based displays has taken off. In 2014, excitement in the tech and display communities skyrocketed after Apple acquired Luxvue, a microLED display start-up. Last October, Oculus, the augmented reality/virtual reality (AR/VR) arm of social networking behemoth Facebook, bought microLED start-up InfiniLED and this May, Sharp, now part of the Hon Hai Foxconn group acquired eLux, another microLED outfit.
Given these acquisitions, the technology is not just a lab curiosity. What is driving this tremendous interest by consumer electronic OEMs and leading brands? It is that this technology, which features individual red, green and blue sub-pixels as independently controllable light sources, is capable of forming displays with high contrast, high speed, and wide viewing angles – attributes also found in the pricey OLED displays.
In fact, microLED displays should have the upperhand over OLED rivals, thanks to a wider colour gamut, a brightness that is orders of magnitude higher, a significantly reduced power consumption, a longer lifetime, greater ruggedness and superior environmental stability. What’s more, as illustrated by Apple’s recent patent filings, microLEDs could allow the integration of sensors and circuits, enabling thin displays with embedded sensing capabilities, such as fingerprint identification and gesture control.
Although microLEDs are still to reach the market, they are far more than just an idea on a drawing board. Back in 2012, at the Consumer Electronic Show, Sony showcased a full HD 55-inch television that featured microLEDs. This display, which received rave reviews from video enthusiasts walking by the booth, contained 6.2 million sub pixels – each an individually controllable microLED chip. However, Sony was noncommittal regarding a commercialisation timeline, and as of today, no microLED TV has ever made it into market.
An inherently complex technology
Today, there isn’t a commonly accepted definition for microLEDs. However, in general, they are considered to be LED die with a total surface less than 2500 µm2. This corresponds to a 50 µm x 50 µm square, or a circular die with a diameter of 55 µm. Based on this definition, microLEDs are on the market today – they were unveiled again by Sony, in 2016, in the form of a small-pitch, large LED video wall, with traditional packaged LEDs replaced by microLEDs.
The big question for both the LED and display industries is this: how far off is the small-pitch, consumer microLED display? It is this that can target cell phones, smartwatches, TVs, laptops and, more recently, virtual, augmented, and mixed reality, head-mounted devices.