MIT Researchers Stack Red, Green, and Blue Micro-LEDs to Build "Completely Immersive" VR Displays

Researchers at the Massachusetts Institute of Technology (MIT), working with collaborators from other global universities, have come up with a way to make screens higher resolution than ever before — by stacking red, green, and blue LEDs vertically, one atop the other.

"This is the smallest micro-LED pixel, and the highest pixel density reported in the journals," says Jeehwan Kim, associate professor of mechanical engineering at MIT and corresponding author on the paper describing the breakthrough. "We show that vertical pixellation is the way to go for higher-resolution displays in a smaller footprint."

Each color pixel of a modern display is made up of three or more sub-pixels — typically red, green, and blue. By varying the light output for each subpixel, the color of the overall pixel can be controlled — but having to put three subpixels side-by-side limits just how small a pixel can be.

Rather than putting the subpixels side-by-side, then, the research team opted to stack them vertically — finding a way to prevent the subpixels on the upper layer occluding the light from those below. In doing so, they've considerably shrunken the size of each pixel. For future displays, that means a big boost in resolution — from the 600-or-so pixels per inch of modern smartphone screens to a whopping 5,000 pixels per inch using vertical micro-LEDs.

“For virtual reality, right now there is a limit to how real they can look," explains first author Jiho Shin of a key application for the new display technology. "With our vertical micro-LEDs, you could have a completely immersive experience and wouldn't be able to distinguish virtual from reality."

In addition to stacking the LEDs vertically, the team's approach uses a new fabrication technique designed to "grow" the LEDs onto a wafer then peel them free for stacking — something which they claim is faster than rival approaches, despite the size of the individual pixels going as low as 4 microns.

At present, though, the technology has only been proven on a small scale — and creating a big-screen display of the pixel density the micro-LEDs can theoretically make possible remains an unsolved problem. "You need a system to control 25 million LEDs separately," Shin explains. "Here, we've only partially demonstrated that. The active matrix operation is something we'll need to further develop."

The team's work has been published under closed-access terms in the journal Nature, with more information available on MIT News.

Main article image courtesy of Younghee Lee.