MIT researchers stack red, green, and blue micro-LEDs to build “fully immersive” VR displays

Researchers at Massachusetts Institute of Technology (MIT), in collaboration with collaborators from other global universities, have found a way to make screens with higher resolution than ever before – by stacking red, green, and blue LEDs vertically on top of each other.

“This is the smallest micro-LED pixel and the highest pixel density reported in peer-reviewed journals,” says Jeehwan Kim, associate professor of mechanical engineering at MIT and corresponding author of the article describing the breakthrough. “We show that vertical pixelation is the way forward for higher-resolution displays with smaller footprints.”

This 4 micron RGB LED uses vertical rather than horizontal stacking to drastically reduce its size. (๐Ÿ“น: Shin and others)

Each color pixel of a modern display consists of three or more sub-pixels – typically red, green and blue. By varying the light output for each sub-pixel, the color of the entire pixel can be controlled โ€” but putting three sub-pixels next to each other limits how small a pixel can be.

Instead of placing the sub-pixels side by side, the research team chose to stack them vertically – to find a way to prevent the sub-pixels on the top layer from blocking the light from those below. In doing so, they shrunk the size of each pixel significantly. For future displays, this means a big increase in resolution – from around 600 pixels per inch of modern smartphone screens to a whopping 5,000 pixels per inch with vertical micro-LEDs.

“There is currently a limit to how real virtual reality can look,” explains lead author Jiho Shin of a key application for the new display technology. “With our vertical micro-LEDs, you could have a fully immersive experience and not be able to distinguish the virtual from reality.”

The manufacturing process “exfoliates” LED foils into flexible layers that can be easily stacked. (๐Ÿ“น: Shin and others)

In addition to stacking the LEDs vertically, the team’s approach uses a new manufacturing technique developed to “grow” the LEDs onto a wafer and then peel them off for stacking — something they claim is possible despite the size of each Pixel is faster than competing approaches As low as 4 microns.

So far, however, the technology has only been tested on a small scale – and the large-scale display of pixel density that micro-LEDs can theoretically enable remains an unsolved problem. “You need a system to control 25 million LEDs separately,” Shin explains. โ€œHere we only partially demonstrated it. We must further develop the active matrix operation.โ€

The team’s work was published in the journal under closed access conditions Naturewith more information below MIT News.

Main article image courtesy of Younghee Lee.