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Vertical LEDs could triple resolution of displays

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Engineers at MIT have developed a method to create vertical multicolor pixels that can greatly increase the pixel density of displays.

Today’s screens use a patterned plate with pixels formed from red, green, and blue LEDs arranged edge-to-edge. These LEDs glow at varying intensities and produce a full spectrum of colors.

Over the years, the size of individual pixels has shrunk, allowing more pixels to be packed into devices to produce sharper, higher-resolution digital displays.

But like transistors in computers, LEDs have reached the limit of how small they can be while still functioning effectively.

This limitation is especially noticeable on near-field displays such as augmented reality and virtual reality devices. In this case, the limited pixel density results in a “screen door effect” where the user perceives streaks in the space between pixels.

The new stacked pixels can produce a full range of colors and are approximately 4 microns wide. Tiny pixels, or “micro-LEDs,” can be packed to densities of 5,000 pixels per inch.

“This is the smallest micro-LED pixel and the highest pixel density reported in a journal,” said Jeehwan Kim, associate professor of mechanical engineering at MIT. “It shows that vertical pixelation is a way to achieve high-resolution displays in a smaller footprint.”

Ji-ho Shin, a postdoc in Kim’s research group, said, “For virtual reality, there is a limit to what can look real at the moment.” , it will no longer be possible to distinguish between the virtual and the real.”

A team at MIT previously developed a technique to produce pure, ultra-thin, high-performance membranes for smaller, thinner, more flexible and functional electronics.

They took this same approach to grow ultra-thin films of red, green, and blue LEDs.

The entire LED membrane was then peeled off from the base wafer and stacked to create a layer cake of red, green and blue membranes. I was able to separate it.

“Traditional displays place R, G, and B pixels horizontally, which limits how small each pixel can be made,” added Shin. “Theoretically, he can reduce the pixel area by a factor of three, because we’re stacking all three pixels vertically.”

As a demonstration, the team fabricated vertical LED pixels and showed that by changing the voltage applied to each of the pixel’s red, green, and blue membranes, a single pixel could produce different colors.

“If the current to red is high and the current to blue is weak, the pixel will appear pink or something like that,” Singh says. “We can create all mixed colors and our displays can cover colors close to the available commercial color spaces.”

The team plans to improve the handling of vertical pixels. So far they have shown that individual structures can be stimulated to produce a full spectrum of colors.

“We need a system to individually control 25 million LEDs,” says Shin. “Here we only partially show it. Active matrix management is something that needs to be further developed.”

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