Curve Your Enthusiasm: The Rise of Flexible Displays

August 14, 2024

For most of us, the televisions, laptops and smartphones we use have flat, rigid screens. That’s changing fast. Smartphone manufacturers, eager to roll out new features, have offered phones with foldable screens for a few years (though adoption has been lagging. Just 1% of smartphones sold are foldable.) The advertising industry uses flexible displays. And there’s an emerging class of wearable screens in healthcare used to monitor and diagnose patients.

Here, we discuss the technology behind the rise flexible screens.

A Little History

Flexible displays have been around for almost 50 years. The earliest relied on eInk, which displayed text in black and white. It’s the same technology used in e-readers. One advantage of this technology is that it consumes very little power.

Recent years have emphasized full-color displays capable of displaying video. Older flat-screen technology that supported this, like LCD displays, never lent itself well to bending.

“Newer OLED technologies are more tolerant of bending, and indeed, some commercially available flexible displays have made it to the marketplace,” said IEEE Life Fellow Stu Lipoff.

Materials Science

Driving the ability to make flexible, bending displays are materials science breakthroughs that allow for thinner and thinner screens. As this article from IEEE Spectrum explains, when something bends, the material on the inside of the bend is compressed, while the material on the outside is under tension.

The electronic components inside the device are also subject to those forces. However, a thinner screen creates less stress on the inside of the bend, making thinner materials more advantageous for phones with folding screens.

What Do You Mean By “Flexible”?

While flexible screens are making more and more appearances in consumer devices, there isn’t much clarity over what people mean when they use the word “flexible.”

Foldable display don’t really fold like a piece of paper, nor do they have hinges. Instead, they are capable of creating a tight curve, making a “U” shape instead of a “V.” It’s commonly seen in smartphones that bend in half. It’s used to make devices more portable.
Conformable displays can be bent to conform to a surface. Unlike foldable devices, however, they cannot be bent repeatedly. Think of screens inside an automobile that are curved to conform to a dashboard or smart watches that have a slight curve to conform to the user’s wrist.
Rollable displays may not be able to manage the tight bending radius of a foldable device, but they wrap around a user’s wrist. Unlike conformable displays, rollable displays can be bent repeatedly. While several consumer electronics companies are working on rollable displays, they haven’t hit the mainstream market yet.
Stretchable displays can extend or compress without breaking. Some are in development for the consumer market. Simple stretchable displays with low resolution are also being integrated into medical device patches.

New Applications

Flexible screens aren’t just used in smartphones. They’re increasingly used in the medical field. Some are incorporated into devices that look like wristwatches but offer significantly more medical information. Screens can also be incorporated into patches that conform to the body.

“A flexible display will allow the display to conform to the mounted body part,” Lipoff said. “Wrist instruments today offer more than simple watch functions, including navigation and fitness monitors. More recently, biomedical sensors for temperature, blood oxygen, pulse, sugar and pressure have been introduced. Battery-operated medical patches are also being deployed to the skin for some of the same applications as wrist-mounted instruments but in a form that works better as a patch to deliver drugs metered by electronics.”

Lipoff said the screens on medical devices don’t need to have the full resolution of a smartphone. They just need to display a few pieces of important information.

“In such patch devices, a simple display to provide battery life and the level of fill of the medication adds value,” he said.

Learn more: IEEE Spectrum provides in-depth, ongoing coverage of the latest developments in flexible displays and stretchable electronics. Check out this story about stretchable batteries, or this one on a stretchable circuit that can read Braille, or this one about the increasing resolution of stretchable OLED patches.