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Bendable display technology takes the stage

Fri, 03/22/2013 - 12:06pm
Kasey Panetta, Managing Editor

It happens to everyone who owns a smart phone or tablet. One ill-fated toss into the car or accidental drop on the hardwood and suddenly the screen is too cracked to read. Not only does this render the phone useless until you can get to a store, it can mean spending hundreds of dollars on a new screen or an entirely new phone.   

Since smartphones became ubiquitous, researchers have been trying to design the touchscreens to be more rugged and durable, which is intrinsically difficult when you consider the screens are made of glass. Phones take a beating and the wear and tear is simply a byproduct of their constant use and necessity. Researchers were faced with the challenge of designing a durable touchscreen that could handle being tossed around without shattering. The solution? Bendable screens.

Technically, bendable screens were a byproduct of the desire to create light weight, unbreakable phones, but the idea evolved from there. What started as bendable cellphone screens grew to include larger displays like televisions and advertisements. Eventually, bendable screens gave way to products that could radically change not only the world of consumer electronics, but hold great potential for the medical and industrial fields.

Where it started
Flexible touch sensor made with ClearOhm  conductive materiaWhile flexible screens are only now hitting the marketplace, the idea has been circulating in labs since the 1990s. Researchers were working on the idea that they could place electronics on novel surfaces like plastic, instead of the traditionally-used glass, says Nick Colaneri, director of the U.S. Army’s Flexible Display Center at Arizona State University. But high-performance electronics were made in systems that used high temperatures, which meant that plastic wasn’t an option until the whole manufacturing approach evolved. As an added complication, at the time there were no viable front plane options besides plasma or LCD screens, which can’t be bent.

However, with the arrival and popularity of front plane options like E Ink (Kindle) and organic light-emitting transistor (OLET) display options, came the ability to bend screens without distorting the image. The challenge remained solely with designing a technique to attach components to plastic that won’t melt or glass that won’t break.

The current solution is plastic film. The plastic is placed on glass or a glass-like material and processed as glass would be, only at adjusted temperatures, with the electronics attached. After processing, the film and components are peeled off the glass, leaving a material that’s not completely rigid, but also not completely foldable.

“At first they’ll be kind of thin and stuff like a credit card, you can’t really roll it up but you can certainly bend it,” says Colaneri. “We’re moving toward thin and unbreakable and ultrathin form factors.”

Corning Willowglass is a flexible glass alternative to plasticThe technology is moving from the lab to the showroom as Samsung introduced its line of flexible organic light emitting diodes (OLED) called “YOUM” at CES 2013 earlier this year. The company used extremely thin plastic instead of their traditional glass and emphasized the technology holds great promise for various consumer electronics.

ITO versus silver nanowires
Another challenge, particularly for bendable touch screens, is designers traditionally use indium tin oxide (ITO) for transparent conductors, which can lead to problems with flexibility and conductivity, not to mention added costs and reduced responsiveness.

Every display requires a transparent electrodes to inject current or apply a voltage to turn the display on or off, says Rahul Gupta, senior director of Business Development for Cambrios Technologies Corporation. Replacing ITO with silver nanowires produces a low resistance, high light transmission, flexible, rugged, transparent electrode.

The silver nanowires, which don’t crack or degrade when bent, offer higher conductivity and higher light transmission, low temperature processing that allows for highly conductive layers on plastic substrates, and because silver is widely available, provide a cheaper alternative to ITO, says Gupta. The material also allows f for brighter screens that are viewable from any angle, which is perfect for flexible advertisements or screens.

Non-rugged components need not apply
When an electronic device is bent, the components are under very different pressures and stresses than if it were a rigid product, so each component must either be flexible like the silver nanowires or so rugged it can withstand a solid beating.

Problem areas include the tab bond and the electrical connections inside the phone or screen, according to Colaneri. Every new component or step forward must be thoroughly tested for endurance.

“We go down to the product guys and say look at this cool new component and the first thing they do is beat the heck out of it”, says Colaneri. “Because they know their customers are
going to break it because that’s how it is. It’s finding things that are going to break and figuring out in the long run how can we make that in a way that is better.”

Unbreakable glass
When flexible products were first considered, glass was dismissed as a viable option because it was too brittle and any shattering would contaminate the otherwise sterile production line. Corning, a manufacturer of glass and ceramics, decided to take on the challenge of making an unbreakable glass screen.

“Corning knows a scary amount about glass and they’ve developed a legitimate, flexible glass alternative,” says Colaneri referring to a product Corning calls “Willow Glass”. Willow Glass, created using the Corning fusion process designed to produce large sheets of high-quality, thin glass, is a smooth, stable, optically clear surface designed for building electronic components, according to Dipak Chowdhury, PhD, Division Vice President and Willow Glass Program Director. Because glass doesn’t degrade during the manufacturing process and is highly durable to heat, chemical and UV exposure, it could prove superior to plastic alternatives, which might scratch or break.

“Willow Glass is a fusion-formed LCD-grade substrate, not a cover glass. The substrate makes the display functional while the cover glass helps protect and enhance the device appearance and function,” according to Chowdhury.

Though the company doesn’t intend to use the class for cell phone screens, they see a large market for touch screen applications, screens requiring better pixel count and resolution, and applications which require dynamic color.

What does this mean for the future?
It seems like the sky is the limit for potential applications of light, flexible display technologies. Flexible, unbreakable cell phone screens are the first step, then perhaps a foldable television screen or larger advertisement. For consumer electronics there are a multitude of creative applications that will improve not only the quality of products, but the portability, lifetime, and uses.

But the potential applications extend far beyond the world of consumer electronics into medical technologies with flexible electronics that resemble skin that will be able to track your pulse rate as your exercise, says Colaneri. That could potentially evolve into an entirely new world of diagnosis and monitoring while closing the gap between biology and electronics.
But that’s all in the future. For now, the world of bendable screens is focused on increasingly flexible or rugged components working in conjunction with flexible front planes and developing  better manufacturing techniques to perfect the products.

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