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Flexible glass: Schott can make a bendable sheet of glass thinner than a hair and half a kilometer long, but it doesn't yet fold.

Imagine a flip phone that fits in your pocket but opens up to reveal a tablet-sized screen. Glassmakers are already manufacturing bendable glass that's thinner than a human hair, and they say foldable glass is just around the corner.

German glassmaker Schott is now mass-manufacturing glass that's ultrathin, strong, and smooth. Electronics can be made on it, and it flexes like plastic. The first consumer product to use Schott's new glass is the fingerprint sensor on a smartphone made by LeTV, a large videostreaming company in China. Company representatives hope that this and other niche applications will give the new material a foothold while industrial designers play around with it.

Rudiger Sprengard, director of business development for ultrathin glass at Schott in Mainz, Germany, says the company can now continuously manufacture flexible glass in kilometers-long sheets. Sprengard recently brought some demos to show off in a San Francisco hotel room. He showed me a spool of glass half a meter wide and half a kilometer long; it looked like a fat roll of cellophane. A machine repeatedly bent a smaller piece of the glass down to a radius of nine millimeters. It doesn't fold yet, but Sprengard says they're working on it and hope to have it in a few years. After giving me gloves and goggles, Sprengard handed me a sheet about the size of a sheet of office paper, but thinner and stiffen Paper is about 100 micrometers thick; this sheet was 70 micrometers. As I flopped it around in my hands, treating it like a piece of plastic, one of the company representatives stepped back. It's still glass, after all, and she wasn't wearing any eye protection. When they first started experimenting with making glass this thin, it broke much more easily, Sprengard explains. "About two years ago you wouldn't have been able to handle it like that," he says.

That fragility is why mass production of flexible glass has been so challenging. To make it work, Schott had to develop new methods that built on those already used to make ultrastrong glass like Coming's Gorilla Glass, which is found on the surface of many smartphones. Gorilla Glass and other products made by both companies are toughened through a process called ion exchange.

To make glass thinner and thinner, and therefore more flexible, glassmakers have to figure out how to strengthen it. Schott is the first company to make ultrathin glass that can be chemically strengthened by ion exchange, which was a challenge, says Eric Urruti, vice president of R&D at Schott North America in Pennsylvania. Molten glass is drawn down out of a huge tank into sheets and ran through rollers. The sheets are then ran through a bath of molten potassium. Smaller sodium ions leave the glass and are replaced by larger potassium ions, creating compression within the glass itself.

The more the glass is squeezed, the stronger it becomes. Controlling this compressive process in ever-thinner glass is difficult--there's simply less material to work with. The company currently makes glass as thin as 20 micrometers. Maintaining continuous thickness across kilometers is also a challenge. And any tiny flaws must be smoothed over--or that's where your phone screen will shatter.

As the glass gets thinner, the challenges change, says Scott Forester, director of Gorilla Glass Innovations at Corning, headquartered in New York. Corning, which is also developing ultrathin glass, sells a product that's 100 micrometers thick. As cover glass (the kind found on the surface of phones) gets thinner, it's more vulnerable to being punctured. Forester says that compared with plastic, glass will always have superior puncture resistance, and they continually run tests to prove it.

Flexible electronics are already making some headway, but not in a way that's obvious to consumers. Today, flexible screens are used in devices like the Galaxy Edge, a phone with a rigid screen that curves at the sides. The OLED display within the phone is made on plastic and laminated to a Corning Gorilla Glass coverslip. If that cover glass were flexible, it would be an important step toward a device that itself could be flexible. Cover glass today is 10 times thicker than the glass Schott is showing off--usually about 550 micrometers (half a millimeter).

Forester says the pieces are in place for more flexible consumer electronics. The glass is ready and the flexible circuits are almost ready. Now they're waiting for the designers--and for consumers. "There has to be a form factor that adds value for people, " he says. Right now it's not clear what that will be. But Coming is also working on glass that will make it possible. Since ion exchange becomes more difficult in thinner materials, the company is looking at altering the underlying matrix of the glass itself--a more fundamental change in the material. Humans have been using glass since the Stone Age, but there's still a lot more chemistry to explore, says Forester: "Our scientists test 30 or 40 new glasses each day."
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Title Annotation:Upfront
Author:Bourzac, Katherine
Publication:MIT Technology Review
Geographic Code:1USA
Date:May 1, 2016
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