Chemical-Sensing Displays and Other Surprising Uses of Glass

Someday your smartphone might be able to help you in a new way when you’re traveling: by telling you whether the water is safe to drink.

Although a water app isn’t close yet, researchers at Corning and elsewhere recently discovered that they could use Gorilla Glass, the toughened glass made by Corning that’s commonly used on smartphone screens, to make extremely sensitive chemical and biological sensors. It could detect, say, traces of sarin gas in the air or specific pathogens in water.

The sensors are just one project I learned about during a visit to Corning’s R&D labs in upstate New York. In the last few decades, Corning’s advances in glass-making have led to technologies such as fiber optics and flat-panel displays. Now, thanks to Gorilla Glass, it’s associated with the latest smartphones. But despite the remarkable success of that product, it is keen to catch the next high-tech boom.

Corning spends about 8 percent of its sales on R&D—which will amount to about $800 million this year. It’s a hedge against the very real possibility that one of its businesses could go dark—as has happened in the past. Between 2000 and 2002, Corning lost more than half of its revenue when its fiber-optics business collapsed with much of the rest of the telecom market. Its stock plummeted from $113 to just over $1. This year, it got another scare when one of its largest customers, Apple, came close to replacing Gorilla Glass in iPhones with sapphire (see “Why Apple Failed to Make Sapphire Phones”).

Displays, in one way or another, account for about half of Corning’s revenue, with roughly a third of that coming from Gorilla Glass. To expand this market and withstand challenges from other materials, Corning is trying to add capabilities to Gorilla Glass, such as the sensor application. And it’s looking for new markets for Gorilla Glass beyond displays.

The ability to turn your phone into a biological and chemical sensor is one of the earliest-stage projects in the lab. Researchers at Corning and Polytechnique Montreal discovered that they could make very high quality waveguides, which confine and direct light, in Gorilla Glass. The researchers were able to make these waveguides very near to the surface, which is essential for sensors. Doing so in ordinary glass would break it. Making the waveguide involves focusing a beam of intense laser light near the surface of the glass, then tracing it along the glass, which locally changes its optical properties.

To make a sensor, the researchers make a waveguide that splits into two identical pathways for light. Then the paths converge, and the light from both paths meet up. One path serves as the sensing path, and the other as a reference. Even a tiny change to the light in the sensing path—such as its intensity—can be detected by observing how the light from the two paths interacts when they meet, producing distinct patterns.

The researchers demonstrated a simple sensor that detects changes in temperature. Heating up the sensing path changes its shape, which changes the properties of the light passing through it. Because the waveguide is so close to the surface, part of the light actually extends out of the glass, and anything placed on the surface of the glass will interact with part of the light. This means that to make a chemical or biological sensor, you could prepare the surface of the glass so that a specific target will bind to it. For example, you might treat it with antibodies that latch onto E. coli. or other contaminants; detecting their presence would be as simple as putting a drop of water on the phone.

The waveguides are microscopically thin, and therefore invisible, so they wouldn’t obscure a display. And because they’re quite small, sensors for several different biological or chemical targets could be incorporated into a smartphone.

Corning researchers have also discovered that Gorilla Glass has useful acoustic properties. The way it vibrates is different than conventional glass—it damps sound waves. The simplest application is noise insulation—it blocks sound better than ordinary glass.

But the same acoustic properties could also turn displays into speakers. I saw such a prototype in one of Corning’s labs. A wire in the display attaches to a small actuator that vibrates the glass to produce sound waves. Because of the way the waves propagate through the glass, they can be more precisely controlled than with ordinary glass, allowing for higher quality sound reproduction.

In another lab, researchers showed off a seemingly ordinary window. Then, with a flip of a switch on a circuit board, it turned into a display—one showing an old Coke commercial—and I could only barely make out what was behind the image. When the ad was over, I could see through the display again. Corning was particularly secretive about how it managed to make this technology work.

The most uncanny thing I saw was a Slinky-like glass toy. It’s made of thin Gorilla Glass cut in a spiral shape with a new laser manufacturing tool. As with a Slinky, if you hold one part and let go of the rest, it extends toward the floor. Ordinary glass would just shatter, but because it’s tougher, this glass springs back like plastic. The key to having glass this flexible is making it thin.

Corning recently developed Willow Glass, which is about 100 micrometers thick, one-fourth the thickness of the Gorilla Glass normally used for displays. It can be shipped to customers in rolls, making it easier and cheaper to use in manufacturing. Potential customers are still evaluating how to use it; one likely application is as a component inside displays. But already, an even more flexible kind of glass is in development, says Corning’s chief technology officer, David Morse. It can fold around the edge of something as thin as a reporter’s notebook, and do so millions of times without breaking. It could be important in future foldable electronic devices.

Founded in 1851, Corning survived in the past because of its ability to keep reinventing the possibilities of glass. At about the same time that the market for fiber optics collapsed, its business selling glass for cathode-ray-tube TVs also took a steep dive. It was saved by a process it had invented for making the high quality glass needed for the transistors that control pixels in LCD displays—the very display technology that was destroying its cathode-ray business. A few years later, the company got a call from Steve Jobs, who needed tough glass for the first iPhone. Corning just happened to have a technology sitting on the shelf—the toughened glass that came to be called Gorilla Glass. Corning hopes to be ready for the next call.