Lightweight, flexible electronics printed over large areas could take the weight out of e-readers and cell phones and could potentially be less expensive. However, it’s a challenge to adapt the processes and materials used to make today’s rigid glass displays to new substrates, such as plastic. Glass manufacturer Corning now suggests an alternative: It’s testing a flexible glass substrate for printed electronics that the company says will offer the performance of glass with the flexibility of plastic.
Most screens currently on the market–in televisions, computers, portable electronics, and other devices–are liquid-crystal displays (LCDs) controlled by thin-film silicon transistor arrays built on rigid glass backplanes. Corning, along with Samsung Corning Precision Materials, a company jointly owned with Samsung, currently supplies more than half the display glass used to make LCDs. But as consumers increasingly adopt portable electronics where weight, durability, and energy efficiency are more critical, new display technologies are emerging that may better meet these needs, and challenge the dominance of LCDs. Corning’s work on flexible glass is a direct response to the emergence of new display technologies, says Jill VanDewoestine, program manager for flexible substrates at Corning. VanDewoestine is demonstrating the glass in an exhibit booth this week at the Society for Information Display’s annual conference in Seattle.
Flexible substrates can also be used to print large-area electronics, including displays and solar cells on roll-to-roll systems like those used to print newspapers, potentially enabling cost-cutting volume production, says VanDewoestine. Companies including Hewlett-Packard, Phicot, Plastic Logic, and Prime View International are working on lightweight, flexible plastic and metal-based display backplanes. These technologies aren’t on the market yet, and it’s not clear that they will match the performance of silicon-on-glass when brought to high-volume production.
“Glass is a great surface for building thin-film devices on,” says Carl Taussig, director of the Information Surfaces Lab at Hewlett-Packard Labs in Palo Alto, CA. Glass is impermeable, meaning water can’t seep into it and damage organic electronics (which tends to be a problem with plastic), and its surface is also very smooth, which means it’s much easier to build perfectly structured, high-performance electronics on top of it. Glass can furthermore be used to make transparent displays, which isn’t possible with metal. And it has the advantage of compatibility with high-temperature processing. Electronics made at high temperatures tend to have better performance; their structure is better, so they switch faster, which in a display means a crisper, more beautiful picture.
Corning’s flexible display glass is just 75 micrometers thick. VanDewoestine acknowledges that the concept of manufacturing durable electronics on flexible glass is counterintuitive. “People think manufacturing on flexible glass is impossible because they think about TVs getting broken by Wii remotes,” she says. The company is not saying how tough and strong the material is, but representatives say these properties should match those of thicker glass because the strength of glass is independent of its thickness.
Corning has sent out samples of the flexible glass to manufacturing partners to test on roll-to-roll manufacturing lines. VanDewoestine says the company’s partners are building electronic devices on the substrate; the company expects to reveal some of this work in scientific publications later this year, but is not currently disclosing any details.
Jennifer Lewis, professor of materials science and engineering at the University of Illinois at Urbana-Champaign, says she is excited about the potential for flexible glass. “This will enable a broader array of materials to be integrated into flexible electronics, and likely ones with better performance than could be achieved on plastic substrates,” she says.
But there is some skepticism about the compatibility of glass with roll-to-roll manufacturing. HP’s Taussig, who is developing roll-to-roll processes for plastic display backplanes, says: “Unfortunately, glass is brittle, so it is still susceptible to scratches, which can lead to cracks and catastrophic failure, which is the last thing you want in a roll-to-roll line.”
VanDewoestine says Corning is aware of such concerns and is addressing the problem by developing packaging that will protect the glass during transport and manufacturing. “The reason flexible glass works is that we make very pure glass with a damage-free surface, and then package it so that it remains defect-free,” she says. The packaging is similar in concept to the packaging the company uses to make glass optical fibers, which are about 125 micrometers wide and flexible.