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Cheap scratch-resistant displays: ultrathin sapphire laminates could lead to new screen covers that are harder to break.

GLASS TOUCH-SCREEN DISPLAYS ARE EASILY CRACKED AND scratched, making them a weak point in today's ubiquitous mobile devices. Sapphire--which is about three times harder than toughened glass--could make such damage a thing of the past. Sapphire is already used on a few luxury smartphones and for small parts of recent iPhones, including the cover of the camera lens and thumbprint reader on the iPhone 5S. And some models of Apple's recently announced watch include a sapphire face.

The problem is that sapphire costs five to 10 times as much as the toughened glass used now in almost all smartphones, limiting its use to small screens or specialized devices. The challenges of this market became apparent in October when a sapphire supplier, GT Advanced Technologies, filed for bankruptcy protection.

But as the company restructures, its engineers say they are solving the cost problem with a new manufacturing process that cheaply and efficiently produces sheets of sapphire just a quarter as thick as a piece of paper. These sheets, when laminated to a conventional glass display, can do a lot to prevent damage; even a thin layer of sapphire will make the display very hard to scratch and less prone to cracking when a phone is dropped.

This next-generation process can make about 10 sapphire sheets from the same amount of material that would go into just one solid display. That could help make sapphire ubiquitous in smartphones. Indeed, it would probably add only a few dollars to the cost of a phone. And it could allow sapphire to be used on displays for larger devices, such as tablets.

The process is being developed at GT Advanced Technologies' facility in Danvers, Massachusetts. It involves a machine called an ion accelerator, the size of a cement mixing truck. The machine generates two million volts of electricity and flings hydrogen ions at sapphire crystal wafers, embedding the ions at a precise depth in the sapphire. Then the material is heated in an oven, causing hydrogen bubbles to form within it and ultimately forcing a layer of sapphire to pop off. When that layer is polished, it becomes transparent.

Though ion accelerators are already used to modify the properties of semiconducting materials, GT Advanced Technologies had to develop a machine 10 times more powerful in order to embed ions deeply and quickly enough to produce usable sheets of sapphire. The method is a big improvement over conventional means of making thin sapphire sheets, which involve sawing up a large chunk of sapphire into wafers and then grinding them down. That process wastes costly sapphire and, at the same time, introduces defects that make the thin sheets easy to break.

Ted Smick, the company's vice president of equipment engineering, expects his ion accelerator to be ready for market next year, after he develops an automated system for moving sapphire through the process. Eventually, the technology could help make sapphire-coated displays commonplace, making many of the hundreds of millions of smartphones sold each year far more durable.

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Title Annotation:Demo; GT Advanced Technologies
Author:Bullis, Kevin
Publication:MIT Technology Review
Geographic Code:1USA
Date:Nov 1, 2014
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