Glass vs. Sapphire: Which Is Best for Smartphone Screens?

Right after Apple announced the new iPhones in September, the author got a lot of media calls asking why Apple had not used sapphire for its screens. Apple had made an investment in a sapphire factory via a partnership with GT Advanced, after all.

The author initially thought that this investment was for Apple's then-rumored smartwatch, but given the size of the factory investment ($578 million), it seemed likely that phone screens would be on the agenda at some point, too. But why would Apple move away from Corning's Gorilla Glass?

The simple answer is that sapphire is the second hardest material behind diamonds. Apparently, GT Advanced convinced Apple that GT could create tens of millions of sapphire screens if it had enough money to build the proper furnaces and a factory to pump them out in huge quantities. Ultimately, that didn't work out. Apple went with Corning for the iPhone 6 lineup, and GT recently filed for bankruptcy.

Still, the author decided to continue his research to find out where things stand when it comes to the glass versus sapphire issue. I enlisted two experts in material science to help give me some clarity on this subject, and find out if sapphire is still a viable option for future smartphones.

The author recorded a podcast with two professors of material sciences. Joining me in the discussion are: Richard Lehman, a professor and chair of the Department of Materials Science and Engineering at Rutgers and director of the school's Advanced Polymer Center; and Dr. Helen Chan, chair of the Department of Materials Science and Engineering at Lehigh University.

You can listen above, but here are some of the key points we discussed:

Glass is used in almost all smartphone screens, and is a great solution. Lehman pointed out that sapphire is used in watches and products that have a long life. However, smartphones have a lifespan of 18 to 24 months, and the extra cost may not be worth it for most people.

Lehman said glass costs about a nickel per square inch to manufacture while sapphire costs several dollars per square inch to make. He also pointed out that manufacturing glass is highly scalable, but Chan explained that it takes a 2,000-degree furnace to melt the sapphire boules, which has an impact on the environment.

While both professors are not experts in manufacturing, they brought up key points on the virtue of sapphire as a potential material for screens, but questioned anyone's ability to make these screens in large volumes. In addition to the melting, the sapphire must be cut razor thin and subjected to extra polishing, according to Chan.

The issue of transparency came up, too. Lehman pointed out that with sapphire, "there is a high reflective index involved that cuts down on the transmission through the screen and it also could give glare."
They also pointed out that hardness (a key attribute of sapphire) might not be the best way to go with next-generation smartphones.

Lehman stated that the new Gorilla Glass 4 by Corning is twice as tough as Gorilla Glass 3 and provides 80 percent more protection in standard tests on survivability.

While the podcast clarifies for me the value of sapphire as an optional screen material for smartphones, it really brings up a key question in my mind about why Apple would make this initial sapphire investment? Also, given the advances in glass screens, it seems that glass is destined to dominate the smartphone landscape for at least the foreseeable future. There would need to be major breakthroughs in cost and sapphire manufacturing if it is to replace glass.

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