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  (Source: Flawless Facets)
Sapphire would be three times as hard as Gorilla Glass

For centuries mankind has enjoyed brilliant blue sapphire gemstones.  Now scientists have learned to grow transparent sapphires and could soon use the lab-made stones to form smartphone screens.

Sapphire is the world's second hardest material, and is tougher than even the strongest Gorilla Glass.  Sapphire's crystalline structure is formed of a network of aluminum and oxygen atoms in a 2-to-3 ratio.

In a new report by the MIT Review, it is suggested that screens of the hard synthetic crystal could soon hit the market, improving the rigidity (drop resistance) and screen integrity (scratch resistance) of smartphones.  The report suggests that a sapphire screen would currently cost $30 USD/unit, versus $3 USD/unit for a Gorilla Glass screen.

That cost would make a sapphire screen to expensive for all but the most premium of flagship smartphones.  It's clear why Corning Inc.'s (GLW) Gorilla Glass has dominated sales to date, selling over 1 billion units.  However, given that sapphire is three times as hard as Gorilla Glass, the MIT Review report argues that some OEMs may feel compelled to make the switch.

Currently a few OEMs -- including Apple, Inc. (AAPL) use smaller sheets of sapphire glass as a cover to their smartphone camera lenses.

Eric Virey, an analyst for the French market research firm Yole Développement, said in an interview that the cost of sapphire screens could eventually drop to $20 USD/unit.  He comments, "I'm convinced that some (manufacturers) will start testing the water and release some high-end smartphones using sapphire in 2013."

Gorilla Glass
The current market leader is Corning's Gorilla Glass.

Corning spokesman Daniel Collins responded to the report, saying he is not convinced that sapphire units will be able to cannibalize the market for his company's product, nor compromise its growth.  He comments, "It is unclear to us if this could provide better overall performance than actual glass.  There also are the questions about cost and product weight that must be addressed before sapphire would be a serious consideration for mass market applications."

The latest Gorilla Glass, Gorilla Glass 3, is twice as hard as its predecessor (Gorilla Glass 2).

GT Advanced Tech
GT Advanced Tech aims to supplement smartphone glass, not necessarily replace it.  
[Image Source: GT Advanced Tech/ExtremeTech]

Ultimately the two technologies may coexist in some smartphones, though.  GT Advanced Technologies, Inc. (GTAT), a New Hampshire device startup, is aiming to produce a clear sapphire layer for smartphone and tablet that's as thick as a human hair (~0.1 mm), which would be added a strengthener/supplement to the currently used Gorilla Glass.  Synthetic glass and sapphire may soon be vying for market dominance, but ultimately they may do their best work as a team.

Sources: MIT Review, CNN [Corning Response]

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RE: Incorrect
By tng on 3/22/2013 8:24:31 AM , Rating: 3
make large enough sheets for large phone screens may be new
It is not new, but it is expensive. Sapphire wafers for semiconductor applications have been around for decades. These are mainly used in radiation hardened ICs used in many military uses, satellites, and oddly enough green/blue/white HI LEDs.

The problem is that a 150mm sapphire wafer at .7mm thick was $600 the last time I checked. That is an expensive screen.

RE: Incorrect
By 3DoubleD on 3/22/2013 10:11:13 AM , Rating: 3
Well non-semiconductor grade sapphire could be less expensive than semiconductor grade sapphire, the problem being that if you relaxed the "cleanliness" of your process to save money, you might end up with impurities causing the sapphire to turn blue or red. But so long as those specific impurities are eliminated, I'd expect that you could have relatively impure, clear sapphire at a reduced cost compared to semiconductor grade.

My major problem with this announcement is that while sapphire is the second hardest substance, that doesn't mean it isn't extremely brittle. Diamond may be the hardest material on earth, but even diamonds can break or chip readily if dropped the wrong way.

[If anyone reading this has worked with semiconductor sapphire substrates and could chime in as to how easy/difficult it was to cleave that would be appreciated]

Any single crystal material is prone to catastrophic failure by cleavage along certain crystal planes. One crack can propagate through the entire crystal. In materials like your average steel product, you have thousands of grains (crystals) between two surfaces. Each grain can be slightly or highly mis-oriented with respect to its neighbors, so a crack in one grain won't readily propagate across the entire material. Metals are also extremely ductile and the combination gives a material that does not shatter under normal conditions (but dents, scratches, and both readily elastically and plastically deforms without catastrophic failure).

In a single crystal, one crack will propagate through the entire material. There is nothing to stop it once enough force was delivered along a cleavage plane (and there are many possible cleavage planes). Gorilla Glass is just that, a glass. It's an amorphous matrix of their special blend of material. Amorphous materials can still crack, but crack propagation is SIGNIFICANTLY deterred due to the lack of crystalline order.

Sapphire also has a slightly higher refractive index than glass (including Gorilla Glass): ~1.7 vs ~1.5. This will lead to worse glare. I'm assuming they don't place any anti-reflective coatings over the sapphire or Gorilla Glass, since that would defeat most of the purpose of using such a hard, scratch resistant material in the first place.

RE: Incorrect
By tng on 3/22/2013 10:23:17 AM , Rating: 2
[If anyone reading this has worked with semiconductor sapphire substrates and could chime in as to how easy/difficult it was to cleave that would be appreciated]
Yes, most of the sapphire wafers that I have seen are fragile for just the reason you mention above. The structure of a single crystal wafer means that even a small hit on the edge can cause a fracture line straight across the whole wafer. The same hit on a glass wafer would cause a chip. Silicon wafers behave the same way.

I have also worked with sapphire with a silicon backing that seem to be tougher, but still fragile. The worst I seen was gallium arsenide wafers, heavy, soft and fragile.

RE: Incorrect
By 3DoubleD on 3/22/2013 3:36:03 PM , Rating: 2
Ya, I love cleaving GaAs wafers, it is so easy... you basically just have to stare at it the right way and it's done and the cleave lines are generally very clean. I hear InP wafers are similar. In my experience Si is much tougher, you have to do a much better job at scribing and notching the edges of the wafer. Even then, sometimes the Si wafers have a mind of their own and cleave in seemingly random directions (I sometimes get square pieces from a Si(111) wafer, which shouldn't be possible given the three dominant cleave directions).

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