"We believe that GTAT Mesa plant has already started producing the sapphire slabs and that the supply chain is currently building up inventory," says Yole's Virey. "We expect full capacity operation at the beginning of Q4. Under our scenario, we expect Mesa to be able to provide about 30 million display covers by the end of September and a total of 42 million by year end (all numbers accounting for downstream manufacturing yields)."
(Virey goes into considerable more detail, on both the GTAT-Apple deal and the global sapphire market, in the March 2014 report, "Sapphire Applications and Market: From LED to Consumer Electronics," offered for sale by Yole.)
That's a capacity unheard of in an industry where sapphire is used as a pricey option in relatively small scale applications.
One example is Ocular LCD, of Dallas, which has used sapphire in its custom capacitive touch displays for medical device, point-of-sale, and gaming customers who have specific, demanding requirements. "It's highly scratch-resistant and impact resistant," says Shahna Kothapally, Ocurlar's vice president of engineering. "It's a nine on the Mohs scale [of mineral hardness]. Diamond is a 10. We've done impact testing and it's one of the best [materials] in terms of cover glass options."
One design challenge Ocular faced was due to the dielectric properties of sapphire. Dielectric is a measure of the relative "permittivity" of a material, which is an indication of how easily an electric field propagates through it (such as happens in a capacitive touch screen). A higher dielectric constant means more propagation, which also increases sensitivity. "The dielectric constant of the cover glass is very important in touch panel designs," says Kothapally.
Sapphire has a very high dielectric constant, higher than other glass substrates currently used for touch panel cover glass. "When designing with a high dielectric constant material such as sapphire, modifications have to be made to the touch sensor stack-up to get the optimum performance," she says. "Based on available thickness of the cover glass, adjustments must be made to the adhesive thickness between the touch panel and the cover glass. The sensor glass thickness must also be adjusted to keep the Y sensing electrodes further away from the finger — from the surface of the cover glass — for a balance in performance." ~~
The why of sapphire
So why is Apple treating sapphire as a strategic investment? Most of the reasoning on this question is speculative and inferential. A sapphire cover screen on at least the high-end iPhone model would seem to do at least three things for Apple, and its customers:
+ Minimize phone screen breakage. GTAT marketing documents claim that "Research indicated there is about a 12% probability that a smartphone display screen will break at some point during the first year of its use (for some models)." In the case of the iPhone's "in-cell technology" which now in effect blends the touch sensing panel with the underlying LCD assembly, replacing a broken screen can require replacing the entire display assembly, a costly process to Apple if the phone is under warranty, or to the phone's owner if it's not.
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