A Look at How GT Advanced Makes Sapphire Glass for Smartphone Displays

Yesterday, the State of Arizona and GT Advanced announced that Apple is building a new 700-employee factory in Arizona to make sapphire glass. Apple will contract with GT Advanced, with that company owning and operating furnaces and related equipment at the facility.

Back in April, Pocketnow went to GT Advanced's factory in Massachusetts to find out how sapphire displays are made. It's likely that the facility in Arizona will use a similar process, though we do not yet know what Apple will use the sapphire for. A safe bet would be the company's rumored smart watch product -- many luxury watches use sapphire glass because of its durability.

The process is relatively straightforward: a sapphire seed, about the size and shape of a hockey puck, is placed at the bottom of a single-use molybdenum barrel called a crucible. The crucible is then filled with a mixture of condensed corundum -a crystalline form of aluminum oxide- and a material called “crackle,” sapphire material left over from previous runs. The full crucible is then placed inside the furnace, where it sits atop the “finger,” a small liquid helium-cooled platform that prevents the sapphire seed from melting too early. The furnace is sealed, the air is evacuated, and the temperature is brought up to 2100 degrees Celsius to allow the materials to melt together. (The video says 2200, but that’s wrong. It’s 2100, for all you making-sapphire-at-home hobbyists.) The material is put through a series of cooling cycles over the next 16 or 17 days, during which time the sapphire slowly crystallizes from bottom to top. The end result is this: a 115kg cylindrical section of industrial sapphire called a “boule.”

The new factory is expected to use next generation, large capacity furnaces with an emphasis on lower cost, higher volume sapphire glass manufacturing.

Apple currently uses small pieces of sapphire glass -- which provides superior durability and scratch resistance to other forms of glass -- to protect the cameras on the iPhone and on the home button for the new Touch ID-equipped iPhone 5s. A report from earlier this year suggested that future smartphones may use sapphire, a crystalline form of aluminum oxide, instead of more traditional forms of glass.