A Brief Overview of Sapphire Crystal Glass

18 May

Recently Apple Inc. took a lot of steps to increase its access to sapphire crystal glass. This led to all kinds of speculations and rumors. People even began to wonder what exactly is sapphire crystal glass, its uses, and its origin. We have compiled many interesting sapphire related questions and offer their answers here.

What exactly is sapphire crystal glass?

What is called “sapphire” in the industry is officially known as “sapphire crystal glass.” It is basically the same as natural sapphire, except the difference is in their impurity levels. The man-made sapphires are generally more pure and have lower cost.


Will the sapphire crystal glass be blue?

Natural sapphires contain a variety of impurities such as iron and titanium which give it a blue color. Although various elements can be added during the manufacturing process to give man-made sapphires different colors, due to the complexity of the procedures most manufacturers opt to leave sapphire glass colorless.

How is sapphire crystal glass made?

The first man-made sapphire crystal glass was made by a French scientist, Auguste Verneuil, in 1902. The process involves the use of aluminum oxide under high temperature and pressure which causes it to crystallize. Currently there are four commercially available production methods. Each has its own advantages and disadvantages, as can be seen in the tables below:

Comparison of existing sapphire crystal growth methods:

Industrial techniques Major manufacturers Crystal growth furnace suppliers Advantages Disadvantages
Kyropoulos Monocrystal, Rubicon, USIO, DK AZTEK Thermo Tech (bought by GTAT), Apeks, Sappire Systems, other Russian providers High optical quality, low defect rate, high ingot size capability, relative low cost Complicated manufacturing process, uneven distribution, low yield rate, difficult to grow C axis crystal
Czochralski Some OCI, LG Siltron Arc Energy Easy to observe growth, easy to control size, relatively even shape High density in defective area, must use YAG in crucible, limited size restrictions,difficult to maintain chemical homogeneity of the crystal along the growth line
EFG Kyocera, Namiki High quality and complicated shapes Complex equipment and techniques
HEM/VHGF OCI, GHTOT, STC GTAT High quality and large size High equipment requirement, complex technique, high cost, a major concern is the ease of crystal cracks.

Comparison of major sapphire single crystal growth method and its volume yield rate

Major Growth Technology Pits/cm2 Purity (%) Impurity (ppm)
Kyropoulos <103 99.996 <1
Czochralski >104 99.990 <4
EFG >103 99.990 <4
HEM/VHGF <3 x 102 99.997 <1

(table source: LEDinside)

What are the applications of sapphire crystal glass?

Because of sapphire crystal glass’s excellent hardness property, early on they were either applied to the surfaces of luxury wrist watches or used as bullet proof material. There are also numerous applications in aeronautics. In the development of LED it can be used as a substrate material. Various smartphones have  begun to use sapphire crystal glass to either replace cameras lenses or protect fragile components such as finger print scanners.

How hard is sapphire in comparison to Corning’s Gorilla Glass?

The Mohs scale of mineral hardness goes from 1 to 10, with 10 being the highest. Talc currently has the lowest hardness rating of 1, whereas the highest 10 rating belongs to diamond. Although the typical score for steel or iron is about 4, the hardness of enhanced steel can reach to as high as 8. Glass normally shows a hardness score of between 5.5 to 7-9. The frequently used Corning Gorilla Glass has a hardness rating of around 7, whereas Sapphire’s hardness is 9, a shade below diamond.

What are the advantages and disadvantages of sapphire?

In addition to its extremely high hardness rating, sapphires possess an above average ductility that is more than four times better than that of Corning Gorilla Glass. Sapphire Crystal Glass’s KIC value is about 3MPa.m0.5, whereas Gorilla Glass’s is about 0.7MPa.m0.5. Furthermore, Sapphire Crystal Glass has excellent heat conductivity, even to the point of being used as a heat sink. Its permittivity is also better than typical glass. Therefore, it will likely have better sensitivity when used as a touch panel.

On the other hand, sapphire has a number of drawbacks. When compared to Gorilla Glass used in smartphones, for example, its transmittance is worse, it is heavier, and tends to be relatively more frangible. The most important factor, though, is its cost, which is up to 5 to 10 times more than that of Gorilla Glass.

Will iPhone use sapphire as a screen?

From Apple’s recent investment in GTAT and market reactions, no one will believe that Apple won’t use sapphire on its iPhone. Judging by our earlier estimates, plus other investments and industrial analysis reports, it appears GTAT’s production capacity won’t be enough to satisfy the needs of iPhones in 2014.

Assessing Apple’s recent purchase of 500 units of crystal grower equipments, Mr. Roger Chu, the research director of LEDinside, derived a series of production capacity and timing estimates. Assuming Apple needs roughly ten million sapphire glass units, you can readily see from the chart below that there is a huge gap between supply and demand. In 2014, the best GTAT can produce may only satisfy one third of the needs of Apple’s iPhones.


image credit: LEDinside


Analysis of Apple iPhone’s possibility of using protective screen

The current sapphire production capacity will easily meet the demands of iPhone camera and Touch ID for finger print identification. Since the size of these two components are not large, even when the next generation iPad lenses and Touch IDs switch to sapphire, the demands can be easily met.

Information obtained from the upstream supply chain suggests Apple had already requested suppliers to stock components. It seems likely Apple plans to use sapphire on the future iPhone touch panels, but based on its overall production capability, it won’t be 2014.

If not this year’s iPhones, then what about the rumored iWatch?

Apple’s iWatch surface is very likely to to include sapphires. Since sapphire has been used for luxurious wrist watches before, using it on iWatch should be no surprise. In fact it should be expected.

According to industry sources, the sapphires used by the iWatch will likely be cut in a square shape. This falls in line with rumors suggesting that the iWatch will highly resemble the 6th generation iPod nano.