A Two-Horse Race: Gorilla Glass versus Sapphire

2014-09-03     seamanlee

Nobody can put up with scratches on their phone screen, even if these scratches do not affect the use of the handset. Corning Incorporated has introduced Gorilla Glass, which improves fragile handset screens. Glass is much softer than sand or quartz, which are the materials that often cause scratches. Because of this, people have reduced enthusiasm for Gorilla Glass. Apple chose Gorilla Glass as the protective cover for iPhone. Version 6 is likely to have a sapphire screen, and the handset industry is expected to usher in the era of sapphire displays soon. Is it time to say goodbye to Gorilla Glass? Is sapphire really a better alternative?


What Makes Corning Dominant?
When Apple released iPhone, with its stunning touch technology, Corning stepped into the spotlight and caught the eyes of users. With its century-old technical R&D capability and strong pool of technical talent, Corning has produced an environmentally friendly alkali-aluminosilicate sheet glass, called Gorilla Glass, which is excellent in terms of thinness, light transmittance, hardness, and scratch resistance. Gorilla Glass is also easy to clean and delivers outstanding capacitive touch performance. All of these make it a great, stylish solution for screens of handheld devices. Its low cost, exemplary effects with first few generations of iPhone, and stable supply also make Gorilla Glass the preferred glass for handset screens.


Why a Sapphire Screen?
Gorilla Glass is not perfect, and sand is its greatest enemy. The Mohs scale ranks mineral hardness from 1 to 10, with 10 being the hardest. Quartz is 7 on the scale, just above Gorilla Glass, which is 6 to 6.5. In daily use, the screen can be easily scratched if dropped or exposed to sand or dust. Moreover, Gorilla Glass screen can be scratched as a result of friction caused by the user putting the phone into their pockets with coins, keys, and other items. Although the main ingredient of Gorilla Glass is quartz, it contains other ingredients. It has a more loose and disordered structure than quartz crystal and is softer than quartz, even after upgrades.


On the other hand, sapphire is a hard, transparent material made of crystalline aluminum oxide. It is 9 on the Mohs scale of mineral hardness, which means it doesn’t scratch as easily. This is why sapphire is more widely used in luxury watches that are resistant to scratches caused by friction. It is also the reason a watch like this can be used for decades and even passed down to future generations. Indeed, some mobile phone manufacturers have chosen sapphire for the screen of their mobile phones. Vertu is one such luxury manufacturer. Today, people paste protective films on the screens to avoid scratches at the cost of reduced brightness and poor sense of touch. When sapphire is used as the screen panel, all these annoyances disappear.
What are We Waiting for?
Despite the unparalleled strength of sapphire, the industry is not optimistic about the large-scale use of sapphire for handset screens because it is costly, is less flexible than glass, and is in low supply. At present, the manufacturing capacity for sapphire screens is not sufficient to meet demand in the global handset market. The long growth cycle of crystal, insufficient manufacturing equipment, and a shortage of skilled labor have all impeded the mass production of sapphire screens. As a result, sapphire is nearly ten times more expensive than glass. Worse still, in some aspects, sapphire is not as strong as it is generally thought to be. Generally, the harder the material, the less elastic it is. Because a digital device has a larger surface area than a watch, the screen needs to be made of more elastic material to prevent shattering.According to a video posted by Corning, glass is less prone to shattering than sapphire.


Over the long term, a major weakness of sapphire is its low elasticity, which means that it cannot bend like a flexible glass substrate. As the world steps into the era of wearable devices, this will be a big drawback.


What will Apple Do?
Apple still seems attracted to sapphire. Apple has already used sapphire for the lens cover and home button of iPhone 5s. Furthermore, Apple has reached an agreement with GT Advanced Technologies (GTAT) to build a new factory for manufacturing sapphire screens. GTAT is working on slicing sapphire so that it is even thinner than a strand of human hair. This will bring the cost down. Also, sliced sapphire can be overlaid over other cheaper material to make it shatter-proof and solve the problem of brittleness.

The hardness of quartz on the Mohs scale is seven, just above that of Gorilla Glass (6 to 6.5), while that of sapphire is 9, which means that a sapphire-made screen is resistant to scratches by sand and gravel. However, the harder the crystal is, the more fragile it will be.


Experiements by Corning



Strength Test


This test shows that Gorilla Glass does not break when greater pressure is applied to it.


Scratch Resistance Test
The test shows very small scratches on the Gorilla Glass. According to the scratches produced on different glasses (left: competitor glass, middle: Gorilla Glass 2, right: Gorilla Glass 3) under a certain load. Gorilla Glass has better retained strength once a scratch occurs.


Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals. It is generally used in mineralogy or gemology. The Mohs scale is divided into 10 levels: Talc 1 (softest), Gypsum 2, Calcite 3, Fluorite 4, Apatite 5, Feldspar 6, Quartz 7, Topaz 8, Corundum 9, and Diamond 10.  

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