People cherish diamonds for their beauty and the sense of status and permanence they convey to the wearer, but someday soon these most precious of stones may serve an even more practical purpose than filling out engagement rings and anniversary pendants: protecting smartphone displays from the chips and spider web–like cracks that develop after countless drops and hours of tapping and swiping.
Unlike the nuggets mined from deep in Earth’s crust, display-screen diamonds would be grown in the lab of AKHAN Semiconductor, a company developing ways to use synthetic diamonds to enhance electronics. By the end of the year AKHAN plans to begin making glass smartphone screens coated with a microns-thick layer of diamond, which the company says will be more scratch-resistant and less prone to shattering. The company will not say, however, which smartphone makers might use its Miraj Diamond Glass or how it would keep the cost of those screens affordable.
Regardless of whether AKHAN delivers, the idea of using diamonds to solve the widespread problem of cracked smartphone screens bears scrutiny. A Motorola study from a couple of years ago noted nearly a third of U.S. smartphone users have handsets with cracked screens and that many continue to use those screens even after cutting a finger on them. Diamond is the hardest bulk material found in nature, and synthetic versions are likely to be more resistant to scratching than the Corning Gorilla Glass used to make most smartphone displays or even the sapphire crystal that Apple uses for its Apple Watch displays.
Despite its scratch and heat resistance, however, diamond is actually a very brittle material. “If you put enough stress on it, it will break and cleave along the weakest planes,” says Jim Butler, a consultant in chemical vapor deposition who spent 38 years as a researcher at the Naval Research Laboratory. Nor would a diamond coating necessarily protect the underlying glass screen from a drop that creates a blunt force into the screen or along its edges. At that point you’re back to counting on the strength of the glass or whatever material is used to make the original display screen, says Anthony Schiavo, an analyst with technology research firm Lux Research who specializes in advanced materials.
Although screens coated with synthetic diamonds are expected to be more shatterproof than existing smartphone screens, their actual strength depends entirely on the way they are made. The process—known as chemical vapor deposition—involves dusting a substrate, such as a piece of glass, with a layer of fine diamond particulates made up of hydrogen–carbon bonds. The diamond-coated glass is then put into a chamber with a combination of hydrogen and a carbon-rich gas such as methane. The next step is to blast the hydrocarbon gas mixture with heat or subject it to an electromagnetic field until it turns into a plasma of carbon atoms and positively charged hydrogen ions. Under these conditions the diamond particles’ carbon–hydrogen bonds begin to break. A continuous diamond film forms as the hydrogen atoms in the diamond particulates are replaced with carbon atoms from the plasma. Structural defects can be introduced during the process due to variations in temperature or the size of the original diamond particles that determine the physical properties of the end product. Making a more shatterproof diamond film would require tweaking these variables.
As the diamond fragments come together, bonds between the carbon and hydrogen are being made or broken at a furious rate, which pumps energy into the diamond film and generates heat. “The optimal temperatures for growing diamond tend to be above 600 degrees centigrade [Celsius] and, depending on the situation, can be as high as 1,200,” Butler says. Diamond, which is extremely good at dissipating heat, stands up just fine in this extreme environment. Unfortunately, the underlying glass begins to melt at about 550 degrees Celsius.
AKHAN founder Adam Khan claims his company can make a synthetic diamond film at temperatures of 350 degrees C or lower. Butler is skeptical, pointing out the glass and its diamond coating will have different reactions even at those temperatures. “If you’re going to put diamond on something and that something is going to go through temperature cycles, there’s going to be a stress between the coating and the substrate,” he says. Such stresses are enough to crack quartz, which is considerably harder than glass. That challenge can be solved, he adds, “but it’s not a trivial problem.”
AKHAN’s ability to solve such problems will determine whether diamonds end up being a smartphone user’s best friend—or just another way for Apple, Samsung and other device makers to justify driving up the cost of their handsets.