Toughening Up

CVD coating improves display scratch resistance

The market for cell phones and other handheld devices is constantly evolving. Manufacturers are always under competitive pressure to differentiate their products with appealing designs, smaller size, lighter weight, extended battery life and more capabilities.

Now manufacturers of high-end cell phones and other handheld devices are also promoting a new innovation said to increase durability: scratch-resistant screens. The need for scratch-resistant screens on handheld devices became especially evident when Apple Corp. released its iPod Nano and users discovered that the device could not stand up to more than minimal wear and tear.

Helping to make this possible is Diamondshield, a water-clear coating developed by the Diamonex Products division of Morgan Advanced Ceramics (MAC; New Bedford, MA). The coating is said to give polycarbonate and acrylic screens, and other plastic components such as keypads and casings, scratch resistance comparable to glass while maintaining the weight savings, impact resistance, formability and other benefits of plastic. Scratch-resistant screens add value to a device without making it more complicated to use—in fact, a scratch-resistant screen actually makes a device more useable by protecting the viewability of the display.

According to MAC, Diamondshield is 4–8× more effective than silicone or acrylic hardcoatings applied by conventional methods such as dipping, spraying, spin coating or flow coating. It is applied via chemical vapor deposition (CVD), and takes on the hardness and smoothness characteristics of natural diamond. Typical coating thickness is 3–5 μm.

Its microhardness of 2–4 GPa is roughly an order of magnitude higher than the 0.2–0.5 GPa of silicone or acrylic hardcoatings and comparable to that of glass (4–5 GPa). According to MAC, another factor contributing to scratch resistance is low friction, which allows objects to slide across the surface without galling. Diamondshield has a friction coefficient of 0.3. The friction coefficient for glass is 0.6; silicone or acrylic hardcoats have a friction coefficient of 0.7.

The product’s optical properties are said to include very high transparency, even at a 10-μm thickness on multi-dimensional parts. It also has a low index of refraction and virtually no absorption in the visible.

Diamondshield also provides good hydrophobicity, a useful attribute MAC says helps prevent the collection of oils from the users hands and face on the device surface, even when users rest the cellphone screen against their cheek.

One high-end phone using the technology is the Luminoso, produced by Mobiado. The phone features a hard-anodized aircraft aluminum frame, sapphire crystal and stainless steel buttons and sapphire crystal camera window in addition to the DiamondShield-coated display.