The iPhone has always been a high-end device, but Apple could be bringing it to a whole new level with the iPhone 5S. 9to5Mac points us to a new research note written by KGI Securities analyst Ming-Chi Kuo, who claims that Apple plans to use scratch-proof sapphire crystal for the iPhone 5S’s home button that will also double as a fingerprint sensor. Kuo says that Apple is sensibly making the switch from plastic to sapphire for the home button to make sure that the fingerprint sensor doesn’t get damaged. Smartphone manufacturers have been eyeing sapphire as a material for more durable smartphone displays, so it makes sense that Apple would use it for the 5S’s fingerprint sensor that will be a critical part of the device’s functionality. Plus, Apple already has experience with the material — Apple currently uses sapphire crystal on the iPhone 5 to protect the handset’s rear camera.