TechCrunch, the Future Interfaces Group shared a video and a research paper demonstrating a display that can grow small, physical bumps that can be felt under the fingers. At the current time, this is emergent technology that's owned by Carnegie Mellon, but it isn't hard to imagine future smartphones that use this kind of functionality. Apple has adopted haptic vibrations for touch-based feedback that's used for notifications and other system feedback, but raised haptics would add another dimension to the display