How does the iPhone touch screen work – and why is it made of glass?

It happens to everyone: you smash the iPhone touch screen and you wonder why Apple would use a screen made of glass on a mobile phone. The answer is behind the technology used for the touch detection. There are a few solutions for touch detection, like near-infrared light, sound waves, or cameras which monitor changes in light. But the most popular technologies used are resistive screens and capacitive screens. Resistive screens are the ones where you have to use a stylus to interact with the device - the pressure from the stylus or finger causes the resistive layers of circuitry to touch each other. This kind of touch screen is regarded as obsolete now as capacitive screens are easier to use and don't require a stylus or any pressure to be applied on the screen. Capacitive screens use a layer of capacitive material to hold an electric charge: touching the screen changes the charge at the point of contact. The glass used for the iPhone screen acts as an insulator and is coated with a transparent conductor. Because the human body is also an electricity conductor, touching the surface of the coated glass results in a distortion of the body's electrostatic field, measurable as a change in capacitance. The location is then sent to the controller for processing. So what are the advantages? Using glass and capacitive technology makes the iPhone's touchscreen very precise compared with resistive screens but also with other types of capacitive screens. The glass panel is also very easy to clean and the functionality is not affected by dirt, grease or moisture. The disadvantage? It is glass and it shatters. But what's underneath the glass? There's another sheet of glass glued to the front one and it is also known as the digitiser. The one below has all the capacitors embedded and is the one responsible for the touch detection. This sheet doesn't usually break and that's why your iPhone's still working after breaking the screen. When we replace the iPhone screen, we also replace the digitiser as these two parts are glued together. So, if your iPhone has stopped responding to touch after breaking the screen, replacing the screen will fix make it work again and it will also make your iPhone look like new. Underneath the front glass panel and the digitiser there's the actual LCD screen, the part responsible for displaying the image. In rare occasions it can be damaged as well and it might turn white or you may see the liquid crystals "leaking". On the iPhone 4 the LCD screen is laminated together with the front glass panel and digitiser - hence a more expensive repair as none of the display assembly parts can be reused. In the future, as stronger glass screens are developed, the problem of the broken iPhone screen might be banished for good. But until then we'll be here to help you!
Published
May 07, 2014