Even if the OnePlus 6T isn't an upgrade over the 6, it's star feature, that in-display fingerprint reader, is interesting enough to be quite the party trick. OnePlus has confirmed that the scanner is an optical scanner, a technology that makes it slower, less reliable and less secure than either capacitive or ultrasonic sensors. Until now, we couldn't take a closer look at it.
When it comes to fingerprint scanners, there are three popular designs, and the optical one is the least popular of the lot, and for obvious reasons.
Optical scanner: This captures an image of the finger and requires light for doing so. That shiny ring of light around your finger when you scan it on the OnePlus 6T isn't just for show, it's there to illuminate your finger so the sensor (usually a camera) can take a photo. This scanner is the least reliable because any dirt or irregularity on your finger or surface, even a scratch, could result in a failed authentication. It's also one of the easiest technologies to fool since all it needs is a 2D image of your fingerprint.
Capacitive sensor: This is by far the most popular option. Unlike the optical scanner, a capacitive scanner uses capacitors (electricity) to take a snapshot of your finger. These sensors are far more reliable because they capture the 3D shape of your fingerprint and not just its image. Most fingerprint scanners, including Apple's TouchID, use this technology.
Ultrasonic sensor: These sensors goes deeper. Where the previous two examples capture the surface of your finger, an ultrasonic scanner uses sound waves to map the dermal layer of your skin, i.e. the layer just under the outer layer of skin. Because of this, these sensors are extremely accurate and almost impossible to fool. They're also undeterred by dirt or scars.
Getting back to the OnePlus 6T, we usually turn to iFixit for teardowns of the latest hardware, but in this case, it was Zack from JerryRigEverything who got to the OnePlus 6T first. If you love phones, it's not a channel you'd want to watch, because Zack makes it a point to scratch, bend and burn every smartphone he can lay his hands on. *shudder*
Anyway, Zack got his hands on the OnePlus 6T and decided that he might as well take a closer look at the in-display fingerprint scanner of the device.
After ripping apart the phone, which is quite easy if you have the right tools, Zack discovered that the sensor resides below the battery. A closer inspection reveals that, as expected, the sensor is basically a camera that's mounted under the phone's OLED display.
Removing the camera reveals a little hole through which the camera can peek at the world. Sort of. Given that the camera must peek between display pixels, the hole is more like a frosted glass window.
The light you see when scanning comes from the OLED display itself, but since the pixels only shine in one direction, the camera is not blinded by the light of the display.