In-display fingerprint readers: How they work plus optical vs ultrasonic
Over the past few years we’ve seen one quite significant difference between Android phones and the iPhone: biometric authentication methods. While iPhones – since the iPhone X – have all used advanced facial recognition technology, most Android phones have opted for in-display fingerprint scanners.
With this shift away from physical buttons, it meant that the likes of Oppo, Samsung, OnePlus and Xiaomi (and their various sub-brands) have put a fingerprint reader in the display.
While some use slightly different technology to others, the user experience is largely the same. You rest your thumb (or finger) on the right part of the display – usually indicated with a fingerprint graphic – and unlock your phone, or authenticate contactless payments. In this guide we’ll explain how it works, and the differences between the two main methods of in-display tech.
Optical vs ultrasonic
Most of the scanners we’ve seen so far are optical scanners – these use light to illuminate your finger. A tiny camera under the screen takes an image of your finger which is then compared to the stored image.
While optical is the method used by most manufacturers, Samsung likes to do things a little differently. It uses an ultrasonic scanner instead of an optical one.
Ultrasonic sensors work using ultrasound to build up an image of your fingerprint (yes, really) and work better with messy fingerprints – if your hands are wet or oily with sun cream, for example. They’re essentially ‘Face ID for your finger’.
Qualcomm announced the 3D Sonic Sensor Gen 2 in January 2021, and it promises to offer a 77 per cent larger fingerprint reader area than its predecessor. It’s 50 per cent faster too as well as taking in 1.7 times the amaount of biometric data, making it more secure. It then followed that up with the 3D Sonic Sensor Max.
Its sensors are so sensitive that they can actually detect bloodflow within someone’s finger and prevent hackers from faking prints using molds or photographs. Add that to sound waves that bounce off the ridges and valleys in your finger, and you have a very secure form of authentication. In the case of the 3D Sonic Sensor Max, it can even read two fingers simultaneously.
Is ultrasonic better?
On the surface of it, the answer is yes. But it won’t matter if more handsets don’t take them up becuase of the extra cost. And in reality, the optical sensors have become a lot better since the early generation of versions used. They’re now fast and less prone to failed scans. Especially on high end phones.
The road to ultrasonic fingerprint readers has been reasonably long. In 2013 Qualcomm acquired a company called Ultra-Scan, a small company with “very good IP for ultrasonic waveform” and with a background in producing ultrasonic readers for the US Government.
“We took that and found a way to manufacture in the millions to keep the costs down,” explained Qualcomm’s Katouzian. “We don’t need to shine a light source through the display. The light source over time can degrade the LCD…it’s very similar to a photocopier.
Qualcomm certainly isn’t the only name in fingerprint sensors though; Synaptics is another while Goodix also makes sensors for a huge number of Android devices including under-display sensors from Huawei, Vivo, Oppo, OnePlus and Xiaomi. Its tech can work under both LCD and OLED displays.
Wider zone optical sensors
We’re expecting plenty more phones to launch with optical sensors – the tech certainly isn’t going away. In fact, some time ago Oppo showcased a “wide zone” optical fingerprint sensor, which recognises an area up to 15 times bigger than current sensors.
A similar technology was also used by Vivo in one of its concept phones a while ago too. Vivo’s Apex concept phone for 2019’s entire screen was a fingerprint sensor.
If this were to be adopted by more manufacturers and was cost effective (and reliable) it would completely change the game for fingerprint scanners. It would allow you to be less precise with where you place your finger or thumb to unlock the phone. You could literally put your thumb down anywhere on the screen and it would unlock the phone.
Sadly, things have gone a bit quiet on this front since 2019, and we’re yet to see it adopted in a proper mass market device from any of the household names. For now, it’s still a dream only brought to life in a concept phone.
