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(Pocket Ribbon) – Almost every major flagship Android phone now has a built-in fingerprint reader. But how do they work and how does technology evolve?

While the iPhone has moved to Face ID on the iPhone X (and never looked back), most major Android phones offer fingerprint ID as the main biometric access point to your phone – even if they also hedge their bets in terms of support improved facial recognition as well.

Oppo and OnePlus were among the first to seriously integrate under-display fingerprint sensors and they remain some of the main advocates, while Samsung and Huawei and many others have also taken advantage of the technology. Let's take a look at the technologies needed to bring under-screen fingerprint readers to our phones.

Optical versus ultrasonic

Most of the scanners we've seen so far are optical scanners – these use some light to illuminate your finger. A small camera below the screen takes an image from your finger which is then compared to the stored image.

We initially thought under-screen fingerprint scanners would be increasingly ultrasonic rather than optical, and it's one of these used by Samsung in its flagship Galaxy S series. But the fact that these sensors are not being used suggests that they are too expensive to run.

Ultrasonic sensors work using ultrasound to build an image of your fingerprint (yes, really) and work better with messy fingerprints, such as if your hands are wet or greasy with sunscreen. They are essentially Face ID for your finger.

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Qualcomm announced the 3D Sonic Sensor Gen 2 in January 2021 and promises to offer a 77 percent larger fingerprint reader surface than its predecessor. It's also 50 percent faster and absorbs 1.7 times the amount of biometric data, making it more secure.

The sensors are so sensitive that they can actually detect the flow of blood in a person's finger and prevent hackers from falsifying prints using templates or photos. Add that to sound waves bouncing off the ridges and valleys in your finger, and you have a very secure form of authentication.

Since this is an upgrade from the sensor in the S20 / S10 and Note 20 / Note 10 series, it should be very good indeed, and it will appear in phones from the beginning of 2021. Whether or not this is in the S21 series, however, has not been confirmed or explicitly stated by either company.

Is ultrasonic better?

On the face of it, the answer is yes. But it doesn't matter if more handsets don't use them because of the extra cost. And in reality, the optical sensors have gotten a lot better since the early generation versions used. They are now fast and less prone to failed scans. Especially on high-end phones.

Qualcomm

The road to ultrasonic fingerprint readers has been quite long. In 2013, Qualcomm acquired a company called Ultra-Scan, a small company with "very good ultrasound waveform IP" and a background in producing ultrasonic readers for the US government.

“We took that and found a way to produce millions to keep costs down,” explains Qualcomm's Katouzian. “We don't need to let a light source shine through the screen. The light source can degrade the LCD screen over time … it is very similar to a photocopier.

Qualcomm is by no means the only name in fingerprint sensors, however; Synaptics is another, while Goodix also makes sensors for a variety of Android devices, including sensors under the display from Huawei, Vivo, Oppo, OnePlus and Xiaomi. The technology can work under both LCD and OLED screens.

Wider optical sensors

We expect many more phones will appear with optical sensors – the technology will certainly not disappear. Some time ago Oppo even presented a "wide zone" optical fingerprint sensor, which recognizes an area that is up to 15 times larger than current sensors.

A similar technology was also used by Vivo in one of its concept phones not so long ago. Vivos Apex concept phone for the full screen of 2019 was a fingerprint sensor.

Oppo

If this were adopted by more manufacturers and were cost-effective (and reliable), it would completely change the fingerprint scanner game. This allows you to be less precise with where you place your finger or thumb to unlock the phone. You can literally put your thumb anywhere on the screen and unlock the phone.

Sadly, it has gone a bit on this front since 2019, and we have yet to see it adopted in a true mass market apparatus from one of the household names. For now, it's still a dream that only comes to life in a concept phone.

Written by Dan Grabham. Editing by Cam Bunton.

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