Under Display Fingerprint Readers – How It Works

Almost all major flagship Android phones now have an in-display fingerprint reader. So how do they work, and how does technology evolve?

While the iPhone moves to Face ID on the iPhone X (and you never look back), most of the large Android phones offer fingerprint recognition as your phone’s main biometric entry point, even if they cover your phone. You also bet in terms of compatibility with advanced facial recognition.

While Oppo and OnePlus remain some of the key advocates first to combine under-display fingerprint sensors, Samsung and Huawei, and others have also taken advantage of the technology. Let’s look at the technologies involved in bringing in-display fingerprint readers to our phones.

Optical vs Ultrasonic Readers

Most scanners we have seen so far are optical scanners; They use some light to illuminate your finger. A small camera at the bottom of the screen takes an image of your finger, which is then compared with the saved image.

Initially, we thought that under-display fingerprint scanners would increasingly become ultrasonic rather than optical, and it’s one of those Samsung uses in its flagship Galaxy S series. However, the fact that these sensors are not accepted points to the fact that they are very expensive to use.

Ultrasonic sensors working principle is based on ultrasound  waves which is used to create an image of your fingerprint, and work best with dirty fingerprints, for example, if your hands are oily, wet or full of stains. These are basically ‘Face ID for your finger.

Qualcomm announced the 3D Sonic Sensor Gen 2 in January 2021 and promised to offer a 77% larger fingerprint reading area than before. It is also 50 percent faster and takes 1.7 times more biometric data, making it more secure.

Its sensors are so sensitive that they can detect blood flow on someone’s finger and prevent hackers from falsifying prints using molds or photos. Add this to the sound waves bouncing off the ridges and valleys on your finger, and you have a very secure form of authentication.

Considering this is a sensor upgrade available on the S20 / S10 and Note 20 / Note 10 series, it should be very good and appear on phones in early 2021. It is expressly approved or specified by any company.

Is the ultrasound better?

At first glance, the answer is yes. But due to the extra cost, it doesn’t matter if more phones don’t use them. And indeed, optical sensors have evolved since the first generation versions were in use. They are now fast and less prone to crawl error, especially on high-end phones.

Developement of Ultrasonic readers are started in 2013, Qualcomm acquired a company called Ultra-Scan, a small company that “has very good IP for ultrasonic waveforms” and has experience in manufacturing ultrasonic readers for the US government.

 “We took this and found a way to make millions to cut costs,” said Katouzian of Qualcomm. “We don’t need to shine a light source from the screen. The light source can distort the LCD screen over time… it’s very similar to a copier.

Although, Qualcomm is not the only company working on fingerprint sensors, there are some others such as Synaptics, and Goodix which also makes sensors for variety of Android devices, including under-display sensors from OnePlus, Oppo, Huawei, Vivo,  and Xiaomi. Its technology can work on both LCD and OLED displays.

Widefield optical sensors

We expect many more phones with optical sensors to be launched; technology is not going away. Oppo showed a “wide area” optical fingerprint sensor that recognizes an area 15 times larger than existing sensors some time ago.

Vivo recently used similar technology on one of its concept phones. Vivo’s 2019 fullscreen Apex phone concept was a fingerprint sensor.

This would completely change the game for fingerprint scanners if adopted by more manufacturers and cost-effective (and reliable). It makes you less precise about where you put your finger or thumb to unlock the phone. You can set your thumb anywhere on the screen, and this will open the phone.

Unfortunately, things have progressed quite a bit on this front since 2019, and we haven’t seen it adopted as a viable mass-market device from any household name yet. For now, only the concept remains a dream come true on the phone.