Optical Versus Ultrasonic Under The Display Fingerprint Scanners Explained


There are two ways an under the display fingerprint scanner can be implemented in a smartphone. One is Optical fingerprint scanner and the other one is Ultrasonic fingerprint sensor. Here in this article we explain both the technologies.

In 2018 we have seen the emergence of smartphones with under the display fingerprint scanners. A number of smartphones have already been released with a fingerprint scanner under the screen. There are two different ways a fingerprint scanner can be embedded under the display.

  • Optical Fingerprint Scanner
  • Ultrasonic Fingerprint Scanner

Below we take at a look at both these ground breaking technologies and explain how they are different from each other and what are their advantages and disadvantages.

Fingerprint scanners under the screen

We saw the first under-the-display fingerprint scanner in Vivo UD X21 which was a prototype device. Vivo Nex was the first phone to have brought an under the display fingerprint scanner to the market. The Huawei Mate 20 Pro is one of the first smartphones in mass production with an under-the-display fingerprint scanner along with the OPPO X21.

The OnePlus 6T is the latest one with a fingerprint scanner under the screen. This is because brands such as OPPO and Vivo have been working on this new way of telephoning for a while. However, these scanners are all optical to date. There are also ultrasonic fingerprint scanners, which the Samsung Galaxy S10 reportedly uses.

Optical fingerprint scanner

The optical fingerprint scanner works very simply. There is a small camera sensor under the screen. The moment your finger touches the display, it lights up to illuminate your fingerprint. As it lights up, the sensor captures a high-resolution scan of our fingerprint.

The disadvantage of optical scanners is that they can work only on AMOLED panels and do not work with LCD screens. The reason is that AMOLED panels can switch individual pixel turn off while LCD can’t.

The optical fingerprint scanner is just as safe as traditional fingerprint scanners. At the moment, Synaptics is a major producer of optical fingerprint scanners. We can also see how fast this scanner is exactly: this is of course partly due to the matching process of the scanner and your profile where many optimizations can be done. As a result, the unlocking speed can differ from phone to phone. Optical scanners are already on the market and good enough to produce in bulk.

Ultrasonic scanners

Another way of processing the fingerprint scanner under the screen is via an ultrasonic scanner. This works with ultrasound. This is where Qualcomm has been busy for several years. During the scanning process, a sound is sent through the screen and the glass layer of the screen that bounces against your finger. The reflection of this is  captured and compared with the profile of your finger.

The advantages of ultrasonic scanners are diverse. The first is that the source for scanning your finger is not light but sound. As a result, you also do not suffer from a bright screen when you unlock in the dark. The technology also works together with LCD screens, which means that the potential can be applied to many more smartphones. In addition, you can have your finger scanned on the entire screen, and not on a limited area as is the case with the optical scanner.

However, there are also disadvantages to this implementation. The biggest reason why we have not yet seen ultrasonic scanners is that it only works through a glass of a limited thickness of 0.8 mm. Since a screen which is usually between 0.4 mm to 1.3 mm thick can be thickened more when a sturdy Gorilla Glass 5 is added, you can already see the difficulties coming. To get the entire screen within this 0.8 mm is still a challenge.

Still, it seems Samsung has now succeeded if we believe the latest rumors. Apparently, they are working hard to implement an ultrasonic under the display fingerprint mechanism in the upcoming Samsung Galaxy S10.


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