GT Explains: How In-Display Fingerprint Sensors Work on Smartphones

Namrata Gogoi

Technology is a never-ending game of innovation. In less than a decade, we've moved from punching PINs to using Face Unlock as authentication measure on our phones. And just as we were thinking that it couldn't get better, we have a brand new innovation which is taking the tech world by storm: the in-display fingerprint sensor.

In Display Fingerprint Sensor 3

In-display fingerprint scanners have been a buzzword for quite some time now. After years of rumors and whispers, it's finally here. Hence it begs the question of how is it different from the conventional capacitive sensors and, more importantly, how does it work.

If you must know, the iPhone X was supposed to carry this revolutionary tech. While Apple opted for Face ID, Samsung postponed the use of display fingerprint reader to the Galaxy S10.

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In 2016, LG Innotek announced a new fingerprint sensor which would sit on the phone's bezels
Finally, the world's first commercial phone with the in-display fingerprint sensor was the Vivo X21. And since then, it has been seen in the hugely expensive Huawei Porsche Design Mate RS and will be seen in the upcoming Xiaomi Mi 8.

How Does the In-display Fingerprint Sensor Really Work

An in-display fingerprint sensor uses an optical fingerprint sensor to capture the fingerprint data and is embedded under the phone's screen. The Vivo X21 and the Xiaomi Mi 8 use Synaptics' Clear ID sensor for high-resolution fingerprint scanning. The Clear ID sensor, which is a CMOS chip named Clear ID FS9500, is supported only on OLED and AMOLED displays.

The Vivo X21 uses Synaptics' Clear ID sensor for high-resolution fingerprint scanning

Synaptics Clear Id Optical Fingerprint Sensor Png

It works by capturing the reflected light of the fingerprint through the OLED pixels. So, when you touch the phone's screen, the display lights up to illuminate the fingerprint. The sensor then captures a high-res scan of your fingerprint through the light reflected from the gaps between the pixels. 

To ensure that the fingerprint data is being read accurately by the sensor, you'd need to press the screen slightly. This is done so that the sensor is able to differentiate between the ridges and valleys of each fingerprint. 

In Display Fingerprint Sensor 10
To ensure that the fingerprint data is being read accurately by the sensor, you'd need to press the screen slightly
Interestingly, the fingerprint matching is done through Synaptics' Quantum Matcher software, instead of the in-house Match-In-Sensor technology. Meanwhile, the fingerprint sensor uses the host's sensors to illuminate the area and activate the scanner. 

Here's a Video Showing Teardown of the In-display Fingerprint Sensor


However, Synaptics' Clear ID optical sensor is not the only one in the market. In March 2018, Goodix started shipping its own version of an optical in-display fingerprint reader. The Huawei Porsche Design Mate RS is the first commercially available phone to feature Goodix's in-display fingerprint sensor.

This sensor also works in a similar way to the Synaptics's FS9500 and claims to have a false acceptance rate of 0.002%.

Advantages of In-Display Fingerprint Sensor

Magically activating the fingerprint sensor on the phone's screen when needed is a fascinating tech. With many manufacturers opting to shift the fingerprint sensors to the rear of the phone, it raised quite a number of issues. 

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The rear fingerprint sensor of the Galaxy S9

For one, if the phone is lying on your desk then you'd have to pick it up to unlock it. The situation gets worse if the phone is hooked to a car mount

Secondly, with rear fingerprint sensors, you can never be sure that you're hitting the right spot. After all, even seasoned phone manufacturers (read Samsung and Nokia) can sometimes mess up the position of the fingerprint reader.

Even seasoned phone manufacturers can sometimes mess up the position of the fingerprint reader

Since in-display fingerprint scanners are usually situated at the bottom of the screen, it's easily accessible and more convinient.

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In-display fingerprint sensors claim to work for both dry, wet or cold fingers

Other than that, in-display fingerprint sensors claim to work for both dry, wet or cold fingers. Plus, optical sensors are thin and don't contribute much to the thickness of the phone. 

More importantly, they are fast. In fact, Synaptics's Clear ID claims to match the fingerprints in 0.7 seconds flat. If you were to compare it with Face Unlock, it takes an average of 1.4 seconds to scan a face.

What Are Its Limitations

As with any new tech, it takes a few iterations to get refined and the same holds true for the in-display fingerprint sensor. It's marginally slower compared to traditional fingerprint scanners. And sometimes, the reader doesn't seem to recognize the registered fingerprints.

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In-Display Fingerprint scanners are marginally slower compared to conventional scanners
Meanwhile, application of any type of tempered glass may most likely give inaccurate results or will cause the sensor to misbehave.  

Are There Any Potential Security Issues

On the security front, the Clear ID in the Vivo X21 is accompanied by a robust anti-spoofing system. Since it's an optical sensor and not a capacitive one, it won't be able to sense a pulse, due to which it can be duped with fake scans.

Enable 2Fa In Firefox

Thankfully, the onboard security measures are smart enough to detect spoofed fingerprints. Other than that, it also depends on the OEMs on how they scale up the authentication measures.

However, it's a bit early to comment on the security of these scanners. Time and additional security tests will undoubtedly yield a far better picture.

Our Experience With the In-Display Fingerprint Sensor

We tried the in-display fingerprint sensor on the Vivo X21 and needless to say, the experience was almost surreal! To be able to place your finger on the glass while the screen and the sensor do its mumbo-jumbo is a one-of-a-kind experience. 

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The Vivo X21 has a thumb-size icon which stays lit most of the time
The phone has a thumb-size icon which stays lit most of the time. All you have to do is place your registered finger on top of it.

Once the phone unlocks, you won't know where the sensor is until you use an authentication app like LastPass which requires your fingerprints. 

How Does In Display Or On Screen Fingerprint Sensor Work
How Does In Display Or On Screen Fingerprint Sensor Work

Unlike the conventional scanner, the in-display fingerprint doesn't always work accurately. One out of seven times the scanner refused to open the door to the phone.

Hello, Future!

With full view display becoming a ubiquitous feature in smartphones, it was high time that the handy fingerprint sensor saw a major upgrade. And with Qualcomm introducing its own variant of ultrasonic in-display fingerprint sensors, there's no doubt that the in-display fingerprint sensor will most likely be the newest trend in the smartphone world.

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Namrata Gogoi

Written By

Namrata Gogoi

An engineer turned tech writer, Namrata used to write software codes before turning to a career in tech- writing. She is passionate about travelling, food and reading about cool new stuff. Apart from that, she holds a bachelors degree in I.T and hails from Guwahati.