Types and Working of Fingerprint Scanner in Smartphones

After years of rumors and leaks, smartphones with a fingerprint scanner under the display are finally launched in 2018. It is the next big thing in the smartphone market. 


It’s been 2 years since we’re used these In-display fingerprint sensors, and we don’t know much about them, so in this article, we discuss fingerprint scanners.


And it looks and feels futuristic. But apart from the looks, is the in-display fingerprint scanner any good? And how does it compare to the common capacitive fingerprint scanner? 


These fingerprint scanners are used not only in mobiles but also in many other gadgets and electronic products for security purposes.


Basically, there are 4 types of fingerprint scanners present in the market.

Types of Fingerprint scanners:

1.Optical scanner

2.Capacitive or CMOS scanner

3.Ultrasonic Fingerprint scanner

4.Thermal scanner


Human being’s fingerprints are actually very unique and no two people will have the same fingerprints. 


Even identical twins will have slightly different fingerprints. So having a fingerprint lock to protect the personal information on our phone is a really good idea. 


Fingerprint scanners work by capturing the pattern of ridges and valleys on your finger. 


The information is then processed by the phone’s pattern analysis and matching software, which then compares it to the list of already registered fingerprints on the phone. 


And if a successful match is found, your identity will be verified, and access will be granted to unlock the phone.


Types of Fingerprint scanners used in Smartphones:

There are actually 3 different types of fingerprint scanners commonly used in phones.

1.Optical Fingerprint Scanner

2.Capacitive Fingerprint Scanner

3.Ultrasonic Fingerprint Scanner


Let’s discuss them one by one.

1.Optical Fingerprint Scanner:

optical fingerprint scanner

The Optical Fingerprint Scanner, as the name suggests, an optical fingerprint scanner that uses a light source usually an LED to illuminate the finger. 


The reflected light is then captured by a light-sensitive microchip to create a digital image of your fingerprint. 


So basically, these scanners just make a photocopy of your finger. The major drawback is that it can easily be fooled with just a high-resolution photograph of your fingerprint. 


Also, it is bulky. So most modern smartphones don’t use optical sensors. It was first used in the Pantech Gi 100 which was launched way back in 2004 but since then it has slowly phased out. 


Optical In-display Fingerprint Scanner Synaptics recently introduced a new type of optical in-display finger scanner at CES 2018. 


It is now being used in a bunch of Chinese Smartphones like the OnePlus 6T, Vivo X21, and Huawei Mate 20 Pro, to name a few. 


It is much smaller but works exactly like the normal optical sensor. The only difference is, the sensor is actually placed under the display and the display itself acts as the light source to illuminate the finger. 


This is why we see those cool light animations when the phone is unlocked. 


The main advantage of this fingerprint scanner is that it can be placed anywhere under the screen or if required the whole screen can be used as a fingerprint scanner and also it works well even with wet fingers Sounds futuristic right? 


But it has a few major flaws though It works only with OLED screens and doesn’t work with LCDs. This is because LCD screens don’t allow light to pass through them. 


But for the optical scanner to work, light has to actually pass through the screen and reach the fingerprint scanner placed below it. 


Another potential issue is that this scanner does not work well with screen protectors. So you might have trouble finding one that’ll work. 


Also, if the display is damaged it would cost more to repair since the scanner is now integrated with the display. 


2.Capacitive Fingerprint Scanner 

capacitive fingerprint scanner

The Capacitive fingerprint scanners are the most commonly used fingerprint scanners in recent smartphones. 


These scanners take advantage of the fact that human skin is a good conductor of electricity. The scanner is actually made up of an array of capacitors. 


When we touch the scanner, the capacitors are charged. But this happens only at the ridges while the capacitors below the valleys remain uncharged. 


This difference in capacitance between ridges and valleys is then captured by the sensor to form the digital image of the fingerprint.


The advantage of a capacitive fingerprint scanner over optical ones is that it can not be easily fooled using just a photograph of the fingerprint. 


Also, it is faster and more accurate. But the capacitive scanner also has a few problems. It requires a clean finger to work properly, as something like dust or sweat can affect the conductivity of the finger. 


Also, it is costlier And doesn’t work when placed under the screen. It is also not completely foolproof and can be fooled by using a mold of our finger. 


3.Ultrasonic Fingerprint Scanner:

ultrasonic fingerprint scanner
Image source: Qualcomm

The Ultrasonic Fingerprint Scanner The Ultrasonic scanners are the newest entry in-display fingerprint scanning technology. 


It uses ultrasound to scan and capture the 3D fingerprint data similar to how bats and dolphins use echolocation to find and identify objects. 


This generates a highly detailed 3D surface map of the fingerprint which is extremely difficult to imitate or spoof. There is virtually no limitation to where the scanner can be placed inside a smartphone. 


As it can work even when placed under the glass screen, metals, or even plastics. It also works well with common contaminants like sweat, dust, and hand lotion to create a more accurate scan than capacitive scanners.


The ultrasonic scanner is currently provided by Qualcomm for mobile phone manufacturers like Samsung and others.


These Ultrasonic Fingerprint scanners are already seen in the Samsung S10 series, Note10 series, and recent Samsung Galaxy S20 series.


It is not as consistent as a normal capacitive scanner and is also considerably slower. 


Also, read the Top 15 sensors used in smartphones here

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