How do in-screen fingerprint sensors work?

Credit: ID 127127404 © Artem Medvediev | Dreamstime.com

Fingerprint sensors are one of the most popular forms of biometric security when it comes to smartphones. Here’s everything you need to know about optical, capacitive, ultrasonic and in-display fingerprint sensors and how they work.

What kind of fingerprint sensor does my phone have?

Regardless of whether your phone’s fingerprint sensor is built into the display, it’s still inevitably going to fall into one of three broad categories: optical, capacitive or ultrasonic.

How do optical fingerprint sensors work?

Optical fingerprint sensors are one of the more simple forms of biometric security out there. They rely on using an LED to illuminate your finger and then capturing that 2D image data using a sensor. Once it has captured that data, an optical fingerprint sensor can then compare subsequent image data against it to determine whether there is a match.

Credit: HTC

How do capacitive fingerprint sensors work?

fingerprint sensors are slightly more advanced. Rather than use light to map out the surface of your fingerprint, they use electricity. A regular capacitive fingerprint sensor relies on an array of capacitor plates to capture what any individual fingerprint looks like. Essentially - a capacitive sensor uses capacitors to map out the areas of your fingerprint which are more and less conductive. It then uses that as a basis for identifying subsequent samples.

Right now, capacitive fingerprint sensors are the most common form of fingerprint sensor in smartphones.

How do ultrasonic fingerprint sensors work?

Like the name suggests, ultrasonic fingerprint sensors use ultrasonic waves to map out a three-dimensional image of your fingerprint in the same that ultrasonic waves are used to in fields like medicine.

In theory, ultrasound presents several key advantages over the other fingerprint scanning technologies due to its ability to detect things like blood flow and also work more reliably in non-ideal conditions, for example if your hands are dirty or wet.

Which type of fingerprint sensor is the best?

I mean, for most everyday users, the best fingerprint sensor is going to be the one available to them. But if you’re asking which is the most versatile and secure, then ultrasonic is probably going to be the way to go.

On paper, at least, it’s more reliable than the other options and the fact that it’s capturing a three dimensional fingerprint rather than a 2D one does suggest it would be more difficult to spoof.

[Related: 3D vs 2D Face Unlock: Which Is More Secure?]

How do in-screen fingerprint sensors work?

Credit: Oppo

Currently, there are both optical and ultrasonic in-screen fingerprint sensors that can be found in modern smartphones.

In-display optical sensors work by capturing an image of your fingerprint based on the light reflected from the gaps between the pixels on your phone’s display.

In-display ultrasonic sensors work by projecting ultrasonic waves through the surface of the screen, since ultrasonic waves can travel through solid materials in a way that light can’t.

How secure are in-screen fingerprint sensors?

Any in-screen fingerprint sensor is only as secure as the component itself. There are several different in-display sensors on the market, some of which are optical and some of which are ultrasonic.

Qualcomm say their Sense ID ultrasonic in-display sensor has a 1% error rate.

Goodix’s in-display fingerprint sensor has a 0.002% false acceptance rate and a false rejection rate of less than 2%.

However, it’s worth remembering that - in consumer electronics especially - convenience often trumps security. As long as the sensor in question at least seem secure enough that you don’t have to think about it, most consumers are likely to opt for a faster and more reliable option over a more secure one.

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Fergus Halliday
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