The Holst Centre, founded by Imec, has developed a new large-area optical fingerprint sensor that is over 70% transparent. Thats making it ideal for integrating on top of LCDs, allowing a wider range of display applications to incorporate biometric security.
The idea of integrating fingerprint scanners into displays is more and more popular in smartphones. These applications place a sensor under a transparent OLED array which acts as both the display and light source for the fingerprint reading.
However, used in automotive applications, public transport systems and cash machines they are more opaque and need a backlight, so are not suited to below-display fingerprint sensors. For that use the sensor must be placed on top of the display which means it needs to be highly transparent so that the display can still be seen.
At 70% transparency in the visible region, the new prototype is the most transparent large-area optical fingerprint sensor at the moment.
It is based on a proven combination of organic photodiodes (OPD), thin-film barrier and oxide thin-film transistors (TFTs) pioneered by Holst Centre.
To achieve the high transparency, the team uses photolithography to pattern the photodiode layer within each pixel, creating microscopic islands of photosensitive material.
The transparent sensor offers high resolution and dynamic range with a low dark current, ensuring excellent sensitivity even in low light conditions.
It can also be produced in large sizes for example to read palmprints or 4 fingerprints at once. This combination of size and performance enables compliance with FAP 60, the FBI’s most-stringent certification category.
It also allows the sensor to work as a document scanner, for example allowing a single system to read passports and fingerprints while also providing user guidance.
Moreover, the new sensor can be used in combination with the highly transparent capacitive touch panels commonly used in LCD screens, enabling simultaneous touch and biometric functionality.
As with Holst Centre’s previous fingerprint sensors, the transparent sensor is also capable of detecting a heartbeat while reading a fingerprint for liveness detection.
Changes to the photodiode chemistry would allow the sensor to work in the near infrared to detect the pattern of veins in the hand, offering additional ways to verify a person’s identity.