Fraunhofer FEP develops OLED microdisplays as high-precision optical fingerprint sensors
Reporter : Hana Oh(HanaOh@ubiresearch.com)
Fraunhofer FEP has been developing various application-specific OLED microdisplays based on OLED-on-silicon technology successfully for many years. This unique technology enables the high-precision integration of an OLED as light source on a microchip. Moreover this microchip can be designed with further sensor elements, e.g. photodiodes. By this, objects can be illuminated and at the same time the reflected light detected and analyzed. Such microdisplays can be integrated into interactive data eyeglasses as a “bi-directional microdisplay”: the tiny display projects the information for augmented-reality applications whereas the camera function detects the viewing direction – thus the content can be controlled by eye-movements.
The fingerprint sensor uses this bidirectional functionality of light-emission and –detection as well: the finger gets illuminated and the reflected light will be detected and analyzed.
Bernd Richter, deputy division manager for OLED microdisplays and sensors at Fraunhofer FEP explains: “We have used an extra-thin encapsulation for the chip of this fingerprint sensor. Thereby the distance between finger and image sensor has been minimized and the fingerprint can be captured excellently. Thus, an additional imaging optics is not necessary for this application.”
The first prototype has a native resolution of 1600 dpi – this is three times more than typically required by the FBI. This high spatial resolution enables the identification even of smallest sweat pores beside the typical papillary lines, which can be used to increase the security.
One of the most promising applications of this new kind of sensor is the user verification in mobile devices. Because of the particularly high resolution in comparison to the typically used capacitive fingerprint sensors these devices are much less vulnerable to so-called spoofing (the manipulation by “false fingers”).
Another nice side effect is the opportunity for using the active area as a normal display e.g. for branding, displaying logos or notifications.
<High resolution OLED-on-silicon fingerprint sensor, Source: Fraunhofer FEP>