Researchers develop transparent, flexible fingerprint sensor that detects tactile pressure and skin temperature

Researchers develop transparent, flexible fingerprint sensor that detects tactile pressure and skin temperature

A team of researchers from the Ulsan National Institute of Science and Technology (UNIST) in Korea have developed a capacitive fingerprint sensor array which is transparent and flexible, with the capability to detect tactile pressure and finger skin temperature, making it potentially suitable for display integration in smartphones, according to an article published by Nature Communications.

Researchers from the Schools of Materials Science and Engineering and Electrical Engineering and affiliated with the Samsung Display-UNIST Center at the University built transparent, flexible electrodes formed from networks of hybrid nanostructures using ultra-long metal nanofibers and nanowires, which they say give the array high resolution, good transparency, and reliability even when subjected to mechanical bending. The sensor lets through more than 89 percent of visible light, which makes it appropriate for its integration into a display, and it provides a resolution of 318 capacitors per inch, easily satisfying the FBI standard for fingerprint extraction of 250 capacitors per inch. The researchers also say it operates with negligible performance degradation from the signal noise present in mobile devices, and the temperature sensor can be used for liveness detection when matching fingerprints.

“The sensing capability, in terms of capacitance variation (between a ridge and a valley) is up to 17 times better than that of an identical sensor structure using conventional ITO electrodes,” the researchers write in their report. “Furthermore, the low R s of the AgNF–AgNW hybrid electrodes can drive this sensor array at 1 MHz reliably to handle typical noise from mobile devices or displays. The demonstration of its integration with pressure and temperature sensors, all of which had transparent and flexible forms, indicates the potential for replacement of the activation button on smartphones.”

Samsung is reportedly set to offer an in-display fingerprint sensor in its forthcoming Galaxy S10 flagship smartphone, and the company also recently patented a combined button and in-display fingerprint sensor system. Both Samsung and Apple have reportedly been working on developing ultrasonic in-display fingerprint sensors, while in-display fingerprint systems currently available in smartphones tend to use optical sensors.

The market for in-display fingerprint sensors will surpass 300 million unites per year by 2022, according to HIS Markit projections.

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