On-screen fingerprint sensor with optically and electrically tailored transparent electrode patterns for use on high-resolution mobile displays
Journal
Microsystems & Nanoengineering
Date
2020.11.02
Abstract
In this study, a mutual capacitive-type on-screen fingerprint sensor, which can recognize fingerprints on a display screen to provide smartphones with full-screen displays with a minimal bezel area, is fabricated. On-screen fingerprint sensors are fabricated using an indium tin oxide transparent conductor with a sheet resistance of ~10 Ω/□ and transmittance of ~94％ in the visible-wavelength range and assembled onto a display panel. Even at this high transmittance, the electrodes can degrade the display quality as they are placed on the display. The interference between periodic display pixel arrays and sensor patterns can lead to the Moir？ phenomenon. It is necessary to find an appropriate sensor pattern minimizing the Moir？ pattern while maintaining the signal sensitivity. To search for appropriate patterns, a numerical calculation is carried out over wide ranges of pitches and rotation angles. The range is narrowed for an experimental evaluation, which finally determines the sensor design. As the selected sensor pitches are too small to detect capacitance variance, three-unit patterns are electrically connected to obtain a unit block generating a larger signal. By applying the selected sensor pattern and circuit driving by blocks, fingerprint sensing on a display is demonstrated with a prototype built on a commercial smartphone.