On-screen fingerprint sensor with optically and electrically tailored transparent electrode patterns for use on high-resolution mobile displays

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/sq. and a transmittance of ~94% (~86% with the substrate effect) in the visible wavelength range, and assembled onto a display panel. Even at this high transmittance, the electrodes can degrade the display quality when they are placed on the display. The interference between periodic display pixel arrays and sensor patterns can lead to the Moire phenomenon. It is necessary to find an appropriate sensor pattern that minimizes the Moire 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 is used to finally determine the sensor design. As the selected sensor pitches are too small to detect capacitance variations, 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 block, fingerprint sensing on a display is demonstrated with a prototype built on a commercial smartphone. Capacitive fingerprint sensor modules have been developed that avoid visual clashing with the pixels of cell phone screens. Capacitive fingerprint modules profile how individual fingerprints change their ability to store small electrical charges. As their electrodes and cell screen pixels share similar intervals, a visual distraction known as a Moire pattern arises when the two are superimposed. Through calculations and experimentation, Hyun-Joon Kim-Lee and a team from the Samsung Advanced Institute of Technology in South Korea assayed a variety of electrode intervals and rotations to find the combination with the least visual interference. The chosen electrode pattern interval was initially too small for fingerprint detection, an obstacle the team overcame by making groups of electrodes send and receive signals together. Further studies could bring capacitive fingerprint sensors to flexible devices or produce combination touch sensors.