A new strategy to produce smartphone-integrated fingerprint sensor arrays that simultaneously detect tactile pressure and finger skin temperature is described in Nature Communications this week. The sensors, which are demonstrated in smartphone displays, could enable users to place their finger anywhere on a display for identification purposes as opposed to using an activation button.

Transparent fingerprint sensors are highly sought after for the consumer electronics market. The current technology, however, is hindered by critical design limitations, such as the need to develop transparent electrodes with high optical transmission and high electronic conductance.

Jang-Ung Park and colleagues have devised a new approach for fabricating flexible, transparent and multifunctional sensor arrays. The secret to their design is the creation of new transparent electrodes based on a random hybrid network nanostructure consisting of ultra-long silver nanofibers and fine silver nanowires. This network shows high optical transmission, low electrical resistance and is extremely resistant to mechanical bending. When incorporated into a fingerprint sensor array, the result is a high-resolution device capable of accurately and reliably detecting the ridge and valley regions of a fingerprint during a touch condition.

The authors demonstrate the applicability of their new technology for mobile devices by integrating the fingerprint sensor arrays, pressure-sensitive transistors, and temperature sensors into smartphone displays. This suggests that the sensors may have the potential to replace finger-print activation buttons in the future.