The ideal pressure sensors can not only identify the pressure, but also feel the texture, elastic response, deformed curvature of the detected objects, just like we can distinguish an apple from a rubber ball just by simply touching their surfaces. Moreover, they should be invisible and can be readily used on any flat or complex surfaces of the objects.
To achieve the objective, we have discussed a type of new sensing mechanism based on Fowler-Nordheim tunnelling effect that could transduce a tiny material deformation caused by external pressure into a pretty large read-out signal change. This unique feature of small deformation to induce high sensitivity could greatly reduce the thickness of pressure sensors, thus decreasing their existing sense during human-computer interaction process.
Based on this new idea, in this work, we have developed a kind of composite material composed of urchin-like hollow carbon spheres and polydimethylsiloxane. The composite material can be large-scale fabricated into a thin transparent pressure sensing film with high sensing sensitivity (260.3 kPa-1 at 1 Pa), high sensing array density and temperature noninterference. What’s more, the minimum detection area can be as small as 31.7 square microns, which is only about 1/200 of the cross-sectional area of a human hair.
The reason why this sensor film has such excellent performance is inseparable from its F-N effect based transduction mechanism. At the start of the material design, we gave up the conventional concepts and tried to find a new sensing system that can obtain a large amount of signal change when feeling a very tiny deformation. To achieve this, we inspected the electrical characteristics of various quantum effects by using statistical amplification method and found that the F-N tunnelling effect from urchin-like hollow carbon spheres dispersed in polydimethylsiloxane can sense the inappreciable deformation change. Additionally, benefitted from the the F-N effect transduction mechanism and extremely low hollow structured filler loading, this composite pressure sensor still exhibits high transparency, high elasticity, skin-friendliness, excellent processability and temperature stability. The excellent comprehensive performance of the pressure sensor and its design concept may provide interesting practical applications on various surfaces, including human skin, monitors, cameras, displays, and broad data collection in big data technology.