Graphene nanoparticle strain sensors with modulated sensitivity through tunneling types transition.

Highly sensitive strain sensors show great potential for use in wearable health monitoring, autonomous intelligent robots and biomimetic prosthetics. The current resistive strain sensors mainly work through piezoresistors. Here, the robust tunneling mechanism based nanoscale strain sensors with high sensitivity are reported. The strain sensors are fabricated from graphene nanoparticle film. The sensitivity of graphene nanoparticle strain sensors could be tunable through the modulation of tunneling type, suggesting a theoretical support in performance optimization of tunneling strain sensors. The output characterization indicates the direct tunneling (DT) and Fowler-Nordheim tunneling (FNT) are dominant for charge carrier transport in the low voltage and high voltage regions, respectively. It is found that gauge factors are ∼79 at low voltage of 0-4 V, and ∼110 at high voltage of 20-40 V, showing profound dependence on DT and FNT types. The strain sensor bearing 0.3% strain shows a great stability over 100 cycles at bias voltage of 1 V and 40 V, respectively. An integrated strain sensor array with 5 × 5 patterned graphene nanoparticle film on a polyethylene terephthalate substrate is fabricated and demonstrates great spatial strain distribution, guiding the design for flexible and transparent strain sensor e-skins.