Piezoresistive strain sensing with flexible MoS2 field-effect transistors

We demonstrate piezoresistive strain sensors based on flexible MoS₂ field-effect transistors made from a highly uniform large-area trilayer film. The origin of the piezoresistive effect in MoS₂ is explained to be a strain-induced band gap change, as confirmed by optical spectroscopy. The results are in good agreement with recently reported simulations and spectroscopic studies on strained exfoliated MoS₂. In addition, the strain sensitivity can be tuned by over one order of magnitude via modulating the MoS₂ Fermi level with an applied gate voltage. The gate-tunable gauge factors can be as high as -40, comparable to polycrystalline silicon, but for a much thinner active layer (~2 nm). For practical sensing applications, the gate-tunable piezoresistivity is a useful property of transistor-based devices, because the relative sensitivity to strain can be adjusted by changing the gate voltage.