Highly sensitive and flexible strain sensors based on vertical zinc oxide nanowire arrays

In this paper, a highly sensitive strain sensor with vertically aligned zinc oxide (ZnO) nanowire arrays on polyethylene terephthalate (PET) film was reported. The device fabrication includes conventional photolithography, metallization, and ZnO nanowire growth through a hydrothermal method. I-V characteristics of the device were highly nonlinear due to the Schottky contact between the nanowire and the gold (Au) electrode. The conductivity of the device is significantly tuned by the change of ZnO/Au Schottky barrier that reflects the strain-induced piezoelectric potential. A gauge factor up to 1813 was obtained from this strain senor, which is higher than the previously reported device based on a lateral ZnO microwire. Theoretical analysis of the piezotronic effect shows that the working nanowire with the largest conductivity change dominates the performance of the device. The non-working nanowire has limited adverse effect on the performance, which explains the robust performance of this novel strain sensor. The stability and fast response of the sensor were also investigated. The sensitive and robust strain sensor is expected to find applications in civil, medical, and other fields.