Since the discovery of the piezotronic effect─arising from the coupling between piezoelectricity and semiconducting properties─most studies have focused on single nano/microstructures or thin films. Here, we report the first experimental evidence of piezotronic behavior in devices based on ZnO nanonets integrated on flexible Kapton substrates. These nanonets consist of two-dimensional networks of randomly oriented ZnO nanowires, with no preferential alignment of the c-axis. The devices were subjected to controlled mechanical loading, including uniaxial tension and bending, under both tensile and compressive strain. We show that the first application of tensile strain above a critical threshold (∼0.3%) induces an abrupt increase in conductivity by 3 to 8 orders of magnitude. This behavior is attributed to the strain-induced subdivision of the nanonet into two effective subnetworks with opposite c-axis orientations, combined with the suppression of potential barriers at nanowire–nanowire junctions by the piezopotential. Upon further elongation, the electrical response becomes dominated by piezoresistive effects. As a proof of concept, mechanically gated transistors based on ZnO nanonets were demonstrated and directly compared with conventional potential-gated transistors. The mechanically gated devices exhibit an ON/OFF ratio approaching 108 for strains as small as ∼0.4%, whereas an ON/OFF ratio of only ∼105 is obtained in a back-gated configuration under a gate voltage of −65 V. These results demonstrate that randomly oriented nanowire networks can sustain strong piezotronic effects, paving the way toward robust, flexible devices based on collective nanostructures rather than single elements.
Sharma et al. (Tue,) studied this question.