Fig. 1: Device design and working mechanism of dual-modal piezotronic transistor (DPT).

a Schematic diagrams of two traditional structures of piezotronic transistors illustrating the mechanism of (I) the vertical structure for vertical force sensing and (II) the lateral structure for lateral strain sensing. Buckling effect occurred in vertical structure decreases the piezoelectric potential and leads to an uneven potential distribution at terminals, which has negative impact on piezotronic effect. b Design of the DPT with two working modes for (I) vertical force sensing and (II) lateral strain sensing. The mode for vertical force sensing is inspired by suspension bridge, in which the vertical force is transformed and amplified to a lateral force that elongates the nano/microwire and avoids the problem of buckling effect in traditional vertical structure. This makes DPT have a lateral structure but can sense vertical force with a high sensitivity. The corresponding energy band diagrams for the piezotronic modulation of Ag/n-ZnO Schottky junction at the contact interfaces are shown in the boxes with dotted lines. \({E}_{{{{{{\rm{C}}}}}}}\) and \({E}_{{{{{{\rm{V}}}}}}}\) are respectively the conduction and valence bands of the ZnO; the dotted line is the Fermi level (\({E}_{{{{{{\rm{F}}}}}}}\)) of the electrodes; \(\Delta {\varphi }_{{{{{{\rm{piezo}}}}}}+}\) and \(\Delta {\varphi }_{{{{{{\rm{piezo}}}}}}-}\) indicate the change in Schottky barrier height induced by positive and negative piezoelectric polarization charges, respectively.