Development of Double Schottky Piezotronic Nano-newton Force Sensor based on Porous ZnO Nanorod Arrays

Force sensors based on piezotronic effect have received significant attention for the application in the internet of things, wearable electronics, biomedical engineering, and high-electron-mobility transistor due to their high sensitivity, fast response, and low energy consumption. The piezotronic force sensors rely on the current changes manipulated by the piezo-potential built at the Schottky interface, where most of them are working based on single-Schottky device, implying that the signals can only be read at either positive or negative bias. Contrarily, Double Schottky based piezotronic force sensors provide a possibility, allowing two modes both at positive and negative bias can be operated within one sensor unit for the advanced micro/nano electronic devices. Among the piezoelectric material, ZnO has been widely developedin applications such as sensors, photocatalysis, and energy harvesting because it is adaptable in multiple nanostructureswith piezotronics/ piezo-phototronic properties. In this study, intrinsic n-type ZnO and p-type Sb-doped ZnO nanorods were demonstrated to perform single and double Schottky piezo-tronic force sensor devices by applying ultra-low compressive force ranging from 20nN to 100nN with conductive atomic force microscopy (C-AFM). To improve the sensitivity of the force sensors, hydrogen annealing was performed to make porous structure to enhance the piezoelectricity of ZnO. To further clarify the contribution from porous structure, oxygen and argon annealing at different temperatures was performed to explore the influence of crystallinity, defects, and carrier concentrations on the sensitivity.In this study, the mechanisms of electrical transport of single and double schottky piezo-tronic force sensors have been comprehensively investigated.