Piezoelectric Energy Harvesting Devices: An Alternative Energy Source for Wireless Sensors

Figure 5

(a) Schematic definition of an NW and the coordination system. (b) Longitudinal strain ε _z distribution in the NW after being deflected by an atomic force microscopy (AFM) tip from the side. (c) The corresponding longitudinal piezoelectric-induced electric field Ez distribution in the NW. (d) Potential distribution in the NW as a result of the piezoelectric effect. (e and f) contacts between the AFM tip and the semiconductor ZnO NW (boxed area in (d)) at two reversed local contact potentials, showing reverse- and forward-biased Schottky rectifying behavior, respectively. This oppositely biased Schottky barrier across the NW preserves the PZ charges and later produces the discharge output. The inset shows a typical current-voltage (I-V) relation characteristic of a metal-semiconductor (n-type) Schottky barrier. The process in (e) is to separate and maintain the charges as well as build up the potential. The process in (f) is to discharge the potential and generate electric current [62].