R. Tao, G. Ardila, R. Hinchet, A. Michard, L. Montès and M. Mouis
IMEP-LAHC/Minatec, CNRS-Grenoble INP, UJF, 38016 Grenoble, France
The piezoelectric effect is the conversion of mechanical strain into electrical energy (direct effect) or, conversely, the production of mechanical deformation by an input electric field (converse effect). It is widely used in applications such as lighters, speakers, medical ultrasound transducers, precise positioning systems, and many others, using mainly bulk materials.1 At a smaller scale, piezoelectric thin films are used in applications ranging from MEMS/NEMS actuators to resonators.2 Other applications include mechanical sensors and energy harvesters used typically for wireless sensor networks (WSNs), with the objective of monitoring human health, environment, or structures such as airplanes or buildings.3 The integration of energy harvesters in WSN systems, in particular, helps to develop battery-less autonomous systems or, in other cases, eliminate complex wiring.
The most used piezoelectric materials in these applications are PZT and AlN thin films.2 At the nanoscale, ZnO and GaN in the shape of nanowires (NWs) are the most studied materials because they are relatively easy to fabricate4 and because of their enhanced electromechanical properties: higher flexibility and higher piezoelectric coefficients compared to their ...