Univ. Grenoble Alpes, CEA, LETI, MINATEC Campus, Grenoble, France, Nanostructures and Synchrotron Radiation Laboratory, Univ. Grenoble Alpes, CEA, INAC-MEM, Grenoble, France

We report a simple and scalable fabrication process of flexible capacitive piezoelectric sensors using vertically aligned gallium nitride (GaN) wires as well as their physical principles of operation. The as-grown N-polar GaN wires obtained by self-catalyst metal-organic vapor phase epitaxy are embedded into a polydimethylsiloxane (PDMS) matrix and directly peeled off from the sapphire substrate before metallic electrode contacting. This geometry provides an efficient control of the wire orientation and an additive contribution of the individual piezoelectric signals. The device output voltage and efficiency are studied by finite element calculations for compression mechanical loading as a function of the wire geometrical growth parameters (length and density). We demonstrate that the voltage output level and sensitivity increases as a function of the wire length and that a conical shape is not mandatory for potential generation as it was the case for horizontally assembled devices. The optimal design to improve the overall device response is also optimized in terms of wire positioning inside PDMS, wire density, and total device thickness. Following the results of these calculations, we have fabricated experimental devices exhibiting outputs of several volts with a very good reliability under cyclic mechanical excitation. © 2018 American Chemical Society.

flexible, gallium nitride, metal-organic vapor phase epitaxy, nanowire, piezoelectricity, self-powered, sensor

Capacitive sensors, Crystallography, Electric sensing devices, Epitaxial growth, Gallium nitride, Metallorganic vapor phase epitaxy, Microchannels, Nanowires, Nitrides, Organometallics, Piezoelectric devices, Piezoelectric transducers, Piezoelectricity, Polydimethylsiloxane, Sapphire, Sensors, Silicones, Vapor phase epitaxy, Wire, flexible, Gallium nitrides (GaN), Mechanical excitations, Metal-organic vapor phase epitaxy, Piezoelectric sensors, Piezoelectric signals, Polydimethylsiloxane PDMS, Self-powered, Gallium compounds