Elie Lefeuvre

Piezo-generator integrating a vertical array of GaN nanowires

We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

From single III-nitride nanowires to piezoelectric generators: New route for powering nomad electronics

Ambient energy harvesting using piezoelectric nanomaterials is today considered as a promising way to supply microelectronic devices. Since the first demonstration of electrical energy generation from piezoelectric semiconductor nanowires in 2006, the piezoelectric response of 1D-nanostructures and the development of nanowire-based piezogenerators have become a hot topic in nanoscience. After several years of intense research on ZnO nanowires, III-nitride nanomaterials have started to be explored thanks to their high piezoelectric coefficients and their strong piezo-generation response. This review describes the present status of the field of piezoelectric energy generation with nitride nanowires. After presenting the main motivations and a general overview of the domain, a short description of the main properties of III-nitride nanomaterials is given. Then we review the piezoelectric responses of III-N nanowires and the specificities of the piezo-generation mechanism in these nanostructures. Finally, the design and performance of the macroscopic piezogenerators based on nitride nanowire arrays are described, showing the promise of III-nitride nanowires for ultra-compact and efficient piezoelectric generators.

Power and frequency bandwidth improvement of piezoelectric energy harvesting devices using phase-shifted synchronous electric charge extraction interface circuit:

This article presents a new way to control the synchronous electric charge extraction interface circuit, which was formerly developed to improve the performances of piezoelectric vibration energy harvesting devices. An analytical model for energy harvesting systems including this new technique, called phase-shift synchronous electric charge extraction, is proposed. This model is then used to study the properties of this new control scheme in the cases of low and high electromechanical coupling. Contrary to the synchronous electric charge extraction technique which exhibited significant improvements in terms of harvested power for piezoelectric devices with low electromechanical coupling, the phase-shift synchronous electric charge extraction technique shows capability to increase the harvested power up to the theoretical limit for piezoelectric devices with high electromechanical coupling. In addition, the presented theoretical results show that the frequency bandwidth of piezoelectric energy harvesting devices may be substantially increased.

Innovative Energy Harvester Design Using Bistable Mechanism With Compensational Springs In Gravity Field

The purpose of the presented work is to introduce the novel design of electrostatic energy harvester using bistable mechanism with compensational springs in gravity field capable of providing the output of several μW under the excitation of extremely small amplitude (up to 0.2g) and low frequency (10-100Hz). Presented energy harvester uses the bistable hysteresis modification to achieve low-frequency low-amplitude sensibility. It was demonstrated with finite element modelling (FEM) that hysteresis width produced by bistability is changing with a constant linear coefficient as a function of a compensational spring stiffness and thus a device sensitivity could be adjusted to the minimum point for the amplitude of external excitation. Further, highly non-linear bistable double curved beam mechanism assures the high sensitivity in frequencial domain due to the non-defined bandwidth. The equivalent circuit technique is used for simulating the device performance.

Nitride Nanowires: From Rigid to Flexible Piezo-generators

Here we employ self-assembled Mg-doped GaN nanowires(NWs) grown by plasma assisted molecular beam epitaxy on Si(111) substrates to fabricate piezogenerators. We will first discuss the fabrication and testing of rigid nanowire-based generators and then a flexible generator prototype will be shown.