Search

The question of the length dependence of the electromechanical response of semiconducting (SC) piezoelectric nanowires (NWs) was explored. We identified a new physical mechanism of piezoresponse saturation, which originates from the combination of the influence of interface traps and piezoelectric polarization in the depleted NW. Our results are in better qualitative agreement with experimental observations than presently existing theories. To do so, we used the finite element method to simulate the coupled set of equations describing mechanical, piezoelectric and SC properties. In order to reduce the number of parameters, simulations focused on the case of uniform ZnO NWs grown along the c-axis. Saturation was explained by the incapacity of surface traps to maintain depletion along the whole NW beyond a certain length, as a result of the electric potential shift induced by piezoelectric polarization. An analytical model was developed to support this analysis. It provided the dependence trends of saturation length and piezoresponse as a function of NW dimensions, doping level, surface traps density and crystal polarity, as well as with external pressure, in fair agreement with simulation results. Moreover, we discovered that one consequence of this mechanism was that crystal polarity had an impact on the smoothness of the radius-dependent transition between high and low piezoresponse under axial stress. These results have important implications for the optimization of electromechanical sensors and nanogenerators based on piezoelectric SC NWs and related composite materials.

Semiconducting piezoelectric nanowires (NWs) are promising candidates to develop highly efficient mechanical energy transducers made of biocompatible and non-critical materials. The increasing interest in mechanical energy harvesting makes the investigation of the competition between piezoelectricity, free carrier screening and depletion in semiconducting NWs essential. To date, this topic has been scarcely investigated because of the experimental challenges raised by the characterization of the direct piezoelectric effect in these nanostructures. Here we get rid of these limitations using the piezoresponse force microscopy technique in DataCube mode and measuring the effective piezoelectric coefficient through the converse piezoelectric effect. We demonstrate a sharp increase in the effective piezoelectric coefficient of vertically aligned ZnO NWs as their radius decreases. We also present a numerical model which quantitatively explains this behavior by taking into account both the dopants and the surface traps. These results have a strong impact on the characterization and optimization of mechanical energy transducers based on vertically aligned semiconducting NWs.

Zinc oxide (ZnO) nanogenerators have attracted increasing interest in the scientific community for use in energy harvesting and mechanical sensing applications. Understanding the interplay between piezoelectricity and semiconductor physics is fundamental to enhancing these devices’ performances, although direct characterization at the nanoscale is challenging. With this work, we present a new strategy to improve piezoresponse force microscopy (PFM) measurements and analysis. This strategy was applied to study the piezoelectric performances of ZnO nanowires grown on seed layers deposited by gravure printing onto flexible substrates. We demonstrate the influence of nanowire diameter and atomic force microscope (AFM) tip position on the piezoresponse amplitude. We also explain our results with simulations showing the importance of considering semiconducting properties in the analysis.

International audience; The formation process of ZnO thin films grown by pulsed-liquid injection metal–organic chemical vapour deposition (PLI-MOCVD) has a major impact on its morphological, structural, electrical and piezoelectric properties, but their correlation has not been elucidated yet nor decoupled from the thickness effects. In this work, we investigate the influence of the O2 gas and diethylzinc (DEZn) solution flow rates on the properties of ZnO thin films with a given thickness and grown on silicon. We show that the O2/DEZn flow rate ratio through the oxygen chemical potential significantly affects the O- and Zn-polarity domain distribution, their related size and shape, the chemical composition, and the incorporation of microstructural defects and residual impurities, resulting in a direct effect on the piezoelectric amplitude of ZnO thin films. In particular, the Zn-polarity domains are found to systematically exhibit a larger piezoelectric amplitude than the O-polarity domains, regardless of the O2/DEZn flow rate ratio. A comprehensive description recapitulating the formation process of ZnO thin films through three different regimes depending on the O2/DEZn flow rate ratio is further gained. These results demonstrate the crucial ability of the PLI-MOCVD system to tune the polarity of ZnO thin films along with other suitable properties for piezoelectric applications by carefully adjusting the O2 gas and DEZn solution flow rates.

ZnO nanowires are excellent candidates for energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. These nanowires are usually non-intentionally n-doped during their growth. The essential role of doping, surface traps and surface Fermi level pinning in the actual response of piezoelectric semiconductors has already been demonstrated. In order to go further, this paper investigates the influence of the density and of the dynamics of surface traps on such important parameters as the output generated potential and the effective piezoelectric coefficient. We implemented numerical simulations based on the finite element method by combining the mechanical, piezoelectric, and semiconducting characteristic of ZnO nanowires array based nanocomposites (the so-called vertically integrated nanogenerator configuration) operated in compression. It was found that a certain amount of surface traps was required to obtain a usable generated output potential from the studied devices in the range of dimensions and doping level reported in most experimental results. Moreover, the surface traps influence was strongly dependent on their dynamics. As a first step towards the analysis of traps dynamics, we compared the two extreme cases of ultra-slow and ultra-fast traps. The symmetry and asymmetry of the piezoelectric response and a comparison to thin film was also discussed. This study demonstrates that the realistic modelling of the piezoelectric response of semiconductor based transducers should account for traps dynamics effects.

International audience; The growth process and post-deposition treatment have strong effects on the structure of ZnO thin films, which can also significantly affect their electrical and piezoelectric properties. In this report, the effect of high temperature annealing under oxygen atmosphere on ZnO stacked thin films grown on silicon by pulsed-liquid injection metal-organic chemical vapor deposition is investigated in detail. By varying the annealing temperature from 600 to 1000 °C, the structural analysis reveals the occurrence of c-axis oriented grain coarsening and growth processes associated with the improvement of crystallinity and removal of carbon impurities. The electrical resistivity also strongly varies with thermal annealing. Those variations are accompanied by an enhancement of the piezoelectric amplitude measured by piezo-response force microscopy (PFM). Interestingly, the PFM measurements reveal the predominant development of O-and Zn-polar domains at low and high temperature annealing, respectively, originating from the anisotropic grain boundary velocity. The present findings show that the high temperature annealing under oxygen atmosphere in ZnO thin films can enhance not only its piezo-amplitude but also its Zn-polarity uniformity, which unambiguously leads to the improvement of its piezoelectric performance.

Online virtual conference; International audience; Piezoelectric semiconductor transducers based on nanowires (NWs) made of ZnO, GaN among other materials have drawn a lot of attention for energy harvesting and sensing applications. Despite the existence of experimental reports on the piezoelectric coefficient of ZnO NWs using Piezoelectric Force Microscopy (PFM), there is a lack of theoretical results predicting such measurements. Here we propose an experimental and a simulation framework consisting in the analysis of the exponential decay of a generated piezoelectric voltage pulse to extract the capacitance of ZnO NW based nanocomposites and the related. The theoretical results show a dependency on the NW radius, thus achieving high values (14 pC/N) at radius smaller than 70 nm.

Zinc oxide (ZnO) nanowires (NWs) are excellent candidates for the fabrication of energy harvesters, mechanical sensors, and piezotronic and piezophototronic devices. In order to integrate ZnO NWs into flexible devices, low-temperature fabrication methods are required that do not damage the plastic substrate. To date, the deposition of patterned ceramic thin films on flexible substrates is a difficult task to perform under vacuum-free conditions. Printing methods to deposit functional thin films offer many advantages, such as a low cost, low temperature, high throughput, and patterning at the same stage of deposition. Among printing techniques, gravure-based techniques are among the most attractive due to their ability to produce high quality results at high speeds and perform deposition over a large area. In this paper, we explore gravure printing as a cost-effective high-quality method to deposit thin ZnO seed layers on flexible polymer substrates. For the first time, we show that by following a chemical bath deposition (CBD) process, ZnO nanowires may be grown over gravure-printed ZnO nanoparticle seed layers. Piezo-response force microscopy (PFM) reveals the presence of a homogeneous distribution of Zn-polar domains in the NWs, and, by use of the data, the piezoelectric coefficient is estimated to be close to 4 pm/V. The overall results demonstrate that gravure printing is an appropriate method to deposit seed layers at a low temperature and to undertake the direct fabrication of flexible piezoelectric transducers that are based on ZnO nanowires. This work opens the possibility of manufacturing completely vacuum-free solution-based flexible piezoelectric devices.

Ambient electromagnetic and RF energy is an ubiquitous energy resource that is found everywhere but difficult to harvest because of the time-varying orientation of incoming radiations and the low efficiency of RF rectifiers resulting from a low input power density operation. In response to these two challenges that come with the design of rectennas for ambient energy harvesting, this paper discusses a figure of merit to evaluate the rectenna performance that combines the rectification efficiency, the radiation efficiency, and the spherical coverage of the antenna. To illustrate this proposed figure of merit, a rectenna with a strengthen RF-to-dc efficiency and also a full spatial coverage is designed using beam-forming networks. The resulting system is demonstrated for a wireless sensor mounted on a pole. To maintain a reasonable size of the prototype, a miniaturization technique of a $4 \times 4$ Butler matrix (BM) is investigated, which allows for the reduction of the footprint of the BM by 2 compared to its classical microstrip design counterpart at 2.4 GHz. The overall rectification efficiency and dc power patterns are reported for the elevation plane of one multidirectional rectenna at 2.4 GHz for an incident power density of $0.45\,\,\mu \text {W}\cdot \text {cm}^{-2}$ . It is shown that the system can triple the dc output power compared to a three-dipole counterpart occupying the same area. Furthermore, while the maximum harvesting capability at $1 \,\,\mu \text {W}\cdot \text {cm}-^{2}$ does not exceed $28\pi $ %.steradian in the literature, it reaches $43.6\pi $ %.steradian with the proposed demonstrator.

If human and fundamental rights are based on human dignity, but to the juridical persons can not be applied this figure, it is not understandable how the Colombian Constitutional Court, as interpreter of our Political Constitution, can be granted such privileges, generating doubts that drive this research, for which a bibliographic review was made on concepts such as a) natural person, b) legal entity, c) human rights, d) fundamental rights, e) human dignity and f) citizenship. Subsequently, the obtained results are described by constructing and validating, through expert criteria, an instrument to later investigate in N = 30 students of last semester of law their conceptions about fundamental rights. The progress of N = 4 lawyers who participated in a training strategy to advance their knowledge on these issues is also presented. It is concluded that students must advance in their conceptions about these aspects, since some conceptual gaps are detected, which are not identified in the lawyers that participated in the training strategy, which improve even more after the intervention. DOI: http://dx.doi.org/10.21017/Rev.Repub.2019.v26.a62

The NEREID project (“NanoElectronics Roadmap for Europe: Identification and Dissemination”) is dedicated to mapping the future of European Nanoelectronics. NEREID’s objective is to develop a medium and long term roadmap for the European nanoelectronics industry, starting from the needs of applications to address societal challenges and leveraging the strengths of the European eco-system. The roadmap will also identify promising novel nanoelectronic technologies, based on the advanced concepts developed by Research Centres and Universities, as well as identification of potential bottlenecks along the innovation (value) chain. Industry applications include Energy, Automotive, Medical/Life Science, Security, loT, Mobile Convergence and Digital Manufacturing. The NEREID roadmap covers Advanced Logic and Connectivity, Functional Diversification (Smart Sensors, Smart Energy and Energy for Autonomous Systems), Beyond-CMOS, Heterogeneous Integration and System Design as well as Equipment, Materials and Manufacturing Science. This article gives an overview of the roadmap’s structure and content., Thanks are extended to the support of the EU, which has been funded the NEREID project as a Cooperation and Support action for three years from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 685559.

ZnO thin films and nanostructures have received increasing interest in the field of piezoelectricity over the last decade, but their formation mechanisms on silicon when using pulsed-liquid injection metal–organic chemical vapor deposition (PLI-MOCVD) are still open to a large extent. Also, the effects of their morphology, dimensions, polarity, and electrical properties on their piezoelectric properties have not been completely decoupled yet. By only tuning the growth temperature from 400 to 750 °C while fixing the other growth conditions, the morphology transition of ZnO deposits on silicon from stacked thin films to nanowires through columnar thin films is shown. A detailed analysis of their formation mechanisms is further provided. The present transition is associated with strong enhancement of their crystallinity and growth texture along the c-axis together with a massive relaxation of the strain in nanowires. It is also related to a prevailed zinc polarity, for which its uniformity is strongly improved in nanowires. The nucleation of basal-plane stacking faults of I1-type in nanowires is also revealed and related to an emission line at about 3.326 eV in cathodoluminescence spectra, further exhibiting fairly low phonon coupling. Interestingly, the transition is additionally associated with a significant improvement of the piezoelectric amplitude, as determined by piezoresponse force microscopy measurements. The Zn-polar domains exhibit a larger piezoelectric amplitude than the O-polar domains, showing the importance of controlling the polarity in these deposits as a prerequisite to enhance the performances of piezoelectric devices. The present findings demonstrate the high potential in using the PLI-MOCVD system to form ZnO with different morphologies and polarity uniformity on silicon. They further reveal unambiguously the superiority of nanowires over thin films for piezoelectric devices.

International audience

finalist, Best paper award; International audience; This paper presents a modular and reconfigurable rectenna unitcell (RU) made up of an antenna, a rectifier and radiofrequency (RF) power combiners intended to form a scalable and adaptative beam-forming network, for autonomous passive tracking or RFID monitoring applications. The reconfigurable rectenna unitcell allows a dual mode operation thanks to both RF and DC possible combinations of multiple rectenna unitcells. On the one hand, the passive beam-forming operation, coming from the RF combination of multiple rectenna unitcells provides oriented communication or localization capabilities. On the other hand, the series DC connection of RF isolated rectenna unitcells delivers DC power to the system with high output voltage under low RF power densities. Prototypes of 4-edges rectenna unitcells are designed in the 2.4 GHz band. The operation of one individual RU is demonstrated, and it is shown that multiple RUs are suitable for RF energy harvesting, multiple-tag communication and tag localization.

International audience; This paper presents a miniaturized microstrip antenna on an air-filled paper substrate. The presence of air in the substrate accounts for low dielectric losses and a high dielectric thickness, resulting in a high radiation efficiency and a large bandwidth. In addition, the edge of the antenna is exploited to feed the antenna with a coplanar line that can be connected to a 50 coaxial probe. This original feeding technique permits the reduction of the frequency of resonance as the air gap increases. The antenna is further miniaturized with the insertion of a slot in the ground plane. As a result, a high degree of miniaturization can be obtained along with a high efficiency. The influence of the air gap and of the slot on the antenna's performances is investigated. Two prototypes with dimensions of 0.29 x 0.29 x 0.065 radiating at 2.45 GHz are fabricated with copper tape and silver ink and the antennas' performances are experimentally validated: a gain of 4.5 dBi and a front-to-back ratio of 9.5 dB are measured, corresponding to a radiation efficiency of 70%. Index Terms-Paper substrate, microstrip antenna, air gap, air-filled, miniaturization, light weight antenna, low cost.

This paper presents a compact paper-based rectenna with dual frequency operation. The rectenna is composed of a microstrip antenna designed on paper, in which an air gap is introduced between the patch and the ground plane to overcome the low-thickness and high-loss characteristics of the conventional paper substrate. This allows the microstrip antenna to reach a high radiation efficiency and a large bandwidth. Additionally, a miniaturization technique is utilized to reduce the antenna dimensions imposed by the low permittivity of the air. The absence of matching network between the antenna and the rectifier ensures a very compact size as well as limited insertion losses at the rectifier level and results in a high RF -DC conversion efficiency in the two frequency bands 1.8 and 2.4 GHz. The rectenna prototype shows experimental conversion efficiencies of 25 and 19 % at 1 $\mu \mathrm{W}/\mathrm{cm}^{2}$ and 55 and 44 % at 10 $\mu \mathrm{W}/\mathrm{cm}^{2}$ at 1.8 and 2.45 GHz, respectively, corresponding to output DC voltages of 208, 190 and 933 and 923 mV. Furthermore, output DC voltages of 93 and 550 $\mathrm{mV}$ are maintained over the band 1.75-2.6 GHz at 1 and 10 $\mu \mathrm{W}/\mathrm{cm}^{2}$ respectively. The rectenna prototype features a weight of 1.5 $\mathrm{g}$ and dimensions of 0.21 $\lambda_{o}\mathrm{x}0.21\lambda_{o}\mathrm{x}0.06\lambda_{o}$ .

International audience; This paper reports the fabrication of arrays of vertical piezoelectric nanowires which are individually contacted at their base, and demonstrates that an electrical response to strain can be obtained from individual nanowires from the array, without external biasing exploiting the piezotronic effect. Such a technology could thus be used for the fabrication of self-powered sensors for mechanical strain mapping, where each individually contacted nanowire would act as the strain sensing equivalent of a pixel. Lateral mapping resolutions in the micrometer range can be obtained. Here, the hydrothermal method was used to grow vertical ZnO nanowires selectively between two electrodes that had been patterned beforehand. For the sake of demonstration, nanowires deflection was produced by subjecting the array of nanowires to an incident lateral gas flow of controlled rate, which was switched on and off repeatedly across the sample while electrical response was measured. Different experimental configurations were tested in terms of flow rate, flow orientation, or nanowire position with respect to tube outlet. Experiments were carried out with compressed nitrogen and air. The experimental results are fully consistent with the piezoelectric and piezotronic response which can be expected with this geometry. Moreover, it is shown that the electrical response under nitrogen flow is a linear function of flow rate and that its sign provides information about flow direction. These results demonstrate the very promising prospects of this new technology for high-resolution mapping, with potential applications in gas or liquid flow sensing, fingerprints detection or human-machine interfaces.

En el municipio de San Antonio del Tequendama (Cundinamarca, Colombia) se esta incentivando la siembra del cultivo de lulo, pero se desconocen muchos aspectos relacionados con la fisiologia y el manejo de la especie en estas condiciones agroecologicas. El objetivo fue realizar el estudio del crecimiento y desarrollo del fruto de lulo cultivar var. Septentrionale. Para lo cual se marcaron flores en antesis y se hicieron nueve muestreos de frutos del tercio medio de las plantas cada 20 dias. En cada muestreo se determinaron las siguientes variables: masa fresca y seca de los frutos, firmeza, solidos solubles totales, acidez total titulable e intensidad respiratoria. A los 180 dias, despues de la antesis (DDA), los frutos alcanzaron la madurez de cosecha con una coloracion naranja intensa y una masa promedio de 209 g. El comportamiento de la masa fresca y la masa seca del fruto fue sigmoideo simple lo cual se ajusta a un modelo no lineal de tipo logistico. La acidez total titulable y los solidos solubles totales se incrementaron con el desarrollo del fruto, mientras que la intensidad respiratoria disminuyo y la firmeza aumento hasta los 80 DDA para luego disminuir hasta la cosecha. La tasa absoluta de crecimiento (TAC) se incremento rapidamente y alcanzo su maximo valor

session: Antenna and Propagation; International audience; The design of antennas on cellulosic flexible materials such as paper can be very challenging because of the limited thickness and the high losses in the Radio Frequency (RF) domain. In this paper, a novel patch antenna with an origami structure is proposed to address the null radiation efficiency obtained with the conventional paper-based structure. As the electromagnetic waves mostly travel in the air, ideal conditions such as no loss and a low dielectric constant allow for the asymptotic value of directivity of microstrip antennas to be reached with a 63 % experimental radiation efficiency. This flexible antenna can be used for RF energy harvesting or sensing applications due to the sensitivity of paper on atmospheric conditions.

session Rectifier and Rectennas; International audience; This paper introduces a novel rectenna with a double-sided ground plane microstiip antenna that has a bidirectional radiation pattern for ambient RadioFrequency (RF) energy harvesting. The microstrip antenna has a supplementary slot that enhances the aperture efficiency of a conventional rectangular patch antenna from 50% to 72% in simulation and allows for a high gain bi-directional pattern. With a maximum experimental gain of 7 dBi, the proposed rectenna can capture as much ambient RF power as a patch antenna and rectify it with an efficiency of 25.8% for a 0.15 nW/cm 2 power density, while being less sensitive to the energy source location. By duplicating the rectenna, two complementary radiation patterns can be obtained allowing incoming RF radiations with four different orientations to be collected.

session poster; International audience; This paper reports the experimental and numerical study of flexible piezoelectric transducers made of a thin active composite material (~3 μm thick) over a thin flexible metallic foil (~25 μm of stainless steel). The active piezo-layer consists of vertical ZnO nanowires (NWs) embedded into dielectric fillers of different composition. The voltage over a known resistance was measured with an automatic bending setup, and the corresponding power was computed and compared to numerical simulations as a function of load resistance and dielectric matrix in the composite structure. FEM simulations show that the output power can be higher than conventional thin-film devices. These results confirm previous findings and provide important guidelines to optimize flexible piezoelectric transducers for applications as sensors and generators for the Internet of Things. Comparison with a commercial thick-film piezoelectric energy harvester was also made experimentally.

International audience; ZnO and GaN semiconducting piezoelectric nanowires (NWs) have attracted much attention because of their improved mechanical and piezoelectric properties compared to bulk materials. They have been integrated into different devices ranging from sensors to energy harvesting devices. In this review article we focalize on the modeling of these nanostructures and devices: First, we synthesize the modeling studies at an individual level including the different approaches developed. Then we consider NW arrays integrated into devices for mechanical energy harvesting applications and the different modeling techniques, including finite element methods, analytical methods and equivalent circuit models, to estimate the performance and the optimization guidelines of such devices. Finally, composite materials integrating piezoelectric NWs and a dielectric matrix are also considered as a route for improved performance compared to piezoelectric thin films.

Best student paper award, session Rectenna Design; International audience; This paper introduces an original strategy to step up the capacity of ambient RF energy harvesters. The low rectification efficiency that comes from weak input power is enhanced through high gain antenna arrays that push the circuit to operate in a more efficient state. The prototype uses beam forming networks to build up a wide coverage since ambient energy can come from any direction, or the orientation of the rectenna may be unknown. By extending the operating range of rectifiers to higher input powers, the system operates as a very efficient narrow beam rectenna or as a synthetic high gain isotropic rectenna. The rectification efficiency pattern of one multi-beam rectenna, functioning in the 2.4 GHz band, is plotted and compared to a dipole rectenna's pattern. For a low incident power density of 4.10-5 mW.cm-2, the rectification efficiency is largely improved in any direction : from 2.6% with a dipole rectenna up to 14%.

session poster; International audience; This paper reports on the experimental and theoretical study of flexible piezoelectric transducers with an active area of ~1cm 2 made of a thin active composite material (~3μm thick) over a thin metallic foil (~25μm of Stainless Steel). The composite material structure is made of vertical piezoelectric nanowires (NWs) embedded into a PMMA dielectric matrix. The open circuit voltage was measured on different devices under manual and automatic bending. The performance was evaluated in function of the thickness of the top layer of PMMA in the composite structure of different devices. It was found that the output voltage increased as the thickness of the top layer was reduced. These preliminary results confirm the theoretical FEM simulations and give important guidelines for the optimization of flexible piezoelectric transducers.

International audience; This paper reports the role of selection of suitable dielectric layer in nanogenerator (NG) structure and its influence on the output performance. The basic NG structure is a composite material integrating hydrothermally grown vertical piezoelectric zinc oxide (ZnO) nanowires (NWs) into a dielectric matrix. To accomplish this study, three materials - poly methyl methacrylate (PMMA), silicon nitride (Si3N4) and aluminium oxide (Al2O3) are selected, processed and used as matrix dielectric in NGs. Scanning electron microscopy (SEM) analysis shows the well-aligned NWs with a diameter of 200±50 nm and length of 3.5±0.3 μm. This was followed by dielectric material deposition as a matrix material. After fabricating NG devices, the output generated voltage under manual and automatic bending were recorded, observed and analyzed for the selection of the best dielectric material to obtain an optimum output. The maximum peak-to-peak open-circuit voltage output for PMMA, Si3N4 and Al2O3 under manual bending was recorded as approximately 880 mV, 1.2 V and 2.1 V respectively. These preliminary results confirm the predicted effect of using more rigid dielectrics as matrix material for the NGs. The generated voltage is increased by about 70% using Si3N4 or Al2O3, instead of a less rigid material as PMMA.

In this paper, we explore the piezotronic effect in a GaN nanowire under a transverse force. The force was applied by bending the end of a single NW using an atomic force microscope (AFM) tip. Our results show that GaN NWs can be used to transduce a shear/bending force into a dramatic current change through the NW due to the piezotronic effect. Owing to the local piezopotential generated by the applied force, the barrier height of the Schottky contact between the GaN NW and the platinum AFM tip can be modulated. Using this transduction mechanism, the transverse force can be correlated to the natural logarithm of the current. Our results indicate that the force sensitivity is about 1.24 ± 0.13 ln(A)/nN, and a force resolution better than 16 nN is demonstrated. The nN sensitivity of GaN NWs shows the potential for piezoelectric semiconductor NWs to act as the main building blocks for micro-/nanometersized force sensor arrays and high spatial resolution artifi cial skin.

In this chapter, we present the advantages of semiconducting nanostructures (nanowires) for energy harvesting applications. Three sources of energy are considered: mechanical inputs, light and thermal energy. Different simulation approaches are used to discuss the prospects of these energy transduction solutions at nanoscale. Some guidelines are brought out for the improvement of energy conversion efficiency by nanowires, when integrated into functional devices.

International audience; Semiconducting piezoelectric nanowires (NWs) show significant potential for application in electronic and electromechanical sensors and energy harvesters. In particular, these nanostructures can be used to build composite piezoelectric materials that could offer several advantages when integrated vertically. First, NWs of various lengths opens the possibility to fabricate composite layers thicker than standard thin films (

International audience; ZnO nanowires (NWs) are excellent candidates for the integration of energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. However, ZnO NWs are usually nonintentionally n‐doped during their growth. Thus, it can be expected theoretically that their piezoelectric response be degraded and mostly geometry‐independent as a result of strong screening effects by free carriers, while experimentally many NW‐based piezoelectric transducers demonstrate quite reasonable performance. In this paper, this apparent contradiction is explained by surface Fermi level pinning (SFLP). Simulations based on the finite element method are developed to investigate the influence of SFLP on the electrical response of ZnO piezogenerators based on arrays of vertical ZnO NWs (the so‐called VING) operated in compression or bending mode. The results show that the nonsymmetrical response with respect to loading direction, which has been observed experimentally when the VING is bent, can be explained when account is taken of the reverse piezoelectric effect associated with SFLP. Influence of geometry and comparison to thin film are also discussed. It is found that the performance improvement, which is observed experimentally at scales much larger than predicted by ab initio models when NWs are compared to thin films, can be partly related to SFLP effects rather than larger piezoelectric coefficients.

International audience; This paper reports on the fabrication and characterization of ZnO based vertically integrated nanogenerator (VING) devices under controlled compression. The basic NG structure is a composite material integrating hydrothermally grown vertical piezoelectric zinc oxide (ZnO) nanowires (NWs) into a dielectric matrix (PMMA). A specific characterization set-up has been developed to control the applied compression and the perpendicularity of the applied force on the devices. The role of different fabrication parameters has been evaluated experimentally and compared with previously reported theoretical models, including the thickness of the top PMMA layer and the density of the NWs array in the matrix. Finally, the performance of the VING structure has been evaluated experimentally for different resistive loads obtaining a power density of 85 μW cm−3 considering only the active layer of the device. This has been compared to the performance of a commercial bulk layer of PZT (25 μW cm−3) under the same applied force of 5 N.

Silver Leaf Award; International audience

session oral presentation D1-1 (invited); International audience; We present nanostructure based piezoelectric and thermoelectric energy harvesters. Using different forms of nanostructuration (heterostrucutration, composite materials, superlattices) further helps improving the performance of such nanodevices that could be used both as self-powered sensors and nanogenerators with IC compatibility. GaN and ZnO nanowires are used as piezoelectric devices. While a specific AFM method is used to investigate the individual nanowire properties, large area prototypes composed of nanowire arrays are realized to evaluate the performance of such nanogenerators. Bottom-up techniques using industrial tools are also used to grow Si/SiGe quantum dot superlattices, both n and p types, mono- or poly-crystalline to be used as thermoelectric elements where nanostructuration improves the ZT figure of merit. Going even further, for the first time we report the realization of Ti and Mo silicide quantum dot superlattices, both n an p type.

chap 6; International audience; Vibration‐powered generators are typically inertial spring and mass systems which employ three main transduction mechanisms to extract energy from vibrations: piezoelectric, electromagnetic and electrostatic. This chapter presents a short overview of the microelectromechanical systems (MEMS) energy harvesters employing both piezoelectric and electromagnetic effects both proposed in the literature and developed in the framework of the Nanofunction project. It presents a short overview of state‐of‐the‐art vibration energy transducers employing the piezoelectric effect. The chapter illustrates the near‐field characterization techniques as well as electromechanical modeling and simulation required for the design of the energy harvesting transducers. It reviews the electromagnetic generators presented in the literature including large‐scale discrete devices and integrated versions, where the results achieved on vibration energy harvester exploiting both electromagnetic and piezoelectric effects are derived. Modeling and simulation results are presented to demonstrate the feasibility of the proposed device concepts.

chap 14; International audience; Nanotubes and metal nanowires (nanolines) are expected to play an important role as high‐frequency interconnects in future nanoelectronics, for transmitting signals between nano‐components and connecting the nano‐devices. Additionally, in wireless communications, nano‐antennas based on nanotubes and nanowires can be investigated for use in connecting nanoelectronic devices to the macroscopic world and making potential high‐density circuitry possible. The on‐chip transmission lines for silicon monolithic‐integrated millimeter‐wave (mm‐wave) circuits are made of metals like copper and aluminum. Their line width and thickness is not less than 1 μm in the most advanced back‐end‐of‐line (BEOL) CMOS technology for RF and mm‐wave applications, thereby ensuring a low insertion loss and a good impedance matching. This chapter describes some recent advances, performed within the EU FP7 NoENanofunction network of excellence. It focuses on nanolines that are horizontal to the Si wafer surface, the fabrication description is limited to the first case of metal deposition and patterning.

session poster; International audience; The combination of processing technologies, low power circuits and new materials integration makes it conceivable to build autonomous integrated systems, which would harvest their energy from the environment. In this paper, we focus on mechanical energy harvesting using piezoelectric materials integrated into flexible substrates. Modeling of these devices is important for the evaluation of their transduction efficiency. Other than classical thin piezoelectric layers, a composite layer using piezoelectric nanostructures is considered in order to evaluate its performance in a bending configuration.

International audience; The integrated nanogenerator (NG) based on vertical nanowire (NW) arrays is one of the dominant designs developed to harvest mechanical energy using piezoelectric nanostructures. Finite element method (FEM) simulations of such a NG are developed using ZnO NWs in compression mode to evaluate its performances in term of piezoelectric potential generated, capacitance, induced mechanical energy, output electrical energy, and efficiency. This evaluation is essential to correctly understand NG operation. Three main issues are highlighted. The mechanical and electrical structures of the NG as an integrated system are optimized, and strategies for concentrating the mechanical strain field in the NWs and increasing the force sensitivity are developed. In addition, the influence of NWs length and diameter on NG performances is investigated. The optimization results in a piezoelectric nano composite material where global performances are improved by mean of long and thin NWs.

International audience; Ultrathin piezoelectric nanogenerator (NG) with a total thickness of ≈16 μm is fabricated as an active or self-powered sensor for monitoring local deformation on a human skin. The NG was based on an anodic aluminum oxide (AAO) as an insulating layer grown on a thin Al foil by anodization, on which a thin film made of aligned ZnO nanowire compacted arrays is grown by solution chemistry. The performance of the NG is characterized with the assistance of the finite element method (FEM) simulation. The extremely thin NG is attached on the surface of an eyelid, and its output voltage/current characterizes the motion of the eye ball underneath. Since there is no external power needed for the operation of the NG, this self-powered or active sensor can be effective in monitoring sleeping behavior, brain activities, and spirit status of a person as well as any biological associated skin deformation.

The application of metallic nanowires as transmission lines at microwave frequencies has attracted interest of the nanoelectronics community in recent years. The size reduction of wires down to nano-scale inevitably introduces more challenges not only in the fabrication but in the characterization techniques. The aim of this work is to build a reliable framework to characterize a single metallic nanowire in the millimeter wave range by means of a tailored-designed coplanar waveguide platform. We conduct a comprehensive analysis on the characteristic impedances and the propagation constants of nano-scale aluminum metallic wires in relation to the change of line dimension as a function of frequency from 1 to 100GHz. A method to subtract the effect of pads and contact impedance from the measurement based on an equivalent circuit model and a cascade-based de-embedding theory is employed. We propose a quasi-TEM equivalent circuit model in the analysis to predict the measured frequency-dependent transmission line parameters. A comparison between simulated and measured result will be presented.

Proceedings of International Conference Nanomeeting - 2013,Minsk, Belarus, 28 - 31 May 2013; International audience; We present the most studied piezoelectric materials at the nanoscale and discuss their vertical integration into harvesting devices. Finite element method (FEM) simulations are used to obtain optimization guidelines rules of a specific design.