Advanced materials, components & processes for integrated autonomous micro-power sources

Resume : Tomorrow’s Industry 4.0 environments raise a growing demand in self-sustained, flexible and low-cost sensors for versatile applications in process control as well as condition and energy monitoring. We present a new concept for direction-sensitive and flexible strain sensors with harvesting potential based on the ferroelectric copolymer P(VDF:TrFE) and a single layer of interdigitated embedded electrodes (EE). Microstructured metal electrodes are formed on plastic substrates and embedded in the copolymer. In one processing approach a combination of (self-aligned) photolithography and electroforming is employed to produce 2-10µm wide and up to 4µm high electrodes that are fully covered by screen-printed P(VDF:TrFE). Alternatively, we present an elegant structuring method based on microfluidic channels hot embossed into P(VDF:TrFE) which are filled with conductive ink to form high aspect ratio EE. Electric poling using the EE allows the orientation of the ferroelectric domains primarily parallel to the P(VDF:TrFE)-substrate interface, thus having an increased piezoelectric coupling with respect to lateral strains present in the surface plane. Tensile tests with sensors having a footprint area of 1cm² were performed and compared with FEM simulations. The results show a highly linear charge response with respect to longitudinal strain, and the coupling strength depends significantly on the strain orientation in the surface plane. In conclusion, the use of the EE allows selectively resolving strain magnitude and orientation. Furthermore, bending at 90Hz excitation frequency yields an average power output of ~500µW/cm³, sufficient for stand-alone applications.

Resume : Electronics wastes (e-waste) are the major concern in the rapidly expansion of smart, wearable and portable electronics in modern high-tech society. Informal processing and enormous gathering of e-wastes can lead to adverse human/animal health effects and environmental pollution worldwide. These issues are big headache in current times and sending serious threat to scientific community to develop effective green energy harvesting technologies using biodegradable/biocompatible materials. Piezoelectric micro-generators (PMGs) are considered as one of the best futuristic renewable green energy sources to convert mechanical/bio-mechanical energies into electricity. However, inorganic/organic materials based PMGs are very much incompatible and, thus, considered as e-wastes for their high toxicity. Here, we have explored the potentiality of inexpensive and bio-waste natural materials such as onion skin, eggshell membrane and spider silk as an efficient piezoelectric material with superior piezoelectric strength. The fabricated bio-microgenerators (BPMGs) provide excellent power density and energy conversion efficiency. The BPMGs are sensitive towards throat movements such as coughing, drinking and swallowing. Single/multiple BPMG devices can turn on LEDs directly and power up smart electronics through capacitor charging. These pollution free and re-useable bio-waste materials based energy harvesting technologies would open-up a new era in in-vitro/in-vivo biomedical applications.

Resume : Using a hydrothermal synthesis method, zinc oxide (ZnO) nanowires (NWs) have been grown on ZnO/Au/Ti/Si substrates. This method shows a low temperature (70 °C) approach for growing ZnO NWs on a ZnO seed layer. ZnO films of about 50 nm thickness were deposited by radio frequency (RF) magnetron sputtering at various sputtering powers (150, 100 and 65W). The formation of ZnO seed layers and ZnO NWs was clarified using X-ray diffraction (XRD), and the surface microstructure of the prepared ZnO NWs and ZnO films was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The results show that the growth behavior of ZnO NWs is strongly impacted by the sputtering power of ZnO seed layers. The decrease of RF sputtering power leads to a diminution in the grain size of ZnO seed layers and a smaller lattice mismatch between seed layers and NWs, thus inducing a morphological improvement and a better alignment of the obtained ZnO NWs. These works aim at optimizing the integration of ZnO NWs for mechanical energy harvesting applications, and to enhance the performance of such piezoelectric devices.

Resume : Advanced piezoelectric materials for sensing, integrated autonomous micro-power sources or frequency-control that could be operated at high temperatures are in particular interest for aerospace, automotive and energy industries. Practical applications of such materials, especially at elevated temperatures, require minimization of electromechanical losses and, thereby maximization of the application relevant quality factor Q, since low Q leads to decrease of a signal-to-noise ratio of a piezoelectric device. Conventionally used piezoelectric materials like lead zirconium titanate or quartz are not suited for high temperature use, while their operation temperature is limited to about 500 °C or less by the intrinsic materials properties. Crystals of the langasite (La3Ga5SiO14, LGS) family are promising piezoelectric materials, which possess high electromechanical coupling coefficients and could be operated even at temperatures above 1300 °C. This work focuses on study of electromechanical loss in undoped LGS and catangasite (Ca3TaGa3Si2O14, CTGS) single crystals as a function of temperature up to 900 °C. To validate the results, the study is performed using two independent methods, namely impedance spectroscopy and a tone-burst excitation technique. The investigations revealed that superposition of different physical mechanisms including point defect relaxation and electrical conductivity contribute to electromechanical loss. Further, steps to minimize loss are discussed.

Resume : Nanostructured Aluminum Nitride (AlN) thin layers were synthesized by Pulsed Laser Deposition for piezoelectric microsystems applications, i.e. a friendly harvester able to generate electric power in the 100µW range. AlN thin films were deposited onto Si(100) wafers at 350 and 450°C and different laser pulse frequencies (3÷40 Hz). A seed layer of AlN was deposited at 800°C to further promote the obtaining of crystalline structures at lower temperatures. Morpho-structural characterizations showed adherent and uniform films, with smooth surfaces, a roughness value around 2 nm (inferred from AFM analysis) and a wurtzite-type structure (found from GIXRD investigations). The thickness (300-800 nm) and optical properties of films were evaluated by spectroscopic ellipsometry. Band gap values were found in the range of (4.0–5.7) eV. The piezoelectric coefficient d33 of AlN films was measured using a PiezoMeter System PM300 and the obtained values were found to be in the range of (1.1‒1.3) pC/N. In conclusion, AlN layers deposited on Si(100) on a seed layer obtained at higher temperature have promising piezoelectric properties which might be used for powering up sensors and portable microsystems. Acknowledgements: The financial support of the projects: PCCDI-2017-0419 SENSIS, EU (ERDF) and Romanian Government under POS-CCE O 2.2.1 project INFRANANOCHEM - Nr. 19/01.03.2009, PD 6/2018 and 3N/2018 are gratefully acknowledged.

Resume : ZnO nanowires (NWs) combine strong piezoelectric properties and the possibility to be grown at low temperature by chemical bath deposition (CBD). They are thus attractive building blocks for nano-generators and stress/strain sensors. Prior to CBD, a polycrystalline ZnO seed layer is usually deposited to favor the nucleation of ZnO NWs and control their morphology. However, their integration into piezoelectric devices requires the use of metallic seed layers. While promising results were obtained on Au seed layers [1], the formation mechanisms of ZnO NWs by CBD on that surface is still largely open. In this work, polycrystalline Au seed layers in the thickness range of 5-100 nm are prepared by vacuum evaporation. ZnO NWs are then grown by CBD under identical conditions [2]. Their structural properties and its relationship with the morphology of the Au seed layers are thoroughly investigated, revealing the presence of two populations of NWs. The majority population is made of vertically aligned ZnO NWs that are hetero-epitaxially formed on the Au (111) underlying grains. Selective area growth is further implemented by electron beam lithography to control the ZnO NW array uniformity. These findings provide an in-depth understanding of the formation mechanisms of ZnO NWs on Au seed layers as a prerequisite for their more efficient integration into piezoelectric devices. [1] S. Xu et al, J. Mater. Res., 2008, 23, 2072. [2] R. Parize et al, J. Phys. Chem. C, 2016, 120, 5242.

Resume : The development of high performance Li-ion micro-batteries (MB) and micro-supercapacitors (MSC) is one of the greatest technological challenges at the dawn of the Internet of Thing (IoT) for transportation, health, environmental and industrial monitoring1,2. The time constant of MB and MSC are compatible with the energy consumption of IoT devices collecting and exchanging data within a wireless network. To improve the performance of MB, the thickness of the sputtered LiMn1.5Ni0.5O4 electrode (LMNO) is increased: the areal capacity is significantly enhanced up to 375 μAh.cm-2 (7.4 µm-thick). The film maintains 84 % of its initial capacity at 10 C. To stabilize the high voltage LMNO electrode, nanometer-thick Li3PO4 coating (3 nm) is deposited by ALD (Atomic Layer Deposition) on our sputtered LMNO films, creating an artificial SEI. The fabrication of 3D Li-ion MB is another attractive solution. We recently achieve the ALD of Al2O3 / Pt / TiO2 and Li3PO4 stacked layers on 3D silicon micro-tubes template. The surface capacity of 150 nm-thick TiO2 film is significantly increased up to 0.37 mAh.cm−2. Ongoing actions on LiMn2O4 and LiMn1.5Ni0.5O4 positive electrode deposited by ALD will be shown. Based on our results on 3D MnO2 electrode, we achieve the collective fabrication of on-chip symmetric MSC with 3D interdigitated electrodes. The 3D MSC based on silicon microtubes scaffold exhibits energy and power densities close to 10 µWh.cm-2 and 20 mW.cm-2. This presentation will focus on recent results obtained in the fabrication of high performance Lithium-ion MB and MSC used to power miniaturized IoT devices. 1. Létiche, M. et al. Adv. Energy Mater. 7, 1–12 (2017). 2. Lethien, C., Energy Environ. Sci. (2018). doi:10.1039/C8EE02029A

Resume : The rapid development of wearable electronics and Internet of Things impose new demands for sustainable and maintenance-free micro power sources. This abstract presents a flexible, all-solid-state micro supercapacitor (MSC) integrated into a triboelectric energy harvesting system that can generate and simultaneously store energy for external use. The system consists of three parts: a triboelectric generator, a power management circuit, and a MSC. The MSC consists of a thin parylene-C membrane as the substrate and polyvinyl alcohol–phosphoric acid polymer gel as the solid electrolyte. The MSC prototype shows a specific capacitance of 31 mF/cm2 in the solid electrolyte. The prototype without a separator has also demonstrated that the capacitance changes from 27.7 to 25.4 mF/cm2 after more than 40 bending cycles and the capacitance retention is 91.7% after 10,000 cycles, which indicates that the fabricated devices have good mechanical and electrochemical stability. The power management circuit can convert pulse AC voltage of ~100 V to DC voltage of 1~4 V and the sustainable DC voltage is permanently stored in the MSC. Therefore, the flexible all-solid-state MSC has excellent potential for wearable electronics applications. The system can be used to efficiently collect and store the energy harvested from the environment, which bridges energy harvesters to the practical applications.

Resume : IOT devices suffer from power buffers between load and their energy source. The simplest solution to overcome such an issue is to place a supercapacitor as a power buffer, as their low equivalent series resistances allow them to deliver high power support during peak power bursts. Although electrochemical supercapacitor based on porous carbon materials are promising for such applications, such devices suffer from low volumetric capacity, as carbon materials exhibit loading densities (< 0.8 g.cm-3) and low charge polarization. Which, increases the volume of the electronic devices for IoT applications, especially in the autonomous operation mode. Through this talk, we show a different class of non-capacitive class of electrochemical energy storage devices based on electrospun carbon-metal oxides, redox-organic molecules and pseudocapacitive based 2-D nanomaterials (MXenes). We compare their performances with the capacitive class of porous carbon-based devices. We demonstrate that such devices function with high electrochemical stability (> 90 % over 10,000 cycles) and as well as cell volumes lower than carbon-based devices. Besides this, we discourse some of our design aspects and strategies for which we implemented while building these devices. Such understanding will be a tool for the community in designing smaller and efficient autonomous IOT devices.

Resume : Constructing on-chip micro-supercapacitors (MSCs) with asymmetric structure have become the predominant choice for applications in miniaturized electronic devices. However, the complex fabricating methods of electrodes and assembling process of devices will result in restricted development of on-chip MSCs. Herein, a planar asymmetric MSCs with MnxCo1-xOH nanosheets as cathode and Fe3O4 nanoparticles as anode is fabricated via a facile one-step electrodeposition method combined with microfabrication technologies. The planar asymmetric MSC exhibits a wider operation voltage window (up to 1.65 V), a higher capacitance (32 mC cm-2) and a higher energy density (7.78 μWh cm-2) than those of previously reported MSCs with alkaline aqueous electrolyte. This work demonstrates a model of the excellent combination of materials synthesis and device fabrication towards large-scale manufacture of on-chip microdevices. Reference 1. L. Q. Mai, F. Yang, Y. L. Zhao, X. Xu, L. Xu and Y. Z. Luo, Nat. Commun. 2 (1), 381 (2011) 2. L. Q. Mai, X. C. Tian, X. Xu, C. L. Chang and L. Xu, Chem. Rev. 114 (23), 11828 (2014) 3. Z. H. Liu, X. C. Tian, L. He, M. Y. Yan, C. H. Han, Y. Li and L. Q. Mai, Nano Research 10 (7), 2471 (2017) 4. W. Yang, L. He, X. C. Tian, M. Y. Yan, H. Yuan, X. B. Liao, J. S. Meng, Z. M. Hao and L. Q. Mai, Small 13 (26), 1700639 (2017).

Resume : The emergence of wearables, smart sensors and internet of things requires adapted power sources to sustain high integration, miniaturization and electrical performances. On-chip micro-supercapacitors are a promising solution to achieve these requests, by providing long cycle life and high power density. Nevertheless, such devices are generally based on a liquid/polymer electrolyte configuration, and consequently present important challenges in terms of process integration, life cycle and physical-chemical stability. Recent studies reported on 2D-planar architecture based LiPON films and showed interesting results in terms of electrical performances and integration, with an energy storage mechanism involving redox reactions at the electrolyte/electrodes interfaces. Still, further efforts are needed to enhance power and energy densities to meet applications demands. In our work, we propose a comprehensive study of the LiPON layer electrochemical behavior as thin film electrolyte for inorganic solid-state on-chip supercapacitors. The fabricated devices exhibit box-shape CV and typical capacitance values as high as 45 µF/cm² over 106cycles. Furthermore, MIM structures using blocking electrodes have been used to investigate (i) the influence of the LiPON ionic conductivity on the cell capacitance, (ii) scan rate dependence, (iii) and potential stability window. The discussed results highlight the very high potential of 2D and 3D LiPON based supercapacitors for on-chip power storage.

Resume : Self-powered system can sustainably operate without an external power supply for sensing, detection, data processing and transmission. Nanogenerators (NG) were first developed for self-powered systems based on piezoelectric and triboelectric effects for converting tiny mechanical energy into electricity. Here, we first present the fundamental theory of the NGs starting from the Maxwell equations. In the Maxwell’s displacement current proposed in 1861, the term ε∂E/∂t gives the birth of electromagnetic wave, which is the foundation of wireless communication, radar and later the information technology. Our study indicates that, owing to the presence of surface polarization charges present on the surfaces of the dielectric media in NG, an additional term for the NG output electric current,(∂P_s)/∂t, should be added in this equation. Thus, our NGs are the applications of Maxwell’s displacement current in energy and sensors, with three major application fields: micro/nano-power source, self-powered sensor and blue energy. We present the applications of the NGs for harvesting human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water, etc. We illustrate the networks based on triboelectric NGs for harvesting ocean water wave energy, a promising sustainable large-scale power supply. Lastly, we show NGs as self-powered sensors for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage/current output signals.

Resume : The most recent energy harvesting technology comes from the triboelectric effect. Triboelectric nanogenerators (TENGs) are an emerging mechanical energy harvesting technology that was recently demonstrated based on the conjunction of triboelectrification and electrostatic induction in which a material becomes electrically charged after it comes into contact with another material through friction. Due to their flexibility, they can be fabricated in various configurations and consequently have a large number of applications. Here, a triboelectric nanogenerator, an electromagnetic generator (EMG) and a piezoelectric nanogenerator (PENG) were hybridized and implemented inside a shoe sole to harvest energy from human walking. To optimize the TENG, we developed and studied three different structures (parallel, arcked and zigzag triboelectric plates) based on the contact-separation mode and suitable to be assembled in footwear. The parallel-plate structure generated the largest electrical outputs, so that the distance between triboelectric layers and the number of tribo-pair in this configuration were also optimized. To further enhance energy generation properties, we fabricated a hybridized nanogenerator using piezoelectric nanowires and electromagnetic induction that doubled the charging capacity of the TENG system alone. References 1. Z.L. Wang, J. Chen, L. Lin, “Progress in triboelectric nanogenerators as a new energy technology and self-powered sensors”. Energy Environ Sci. 8(8), 2250-2282 (2015). 2. L. Liu, W. Tang, C. Deng, B. Chen, K. Han, W. Zhong, Z. L. Wang, “Self-powered versatile shoes based on hybrid nanogenerators”. Nano Research, 11 (8), 3972-3978 (2018). 3. C. Rodrigues, C.A. Alves, J. Puga, , A.M. Pereira, J.O. Ventura, “Triboelectric driven turbine to generate electricity from the motion of water”. Nano Energy, 30, 379-386 (2016). 4. Y. Zi, L. Lin, J. Wang, S. Wang, J. Chen, X. Fan, P.-K. Yang, F. Yi, Z. L. Wang, “Triboelectric-Pyroelectric-Piezoelectric Hybrid Cell for High-Efficiency Energy-Harvesting and Self-Powered Sensing”. Advanced Materials, 27 (14), 2340-2347 (2015).

Resume : Triboelectric energy harvesting is foreseen as a major source for powering upcoming miniaturized electronics. However, fully understanding the working principles of Triboelectric Nanogenerators (TENGs) has been challenging [1,2]. Herein, for the first time, we expand on the knowledge on the fundamentals of TENGs through the distance-dependent electric field (DDEF) concept, revealing several new parameters and their effect on the output trends of a TENG. In particular, the nature of the contact during the operation of a contact-mode TENG is closely analysed, and its effect on the electrical output is explained, using experimental results as well as theoretical simulations [3]. Furthermore, regulating the output of TENGs internally through the structural design, which a critical issue of using TENGs in practical applications, is addressed in this work. These findings are then used to develop high performance TENG architectures for different applications targeting properties such as enhanced uniformity, improved output current and power, compared to a typical TENG device [3]. 1. Dharmasena et. al, Energy Environ. Sci. 10 (2017), 1801-1811. 2. Dharmasena et. al, Nano Energy. 48 (2018), 391-400. 3. Dharmasena el. al, Advanced Energy Materials. 8.31 (2018): 1802190.

Resume : Fiber-based triboelectric nanogenerators exhibit compelling attributes for wearable and sustainable power supplies, especially given their potential to be integrated into textiles. However, the current processing approaches for such systems mainly rely on consecutive wrapping, depositing or coating processes, which result in thick fibers that may suffer from delamination or exfoliation under large deformations. Here, we demonstrate the fabrication of inherently ultra-stretchable and soft triboelectric fibers of controlled size and shapes via the thermal drawing technique. The resulting fibers show excellent mechanical deformability (up to 557% strain), energy harvesting, and self-powered mechanical sensing performance. By virtue of their unique mechanical properties, the fibers can be integrated into clothing or directly woven to form textiles, meanwhile exhibiting higher electrical outputs than 2D planar devices. By exploiting the particular attributes of the thermal drawing process, we optimized the outputs by introducing textured pattern to the triboelectric fiber surface. Triggered by cyclic tapping, a triboelectric textile (6 cm * 6 cm) made out of thermally drawn multimaterial fibers could deliver an open circuit voltage as high as 490 V, and a surface charge of 175 nC, which remain stable after 50 000 cycles. The drawing process being simple and scalable, it can potentially produce tens-of-kilometers long fibers in a single draw, which provides a promising route for the integration of energy harvesting and sensing functions in fiber- and textile-based products.

Resume : Triboelectric Nanogenerators (TENGs) are a strong candidate in powering the next generation of portable electronics, via motion energy harvesting. However, the lack of understanding on their power generation and optimization has impeded the exploitation of full potential of TENGs, and the development of sustainable applications. We introduced the distance-dependent electric field (DDEF) model, first analytical theoretical model based on Maxwell’s equations to fully describe the working principles of TENGs, providing higher accuracy over existing models [1,2]. Herein, we present a novel optimization method to significantly increase the average output power and to reduce the impedance of the TENG by several orders of magnitude, addressing the most critical drawbacks of this technology [3]. Norton’s theorem, first developed in 1926, is used in combination with the DDEF model to analyze the effects of structural, material and motion parameters of the TENG on its power generation and internal impedance. This presents a series of new optimization techniques including the TENG impedance plots. These methods result in over 10-100 times improvement in output power and a similar reduction in device impedance, leading the way towards developing effective and efficient energy harvesting devices. 1. Dharmasena et. al, Energy Environ. Sci. 10 (2017), 1801-1811 2. Dharmasena et. al, Nano Energy. 48 (2018), 391-400 3. Dharmasena el. al, Advanced Energy Materials. 8.31 (2018): 1802190

Resume : Batteries, with inherent limited capacity, have dominated the power supply of small devices for decades. However, despite the fast evolution in the field, the energy gap between the capacity of the current battery technology and the power requirements is increasing year by year. This energy divergence brings a great challenge on portable generation that opens new opportunities for technologies beyond Li-ion. In this new scenario, a major breakthrough on the miniaturization of uninterrupted and efficient generators is crucial. The dream of miniaturizing one of the most efficient known generators, i.e. a fuel cell, has been unsuccessfully pursued for years until recent advances in silicon integration of Solid Oxide Fuel Cells (µSOFCs) converted this disruptive technology into a serious candidate to power next generations of portable devices. In this talk, we will present the integration in mainstream silicon technology of SOFC devices. Acknowledgements: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC-2015-CoG, grant agreement No #681146- ULTRA-SOFC)

Resume : The rise of emerging materials, including low-bandgap donors and non-fullerene acceptors, has led organic solar cells (OSC) to reach efficiencies beyond the 14% mark. [1] The increased performance of OSCs along with flexibility and stretchability, as well as the versatility and low costs associated with solution processing has rendered them attractive for unconventional applications such as conformable and disposable electronics. Inkjet printing has proven to be a viable fabrication technique to exploit the advantages of solar cells and transition from laboratory-made devices into consumer-ready products due to its low material usage, customization through digital design, and high-resolution of printed features. This work demonstrates the fabrication of fully inkjet-printed high efficiency solar cells based on the PCE10:4F and P3HT:O-IDTBR blends autonomous and micro-powered applications. The engineering of functional inks for the different layers is centered on tuning the rheological properties for proper droplet jetting, compatibility of surface energies between the ink and the underlying films, as well as controlling the drying behavior for optimized electronic properties. The optimization of printing parameters allows for a repeatable process yielding devices with efficiencies of up to 10.4%, comparable with that of coating techniques. Fully printed devices will allow end-users to design and use OSC’s as a power source throughout a wide range of applications.

Resume : Flexible transparent electrodes (FTEs) are prerequisite components for emerging flexible and wearable optoelectronics. The current dominating transparent electrode material indium tin oxide (ITO) is not suitable for next generation optoelectronics because of the brittle nature of oxide film and increasing cost of indium source. Metal mesh, as one kind of most promising transparent electrode materials to replace ITO, has attracted considerable interest because of the impressive optoelectronic properties. However, all reported fabrication processes for metal meshes involve complicated and high-cost patterning techniques, which is one important obstacle for their widely practical application. To address this challenge, we herein develop a low-cost and facile fabrication process combining electrochemical replication and transfer (ERT) techniques to produce embedded metal mesh-based FTEs. The adoption of a reusable Au-mesh template in the ERT process avoids the complicated lithography or printing steps, which significantly simplifies the fabrication of metal mesh. Furthermore, as-made embedded metal mesh-based FTEs show remarkable electro-optical performances. Particularly, the figure of merit (FoM) soars up to 25,000, which is one new record while compared with those of previous transparent electrodes. On the other hand, the embedded metal mesh-based FTEs present excellent mechanical flexibility and environmental stability. Several typical optoelectronic devices, flexible transparent heater, touch screen panel, solar cell, and organic light-emitting diode (OLED), are successfully assembled based on as-made embedded metal meshes. Considering the low-cost, facile and scalable fabrication, excellent optoelectronic properties, mechanical flexibility and environmental stability, we believe our ERT fabrication strategy could effectively promote widely practical application of metal mesh in flexible and wearable optoelectronics.

Resume : Natural photosynthesis is a profound source of inspiration for energy conversion and storage systems because it harnesses the most abundant source of energy. Most approaches for generating more electricity in biophotovoltaics have predominantly focused on placing a cell on the electrode. The power outputs from the photo-bioelectrochemical cells, however, have remained at lower efficiencies than those of other artificial materials. In this paper, for the first time, we report a Synechococcus sp.-iron oxide nanoparticle(IONPs)-NdFeB complexes that enable high performance via a long electron transfer conduit to the electrode. During the light illumination, water oxidation takes place at the complexes and electrons are transported through the electrode, yielding a peak power density of 0.806 and 0.534 W/m2 for Synechococcus sp.-γ-Fe2O3-NdFeB(Ni-NixOy) and Synechococcus sp.-Fe3O4-NdFeB(Ni-NixOy) complexes, respectively. Different electron transport mechanisms were evaluated by changing the combination of materials and experimental conditions. This approach has not been explored before for conventional biophotovoltaics. Furthermore, a green LED bulb was turned on as the result of the energy harvesting. The approach introduced in this study can boost solar energy harvesting remarkably by combining natural photocatalysts with artificial ones.

Resume : The necessity of monitoring biological parameters has gain a lot of attention in the past years. Although many solutions have been implemented to monitor physical parameters such as heartbeat, breathing rhythm and even any physical activity, but the inside of the body in everyday life remains unknown. Due to the easy accessibility, it seems that sweat is best candidate to analyse and monitor different chemical parameters. As a first approach, in this work we present a self-powered single-use patch for sweat conductivity measurement, focused in the screening Cystic Fibrosis. The core of the patch consists on a paper battery-sensor, whose power output directly depends on the conductivity of the sample introduced in the battery, which acts as the electrolyte. Then, with a simple electronic circuit and two electrochromic displays, the result is shown to the user. The first display, the Control Display, turns on at all the conductivities, since it is used to confirm that the device is working properly and then, the second display, the Test Display, which turns on only when the threshold conductivity that indicates the presence of Cystic Fibrosis is detected. The patch is made of medical grade materials to guarantee the skin-friendliness of the device and printed electronic components to make it as flexible as possible and ensure a pleasant attachment. This device paves the way to a new generation of medical devices to monitor chemical parameters with a non-invasive approach.

Resume : Thermistors are materials with either positive or negative temperature coefficient of resistance (NTCR) and are used to protect a circuit against inrush over-voltage/current conditions and to a lesser extent as temperature sensors1, since determination of temperature is of critical importance for a number of applications. In this work, we report a novel NTCR spinel utilized as a printable temperature sensor exhibiting a stability and a characteristic sensitivity to determine the temperature with an accuracy of 0.1°C. The material is a composite that consists of a manganese spinel oxide particles dispersed in a BCB matrix. These sensors can have a sensitivity as high as 4% of resistivity change per °C with a β coefficient of 3512K at RT. The composition of the spinel oxide (Mn1.71Ni0.45Co0.15Cu0.45Zn0.24O4), confirmed by XRF while the cubic spinel phase determined by XRD. Critical factor for the application of printable temperature sensors is the stability to changes in various environmental conditions. The I-V characteristics will be presented, showing no hysteresis upon heating and cooling. The log scale of the electrical measurements when applied low voltages have shown an Ohmic behaviour. However, beyond that point, a deviation of linearity was observed indicating that another transport mechanism is also involved in the conduction mechanism. Acknowledgements: Part of this work was financially supported by the Stavros Niarchos Foundation within the framework of the project ARCHERS (“Advancing Young Researchers’ Human Capital in Cutting Edge Technologies in the Preservation of Cultural Heritage and the Tackling of Societal Challenges”). 1. Feteira A. J. Am. Ceram. Soc., 92 [5] 967-983 (2009); doi: 10.1111/j.1551-2916.2009.02990.x

Resume : The vast proliferation of new gadgets and electronic devices in the ICT sector allows foreseeing a significant rise in battery consumption. Generally, these devices are to be powered with primary cells that are disposed of after depletion. Despite governmental efforts towards reinforcement of recycling policies around the globe, there is a huge number of batteries that are still discarded in an uncontrolled way. We present a new concept of single-use portable battery specifically made to power small electronic devices that when disposed of, breaks down into simple compounds as a result of the biotic degradative processes of microorganisms present in soils and natural water bodies. The battery is designed using organic materials such as cellulose, carbon electrodes, biopolymers and beeswax and delivers power within the range of mW for several hours. Our device is completely aligned with the circular economy principles focusing in the utilization of raw materials that do not cause exhaustion of natural elements, do not require large amounts of energy to be produced, do not produce toxic by-products during their manufacture and feature biodegradability in mild degradation conditions at the end of their life cycle. Such components would thus bypass the need for complex recycling structures and associated investments.

Resume : The emergence of autonomous microsystems raises need for highly integrated and low-footprint power sources. In this context, an investigation to increase the performances of all-solid-state thin-film microbatteries sputter-deposited LiCoO2 electrodes in the 20 µm thickness range is described. The effect of LiCoO2 post-deposition annealing conditions on the cathode structural properties is examined. It was found that temperature and duration may affect the degree of c-axis orientation, and promote more favorable crystalline orientations for Li-ions intercalation and diffusion. As a consequence, improvement of properties of primary importance for off-grid electronic devices are expected. The influence of these microstructural changes on first cycle irreversibility, c-rate capability, and capacity retention are presented.

Resume : Keywords: Garnet-type solid electrolyte, cubic phase LLZO, sol-gel process, Li-ion battery A battery is a device that converts the chemical energy contained in its active materials directly into electric energy through an electrochemical oxidation-reduction reaction. The battery is composed by an anode (the negative electrode) where, upon discharging, the oxidation reaction takes place, a cathode (the positive electrode) where the reduction reaction takes place, and an electrolyte (usually an organic, flammable liquid) that allows the migration of the ions between the electrodes. Currently, some research on this topic tends towards the manufacturing of flexible Li-ion micro-batteries for uses in microsystems. To do so, it is necessary to replace the widely used liquid electrolyte by a solid-type one because the flexible/micro configuration is not compatible with liquid electrolytes: (i) it is difficult to process microsystems with liquid electrolytes and (ii) the flexibility of the battery may lead to leakages. In addition, this replacement could also open the way to new battery types in order to solve the safety issues related to the use of flammable organic electrolytes in larger batteries.(ref 1) Recently, a low-cost and energy-efficient spray-coating process of lithium cobalt oxide (LCO), i.e. a cathode material, has been developed in our lab to obtain flexible microelectrodes. As the final objective is to use a solid state electrolyte such as Gel Polymer Electrolyte (GPE) or Lithium Phosphorous Oxynitride (LiPON), the coating process still needed to be adapted to the production of solid state batteries. In fact, due to the presence of 50-60% porosity inside the cathode layer, the migration of the lithium ions is hindered, which leads to the decrease of the ionic conductivity. The main challenge was to use a nanostructured electrolyte such as LLZO to fill the LCO coating porosity (between 50 - 60 %) in order to improve the ionic conductivity of the layer without changing the electrochemical properties of the LCO, to finally be able to build an all solid-state battery. Three different crystalline structures of LLZO can be synthesized. The first one, the high-temperature cubic phase (HT-LLZO), is obtained at temperature over 1000°C and is not stable at room temperature; the second one is the tetragonal phase (t-LLZO), which is obtained above 700°C; recently, Murugan et al.(ref 2) have shown that a second cubic phase could be obtained at temperature below 700°C. Among these three polymorphs, the low temperature cubic phase (c-LLZO) has been chosen because it is possible to synthesize it using a low-temperature sol-gel process and because the obtained material is stable at room temperature(ref 3,4). Moreover, c-LLZO is a very promising material for solid state electrolyte applications due to its chemical stability in contact with Li metal and its relatively high ionic conductivity (~10-6 S/cm)(réf 5). Nanostructured LLZO samples obtained by the above-mentioned sol-gel synthesis were characterised by Transmission Electron Microscopy (TEM), mixed (30% w/w) with LCO in ethanol, and then coated by spray-coating on stainless steel disks (used as current collector) in order to prepare µm-thick films as battery cathodes without the use of any binder or conductive additive. X-Ray Diffraction was used to analyse the obtained film and shows that the crystalline structure of the two materials (c-LLZO, LCO) was not modified. The LLZO/LCO cathode film was then inserted into a coin-cell with a liquid electrolyte. Preliminary electrochemical characterisation was performed, consisting in checking the capacity during battery discharge. The potential (V) versus the capacity (mAh/g) discharging curve of LCO coating and mixed LLZO/LCO coating, reach close values of capacity around ~137 mAh/g, which means that mixing the solid electrolyte with LCO did not modify the electrochemical properties of the latter. Finally, pore texture measurements using Archimedes’ principle6 showed that the void fraction of the LCO film was decreased from 50% to 37% without changing the crystalline structure of c-LLZO or LCO or the capacity of the battery. 1 Kerman et al. J. Electrochem. Soc., 2017, (164-7), A1744. 2 Murugan et al. Angew. Chem. Int. Ed. Engl., 2007 (46) 7778. 3 Janani, et al. Ionics 2011 (17), 575. 4 Kokal et al. Solid State Ionics 2011 (185) 42. 5 Yang, et al, J. Phys. Chem. C., 2015 (119) 14947. 6 Panneton et al, Acta Acustica 2005 (91), 342.

Resume : CBRAM (Conductive Bridge Random Access Memories) are a type of resistive switching memories considered a major candidate as next generation memories, promising high scalability, low power consumptions, fast write and read times. Information storage is achieved through the electro-chemical deposition and dissolution of a thin metallic filament inside a dielectric (solid electrolyte). This work puts in evidence that in our Ag-GeS2-W memories, energy storage is also possible and could be exploited to further reduce the overall power consumption or in tailored applications. Preliminary experimental demonstration was presented in [1-2]. The electrical characterization conducted evaluates the impact of the sweep rate and the area dependence of the current peaks we observe in our devices, confirming that we are indeed dealing with faradaic currents. After battery operation, memory operation can happen uncompromised, as the forming voltage is unchanged. As the reduction peak appears as a one-shot phenomenon, impact of temperature and bias is studied as a mean to trigger reversibility. Ab initio calculations are used to investigate involved chemical species and their interplay during the battery-like operation where Ag ion diffusion and reduction currents dominate. Finally, the charge that can be stored per cell is derived. Further study to evaluate the efficiency and the energy/cell, as well as means to maximize stored energy are the very next prospectives of this work. [1] Lee D., Oukassi S., Molas G., Carabasse C., Salot R., Perniola L. (2017). Memory and Energy Storage Dual Operation in Chalcogenide-Based CBRAM. IEEE Journal of the Electron Devices Society, 5(4), 283–287. [2]Schindler C., Valov I. Waser R. (2009). Faradaic currents during electroforming of resistively switching Ag–Ge–Se type electrochemical metallization memory cells. Physical Chemistry Chemical Physics, 5974-5979.

Resume : The emerging market of the Internet of Things, smart objects and others increase the demand for micro energy sources. Rechargeable Li-ion batteries are a well-known technology for energy storage. However, safety issues and high production costs constrain progress. Research on solid electrolytes, such as LiPON, was performed to evade leakage. But LiPON suffers from low ionic conductivity and a cost and time intensive production process. Another approach is the substitution of volatile and flammable organic electrolyte solvents with ionic liquids (IL), which display negligible vapor pressure and wide chemical, electrochemical, and thermal stability. Electrolyte solution based on ILs can be confined into inorganic porous networks forming so-called ionogels (IG), which are investigated as solid electrolyte materials. IGs combine low hazard and good ionic conductivity [1]. Silica-based IGs compatible with Li/LiCoO2 systems were prepared in a one-pot sol-gel process. The composition of the IG precursor solution and the influence of trifluoroacetic acid as catalyst were studied to obtain a fast condensation. Homogeneous and transparent IGs were obtained with a gelation time of less than 4 h. The physical properties of the host matrix were characterized by N2 sorption, Hg porosimetry and SEM. The silica host matrix is a 3D network predominantly built from 3-fold condensed silicon centres. Its structure changes from µm-sized spheres to small particles by increasing the IL amount in the gel. The electrochemical performances of the IG were evaluated with complex impedance spectroscopy measurements and galvanostatic cycling. First results show that these promising IGs may be successfully used as solid electrolyte in Li/LiCoO2 cells. Batteries were prepared, which cycle more than 100 cycles at a rate of C/2 with no evidence of dendritic growth. Impedance characterization reveals the high internal resistivity of this battery. Reference [1] A. Guyomard-Lack, B. Said, J. Le Bideau, New J. Chem., 2016, 40, 4269-4276.

Resume : The increasing miniaturization of electronic devices and the needs for stand-alone systems require adapted power sources in terms of dimensions and energy. With these new demands, new constraints come out like flexibility, limited thickness or tighter security requirements. To achieve these requests, both battery core materials and packaging need to be redesigned. In this work, we developed simultaneously a new gel polymer electrolyte (GPE) material and a new battery design to reach both security (no leakage concern, no flammability, thermal stability) and application requirements (flexibility, thin system (<400µm)). We worked on a quaternary GPE based on a bi-components UV-curable polymer network giving the mechanical strength combined with a binary liquid phase composed of ionic liquid and Li salt. The GPE was optimized in terms of mechanical and electrochemical properties by varying the nature and the proportion of each components (polymer network, ionic liquid and Li salt) and the UV-curing parameters. The optimized GPE exhibits a good conductivity at room temperature (0.375mS.cm-1) and a Li+ transference number of 0.299 (NMR measurements) which is relatively high for this GPE type. Our new battery design is composed of LiCoO2 cathode realized by standard coating processes. The liquid solution of GPE precursors is then deposited on the LiCoO2 cathode and directly polymerized by UV-curing. This step allows a good soaking of the electrolyte in the electrode pores. This system was then integrated in our thin battery design with Li metal foil as anode material. By optimizing each component dimension and sealing parameters (sealing conditions and adhesive type), we succeeded in producing a flexible, less than 400µm thick working battery with interesting electrochemical performances (more than 2mAh.cm-2). This work was done as part of the project EnSO. EnSO has been accepted for funding within the Electronic Components and Systems For European Leadership Joint Undertaking in collaboration with the European Union's H2020 Framework Programm (H2020/2014-2020) and National Authorities, under grant agreement n° 692482.

Resume : Electrical stimulation may influence cell behavior associated with proliferation, differentiation, and migration, among others. The need for electrical tools to interact with living cells has pushed the technology to progressively developed less invasive devices. Technologies like energy harvesting have enabled wireless biological applications. Here we report the use of a microphotodiode based on silicon, with smaller dimensions than a cell, as a wire-free interface to stimulate single cells with high spatial resolution. We demonstrate the effectivity of this microtool on osteoblast cells. We will present the technology for microphotodiodes fabrication and the characterization of single microphotodiode characteristics under in vitro conditions. We also demonstrate their capability to harvest energy from light and instantaneously convert it to an electric stimulus provides a stimulation tool of single cells without the limitation of external cables and electrodes. The electrical stimulation triggered intracellular calcium transients as a response in 46% of the cells. Furthermore, induction of cytosolic Ca2+ transients triggered by the electrical stimuli generated by the microphotodiodes, on which osteoblasts cells were grown, shows the feasibility of this approach towards localized activation of excitable cells in a simple way. In summary, this technology affords new possibilities for the electric stimulation of single cells as a tool for life science explorations as well as for future biomedical applications based on controlling bioelectric signaling.

Resume : p-type CdTe semiconductor are used as absorbent material in solar cells, it exhibits high electrical resistivity and a large superficial work function (approx. 5 eV), limiting the mobility of charge carriers. In order to solve these limitations, we create a p+ region in CdTe using a region with Te. In previous reports after CdCl2 treatment appears oxides on CdTe surface that improves the electrical parameters on back contact. In this way TeO2 was implemented in order to reduce losses and recombination process. This region was implemented by CSVT system using a special close evaporation chamber. Structural, morphological, optical and electrical properties were studied. Solar cells with this region was manufactured and evaluated.

Resume : Triboelectric nanogenerator (TENG) which converts ambient mechanical energy into the electrical energy is spotlighted as energy harvesting technology for a portable power generator. In previous researches, the electrical power output of TENG has been improved via applying new materials or combining with other energy harvesting technologies. However, it is difficult to combine TENGs with existing portable devices because of shape differences between the TENG-based charging system and electronic devices. Therefore, it is necessary to overcome the spatial limitation of TENGs for developing portable generators. In this work, we demonstrate elastic spiral triboelectric nanogenerator (ES-TENG) that can harvest mechanical energy through an extraction and self-retraction process without additional components for retraction. ES-TENG utilizes the elastic force of the sheet itself and is thereby operate as a spiral spring. Besides, in the process of the extraction and retraction, it generates additional multiple power peaks in a single input, from a stacking/fluttering motion and changes of the sheet shape. We designed ES-TENG considering two major factors for maximizing the output: the overall length and initial number of turns of the rolled sheet. Furthermore, ES-TENG was able to operate and recharge some portable electronic devices. This study shows possibility of practical applications for ES-TENG which is usable when attached to portable electronic devices in the future.

Resume : Well aligned crystalline zinc oxide (ZnO) nanowires (NWs) on ZnO/Au/Ti/Si substrates were grown by the so-called “hydrothermal synthesis”. ZnO seed layers with different thicknesses ranging from 5 to 100 nm, by controlling the deposition time, were prepared by radio-frequency sputtering followed by a post-annealing treatment in air at 400°C. The effects of deposition time and annealing treatment of ZnO seed layers on the subsequent growth of ZnO NWs were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The experimental results reveal that the quality and growth behavior of ZnO NWs are strongly dependent on both the thickness and the heat treatment of the ZnO seed layers. This work is an optimization step of the facile, cost-effective and industrially scalable process flow recently developed for the fabrication of a high performance nanocomposite-based stretchable nanogenerator (SNG) on polydimethylsiloxane (PDMS) substrate. The morphological improvement of hydrothermally grown ZnO NWs may therefore lead to higher performance SNGs for the targeted application of mechanical energy harvesting in order to supply flexible and wearable electronics.

Resume : Controlling the physical properties of ZnO nanorods is a crucial issue for their use as building blocks in a wide variety of devices. In this work, an analysis of the electrical properties of selective area grown O- and Zn-polar ZnO nanorods by chemical bath deposition is performed by four-point probe resistivity measurements in patterned metal contact and multiprobe scanning tunneling microscopy configurations, showing their typical high electrical conductivity. From Raman scattering and spatial resolved 5 K cathodoluminescence measurements, it is revealed that the high carrier density of ZnO nanorods with O- or Zn-polarity is due to the massive incorporation of hydrogen in the form of interstitial hydrogen in bond-centered sites (HBC), substitutional hydrogen on the oxygen lattice site (HO), and multiple O-H bonds in a zinc vacancy (VZN-Hn) [1]. These hydrogen-related defects are further expected to present different ranges of stabilities, depending on their nature [2]. Post-deposition annealing is thus considered as a strategy for controlling the carrier density of ZnO nanorods and hence optimizing its physical properties for their efficient integration into nanoscale engineering devices. These findings cast a broad light on the dominant role of hydrogen when ZnO nanorods are grown by the widely used chemical bath deposition technique. [1] T. Cossuet et al., J. Phys. Chem. C 122, 22767−22775 (2018) [2] S. G. Koch et al., Physical Review B 89, 235203 (2014)

Resume : An innovative roly-poly triboelectric nanogenerator (RP-TENG) that can harvest mechanical energy and sense impact without an external power source was designed. The RP-TENG simply consists of a PMMA hemisphere shell with an Al electrode and a base plate with a Cu electrode. When just a single input such as a certain external excitation or impact is applied to the RP-TENG, the hemisphere shell oscillates in any direction, and accordingly, an electrical output is sustainably generated by a triboelectrification and electrostatic induction coupling effect. Furthermore, based on such an energy harvesting ability, we fabricated RP-TENG for a self-powered impact sensor by constructing meshed Cu cell arrays on a base plate of RP-TENG, which was connected to a circuit. When an impact was applied, the RP-TENG could determine the magnitude and direction of the impact without breaking the material. Finally, we successfully demonstrated that our TENG could be utilized for a real-world impact sensor system.

Resume : We present a new method for the synthesis of conductive, highly flexible, thin thermoelectric films. Micron-thick, 2D-laminate films on a porous nylon membrane are synthesised by intercalation-assisted liquid phase exfoliation. This scalable process avoids the need for high temperature sintering while nitrogen protection during solution processing limits oxide formation which may lead to an improved electrical conductivity. Both Bi2Se0.3Te0.7 (n-type) and Bi0.5Sb1.5Te3 (p-type) films are designed to be highly flexible while attempting to retain the superior thermoelectric performance of their bulk variants. Resultant thin films had Seebeck coefficients and electrical conductivity exceeding 180 (uV/K) and 100 (S/cm) respectively. The films? mechanical performance was studied in detail in order to quantify flexibility and durability when subjected to thousands of repeated, highly tuneable bending cycles. Bending cycle parameters were also compared. Film enhancements using copper and graphene oxide to improve electrical conductivity and mechanical resilience were also explored.

Resume : Analysis of the results of Auger electron spectroscopy of the Pd-Ba alloy, taken after each treatment cycle, showed that, both during thermal and laser processing, along with cleaning the surface from contamination, Ba atoms diffuse to the surface, as a result of which the composition and, accordingly, emission surface properties. In the case of heating at relatively low temperatures (T ≤ 600 K), when a significant amount of impurity atoms is contained on the Pd-Ba surface, and the diffusion of Ba to the surface is still small, the secondary emission characteristics of the surface change only slightly. The greatest change in the parameters takes place in the temperature range T ≃ 1050-1150 K. At the same time, the intensity of Auger peaks, characteristic impurity atoms are reduced to a minimum. Starting from T = 1200 K, intense desorption of barium from the surface is observed. In the case of laser activation, an increase in σm and a decrease in eφ begins with an energy density W ≈ 0.8 - 1.0 J ∙ cm-2 and at W ≈ 2.0 - 2.2 J ∙ cm-2 reaches its maximum value and is ~ 3.5, which is much more than the temperature of the heating. With laser activation, the optimum energy density was W ≈ 2 J ∙ cm-2. A comparative analysis has shown that under high vacuum conditions, laser activation leads to a significantly larger increase in σm than in the case of temperature activation. This is explained by the intense removal of O, C, S impurity atoms under the action of laser beams.

Resume : In the next years, swarms of wireless sensor nodes will be spread all around our environment and inside human bodies. They will be permanently interconnected, capturing and sharing information, to generate useful data and take decisions by themselves. This disruptive concept is known as Internet of Things (IoT), however there are still some important difficulties to achieve a global deployment. One of these difficulties is the energy dependency. A promising alternative, explored for more than 10 years, is harvesting the required energy from ambient sources. Now, this option becomes possible thanks to the great reduction in power consumption and price of electronic circuits. This work is mainly focused on energy harvesting from ambient vibrations by means of piezoelectric resonant devices. ENSO project (ECSEL-H2020) is dealing with this and other approaches (mechanical, thermal and solar harvesting, wireless charging, and flexible batteries) to develop new energy efficient systems for Smart Objects. Here, in collaboration with ENERGIOT, we propose several vibration-driven energy harvesters based on different lead-free piezoelectric technologies: (1) AIN by RF sputtering deposited and (2) ZnO nanostructures integrated with SOI-based MEMS structures and (3) polymer-based materials deposited by screen and inkjet printing. A self-powered IoT node (~100 μW – 80 Vpp) has been developed to measure temperature and voltage and wirelessly transmit the information (ISM band) every 15 s.

Resume : As fossil fuel depletion and environmental pollution become an issue, lot of efforts to develop renewable energy continue to increase. As part of these efforts, energy harvesting technologies are gaining attention as green energy source. One of energy harvesting technology, triboelectric nanogenerator has the advantage of low-cost, high-efficiency, and research is being carried out with a variety of materials and energy sources. There are triboelectric nanogenerator using solid and using fluids. There are many studies that utilize water that is sustainable and clean power source with not affected by friction as well as polar molecules in the fluid, but research that is insufficient due to condensation, which is a change in water condition. Therefore, demand for condensation research is increasing In this study, we demonstrate condensed droplets triboelectric nanogenerator(CD-TENG). Which is harvest using droplets produced by condensation on the surface. Flows of droplets were analyzed through simulation. Correlation of energy generation by water droplets, energy generation and temperature difference has analyzed. Additionally, the correlation between heat transfer and energy generation resulted in an analysis of the electrical and thermal characteristics of the water flow. It is expected to be used as a complement the efficiency of equipment that is degraded by condensation of water and can be a sensor to inform condition of equipment.

Resume : Paper presents comparative analysis of energy capture methods based on specific conversion systems, such as piezoelectric, electromagnetic and thermoelectric. Several techniques have been proposed and developed to extract energy from the environment. The most common available sources of energy are: wind, solar, temperature and stress (pressure). In general, vibration energy could be converted into electrical energy using one of three techniques: electrostatic charge, magnetic fields, and piezoelectric materials. The piezoelectric elements store the energy in two forms, as an electric field (electrical energy) and as a strain (mechanical energy). Energy harvesting is an attractive concept because of energy sources, such as light, heat, and mechanical vibration that exist in our ambient living could be converted into usable electricity. Some applications refer to the potentials of piezoelectric and thermoelectric technologies for harvesting energy. Super-capacitors and rechargeable batteries could appropriate store the electricity from such special structures of various materials. Laminate composites consisting of longitudinally magnetized magnetostrictive material and longitudinally poled piezoceramic layers could enhance magnetoelectric effects when driven near resonance. For instance, the composites give criteria for optimizing the magnetoelectric effect in terms of the choice of the individual constituents. The goal is to highlight research efforts for new important applications of advanced materials and structures, such as in self-powered devices, and components for integrated autonomous micro-power sources.

Resume : The microbeads (MBs) are plastic particles with size from 5 μm to 1 mm, which are used in various applications such as facial scrub and drug delivery materials. However, the environmental issue is recently raised due to their non-degradation and adsorption property of persistent organic pollutants (POPs) in the sea, resulting in the ecocide of marine environment. Above all, almost the MBs have been prepared by wet process which use a number of toxic solvents. Therefore, it is urgent to develop biodegradable MBs via eco-friendly methods. Poly(lactic acid) (PLA) is a biodegradable aliphatic polyester which can obtain using raw materials from nature. PLA has many excellent properties, such as biocompatibility, high mechanical strength, cost effectiveness, and melt processability. Electrospray is a simple and effective method for bead preparation, and is applicable to both polymer solution and melt. Also, this process is affected by various processing parameters, such as voltage and needle diameter. In this study, the rheological properties of PLA was controlled by electron beam irradiation. Then the MBs were prepared by melt electrospraying process and effects of process parameters on beads morphological properties were studied. The various physical/chemical properties, such as morphology, biodegradability and POPs adsorption properties were investigated, and the possibility of PLA MBs for an alternative to non-degradable MBs was confirmed.

Resume : We have succeeded in hydrothermal synthesis of well-crystallized micrometer-sized particles of Zn-Terephthalic acid (TPA) metal organic framework (MOF) in which layered hydroxide of Zn is bridged by TPA. The MOF electrode prepared by doctor blade coating onto an F-doped SnO2 conductive glass exhibited reversible redox at around -1 V vs. Ag/AgCl in a neutral KCl solution. Electrochemical stoichiometry as, Zn4(OH)6(C8H4O4) + 2H+ + 2e- ⇄ Zn4(OH)6(C8H6O4) has been suggested with its redox active fraction of the coated amount close to 18% and coulombic reversibility over 95%, indicating redox reactions not only at the surface but in the bulk of the MOF grains. Proton exchanging capability as well as structural rigidity by TPA result in the proton selective stable redox of the MOF. When the electrolyte solution was replaced with KI as a redox electrolyte (3I- ⇄ I3- + 2e-), the system worked as a rechargeable redox battery without a membrane owing to the proton selectivity of the redox of MOF. Since all the materials used are cheap, safe and the battery can also be made flexible, it is ideally suited as an autonomous power source for IoT applications.

Resume : Structural, electronic, magnetic and transport properties of Co-rich spin gapless semiconductor CoFeCrGa is studied using theoretical and experimental techniques. The quaternary Heusler alloys Co1+xFe1-xCrGa (x = 0.1 to 0.5) are found to crystallize in LiMgPdSn-type structure having space group F43m (# 216). The ab-initio simulation predicts almost spin gapless semiconducting behaviour for x  0:375, above which it shows half-metallic ferromagnetic (HMF) characteristics. The calculated magnetization is found to be in fair agreement with experiment as well as the prediction of the Slater-Pauling rule. The magnetic transition temperature is found to be well above the room temperature for all the concentrations. Measured electrical resistivity in the temperature range of 5-350 K suggests that the alloys retain the SGS behavior upto x =0.4 and for x = 0.5 it shows a half-metallic character with a minimum in the resistivity attributed to the weak localisation effect. The conductivity value at 300 K lies in the range of 2289 S/cm to 3294.3 S/cm, which is close to that of other reported SGS materials. Transport properties are studied in detail using the scaling of Hall resistivity data with longitudinal resistivity data. The increase in the intrinsic anomalous Hall contribution with x is correlated with the enhancement in chemical order. The anomalous Hall coefficient is estimated to be 37.92 and 42.67 S/cm at 5K for x= 0.1 and 0.3 respectively. The conductivity behaviour and almost zero Seebeck coefficient support the SGS behaviour in alloys with x upto 0.4. Thus, with the substitution of Fe by Co in CoFeCrGa, the SGS nature is found to change to HMF as x increases. These materials are potential candidates real-time spintronic devices.

Resume : Piezoelectric materials attract great interest due to their possible application in various fields such as energy harvesting or electronic bio-integration [1]. In the present communication, we describe nanocomposite films, incorporating piezoelectric inorganic nanomaterials, as barium titanates (e.g. BaTiO3) in polymers as polydimethylsiloxane (PDMS) or polyvinylidene fluoride (PVDF). The encapsulation in polymers improves the mechanical properties of the materials such as flexibility and stretchability. Moreover, in the case of PVDF composites, it contributes to enhance the piezoelectric response of the multicomponent film [2]. Piezoelectric inorganic materials in different forms (nanoparticles, nanorods or nanotubes) are prepared by wet chemistry techniques (e.g. hydrothermal synthesis). The structural properties and purity of the phases are investigated by X-ray diffraction while the morphology is analyzed with electron microscopy techniques. In particular, the multicomponent films are investigated by scanning electron microscope to probe the heterogeneity and the thickness of the films. The piezoelectric properties of the nanocomposite films will be considered in order to correlate the piezoelectric performance of the nanocomposites to the film compositions as well as to the preparation conditions. References [1] K. Uchino, “Glory of piezoelectric perovskites,” Sci. Technol. Adv. Mater., vol. 16, no. 4, p. 46001, 2015. [2] C. Baek et al., “Applied Surface Science Enhanced output performance of a lead-free nanocomposite generator using BaTiO 3 nanoparticles and nanowires filler,” Appl. Surf. Sci., vol. 429, pp. 164–170, 2018.

Resume : Recently, with the miniaturization of electronic devices, problems with regard to the size and capacity of batteries have arisen. Energy harvesting is receiving significant attention to solve these problems. In particular, the thermoelectric generator (TEG) is being studied for its ability to harvest waste heat energy. However, studies on organic TEGs conducted thus far have mostly used conductive polymers, making the application range of TEGs relatively narrow. In this study, we fabricated organic TEGs using carbonaceous nanomaterials (i.e., graphene nanoplatelet and single-walled carbon nanotube) with polyelectrolytes via layer-by-layer (LbL) coating on polymeric substrates. The thermoelectric performance of the carbonaceous multilayer structure was measured, and it was confirmed that the thermoelectric performance of the TEG in this study was not significantly different from that of the existing organic TEG fabricated using the conductive polymers. Moreover, by simply changing the electrolyte, p- or n-type TEGs could be easily fabricated with carbonaceous nanomaterials via the LbL process. Triboelectric nanogenerators (TENGs) are also a promising next-generation mechanical energy harvester because of their light weight, portability, and eco-friendliness. However, some requirements such as cost-effectiveness, high performance, scalability, and simple process make the real industrial applications of TENGs difficult. In this study, we first reported graphene-based TENG LbL technique that enables low cost, durable, scalable, and wearable TENGs. The LbL-based graphene multilayer was deposited on a flat, undulated polymer substrate or textile structure, where the graphene multilayers role as a positive triboelectric-material and electrode of devices. A graphene multilayer on a textile was demonstrated for scalable and wearable TENG operated by a single electrode mode. The simple and versatile graphene-based LbL assembly can provide some portable microelectronic applications like self-powered wireless sensors and further wearable energy harvesting devices.

Resume : Four new conjugated microporous polymers (CMPs) were synthesised through Buchwald-Hartwig cross coupling reaction by using the monomers of 1,3,5-tris(4-bromophenyl)amine, tetrakis(4-bromidephenyl)ethylene, 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris-(4-aminophenyl)triazine as building block. All the CMPs material possess not only high Brunauer–Emmett–Teller (BET) specific surface area (the highest one is up to 1040 m2 g-1), high chemical and thermo stability but also good luminescent property. They show very fast responses and high sensitivity to the nitroaromatic explosives. The CMPs may be a new kind of material for detecting explosives. Moreover, the LPCMP1 and LPCMP3 show outstanding swelling ability in many organic solvents such as Toluene, tetrahydrofuran (THF) and methanol. For the LPCMP1 and LPCMP3 in THF, the swellability (be defined by the volume change of the before and after swollen polymer (mL) divided by the mass of polymer used (g)) can reach about 16 mL g-1. Owing to such excellent swelling ability, we further studied the adsorption capacity of the CMPs for different harmful organic vapours such as toluene and methanol. For the LPCMP1, the adsorbed amount of toluene is 1168 mg g-1 and the adsorbed amount of methanol is 2571 mg g-1. As far as we know, the both two adsorption capacities are the highest one compare with other CMPs materials and even other porous materials. So we believe that they are the greatest potential materials for harmful organic vapours elimination and chemical warfare agent uptake.

Resume : It is defined as high-performance engineering plastic (Super EP, Super Engineering Plastic) at 150℃ or higher. Super engineering plastics generally have a tensile strength of 500 kgf/cm2 or more at 150°C or higher and a bending elastic modulus of 25,000 kgf/cm2 or more. They can compete with metal products, which is advantageous for weight reduction and can precisely shape complex shapes. It has the advantages of low product manufacturing process cost than metal, high abrasion resistance, creep resistance and dimensional stability. In this study, the properties of fiber structure and morphological behavior of amorphous Super EP resin according to melt spinning process conditions, hole diameter and hole diameter, L/D, shear rate and draft draft in nozzle hole were studied. First, three types of amorphous Super EP resin, PSU (Polysulfone), PES (Polyethersulfone) and PEI (Polyetherimide) were fabricated in various processes using single-, twin-screw extruder and lab.- pilot-scale winder , Fiber diameter and linear density and tensile properties were determined according to melt spinning process conditions (temperature, discharge amount, pressure, etc.) and winding speed.

Resume : Incorporating a photovoltaic energy harvester with lithium battery storage into a single module has the potential to solve the challenges facing miniature autonomous electronics used in internet of things (IoT) and remote sensors. However, the two technologies are usually not current and voltage compatible and require voltage up-conversion for useful integration, performance and overcharge protection. At the same time, variations in illumination intensity and spectrum make maximum power point tracking (MPPT) an important tool for regulating a PV-Battery device. Both voltage matching and MPP-tracking can be accomplished with modern dc-dc converter units. In our development towards a PV-battery device with a lead-halide Perovskite solar cell, we found that using typical DC-DC converters optimized for silicon PV modules to be sub-optimal and also found that converter MPPT algorithm choice has an effect on Perovskite solar cell performance and subsequently affects the solar-to-battery efficiency of the system. By optimizing PV cell parameters and converter choice we have shown a record setting solar-to-battery efficiency of 11 % with a Perovskite solar cell charging a LTO/LFP battery.

Resume : Triboelectric nanogenerator (TENG) is of great interest as an emerging power harvester due to its simple architecture and high efficiency. Despite development of various surface chemical and mechanical modification techniques for enhancing the performance of a TENG with a given triboelectric pair of materials, a method capable of being used universally on a variety of surfaces and improving the performance of TENGs with diverse surfaces remains a challenge. Here, we demonstrate a novel transfer-printing of hierarchically dewetted polymer microdroplets on various TENG surfaces for performance enhancement of the TENGs. Our method is based on controlled dewetting of a thin supramolecular assembled film of two end-functionalized polymer blends on a prepatterned poly(dimethyl siloxane) mold, followed by the physical pattern-transfer of arrays of the dewetted droplets consisting of supramolecular assembled nanostructures on a TENG contact surface. The hierarchically dewetted microdroplets comprising soft-etched nanopores efficiently improve the performance of a TENG by more than three times compared to one without the transferred pattern. The pattern-transfer is successfully achieved on various surfaces including not only oxides, plastics and metals, but also fabrics, coins, vegetables, and shells, making our approach a convenient way for enhancing the triboelectric performance of a given TENG.

Resume : There are several types of energy loss, including loss caused by thermal, vibrational, acoustic, and electromagnetic effects. Electric fields, which are induced by all electric systems, affect the adjacent dielectric material, changing its polarization direction. Thus, some of the input energy is used in heating the dielectric material, causing energy loss in the form of heat dissipation. In other words, materials unrelated to the electric system are polarized by electrostatic induction, thereby decreasing the electric efficiency due to dielectric loss. Many methods have been studied to reduce dielectric loss; however, no fundamental approach has yet been proposed for converting dielectric loss into available electric energy for the operation of electronic systems. This suggests an opportunity to design a highly efficient mechanism for dielectric loss reduction by introducing an energy-loss return process. To develop this process, it is necessary to select a stable material that can transfer substantial amounts of energy without additional energy loss. Among the possible materials, liquid dielectrics provide significant benefits in that they offer high dielectric strength, can serve as a refrigerant, prevent corona discharge, and suppress electric arcing. These characteristics are well suited for energy transfer, while maintaining electric stability, and provide the basis for an efficient energy return system. To minimize the energy loss arising from dielectric loss, an investigation of the relationship between liquid dielectric properties and energy transfer is performed. The result is an increase in both the available electric power and the efficiency of the overall system. Through studies of electric field effects on liquid dielectric polarization, we investigate the energy-loss return gate (ELRG) as a novel method for converting dielectric loss into available energy. The primary mechanism is demonstrated using a triboelectric generator (TEG), which generates electrical potential in the form of a pulsed AC signal. We have successfully designed an amplified TEG with an energy-loss return system that can amplify electrical peak power by 350%, and charging performance by 240%, with equivalent input energy. Furthermore, we show how the liquid dielectric polarization effect, due to the molecular polarization characteristics, can be used in the ELRG to harvest the energy loss from a wide array of electronic devices used in daily life. These electric/electronic systems can be operated more efficiently through the cooling effect arising from decreased power consumption. Most importantly, this approach of using returned energy loss as an available electric energy source can be implemented without a complex fabrication process. The method is simple and intuitive and provides a means for addressing the problem of energy loss and electric/electronic efficiency in a given system, while amplifying energy harvesting efficiency, reducing the power consumption of electronics, and storing the retrieved energy for use in another system. The ELRG is an innovative approach in the sense that it can enhance many other superior energy harvesting technologies, in addition to improving electronics efficiency. Thus, adapting this methodology will aid in the development of energy harvesting research as well as other energy-related engineering disciplines.

Resume : Nanogenerators harvesting energy from triboelectrification between liquid and solid are gaining remarkable interest as a new energy conversion method due to its sustainability. To ensure complete detachment of liquid from the surface, superhydrophobic surfaces have been considered as an attractive material. In this regard, the hierarchy of the structure of superhydrophobic surfaces is important for retention of the superior wetting properties, but the effects of the hierarchical structures on the energy harvesting performance of triboelectric nanogenerators have only been rarely examined. In this work, we first report the significance of the hierarchical structure on durable and stable output generation of superhydrophobic triboelectric nanogenerators. For the first time, we investigate the relationship between the electrical output of TENGs and the behavior of impact droplets on superhydrophobic surfaces with different scale lengths under various drop impact conditions. Furthermore, we evaluate which non-wetting surface with a hierarchical structure is suitable for generating electricity from various liquids with a wide range of surface tension and viscosity levels. Based on these findings, we suggest a practical self-powered sensor application that can easily and quickly measure the concentration of liquids such as ethylene glycol.

Resume : Triboelectric nanogenerator (TENG) is a spotlighted energy harvesting that can convert mechanical energy into electrical energy. However, as triboelectric effect is the main principle of TENG, friction damage occurs naturally when two surfaces contact. To overcome this issue, previous researches have utilized water as a triboelectric material itself. This water-solid contact TENG have shown much longer lifespan compared to solid-solid contact TENG, but most of water-solid TENG has produced single peak output per waterdrop. In this work, we demonstrate the screw pump TENG (SP-TENG) that can continuously generate electrical output by spinning screw inside the water reservoir. SP-TENG is designed based on Archimedes’ screw pump which consists of a shaft with spinnable screw inside a housing pipe. The spin of screw causes water to be pumped up inside the screw, which makes electrical potential difference between the water and the electrode on screw surface. We considered two major factors to design SP-TENG in the way to maximize the output: the rotational speed of screw, and the dimension of electrode. Furthermore, as a final demonstration, we introduce self-powered sensor for water circulation system utilizing SP-TENG.

Resume : This work studies the properties of a device that converts thermal gradients to electrical power on a micro scale. Our thermoelectric micro/nanogenerator (μTEG) consists of a suspended silicon platform isolated from a bulk silicon by dense arrays of doped silicon nanowires (Si NWs). The NWs work as a thermoelectric material. This device has been designed to work as an energy harvester and not to characterize the Seebeck coefficient of the thermoelectric material. Despite that, by measuring the temperature on both hot and cold sides of the device through two different temperature sensors placed on the platform and on the surrounding bulk structure, it is possible to obtain an estimation of an effective Seebeck coefficient of the whole array of Si NWs. To accomplish this, we assume that temperatures are mostly uniform both on the suspended platform and on the bulk silicon structure. Therefore, the highest thermal gradient results across the Si NWs. To validate such assumption, a finite element model of our device has been built with COMSOL under appropriate boundary conditions. A set of simulations show the temperature distribution in the device with respect to underestimating or overestimating the effective value of the Seebeck coefficient of the array of Si NWs. Keywords: Thermoelectric, Silicon, simulation

Resume : 8 mol % Yttria-stabilized zirconia (8YSZ) thin films of various thickness were firstly deposited by Pulsed Laser Deposition (PLD) on Si (100)/ BK7 glass substrate at 500C and 600C, at repetition rate of 10Hz, fluences of 3 J/cm2 and 4 J/cm2, oxygen partial pressures 5 and 4 x 10-2 mbar. 20 mol% Samaria doped ceria Smx Ce1-xO2-x/2 (x= 0,2, Sm0,2Ce0,8O1,9) was deposited on the top of 8YSZ thin films under the same PLD control parameters. The aim is to study the effect of different 8YSZ thickness and other PLD control parameters on structural and optical properties of bilayer 20SDC/8YSZ, with a constant thickness of 20SDC like an efficient technology for planar ceramic electrolytes implemented in miniaturized Solid Oxide Fuel Cell (µSOFC) and λoxygen sensors. The bilayer thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy measurements (XPS) and spectroscopic ellipsometry (SE). The XRD showed a great influence of the crystalline structure of 20SDC/8YSZ bilayer on system properties; SEM identified a nanolaminatinate of uniform thickness with collumnar vertically – oriented morphology. Refractive index was calculated by an advanced GenOsc Tauc-Lorentz model. Keywords: Samaria doped ceria, PLD, bilayer electrolyte, µSOFC, λ oxygen sensors Acknowledgment: This work has been financed by the National Authority for Research an Innovation in the Frame of Nucleus Programme

Resume : A super-engineering-plastic polyphenylene sulfide (PPS)-based composite was fabricated for circuit board application. A small amount of liquid crystal polymer (LCP) was blended with PPS in order to enhance the copper plating performance. In addition, 4 wt% of laser activated particles (LAPs) were added to the polymer blend. LCP/LAP exhibited a better interfacial affinity than that of PPS/LAP. Moreover, a layered structure was observed for the PPS–LCP blend; a small number of LAPs were observed at the LCP region, while a larger amount was observed at the PPS region. This LAP leaning led to a lower mechanical-strength degradation, which originated from the weak interaction between the LAPs and polymer. Moreover, the high LAP concentration at the surface enabled the enhancement of the plating performance with a lower total LAP concentration.

Resume : We have demonstrated a direct laser writing (DLW) process that uses a femtosecond laser to fabricate a nano-micro hierarchical structure for a large capacitance microsupercapacitor (MSC) electrode. By applying a two-photon polymerization (TPP) based DLW technique, a photoresist (PR) nano-pillar pattern was fabricated on a pre-defined PR interdigitated electrode (PR-IDE) pattern to form a nano-micro hierarchical structure. Carbon pyrolysis converted a PR-IDE with a nano-micro hierarchical structure to a PR derived carbon (PRC)-IDE while maintaining the aspect ratio of the pillar structure. The electrochemical performance of the PRC-MSC is improved by introducing the nano-pillar pattern to the PRC-IDE, resulting in larger areal capacitance of the as-fabricated PRC-IDE compared to the PRC-IDE with a micropattern only. The PRC-IDE with a nano-micro hierarchical structure in this study could be further applied as a backbone electrode structure for a high power pseudo-capacitor.

Resume : Metal-organic framework (MOF) is a class of inorganic/organic compounds whose crystalline structure is made by bridging inorganic ions with organic ligands. We have recently reported microwave assisted hydrothermal synthesis of MOFs with various layered structures, in which Zn2+ ions are bridged by terephthalic acid (TPA). These Zn-TPA MOFs exhibited proton-selective reversible redox reactions. In this study, we have achieved one-step electrodeposition of Zn-TPA MOF thin film in a Zn3(OH)4(TPA)•6H2O composition by addition of TPA into the bath for electrodeposition of ZnO, namely, O2-saturated aqueous solution of ZnCl2. Although a homogeneous and strongly adherent thin film made of platelets of MOF was obtained, its thickness was limited to about 2 µm due to strong passivation of the surface towards O2 reduction. The proton-coupled redox properties of the electrodeposited Zn-TPA MOF thin films as well as their use in redox batteries are to be presented.

Resume : The search for autonomous power sources to feed electronic devices anytime and anywhere is the main challenge for science. One solution is hybrid thermally chargeable supercapacitor [1?4] that combines the use of a temperature gradient, ?T, to be the trigger for energy harvesting with the advantage of accumulating energy has a supercapacitor at the same time. In the presented work an innovative planar 2D solid-state interdigital ionic thermoelectric micro-supercapacitor was produced through a photolithography process using carbon nanotubes (electrodes) and a solid polyelectrolyte. The thermoelectric performance was address by measuring the output performance under different temperature gradients up to 20 K, leading to a linear slope of 2.35 mV K-1, under steady-state conditions. The evaluation of the electrochemical energy storage properties revealed a volumetric energy density of 1.05 mWh cm-3 and a volumetric power density of 1.21 W cm-3. Remarkable low-cost production, possibility to scale-up and flexibility makes this device sustainable for low-grade applications. [1] H. W. Zhao et al. Energy Environ. Sci. 2016, 9, 1450. [2] A. Kundu, T. S. Fisher, Electrochim. Acta 2018, 281, 357. [3] F. Jiao, et al. J. Mater. Chem. A 2017, 5, 16883. [4] S. L. Kim, et al. Nano Energy 2018, 48, 582. Acknowledgements: Work funded by FEDER through COMPETE 2020 and by Portuguese funds through FCT/MEC under Program PT2020 in the framework of the projects PTDC/CTM-MAN/5414/2014, PTDC/CTM-TEX/31271/2017, UID/QUI/50006/2013-POCI/01/0145/FEDER/007265, UID/NAN/50024/2013 and NORTE-01-0145-FEDER-022096 from NECL. CP thanks FCT for Investigator contract IF/01080/2015. RSC thanks UniRCell Project (POCI-01-0145-FEDER-016422) for a MSc. grant.

Resume : New generations of connected objects challenge researchers to find new ways to power these micro-systems and to make them fully autonomous, smart, connected, secure and trusted. In this context, energy-harvesting technologies such as photovoltaics, piezoelectrics or thermoelectrics show great promises as they enable the conversion of solar radiation, motion or thermal energy into useful electrical energy to charge micro-batteries for example. Micro-thermoelectric generators (μ-TEG) exhibit several key benefits (no-moving parts, high reliability, no emission of hazardous gas) and take advantage of any temperature difference between their two surfaces. However, their performance critically depends on the shape of the TEG. In this communication, using numerical tools, we discuss the potential of a new flexible μ-TEG design used for thermal energy harvesting. The thermocouples are made of bismuth telluride thin films. The influence of several boundary conditions (fixed temperature, electrical contact resistance) on the electrical performance is presented using a finite element analysis with the commercial software Comsol Multiphysics©. Under a temperature difference of 10 K and assuming the absence of any electrical contact resistance, the study shows the possibility to achieve a net output power of 0.22 μW per thermocouple. However, when electrical contact resistances above 10-5 Ω.cm2 are considered, the performance is drastically reduced

Resume : We have been pursuing an all-silicon microthermoelectric generator to exploit the material abundance and the miniaturization capabilities and scalability of silicon technologies. In our approach, silicon is employed as a structural material in a way that with top-down microfabrication technologies, a microstructure is fabricated where a temperature difference can be established between two regions. Hundreds of thousands of Si NWs are grown across this region of temperature contrast by means of bottom-up techniques. Si NWs can be considered as a moderately good thermoelectric material as they exhibit a reduced thermal conductivity (compared to its bulk counterpart). In addition, the integration of a heat exchanger can boost power densities up to 10-100 µW/cm2 at 50-150 °C hot side temperatures. In this work we present a novel geometry configuration which improves the power density obtained on our previous designs, and connecting in series up to 50 of such microthermoelectric generators in a single 0.5cm2 chip. Some of the new devices include silicon microbeams, instead of nanowires, bridging the hot and cold areas of the microstruture for test purposes, so that we can compare how much of the power generated is due to the nanostructuring of silicon in nanowires form. We will show the preliminary power outputs of these new designs with silicon microbeams instead of silicon nanowires and will compare them to previous designs to evaluate the expected improvement in power density.

Resume : With the emergence of low power communication protocols, there is a real demand for autonomous micro-sources of energy that can deliver ~ 10 - 100 μW. That range of power can easily be supplied by standard thermoelectric (TE) module under stationary operating conditions. However these conditions of use are not necessarily adapted for wireless sensors. For example, the energy input can be very intermittent, or the volume available too small to use a TE module and its heat sink. The expertise developed at the Institut Néel in the elaboration of suspended thermal sensors has been used to design suspended thermoelectric nano-TEG. Planar nano-TEG are made of silicon nitride membranes suspended with the help of several arms. Thermoelectric materials are deposited onto these arms. Since membranes have a negligible mass, their temperature can fluctuate contrary to the bulk silicon frame which conducts well the heat. Thus a temperature gradient appears between membranes and the bulk silicon frame. The proof of concept has been validated using poorly optimized Bi2Te3 TE thin films (ZT ~ 0.2). In that case, for temperature gradient of 8 K the power generated by one membrane is about 1 nW. The duplication of this nano-TEG thanks to standard MEMS clean room techniques enabled us to obtain 1800 membranes which harvest microwatts from a temperature gradient of few degrees and a surface of 4 cm². For standard ZT values that power may increase to several hundreds of μW in the same conditions (10°C and 10 cm²). This power is enough for suppling sober sensors would then be made autonomous. Moreover the patented design of the nano-TEG array permits to arrange the nano-TEG in serial and/or in parallel depending of the final resistance expected, allowing to decrease the resistance to tenth ohms. That low resistance permit to use standard DC/DC converter to process the harvested energy. Prototypes have been built with two industrial groups and coupled to an ASIC in order to get an operational autonomous sensor. MOÏZ, a start-up commercializing that solution is going to be created.