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[Invited] Bio-inspired hierarchical phononic crystals and metamaterials: Bioinspired metamaterials
No full textInternational audienceMarco Miniaci is a permanent researcher at the French National Scientific Research Centre (CNRS) appointed at the Institute of Electronics, Microelectronics and Nanotechnology (IEMN) of Villeneuve D’Ascq, in France. His research interests cover theoretical, numerical, and experimental aspects of wave propagation and structural mechanics of phononic crystals and elastic metamaterials. Marco Miniaci currently is the principal investigator of the ERC StG « POSEIDON » (dealing with bioinspired metamaterials, topological protection and underwater acoustics), coordinator of the MAGNIFIC HORIZON-CL4-2022-RESILIENCE-01-10 (dealing with materials for a next generation of (nano-)opto-eòectro-mechanical systems), and participate into the MetAcMed HORIZON-MSCA-2022-DN-01 (dealing with acoustic and mechanical metamaterials for biomedical and energy harvesting applications)
Estimation d'une loi de saut en fréquence par une analyse de la transformée de Fourier bidimensionnelle du spectrogramme
No full textInternational audienceThe estimation of frequency-hopping spread spectrum (FHSS) signals plays a crucial role in the analysis and detectionof communications in dynamic and complex environments. In this paper, we introduce a novel method based on the frequencyanalysis of the spectrogram of an FHSS signal, specifically the 2D Fourier Transform (TF2D), to accurately characterize the hoppingpattern parameters. This approach enables the estimation of dwell time, hop frequency, as well as the periodicity of hops in bothtime and frequencyL'estimation des signaux à sauts de fréquence (FHSS) joue un rôle crucial dans l'analyse et la détection des communications dans des environnements dynamiques et complexes. Dans cet article, nous présentons une nouvelle méthode basée sur l'analyse fréquentielle du spectrogramme d'un signal FHSS, en particulier la transformée de Fourier 2D (TF2D), pour caractériser avec précision les paramètres de la loi de saut. Cette approche permet d'estimer la durée et la fréquence de maintien des plots, ainsi que la périodicité des sauts en temps et en fréquence.</div
A Universal Implementation Approach for Multivalued Logic Gates Based on Negative Transconductance in Series-Connected Two-Dimensional Transistors
No full textInternational audienceMultiple-valued logic (MVL) is highly desired for algebra, logic, and artificial intelligence due to its higher information density. However, its practical adoption has been hindered for decades by extensive hardware requirements. Two-dimensional (2D) materials with exceptional electronic properties provide possibilities for the development of MVL devices with simple structures. Despite several reports on ternary logic (r = 3) hardware, extending their design to higher logic radix devices (r > 3) is challenging. The construction of elementary MVL gates with a higher radix is still relatively underexplored, and a universal device implementation approach is lacking. In this study, we exploit transconductance (g) matching between the negative transconductance (NTC) effect in series-connected molybdenum disulfide (MoS) and black phosphorus (BP) transistors, along with the multiple current valleys of BP transistors, to realize a series of multivalued logic (MVL) gate families (r = 3, 4, 5). Our design achieves reduced transistor counts, higher DC gains, and lower power consumption. Standard quaternary (r = 4) and quinary (r = 5) inverters are demonstrated using only four and five planar transistors, respectively. Additionally, compact models of 2D transistors and equivalent circuits of the MVL gate are established, supporting future large-scale MVL system design and simulation
The 2024 General Election in Scotland: Persistent Instability or Realignment?
No full textInternational audienceOn 4 July 2024, the number of Scottish Labour MPs soared from 1 in 2019 to 37, mostly at the expense of the SNP which retained only 9 MPs. This resulted both from the momentum for Labour at UK level and from the SNP’s growing divisions over policies and between individuals. The SNP lost its reputation for competence, probity, with a clear path to independence. The article analyses the reasons for these changing patterns which weakened the SNP’s dominance over the months leading to the election. Yet it casts doubts about a possible realignment, for Scottish Labour’s victory lacks sound foundations in terms of popular support, distinctive policies, and vision for Scotland’s place in the UK.Le 4 juillet 2024, le nombre de députés travaillistes écossais a fait un bond, passant de 1 en 2019 à 37, aux dépens du SNP qui n’en conserve que 9. Ce succès, qui s’inscrit dans une dynamique porteuse pour les Travaillistes au plan britannique, a été favorisé par les déchirements du SNP autour de personnes et de politiques, qui ont terni la réputation de ce dernier reposant sur sa compétence, sa probité et sa stratégie pour accéder à l’indépendance. Cet article analyse les raisons de ces bouleversements qui ont fragilisé la position dominante du SNP dans les mois précédant les élections, tout en s’interrogeant sur un éventuel réalignement car la victoire des Travaillistes ne repose pas sur des fondations solides, s’agissant des suffrages émis, du programme, ou encore de la vision de la place de l’Écosse dans le Royaume-Uni
Electrochemical Additive Manufacturing to Electropolymerize Devices on a Chip
No full textInternational audienceFabricating electronic devices spoiling the least resources is of an increasingly high importance. Also, micro-electronics hardly embeds chemical functionalities on silicon, as soft materials suffer from harsh conditions of conventional processes. In this study, electrochemistry on a chip is investigated to pattern conductimetric devices at small scale via electropolymerization. To comply with additive manufacturing, a dewetting coating and local quasi-reference/counter micro-electrodes shall be integrated on each chip. The process reliability is challenged using minimalist chemical and energy resources, such that a µL droplet of an electro-active solution composed mostly of a non-toxic and affordable solvent suffices to coat 16 conductimetric elements on a 3×3 mm 2 chip. Despite the complexity of electrochemistry at such scales, the coatings variability is dominated by the chemical composition of the droplet. Avoiding a vessel to confine large volumes of solutions and integrating all electrodes is required to reduce drastically the electrochemical signal noise. This demonstrates its sufficient stability to screen conducting polymer materials when their precursors are not available in large amount to be coated with conventional techniques. It also demonstrates its compliance for chips microfabrication using conducting polymers as functional materials for electrochemically-assisted additive manufacturing production.</div
Impact of Multi-Bias on the Performance of 150 nm GaN HEMT for High-Frequency Applications
No full textInternational audienceThis study examines the performance of a GaN HEMT with a 150 nm gate length, fabricated on silicon carbide, across various operational modes, including direct current (DC), radio frequency (RF), and small-signal parameters. The evaluation of DC, RF, and small-signal performance under diverse bias conditions remains a relatively unexplored area of study for this specific technology. The DC characteristics revealed relatively little Ids at zero gate and drain voltages, and the current grew as Vgs increased. Essential measurements include Idss at 109 mA and Idssm at 26 mA, while the peak gm was 62 mS. Because transconductance is sensitive to variations in Vgs and Vds, it shows “Vth roll-off,” where Vth decreases as Vds increases. The transfer characteristics corroborated this trend, illustrating the impact of drain-induced barrier lowering (DIBL) on threshold voltage (Vth) values, which spanned from −5.06 V to −5.71 V across varying drain-source voltages (Vds). The equivalent-circuit technique revealed substantial non-linear behaviors in capacitances such as Cgs and Cgd concerning Vgs and Vds, while also identifying extrinsic factors including parasitic capacitances and resistances. Series resistances (Rgs and Rgd) decreased as Vgs increased, thereby enhancing device conductivity. As Vgs approached neutrality, particularly at elevated Vds levels, the intrinsic transconductance (gmo) and time constants (τgm, τgs, and τgd) exhibited enhanced performance. ft and fmax, which are essential for high-frequency applications, rose with decreasing Vgs and increasing Vds. When Vgs approached −3 V, the S21 and Y21 readings demonstrated improved signal transmission, with peak S21 values of approximately 11.2 dB. The stability factor (K), which increased with Vds, highlighted the device’s operational limits. The robust correlation between simulation and experimental data validated the equivalent-circuit model, which is essential for enhancing design and creating RF circuits. Further examination of bias conditions would enhance understanding of the device’s performance
Review of 3D topography stitching and registration algorithms: procedure, error evaluation and mathematical modelling
No full textInternational audienceSurfaces are the privileged places of interaction between physical phenomena and objects. Roughness studies, especially when performing multiscale analysis, are tools of choice to understand physical phenomena and their scales of application. However, profilometers, especially optical systems, must compromise between field of measurement and resolutions. Stitching is an assembling technique aiming to solve this compromise by combining elementary maps, such as images or topographies. Stitching generates high resolution over a large field of measurement maps, which increases the measurable scale range and facilitates the correct identification of physical phenomena at their scales of application. This article proposes a review of 3D topography stitching algorithms. After explanations on the use cases of 3D topography stitching, the stitching procedure from elementary maps acquisition to the obtention of the stitched map is described step-by-step. Secondly, errors in measurement and stitching are presented with the sources of errors and the error evaluation methods. Lastly, the mathematical modelling of 3D topography is detailed to better understand the optimization process used in the in-plane and out-of-plane registration steps of the stitching algorithms. Comparison of algorithms involved in stitching are proposed so that researchers might find the most suitable algorithm to their needs. Overall, this work aims at introducing researchers and metrologists to important multidisciplinary notions for the use and design of 3D topography stitching algorithms and offers a tutorial-based approach
Terahertz Self-Induced Dynamic Slow-Light Behavior in Metasurfaces
No full textInternational audienceDynamically reconfigurable metasurfaces are complex to realize because they require exotic materials, external stimuli, or both. However, with the advent of intense THz transients, these conventional preconditions can be bypassed. Strong THz fields are capable of invoking modulation of the electronic configuration in materials through impact ionization. In this context, we report the diligent intertwining of strong THz field-induced nonlinearities and the structural interactions of near-field coupled metastructures. We experimentally demonstrate a well-established metal-on-silicon metasurface framework to achieve reconfigurability that is devoid of any exotic materials or external stimuli. Aided by meta-geometry, intense THz transients modify the dispersion of the silicon substrate, leading to self-induced nonlinear modulations in conductivities. Altering the conductivity through impact ionization results in dynamically reconfigurable electromagnetically induced transparency (EIT) effects in a self-sustained manner, controlling the slow-light characteristics (group delay and the group velocity) by more than 6 times. These outcomes could potentially enable versatile applications in upcoming 6G technologies and on-chip silicon-based integrated photonics
Non-line-of-sight 300 GHz band Wireless link enabled by a frequency dependent reflective surface
No full textInternational audienceReconfigurable Intelligent Surface is a promising technology for the up-coming sixth-generation (6G) of cellular communication networks. In this context, an experimental study of specular and nonspecular reflections of a reflective surface by scattering parameter measurements in the 300 GHz range is presented. Here we compare the insertion loss of a fixed and passive reflective surface at its optimal output deflection angle with respect to the specular reflection on a metallic plate. We propose a methodology to assess the losses induced by the surface and validate the use of the device within a THz link. At its best, around 290 GHz, the surface insertion loss is less than 3 dB compared to the metallic plate. We then investigate a nonline-of-sight THz link operating in QSPK and QAM-16 coherent transmission using the reflective surface. Data rates up to 10 Gbits/s for QSPK and 20 Gbits/s for QAM-16. This is, to the best authors knowledge, the first demonstration of a non-line-ofsight THz data-link including such reflective surface.</div