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In this paper, we investigate, by combining electrical measurements with an atomistic-To-circuit modeling approach, the conductance of doped standalone multiwall carbon nanotubes (CNTs) as a viable candidate for the next generation of back-end-of-line interconnects. Ab initio simulations predict a doping-related shift of the Fermi level, which reduces shell chirality variability and improves electrical resistivity up to 90% by converting semiconducting shells to metallic. Electrical measurements of Pt-salt-doped CNTs provide up to 50% of resistance reduction, which is a milestone result for future CNT interconnect technology. Moreover, we find that defects and contacts introduce additional resistance, which limits the efficiency of doping, and are the primary cause for the mismatch between theoretical predictions and experimental measurements on doped CNTs.

In this paper, we report a hierarchical simulation\ud study of the electromigration problem in Cu-CNT composite\ud interconnects. Our work is based on the investigation of the\ud activation energy and self-heating temperature using a multiscale\ud electro-thermal simulation framework. We first investigate the\ud electrical and thermal properties of Cu-CNT composites, including\ud contact resistances, using the Density Functional Theory and\ud Reactive Force Field approaches, respectively. The corresponding\ud results are employed in macroscopic electro-thermal simulations\ud taking into account the self-heating phenomenon. Our simulations\ud show that although Cu atoms have similar activation\ud energies in both bulk Cu and Cu-CNT composites, Cu-CNT\ud composite interconnects are more resistant to electromigration\ud thanks to the large Lorenz number of the CNTs. Moreover,\ud we found that a large and homogenous conductivity along the\ud transport direction in interconnects is one of the most important\ud design rules to minimize the electromigration.

National audience

In this paper, we report a hierarchical simulation study of the electromigration (EM) problem in Cu-carbon nanotube (CNT) composite interconnects. This paper is based on the investigation of the activation energy and self-heating temperature using a multiscale electrothermal simulation framework. We first investigate the electrical and thermal properties of Cu-CNT composites, including contact resistances, using the density functional theory and reactive force field approaches, respectively. The corresponding results are employed in macroscopic electrothermal simulations taking into account the self-heating phenomenon. Our simulations show that although Cu atoms have similar activation energies in both bulk Cu and Cu-CNT composites, Cu-CNT composite interconnects are more resistant to EM thanks to the large Lorenz number of the CNTs. Moreover, we found that a large and homogenous conductivity along the transport direction in interconnects is one of the most important design rules to minimize the EM.

International audience; The emergence of nanoelectronics applied to neural interfaces has started few decades ago, and aims to provide new tools for replacing or restoring disabled functions of the nervous systems as well as further understanding the evolution of such complex organization. As the same time, graphene and other 2D materials have offered new possibilities for integrating micro and nano-devices on flexible, transparent, and biocompatible substrates, promising for bio and neuro-electronics. In addition to many bio-suitable features of graphene interface, such as, chemical inertness and anti-corrosive properties, its optical transparency enables multimodal approach of neuronal based systems, the electrical layer being compatible with additional microfluidics and optical manipulation ports. The convergence of these fields will provide a next generation of neural interfaces for the reliable detection of single spike and record with high fidelity activity patterns of neural networks. Here, we report on the fabrication of graphene field effect transistors (G-FETs) on various substrates (silicon, sapphire, glass coverslips, and polyimide deposited onto Si/SiO 2 substrates), exhibiting high sensitivity (4 mS/V, close to the Dirac point at V LG < V D) and low noise level (10 −22 A 2 /Hz, at V LG = 0 V). We demonstrate the in vitro detection of the spontaneous activity of hippocampal neurons in-situ-grown on top of the graphene sensors during several weeks in a millimeter size PDMS fluidics chamber (8 mm wide). These results provide an advance toward the realization of biocompatible devices for reliable and high spatio-temporal sensing of neuronal activity for both in vitro and in vivo applications.

Graphene, the atomically-thin honeycomb carbon lattice, is a highly conducting 2D material whose exposed electronic structure offers an ideal platform for sensing. Its biocompatible, flexible, and chemically inert nature associated to the lack of dangling bonds, offers novel perspectives for direct interfacing with bioelements. When combined with its exceptional electronic and optical properties, graphene becomes a very promising material for bioelectronics. Among the successful bio-integrations of graphene, the detection of ionic currents through artificial membrane channels and extracellular action potentials in electrogenic cells have paved the road for the high spatial resolution and wide-field imaging of neuronal activity. However, various issues including the low signals amplitude, confinement and stochasticity of neuronal signals associated to the complex architecture and interconnectivity of neural networks should be still overcome. Recently, grain boundaries found in CVD graphene were shown to drastically increase the sensitivity of graphene transistors providing nanoscale sensing sites. Here we demonstrate the ability of liquid-gated graphene field effect transistors (G-FET) on which hippocampal neurons are grown for real-time detection of single ion channels activity. Dependence upon drugs and reference potential gating is presented and is found compatible with the nanoscale coupling of a few ion channels to graphene grain boundaries., 31 pages , 5 figures + Supplementary Info

We present a transfer-free preparation method for graphene on hexagonal boron nitride (h-BN) crystals by chemical vapor deposition of graphene via a catalytic proximity effect, i.e. activated by a Cu catalyst close-by . We demonstrate the full coverage by monolayer graphene of half-millimeter-sized hexagonal boron nitride crystals exfoliated on a copper foil prior to growth. We demonstrate that the proximity of the copper catalyst ensures high yield with the growth rate estimated between of 2\mu m/min to 5\mu m/min . Optical and electron microscopies together with confocal micro-Raman mapping confirm that graphene covers the top surface of h-BN crystals that we attribute to be a lateral growth from the supporting catalytic copper substrate. Structural and electron transport characterization of the in-situ grown graphene present an electronic mobility of about 20, 000cm2/(V.s). Comparison with graphene/h-BN stacks obtained by manual transferring of similar CVD graphene onto h-BN, confirms the better neutrality reached by the self-assembled structures.

Though graphene is strong candidate to make various applications, still there are issues that need to be resolved. The purpose of this thesis is to grow high quality graphene and transfer it to make new graphene based devices and to engineer defects into graphene structure. We have been able to increase the growth polycrystalline monolayer graphene from few centimeter scale to wafer scale without changing the CVD chamber. At the same time, we have demonstrated a method to decrease the nucleation density which allows us to grow large single crystal graphene from few to hundreds of micrometer. Concerning new design of graphene based devices, the polycrystalline graphene was trans- ferred to create artificial bilayer crossbars where the bilayer region behaved like naturally grown bilayer graphene. We have also developed a novel method of suspending graphene in macroscopic scale in pillared surface. In such a system, the strain in graphene is found to be less than 0.2%. Thereafter a completely dry method of depositing electrodes was developed which prevents damaging of graphene. The scale and process of transferring graphene was improved to different substrates such as 4 inch Si and sapphire substrates. It was used as transparent electrode to in a quantum well LED to replace the Ni/Au electrodes. We have been able to engineer defects into graphene. Firstly defects were induced in a controllable way using chemical method and were analyzed using Raman spectroscopy and Transmission Electron Microscopy which revealed a two step mechanism of defect formation in the graphene structure. We have also studied the effect of charged defects which adsorb onto the graphene surface without forming bonds with it. Unlike in literature where charged particles were deposited onto graphene, here the charged nano particles were present dur- ing the growth process in the copper foil. We believe that due to these nano particles, the intensity of D' phonon is greatly enhanced. Such anomalously higher intensity of D' band compared to D band has not been reported before, Si le graphène est un candidat prometteur pour de nombreuses applications, il reste des questions fondamentales à résoudre. Les objectifs de cette thèse visent à obtenir une crois- sance de graphène de haute qualité, à développer de nouveaux concepts de transfert pour réaliser de nouveaux dispositifs tout en contrôlant la formation de défauts dans sa struc- ture. Nous avons été en mesure d'augmenter la surface d'une monocouche polycristalline de graphène d'une échelle de quelques centimètres à celle d'une plaquette de silicium sans changer de chambre CVD. D'autre part, nous avons démontré une méthode permettant de diminuer la densité de nucléation et ainsi d'obtenir du graphène monocristallin de quelques centaines de microns. Concernant la réalisation de nouveaux dispositifs, nous avons obtenu des circuits à base de graphène polycristallin empilés par transferts successifs où la région de bicouche artificielle se comporte comme un bicouche intrinsèque. Nous avons également développé une nouvelle méthode pour suspendre le graphène à l'échelle macroscopique sur des supports en piliers. Dans un tel système, les contraintes dans le graphène restent in- férieures à 0,2%. Par la suite une méthode de dépôt d'électrodes par voie sèche a été développée pour éviter toute dégradation du graphène. Ce processus de transfert a été amélioré pour atteindre des tailles de substrats allant jusqu'à 4 pouces pour le silicium et le saphir. Il a été enfin utilisé comme électrode transparente d'une LED à puits quantiques pour remplacer des électrodes Ni / Au . Nous avons mis au point des procédés de création sélective de défauts sur le graphène. Tout d'abord des défauts ont été induits chimiquement de façon contrôlable et ont été analysés par spectroscopie Raman et microscopie électronique en transmission qui ont révélé un mécanisme en deux étapes de formation de défauts dans la structure de graphène. Nous avons également étudié l'effet des défauts chargés adsorbés sur la surface du graphène sans former de liaisons avec lui. Contrairement à la littérature où les particules chargées sont déposées a posteriori, les nanoparticules chargées étaient présentes pendant la croissance sur cuivre. Nous interprétons l'existence d'une bande de phonons D' très intense devant celle de la D, et encore jamais signalée avec la présence de ces nanoparticules

We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars' apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications.