Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Nonsmooth time-stepping methods for 3D frictional contacts with geometrically nonlinear kinematics

Département Intelligence Ambiante et Systèmes Interactifs (LIST)

Laboratoire de Simulation Interactive

01-10-2019

SL-DRT-19-0801

xavier.merlhiot@cea.fr

The simulation of the dynamics of multi-body systems with intermittent contacts has several applications, ranging from the engineering of the design of industrial products (circuit breakers, clockwork mechanisms ...) to the development of real-time simulators of complex systems (teleoperated robots operating in a hostile environment, offshore lifts, prototyping of assembly processes in the manufacturing industry, etc.) through the study of granular media. Even if numerical methods provided by nonsmooth mechanics nowadays lead globally to robust and efficient simulations of such systems, a certain number of application cases reach the limits of the state-of-the-art schemes and associated solvers. In particular, it is often necessary to invoke models of dry friction in 3D contact models (e.g. the Signorini-Coulomb contact law), in the presence of nonlinear contact kinematics. Indeed, the nonlinearity of those kinematics can come not only from the curvature of the surfaces in contact, but also from the kinematics of relative motion of the solids, which are often intrinsically nonlinear due to the presence of large rotations. This thesis aims to overcome the current limitations of the numerical methods in this type of situation, by proposing new numerical schemes as well as solvers adapted to application constraints. In this sense, particular attention will be paid to the robustness of the proposed methods (energy behavior, solvability of the constructed algebraic systems, etc.) and to the overall efficiency of the methods (achievable performance levels, possibilities of parallelization, applicability to real-time simulation contexts).

New intelligent GaN power chips : Study and implementation into an industrial application

Département Systèmes

Laboratoire Electronique Energie et Puissance

01-10-2019

SL-DRT-19-0832

leo.sterna@cea.fr

The new HEMT GaN transistors emergence in power electronics opens up many possibilities for improving power converters performances: increase power density and efficiency, high temperature operation. In order to make the GaN transistors implementation reliable in a converter environment, the monitoring of the various signals at the terminals of the component is essential. The HEMT GaN transistors instantaneous current measurement remains a problem, and not so much studied. CEA Leti has a technology and specific components allowing the measurement of instantaneous current with a very good dynamic. This thesis proposes to study and implement current mirror measurement circuits for HEMT GaN power transistors. The doctoral student will reflect on the possible applications of the current mirror sensor that can protect the transistor current, or make possible the dynamic control of the switching. This monitoring function will be integrated within a specific driver circuit, the final objective of the thesis being to propose a driver circuit with integrated current sensor and control feedback on the transistor. The PhD student will be hosted at L2EP, within the power electronic team. Scientific supervision will be provided by researchers from the G2ELab university laboratory in co-supervision with CEA Leti's research engineers. The doctoral student will evolve in an innovative and multidisciplinary environment.

Fabrication of an innovative logic/memory CUBE for In-Memory-Computing

Département Composants Silicium (LETI)

Laboratoire d'Intégration des Composants pour la Logique

01-10-2019

SL-DRT-19-0841

francois.andrieu@cea.fr

For integrated circuits to be able to leverage the future ?data deluge? coming from the cloud and cyber-physical systems, the historical scaling of Complementary-Metal-Oxide-Semiconductor (CMOS) devices is no longer the corner stone. At system-level, computing performance is now strongly power-limited and the main part of this power budget is consumed by data transfers between logic and memory circuit blocks in widespread Von-Neumann design architectures. An emerging computing paradigm solution overcoming this ?memory wall? consists in processing the information in-situ, owing to In-Memory-Computing (IMC). However, today's existing memory technologies are ineffective to In-Memory compute billions of data items. Things may change with the emergence of three key enabling technologies, under development at CEA-LETI: non-volatile resistive memory, new energy-efficient nanowire transistors and 3D-monolithic integration. CEA-LETI received a prestigious European ERC grant to support a 5 year project and 3 new PhD students on a new project. This project will leverage the aforementioned emerging technologies towards a functionality-enhanced system with a tight entangling of logic and memory. A 3D In-Memory-Computing accelerator circuit will be designed, manufactured and measured, targeting a 20x reduction in (Energy x Delay) Product vs. Von-Neumann systems. This project that adds smartness to memory/storage will not only be a game changer for artificial intelligence, machine learning, data analytics or any data-abundant computing systems but it will also be, more broadly, a key computational kernel for next low-power, energy-efficient integrated circuits. The PhD candidate will fabricate in clean room and characterize the logic/memory CUBE dedicated for In-Memory-Computing.

Towards a better understanding of chemical species transfer while performing industrial materials post-functionalization under supercritical CO2 impregnation

Département des Technologies des NanoMatériaux (LITEN)

Laboratoire des Eco-procédés et EnVironnement

01-10-2019

SL-DRT-19-0854

olivier.lebaigue@cea.fr

Post-functionalization (particularly under supercritical CO2 impregnation in our proposal) allows us to give new properties to a polymer by core impregnation with selected molecules. In this process, supercritical CO2 has two effects: it swells the polymer and transports additional molecules. Hydrophobia, thermal or mechanical reinforcement, improvement of electrical conductivity, colouring, UV resistance... are new targeted properties. A large part of the thesis will be devoted to experimental research and new measurement techniques. In addition, the measurement results will also feed into a multi-scale multi-physical (and chemical) modelling process. Once carefully validated, these physico-chemical models are expected to accurately predict the different stages of existing processes and help to develop new processes.

Epitaxial diamond films of high crystalline quality for power electronic applications

DM2I (LIST)

Laboratoire Capteurs Diamants

01-10-2019

SL-DRT-19-0856

samuel.saada@cea.fr

According to its nonstandard thermal conductivity combined with outstanding electronic properties, diamond is an ultimate material for power electronics. However, these properties are highly dependent on the material crystalline quality. Epitaxial diamond on iridium is currently an attractive material to fabricate diamond wafers of high crystalline quality. Such a wafer sector is not yet available. The quality of heteroepitaxial diamond was successively improved. Recently, a Japanese group reported a dislocation density of 10^7 / cm2 for a film, 60 microns thick, obtained by lateral growth [1]. At CEA LIST, heteroepitaxial diamond films are grown on Ir/SrTiO3/Si(001) pseudo-substrates of 1 cm2. The Bias Enhanced Nucleation method (BEN) is performed in a plasma-assisted chemical vapor deposition (CVD) reactor connected to a UHV surface analysis chamber. The crystalline quality of films 300 microns thick is at the state of art with a mosaicity of 0.6° and an in-plane misorientation of 0.7° [2, 3]. From local measurements in Cathodoluminescence, the dislocation density was estimated to 4 × 10^6 / cm2. These films are homogeneous on 1 cm2 surfaces. The main objective of this PhD is to better control and reduce the density of structural defects in heteroepitaxial diamond grown on 1 cm2 pseudo-substrates applying an innovative growth strategy recently patented by our laboratory [4]. The involved experimental parameters will be determined and the crystalline quality and structural defects will be finely characterized for different heteroepitaxial film thicknesses by X-Ray diffraction, Raman spectroscopy and cathodoluminescence. The best films will be used as substrates to grow boron doped diamond epilayers (p-type doping). Electrical characteristics will be then measured in collaboration with GEEPS (Paris-Saclay University). [1] Ichikawa et al, High crystalline quality heteroepitaxial diamond using grid-patterned nucleation and growth on Ir, Diam. Relat. Mater. (2019) doi.org/10.1016/j.diamond.2019.01.027 [2] Lee et al, Epitaxy of iridium on SrTiO3/Si (001): A promising scalable substrate for diamond heteroepitaxy, Diam. Relat. Mater. 66 (2016) 67. [3] Bensalah et al, Mosaicity, dislocations and strain in heteroepitaxial diamond grown on iridium, Diam. Relat. Mater. 66 (2016) 188. [4] Delchevalrie, Arnault, Saada (décembre 2018).

Consistent Visual-Inertial-Magnetometric Map Creation and Fusion via Collaborative SLAM

Département Intelligence Ambiante et Systèmes Interactifs (LIST)

Vision & Ingénierie des Contenus (SAC)

01-10-2019

SL-DRT-19-0861

vincent.gay-bellile@cea.fr

Since the last decade, indoor localization is a booming research area in the scientific community. Indeed, many applications with a strong potential for industrial opportunities are possible. For example, marketing agencies are considering adapting the display of advertising according to a user's position. For military and firefighters, a precise localization is useful during an intervention in buildings to facilitate and make more effective the outside support. This thesis will investigate the fusion of Visual/inertial/magnetic sensor to deal with large scale indoor localization. Adding a magnetometer to a visual/inertial sensor system would allow correcting the estimated trajectory, when the user returns to the same location several times, more regularly and with less error. The first work of the thesis is the integration of magnetometric measurement into a visual/inertial fusion algorithm. Then, the magneto/visual relocalization will be investigated. A magneto/visual map will be built during the localization and used to estimate and correct the drift. Finally, the latest work will aim to automatically build a large-scale magneto/visual map with several carriers collaborating together.

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