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

PhD : selection by topics

Chalcogenide nanocomposite materials with improved thermal properties for development of phase-change memories with low power consumption and high thermal stability

Département Technologies Silicium (LETI)




Phase-change memories (PCM) are the best candidates in order to replace Flash memories, for the realization of universal SCM memory (Storage Class Memory) bridging the gap between volatile and non volatile memories as well as for neuromorphic and articificial intelligence. Nevertheless, PCM face a major limit related to programming currents that are too high for future memory generations. Thus, the control of thermal transport at the nanoscale to limit energy consumption is a key parameter in order to optimize the Joule effect at play during programming of the PMC memory cell. Nevertheless, the thermal management at nanoscale is still poorly understood. Thus, this thesis aims at developing new Ge-Sb-Te phase-change materials and new architectures for manufacturing PCM memories operating at lower power and improved thermal stability for Embedded applications. These objectives can be achieved both by optimizing the Ge-Sb-Te phase-change material (nanostructuring, multilayer, composition) and thermal confinement of the memory cell. The development (PVD deposits on industrial tool in clean rooms) and the characterization of these new nanostructured GST materials (XRD, resistivity and magneto-transport/Hall, FTIR/Raman/reflectivity, Synchrotron characterization, etc.) will be carried out at CEA-Leti. The characterization of the thermal transport (thermal conductivity Kth, RUS, Brillouin Scatt., US Laser, Inelastic Scatt., VDoS, ...) and its modeling will be performed at the ILM (CNRS-Univ. C. Bernard-Lyon). PCM devices in order to assess the properties of the new materials developped in this thesis (performance, reliability) will be fabricated on the Si technological Platform of LETI as well as at our industrial partner STMicroelectronics at Crolles.

Biocrude production through hydrothermal liquefaction of micro-algae : study of the biochemical composition of algal biomass on biocrude quality and interest for biofuel production

Département Thermique Biomasse et Hydrogène (LITEN)

Laboratoire de ThermoConversion de la Bioressource



Among the various processes which can be applied to convert micro-algal biomass into biofuels precursors, hydrothermal liquefaction (HTL) is regarded as a highly promising technology for treating a wide variety of biomasses (or biomass wastes) and obtaining valuable products, such as bio-crude. Compared to conventional approaches based on dry extraction and transesterification of algal lipids to produce biodiesel, HTL allows avoiding energy-intensive thermal drying of the biomass. HTL is using the unique properties of water in subcritical conditions. In those conditions, water is a solvent but also a reactant for the conversion of biomass. Algae biomass is made of different kinds of natural polymers (lipids, proteins, carbohydrates). Under hydrothermal conditions (250-350°C; 10-20 MPa, those compounds are converted through depolymerization and successive dehydration reactions, and also deamination and decarboxylation reactions. All those transformations lead to the reduction of oxygen and nitrogen in the final product, a kind of green bio-crude, compared to the initial biomass. The precise mechanism for this conversion is still not well known. A first work of this kind have been done at CEA for agro-industrial residues. The composition of the bio-crude obtained from HTL conversion is strongly dependent to the conversion of lipids, proteins, carbohydrates and other organic molecules originally contained in the biomass and thus vary greatly according to the nature of the micro-alga. The objective of this phD work is then to determine the relationship between the algal biochemical composition and the biocrude composition in order to optimise the biocrude adaptation for a future use as biofuel after a catalytic upgrading. This will include selection of the best process parameters, the establishment of a chemical conversion mechanism for a full comprehension of the transformation but also the selection of the best algae specie and cultivation conditions as the biochemical is influenced by both parameters. In this objective, HTL conversion of well calibrated algal biomasses will be studied. This work will be done using the experimental equipment of the laboratory, in batch reactor or with the continuous pilot. It will also need an important analytical work to characterize and identify the different products of the reaction. A simulation of the hydrothermal conversion will be needed to test the chemical mechanism and to seek for the optimisation of the process. This phD work will be done in collaboration with the Rafbioalg ANR project partners, in particular IRCELYON involved in the catalytic up-grading of the bio oil and CEA DPACA for the selection, characterization and cultivation of the micro-algae.

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

Département Systèmes

Laboratoire Electronique Energie et Puissance



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.

Simulation and characterization of electronic transport in AlGaN / GaN power transistors

Département Composants Silicium (LETI)

Laboratoire de Simulation et Modélisation



The AlGaN / GaN components currently developed at LETI are high voltage components (> 650V) with low on-state resistances for driving high currents (from the tens to the hundreds of amps). These components particularly address the market of power converters currently in full expansion (electric vehicles, renewable energies including solar, smart grids, etc.). The preliminary work carried out at CEA-LETI allowed to determine the main phenomena limiting the transport of electrons in the accesses of the HEMT (High Electron Mobility Transistor) transistors but also under the MIS (Metal-Insulator-Semiconductor) gate of these transistors. It is now necessary to precisely define the transport properties of GaN material in case of low and high electric fields (necessary for GaN power but also for GaN RF) and to model this electronic transport in order to identify ways of improving performance. electrical devices. The PhD student will be required to perform the following tasks: Electrical characterization (consolidation of the mobility measurement protocol, measurements of mobility as a function of charge and temperature, mobility spectroscopy measurements), simulation and modeling (simulation of the low-field and high-field mobility in the electron 2D gas formed at the AlGaN/GaN heterojunction and under the transistor gate: carrier scattering probability and electron transport with the Boltzmann equation or the non-equilibrium Greeen functions (NEGF) quantum formalism, development of analytical models of mobility, proposals for improvement of device performance.

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

Département Composants Silicium (LETI)

Laboratoire d'Intégration des Composants pour la Logique



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.

Bio-inspired approach for an energy producing building envelope with evolving functionalities

Département des Technologies Solaires (LITEN)

Laboratoire Composants d'Enveloppe du Bâtiment



In order to obtain Nearly Zero-Energy Buildings (NZEBs), the building envelope must increasingly be perceived as an adaptive barrier that must be flexible enough to reduce or capture the effects of the environment and climate according to the quality of the indoor ambiances (thermal, visual and acoustic). Following a disruptive bio-inspired approach, this thesis aims to develop innovative adaptive technical solutions limiting the use of mechanical actuators main causes of failures of active systems (solar tracking) and allowing better management of the basic energy functions of the envelope (airtightness, heat transfer, ventilation and indoor comfort) according to external stimuli. The thesis work will consist in valuing the surrounding energy potential (capture, collection and energy storage) through numerical and experimental studies based on the analysis of the physical mechanisms implemented by plants to make the best use of climatic conditions (natural flow of sap, sunflower, leaves) combined with the development of active composite materials (smart materials and assembly of materials with differential thermal and optical properties). The solutions defined will lead to the development of two prototypes for the experimental validation of the concept and the achievement of a predefined configuration.

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