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

PhD : selection by topics

Engineering science >> Materials and applications
9 proposition(s).

Flexible nanosensors matrix for impact detection on sensitive surface

Département Systèmes

Laboratoire Autonomie et Intégration des Capteurs

01-09-2019

SL-DRT-19-0434

elise.saoutieff@cea.fr

The aim of the PhD thesis is to implement a matrix of flexible piezoelectric nanosensors, which enable the 3D reconstruction of a force or deformation field. The nanosensors based on GaN nanowires obtained by directed growth are fabricated and assembled at CEA. The candidate will tackle experimental aspects, which include the fabrication and the assembly of sensors and sensor networks (matrix) via controlled growth and deposition processes, first-level flexible electronic layers (interconnects), system integration on an object (mechatronics) and finally signal collection and processing through a dedicated reading electronics, to be designed based on the competences present in our laboratory. In parallel, the candidate will carry out studies at the fundamental level, such as investigating the mechanical transfer between the nanowire and its environment and its effect on the generated signal under deformation, or the study of the piezoelectric / pyroelectric coupling intrinsic to GaN nanowires. For this purpose, the candidate will have access to multi-physics simulation tools. Finally, investigations on the choice of materials and the characterisation thereof (structural, mechanical, thermal, optical, electrical) will be pertinent and may pursued. More generally, this PhD thesis will also provide the opportunity to develop applicable solutions in various fields such as deformation and impacts detectors for predictive maintenance, sensitive surfaces or electronic skin.

Atomic resolution imagery composition measure applied to superarrays

Département technologies silicium (LETI)

Autre laboratoire

01-10-2019

SL-DRT-19-0639

nicolas.bernier@cea.fr

For crystalline materials sensitive to electron beam radiation damage, it is necessary to quantify the chemical composition at the atomic scale while minimizing the electron dose. The usual analytical techniques in the transmission electron microscope (TEM) can not be used because of the high probe current and the relatively long acquisition time. On the other hand, atomic imaging, more precisely using the high-angle annular dark field (STEM-HAADF), is performed at a reduced dose and exhibits contrasts proportional to the atomic number of the elements. In addition, the TEMs Titan on the PFNC are equipped with an aberration corrector to acquire state-of-the-art HAADF images in terms of atomic resolution. However, for the contrast in these images to be quantitatively related to the chemical composition of the material, controlled TEM acquisition conditions and electronic scattering simulations must be developed. In parallel, another imaging technique in the TEM is attracting growing interest: ptychography, or "4D data STEM". This technique, consisting in acquiring a diffraction pattern for each position of the incident electron beam, provide the projected potential in the sample. The development of the quantitative aspect of these imaging techniques has many applications: the one targeted in this thesis is the understanding of the atomic order of GeTe / Sb2Te3 superlattices, materials considered as the most promising for phase change memories (PCRAM).

Embedding of high temperature resistant Fiber Bragg Gratings into metal structures obtained by additive manufacturing processes

DM2I (LIST)

Laboratoire Capteurs et Architectures Electroniques

01-10-2019

SL-DRT-19-0675

guillaume.laffont@cea.fr

LCAE laboratory from the Technological Research Division at CEA List, in partnership with the LISL laboratory from the CEA DEN, specialized in metal additive layer manufacturing processes, proposes a PhD thesis aiming at developing methods to integrate optical fiber sensors (OFS) based on high temperature resistant Fiber Bragg Gratings (FBGs) in metallic components obtained thanks to metal additive layer manufacturing processes either for the aerospace or for the nuclear industry. Thanks to recent developments, ultra-stable FBGs have been realized using direct writing processes into silica optical fibers with femtosecond lasers. These temperature and strain transducers combined with special optical fibers designed for very high temperature environments will be considered for the instrumentation of components obtained by metal additive layer manufacturing. This project aims at contributing to the adoption of in situ monitoring of 3D-printed metallic components, paving the way for their Structural Health Monitoring (SHM) to anticipate failures in the fabrication process and to optimize operating costs thanks to the development of predictive and conditional maintenance-based procedures.

Strain engineering for 12nm FDSOI technology and beyond

Département technologies silicium (LETI)

Laboratoire

01-09-2019

SL-DRT-19-0720

shay.reboh@cea.fr

Strain engineering is a major tool to boost the performance of transistors. Tensile strain increases electron mobility and compression improves holes mobility. Hole mobility is also favored by the use of SiGe channel. In advanced FDSOI the co-integration of Si channels for nMOS and and SiGe channels for pMOS is done by the transformation of the top-Si layer into SiGe via Ge condensation. For this, an epitaxy of a SiGe is done on a selected Si area. During thermal oxidation, Ge atoms are rejected into the underlying Si layer. The buried-oxyde (BOX) of the SOI wafer acts as a diffusion barrier for Ge, the result is a local SiGe-On-Insulator (SGOI) substrate. The SiGe film is obtained such as it keeps the in-plane lattice parameter of Si and therefore is found under biaxial compressive strain in the plane of growth. Today, the condensation technique allows a co-integration of Si-based nMOS and compressively strained SiGe-based pMOS transistors. The Problem: when the cSiGe made by Ge-condensation is discontinued for the fabrication of the STI, a local elastic relaxation of the compressive stress close to the STI edge is naturally expected. However, experiments show more than elastic relaxation over large distance from the STI discontinuity causing a significant loss of compressive strain in the layer, and therefore, a lower contribution to the performance of devices. In summary, the physical mechanisms behind this behavior are unknown today and of major impact on advanced CMOS. This work is aimed to bring light on this subject and propose/develop technologycal solutions.

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)

Laboratoire

01-10-2019

SL-DRT-19-0816

pierre.noe@cea.fr

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.

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.

Van der Waals epitaxy of CdTe on 2D materials

Département technologies silicium (LETI)

Laboratoire

01-10-2019

SL-DRT-19-0887

philippe.ballet@cea.fr

2D materials nowadays attract a great amount of research because of their unique properties directly derived from their graphene-like electronic structure and crystalline organization. These materials have strong in-plane chemical bounds while extremely weak, van der Waals type, out-of-plane interaction describing them a 2D sheets of monolayer material. 2D material epitaxy on conventional 3D semiconductors may thus occur without any lattice parameter mismatch strain. The opposite is also true when depositing a 3D onto a 2D. The PhD work consists in studying in details these new epitaxial systems with the proposal of realizing the strain free epitaxial growth of photovoltaics CdTe or infrared sensitive HgCdTe on 2D layers. These materials (2D and 3D) will be grown by molecular beam epitaxy allowing for an in-situ control of the interface. The growth mode of 3D(CdTe)/2D and 2D/3D(HgCdTe) will be first independently studied with the goal of providing a full 3D(CdTe)/2D/3D(HgCdTe) heterostructure where the 3D(CdTe) will promote, through the very thin 2D, the crystalline structure and orientation for the ultimate growth of HgCdTe. Inserting a weakly bonded 2D material also offer promising new functions by enabling the HgCdTe layer to be detached and transferred onto another substrate opening the way towards new optoelectronic applications. The thesis scientific environment will be brought to a broader range by considering the availability and proximity of the nano-characterization platform (CEA-PFNC) where skilled teams and last generation of equipment are dedicated to revealing the chemical nature and crystallographic structure of the epitaxial stacks.

Design and fabrication of miniaturized wireless-powered sensors on flexible substrate

Département Composants Silicium (LETI)

Laboratoire de Caractérisation et Fiabilité des Composants

01-10-2019

SL-DRT-19-0959

alexandra.koumela@cea.fr

The goal of this thesis is to develop a Wireless-powered sensors on flexible substrate. The measured quantity can be the pressure, the temperature, the acceleration, the strain, the magnetic field etc. The M&NEMS technology developed by the CEA-LETI could meet the demands of extreme miniaturization, ultra-low consumption, high performances and low cost. In order to identify the more suitable M&NEMS sensors a comparative study of the available sensors will be performed. The criteria will include the pairing with an RF antenna for circuit alimentation and information transmission. The fabrication of the sensor, the antenna and its electronics will be performed on a flexible substrate which will be chosen in function of the application. This work will rely on the Systems Department (DSYS) at CEA-LETI for the design of the antenna and on the packaging 3D laboratory (LP3D) for the fabrication on the flexible substrate. An innovative actuation principle based on the thermopiezoresistive back-action effect will also be examined in function of the integrated sensor.

Optical laser waveguides III-V (AsGa/InP) growth directly onto SOI-300mm.

Département d'Optronique (LETI)

Laboratoire d'integration technologique pour la photonique

01-10-2019

SL-DRT-19-1055

christophe.jany@cea.fr

For more than 25 years, the heart of telecom networks has become one of the fields of application of the III-V components (InP_like, and AsGa_like). This field is based on the transmission of IR waves in optical fibers, powered by laser sources in III-V materials. Over the past ten years, a new technological path has been developed, based Silicon-Photonics, which makes it possible to lower manufacturing costs by increasing integration (3D integration, Wafer Level Packaging). The approach usually chosen here consists of a molecular bonding of a III-V wafer (epitaxial) on an SOI previously structured optical guides. A technological treatment is then applied to make III-V transmitter guides connected to the silicon guides. Since less than 5 years; a new integration scheme is developing, it is the direct epitaxy of III-V materials on silicon. For 3 years, the CEA / LETI laboratories, already experts in the development of photonics on Silicon by bonding process, have decided to investigate this highly innovative approach with high potential. The proposed thesis will thus rely heavily on the CNRS / LTM laboratory, which has been developing for the last 4 years new MOCVD epitaxial concepts for III-V materials (AsGa base) on textured silicon wafer. This subject of study will enable the establishment of a new roadmap of III-V epitaxy on Silicon, with the aim of designing a new generation of photonic circuits. The PhD student will be involved both in the development of III-V materials on silicon, as well as in the design and realization of photonic circuits 2.0.

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