Scientific direction Development of key enabling technologies
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PhD : selection by topics

Technological challenges >> Advanced nano characterization
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Advanced carrier recombination characterization for AlGaN/GaN HEMT, stack understanding from epitaxy to etching

Département des Plateformes Technologiques (LETI)

Laboratoire Analyses de Surfaces et Interfaces

01-09-2021

SL-DRT-21-0377

Lukasz.Borowik@cea.fr

Advanced nano characterization (.pdf)

To penetrate into the power electronics market, the main challenges for GaN remains the development of a reliable normally-off HEMT solution. CEA-LETI has chosen to develop recessed hybrid MISHEMT, fabricating normally-off devices which give functionality similar to a classic silicon based MOS. Since etching of AlGaN/GaN MISHEMT heterostructure can induce defects, it is critical to be able to characterize them in order to optimize gate processing and therefore overall device performance. Work will consist of: (1) CL and KPFM characterization realized and interpreted in term of radiative/non radiative carrier recombination for understanding of integration processes impact. Already optimized during previous internship sample preparation for correlated characterization will be refined for MISHEMT samples. (2) KPFM-CL correlation for a deep understanding of carrier dynamic in the gate stack (3) Correlation with electrical performances of theses devices will be performed. Instrumentation, besoins spécifiques: LETI owns all necessary equipment (CL and KPFM under illumination) for this thesis. Additionally, time-resolved CL is currently in PFNC investment road map and could be an interesting improvement during the third year of this PhD thesis.

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A new energy scale for X- and gamma-rays below 100 keV using high-resolution metallic magnetic calorimeters

Département Métrologie Instrumentation et Information (LIST)

Laboratoire de Métrologie de l'Activité

01-09-2021

SL-DRT-21-0608

matias.rodrigues@cea.fr

Advanced nano characterization (.pdf)

Currently, many physics experiments are probing exotic atoms (hydrogenic, pionic or kaonic) by X-ray spectrometry to study the structure of the nucleus and the nucleus-particle interaction or to test quantum chromodynamics (QCD) under extreme conditions. They are looking at electromagnetic transitions using very precise photon spectrometry. Other experiments aim at precisely measuring the weakest known isomeric transition, emitted by Th-229m, a candidate transition for the development of future nuclear clocks. New cryogenic detectors are being increasingly developed and used for these areas of research, but they require extremely precise energy calibration from reference lines. However, above 8 keV, the uncertainties of the evaluated and tabulated X and gamma lines increase sharply. The aim of the thesis is therefore to define a new scale in X and gamma-ray energy below 100 keV with a relative uncertainty of a few 10^-6. For this, two experimental set-ups will be developed and will integrate cryogenic detectors based on metallic magnetic calorimeters (MMC). These detectors, operating around 20 mK, offer an energy resolution one order of magnitude better than those of semiconductor detectors. An in-depth study of the whole measurement chain will have to identify and correct non-linearities and distortions. In addition, the MMCs will be pixelized to increase the counting rate and limit the statistical uncertainty. Once characterized and operational, the two cryogenic spectrometers will measure the X and gamma-ray energy spectra emitted by carefully selected radionuclides. The energies of the metrologically established lines will then be used as references, both for calibrating spectrometers used in fundamental physics and those used for materials analysis. Moreover, these energies will be a benchmark to validate complex theoretical calculations of radiative transitions.

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Understanding the structure and properties of metavalent phase-change materials based on innovative chalcogenide compounds for a technological breakthrough in embedded Phase-Change Memory

Département des Plateformes Technologiques (LETI)

Laboratoire

01-10-2021

SL-DRT-21-0854

pierre.noe@cea.fr

Advanced nano characterization (.pdf)

Owing to their high scalability, short switching time (~ns), Phase-Change Materials (PCM) are very promising for new generations of Non-Volatile Memories (NVMs). For high temperature embedded applications (ePCM), the most promising PCMs are multiphased complex composition alloys (Ge-rich GeSbTe chalcogenide alloys), which raise critical issues due potential unwanted Ge phase separation occurring at crystallization. In that context, this PhD project targets a breakthrough with the study of innovative very high temperature PCM compounds (data retention of the RESET amorphous state >> automotive criteria & soldering reflow thermal budget) without any parasitic phase separation upon crystallization. Recently, a Leti team has proposed a particular Ge-Se-Te composition that is remarkably stable (>250°C for 10 years) in the amorphous state but that also exhibits very interesting crystalline state properties that have not been reported before (no description of the atomistic or electronic structure). The aim of this PhD is to couple advanced structural characterizations (electron microscopy, synchrotron X-ray experiments ?) with modern simulations (AIMD/DFT ) to get an understanding and further master the properties of such new PCMs.

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New overlay techniques for advanced technologies measurement

Département des Plateformes Technologiques (LETI)

Laboratoire Microscopie Mesures et Défectivité

01-09-2021

SL-DRT-21-0956

yoann.blancquaert@cea.fr

Advanced nano characterization (.pdf)

Overlay (OVL) is one of the key parameters to be monitored during the microelectronic components fabrications. Currently, this parameter is monitored by imaging techniques or by scatterometry. For the most advanced technologies - CMOS10nm and beyond - these techniques, although accurate (<0.4nm in 3 sigma), have difficulty to meet the needs of the process. Other techniques need to be evaluated by simulations and experimentally to achieve lower accuracies. CD-SAXS and CD-SEM are the two techniques that need to be evaluated for this ultimate metrology. The accuracy of current techniques will be evaluated, new measurement methodologies will be defined and inter-technique reference standards will be created. This subject is in the continuity of ongoing European collaborations and programs.

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Electron Holography for the mapping of the electrostatic potentials in LED devices.

Département des Plateformes Technologiques (LETI)

Laboratoire Microscopie Mesures et Défectivité

01-10-2021

SL-DRT-21-0969

david.cooper@cea.fr

Advanced nano characterization (.pdf)

To develop the latest generations of IIIV light emitting diodes at visible wavelengths for lighting and UV for applications such as water purification, it is important to be able to control the composition, and internal fields such as the dopants and piezoelectric potentials. This stage will teach the basics of electron holography that can similtaniously measure these components and modelling will be performed in order to separate them and provide important feedback to the device processing team to understand and then improve their performance. The candidate will learn how to apply electron holography in a transmission electron microscope to measure the potentials in LED structures. Modelling will be applied to understand the different components of the measured electrostatic potentials. Maps of the dopant potentials, piezoelectric potentials, structure and composition will be generated from a single data set. 1) doi.org/10.1016/j.ultramic.2018.06.004 2) doi.org/10.1088/1361-6528/abad5f 3) doi.org/10.1063/5.0020717

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