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

PhD : selection by topics

Technological challenges >> Advanced nano characterization
6 proposition(s).

See all positions [+]

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.

Download the offer (.zip)

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.

Download the offer (.zip)

ab initio simulation for X-ray spectroscopy

Département Composants Silicium (LETI)

Laboratoire de Simulation et Modélisation

01-10-2020

SL-DRT-21-0665

jing.li@cea.fr

Advanced nano characterization (.pdf)

Context: Photoemission Spectroscopy (PES) is the most powerful experimental technique to directly access the electronic structure of matter. X-ray Photoemission Spectroscopy (XPS) is common and useful to characterize the chemical composition of materials by detecting the energy level of core electron states. Recent XPS experiments performed at CEA-Leti show that the electron core levels in an alloy material with dopant are shifted systematically with the doping concentration and the alloy-mixing ratio. Such a fact suggests that XPS experiments may give more information on the local atomic structure other than the standard chemical composition. The XPS spectra can be simulated directly by ab initio methods, which helps to correlate the core-level shifts and local structures. Objectives and Tasks: This Ph.D. thesis is devoted to exploring the physical origin of the core-level shift by using a range from ab initio methods at different levels of theory, from density functional theory (DFT), many-body perturbation theories (GW), and quantum-chemistry approaches (coupled-cluster, configuration-interaction, and so on?). The second objective of the Ph.D. is to develop an efficient and reliable method to simulate XPS spectra, to interact with experimentalists internally in CEA-Leti. · Performing ab initio calculations. · Investigate and identify the physical origin of the core-level shift. · Propose and develop an efficient method to simulate XPS spectra. · Apply the developed method to the problems, the systems and experiments carried at CEA-Leti within a collaboration with experimentalists.

Download the offer (.zip)

Deep learning for multi-modal and multi-resolution electron tomography reconstructions

Département des Plateformes Technologiques (LETI)

Laboratoire Microscopie Mesures et Défectivité

01-09-2021

SL-DRT-21-0674

zineb.saghi@cea.fr

Advanced nano characterization (.pdf)

With recent advances in instrumentation and numerical methods for inverse problems, electron tomography is becoming a key 3D characterization tool capable of addressing current challenges of miniaturisation of microelectronic devices. With ultra-fast spectrometers for electron energy loss spectroscopy (EELS) and multi-detector systems in energy dispersive X-ray spectroscopy (EDX), it is now possible to acquire several signals simultaneously to reconstruct in 3D the structure and morphology of an object with sub-nanometric resolution, as well as its chemical composition with a resolution of a few nanometres. In the framework of an interdisciplinary project, we have implemented compressed sensing approaches for EELS/EDX tomographic reconstruction from a very limited number of projections. The quality and resolution of the chemical reconstructions were greatly improved, but the volumes were reconstructed separately. The objective of this PhD thesis is to develop a deep learning based methodology to take advantage of the multi-modal and multi-resolution aspect of EELS/EDX tomography. This approach would allow: 1) A gain in execution time and signal-to-noise ratio, 2) Simultaneous reconstruction of the volumes from all signals, 3) An improvement in the resolution of chemical volumes by taking into account morphological information.

Download the offer (.zip)

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.

Download the offer (.zip)

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.

Download the offer (.zip)

See all positions