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

PhD : selection by topics

Technological challenges >> Solid state physics, surfaces and interfaces
2 proposition(s).

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Clean, architectured materials with controled grain size for high frequency new magnetic components

Département des Technologies des NanoMatériaux (LITEN)

Laboratoire des Matériaux et Composants Magnétiques



The deployment of the high frequency GaN technology paves the way for a substantial improvement of the compactness of power converters leading, at short term, to an environmental benefit (higher efficiency, weight reduction, lifetime enhancement) and to a strong economic impact (competitiveness in large sized markets). For achieving such gains, the technology relies on perfectly calibrated magnetic components with accurate electrical properties for high frequency operation of converters. Elsewhere, the integration of multiple functions in a single magnetic device for large band communication system follows the same objectives and requires implementing new manufacturing technologies. Additive Manufacturing of multi materials offers new possibilities for designing innovative architecture that could improve the performance of magnetic components. The intrinsic efficiency of such process allows minimizing material and energy consumption during manufacturing. However, this approach involves a better understanding of the relations between the material properties and the microstructural features that derive from the AM. The characterization of grain size distribution in the polycristalline material and its influence on the magnetization is a key point to be addressed in the thesis. Grain size is known as a factor controlling the dynamic magnetic process involving magnetic wall vibration. Optimal grain size lies within the domain size (1-2 µm) for reducing losses in inductors and transformer while for electromagnetic absorbents, the ideal size is larger in order to adjust the wall resonance to the frequency to be shielded. The thesis work will focus on the establishment of the relations in the case of some AM techniques already studied in the frame on an on-going thesis (A. Harmon) or other techniques to be deployed in the Poudrinnov plateform (binder jetting, robocasting). The experimental work aims at identifying the domain wall contribution on samples manufactured with such techniques intentionally designed with homogeneous microstrucres and then with heterogeneous features such as gradient or interfaces which are interesting for the components. Microstructural data will be correlated to magnetic measurement (permeability sprectra with application of a magnetic DC field, a stress and under temperature) performed at CEA Le Ripault. State of the at powder will be ordered. The generic feature of the work will contribute to the efficiency improvement of converters widely used in the frame of the circular economy : mobility, energy grids, ?. They also take part to the change in the manufacturing paradigm of components in industry complying with eco-design, recycling and reuse purposes.

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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)




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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