Thèses

Lundi 13 Novembre 2023 à 13h30.

GeTe-based nanocomposites for thermal optimisation and energy harvesting in microelectronics: from understanding to applications

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Directeur de thèse / thesis director :

Stéphane Pailhès

Membres du jury / jury members :

Guilmeau Emmanuel, Directeur de recherche CNRS, CRISMAT Rapporteur
Lacroix David, Professeur des universités, LEMTA Rapporteur
Bougrioua Zahia, Chargée de recherche CNRS, IEMN Examinatrice
Del Fatti Natalia, Professeure des universités, ILM Examinatrice
Pailhès Stéphane, Directeur de recherche CNRS, ILM Directeur de thèse
Giordano Valentina, Chargée de recherche CNRS, ILM Co-directrice de thèse
Bourgeois Olivier, Directeur de recherche CNRS, Institut Néel Co-directeur de thèse
Noé Pierre, Chercheur, CEA-Leti Invité

Résumé / Abstract :

The aim of this thesis is to understand thermal transport in germanium telluride (GeTe) nanocomposites. The issues that gave rise to this subject are diverse: from a technological point of view, heat management is an important challenge for the lifespan of electronic objects, but also from an economic point of view. On the other hand, there’s an ecological challenge: thermal management could reduce waste heat production or recycle it as electrical energy. Basically, the aim of this thesis is to understand the impact of nanostructuring and nanocomposition on heat propagation in materials. Specifically, our study has been carried out on GeTe and a composite made of nanocrystalline GeTe and amorphoud carbon (GeTeC), of interest for applications in microelectronics as a material for phase change memories, and in thermoelectricity, two fields for which thermal management is critical. In order to answer the questions posed, various experimental techniques were employed. The 3ω method was used to measure thermal conductivity at temperatures between 100K and 300K in amorphous and crystalline GeTe thin films and nanocomposites composed of crystalline GeTe and amorphous carbon. These measurements revealed a decrease in thermal conductivity in the nanocomposite, but it was not clear from the measurements alone whether this reduction was due to grain size (reduced when going from crystal to nanocomposite) or to the amorphous carbon phase. To disentangle the different factors, it is necessary to measure a nanoGeTe, composed of crystalline grains of a size close to that of the nanocomposite. Preparation of the nanoGeTe samples was not possible for 3ω measurements. A thermoreflectance technique was therefore used for thermal conductivity measurements above ambient temperature, with which measurements of crystalline GeTe, nanocomposites and nanoGeTe were carried out. Using the results of these measurements, it was possible to conclude on the impact of grains and carbon phase in nanocomposites. Brillouin spectroscopy measurements were carried out on crystalline GeTe and a nanocomposite GeTeC to extract the elastic constants of these materials and deduce longitudinal and transverse sound velocities. Finally, Seebeck and resistivity measurements were carried out to calculate the thermoelectric figure of merit and see if the nanocomposite could make a better thermoelectric material than crystalline GeTe.

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