Thesis defence

Théo LEVERT

Vendredi 13 mars 2019 à 10h00
Amphithéâtre IEMN – Avenue Henri Poincaré CS 60069 – 59652 Villeneuve d’Ascq

Jury:

• Henri HAPPY (Université de Lille, Directeur de thèse),
• Aziz BENLARBI-DELAI (Université Pierre et Marie Curie, Rapporteur)
• Laurent PICHON (Université de Rennes 1, Rapporteur)
• Christelle AUPETIT-BERTHELEMOT (Xlim, Examinateur)
• Bérengère LEBENTAL (IFSTTAR, Examinateur)
• Philippe COQUET (CINTRA UMI 3288, CoDirecteur de thèse)
• Emiliano PALLECCHI (Université de Lille, Examinateur)
• Edwin TEO HANG TONG (NTU, Examinateur)

Summary:

Abstract:

Flexible electronics has become an important field of research for many applications, such as flexible batteries. In this goal, several materials have been used such as PEN, PET or polyimide (PI). All these materials present a good flexibility and a chemical compatibility with microelectronics process but they suffer from poor thermal conductivity, leading to lower utilization of power of devices deposited compared to classic microelectronic substrate such as SiO2. Several way have been recently investigated to bypass this problem and a
good solution is to fill the matrix of the polymer or polyimide with nanomaterials or nanofillers. We choose to use graphene and h-BN as the filler in a 3D shape: a foam of graphene or h-BN as the nanofiller and we chose a PI as the matrix. In the second part, we will explain in details how we achieve novel flexible substrates with enhanced thermal properties.
We succeed in producing polycrystalline graphene on copper with quite a good quality, fully covering the metallic substrate with a size of 2x2cm. We tried to grow monocrystalline graphene using standard CVD and achieved hexagonal single crystals of 30µm, which is quite small compared to other methods used in literature. We synthetized polycrystalline h-BN using copper as a catalyst and ammonia borane as the precursor with a size of 6x2cm with a good homogeneity on all available substrate. We were able to transfer both graphene an h-BN on Si02 substrate using both classical wet transfer and bubbling transfer, leading to a fastest transfer and resulting on clean transfer of our materials, free of cracks, bubbles and resist residues. We succeed in producing both 3D graphene and 3D h-BN as foam using a Nickel foam as the catalyst, resulting in multilayer graphene and h-BN with a good quality. We produced new flexible and thermal efficient substrates using these foams as a filler in a matrix of PI, already commonly used as a classical flexible substrate for microelectronics. We developed two generations of substrates. We found similar mechanical properties and thermal stability as the commercial Kapton. We deposited thermistors on the surface in order to study the thermal dissipation of our samples. We improved the maximum power applied on the thermistors up to 100% before breakdown.