Croissance et transfert de graphène et nitrure de bore hexagonal : applications thermiques pour l'électronique flexible

L'électronique flexible est devenue un sujet au cœur des recherches actuelles. Dans ce but, plusieurs matériaux ont été utilisés tels que le PEN, PET ou le polyimide (PI). Ces matériaux présentent une bonne flexibilité et une compatibilité chimique avec les différents procédés utilisés en microélectronique, mais souffrent d'une faible conductivité thermique, menant à une réduction des puissances de travail des composants électroniques transférés sur de tels substrats, comparé à des substrats rigides plus classiques tels que le Silicium. Plusieurs pistes ont été investiguées pour contourner ce problème, et l'une des solutions consiste à remplir la matrice du polymère ou PI avec des nanomatériaux. Dans ce sens nous avons utilisé des structures 3D de graphène et de nitrure de bore hexagonal sous forme de mousse afin de remplir la matrice d'un PI. Nous expliquerons en détail comment nous avons obtenu un nouveau substrat flexible avec des propriétés thermiques améliorées.A major challenge is to find a way to grow those materials in order to achieve an easy and economically attractive way to produce large area of those materials with a good quality. Another challenge is to transfer those materials on substrate compatible with electronics (mainly SiO2). We will focus the first part of our work on investigation of the growth conditions required to produce large area graphene and h-BN of good quality and their transfer on SiO2. 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