Towards the fabrication of all-SiC electrode arrays for neural interfaces: passivating amorphous SiC film, surface functionalization, and electrical characterization

Defense of doctoral thesis by Scott GREENHORN, for the  University  Grenoble Alpes, speciality  " NANO ELECTRONIC & NANO TECHNOLOGIES "

Keywords :
Brain-machine interface,SiC,implantable,biocompatibility,a-SiC,functionalization

Abstract :
Silicon carbide (SiC) has shown great promise for neural interfaces. SiC can display a variety of electrical properties, ranging from insulating to conducting, and also shows high biocompatibility and high chemical inertness. Therefore, these material polymorphs provide a strong foundation for long-lifetime neural interface devices. This thesis investigates the silicon carbide material properties for key points of neural interfaces. An emphasis is given on amorphous SiC (a-SiC) as a surface-passivating film. An a-SiC PECVD deposition recipe is used, with silane and ethylene precursor gasses, for the first time for bio-applications. Multi-modal, multi-parameter studies further clarify the landscape of optimization for a-SiC film properties, and identifies the most significant difficulties. This approach provided excellent results in terms of the a-SiC chemical resistance. In parallel, monocrystalline SiC is investigated as a conducting channel material, focusing on charge transfer and channel cross-talk isolation geometry. The latter has been studied using conventional epitaxial (1), implanted (2) NPN junctions or semi-insulating (3) epitaxial layers.  Lastly, the a-SiC surface has been functionalized by grafting organic polymers with desirable mechanical and wettability properties to a-SiC towards improving the brain tissue-device interface. A crosslinked layer of  hyaluronic acid layer with tissue-like mechanical properties was reliably fixed to a-SiC. All of these results advance the usage of SiC for neural interfaces, and together make possible an all-SiC neural interface for in-vivo applications with state-of-the-art properties ensuring high biocompatibility and extremely long lifetime compared to existing devices.

Jury members :

• Mme Edwige BANO, Grenoble Alpes University : Supervisor
• Mme Gaëlle LISSORGUES, ESIEE Paris : Reviewer
• M. George MALLIARAS, University of Cambridge : Reviewer
• M. Nikolaos A. VAINOS, University of Patras : Examiner
• M. Alexandros GEORGAKILAS, University of Crete- Examiner
• Mme Valérie, STAMBOULI, CNRS : Co-Supervisor
• M. Konstantinos ZEKENTES, University of Crete : Co-Supervisor
• M. Georgios DELIGEORGIS, University of  Crete Examiner