Integration of 2D and 3D nanostructure fabrication with wafer-scale microelectronics: Photonic crystals and graphene: Dissertation

This Thesis considers different aspects of heterogeneous integration of 2- and 3- dimensional nanostructures with today's microelectronics process flow. The applications in the main focus are integrated 3D photonic crystals on a photonic chip and graphene biosensors, both exploiting directed self-assembly but at different length scales. View point is from the fabrication and integration challenges, but the future prospects of the selected fields of applications are also reviewed. Utilization of new materials and structures in microelectronics and photonics applications typically requires integration with the existing platforms. The fabrication processes are optimized for the established materials and generally require both high thermal budget and elemental purity to avoid contamination, thus the novel elements need to be integrated at the back-end phase and aligned with the pre-existing structures on the substrate. For that, there are basically three alternatives; (i) directed self-assembly, (ii) high precision placement and (iii) methods exploiting thin film growth and lithographic definition of the nanostructures. Whereas the 2D photonic crystals can be conveniently fabricated with advanced nanolithographic methods such as deep-UV lithography and etching, for the 3D photonic crystals the lithographic approach may not be the most efficient method. This Thesis presents a scalable directed self-assembly method for the fabrication of artificial opal photonic crystals on a photonic chip and defines the processing steps required for the inversion of the opal with silicon to obtain full photonic band gap without damaging the underlying chip. The existence of the full photonic band gap in the inverted silicon photonic crystal is demonstrated by measurements via the integrated waveguides. The integration of graphene with microelectronics processes is, in principle, simple due to the sheet-like structure of the material. The atomically thin 2D crystal can be processed in a manner similar to traditional thin films, as soon as graphene is on the substrate. This Thesis presents different methods aiming for scalable production of high quality graphene on different substrates, ranging from mechanical exfoliation based on step-and-stamp printing to rapid chemical vapour deposition with subsequent thin film transfer, which is the most promising method for large area graphene production. From the physical and chemical point of view, however, graphene is not a traditional thin film. Due to the single atom thickness, environment has a significant influence on the electronic properties of graphene. This has to be taken into account in the processing and design of graphene devices, but it also provides means to highly efficient sensing applications. The key issue in graphene based sensors is in the specific recognition, which has to be introduced by functionalization. This Thesis addresses the functionalization of graphene field-effect-transistors with selfassembled bio-receptors, utilizing non-covalent hydrophobic interactions between graphene and hydrophobin proteins.