Advanced fabrication of nanowire arrays and three-dimensional nanostructures

Vlad, Alexandru [UCL]

(eng) Faster, smaller, cheaper are the three magic words that define the goal of modern semiconductor manufacturing industry. While speed and price behave satisfactorily, downscaling is the culprit. The "More than Moore" era pushes the scientist to dream about innovative devices, performing more operations at smaller and smaller scales and based on different physical principles. Molecular and organic electronics, spintronics and quantum computing as well as carbon nanotubes and "Graphenium Inside" exponentially emerging fields are only few to be cited. These concepts for sure will have their place in the tomorrow technologies. What we don't know is how they will perform. One typically thinks that sizing down or changing the structural and operating philosophy of the electronic circuit elements will allow us to continue the progress. This is essentially true and remains the major tendency in advancing the information technology. Vertical stacking of multiple active components, providing identical functionality, can be regarded as a relatively long term option. Instead of shrinking, we can pile them up at their nominal size and fit the same number of active elements on a given surface area. Technologically, both approaches could require the same degree of processing complexity. Other option is to use photons instead of electrons to manipulate, store and transmit data. The electrons are operated at a few GHz for everyday computing and the increase of the operation frequency can seriously complicate the fabrication tasks; the visible and infrared spectrum range photons are already "operating" at hundreds of terahertz. In this thesis, we bring together these two fields, which are closely related in their fabrication methodology. Nanoporous templates have been found to be excellent candidates for this study since their peculiar morphology is well suited for both purposes. Ordered, modulated dielectric media could be directly employed to mold the flow of light. Indirectly, they can be used to confine and stack various electronic components in the nanoscale channels. By combining them novel optoelectronic devices could be advanced. Two types of porous materials have been extensively exploited. First, we consider the nano- to macro-scale manipulation of self-organized, anodic aluminum oxide templates. Parallel integration of single nanowires is highlighted. We provide a full processing technology, starting from a bulk silicon substrate and finishing with a cross-bar latch having at its heart single, template-embedded nanowires. A novel statistical protocol for template processing is put forward. The comprehensive explanation of the experimental and simulated stochastic behavior relies on a straightforward analytical formalism and the technology is interpreted in terms of surface and packing optimization. The method is scalable and can be generalized to virtually any type of templates. Simultaneously, high resolution electron beam lithography was used to generate highly ordered 2D and 3D templates. A novel type of resist and dose-modulated electron beam lithography (RDM-3D-EBL), extensively exploiting the intrinsic properties of resist-electron beam interaction was developed. Surface initiated and template confined aniline polymerization was then used to provide a genuine method for controlled nanoscale processing of polyaniline, a prototypical conjugated polymer that definitively settled the concept of synthetic metals. Using nanoscale polymerization reactors, ultimate resolution patterning and processing control of single polyaniline nanostructures was feasible. Near teradot/inch2 pattern transfer technology, complex 3D structuring and physico-chemical functionalization of polyaniline have been subsequently harnessed to build a large variety of architectures with potential for emerging optoelectronic technologies. This allowed the implementation of a simple scheme for single polyaniline nanowire fabrication, processing and device integration.