Vertical hybrid inorganic-organic nanoelectronic devices

Abstract

The implementation of organic building blocks into nanoelectronics devices is finding increased interest due to the huge potential for low-cost, large-area, flexible electronics. However, contacting molecules for investigating their properties is not straightforward. In this thesis, several device structures for contacting and electrical characterization of organic materials are discussed. After a short introduction in Chapter 1, a theoretical background about organic electronics especially of organic field-effect transistors and the charge transport mechanisms in organic materials is covered in Chapter 2. In Chapter 3, the experimental methods utilized for the fabrication of our vertical hybrid nanodevices discussed in Chapters 4 – 6 are explained. The fabrication and electrical characterization of large-area, symmetric metal- molecular monolayer- metal junctions with ultrasmooth template-stripped bottom electrodes and top contacts applied by wedging transfer are covered in Chapter 4. The soft-landing technique wedging transfer was also used for top-contacting thin films of organic semiconductors. These top-contacts were subsequently used as an etch mask to fabricate vertical metal- organic semiconductor- metal pillar structures. We fabricated these pillar structures as two-terminal devices with source and drain electrodes (Chapter 5) as well as three-terminal devices with the addition of a gate electrode (Chapter 6). The vertical configuration enables extremely thin junction lengths allowing for very high current densities. The trapping of DNA over vertical nanogaps towards a chip to electrically detect hypermethylated DNA for early cancer diagnostics is discussed in Chapter 7. In Chapter 8, we introduce the fabrication of silicon nanocrystals and nanochannels with openings below 10 nm. These nanochannels will in the future be filled with molecules to enable one-dimensional molecular transport. In summary, this thesis focuses on investigating the electrical properties of organic materials in different configurations, providing efficient ways for electrical contacting and device fabrication. It additionally suggests methods to proceed to building of zero-dimensional devices by further confining the vertical organic field-effect transistors in the vertical dimension by very thin organic films and also in the lateral dimension by first reducing the pillar diameter and secondly by applying a side-gate. This promises interesting physics to investigate in the quantum mechanical regime.