Ultratin metal oxide films for thin film transistors

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Multilayer oxide materials have gained increasing importance as active semiconductors in thin film transistor devices. From their performance they outperform amorphous silicon and have thus found widespread applications in various electronic devices. Compared to amorphous oxide structures crystalline oxide heterostructures have certain additional advantages. Whereas the structure of amorphous oxides often depends on various conditions like deposition technique, annealling temperature and oxygen pressure, crystalline oxides are not metastable, their stoichiometry is discrete and they can thus be tuned under controlled synthesis conditions. Moreover, crystalline oxides are not prone to structural relaxation effects as amorphous oxides are and are thus more stable under operational conditions e.g. in a field effect transistor (TFT) device. This proposal deals with multilayered ultrathin crystalline metal oxide films of thicknesses in the range of 5-10 nm serving as semiconductor entity in TFTs. These oxide films will be of relevance for understanding how such heterostructures can be employed to increase performance as well as to ensure long-term reliability of semiconductor thin films. Thus, the proposed work focuses on the elucidation and understanding of the unique characteristics which are inherent to multilayered crystalline metal oxide heterostructures. Such heterostructures could allow for external control of properties through the manipulation of carrier concentration by composition, electrostatic or modulation doping as well as field effect. The aim in particular will be to identify phenomena which are of predominant relevance for heterostructures fabricated by means of atomic layer deposition (ALD). How can the special requirements for a semiconducting heterostructure within a TFT be translated in a chemistry based synthetic approach? To reach these goals multilayered crystalline oxide structures consisting of In2O3/SnO2/ZnO or HfO2/In2O3/ZnO stacks will be synthesized. The resulting TFTs will be characterized by a combination of electrical measurements as well as spectroscopic and microscopic techniques. The interpretation of the electrical characterization will be supported by spectroscopic methods which are capable to probe complex heterostructures. They will provide particular information about the nature of the buried interfaces within a heterostructured stack and the degree of charge transfer between the different metal oxide layers. In this way a comprehensive characterization of the multi-layered metal oxide heterostructures will be possible. Since these material systems possess a high degree of flexibility, we expect new discoveries and an in depth understanding in this field of research.