Ultratin metal oxide films for thin film transistors

多层氧化物材料作为有源半导体在薄膜晶体管器件中越来越重要。从它们的性能来看，它们优于非晶硅，因此在各种电子器件中得到了广泛的应用。与非晶氧化物结构相比，晶体氧化物异质结构具有一定的优势。而非晶氧化物的结构往往取决于各种条件，如沉积技术，退火温度和氧压，晶体氧化物不是亚稳态的，它们的化学计量是离散的，因此它们可以在受控的合成条件下调谐。此外，晶体氧化物不像非晶氧化物那样容易产生结构松弛效应，因此在诸如场效应晶体管（TFT）器件等操作条件下更稳定。该方案涉及厚度在5-10 nm范围内的多层超薄晶体金属氧化物薄膜在tft中作为半导体实体。这些氧化膜对于理解如何利用这种异质结构来提高性能以及确保半导体薄膜的长期可靠性具有重要意义。因此，提出的工作重点是阐明和理解多层晶体金属氧化物异质结构固有的独特特征。这种异质结构可以通过组合、静电或调制掺杂以及场效应来操纵载流子浓度，从而实现对性能的外部控制。特别的目的将是确定与原子层沉积（ALD）方法制备的异质结构主要相关的现象。如何在基于化学的合成方法中转化TFT中半导体异质结构的特殊要求？为了达到这些目标，将合成由In2O3/SnO2/ZnO或HfO2/In2O3/ZnO堆叠组成的多层晶体氧化物结构。由此产生的tft将通过电测量以及光谱和微观技术的组合来表征。能够探测复杂异质结构的光谱方法将支持对电特性的解释。它们将提供关于异质结构堆叠中埋藏界面的性质和不同金属氧化物层之间电荷转移程度的特定信息。通过这种方法，可以对多层金属氧化物异质结构进行全面的表征。由于这些材料系统具有高度的灵活性，我们期待在这一研究领域有新的发现和深入的理解。

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.