Dissertation Defense

Yttrium and Scandium in Solutions-processed Oxide Electronic Materials

Wenbing HuPhD Candidate

Large area electronics are critical for many novel applications such as smart windows, wearable electronics and Internet of Things. Among candidate materials, metal oxides have relatively good performance and stability and can be deposited by low-cost solution processes. Multi-component oxides are increasingly used to tune and improve electrical performance via oxygen gettering and to improve material thermal and electrical stability via alloy mixing. This thesis investigates the roles of rare-earth elements yttrium and scandium as alloy components in a variety of solution-processed metal oxide thin films. First we develop a zinc tin oxide semiconductor based thin film transistor technology and characterize charge transport mechanisms and device contact resistance. The addition of a low concentration of yttrium enhances transistor DC performance, likely through oxygen gettering. Higher yttrium concentrations compromise device DC performance while improving transistor negative bias illumination stress stability due to competing mechanisms of increased structural disorder and reduced oxygen vacancy-related defects. Second, forming-gas annealed scandium- or yttrium-doped zinc oxide forms a transparent conducting oxide. However the rare earth elements do not act as substitutional donors but instead form insulating structures along grain boundaries, causing surface depletion, decreasing film conductivity. Third, alloys of yttrium and scandium oxide form high-k dielectrics having high breakdown field, low leakage current and low dielectric frequency dispersion. The alloys maintain a high breakdown field even after crystallization is induced by 900Â °~C anneal. The yttrium- and scandium-doped solution-processed oxides developed here form a complete suite of electronic materials suitable for fabrication of future large-area electronic devices.

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Becky Peterson