Lee, S; (2013) Physics and Modeling of Oxide Semiconductor Thin Film Transistors. Doctoral thesis (PhD), UCL (University College London).

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Abstract

In this thesis, we present an intensive investigation on the analytical models to describe the field-effect mobility, the current-voltage (I-V) characteristics, and the instability mechanisms in oxide TFTs, e.g. amorphous In-Ga-Zn-O TFTs. Here, we considered the unique material properties and underlying physics of it, such as the localized tail states, the potential barriers, and the oxygen vacancies. The derived mobility model and the I-V relation for oxide TFTs have been proposed for the first time, yielding a physically-based transistor model for the circuit design and simulation. Also, we developed an analytical method to extract the localized tail state profile to be used as a basis to derive those mobility and I-V models. Here, the relationship between the Fermi-level and gate voltage is derived analytically for the gate voltage-dependent expressions of each model. These models were simulated and compared with the experiments, providing a good agreement with each other. Regarding the instability study, we developed a quantitative analysis on the photoconductive gain due to the oxygen vacancy ionized under illumination, and proposed a gate-pulse spectroscopy to get the ionized oxygen vacancy profile in energy. These studies suggest a visible light sensor application to be embedded into a display panel, e.g. an interactive display, intentionally using the oxygen vacancy-rich layer, e.g. the In-Zn-O, incorporated into a bi-layer channel photo-TFT structure. Consequently, a complete analysis on device physics and modelling of the oxide TFTs is presented in this thesis, providing analytical and quantitative insights into the physics of the oxide TFTs, and their potential for future interactive and transparent electronic systems.

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