Fabrication and Properties of Transparent Thin-film Transistors by Combinatorial Approach

다국어 초록 (Multilingual Abstract)

Nowadays, the remarkable development of thin-film transistors (TFTs) is becoming one of the revolutionary technologies in the flat-panel display industry. Most of all, in order to achieve a successful realization of next-generation transparent electronics, it should require new materials that have the higher TFT performances (i.e. high-mobility, high-stability, and low-temperature fabrication) than the current a-Si TFTs. The purpose of this thesis is to investigate the electronic properties of multi-composition oxide-based TFTs (such as In-Ga-Zn-O, In-Ga-Sn-O, and In-Zn-Sn-O system) and to define the best composition among the libraries by using combinatorial approach. In addition, by simultaneously depositing multi-composition channels within the same fabrication-conditions, it was possible to analyze the effects dependent only to composition-ratios.
In this thesis, the fabrication of high-performance TFTs was also reported. The largest mobility of 21.1 cmV^-1s^-1 was obtained in In-Zn-Sn-O TFTs. Polycrystalline In-Ta-O TFTs exhibited the high-performance and stability. (i.e. the mobility, threshold voltage, on/off current ratio, sub-threshold voltage swing, and gate-bias voltage shift were 11.1 cmV^-1s^-1, 0.15 V, 6.0x10^8 , 0.14 V/decade and ~ 1V) The composition-dependent transfer curve variations made the empirical establishment for the role of each element in the performance of the TFTs possible. In the In-Ga-Zn-O and In-Ga-Sn-O TFTs, gallium addition plays an effective role in suppressing the formation of oxygen vacancies, which is believed to be the primary source of carrier density. Whereas, the TFTs with increasing indium ratio enhanced higher on-current and motilities since the main component of the conduction band bottom is the indium 5s orbital.
Furthermore, multi-composition oxide TFTs had highly sensitive characteristics by altering composition-ratios and was able to find the appropriate ratios for the optimum TFT operation. Combinatorial synthesis technique can be an effective method to investigate the best composition-ratio through the numerous libraries. It can be one of the most efficient tools to explore new materials required for specific application needs.