| 초록 |
The amorphous oxide thin-film-transistors (TFT) have been widely used and investigated in the flat panel display industry. Oxide TFTs have better mobility in comparison to amorphous-silicon, outstanding uniformity in wide panel display, and can be used in flexible display with lower fabrication temperature. However, since amorphous oxide TFTs degrades under stress condition, instability of amorphous oxide TFT should be understood prior to its application. One example of the oxide TFT is amorphous-Indium-Gallium-Zinc Oxide (a-IGZO) TFT. Different compositions of InGaZn and ratio of composition affect the degree of degradation under stress condition. In this paper, three different mixtures of InGaZn powder at a molar ratio of 5:1:4, 6:1:3 and 7:1:2 in 2-methoxyethanol were used for TFT fabrication and their properties were compared. Bottom-gate and top-contact (BGTC) a-IGZO TFTs were fabricated on SiNx substrates with spin-coated IGZO film. The Al source/drain electrodes were deposited by thermal evaporation. The oxide TFTs thereby obtained, had a channel length (L) and width (W) of 100 and 1000 μm, respectively. Poly (methyl methacrylate) (PMMA) was used as a channel passivation layer. The passivation layer prevents the adsorption of oxygen and water molecules on IGZO surface. The positive bias stress (PBS) was applied to compare threshold voltage shift, mobility, and sub-threshold swing for each composition ratio. In all the three devices, mobility and sub-threshold swing did not change under positive bias stress. On the other hand, threshold voltage significantly changed after increasing the bias time for 0, 10, 30, 100, 300, 1000 and 3000 sec. At 3000 sec of positive bias time, the threshold voltage positively shifted to 4.07 V for 5:1:4, 3.11 V for 6:1:3 and 2.73V for 7:1:2 ratio, respectively. |
