Indium tin zinc oxide (ITZO) thin-film transistors (TFTs) with different channel structures are investigated. The electrical performance and bias stress stability of bilayer-channel ITZO TFTs are enhanced in comparison with those of single-channel ITZO TFTs. The bilayer channel consists of an oxygen-uncompensated channel layer and an oxygen-compensated capping layer, while the single channel is an oxygen-uncompensated channel layer. The electrical properties of the bilayer-channel films are fine-tuned by adjusting their oxygen stoichiometry using the oxygen-compensated capping layer. The X-ray photoelectron spectroscopy measurements reveal that the bilayer channel shows advantages over the single channel in terms of increased metal oxide concentration and decreased oxygen vacancy and hydroxyl concentration. As a result, the bilayer-channel ITZO TFT exhibits a saturation field-effect mobility of 17.31 cm2/Vs, a sub-threshold swing of 0.24 V/dec, and a good operational bias stress stability in comparison with the single-channel TFT. This work demonstrates that the bilayer-channel ITZO TFTs have great potential for next-generation display applications.

We investigated the electrical properties and operational stability of amorphous indium-tin-zinc-oxide (a-ITZO) thin-film transistors (TFTs). We fabricated the a-ITZO TFTs using deposition by radio frequency sputtering at room temperature followed by a rapid thermal annealing (RTA) process at different temperatures and oxygen pressure (P O2). This is a more practical annealing route compared to a conventional furnace. Based on film densification and oxygen vacancy optimization, the a-ITZO TFTs exhibited 9.8 cm2 Vs−1, 0.82 V/decade and 1.39 V, for saturation mobility, sub-threshold swing and threshold voltage, respectively. Operation stability tests and hysteresis behavior of a-ITZO TFTs suggest that oxygen vacancy concentration of a-ITZO thin films gradually decreases under higher P O2, consequently affecting the threshold voltage and the shift seen after a gate bias stress test. This observation suggests that gate bias stress and hysteresis stability of an a-ITZO device is due to the effect of oxygen-controlled pressure in the RTA process. This a-ITZO TFTs electrical characterization qualitatively coincides with x-ray photoelectron spectroscopic analyses of oxygen vacancy concentration in a-ITZO thin films. Thus, our systematic a-ITZO thin film optimization using the oxygen-ambient RTA process is a practical basis for high-performance amorphous oxide semiconductor TFT post-annealing methods.

Solution-processed indium gallium tin oxide (InGaSnO, IGTO) thin film transistors (TFTs) are investigated as promising low-cost and stable materials for high-performance amorphous oxide semiconductor (AOS)-based TFTs in display applications. After tailoring the metal cation composition in IGTO thin films, the IGTO (7:1:1) AOS TFT shows a saturation mobility and current on/off ratio of 2.13 cm 2 V −1 s −1 and 2.55 × 10 7 , superior to the IGZO TFT. It was found that the threshold voltage (V th ) shifts of IGTO TFTs with higher Sn molar ratios became gradually diminished both under the positive bias stress (PBS) test, from +7.3 to +1.1 V, and under the negative bias stress (NBS) test, from −2.83 to −0.94 V, due to the increased concentration of Sn−O complexes with relatively higher bonding energies within IGTO thin films. X-ray photoelectron spectroscopy (XPS) analysis also reveals that IGTO thin films with higher Sn composition ratio tend to effectively suppress the formation of oxygen vacancy, which consequently led to the improved stability of IGTO-based TFTs under the gate bias stress. Therefore, these results can be the basis for improving the characteristics of IGTO semiconducting channel systems for low-cost switching devices in the display applications.