In–Ga–Sn–O (IGTO) thin-film transistors (TFTs) were fabricated, in which the metal cationic compositions of the IGTO channel were controlled by subcyclic ratio design of each precursor during atomic-layer deposition (ALD). When the number of Sn precursor subcycles increased, the cationic composition of Sn increased from 0.3 to 1.9. It was found that the field-effect mobility gradually increased, and the threshold voltage shifted negatively with higher Sn molar ratios. As a result, the devices using the IGTO channel with a cationic composition of 4.2:1.3:1.9 (In:Ga:Sn) exhibited the highest field-effect mobility of 66.9 cm2/V·s as well as the most stable behavior against external gate bias stress (ΔVth < 2 V). These characteristics are attributed to the free electrons generated by Sn4+ diffusion between In and Sn layers contributing to the conduction band during the ALD process and the effective suppression of oxygen vacancy formation with a higher Sn composition ratio.
Lee et al. (Tue,) studied this question.