Effects of Target Quality on Electrical Performance and Stability of In-Sn-Zn-O Thin-Film Transistors

In this work, we study the intrinsic connection between target quality and performance of sputtered In-Sn-Zn-O (ITZO) thin-film transistors. Using a dense target, the ITZO device overall performance can be improved synergistically. The optimized device exhibits a steep subthreshold swing of 0.13 V/decade, a high on/off current ratio of $2.47\times 10^{{8}}$ , a threshold voltage of −0.03 V, a saturation field-effect mobility ( $\mu _{{FE}}$ ) of 36.1 cm2/Vs, and a small threshold voltage shift ( $\Delta ~{V} _{{th}}$ ) of −0.55 V under negative bias stress (−20 V, 3600 s). In contrast, the $\mu _{{FE}}$ shows a reverse trend to $\Delta {V} _{{th}}$ when using a target with a relatively small density and poor crystallinity. In this case, although the amount of oxygen vacancy in the films can be reduced for better stability via increasing the sputtering power, the film density observably drops due to serious preferential sputtering, leading to smaller $\mu _{{FE}}$ .