Self-Aligned Top-Gate IGZO TFT With Stepped Structure for Suppressing Short Channel Effect

In this work, the self-aligned coplanar top gate In-Ga-Zn-O thin-film transistor with a stepped substrate structure was investigated to suppress the short-channel effect. Usually, $\text{V}_{\text {th}}$ roll-off occurs as channel length decreases due to a large gate and source/drain overlap ( $\Delta \text{L}$ ), attributed to the significant diffusion of high carrier density from $\text{n}^{+}$ S/D regions into the main IGZO channel. In the proposed structure, the stepped structure induces gate insulator extension that covers the side edge of the main IGZO channel and protects from Ar plasma treatment, which forms $\text{n}^{+}$ regions. The fabrication results show that the short-channel effect can be successfully suppressed up to $2~\mu \text{m}$ channel length with $0.23~\mu \text{m}~\Delta \text{L}$ .