Formation of F-Doped Offset Region for Spray Pyrolyzed Self-Aligned Coplanar Amorphous Zinc–Tin–Oxide Thin-Film Transistor by NF₃ Plasma Treatment

Abstract

We report the high performance of self-aligned (SA), amorphous zinc–tin–oxide (a-ZTO) coplanar thin-film transistor (TFT) by spray pyrolysis. The a-ZTO thin film deposited by spray at 350 °C has a low surface roughness (0.39 nm) and no bubble. The resistivity of a-ZTO could be decreased to $2\times 10^{-3} \Omega $ cm by NF3 plasma exposure and it was used for the offset regions of SA coplanar TFT. The coplanar a-ZTO TFT exhibits the field-effect mobility ( $\mu _{{\mathrm {FE}}}$ ) of 5.13 cm $^{2}\text{V}^{-1}\text{s}^{-1}$ , turn-on voltage ( ${V}_{ \mathrm{\scriptscriptstyle ON}}$ ) of ~0 V, the subthreshold swing of 139 mV/decade, and high On/Off-current ratio over $\sim 10^{7}$ . The SA coplanar a-ZTO TFT exhibited high stability with a threshold voltage shift ( $\Delta {V}_{{\mathrm {TH}}}$ ) of 0 V under the gate bias stress of ${V}_{{\mathrm {GS}}} = +20$ V for 1 h.