Characteristics of Amorphous Indium-Zinc-Oxide Thin-Film Transistors Fabricated with a Self-Aligned Coplanar Structure and an NH3 Plasma Contact Doping Process

Abstract

We report an NH3 plasma contact doping process for amorphous indium-zinc-oxide (a-IZO), which we use to fabricate thin-film transistors (TFTs). By combining a self-aligned coplanar structure with the NH3 plasma doping process, and using an a-IZO active layer with a 9:1 atomic composition of In:Zn, we succeeded in fabricating high-performance a-IZO TFTs, with a field-effect mobility value of 75.5 cm(2) V-1 s(-1) and a sub-threshold slope of 0.18 V/dec. Devices formed with a-IZO active layers with 1:1 ratio of ln:Zn and 9:1 In:Zn resulted in opposite dependences of both the field-effect mobility and the threshold voltage on the ratio of the channel width to length, W/L. This can be explained by considering the difference in the initial charge carrier density of the a-IZO layers, and we find that a high In content is beneficial for fabricating high-performance a-IZO TFTs with long channels. However, a low In-content a-IZO active layer can be used for short channel a-IZO TFTs because the dependence of field-effect mobility on the In content is small for short channel devices.