Suppressing channel-shortening effect of self-aligned coplanar Al-doped In-Sn-Zn-O TFTs using Mo-Al alloy source/drain electrode as Cu diffusion barrier

Abstract

Developing high-resolution displays to achieve realistic images have been in a great demand recently regardless of the display size. However, in the backplane technology, the channel-shortening effect is a serious obstacle in realizing oxide thin film transistors (TFTs) with short channel lengths. In this study, we investigated the channel-shortening effect of Al-doped InSnZnO (Al:ITZO) thin-film transistors (TFTs) with Mo and Mo-based alloy Cu diffusion barriers and proposed Mo‒Al alloy as a Cu diffusion barrier to effectively reduce the channel-shortening effect. The TFTs with the Mo (Cu diffusion barrier) exhibited negative Von shifts and a channel-shortening length (ΔL) of 3.52 µm at an annealing temperature of 290 °C, although no chemical reaction occurred at the Mo/Al:ITZO interfaces. In addition, the TFTs with the Mo‒Ti (Cu diffusion barrier) showed the largest ΔVon and ΔL values at various annealing temperatures. The material and electrical analysis results confirmed that the hydrogen diffusion from the source/drain region is the main cause of the channel-shortening effect. Thus, the TFTs with the Mo‒Al (Cu diffusion barrier) exhibited excellent characteristics against the channel-shortening effect by forming a uniform and thin Al2O3 layer at the Mo‒Al/Al:ITZO interface and preventing the hydrogen diffusion. The ΔVon remained almost unchanged, and the ΔL was 1.61 µm up to an annealing temperature of 290 °C. This study suggests a highly beneficial method for producing oxide TFTs, while suppressing the channel-shortening effect by tailoring the interface between source/drain and active layer using an appropriate Cu diffusion electrode.