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.