Specific contact resistivity reduction in amorphous IGZO thin-film transistors through a TiN/IGTO heterogeneous interlayer

Oxide semiconductors have gained significant attention in electronic device industry due to their high potential for emerging thin-film transistor (TFT) applications. However, electrical contact properties such as specific contact resistivity (ρ_C) and width-normalized contact resistance (R_CW) are significantly inferior in oxide TFTs compared to conventional silicon metal oxide semiconductor field-effect transistors. In this study, a multi-stack interlayer (IL) consisting of titanium nitride (TiN) and indium-gallium-tin-oxide (IGTO) is inserted between source/drain electrodes and amorphous indium-gallium-zinc-oxide (IGZO). The TiN is introduced to increase conductivity of the underlying layer, while IGTO acts as an n⁺-layer. Our findings reveal IGTO thickness (t_IGTO)-dependent electrical contact properties of IGZO TFT, where ρ_C and R_CW decrease as t_IGTO increases to 8 nm. However, at t_IGTO > 8 nm, they increase mainly due to IGTO crystallization-induced contact interface aggravation. Consequently, the IGZO TFTs with a TiN/IGTO (3/8 nm) IL reveal the lowest ρ_C and R_CW of 9.0 × 10⁻⁶ Ω·cm² and 0.7 Ω·cm, significantly lower than 8.0 × 10⁻⁴ Ω·cm² and 6.9 Ω·cm in the TFTs without the IL, respectively. This improved electrical contact properties increases field-effect mobility from 39.9 to 45.0 cm²/Vs. This study demonstrates the effectiveness of this multi-stack IL approach in oxide TFTs.