Investigation of IGZO Thin Film Transistors with Copper Electrode Under Varied Channel Lengths and Different Gate Insulator Annealing Temperatures

IGZO TFTs incorporating copper (Cu) electrodes undergo hydrogen treatment to prevent the formation of copper oxide on Cu. However, this treatment introduces hydrogen into IGZO, increasing donor states, boosting majority carriers, and resulting in a negative threshold voltage (Vth) shift, thereby posing reliability concerns. This study explores the characteristics of IGZO TFTs with varying channel lengths and gate insulator (GI) annealing temperatures. Devices subjected to GI annealing at 350°C exhibit a negative <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vₜₕ</tex> and higher mobility compared to those annealed at 280°C. In addition, due to the hydrogen plasma treatment from interlayer dielectric, hydrogen lateral diffusion will cause the difference of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vₜₕ</tex> in short channel and long channel devices. The capacitance-voltage diagram also shows the C-V earlier turn-on in short channel devices. After positive bias temperature stress, the results indicate devices under GI annealing at 350°C will display a smaller <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vₜₕ</tex> shift. Plausible physical models are proposed subsequently.