Amorphous NdIZO Thin Film Transistors with Contact-Resistance-Adjustable Cu S/D Electrodes

High-performance amorphous oxide semiconductor thin film transistors (AOS-TFT) with copper (Cu) electrodes are of great significance for next-generation large-size, high-refresh rate and high-resolution panel display technology. In this work, using rare earth dopant, neodymium-doped indium-zinc-oxide (NdIZO) film was optimized as the active layer of TFT with Cu source and drain (S/D) electrodes. Under the guidance of the Taguchi orthogonal design method from Minitab software, the semiconductor characteristics were evaluated by microwave photoconductivity decay (μ-PCD) measurement. The results show that moderate oxygen concentration (~5%), low sputtering pressure (≤5 mTorr) and annealing temperature (≤300 °C) are conducive to reducing the shallow localized states of NdIZO film. The optimized annealing temperature of this device configuration is as low as 250 °C, and the contact resistance (R_C) is modulated by gate voltage (V_G) instead of a constant value when annealed at 300 °C. It is believed that the adjustable R_C with V_G is the key to keeping both high mobility and compensation of the threshold voltage (V_th). The optimal device performance was obtained at 250 °C with an I_on/I_off ratio of 2.89 × 10⁷, a saturation mobility (μ_sat) of 24.48 cm²/(V·s) and V_th of 2.32 V.