Improvement of Electrical Characteristics and Stability of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using Nitrocellulose Passivation Layer

In this research, nitrocellulose is proposed as a new material for the passivation layers of amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The a-IGZO TFTs with nitrocellulose passivation layers (NC-PVLs) demonstrate improved electrical characteristics and stability. The a-IGZO TFTs with NC-PVLs exhibit improvements in field-effect mobility (μ_FE) from 11.72 ± 1.14 to 20.68 ± 1.94 cm²/(V s), threshold voltage (V_th) from 1.85 ± 1.19 to 0.56 ± 0.35 V, and on/off current ratio (I_on/off) from (5.31 ± 2.19) × 10⁷ to (4.79 ± 1.54) × 10⁸ compared to a-IGZO TFTs without PVLs, respectively. The V_th shifts of a-IGZO TFTs without PVLs, with poly(methyl methacrylate) (PMMA) PVLs, and with NC-PVLs under positive bias stress (PBS) test for 10,000 s represented 5.08, 3.94, and 2.35 V, respectively. These improvements were induced by nitrogen diffusion from NC-PVLs to a-IGZO TFTs. The lone-pair electrons of diffused nitrogen attract weakly bonded oxygen serving as defect sites in a-IGZO TFTs. Consequently, the electrical characteristics are improved by an increase of carrier concentration in a-IGZO TFTs, and a decrease of defects in the back channel layer. Also, NC-PVLs have an excellent property as a barrier against ambient gases. Therefore, the NC-PVL is a promising passivation layer for next-generation display devices that simultaneously can improve electrical characteristics and stability against ambient gases.