Enhanced Reliability of In–Ga–ZnO Thin-Film Transistors Through Design of Dual Passivation Layers

This paper investigates the effects of different passivation layers (PVLs) on the electrical performance and reliability of amorphous indium gallium zinc oxide (a-In-Ga-ZnO) thin film transistors (TFTs). By rational design, the fabricated a-InGaZnO TFT with hafnium oxide and aluminum oxide (HfO ₂ /Al ₂ O ₃ ) dual PVLs exhibits a field-effect mobility of 13.5 cm ² /Vs, low sub threshold swing of 0.32 V/decade, and especially, small threshold voltage shifts of 0.5 (-0.6) V and 1.1 (-1.2) V under positive (negative) gate bias, and light illumination stress at the relative humidity of 40%. Furthermore, the a-In-Ga-ZnO TFTs with HfO ₂ /Al ₂ O ₃ dual PVLs maintain reasonable mobility and electrical performance even exposure to ambient condition for up to four months. This enhanced stability is attributed to the presence of high-quality HfO ₂ /Al ₂ O ₃ dual PVLs, which not only could suppress the photodesorption, reduce the total trap density and subgap photoexcitation behavior, but also protect the channel from environmental effects. Thus, the rational-designed HfO ₂ /Al ₂ O ₃ dual PVLs passivated a-In-Ga-ZnO TFTs with superior reliability represent a great step toward the achievement of long-term reliable zinc oxide-based oxide TFTs.