Passivation-Dependent Device-Level Thermal Robustness of Indium Gallium Oxide Thin-Film Transistors under Dynamic Random-Access Memory Relevant 600 °C Nitrogen Annealing

As conventional silicon-based dynamic random-access memory (DRAM) approaches its physical and electrical scaling limits, oxide semiconductors have emerged as promising channel materials for next-generation memory devices because of their low off-state current and process compatibility. Among them, indium gallium oxide (IGO) thin-film transistors (TFTs) have attracted considerable attention for DRAM-related applications; however, their implementation remains challenging because the device stack must withstand high-thermal-budget back-end-of-line processing, including annealing at 600 °C in a N2 ambient which can promote oxygen-deficient conditions in oxide layers. Here, we systematically investigate the effects of passivation-layer selection on the electrical performance and thermal reliability of IGO TFTs by comparing Al2O3-, HfO2-, and SiO2-passivated devices before and after 600 °C N2 annealing. Among the passivation layers examined, Al2O3 uniquely preserved stable transistor operation after the high-temperature process, whereas the HfO2- and SiO2-passivated devices exhibited severe degradation of switching behavior and became electrically unextractable after 10 min annealing. In contrast, the Al2O3-passivated TFTs retained excellent electrical characteristics, including a field-effect mobility of 94.08 cm2V–1s–1 and a subthreshold swing of 84 mVdec–1 after 10 min annealing. Moreover, the positive-bias temperature stress stability was markedly improved, with the threshold-voltage shift at 100 °C decreasing from 63 to 20 mV after extended annealing. The superior reliability of Al2O3 layer may be attributed to its strong Al–O bonding and high film density, which provide enhanced chemical and structural stability during high-temperature N2 annealing. These findings suggest that Al2O3 passivation is an effective strategy for enabling thermally robust and electrically reliable IGO TFTs for advanced DRAM applications.