Long-Term Sustainability of High-Mobility Ultrathin a-IGZO TFT with Double-Layered Passivation

The development of ultrathin amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) technology, capable of delivering high mobility and robust device reliability, is essential for next-generation oxide-TFT applications such as 3D monolithic highly integrated circuits. While using In-rich a-IGZO channels is a straightforward strategy to enhance device mobility, it causes serious TFT instability due to the increase in the weakly bonded In-O. Therefore, overcoming the trade-off between mobility and stability is critical for the advancement of oxide-TFT technology. In this study, we developed an ultrathin high-mobility a-IGZO-TFT using the In-rich channel with In/Ga/Zn = 2:1:1, equipped with double-layered passivation consisting of plasma-enhanced chemical vapor deposition (PECVD)-SiO₂/ALD-Al₂O₃, and demonstrated a high device mobility of ∼40 cm² V^-1 s^-1 and excellent positive and negative bias stability even after one year. The PECVD-SiO₂ layer contributes to mobility enhancement in the a-IGZO channel, while the ALD-Al₂O₃ layer ensures long-term stability by effectively suppressing oxygen vacancy (V_O) formation through the prevention of oxygen out-diffusion from the channel. This study highlights the significance of back-channel passivation engineering in simultaneously enhancing both the mobility and the reliability of a-IGZO TFTs, paving the way for their application in high-performance, long-lifetime electronics.