Hydrogen Barriers Based on Chemical Trapping Using Chemically Modulated Al₂O₃ Grown by Atomic Layer Deposition for InGaZnO Thin-Film Transistors

Abstract

In this study, the excellent hydrogen barrier properties of the atomic-layer-deposition-grown Al₂O₃ (ALD Al₂O₃) are first reported for improving the stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). Chemical species in Al₂O₃ were artificially modulated during the ALD process using different oxidants, such as H₂O and O₃ (H₂O-Al₂O₃ and O₃-Al₂O₃, respectively). When hydrogen was incorporated into the H₂O-Al₂O₃-passivated TFT, a large negative shift in <i>V</i>_th (ca. -12 V) was observed. In contrast, when hydrogen was incorporated into the O₃-Al₂O₃-passivated TFT, there was a negligible shift in <i>V</i>_th (ca. -0.66 V), which indicates that the O₃-Al₂O₃ has a remarkable hydrogen barrier property. We presented a mechanism for trapping hydrogen in a O₃-Al₂O₃ via various chemical and electrical analyses and revealed that hydrogen molecules were trapped by C-O bonds in the O₃-Al₂O₃, preventing the inflow of hydrogen to the a-IGZO. Additionally, to minimize the deterioration of the pristine device that occurs after a barrier deposition, a bi-layered hydrogen barrier by stacking H₂O- and O₃-Al₂O₃ is adopted. Such a barrier can provide ultrastable performance without degradation. Therefore, we envisioned that the excellent hydrogen barrier suggested in this paper can provide the possibility of improving the stability of devices in various fields by effectively blocking hydrogen inflows.