Nitrogen Doping Strategy in SiO2 Insulators for Stable and Hydrogen-Resistant ALD–IGZO TFTs

Abstract

In–Ga–Zn–O (IGZO) thin-film transistors (TFTs) fabricated via atomic layer deposition (ALD) show promise for future display applications. However, they face challenges related to bias stability and hydrogen vulnerability. We propose an N doping strategy for SiO₂ gate insulators (GI) using nitrous oxide (N₂O) plasma reactants to control the active layer/GI interface and GI bulk properties of top-gate bottom-contact (TG–BC) IGZO TFTs. Increasing the N content in the SiO₂ from 0.7 to 2.2 at.% by adjusting N₂O plasma power from 100 to 300 W resulted in a 10-fold increase in trap densities within the interface and IGZO bulk region. Positive bias temperature stress (PBTS) stability exhibited a U-shaped threshold voltage (V_TH) shift from −4.1 to 4.9 V, driven by H concentration in the GI and interface trap densities. After H₂ annealing, devices demonstrated improved H resistivity, with the V_TH shift reduced from −2.1 to 0.0 V, attributed to H being chemically trapped by N atoms with lone pairs or unbonded electrons. Furthermore, a hybrid GI structure combining N₂O plasma powers of 150 and 300 W further enhanced PBTS stability and H resistivity by 60% and 71%, respectively, demonstrating the effectiveness of this approach.