Three-Stage Defect-State Regulation in ITPO/ITO Bilayer TFTs for Simultaneously Enhanced Mobility and NBTIS Stability

Amorphous oxide semiconductor thin-film transistors (AOS TFTs) based on indium tin oxide (ITO) channels offer intrinsically high mobility due to their extended InO conduction network but suffer severe negative-bias illumination stress (NBIS) instability caused by oxygen-vacancy-induced hole trapping. Here, a three-stage stabilization strategy is applied to an ITPO/ITO bilayer channel system. Pr ${}^{{3}+}$ incorporation in ITPO forms deep recombination centers that suppress photo-induced hole accumulation, while the underlying ITO layer retains high electron transport within a charge-relaxation/charge-transport layer (CRL/CTL) configuration. A sputtered ZSO passivation layer further reduces surface vacancy-related interface states and mitigates thermally driven oxygen loss. The optimized device achieves a mobility of 41.7 cm ${}^{{2}}\cdot $ V ${}^{-{1}}\cdot $ s ${}^{-{1}}$ , a subthreshold swing (SS) of 0.23 V $\cdot $ dec ${}^{-{1}}$ , and ${V}_{\text {th}}$ shifts of 0 V negative-bias stress (NBS), −0.9 V (NBIS), and −1.1 V negative-bias temperature illumination stress (NBTIS). These results demonstrate that the mobility-stability trade-off in ITO TFTs can be resolved through coordinated defect and interface regulation.