Enhanced Performance and Gate Bias Stress Stability of Atomic-Layer-Deposited Amorphous Zn–Sn–O Thin-Film Transistors with HfO₂ and Al-Doped TiO₂ Interlayers on SiO₂ Gate Oxide

Abstract

10-nm-thick hafnium dioxide (HfO 2 ) and aluminum-doped titanium dioxide (Al-doped TiO 2, ATO) thin films were respectively interposed between the 20-nm-thick amorphous Zn–Sn–O ( a -ZTO) channel layer and 30-nm-thick silicon dioxide (SiO 2 ) gate insulator for thin-film transistor (TFT) performance evaluation. Despite using the identical atomic-layer deposition process, the a -ZTO thin films with higher Sn concentration were deposited on the HfO 2 and ATO film (Sn/Zn atomic ratio 0.82 and 0.81, respectively) than on the SiO 2 film (0.74). Ion interdiffusion between Zn 2+ and Ti 4+ ions occurred in the a -ZTO films deposited on the ATO film, which mitigated oxygen-related defect formation within the a -ZTO channel. As a result, a low subthreshold swing (SS) of 95 mV/decade was achieved from the ATO-based a -ZTO TFT. In contrast, the HfO 2 -based a -ZTO TFT with no defect mitigation effect exhibited the highest SS of 119 mV/decade. In negative and positive gate bias stress (NBS and PBS) tests, SiO 2 -based a -ZTO TFT exhibited an abnormal hump in the NBS test due to the diffused Sn atoms from the a -ZTO channel, resulting in the largest shift of threshold voltage (Δ V th ). HfO 2 -based a -ZTO TFT exhibited Δ V th values of −1.12 and 0.84 V in NBS and PBS tests, respectively, indicating limited device reliability. Remarkably, ATO-based a -ZTO TFT showed minimal Δ V th of −0.11 and 0.09 V in NBS and PBS tests even without a passivation layer, attributed to the low border trap density of ATO film and suppressed oxygen-related defects of the a -ZTO channel.