Bias stress stability of zinc-tin-oxide thin-film transistors with Al2O3 gate dielectrics

TitleBias stress stability of zinc-tin-oxide thin-film transistors with Al2O3 gate dielectrics
Publication TypeJournal Article
Year of Publication2010
AuthorsTriska, J., J. F. Conley, R. E. Presley, and J. F. Wager
JournalJournal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
Volume28
Issue4
PaginationC5I1
Date Published07/2010
ISSN10711023
KeywordsAl2O3, aluminium compounds, amorphous semiconductors, atomic layer deposition (ALD), atomic layer epitaxial growth, bias stressing, device stability, dielectric materials, electron mobility, electron traps, plasma CVD, reliability, silicon compounds, thin film transistors, zinc compounds, zinc tin oxide (ZTO)
Abstract

The bias stability of zinc-tin-oxide (ZTO) thin-film transistors (TFTs) with either Al₂O₃ gate dielectrics deposited via atomic layer deposition (ALD) or SiO₂ gate dielectrics deposited via plasma-enhanced chemical vapor deposition (PECVD) was compared. Both device types showed incremental mobility ≥ 11 cm²/V s, subthreshold slopes <0.4 V/dec, and ION/IOFF ratios of ∼ 10⁷. During repeated ID-VGS sweeping, both device types showed positive parallel shift of the turn-on voltage (VON) without significant degradation of subthreshold slope or mobility, consistent with electron trapping without creation of new traps. A smaller VON shift was observed in the SiO₂/ZTO devices. In an effort to improve the bias stress stability of the Al₂O₃/ZTO devices, the impact of ALD temperature, plasma exposure of the Al₂O₃, and the addition of an interfacial PECVD SiO₂ capping layer were investigated. The positive bias stress stability of the Al₂O₃/ZTO TFTs was found to be relatively unaffected by the Al₂O₃ ALD temperature, degraded with plasma exposure, and improved by the addition of a thin ( ∼ 3 nm) PECVD SiO₂ interfacial layer between the Al₂O₃ dielectric and the ZTO channel. These results point to the vicinity of the Al₂O₃/ZTO interface as the dominant source of charge trapping.

DOI10.1116/1.3455494
Short TitleJ. Vac. Sci. Technol. B