Enhanced dielectric properties of alternative NO-gas-based SiO2 films via plasma-enhanced chemical vapor deposition for high-performance indium–gallium–zinc oxide thin-film transistors

Abstract

Nitric oxide (NO) is proposed as an alternative gas to nitrous oxide (N₂O) for the formation of silicon dioxide (SiO₂) films by plasma-enhanced chemical vapor deposition. Post-thermal annealing in a N₂ atmosphere is employed to improve the current–voltage and capacitance–voltage characteristics of the films by removing charge impurities and curing defect states, thereby restoring the intrinsic dielectric properties of the NO-based SiO₂ films. The effects of the enhanced dielectric properties of the NO-based SiO₂ films on the device performance of indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) were subsequently investigated. The IGZO TFT consisting of a NO-based SiO₂ dielectric film annealed at 300 °C in a N₂ atmosphere exhibits excellent electrical characteristics, including a low off-current, large on/off ratio, low subthreshold swing, high field-effect mobility, and threshold voltage near 0 V. Improvements in electrical stability of the IGZO TFTs against a prolonged bias stress are also achieved owing to the introduction of N₂-annealed SiO₂ dielectric films. Finally, charge-transport properties are investigated via temperature-dependent field-effect mobility analysis to determine the activation energy and interfacial trap density of states, which agree well with the improved device performance of the IGZO TFTs consisting of NO-based SiO₂ films with enhanced dielectric properties.