Selective SnO x Atomic Layer Deposition Driven by Oxygen Reactants.

SnO x thin films were successfully deposited by the thermal atomic layer deposition (ALD) method using N, N'- tert-butyl-1,1-dimethylethylenediamine stannylene(II) as a precursor and ozone and water as reactants. The growth of SnO and SnO2 films could be easily controlled by employing different reactants and utilizing different ozone and water concentrations, respectively. The formation of both SnO and SnO2 films exhibited typical surface-limiting reaction characteristics, although their growth behaviors differ from one another. The combined studies of density functional theory calculations and experimental analyses showed that the difference in growth behavior of the SnO and SnO2 films can be attributed to the stability of ozone and water on the SnO2 and SnO films. SnO and SnO2 films have different crystal structures and both films were crystallized from the amorphous to polycrystalline states following an increase in the deposition temperature. The absorbance and refractive index of the thin films were investigated using ultraviolet-visible spectroscopy (UV-vis) and spectroscopic ellipsometry (SE), respectively. SnO x films formed using ozone and water as a reactant showed an optical band gap of 3.60-3.17 eV and 2.24-2.30 eV and refractive indices of ∼2.0 and ∼2.6, respectively, which correspond to values typical of SnO2 and SnO. The bilayer structure of SnO/SnO2 was successfully fabricated on indium tin oxide (ITO) glass with nickel as a top electrode at 100 °C. The SnO/SnO2 bilayer exhibited diode characteristics with a current rectification ratio of 15. Our results present a simple but highly versatile growth method for producing multilayer oxide films with electronic properties that can be finely controlled.

Performance and Stability Enhancement of In-Sn-Zn-O TFTs Using SiO2 Gate Dielectrics Grown by Low Temperature Atomic Layer Deposition.

Silicon dioxide (SiO2) films were synthesized by plasma-enhanced atomic layer deposition (PEALD) using BTBAS [bis(tertiarybutylamino) silane] as the precursor and O2 plasma as the reactant, at a temperature range from 50 to 200 °C. While dielectric constant values larger than 3.7 are obtained at all deposition temperatures, the leakage current levels are drastically reduced to below 10-12 A at temperatures above 150 °C, which are similar to those obtained in thermally oxidized and PECVD grown SiO2. Thin film transistors (TFTs) based on In-Sn-Zn-O (ITZO) semiconductors were fabricated using thermal SiO2, PECVD SiO2, and PEALD SiO2 grown at 150 °C as the gate dielectrics, and superior device performance and stability are observed in the last case. A linear field effect mobility of 68.5 cm2/(V s) and a net threshold voltage shift (ΔVth) of approximately 1.2 V under positive bias stress (PBS) are obtained using the PEALD SiO2 as the gate insulator. The relatively high concentration of hydrogen in the PEALD SiO2 is suggested to induce a high carrier density in the ITZO layer deposited onto it, which results in enhanced charge transport properties. Also, it is most likely that the hydrogen atoms have passivated the electron traps related to interstitial oxygen defects, thus resulting in improved stability under PBS. Although the PECVD SiO2 contains a hydrogen concentration similar to that of PEALD SiO2, its relatively large surface roughness appears to induce scattering effects and the generation of electron traps, which result in inferior device performance and stability.