Effect of thickness-dependent structural defects on electrical stability of MoS2 thin film transistors

Abstract

The electrical stability and reliability of molybdenum disulfide (MoS2) thin film transistors (TFTs) were investigated by associating thickness-dependent structural defects with degradation mechanism. Patterned MoS2 films with different thicknesses were fabricated for use as transistor channels via the modified multi-step chemical vapor deposition method. X-ray photoelectron spectroscopic (XPS) analyses revealed that highly layered and stoichiometric MoS2 films of up to ∼3 nm thickness were formed around the surface, whereas Mo metal bonds were dominant around the bottom of the films (9 nm). Variations in transistor properties of the thus prepared MoS2 films were examined by applying positive and negative bias stress (PBS and NBS, respectively). The experimental data indicated that MoS2 TFTs with 3-nm-thick films exhibited stable behavior under both PBS and NBS conditions, whereas those with 9-nm-thick films exhibited clear shifts in electrical performance (△Vth < 1.15 V, △μsat < 0.10 cm2/V·s). These results, together with XPS analyses, revealed that the instability of the MoS2 TFTs under PBS is dominated by sulfur interstitials, whereas their instability under NBS is caused by oxygen vacancies and metallic Mo defects. Additional details about the correlation between the atomic structural defects, which are generated due to insufficient sulfurization of thick films, and the electrical instability of the MoS2 TFTs were discussed.