The effect of Nb doping on the performance and stability of TiOx devices

Abstract

The effect of niobium (Nb) doping on the performance and stability of TiO x -based thin-film transistors (TFTs) was studied. While sputtered TiO x has an initial amorphous phase and begins to crystallize to anatase at an annealing temperature of 450 °C, Nb-doped TiO x preserves the amorphous structure up to annealing temperatures as high as 550 °C. TFT devices fabricated using Nb-doped TiO x as the active layer exhibit higher field-effect mobility and better stability upon negative and positive bias stress compared to pure TiO x devices. X-ray photoelectron spectroscopy analyses indicate that Nb doping induces higher levels of oxygen deficiency and a considerable amount of defect states near the valence band, which cannot account for the higher device stability. It is thus suggested that the grain boundaries in crystalline TiO x TiO x may act as the major charge traps, which induce larger shifts in threshold voltage ( V th ) upon bias stress.