Device instability of postannealed TiOx thin-film transistors under gate bias stresses

Abstract

This paper investigates the negative bias instability (NBS) and positive bias instability (PBS) of titanium oxide (TiOx) thin-film transistors (TFTs) with different annealing temperatures. Structural analyses suggested that TiOx films annealed at 450 and 550 degrees C had average grain sizes of 200 and 400 nm, respectively. A TiOx TFT annealed at 550 degrees C exhibited respective threshold voltage (V-th) shifts of only -1.4 and 10.2V under NBS and PBS conditions. The origin of the instability was found to be a charge trapping mechanism caused by different grain sizes, boundaries, and changes in band edge states below the conduction band, which acted as electron and hole trap sites.