Instability mechanisms in amorphous oxide semiconductors leading to a threshold voltage shift in thin film transistors

Abstract

Amorphous indium gallium zinc oxide (a-IGZO) has been successfully employed commercially as the channel layer in thin film transistors (TFTs) for active-matrix flat panel displays. However, these TFTs are known to suffer from a threshold voltage shift upon application of a gate bias. The threshold voltage shift is reversible through annealing. A similar phenomenon is observed in other TFTs with an amorphous oxide semiconductor channel. The migration of oxygen vacancies is proposed as being the microscopic mechanism causing this effect as it can lead to a change in the equilibrium distribution of defect states in the band gap of the semiconductor. This would manifest itself as a reversible threshold voltage shift in the TFT transfer characteristics, as observed experimentally.