Impact of Variant Gate Insulator Fabrication Process on Reliability of Dual-Gate InGaZnO Thin-Film Transistors

The effect of hydrogen diffusion in the bilayer bottom gate insulator (BGI) in dual-gate InGaZnO (IGZO) thin-film transistors (TFT) is investigated. It is discovered that hydrogen diffuses from the first deposited GI, migrates toward the second one, and forms a weak chemical bond with a dangling bond at the interface between the GI and the active layer. The stress condition with a positive gate bias at various temperatures makes the weakly bonded hydrogen break, thereby forming defects that can induce electron trapping in the interface and bulk, causing the threshold voltage to increase. With the rising temperature of positive bias temperature stress (PBTS), more broken bonds appear at the interface, which results in more trapped electrons. Through a charge trapping model and data fitting, the parameter that indicates the quality of the film can be extracted and compared. The trend of degradation between threshold voltage, bond breaking, and defect generation is examined.