Positive Bias Instability of Bottom-Gate Zinc Oxide Thin-Film Transistors with a SiOx/SiNx-Stacked Gate Insulator

The positive bias instabilities of the zinc oxide thin-film transistors (ZnO TFTs) with a SiO x /SiN x -stacked gate insulator have been investigated. The film quality of a gate insulator of SiO x , which forms an interface with the ZnO channel, was varied by changing the gas mixture ratio of SiH 4 /N 2 O/N 2 during plasma-enhanced chemical vapor deposition. The positive bias stress endurance of ZnO TFT strongly depended on the deposition condition of the SiO x gate insulator. From the relaxations of the transfer curve shift after imposition of positive bias stress, transfer curves could not be recovered completely without any thermal annealing. A charge trapping in a gate insulator rather than that in bulk ZnO and its interface with a gate insulator is a dominant instability mechanism of ZnO TFTs under positive bias stress.