Investigation of charge storage and retention characteristics of silicon nitride in NVM based on InGaZnO channels for system-on-panel applications

Si-rich silicon nitride (SiN _x) is a good charge storage material for the charge trap type of nonvolatile memory (NVM) because of its high density of charge traps. In this study, NVM devices were fabricated with nitride-nitride-oxynitride (NNO) stack structure using Si-rich SiN _x as the charge trapping layer and amorphous InGaZnO (a-IGZO) films as the active layer. The charge storage characteristics of Si-rich SiN _x were studied by controlling the gas flow ratio of SiH ₄:NH ₃ from 6:1 to 6:5. The characteristics were used to determine the optimal condition for the charge-trapping layer. The amorphous silicon clusters in the Si-rich SiN _x layer enhance the charge storage capacity of devices. High-k and high-density N-rich SiN _x films, which are used as a blocking layer, improve the vertical scaling and charge retention characteristics of NVM devices. NVM devices of the NNO structure with SiO _xN _y tunneling thickness of 2.5 nm and Si-rich SiN _x charge-trapping layer were investigated as the gas flow ratio of SiH ₄:NH ₃ was changed from 6:1 to 6:5. The NVM device with SiO _xN _y tunneling thickness of 2.5 nm at gas flow SiH ₄:NH ₃ ratio of 6:3 showed a large memory window of 3 V at a low operating voltage with a programming voltage of only +10 V in 1 ms. Moreover, the retention properties of the memory exceeded 94% after 10 years. Therefore, the bottom-gate NNO NVM using a-IGZO active layer at low temperature has become a potential device for flexible substrate memory display systems.