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 2.5nm 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 2.5nm at gas flow SiH"4:NH"3 ratio of 6:3 showed a large memory window of 3V at a low operating voltage with a programming voltage of only +10V in 1ms. Moreover, the retention properties of the memory exceeded 94% after 10years. 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.