Program-state-dependent recovery effect in 3D NAND flash following total ionizing dose irradiation

Abstract

The growing demand for aerospace data storage necessitates understanding the radiation response mechanisms of 3D NAND technology to design reliable systems. In this study, we observe that irradiation leads to a program-state-dependent threshold-voltage shift: positive for the lowest states (e.g., P1) and increasingly negative for higher states (P2–P7). Furthermore, the recovery effect observed after a 20-h retention period also exhibits program-state dependence, with a greater recovery magnitude in higher states. These phenomena are explained by the interplay of electron dynamics within the charge-trapping layer, the accumulation and detrapping of positive charges within both tunnel and blocking oxides, and the generation and passivation of irradiation-induced nascent defects. The observed net shifts result from the dynamic balance of these competing processes, which is modulated by the state-dependent internal electric field. During irradiation, electron detrapping becomes the dominant mechanism in higher programmed states, leading to a negative threshold voltage shift. In the subsequent recovery phase, the kinetics of hole detrapping from the oxide layers prevail, resulting in a state-dependent positive recovery. These results elucidate post-irradiation charge dynamics and inform mitigation strategies for memory devices in high-radiation applications.