Based on the Atmospheric Neutron Irradiation Spectrometer (ANIS) at the China Spallation Neutron Source (CSNS), this paper conducts an experimental study on the atmospheric neutron single-event effects in 128-layer charge trapping (CT) 3D NAND flash memory. By integrating irradiation experiments, reverse analysis, and Monte Carlo neutron transport simulations, this research aims to investigate the impact of atmospheric neutron irradiation on the multiple-cell upset (MCU) susceptibility of CT 3D NAND flash memory and analyze the underlying mechanisms, including the distribution of secondary particles within the sensitive volume and the characteristics of deposited charge.
The results indicate that under broad-spectrum neutron irradiation, the primary failure modes in CT 3D NAND flash memory are single-bit upsets (SBU) and MCU, with SBU accounting for 82.55% of the total events. By constructing a three-dimensional spatial distribution map of single-event upset (SEU), it was observed that, compared to the dense "string-like" distribution formed by ⁷⁸Kr ion irradiation (LET=11.4MeV·cm²·mg^-1), neutron-induced SEU exhibit a significantly more random spatial distribution, with only a small number of MCU showing a "string-like" pattern. Among the MCU events, 2-bit MCUs dominate, constituting 83.6% of all MCUs, while larger sized MCUs (>2 bits) account for 14.3%. The maximum observed MCU size was 7 bits. Furthermore, the spatial distribution of MCUs is primarily aligned along the direction of neutron incidence.
Based on the reverse analysis results, a device model was constructed, and Monte Carlo neutron transport simulations were performed. The simulation results reveal that secondary particles generated in the sensitive volume (SV) of the device by neutrons with energy E > 1 MeV are predominantly silicon ions (37.98%) and nitrogen ions (27.95%). Since the SV material is nitride, the interaction between neutrons and the SV is mainly elastic scattering, during which secondary particles are produced. Among the secondary particles generated in the SV, most propagate along the direction of neutron incidence, with a small number of secondary particles in the central region producing oblique tracks. The majority of secondary particles generated in the SV exhibit low LET values (<5 MeV·cm²·mg^-1) and short ranges (<100 nm), and these secondary particles are the primary cause of SBU. However, approximately 1.2% of the ions exhibit high LET values (>10 MeV·cm²·mg^-1), with the maximum LET value of secondary particles inthe SV reaching 12.05 MeV·cm²·mg^-1. A small number of secondary particles with high LET values and long ranges are responsible for the generation of MCUs.