Impact of incident direction on atmosphere neutron-induced single event upset in 128-layer dual-deck 3D NAND flash memories

Abstract: Based on the meV-GeV wide-energy neutron beam from the China Spallation Neutron Source (CSNS), this study investigates the direction dependence of single-event upsets (SEUs) in 128-layer dual-deck CT 3D NAND Flash memories. Irradiation tests were performed from the front, side, and back of the chip. By mapping SEU addresses into 3D distributions, multiple-cell upset (MCU) patterns and formation mechanisms were analyzed. Results show the front direction is the "worst case", with SEU cross-section 27.3% higher and MCU count 52.5% greater than side/back incidence. MCUs are mainly double-bit upsets(DBUs), with a maximum size of 7 bits, and primarily exhibit "string-like" patterns along through-holes, along with some L-shaped distributions along word lines(WL). Neutron transport simulations further reveal that secondary particles in the sensitive region are predominantly nitrogen and silicon ions; side and back incidence additionally yields minor high-Z species (Er, Yb, Ta, Lu, W) owing to tungsten layers. The frontal incidence produces 13.77% of secondary particles with LET > 5 MeV•cm²•mg⁻¹, markedly higher than side (4.87%) and back (9.96%) incidence. This explains the elevated SEU cross-section for frontal incidence and the experimentally observed directional sensitivity variation. The work clarifies the directional dependence of atmospheric neutron sensitivity in CT 3D NAND Flash, supporting accurate reliability prediction and radiation-hardening design.