LAUSR

The angular sensitivity of neutron-induced single-event upsets (SEUs) is studied in 12-nm FinFET SRAMs. Irradiation experiments are performed using a terrestrial environment-compatible source with varying incidence angles. The analyses of the occurrence rates of SEUs and multiple-bit upsets (MBUs) demonstrate that although the SEU rate decreases at grazing incidence, the MBU rate increases when the incidence direction is parallel to the word lines (WLs) of the SRAM array, as similarly observed in our previous experiments for 20-nm planar SRAMs. It is found that the angular response of multiple-cell upsets (MCUs) is different between the 12-nm FinFET and 20-nm planar SRAMs. The comparative analysis of the voltage dependence of the MCU ratio reveals that this difference is due to the different contribution of parasitic bipolar effects (PBEs), which are more significant in the 20-nm planar SRAMs. It is also indicated that in the 12-nm FinFET SRAMs, the contribution of PBEs is relatively large when the incidence angle is parallel to the WLs. Through the characterization of the MCU events, the validity of this picture is confirmed based on the voltage dependence of the pattern-wise MCU ratio with the consideration of the impact of PBEs on fail bit patterns.