# Mechanism and Equivalence of Single Event Effects Induced by 14 MeV Neutrons in High-Speed QDR SRAM
## 5 Conclusions  
In this work, the characteristics and inner mechanisms of 14 MeV neutron-induced SBUs and MCUs in 65 nm high-speed and high-capacity QDR SRAM are studied and compared with high-altitude real atmosphere test results. It is found that, for the 14 MeV neutron irradiation, the effect types are mainly SBU and MCU. SBU accounts for 93.8%, the MCU ratio is 6.2%, and the largest MCU involves 3 bits. While for the high-altitude test, the largest MCU involves 9 bits, with SBU and MCU cross-sections 22.8% and 85.7% higher than those under the 14 MeV neutron irradiation, respectively. Compared with the 65 nm plane process, the SBU cross-section of the 14 nm FinFET SRAM decreases to 1/58, and the difference between the MCU proportions in the two kinds of devices is small. The reason is that the shallow channel isolation in the 14 nm FinFET process makes the channel between FinFET and the substrate very narrow, and the charge sharing effect between FinFET would be weakened. In addition, the MCU shape tends to be vertical, resulting from the smaller vertical spacing of SVs (about 100 nm).  
Monte-Carlo simulations have been used in the experiment to investigate the characteristics of secondary ions in the device SV further, including ion species, LET, and deposited charge and could compare two experimental environments, 14 MeV neutrons and atmospheric neutrons. The total yield of secondary ions generated by atmospheric neutrons is higher than that generated by 14 MeV neutrons. The majority of the \"useful\" reaction products are p, Si, \(\alpha\), etc., which are the main cause of SBU events. Besides, compared with 14 MeV neutrons, atmospheric neutrons generate more kinds of secondary ions in the SV within the scope of p to W; the heavier products are the main cause of MCU events. Atmospheric neutrons with a wide energy spectrum are able to generate secondary ions with larger LET, longer range, and thus more deposited charge in the SV of the 65 nm QDR SRAM, with also higher probability.  
The equivalence of 14 MeV neutrons for atmospheric neutron-induced SEE evaluation is closely related to the critical charge of the DUT. Additionally, for MCU and other SEE types with high critical charge, the discrepancy between 14 MeV neutrons and atmospheric neutrons will increase.  
Conceptualization, S.Y. and F.W.; methodology, S.Y. and Z.L.; software, Z.Z.; validation, S.Y., Z.Z. and Z.L.; formal analysis, S.Y.; investigation, S.Y. and T.T.; resources, K.X. and F.W.; data curation, S.Y.; writing--original draft preparation, S.Y.; writing--review and editing, X.L.; visualization, S.Y. and Z.Z.; supervision, F.W.; project administration, S.Y.; funding acquisition, F.W., Z.L., T.T. and K.X.. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant numbers 12075065 and 12175045.  
All data included in this study are available upon request by contact with the corresponding author.  
Figure 10: Deposited charge distribution induced by 14 MeV and atmospheric neutrons in the device SV.  
**Acknowledgments:** The 14 MeV neutron irradiation test was completed at the Key Laboratory of Nuclear Data, China Institute of Atomic Energy. All the authors are grateful for their support and contribution to this work.  
**Conflicts of Interest:** The authors declare no conflict of interest.