# Mechanism and Equivalence of Single Event Effects Induced by 14 MeV Neutrons in High-Speed QDR SRAM
## 3 Results and Analysis
### SEU Cross-Section  
#### 3.1.1 Results and Comparison  
Under the 14 MeV neutron irradiation, the effect types are mainly single bit upset (SBU) and MCU. It should be noted that one MCU is marked as one error in the calculation of the MCU cross-section. Compared with the 65 nm plane devices, the SBU cross-section of the 14 nm FinFET device is reduced to 1/58. There is no significant difference in the proportion of MCU between the two devices. For the 65 nm plane devices, the SBU accounts for 93.8%, and the MCU ratio is 6.2%. For the 14 nm FinFET device, the MCU ratio is 5.3% and the largest MCU involves 3 bits. In addition, several motherboard malfunctions occurred, resulting from the scattering of neutrons, which can be recovered after resetting.  
The height of the FinFET device is 45 nm, the width of the FinFET device is 15 nm, and the distance between the two FinFET devices is about 35 nm. The Shallow Trench Isolation (STI) physically separates the FinFET devices. Compared with the 65 nm plane devices (the area of a single memory cell is 1 \(\upmu\)m \(\times\) 0.5 \(\upmu\)m), the area of a single memory cell of 14 nm FinFET devices is reduced to only 0.37 \(\upmu\)m \(\times\) 0.18 \(\upmu\)m, and the size of SEU sensitive region decreases accordingly, which is the main reason for the decreasing of the SEU cross-section of the 14 nm FinFET device under 14 MeV neutron irradiation. For the MCU, although the spacing of 14 nm FinFET devices is only about 35 nm, and the critical charge is reduced to sub-Fc, the STI narrows the channel between 14 nm FinFET and substrate, and the charge sharing effect between FinFET would be weakened, which is the main reason why the MCU proportion of the 14 nm FinFET devices does not change significantly.  
Figure 1: Diagram of the irradiation experiment.  
Figure 2: Experimental setups.  
Figure 3 shows the SEU cross-sections of the QDR SRAM of 14 MeV neutron, high-altitude, and spallation source tests. The spallation source test results were obtained at the temporary terminal (BL09) of the China Spallation Neutron Source (CSNS) [11]. Moreover, the high-altitude test results are demonstrated in the next section in detail. It should be noted that the MCU cross-section is obtained by counting one MCU as one event. It can be seen in Figure 3 that SBU and MCU cross-sections induced by 14 MeV neutrons are about 22.8% and 85.7% lower than those in the real atmosphere, respectively.  
Figure 4 shows the neutron energy spectrums and distribution ratios of the high-altitude and spallation source tests. It can be seen that, in the high-altitude test, the proportion of neutrons with energy greater than 14 MeV is 58.2%. Due to the lower proportion (5.5%) of E > 14 MeV neutrons at the temporary terminal of CSNS, SBU and MCU cross-sections of the spallation source test in Figure 3 are both lower than those of the high-altitude test.  
Figure 4: Neutron energy spectrums and distribution ratios of high-altitude and spallation source test. \"JESD89A\" denotes the energy spectrum of atmospheric neutrons in the JEDEC standard [13], which is the same as the neutron energy spectrum of the high-altitude test and includes the contributions from both galactic cosmic rays and solar wind.  
Figure 3: SEU cross-sections of 14 MeV neutron, high-altitude, and spallation source test.