Characterizing Energetic Dependence of Low-Energy Neutron-Induced SEU and MCU and Its Influence on Estimation of Terrestrial SER in 65-nm Bulk SRAM

Abstract

Characterizing low-energy neutrons (<10 MeV)-induced single-event upsets (SEUs) and multiple cells upsets (MCUs) is essential to validate the current standard for terrestrial soft error rate (SER) and investigate its enhancement. Following our preliminary analysis on the contribution of the low-energy neutrons to the total terrestrial SER at the nominal operating voltage of 1.0 V by Liao et al. (2020), this article newly presents and analyzes the data measured at the low operating voltage of 0.4 V. The dependence of SEU cross section on the neutron energy is similar between the operating voltages of 0.4 and 1.0 V, including onset energy of around 6 MeV. The existence of MCUs at 4.1-MeV neutrons was also confirmed at both the operating voltages. Based on the measurement, we approximate the dependence of SEU and MCU cross sections as Weibull functions of the neutron energy. The terrestrial SER of SEUs and MCUs was calculated by folding the Weibull function and the flux spectrum. The calculated result indicates that the SER originating from the low-energy neutrons is less than 6% in the terrestrial environment at New York and Tokyo City. We confirm that disregarding the flux of neutrons below 10 MeV in the acceleration factor calculation at accelerated neutron tests, which follows the current standard defined in JESD89, could give a reasonable SER estimation accuracy for both SEUs and MCUs. On the other hand, for covering the beams having an extremely high proportion of low-energy neutrons, considering the flux of neutrons above 6 MeV would be an option for better SER estimation.