A Terrestrial SER Estimation Methodology Based on Simulation Coupled With One-Time Neutron Irradiation Testing

Terrestrial soft error rates (SERs) are generally estimated by performing an experiment using a spallation neutron beam with the energy spectrum being similar to that of the terrestrial neutrons or at least four measurements using various (quasi-)mono-energetic neutron and/or proton sources to determine the parameters of the Weibull function. We here propose a method to estimate the terrestrial SERs based on simulation coupled with one-time neutron irradiation testing which can be applied to various kinds of neutron sources. In this method, the dependences of single-event upset (SEU) cross sections on the neutron energy and the critical charge are calculated by simulation using a particle and heavy ion transport code system (PHITS). The critical charge is used as the only calibration parameter, which is adjusted to reproduce the SER measured by one-time neutron irradiation. The validity of our method is investigated for 65-nm bulk SRAMs with the measured data using various neutron sources in Japan. Our method generally provides reasonable terrestrial SERs compared with those obtained by the Weibull function method. This result indicates the feasibility of evaluating the terrestrial SER using one of the various neutron sources available all over the world, including those not dedicated to SER measurement. We also investigate the necessity of the elaborated geometry of the device under test (DUT) for the accuracy of the simulation. It is shown that detailed material compositions of DUT are not necessary for our method except when the one-time irradiation is performed using the neutron source that contains a high quantity of low-energy neutrons below 8 MeV. Furthermore, we confirm that the configuration of the sensitive volume can be simplified without sacrificing the estimation accuracy. These simplifications in the simulation help to reduce the modeling and calculation costs in SER estimation.