Impact of Irradiation Side on Muon-Induced Single Event Upsets in 65-nm Bulk SRAMs

We have newly analyzed negative and positive muon-induced single event upset (SEU) data in irradiation tests from the package side (PS) of 65-nm bulk static random access memory (SRAM) and compared with previous results of irradiation tests from the board side (BS). The peak SEU cross section is at 28 MeV/c for PS irradiation, which differs from 38 MeV/c for BS irradiation. The magnitude of the peak SEU cross section for PS irradiation is approximately twice that of BS irradiation for both positive and negative muons. Through simulations using Geant4, we explain the difference quantitatively. This simulation also reproduces the experimental SEU cross sections for tilted incidence of the muon beam onto the device board. The soft error rates (SERs) are estimated under a realistic environment considering the zenith angle distribution of muon flux. As a result, it was found that the estimated SERs were not significantly different from the case without zenith angle distribution. This result indicates that experimental data from irradiation tests in which the device board is placed perpendicular to the incident beam are expected to be useful for estimating muon-induced SERs in terrestrial environments.