Similarity Analysis on Neutron- and Negative Muon-Induced MCUs in 65-nm Bulk SRAM

Abstract

Multiple-cell upset (MCU) in static random access memory (SRAM) is a major concern in radiation effects on very large scale integration (VLSI) since it can spoil error correcting codes (ECCs). Neutron-induced MCUs have been characterized for terrestrial environment. On the other hand, negative muon-induced MCUs, which are caused by secondary ions generated through muon capture process, were recently reported. Neutron- and negative muon-induced MCUs are both caused by secondary ions, and hence, they are expected to have some similarity. In this paper, we compare negative muon- and neutron-induced MCUs in 65-nm bulk SRAMs at the irradiation experiments using spallation and quasi-monoenergetic neutrons and monoenergetic negative muons. The measurement results show that the dependencies of MCU event cross section on operating voltage are almost identical. The high operating voltage makes both negative muon- and neutron-induced MCU cross sections larger due to parasitic bipolar action. Consequently, large-bit MCUs are observed under the irradiation using both neutrons and muons. On the other hand, at 0.4 V, neutrons induce larger-bit MCUs (> 12 bits) whereas negative muons cause up to 11-bit MCUs. Upsets of 3 or larger bits along word line (WL) are observed at spallation neutron beams. To explain the similarity of MCUs induced by neutrons and negative muons, the Monte Carlo simulation is conducted to investigate the deposited charge. The distributions of deposited charge obtained by the simulation are consistent with the above-mentioned experimental observations.