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The Impacts of Heavy Ion Energy on Single Event Upsets in SOI SRAMs

The dependence of single event upset (SEU) on heavy ion energy was investigated for partially depleted silicon-on-insulator static random access memories. An unexpected phenomenon has been shown that the SEU cross sections decrease 70% with the increase of 12C ion linear energy transfer (LET) from 1.7 to 3.0 MeV/(mg/cm2). Furthermore, data from angled irradiations show that the SEU cross sections almost remain unchanged with the increase of effective LET in the subthreshold LET region. Geant4 simulation indicates that this anomalous trend of SEU cross sections is mainly attributed to energy effects of nuclear reactions between primary ions and material atoms. The SEU cross sections at subthreshold LET values are closely related to the energy of incident ions. Secondary Mg and Al ions produced by primary 12C ion nuclear reactions are the main ions to introduce the SEUs. A method is proposed for calculating the SEU cross sections induced by low LET heavy ions. The SEU cross sections calculated by Geant4 simulation with low LET heavy ions match well with the experimental results. The energy dependence of SEUs produced by low LET heavy ions implies that at accelerator-based SEU tests, the high-energy heavy ions with low LETs need to be utilized to estimate the contribution of indirect ionization to SEU cross sections for hardened devices with high-LET thresholds.