Mechanism and Equivalence of Single Event Effects Induced by 14 MeV Neutrons in High-Speed QDR SRAM

Abstract

Single-bit upset (SBU) and multiple-cell upset (MCU) features of high-speed QDR-SRAM are revealed under the 14 MeV neutron irradiation. By comparing with the high-altitude real atmosphere test results directly, the equivalence of 14 MeV neutrons for atmospheric neutron-induced single event effect (SEE) evaluation is investigated. It is found that, compared with the 65 nm planar device, the SBU cross-section of 14 nm FinFET SRAM decreases to 1/58 and the proportion of MCU shows little difference, which results from the narrow channel between fin and substrate caused by shallow channel isolation in 14 nm FinFET process, and the charge sharing effect between fins is weakened. The SBU and MCU cross-sections under the 14 MeV neutron irradiation are underestimated by 22.8% and 85.7%, respectively. Besides, the probability and maximum size of MCU are both smaller than those in the real atmosphere. The MCU shape tends to be vertical, resulting from the smaller vertical spacing of sensitive volumes (about 100 nm). Further Monte-Carlo simulation shows that the total yield of secondary ions produced by atmospheric neutrons is higher than that produced by 14 MeV neutrons. Major Components of the “useful” products are p, Si, α, etc., which are the main cause of SBU events. Besides, compared with 14 MeV neutrons, atmospheric neutrons generate more kinds of secondary ions in the SV within the scope from p to W, and the diverse high-Z elements, such as W, Ta, Hf, etc., are the main cause of MCU events. Moreover, the maximum LET of secondary ions can reach 31.5 MeV·cm2/mg. The equivalence of using 14 MeV neutrons for atmospheric neutron-induced SEE evaluation is closely related to the critical charge of the device under test.

Keywords

• SEE
• SBU
• MCU
• QDR-SRAM