Thermal Neutron-Induced Single-Event Upsets in Microcontrollers Containing Boron-10

Single-event upsets (SEUs) were measured in thermal neutron-irradiated microcontrollers with 65- and 130-nm-node static random-access memories (SRAMs). The suspected upset mechanism is charge deposition from the energetic byproducts of B-10 thermal neutron capture. Although elemental analysis confirmed that both microcontrollers contain B-10, only the 65-nm node microcontroller exhibited a strong response to thermal neutrons. Monte Carlo simulations were performed to investigate the effects of B-11 enrichment on thermal neutron-induced SEUs in a 65-nm SRAM node when boron is present in the p-type well, p-type source and drain, or tungsten plug. Simulations indicate that the byproducts of B-10(n, alpha) Li-7 reactions are capable of generating sufficient charge to upset a 65-nm SRAM. The highest amount of charge deposition from B-10(n, alpha) Li-7 reaction byproducts occurs when natural boron is used to dope the p-type source and drain regions. Simulations also show that the SEU cross section is nonnegligible when B-11-enriched boron is used for doping.