Neutron Induced Single Event Upset Dependence on Bias Voltage for CMOS SRAM With BPSG

We have measured the Single Event Upset (SEU) probability of a static random access memory (SRAM) under neutron irradiation as a function of the memory 6 T cell bias voltage supply. In these memories the presence of a BoronPhosphorSilicateGlass layer induces the memory state upset as a consequence of ¹⁰B neutron capture reactions. The Single Event Upset (SEU) probability versus voltage bias curve was evaluated in the neutron radiation field produced by various electron linacs and in a thermal neutron beam of a nuclear reactor. For these different spectra with neutron energies below 5 MeV the upset behavior curve exhibits a universal shape independent of the installation. The circuit level together with the physical level ion energy deposition simulations allow to reproduce the measured curve. The experimental curve shows a characteristic shape that depends on the statistical distribution of ionization on the charge collecting volume, and consequently on the geometry details of the SRAM and alpha and lithium transport. When the SEU effects in such components are considered for thermal neutron fluence estimation, the present work allows the selection of optimal bias voltage.