SEU Rate in Avionics: From Sea Level to High Altitudes

Energy fluxes of particles at flight altitudes are calculated using the QARM or EXPACS codes. These fluxes for charged particles are extrapolated, by the inverse LET law, to low energies where the particles have their highest capability to induce SEU. The fluxes in air are used to calculate energy and LET fluxes in silicon. Secondary ion fluxes are calculated by our analytical model. All calculations have no adjustable parameters! The LET fluxes allow easy calculation of SEU rates in avionics by using the SEU cross section versus LET of the devices. We use the MULASSIS code to verify our approach. The model is particularly good for small feature size devices like modern SRAMs. The important ionizing particles (with increasing critical LET of the device), are protons, deuterons, alpha particles, and heavier ions. Muons, pions, tritons,
³
He ions, and electrons have minor contributions. Examples of calculations of SEU rates in the atmosphere are provided.