Uranium and Thorium Contribution to Soft Error Rate in Advanced Technologies

238U and232Th and their relative daughters are impurity sources responsible for soft errors induced by alpha particles. In this paper, the contribution of each decay chain to the alpha emission rate is evaluated by assuming that secular equilibrium is reached. We show that for the same concentration of uranium and thorium in secular equilibrium, uranium decay chain has an alpha emission rate (AER) two times higher than the thorium decay chain. Furthermore, the contribution of these two decay chains to the Soft Error Rate (SER) and Multiple Cell Upset (MCU) is calculated for a 90 nm and a 65 nm CMOS technology by Monte Carlo simulations by considering a concentration of thorium 1.33 higher than uranium in secular equilibrium condition, which is representative to measurements found in literature. We show in these conditions that uranium has a contribution to the SER and MCU higher than that of thorium.