Mechanisms and shielding characteristics of alpha particle-induced soft errors in 28 and 40 nm configuration memories of SRAM-based FPGAs

The Am-241 radioactive source is used to investigate the mechanism of alpha particle-induced soft errors in configuration memories of SRAM-based FPGAs. Aluminum foils with different thicknesses are inserted between the Am-241 source and the devices under test (DUTs) to investigate shielding characteristics. The results show that the per-bit single event upset (SEU) cross section of the 28 nm device is 14.4 % smaller than that of the 40 nm device. The SEU cross section of the devices increases as the operating voltage decreases. After inserting an aluminum foil, a significant drop in the SEU cross section is observed. For an aluminum foil thickness of 18 mu m, the SEU cross section of the 28 nm device drops to zero. The particle transport and SEU generation processes are investigated using Monte Carlo simulations. For a 6 mu m aluminum foil thickness, the deposited energy (Ed) at the peak of the Ed spectrum is larger than that without the aluminum foil. If the critical charge of the DUT is lower than 1.33 fC, the SEU cross section will decrease, as the thickness of the aluminum foil increases. However, if the critical charge is higher than 1.33 fC, the introduction of the aluminum foil may lead to an increase in the SEU cross section. This is because that, although the aluminum foil slows down the alpha particles and shields part of low-energy alpha particles, the linear energy transfer (LET) value of the alpha particles reaching the sensitive volume increases.