Influence of Voltage and Particle LET on Timing Vulnerability Factors of Circuits

Flip-flop soft errors caused due to direct strikes on flip-flops as well as soft errors caused due to latched transients from combinational logic show frequency dependence. This frequency dependence in the case of high-speed sequential circuits can derate the soft error rate by as much as 5X. Circuit variables, such as voltage, frequency, logic delay, as well as environmental factors, such as particle type and linear energy transfer that affect the frequency dependence are studied. Heavy-ion irradiation of 28-nm sequential circuits shows that the cross-section decreases with frequency for low-LET particles and increases with frequency for higher-LET particles. Competing trends involving combinational logic and flip-flops are shown to be the reason. The voltage dependence of this trend is evaluated. The key insight that emerges from this work is that at sufficiently high frequencies, the cross-section of certain sequential circuits can be lower than that at lower frequencies. Similarly, lowering voltage may not always result in increased soft error rate at certain frequencies.