Workload-aware worst path analysis of processor-scale NBTI degradation

Abstract

As technology further scales semiconductor devices, aging-induced device degradation has become one of the major threats to device reliability. In addition, aging mechanisms like the negative bias temperature instability (NBTI) is known to be sensitive to workload (i.e., signal probability) that is hard to be assumed at design phase. In this work, we analyze the workload dependence of NBTI degradation using a processor, and propose a novel technique to estimate the worst-case paths. In our approach, with careful examination, we exploit the fact that the deterministic nature of circuit structure limits the amount of NBTI degradation on different paths, and proposes a two-stage path extraction algorithm to identify the invariable critical paths in the processor. Through numerical experiment on a MIPS32 processor, we performed a detailed signal probability analysis, and successfully extracted 85 invariable critical paths out of the 24,978 path candidates, achieving nearly 300× reduction in the sheer number of paths.