Characterizing the Activity Factor in NBTI Aging Models for Embedded Cores

In deeply scaled CMOS technologies, device aging causes cores performance parameters to degrade over time. While accurate models to efficiently assess these degradation exist for devices and circuits, no reliable model for processor cores has gained strong acceptance in the literature. In this work, we propose a methodology for deriving an NBTI aging model for embedded cores. Based on an accurate characterization on the netlist of the core, we were able to (1) prove the independence of the aging on the workload (i.e., executed instructions), and (2) calculate an equivalent average constant aging factor that justifies the use of the baseline model template. We derived and assessed the proposed model by using a RISC-like processor core implemented in a 45nm process technology as a reference architecture, achieving a maximum error of 2.2% against simulated data on the core netlist.