Workload-aware static aging monitoring of timing-critical flip-flops

Abstract

In advanced technology nodes, Bias Temperature Instability (BTI) has emerged as a prominent reliability concern. The worst-case effects of BTI occur during specific workload phases in which flip-flops on a critical path do not switch their logic values for a long duration. These inactive flip-flops in the circuit experience accelerated workload-dependent static-BTI stress. The aging effect of static BTI for a few hours has been shown to be equivalent to one year of aging due to dynamic BTI, which can eventually cause circuit failure. The techniques available to mitigate static-BTI stress during standby mode of circuits are pessimistic, thereby limiting the performance of the circuit. To address this problem, we propose a runtime monitoring method to raise a flag when a timing-critical flip-flop experiences severe static-BTI stress. To reduce the monitoring costs, we select a small representative set of flip-flops offline based on workload-aware correlation analysis and these selected flip-flops are monitored online for static aging phases. Our experiments conducted on two processors show that, less than 0.5% of the total number of flip-flops is required to be selected as representative flip-flops for S-BTI stress monitoring.