SRAM Stability Analysis and Performance-Reliability Tradeoff for Different Cache Configurations

Bias temperature instability (BTI), hot carrier injection (HCI), gate-oxide time-dependent dielectric breakdown (GTDDB), and random telegraph noise (RTN) degrade the stability of the deeply scaled transistors and the overall circuit reliability. These front-end wearout mechanisms are especially acute in the static random access memory (SRAM) cells of first-level (L1) caches, which are crucial for the performance of microprocessors due to frequent accesses. This article presents a methodology to analyze cache reliability degradation due to the combined effect of BTI, HCI, GTDDB, and RTN for different cache configurations, including variations due to associativity, cache line size, cache size, and the error-correcting codes (ECCs). Time-zero variability due to process and environmental parameters are also considered. First, we analyze how each wearout mechanism affects reliability degradation. Then we analyze the relationship between reliability (probability of failure) and performance (hit rate) of the L1 cache within a LEON3 microprocessor, while the LEON3 is running a set of benchmarks, which determine cell array activity, characterized by the duty cycle, toggle rate, temperature, and supply voltage distributions of cells. Insights on the performance-reliability tradeoff are provided for cache designers.