Mitigating NBTI in the physical register file through stress prediction

Abstract

Degradation of transistor parameter values due to Negative Bias Temperature Instability (NBTI) has emerged as a major reliability problem in current and future transistor generations. NBTI Aging of SRAM cell leads to a lower noise margin, thereby increasing the failure rate. The physical register file, which consists of an array of SRAM cells, can suffer from data loss, leading to system failure. In this paper, we explore a novel approach by investigating NBTI stress and mitigation at the instruction granularity. While a wide range of NBTI stress exists in different registers, the stress induced by specific instructions is highly predictable. Using such a prediction mechanism, we propose an NBTI tolerant power efficient physical register file design. Our approach improves the noise margin in a register file by 20%, 32%, and 125% for the 45nm, 32nm, and 22nm technology nodes, respectively. Overall, we observe 14.8% power saving and a 19.8% area penalty in the register file.