On-Chip Adaptive Body Bias for Reducing the Impact of NBTI on 6T SRAM Cells

Abstract

Negative bias temperature instability (NBTI) is a major reliability issue with the scaled devices at elevated temperature. The effect of NBTI increases with the time, and it increases the threshold voltage of pMOS. In this paper, an on-chip adaptive body bias (O-ABB) circuit to compensate the degradation due to NBTI aging is presented. The O-ABB is used to compensate the parameter variations and improves the SRAM circuit yield regarding read current, hold SNM, read SNM, write margin, and word line write margin (WLWM). The O-ABB consists of standby leakage current ( ${I}_{{ddq}}$ ) sensor circuit, decision circuit, and body bias control circuit. Circuit level simulation for SRAM cell is performed for pre- and post-stress of ten years NBTI aging. The proposed O-ABB reduces the effect of NBTI on the stability of SRAM cell. The simulation results show the hold SNM, read SNM, and WLWM decreases by 10.55%, 8.55%, and 3.25%, respectively, in the absence of O-ABB, whereas hold SNM, read SNM, and WLWM decreases by only 0.47%, 1.15%, and 0.62%, respectively, if O-ABB is used to compensate the degradation.