Impact of negative and positive bias temperature stress on 6T-SRAM cells

[摘要] With introduction of high-k gate oxide materials, the degradation effectPositive Bias Temperature Instability (PBTI) is starting to play an importantrole. Together with the still effective Negative Bias Temperature Instability(NBTI) it has significant influence on the 6T SRAM memory cell. We presentsimulations of both effects, first isolated, then combined in SRAM operation.During long hold of one data, both effects add up to a worst case impact.This leads to an asymmetric cell, which, in a directly following read cycle,combined with the generally unavoidable production variations, maximizes therisk of destructive reading. In future SRAM designs, it will be important toconsider this combination of effects to avoid an undesired write event.

[学科分类] 电子、光学、磁材料