NBTI in n-Type SOI Access FinFETs in SRAMs and Its Impact on Cell Stability and Performance

We identify the possibility of negative-bias temperature instability (NBTI) in n-type silicon-on-insulator (SOI) FinFETs used as access transistors in SRAMs. We discuss that in the hold state of the SRAM cell, one of the access transistors may operate in the accumulation region and experience NBTI degradation. We compare NBTI in p- and n-type SOI FinFETs and show that NBTI in n-FinFETs affects only a part of the channel due to the presence of n⁺ source/drain regions. Worst case analysis of the joint effect of NBTI in access and pull-up FinFETs on cell stability and performance of 6T SRAMs is carried out and compared with the conventional approach of considering NBTI in pull-up FinFETs only.