Variability Analysis of Sense Amplifier for FinFET Subthreshold SRAM Applications

摘要

This paper investigates the impact of intrinsic random variability on the robustness of sense amplifier (SA) for fin-shaped field-effect transistor (FinFET) subthreshold static random access memory (SRAM) applications. We employ a model-assisted statistical approach to consider both fin line edge roughness (fin LER) and work function variation, which are regarded as the major variation sources in an advanced FinFET device. Our results indicate that fin LER dominates the overall variability of subthreshold SA robustness and sensing margin. In addition, it is observed that the offset voltage $(hbox{V}_{rm OS})$ of current latch SA calculated solely from threshold voltage $(hbox{V}_{rm T})$ mismatch underestimates the actual variation and is shown to be optimistic. For large-signal single-ended inverter sensing, we find that sense “0” hinders the allowable sensing margin and needs to be carefully designed. Compared with bulk CMOS, the superior electrostatic integrity and variability of FinFET enhance the feasibility of differential sensing in subthreshold SRAM applications.