Impacts of intrinsic device variations on the stability of FinFET subthreshold SRAMs

In this work, we investigate the impacts of intrinsic device variations on FinFET subthreshold SRAMs, including the conventional tied-gate 6T SRAM, tied-gate 10T Schmitt Trigger based SRAMs, and recently proposed independent-gate controlled 8T Schmitt Trigger based SRAMs. The impacts of intrinsic random device variations, including Fin Line-Edge Roughness (LER) and Work Function Variation (WFV), on the device threshold voltage V_th, Subthreshold Swing (S.S.) and stability of FinFET SRAMs operating in subthreshold region are assessed using 3D atomistic mixed-mode Monte-Carlo simulations. The results indicate that Fin LER is the dominant factor limiting the stability of FinFET subthreshold SRAMs, since Fin LER degrades both V_th fluctuation and S.S., while WFV mainly affects only V_th fluctuation. The independent-gate controlled Schmitt Trigger SRAMs are shown to offer adequate stability for the intended subthreshold applications even considering intrinsic device variations.