Subthreshold FinFET SRAM cell optimization considering surface-orientation dependent variability

This work investigates the impact of device intrinsic variation on the stability/variability of subthreshold 6T FinFET SRAM cells with (110)/(100) surface orientations. Due to the difference in the degree of quantum confinement, NFET with (110) orientation shows larger fin Line-Edge-Roughness (LER) induced threshold-voltage variation than the (100) one, while PFET shows the opposite trend. Therefore, the stability of conventional (PU, PD, PG) = (110, 110, 110) cell is inferior and fails to provide sufficient margin. With the optimized orientation, significant μ/σ ratio improvement can be achieved by using (PU, PD, PG) = (110, 100, 100) SRAM cell. Our analysis establishes the potential of 6T FinFET cells with appropriate optimization for emerging subthreshold SRAM applications.