Variability analysis of FinFET-based devices and circuits considering electrical confinement and width quantization

FinFET is considered as the most likely candidate to substitute bulk CMOS technology. FinFET-based design, however, requires special attention due to its exclusive properties such as width quantization and electrical confinement (quantummechanical effect) even in subthreshold regime. Considering these exclusive properties of FinFETs, the sources of process variations and their effects on FinFET-based circuit characteristics can be significantly different from that in bulk CMOS devices. This paper identifies a new source of random process variation due to the gate work-function variation and resulting electrical confinement in emerging high-k/metal-gate FinFET devices. In order to capture the effect of the variations on the characteristics of multifin FinFETs (considering their width quantization property), this paper also presents a new statistical framework to accurately predict the effective threshold voltage of multifin FinFET devices. This framework is subsequently used to predict the leakage profile of FinFET-based SRAM cells. Since FinFETs are optimal for ultra-low-voltage operations due to near-ideal subthreshold swing (60 mV/dec), we focus on FinFET-based SRAM (including subthreshold SRAM) design. Contrary to the low sensitivity of the static noise margin (SNM) to the width of the pull-down devices in bulk-CMOS subthreshold SRAMs, our analysis shows, for the first time, the significant impact of employing multifin pull-down devices on the SNM of subthreshold FinFET SRAMs.