A 4.6GHz 162Mb SRAM design in 22nm tri-gate CMOS technology with integrated active VMIN-enhancing assist circuitry

Future product applications demand increasing performance with reduced power consumption, which motivates the pursuit of high-performance at reduced operating voltages. Random and systematic device variations pose significant challenges to SRAM V_MIN and low-voltage performance as technology scaling follows Moore´s law to the 22nm node. A high-performance, voltage-scalable 162Mb SRAM array is developed in a 22nm tri-gate bulk technology featuring 3^rd-generation high-k metal-gate transistors and 5^th-generation strained silicon. Tri-gate technology reduces short-channel effects (SCE) and improves subthreshold slope to provide 37% improved device performance at 0.7V. Continuous device width sizing in planar technology is replaced by combining parallel silicon fins to multiply drive current. Process-circuit co-optimization of transient voltage collapse write assist (TVC-WA) and wordline underdrive read assist (WLUD-RA) features address process variation and fin quantization at 22nm and enable a 175mV reduction in the supply voltage required for 2GHz SRAM operation. Figure 13.1.1 shows an SEM top-down view of a 0.092μm² high-density 6T SRAM bitcell (HDC) and a 0.108μm² low-voltage 6T SRAM cell (LVC) after gate and diffusion processing. Computational OPC/RET techniques extend the capabilities of 193nm immersion lithography to allow a 1.85× increase in array density relative to 32nm designs [1].