A Comparative Study of 6T and 4T SRAM Cells in Double-Gate CMOS with Statistical Variation

This paper presents a comparative study of sub-32 nm CMOS 6T and 4T SRAM cells in fully depleted (FD) double-gate (DG) silicon-on-insulator (SOI) technology with planar independent self-aligned gates. Both independent- and connected-gate operation is analyzed by modulating the drain current with both front and back gate voltages. An improved 4T driver-less (DL) SRAM cell is proposed which takes advantage of the back gate to improve stability in read and retention mode by applying feedback between access transistor and storage node. The results of statistical characterization of read-, retention- and write margins, power and access time are presented for all cells in the presence of process variability.