Asymmetric Independent-Gate MOSFET SRAM for High Stability

In this paper, the application of an asymmetric independent-gate MOSFET (IG-MOSFET) to the bit-cell structures of the SRAM schemes that were previously proposed using the symmetric IG-MOSFET is analyzed. In addition, a novel SRAM scheme with the asymmetric IG-MOSFET is proposed to improve read stability and writeability by controlling the back gates of pass-gate and pull-up transistors. New array architecture is also suggested to prevent read stability degradation in the half-selected cell, where word line is selected but bit line is unselected. The previous SRAMs with IG-MOSFET (IG-SRAMs) fail to simultaneously improve read stability and writeability compared to the SRAM with the tied-gate MOSFET. The proposed IG-SRAM significantly improves both read stability and writeability at the cost of slightly increased bit-cell area and read delay, as compared to the previous IG-SRAMs.