A new asymmetric 6T SRAM cell with a write assist technique in 65 nm CMOS technology

Abstract

A new asymmetric 6T-SRAM cell design is presented for low-voltage low-power operation under process variations. The write margin of the proposed cell is improved by the use of a new write-assist technique. Simulation results in 65nm technology show that the proposed cell achieves the same RSNM as the asymmetric 5T-SRAM cell and 77% higher RSNM than the standard 6T-SRAM cell while it is able to perform write operation without any write assist at VDD=1V. Monte Carlo simulations for an 8Kb SRAM (256×32) array indicate that the scalability of operating supply voltage of the proposed cell can be improved by 10% and 21% compared to asymmetric 5T- and standard 6T-SRAM cells; 21% and 53% lower leakage power consumption, respectively. The proposed 6T-SRAM cell design achieves 9% and 19% lower cell area overhead compared with asymmetric 5T- and standard 6T-SRAM cells, respectively. Considering the area overhead for the write assist, replica column and the replica column driver of 2.6%, the overall area reduction in die area is 6.3% and 16.3% as compared with array designs with asymmetric 5T- and standard 6T-SRAM cells.