A near-threshold 7T SRAM cell with high write and read margins and low write time for sub-20 nm FinFET technologies

• DOI: 10.1016/j.vlsi.2015.02.002
• Publication Date: 2015-02-20T05:18:45Z
• Authors: Mohammad Ansari; Hassan Afzali-Kusha; Behzad Ebrahimi; Zainalabedin Navabi; Ali Afzali-Kusha; Massoud Pedram
• Keywords: Leakage (economics); Access time; Leakage power; Memory cell

In this paper, a 7T SRAM cell with differential write and single ended read operations working in the near-threshold region is proposed. The structure is based on modifying a recently proposed 5T cell which uses high and low VTH transistors to improve the read and write stability. To enhance the read static noise margin (RSNM) while keeping the high write margin and low write time, an extra access transistor is used and the threshold voltages of the SRAM transistors are appropriately set. In addition, to maintain the low leakage power of the cell and increase the Ion/Ioff ratio of its access transistors, a high VTH transistor is used in the pull down path of the cell. To assess the efficacy of the proposed cell, its characteristics are compared with those of 5T, 6T, 8T, and 9T SRAM cells. The characteristics are obtained from HSPICE simulations using 20nm, 16nm, 14nm, 10nm, and 7nm FinFET technologies assuming a supply voltage of 500mV. The results reveal high write and read margins, the highest Ion/Ioff ratio, a fast write, and ultra-low leakage power in the hold "0" state for the cell. Therefore, the suggested 7T cell may be considered as one of the better design choices for both high performance and low power applications. Also, the changes of cell parameters when the temperature rises from -40?C to 100?C are investigated. Finally, the write margin as well as the read and hold SNMs of the cell in the presence of the process variations are studied at two supply voltages of 400mV and 500mV. The study shows that the proposed cell meets the required cell sigma value (6?) under all conditions. Proposing a near-threshold 7T SRAM cell with high read and write stabilities.Presenting a comparative study of the read and hold SNM and write margin (speed).Presenting a comparative study of area, read current, Ion/Ioff, and power.Providing a comparative study of process variation and temperature sensitivity.