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

作者：Ansari Mohammad; Afzali Kusha Hassan; Ebrahimi Behzad; Navabi Zainalabedin; Afzali Kusha Ali; Pedram Massoud

来源：Integration, the VLSI Journal, 2015, 50: 91-106.

DOI：10.1016/j.vlsi.2015.02.002

• SRAM
• FinFET
• Low power
• Near-threshold
• Process variation

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 V-TH 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 I-on/I-off ratio of its access transistors, a high V-TH 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 51, 61, 81, and 9T SRAM cells. The characteristics are obtained from HSPICE simulations using 20 nm, 16 nm, 14 nm, 10 nm, and 7 nm FinFET technologies assuming a supply voltage of 500 mV. The results reveal high write and read margins, the highest I-on/I-off 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 degrees C to 100 degrees 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 400 mV and 500 mV. The study shows that the proposed cell meets the required cell sigma value (6 sigma) under all conditions.

• 出版日期2015-6