0.5-V 25-nm 6-T Cell with Boosted Word Voltage for 1-Gb SRAMs

Akira KOTABE  Kiyoo ITOH  Riichiro TAKEMURA  

IEICE TRANSACTIONS on Electronics   Vol.E95-C   No.4   pp.555-563
Publication Date: 2012/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.555
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design – Architecture, Circuit, Device and Design Methodology)
0.5-V 25-nm 6-T SRAM cell,  boosted word voltage,  FD-MOSFETs,  repair,  worst design,  

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It is shown that it is feasible to apply 0.5-V 6-T SRAM cells in a 25-nm high-speed 1-Gb e-SRAM. In particular, for coping with rapidly reduced voltage margin as VDD is reduced, a boosted word-voltage scheme is first proposed. Second, Vt variations are reduced with repair techniques and nanoscale FD-MOSFETs to further widen the voltage margin. Third, a worst case design is developed, for the first time, to evaluate the cell. This design features a dynamic margin analysis and takes subthreshold current, temperature, and Vt variations and their combination in the cell into account. Fourth, the proposed scheme is evaluated by applying the worst-case design and a 25-nm planar FD-SOI MOSFET. It is consequently found that the scheme provides a wide margin and high speed even at 0.5 V. A 0.5-V high-speed 25-nm 1-Gb SRAM is thus feasible. Finally, to further improve the scheme, it is shown that it is necessary to use FinFETs and suppress and compensate process, voltage, and temperature variations in a chip and wafer.