A Dependable SRAM with 7T/14T Memory Cells

Hidehiro FUJIWARA  Shunsuke OKUMURA  Yusuke IGUCHI  Hiroki NOGUCHI  Hiroshi KAWAGUCHI  Masahiko YOSHIMOTO 

Publication
IEICE TRANSACTIONS on Electronics  Vol.E92-C  No.4  pp.423-432
Publication Date: 2009/04/01
Online ISSN: 1745-1353
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Low-Leakage, Low-Voltage, Low-Power and High-Speed Technologies for System LSIs in Deep-Submicron Era)
Category: 
Keyword: 
SRAM,  dependability,  quality of a bit, 

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Summary: 
This paper proposes a novel dependable SRAM with 7T/14T memory cells, and introduces a new concept, "quality of a bit (QoB)" for it. The proposed SRAM has three modes: a normal mode, high-speed mode, and dependable mode, and dynamically scales its reliability, power and speed by combining two memory cells for one-bit information (i.e. 14 T/bit). By carrying out Monte Carlo simulation in a 65-nm process technology, the minimum voltages in read and write operations are improved by 0.21 V and 0.26 V, respectively, with a bit error rate of 10-8 kept. In addition, we confirm that the dependable mode achieves a lower bit error rate than the error correction code (ECC) and multi module redundancy (MMR). Furthermore, we propose a new memory array structure to avoid the half-selection problem in a write operation. The respective cell area overheads in the normal mode are 26% and 11% in the cases where additional transistors are pMOSes and nMOSes, compared to the conventional 6T memory cell.