2016 Fiscal Year Annual Research Report

ＳＲＡＭセルにおけるばらつきの影響とその抑制方法

Research Project

Project/Area Number	15J09095
Research Institution	The University of Tokyo
Principal Investigator	QIU HAO 東京大学, 生産技術研究所, 特別研究員(PD)
Project Period (FY)	2015-04-24 – 2017-03-31
Keywords	SRAM / variability / write stability / low voltage / write butterfly curve
Outline of Annual Research Achievements	We have gained further understanding of two write stability methods (write butterfly curve and write N-curve). Firstly, the reason why write noise margin (WNM) in write N-curve deviates from a normal distribution at low VDD is clarified. Two modes are found in WNM's distribution. And the new mode is ascribed to cell transistor's sub-Vth operation. Secondly, a new write stability method based on write butterfly curve is proposed. By extending the voltage sweeping range of two internal nodes in SRAM, the extended write butterfly curve can be obtained. It is found that the extended WNM (E-WNM) follows a normal distribution even at low VDD. In addition, good correlation between E-WNM and WNM of bit-line method is obtained. Thus, the proposed one is a good candidate for low-VDD yield estimation.
Research Progress Status	28年度が最終年度であるため、記入しない。
Strategy for Future Research Activity	28年度が最終年度であるため、記入しない。