| 研究実績の概要 |
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.
|
