ＳＲＡＭセルにおけるばらつきの影響とその抑制方法

我们进一步了解了两种写稳定性方法（写蝴蝶曲线和写n曲线）。首先，澄清了低VDD时写n曲线中写噪声裕度偏离正态分布的原因。WNM的分布有两种模态。并将这种新模式归因于单元晶体管的次v次运算。其次，提出了一种基于写蝴蝶曲线的写稳定性方法。通过扩展SRAM中两个内部节点的电压扫描范围，可以得到扩展的写蝴蝶曲线。发现即使在低VDD下，扩展WNM （E-WNM）也服从正态分布。此外，E-WNM与位线法的WNM具有良好的相关性。因此，所提出的方法是低vdd产量估计的良好候选方法。

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.