As a unique mechanism for MRAMs, magnetic coupling needs to be accounted for when designing memory arrays. This paper models both intra- and inter-cell magnetic coupling analytically for STT-MRAMs and investigates their impact on the write performance and retention of MTJ devices, which are the data-storing elements of STT-MRAMs. We present magnetic measurement data of MTJ devices with diameters ranging from 35nm to 175nm, which we use to calibrate our intra-cell magnetic coupling model. Subsequently, we extrapolate this model to study inter-cell magnetic coupling in memory arrays. We propose the inter-cell magnetic coupling factor Psi to indicate coupling strength. Our simulation results show that Psi=2% maximizes the array density under the constraint that the magnetic coupling has negligible impact on the device's performance. Higher array densities show significant variations in average switching time, especially at low switching voltages, caused by inter-cell magnetic coupling, and dependent on the data pattern in the cell's neighborhood. We also observe a marginal degradation of the data retention time under the influence of inter-cell magnetic coupling.

中文翻译：

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磁耦合和密度对STT-MRAM性能的影响

作为MRAM的独特机制，在设计存储阵列时需要考虑磁耦合。本文对STT-MRAM的单元内和单元间磁耦合进行了建模，并研究了它们对作为STT-MRAM数据存储元素的MTJ器件的写入性能和保留的影响。我们提供了直径范围从35nm到175nm的MTJ设备的磁测量数据，这些数据用于校准细胞内磁耦合模型。随后，我们推断该模型以研究存储器阵列中的小区间磁耦合。我们提出小区间磁耦合系数Psi来指示耦合强度。我们的仿真结果表明，在磁耦合对器件性能的影响可忽略不计的约束下，Psi = 2％可使阵列密度最大化。较高的阵列密度显示出平均开关时间的显着变化，尤其是在低开关电压下，这是由单元间磁耦合引起的，并且取决于单元附近的数据模式。我们还观察到在单元间磁耦合的影响下数据保留时间的边际下降。