To increase the density of magnetoresistive random access memory (MRAM) beyond the 1T1MTJ MRAM cell in use today, the design space for 1S1MTJ MRAM array is analyzed by cooptimizing both selectors and MTJs. Current low-resistance MTJs for 1T1MTJ MRAM are not suitable for 1S1MTJ MRAM. Threshold-type selectors would induce a strong read disturb on the MTJ due to the snapback voltage (VTH-VHOLD) when the selector is turned on. Also, exponential-typeselectors would degrade the read margin (RM) due to its large ON-state resistance. When using existing selectors to achieve a 1-M-bit 1S1MTJ array, it is necessary to adjust the product of resistance and area(RA) and the diameter of the MTJ. An MTJ with the RA = 15 Ω · μm2 and the diameter = 50 nm can meet the criterion of RM > 10% for both exponential-type selectors (exponential slope = 300-500 mV/decade with the current density ~ 1 MA/cm2) and threshold-type selectors (VTH-VHOLD ~ 250 mV). A design space accommodating a selector variation of around 1% can be found for MTJs with tunnel magnetoresistance ratio (TMR) <; 250%. With an increased TMR of 250%-350% of the MTJ, the tolerance of variations for exponential-type selectors and threshold-type selectors can be improved to 2% and 4%, respectively. This provides a chance for the 1S1MTJ MRAM with existing selectors.

中文翻译：

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交叉点 1S1MTJ MRAM 的设计空间分析：选择器 - TJ 协同优化


为了提高磁阻随机存取存储器 (MRAM) 的密度，使之超越目前使用的 1T1MTJ MRAM 单元，通过共同优化选择器和 MTJ 来分析 1S1MTJ MRAM 阵列的设计空间。目前用于 1T1MTJ MRAM 的低电阻 MTJ 不适用于 1S1MTJ MRAM。当选择器开启时，阈值型选择器会由于回跳电压（VTH-VHOLD）而对 MTJ 产生强烈的读取干扰。此外，指数型选择器由于导通电阻较大，会降低读取裕度 (RM)。当使用现有选择器实现1M位1S1MTJ阵列时，需要调整电阻与面积（RA）的乘积以及MTJ的直径。 RA = 15 Ω·μm2 且直径 = 50 nm 的 MTJ 对于两种指数型选择器都可以满足 RM > 10% 的标准（指数斜率 = 300-500 mV/decade，电流密度 ~ 1 MA/ cm2）和阈值类型选择器（VTH-VHOLD ~ 250 mV）。对于隧道磁阻比 (TMR) < 的 MTJ，可以找到容纳 1% 左右选择器变化的设计空间； 250%。随着MTJ的TMR增加250%-350%，指数型选择器和阈值型选择器的变化容限可以分别提高到2%和4%。这为 1S1MTJ MRAM 与现有选择器提供了机会。