Stopping Resistance Drift in Phase Change Memory Cells
Stopping Resistance Drift in Phase Change Memory Cells
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DOI：
10.1109/drc50226.2020.9135147
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
R. Khan;A. Talukder;F. Dirisaglik;A. Gokirmak;H. Silva
中科院分区：
文献类型：
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作者：
R. Khan;A. Talukder;F. Dirisaglik;A. Gokirmak;H. Silva
相变存储器（PCM）是一种高速、高耐久性、高密度的非易失性存储器技术，其利用诸如Ge 2 Sb 2 Te 5（GST）的硫属化物材料，该硫属化物材料可以在高电阻非晶相和低电阻结晶相之间电循环。PCM单元的非晶相的电阻遵循幂律[1]随时间增加（漂移），这随时间增加了存储器窗口，但限制了每单元多位PCM的实现。有许多理论解释了漂移的起源[1] - [4]，大多数将其归因于结构弛豫，即无定形结构中原子的热激活重排[2]。大多数关于电阻漂移的研究都是基于室温或室温以上的实验，其中可能同时发生多个过程。在这项工作中，我们熔融淬火非晶化GST线电池的宽度约为120-140 nm，长度约为390-500 nm，厚度约为50 nm（图1），并使用参数分析仪在85 K至350 K范围内监测电流-电压（I-V）特性（图2）。我们从电阻与时间曲线的斜率中提取了漂移系数（使用低压测量），并在125 K-300 K温度范围内观察到电阻漂移（图3）。我们发现漂移系数随温度的变化近似线性增加，从125 K时的~ 0.07增加到200 K时的~ 0.11，并且在200 K至300 K范围内漂移系数近似恒定（图3插图）。这些结果表明，结构弛豫本身不能解释电阻漂移，其他机制有助于这种现象[5]，[6]。
Phase change memory (PCM) is a high speed, high endurance, high density non-volatile memory technology that utilizes chalcogenide materials such as Ge 2 Sb 2 Te 5 (GST) that can be electrically cycled between highly resistive amorphous and low resistance crystalline phases. The resistance of the amorphous phase of PCM cells increase (drift) in time following a power law [1] , which increases the memory window in time but limits in the implementation of multi-bit-per-cell PCM. There has been a number of theories explaining the origin of drift [1] – [4] , mostly attributing it to structural relaxation, a thermally activated rearrangement of atoms in the amorphous structure [2] . Most of the studies on resistance drift are based on experiments at or above room temperature, where multiple processes may be occurring simultaneously. In this work, we melt-quenched amorphized GST line cells with widths ~120-140 nm, lengths ~390-500 nm, and thickness ~50nm ( Fig. 1 ) and monitored the current-voltage (I-V) characteristics using a parameter analyzer ( Fig. 2 ) in 85 K to 350 K range. We extracted the drift co-efficient from the slope of the resistance vs. time plots (using low-voltage measurements) and observed resistance drift in the 125 K -300 K temperature range ( Fig. 3 ). We found an approximately linear increase in drift coefficient as a function of temperature from ~ 0.07 at 125 K to ~ 0.11 at 200 K and approximately constant drift coefficients in the 200 K to 300 K range ( Fig. 3 inset). These results suggest that structural relaxations alone cannot account for resistance drift, additional mechanisms are contributing to this phenomenon [5] , [6] .