Improved performance of a conducting-bridge random access memory using ionic liquids
Improved performance of a conducting-bridge random access memory using ionic liquids
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DOI：
10.1039/c6tc01486k
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发表时间：
2016-07
影响因子：
6.4
通讯作者：
A. Harada;Hiroki Yamaoka;S. Tojo;K. Watanabe;Atsushi Sakaguchi;K. Kinoshita;S. Kishida;Y. Fukaya;K. Matsumoto;R. Hagiwara;H. Sakaguchi;T. Nokami;T. Itoh
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文献类型：
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作者：
A. Harada;Hiroki Yamaoka;S. Tojo;K. Watanabe;Atsushi Sakaguchi;K. Kinoshita;S. Kishida;Y. Fukaya;K. Matsumoto;R. Hagiwara;H. Sakaguchi;T. Nokami;T. Itoh
导电桥随机存取存储器（CB-RAM）是下一代存储器的有希望的候选者。本研究研究了18种离子液体（ILs）对Cu/HfO2/Pt型CB-RAM性能的添加影响；通过向 Cu/HfO2/Pt 电池的 HfO2 层提供微量 IL 来降低开关电压。结果表明，IL 的离子电导率 (σi) 和 IL 中的阴离子对铜 (Cu) 离子的配位能力 (β) 是决定形成铜丝 (Vset) 所需电压的关键竞争因素； σi的增加和β的减少有效地增强了Cu原子的电离和扩散，导致Vset的降低。因此，在测试的IL中，1-丁基-3-甲基咪唑鎓双(三氟甲磺酰基)酰胺([bmim][Tf2N])、1-乙基-3-甲基咪唑鎓双(三氟甲磺酰基)酰胺([emim][Tf2N])和1-丁基-3-甲基咪唑鎓双(氟磺酰基)酰胺([bmim][FSA]) 具有高 σi 和低 β 值，被发现是 Cu/HfO2/Pt 电池的最佳添加剂。另一方面，可知由于焦耳热引起的Cu原子的热扩散导致Cu细丝断裂而发生复位。降低Vset和制作细丝对于降低复位电压是有效的。我们进一步追踪了通过在 HfO2 薄膜中添加 Cu(Tf2N)2 掺杂 [bmim][Tf2N] 来改善开关电压色散的根源，我们最近对此进行了报道。复阻抗测量表明，添加铜掺杂离子液体涉及两个相互竞争的因素：铜离子扩散的减弱和铜离子化的增强。这两个因素的平衡决定了Vset及其色散等重要参数。考虑到本研究揭示的竞争因素的平衡，可以通过调整 IL 来优化 CB-RAM 的性能。
The conducting-bridge random access memory (CB-RAM) is a promising candidate for the next-generation memory. In this study, the addition effect of 18 types of ionic liquids (ILs) on the performances of the Cu/HfO2/Pt type CB-RAM has been investigated; the switching voltage was lowered by supplying a trace amount of the IL to the HfO2 layer of the Cu/HfO2/Pt cell. It was revealed that the ionic conductivity (σi) of the IL and the coordinating ability (β) of the anion in the IL towards the copper (Cu) ion are key competing factors that determine the voltage required for the formation of the Cu filament (Vset); the increase in σi and the decrease in β are effective in enhancing the ionization and diffusion of the Cu atoms, resulting in the reduction of Vset. Therefore, among the tested ILs, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([bmim][Tf2N]), 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)amide ([emim][Tf2N]) and 1-butyl-3-methylimidazolium bis(fluorosulfonyl)amide ([bmim][FSA]), which have high σi and low β values were found to be the best additives for the Cu/HfO2/Pt cell. On the other hand, reset was revealed to occur due to the rupture of the Cu filament by the thermal diffusion of the Cu atoms by Joule heat. Reducing Vset and making a thin filament are effective in reducing the reset voltages. We further traced the origin of the improved dispersion of the switching voltages by the addition of the Cu(Tf2N)2 doped [bmim][Tf2N] to the HfO2 film, which we recently reported. A complex-impedance measurement suggested that the addition of Cu doped IL involves two competing factors: the decline of the Cu ion diffusion and enhancement of the Cu ionization. The balance of these two factors determines the important parameters such as Vset and its dispersion. The performance of the CB-RAM can be optimized by the adjustment of the IL, considering the balance of the competing factors revealed by the present study.