Rahaman Sheikh Ziaur, Maikap Siddheswar, Tien Ta-Chang, Lee Heng-Yuan, Chen Wei-Su, Chen Frederick T, Kao Ming-Jer, Tsai Ming-Jinn
Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd,, Kwei-Shan, Tao-Yuan, 333, Taiwan.
Nanoscale Res Lett. 2012 Jun 26;7(1):345. doi: 10.1186/1556-276X-7-345.
Excellent resistive switching memory characteristics were demonstrated for an Al/Cu/Ti/TaOx/W structure with a Ti nanolayer at the Cu/TaOx interface under low voltage operation of ± 1.5 V and a range of current compliances (CCs) from 0.1 to 500 μA. Oxygen accumulation at the Ti nanolayer and formation of a defective high-κ TaOx film were confirmed by high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photo-electron spectroscopy. The resistive switching memory characteristics of the Al/Cu/Ti/TaOx/W structure, such as HRS/LRS (approximately 104), stable switching cycle stability (>106) and multi-level operation, were improved compared with those of Al/Cu/TaOx/W devices. These results were attributed to the control of Cu migration/dissolution by the insertion of a Ti nanolayer at the Cu/TaOx interface. In contrast, CuOx formation at the Cu/TaOx interface was observed in an Al/Cu/TaOx/W structure, which hindered dissolution of the Cu filament and resulted in a small resistance ratio of approximately 10 at a CC of 500 μA. A high charge-trapping density of 6.9 × 1016 /cm2 was observed in the Al/Cu/Ti/TaOx/W structure from capacitance-voltage hysteresis characteristics, indicating the migration of Cu ions through defect sites. The switching mechanism was successfully explained for structures with and without the Ti nanolayer. By using a new approach, the nanoscale diameter of Cu filament decreased from 10.4 to 0.17 nm as the CC decreased from 500 to 0.1 μA, resulting in a large memory size of 7.6 T to 28 Pbit/sq in. Extrapolated 10-year data retention of the Ti nanolayer device was also obtained. The findings of this study will not only improve resistive switching memory performance but also aid future design of nanoscale nonvolatile memory.
在±1.5 V的低电压操作以及0.1至500 μA的一系列电流顺应性（CC）条件下，Al/Cu/Ti/TaOx/W结构（在Cu/TaOx界面处有Ti纳米层）展现出优异的电阻开关记忆特性。通过高分辨率透射电子显微镜、能量色散X射线光谱和X射线光电子能谱证实了Ti纳米层处的氧积累以及有缺陷的高κ TaOx薄膜的形成。与Al/Cu/TaOx/W器件相比，Al/Cu/Ti/TaOx/W结构的电阻开关记忆特性，如高电阻状态/低电阻状态（约为104）、稳定的开关循环稳定性（>106）和多级操作，都得到了改善。这些结果归因于通过在Cu/TaOx界面插入Ti纳米层来控制Cu的迁移/溶解。相比之下，在Al/Cu/TaOx/W结构中观察到在Cu/TaOx界面形成了CuOx，这阻碍了Cu细丝的溶解，并导致在500 μA的CC下电阻比约为10，较小。从电容 - 电压滞后特性在Al/Cu/Ti/TaOx/W结构中观察到6.9×1016 /cm2的高电荷俘获密度，表明Cu离子通过缺陷位点迁移。成功解释了有和没有Ti纳米层的结构的开关机制。通过使用一种新方法，随着CC从500 μA降低到0.1 μA，Cu细丝的纳米级直径从10.4减小到0.17 nm，从而实现了7.6 T至28 Pbit/sq in的大存储容量。还获得了Ti纳米层器件推断的10年数据保持率。这项研究的结果不仅将改善电阻开关记忆性能，还将有助于未来纳米级非易失性存储器的设计。
