Hsieh Yu-Ling, Su Wen-Hsuan, Huang Cheng-Chun, Su Ching-Yuan
Dep. of Mechanical Engineering, National Central University, Tao-Yuan 32001, Taiwan.
Nanotechnology. 2019 Nov 1;30(44):445702. doi: 10.1088/1361-6528/ab3606.
In this study, we demonstrated the integration of black phosphorus (BP) nanoflakes in a resistive random access memory (RRAM) with a facile and complementary metal-oxide-semiconductor-compatible process. The solution-processed BP nanoflakes embedded in polystyrene (PS) as an active layer were sandwiched between aluminum electrodes (Al/BP:PS/Al). The device shows a figure of merit with typical bipolar behavior and forming-free characteristics as well as excellent memory performances such as nonvolatile, low operation voltage (1.75 V) and high ON/OFF ratio (>10) as well as the long retention time (>1500 s). The improved device performances were attributed to the formation of effective trap sites from the hybrid structure of the active layer (BP:PS), especially the BP nanoflakes and the partly oxidized species (P O ). Moreover, the extrinsic aluminum oxide layer was observed after the device operation. The mechanism of switching behavior was further unveiled through the carrier transport models, which confirms the conductive mechanisms of space-charge-limited current and Ohmic conductance at high resistance state (HRS) and low resistance state, respectively. Additionally, in the high electric field at HRS, the transfer curve was well fitted with the Poole-Frenkel emission model, which could be attributed to the formation of the aluminum oxide layer. Accordingly, both the trapping/de-trapping of carriers and the formation/rupture of conductive filaments were introduced as transport mechanisms in our devices. Although the partial P O species on BP were inevitable during the liquid phase exfoliation process, which was regarded as the disadvantages for various applications, it turns to a key point for improving performances in memory devices. The proposed approach to integrating BP nanoflakes in the active layer of the RRAM device could pave the way for next-generation memory devices.
在本研究中，我们展示了通过一种简便且与互补金属氧化物半导体兼容的工艺，将黑磷（BP）纳米片集成到电阻式随机存取存储器（RRAM）中。嵌入聚苯乙烯（PS）作为活性层的溶液处理BP纳米片夹在铝电极（Al/BP:PS/Al）之间。该器件具有典型的双极行为和无形成特性的品质因数，以及优异的存储性能，如非易失性、低工作电压（1.75 V）、高开/关比（>10）以及长保持时间（>1500 s）。器件性能的提升归因于活性层（BP:PS）的混合结构，特别是BP纳米片和部分氧化物种（P O ）形成了有效的陷阱位点。此外，在器件运行后观察到了外在的氧化铝层。通过载流子输运模型进一步揭示了开关行为的机制，该模型分别证实了在高电阻状态（HRS）和低电阻状态下的空间电荷限制电流和欧姆电导的导电机制。此外，在HRS的高电场下，转移曲线与普尔-弗伦克尔发射模型拟合良好，这可归因于氧化铝层的形成。因此，载流子的俘获/去俘获以及导电细丝的形成/断裂都被引入作为我们器件中的输运机制。尽管在液相剥离过程中BP上的部分P O 物种是不可避免的，这在各种应用中被视为缺点，但它却成为提高存储器件性能的关键点。所提出的将BP纳米片集成到RRAM器件活性层中的方法可为下一代存储器件铺平道路。
