阻变存储器复合材料界面及电极性质研究

采用基于密度泛函理论的第一性原理对比研究了Cu（111）/HfO₂（001），Cu（111）/HfO₂（010），Cu（111）/HfO₂（100）三种复合材料界面模型的失配率、界面束缚能、电荷密度、电子局域函数以及差分电荷密度. 计算结果表明：Cu（111）/HfO₂（010）失配率最小，界面束缚能最大，界面体系相对最稳定；对比电荷密度及电子局域函数图显示，只有HfO₂（010）方向形成的复合材料体系出现了垂直Cu电极方向完整连通的电子通道，表明电子在此方向上具有局域性、连通性，与阻变存储器（RRAM）器件导通方向一致；差分电荷密度图显示，Cu（111）/HfO₂（010）复合材料体系界面处存在电荷密度分布重叠的现象，界面处有电子的相互转移、成键的存在；进一步计算了Cu（111）/HfO₂（010）体系距离界面不同位置的间隙Cu原子形成能，表明越靠近界面Cu原子越容易进入HfO₂ 体内，在外加电压下易发生电化学反应，从而导致Cu导电细丝的形成与断裂. 研究结果可为RRAM存储器的制备及性能的提高提供理论指导和设计工具. 关键词： 阻变存储器 复合材料 界面 电子通道

Composite interfaces and electrode properties of resistive random access memory devices

For the three kinds of composite materials, i.e., Cu(111)/HfO₂(001), Cu(111)/HfO₂(010) and Cu(111)/HfO₂(100), the first-principles method based on the density functional theory is adopted to calculate their rates of mismatching of interface model, interface adhesion energies, the electric charge densities, the electron localization functions, and the charge density differences separately. The results indicate that the rate of mismatching of the Cu(111)/HfO₂(010) interface model is lowest and its interface adhesion energy is higher than the others’, which means that the Cu(111)/HfO₂(010) is most stable. From the analyses of charge densities and electron localization functions of the three interfaces, it can be found that only the Cu(111)/HfO₂(010) interface is able to form the connective electronic channel along the vertical direction of the Cu electrode. This indicates that electrons possess the localizabilty and connectivity along the HfO₂(010) direction, which corresponds to the switching-on direction of the resistive random access memory (RRAM) device. The charge density difference analysis reveals that the charge density distributions overlap, the electrons transfer mutually and bond at the interface of the Cu(111)/HfO₂(010). In addition, based on the model of Cu (111)/HfO₂ (010) interface, the formation energies of the interstitial Cu at different positions are also calculated. The results show that the closer to the interface the Cu atom, the more easily it migrates into HfO₂. This indicates that the electrochemical reaction takes place more easily under the applied voltage, which results in the formation and rupture of Cu conductive filaments. All the above findings will provide a theoretical guidance for improving the performances of RRAM devices.
Keywords： resistive random access memory composite material interface electronic channel