Interface dipole effect on thin film ferroelectric stability: First-principles and phenomenological modeling
Interface dipole effect on thin film ferroelectric stability: First-principles and phenomenological modeling
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DOI：
10.1103/physrevb.85.125407
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发表时间：
2012-03
影响因子：
3.7
通讯作者：
Xiaohui Liu;Yong Wang;P. Lukashev;J. Burton;E. Tsymbal
中科院分区：
文献类型：
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作者：
Xiaohui Liu;Yong Wang;P. Lukashev;J. Burton;E. Tsymbal
利用铁电材料的可切换自发极化为纳米电子存储器和逻辑器件的未来提供了一个有前途的途径，前提是纳米级金属-铁电-金属异质结构可以被设计成通过施加的电场保持可切换的双稳态极化。这种方法的最具挑战性的方面是克服有害的界面效应，该界面效应倾向于使铁电极化不稳定或不可切换，并且随着铁电材料越来越薄而变得越来越重要。在这里，我们使用第一性原理的密度泛函计算和唯象建模，以证明在SrRuO 3/BaTiO 3/SrRuO 3上生长的外延异质结构中的BaO/RuO 2界面终止序列可以导致由于固定的界面偶极子薄BaTiO 3薄膜的不可切换的极化状态。在BaO/RuO 2界面处的不利界面偶极子导致对一个偏振态的强烈偏好，并且在薄膜结构中，导致低于某一临界厚度的第二状态的不稳定性，从而使得偏振不可切换。我们分析了这些异质结构的能量稳定性的界面偶极子的贡献。此外，我们提出并证明，这种不利的界面偶极效应可以通过在BaO/RuO 2终止界面处沉积一薄层SrTiO 3来减轻。我们的第一性原理和唯象模型预测，相关的变化的界面终止序列SrO/TiO 2的异质结构的两侧，导致恢复的双稳定性与一个较小的临界厚度，沿着与增强的势垒极化反转。这些结果表明，界面工程是一种可行的方法，以提高铁电性能在纳米尺度。
Utilization of the switchable spontaneous polarization of ferroelectric materials offers a promising avenue for the future of nanoelectronic memories and logic devices provided that nanoscale metal-ferroelectric-metal heterostructures can be engineered to maintain a bi-stable polarization switchable by an applied electric field. The most challenging aspect of this approach is to overcome the deleterious interface effects which tend to render ferroelectric polarization either unstable or unswitchable and which become ever more important as ferroelectric materials are produced thinner and thinner. Here we use first-principles density functional calculations and phenomenological modeling to demonstrate that a BaO/RuO2 interface termination sequence in SrRuO3/BaTiO3/SrRuO3 epitaxial heterostructures grown on SrTiO3 can lead to a nonswitchable polarization state for thin BaTiO3 films due to a fixed interface dipole. The unfavorable interface dipole at the BaO/RuO2 interface leads to a strong preference for one polarization state and, in thin film structures, leads to instability of the second state below a certain critical thickness, thereby making the polarization unswitchable. We analyze the contribution of this interface dipole to the energetic stability of these heterostructures. Furthermore, we propose and demonstrate that this unfavorable interface dipole effect can be alleviated by deposition of a thin layer of SrTiO3 at the BaO/RuO2 terminated interface. Our first-principles and phenomenological modeling predict that the associated change of the interface termination sequence to SrO/TiO2 on both sides of the heterostructure leads to a restoration of bi-stability with a smaller critical thickness, along with an enhancement of the barrier for polarization reversal. These results demonstrate that interface engineering is a viable approach to enhance ferroelectric properties at the nanoscale.