Wei Yingfen, Nukala Pavan, Salverda Mart, Matzen Sylvia, Zhao Hong Jian, Momand Jamo, Everhardt Arnoud S, Agnus Guillaume, Blake Graeme R, Lecoeur Philippe, Kooi Bart J, Íñiguez Jorge, Dkhil Brahim, Noheda Beatriz
Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands.
Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, CNRS-UMR8580, Université Paris-Saclay, Gif-sur-Yvette, France.
Nat Mater. 2018 Dec;17(12):1095-1100. doi: 10.1038/s41563-018-0196-0. Epub 2018 Oct 22.
Hafnia-based thin films are a favoured candidate for the integration of robust ferroelectricity at the nanoscale into next-generation memory and logic devices. This is because their ferroelectric polarization becomes more robust as the size is reduced, exposing a type of ferroelectricity whose mechanism still remains to be understood. Thin films with increased crystal quality are therefore needed. We report the epitaxial growth of HfZrO thin films on (001)-oriented LaSrMnO/SrTiO substrates. The films, which are under epitaxial compressive strain and predominantly (111)-oriented, display large ferroelectric polarization values up to 34 μC cm and do not need wake-up cycling. Structural characterization reveals a rhombohedral phase, different from the commonly reported polar orthorhombic phase. This finding, in conjunction with density functional theory calculations, allows us to propose a compelling model for the formation of the ferroelectric phase. In addition, these results point towards thin films of simple oxides as a vastly unexplored class of nanoscale ferroelectrics.
基于铪的薄膜是将纳米级强铁电性集成到下一代存储器和逻辑器件中的理想候选材料。这是因为随着尺寸减小，它们的铁电极化变得更强，展现出一种其机制仍有待理解的铁电性。因此需要晶体质量更高的薄膜。我们报道了在（001）取向的LaSrMnO/SrTiO衬底上外延生长HfZrO薄膜。这些薄膜处于外延压缩应变下，主要为（111）取向，显示出高达34 μC/cm的大铁电极化值，并且不需要唤醒循环。结构表征揭示了一种菱方相，不同于通常报道的极性正交相。这一发现与密度泛函理论计算相结合，使我们能够提出一个关于铁电相形成的令人信服的模型。此外，这些结果表明简单氧化物薄膜是一类尚未得到充分探索的纳米级铁电体。
