Breakthrough in the field of atomic-scale ferroelectrics by Yue-Wen Fang published in Science

Revolutionizing Electronics: Bismuth Oxide Film Stabilizes Ferroelectricity down to 1 nanometer

  • This research presents a breakthrough in the field of atomic-scale ferroelectrics by demonstrating the stability of ferroelectricity in a layered film of bismuth oxide down to 1 nanometer through samarium bondage.
  • The research findings have been published in the journal Science, where Linxing Zhang from the University of Science and Technology Beijing and Yue-Wen Fang from the Centro de Física de Materiales (CSIC-UPV/EHU) led the experimental and theoretical work, respectively.

Science 379, 1218 (2023)

Ferroelectrics, a type of functional material with a century-long scientific history since its discovery by Joseph Valasek in 1920, exhibit a spontaneous electric polarization that can be reversed by an external electric field. These materials are also typically associated with excellent piezoelectric and thermoelectric properties, making them highly versatile and widely applied in both life and industry from low-cost bus cards to cutting-edge aerospace devices. Today, the ferroelectric industry is valued at approximately $7 billion and continues to grow. Dr. Yuewen Fang, a computational physicist at the Centro de Física de Materiales (CFM, CSIC-UPV/EHU), has collaborated with an experimental team led by Dr. Linxing Zhang at the University of Science and Technology Beijing to design a new ferroelectric material that pushes the limits of size for room-temperature ferroelectric materials down to the atomic scale. The work has been published today in Science.

The material, which consists of a layered structure of bismuth oxide stabilized by samarium bonding, exhibits a remanent polarization of up to 17 microcoulombs per square centimetre even at thicknesses as small as 1 nanometer. The ab initio molecular dynamics simulations conducted by Dr. Fang, and experimental X-ray diffraction (XRD) measurements, performed by Dr. Zhang’s team show that this ferroelectric material has a large Curie temperature of approximately 500 K, making the room-temperature applications possible.

The crystal structure prediction was primarily led by CFM (CSIC-UPV/EHU) and involved a collaboration with Dr. Oswaldo Dieguez at Tel Aviv University in conducting the unbiased high-throughput first-principles structure screening. The proposed crystal structures were determined by combining this unbiased screening with crystal structure prediction guided by transmission electron microscopy (TEM) images, as part of the CFM-led research.The theoretically proposed crystal structure is in a good agreement with the cross-sectional high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images observed in different directions, implying the accuracy of the crystal structure prediction (see Fig. 1).

Figure 1: The proposed crystal structure and the interpretation of ferroelectricity. (A) The computed ferroelectric transition between the polar and non-polar structures. (B) The electron localization function of the two phases demonstrating the role of long-pair electrons of Bi in driving the ferroelectricity. (C) The Sm doped Bi6O9 structure in which the polar symmetry is preserved. (D) The comparison between the theoretical structure and the HAADF-STEM images. (E and F) The polarization hysteresis loops of the films with thicknesses of 1 nm (E) and 4.56 nm (F). (G) The comparison with other ferroelectric systems in remanent polarization.

The in-depth first-principles calculations revealed that the observed ferroelectricity is driven by the lone-pair electrons of Bi ions. These electrons do not participate in the chemical bonding, and are resided in one site of Bi ions asymmetrically, which breaks the inversion space symmetry and induces the ferroelectricity in this new material. In addition, the study also finds that the doping of samarium into the sample is crucial although it is thought to make neglect contribution to the ferroelectricity, but it helps improve the thermodynamic stability of the polar structure especially when the scale it reduced to 1 nanometer, according to the ab initio molecular dynamics simulations by Dr. Fang. Using a cost-effective chemical solution deposition method, the researchers successfully prepared a Bi6O9 thin film with good crystallinity that can be grown on a variety of widely used commercial substrates. This material offers advantages over commercial perovskite oxides, which typically require more expensive synthesis methods. The thin films, ranging in thickness from 1 to 4.56 nm, exhibit relatively large remanent polarizations, ranging from 17 to 50microcoulombs per square centimetre . This places the layered bismuth oxide among the most excellent ferroelectric materials at both the nanometer and subnanometer scales (see Fig.).

According to the study, these ultrathin ferroelectric films are highly suitable for future nano-electronic devices, particularly in the areas of field-effect-transistors, low-power logic, and non-volatile memories. The structure design of these films has enormous potential for manufacturing atomic-scale electronic devices.

Figure 2. The future subnanometer untrathin memory devices based on atomic scale ferroelectrics.

Figure 3. The future subnanometer untrathin memory devices based on atomic scale ferroelectrics.



“Ferroelectricity in layered bismuth oxide down to 1 nanometer”

Qianqian Yang, Jingcong Hu, Yue-Wen Fang, Yueyang Jia, Rui Yang, Shiqing Deng, Yue Lu, Oswaldo Dieguez, Longlong Fan, Dongxing Zheng, Xixiang Zhang, Yongqi Dong, Zhenlin Luo, Zhen Wang, Huanhua Wang, Manling Sui, Xianran Xing, Jun Chen, Jianjun Tian, Linxing Zhang.

Science 379, 1218 (2023)

DOI: 10.1126/science.abm5134