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Vertical Voltage Flips Horizontal Polarization in Ferroelectric Material

Scientific Achievement

Using the Advanced Light Source (ALS), researchers showed that a vertical voltage reversed the horizontal polarization of a Bi₄Ti₃O₁₂ ferroelectric thin film.

Significance and Impact

This flip in polarization removes a key design limit of conventional ferroelectrics and enables stable, low-voltage, high-density memory that could cut the energy use of electronics.

Research Details

  • Synthesized a Bi₄Ti₃O₁₂ thin film, a ferroelectric material that supports in-plane and out-of-plane polarization.
  • Applied a positive vertical voltage to one region of the film surface and negative voltage to a second region.
  • Used X-ray linear dichroism photoemission electron microscopy at ALS beamline 11.0.1.1 to reveal a contrast between the two voltage-treated regions, confirming that the vertical voltages can be used to reverse the direction of the horizontal polarization.
Diagram of electrically switching polarization in a layered bismuth-containing crystal: an atomic model, an XLD-PEEM image showing a switched rectangular region inside a larger one, and two boxes showing the structure under +15 V (polarization P_X, pointing right) and -15 V (polarization P_-X, pointing left).
Far left: Side view of the pristine atomic structure of ferroelectric Bi₄Ti₃O₁₂ depicting layered titanium atoms (blue) bonded with oxygen atoms (brown). Center left: The XLD-PEEM image (top view) from ALS beamline 11.0.1.1 reveals two contrasting regions within the treated area: the dark region at the center (inside the blue rectangle) and the lighter area around it (between the blue and red rectangles), indicating a presence of in-plane polarized regions. Right: The atomic origin of this unusual polarization (PX, P-X), caused by atomistic rearrangement after the material was polarized by externally applied voltages (Credit: Barat Achinuq/Advanced Light Source).

Research Summary

Ferroelectric materials store data in the direction of their built-in electric polarization. In thin films, vertical (out-of-plane) polarization creates a depolarizing field, caused by imperfect charge screening at the electrodes, that destabilizes it as films get thinner. Horizontal (in-plane) polarization largely avoids this field, so it is more stable and better retains data. The tradeoff is that flipping a large, horizontal polarization in a thin film normally takes more voltage than flipping a thin, vertical one, and conventional understanding holds that the voltage must be applied along the same direction as the polarization being flipped.

In this study, researchers found that a thin film of Bi₄Ti₃O₁₂ breaks that rule. They synthesized the crystalline film and applied vertical voltages of +15 V to one rectangular region and -15 V to another. At ALS beamline 11.0.1.1, the team used X-ray linear dichroism photoemission electron microscopy (XLD-PEEM), which is sensitive to a material’s polarization, to map the horizontal polarization in each voltage-treated region.

The data showed clear contrast between the regions, confirming that the vertical voltages had flipped the horizontal polarization and that the direction of the polarization can be reversed simply by reversing the applied voltage. This study revealed that the vertical and horizontal polarizations of Bi₄Ti₃O₁₂ are coupled, so the vertical polarization acts as a “switch” for the horizontal one.

This “transverse switching” combines the stability of a large, horizontal polarization with the low-voltage vertical control. It opens the door to potential ultra-low-power memory devices and new device architectures for computing, and could help reduce the energy footprint of future electronics and data centers.

Contacts: Barat Achinuq and Ramamoorthy Ramesh

Institutions and Affiliations: Lawrence Berkeley National Laboratory: Advanced Light Source, Materials Sciences Division; Kepler Computing; Rice University; Universidad de Cantabria; Université de Liège; University of California, Berkeley; University of Southern California.

Funding: Army Research Office; Consortium for High-Performance Computing Equipment (Belgium); European Regional Development Fund; European Union Marie Skłodowska-Curie Actions Postdoctoral Fellowship; Fund for Scientific Research (Belgium); Kepler Computing; Ministry of Science, Innovation and Universities (Spain); National Science Foundation; Rice University; Tier-1 Lucia supercomputer of the Walloon Region (Belgium); Welch Foundation. Operation of the ALS is supported by the US Department of Energy, Office of Science, Basic Energy Sciences program.

P. Gupta, S. Puebla, F. Gómez-Ortiz, X. Li, S. Husain, T.-R. Liu, P. Meisenheimer, V. Srikrishna, D. Nikonov, M. Chen, Y. Kumar, A. Omar, K. Das, B. Achinuq, S. Roy, Y.-T. Shao, Y. Han, S. Salahuddin, A. Mathuriya, S. Manipatruni, P. Ghosez, J. Junquera, and R. Ramesh, “Perpendicular switching of polarization in layered ferroelectrics,” Nature 656, 67 (2026), doi:10.1038/s41586-026-10839-3.