Manipulating ferroelectricity without electrical bias: A perspective

TL;DR

Ferroelectric thin films offer non-volatile polarization that typically requires bias to switch; this paper provides a perspective on electrode-free manipulation routes. It reviews three main strategies: polarizing surfaces/crystal chemistry, mechanical and chemical pressure, and optical modulation. It discusses mechanisms such as interface electrostatics, depolarizing-field tuning, flexoelectricity, chemical-pressure effects, and photo-induced carrier dynamics, with examples including $BiFeO_3$ insertions in Aurivillius or PTO/STO-based polar textures and BaTiO$_3$ with BaO, illustrating multilevel polarization states. The authors highlight opportunities for low-power, non-invasive devices and note challenges in fatigue, switching speed, and integration, particularly in freestanding membranes for ultrafast optical control.

Abstract

Ferroelectric materials are established candidates for beyond complementary metal-oxide-semiconductor technology, owing to their non-volatile spontaneous electrical polarization. The recent boom in electric dipole texture engineering and manipulation in such materials has revealed exciting routes for controlling ferroelectric polarization, offering alternatives to the classical, sometimes challenging, application of electrical fields. In this short perspective, we shed light on electrode-free external stimuli enabling control over polar states in thin films. We bring awareness to the polarizing role of chemically-engineered surface contributions and provide insights into the combination of chemical substitution and mechanical pressure, complementing the polar state tuning capabilities readily enabled by flexoelectricity. Finally, we describe recent developments in the optical modulation of polarization. Thus, our perspective aims to stimulate the advancement of alternative means to act on polarization states and facilitate the development of ferroelectric-based applications.

Figures (4)

• Figure 1: Electrical-bias-free means for manipulating ferroelectric polarization. Three routes employing crystal chemistry (top left), mechanical pressure (top right), and light illumination (bottom) are highlighted and schemed. The intersections show possible complementary mechanisms. Solid arrows in the films represent local electrical dipoles, and the hollow arrows represent the macroscopic ferroelectric polarization. $E_{\text{imp}}$ denotes the electric imprint field in the heterostructure and $V_{\text{bi}}$ denotes the built-in voltage near the interface. Both will be discussed in detail in section \ref{['sec_l']}.
• Figure 2: Control electric dipole orientations using polarizing surface and crystal chemistry. (a) Polar vortices in PbTiO$_3$/SrTiO$_3$ (PTO/STO) superlattices. Left: $A$-site ($A$: Pb or Sr) displacement vectors (yellow arrow) and curl of displacement (red/blue color) overlaid on the high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM) image. The color bar indicates the magnitude of the curl of the displacement vector. Right: schematic representing the rotation of TiO$_6$ octahedra within one vortex domain. Reprinted with permission from Ref. susarla2021atomic. Copyright 2021 by the Authors under Creative Commons Attribution 4.0 International License published by the Nature Publishing Group. (b) HAADF-STEM image with the measured electric dipole distribution overlaid (left) and schematic (right) of the Aurivillius Bi$_5$FeTi$_3$O$_{15}$ (BFTO) unit cell. Each half unit cell includes four perovskite layers and a Bi$_2$O$_2$ sheet. The negatively charged oxygen atomic layer in the Bi$_2$O$_2$ is highlighted in red. The arrows represent the electric dipoles pointing toward the nearest Bi$_2$O$_2$ layer. The arrows in the left panel are colored according to the given 360° color wheel and show the polarization vector at each B-site cation position. (c) Schematic of the insertion of BiFeO$_3$ (BFO) into the Aurivillius layered framework (top), local piezoresponse switching spectroscopy and scanning nitrogen vacancy (NV) magnetometry image of the composite film (bottom). The phase of the vertical piezoresponse force microscopy (VPFM) and lateral piezoresponse force microscopy (LPFM) signal recorded during the poling of the film reveals the existence of a net polarization along both the in-plane and out-of-plane directions. Scanning NV magnetometry image revealing antiferromagnetic domains. (b) and (c) are reprinted with permission from Ref. efe2025nanoscale. Copyright 2025 by the Authors under Creative Commons Attribution 4.0 International License published by the Nature Publishing Group.
• Figure 3: Acting on polar states using mechanical and chemical pressure (a) PFM phase images showing the mechanically induced ferroelectric polarization reversal in BaTiO$_3$ (BTO) thin film. The top panel shows a $1\times1$ µm$^2$ area (shown by the dashed frame) scanned with the tip under an incrementally increasing loading force on the electrically written bidomain pattern. The bottom panel shows an array of mechanically written nanodomains. Reprinted with permission from Ref. lu2012mechanical. Copyright 2012, The American Association for the Advancement of Science. (b) Negative chemical pressure in BTO thin film using BTO:BaO composite (c-BTO), the $P$-$E$ loop on the left shows the difference compared with single phase BTO (s-BTO) and BTO ceramic (green), indicating the enhanced ferroelectric polarization by introducing chemical pressure. The cross-sectional STEM image of c-BTO, with two BTO unit cells magnified on the right panel, shows the increase of tetragonality by chemical pressure. Reprinted with permission from Ref. wang2021chemical. Copyright 2021, American Chemical Society. (c) Ferroelectric-antipolar phase conversion achieved by the synergetic strategy in La-substituted BFO. The AFM image (middle) shows the distinct topography feature of the pristine and pressed region. The HAADF-STEM micrographs of the pristine ferroelectric phase (left) and the stress-induced antipolar phase (right) indicate the pressure-induced phase conversion. Reprinted with permission from Ref. muller2025reversible. Copyright 2025 by the Authors under Creative Commons Attribution 4.0 International License published by the Nature Publishing Group.
• Figure 4: Optical control of polarization states in ferroelectric thin films (a) Light induced flexoelectricity. Topography image of an as-grown mixed-phase BFO thin film. The white square indicates the illuminated area, the same area after light illumination shows a clear phase redistribution of T-BFO and R-BFO phases. Reprinted with permission from liou_deterministic_2019. Copyright 2019, The Author(s), under exclusive licence to Springer Nature Limited. (b) Transient light-induced polarization enhancement. VPFM image of the single-domain PZT$_{20/80}$ thin film after box-in-box poling. Second harmonic generation (SHG) polarizer measurement on the upward-polarized film for fixed $p$-polarized SHG light before (black) and during UV-light exposure (blue). The solid lines represent the fits to the $4mm$ point group. SHG time trace under repeated UV-light exposure for $p$-polarized incident probe light and detected SHG light. Reprinted with permission from Ref. Sarott_reversible. Copyright 2024 by the Authors under Creative Commons Attribution 4.0 International License published by Wiley-VCH. (c) Domain erasure by combining the optical response and imprint. PFM phase images collected before and after illumination for the BTO/SRO sample. Reproduced from Ref.tan2022control with permission from the Royal Society of Chemistry.