Evolution of ferroelectricity in ultrathin PbTiO3 films as revealed by electric double layer gating

Ryutaro Nishino,Fumitaka Kagawa,Masashi Kawasaki,Takahiro C Fujita

doi:10.1038/s41598-020-67580-8

Ryutaro Nishino, Fumitaka Kagawa + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-67580-8

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Abstract

Ferroelectricity in ultrathin films is destabilized by depolarization field, which leads to the reduction of spontaneous polarization or domain formation. Here, thickness dependence of remnant polarization in PbTiO3 films is electrically revealed down to 2.6 nm by controlling the polarization direction with employing an electric double layer gating technique to suppress leakage current in ultrathin films. The remnant polarization for a 17 nm-thick film is similar to bulk value ~ 60 μC cm−2 and reduces to ~ 20 μC cm−2 for a 2.6 nm-thick film, whereas robust ferroelectricity is clearly observed in such ultrathin films. In-situ X-ray diffraction measurements under an external electric field reveal that the reduced tetragonality in ultrathin films is mostly recovered by cancelling out the depolarization field. Electric double layer gating technique is an excellent way for exploring physical properties in ultrathin ferroelectric films.

Highlights

Ferroelectricity in ultrathin films is destabilized by depolarization field, which leads to the reduction of spontaneous polarization or domain formation
Mobile ions in the ionic liquid (IL) are accumulated on the ferroelectric surface by applying an external electric field and the polarization is reversed to screen the charge of these ions
Since IL is ionically conductive but electrically insulative, this technique has the great advantage of suppressing leakage current and evaluating polarization in ultrathin films compared to the conventional measurement with a capacitor structure

Summary

Introduction

Ferroelectricity in ultrathin films is destabilized by depolarization field, which leads to the reduction of spontaneous polarization or domain formation. We report the thickness-dependent ferroelectric properties in P bTiO3 films measured with the EDL structure. We demonstrate that the EDL gating technique enables us to control polarization direction and to measure remnant polarization of ultrathin PbTiO3 films down to 2.6 nm.

Results

Conclusion