Ferroelectricity in atomic-scale titanium dioxide dielectric films

Ferroelectricity at atomic-scale thickness would have important applications in next-generation electronics. Here, we report that a ferroelectric phase can be stabilized in titanium dioxide (TiO₂) films, a commonly known dielectric widely used in semiconductor technologies, by reducing thickness below 3-nm. Importantly, this ferroelectricity persists down to one nanometer thickness, approximately twice the unit-cell dimension. This thickness-dependent dielectric-to-ferroelectric phase transition demonstrates that an otherwise centrosymmetric, non-ferroic fluorite-structure oxide can undergo structural inversion-symmetry breaking and exhibit voltage-switchable polarization. Atomic-layer deposition (ALD) based low-temperature (below 400 Celsius) synthesis and the stability of this ferroelectricity on both Si and amorphous surfaces (such as amorphous SiO₂, amorphous carbon films) demonstrate the feasibility of integration with a large variety of materials.