Ferroelectricity in Epitaxial Tetragonal ZrO 2 Thin Films

The crystal structure and ferroelectric properties of epitaxial ZrO 2 films ranging from 7 to 42 nm thickness grown on La 0.67 Sr 0.33 MnO 3 buffered (110)‐oriented SrTiO 3 substrate are reported. By employing X‐ray diffraction, a tetragonal phase (t‐phase) at all investigated thicknesses, with slight in‐plane strain due to the substrate in the thinnest films, is confirmed. Further confirmation of the t‐phase is obtained through infrared absorption spectroscopy with synchrotron light, performed on ZrO 2 membrane transferred onto a high resistive silicon substrate. Up to a thickness of 31 nm, the ZrO 2 epitaxial films exhibit ferroelectric behavior, at variance with the antiferroelectric behavior reported previously for the t‐phase in polycrystalline films. However, the ferroelectricity is found here to diminish with increasing film thickness, with a polarization of 13 µC cm −2 and down to 1 µC cm −2 for 7 and 31 nm thick ZrO 2 films, respectively. Given that the t‐phase is nonpolar, the observations emphasize the influence of external factors, in promoting polarization in t‐ZrO 2 thin films. These findings provide new insights into the ferroelectric properties and structure of ZrO 2 thin films, and open up new directions to investigate the origin of ferroelectricity in ZrO 2 and to optimize this material for future applications.