Thickness-dependent crystal structure and electric properties of epitaxial ferroelectric Y2O3-HfO2 films

The thickness dependences of the crystal structure and electric properties of (111)-oriented epitaxial 0.07Y(2)O(3)-HfO2 (YHO7) ferroelectric films were investigated for the film thickness range of 10-115 nm. The YHO7 films were grown by pulsed laser deposition or sputtering at room temperature and subsequent heat treatment. As a substrate for the epitaxial growth of the YHO7 film, (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia was used. X-ray diffraction measurements confirmed that the main crystal phase of these YHO7 films was ferroelectric orthorhombic for up to 115-nm-thick films. Small film-thickness dependences of remanent polarization (P-r) and saturation polarization (P-s) were observed. Thickness dependence of the coercive field (E-r) is also small, and this behavior does not resemble that of conventional ferroelectric films such as Pb(Zr,Ti)O-3. Additionally, non-oriented polycrystalline YHO7 films are reported to have similar thickness dependence of E-c and almost the same E-r value to epitaxial YHO7 films. We suggest that the ferroelectric domain is significantly small for both epitaxial and polycrystalline films. Such small domains remain even in thicker films, giving rise to thickness-independent E-c. Published by AIP Publishing.