Ferroelectricity in YO_1.5-HfO₂ films around 1 μm in thickness

Ferroelectricity has been demonstrated in polycrystalline 7%Y-doped HfO₂ (YHO7) films with thicknesses ranging from 10 to 930 nm, which were grown on (111)Pt/TiO_x/SiO₂/(001)Si substrates by pulsed laser deposition at room temperature and subsequent annealing at 1000 °C. The X-ray diffraction pattern suggested that the major crystal phase consists of orthorhombic/tetragonal phases with a small amount of monoclinic phase even for the 930-nm-thick film despite its thickness. Moreover, the hysteresis loops associated with the ferroelectric orthorhombic phase were clearly observed for all samples including even the 930-nm-thick film. The remnant polarization (P_r) and the coercive field (E_c) are 14–17 μC/cm² and 1300–1600 kV/cm, respectively, at max applied electric fields of ∼4000 kV/cm for all YHO7 films within the present study. These results indicate that the ferroelectric structure and properties of YHO7 films are insensitive to the film thickness.