Room-temperature deposition of ferroelectric HfO_2-based films by the sputtering method

摘要

Ferroelectricity has been demonstrated in epitaxial 7%Y-doped HfO_2 (0.07YO_(1.5)-0.93HfO_2) YHO7) films grown by the RF magnetron sputtering method at room temperature without any subsequent annealing. The x-ray diffraction patterns of such films suggested that the decrease in RF power and in the partial oxygen pressure changes the crystal structures of the films from the monoclinic phase to the tetragonal/orthorhombic phase. Clear polarization-electric-field (P-E) hysteresis loops were observed for these epitaxial films with the tetragonal/orthorhombic phase. The obtained remanent polarization (P_r) and coercive field (E_c) values were 14.5 and 12.8 μC/cm~2 and 2300 and 2200 kV/cm for the epitaxial films on (111) indium tin oxide (ITO)//(111) yttria-stabilized zirconia (YSZ) and (100)ITO//(100)YSZ substrates, respectively. Moreover, ferroelectricity was also observed in room-temperature-deposited polycrystalline YH07 films prepared on Pt/TiO_x/SiO_2/(100)Si, crystallized ITO/soda glass, and amorphous ITO/polyethylene terephthalate substrates, namely, crystalline ferroelectric Hf02-based films were prepared at room temperature on various substrates, including organic flexible substrates, by using the RF magnetron sputtering method. The present results open a path to novel applications of ferroelectric HfG_2-based films such as ferroelectric flexible memory.