Investigation of temperature-dependent ferroelectric properties of Y-doped HfO2 thin film prepared by medium-frequency reactive magnetron co-sputtering

The crystal structure as well as electrical properties of Y-doped HfO2 thin films were evaluated. The thin films were produced by co-sputtering with Y and Hf metal targets in an argon/oxygen atmosphere. A 10 nm-thick HfO2 thin film with 1.5 at.% yttrium content deposited at 200 °C and annealed at 850 °C for 40 s in an inert nitrogen atmosphere shows excellent ferro-electricity with a significant remnant polarization (Pr~20 μC/cm2) and a low leakage current density (about 10−6 A/cm2 at 1 MV/cm). The crystal structure and ferroelectric properties of Y-doped HfO2 thin films exhibit strong temperature dependence. The ferroelectric phase (orthorhombic phase) fraction was observed to be suppressed in favor of the para-electric phase (monoclinic phase) with increasing deposition temperature through analyses grazing incidence X-ray diffraction and high resolution transmission electron microscopy. Through the analysis of polarization and current density characteristics, a correlation between decreasing remnant polarization and a greater leakage current density was revealed as the deposition temperature was increased. The origin of the degradation of the ferro-electricity of Y-doped HfO2 films with elevated deposition temperature was attributed to the formation of m-phase which was unfavorable for promoting transition to the ferroelectric o-phase during post-deposition annealing.