Improvement in ferroelectricity of HfxZr1−xO2 thin films using top- and bottom-ZrO2 nucleation layers
Takashi Onaya,
Toshihide Nabatame,
Naomi Sawamoto,
Akihiko Ohi,
Naoki Ikeda,
Takahiro Nagata,
Atsushi Ogura
Affiliations
Takashi Onaya
Department of Electrical Engineering, Graduate School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
Toshihide Nabatame
National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Naomi Sawamoto
Department of Electrical Engineering, Graduate School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
Akihiko Ohi
National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Naoki Ikeda
National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Takahiro Nagata
National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Atsushi Ogura
Department of Electrical Engineering, Graduate School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
A ferroelectric HfxZr1−xO2 (HZO) thin film crystallized with nanocrystalline top- and bottom-ZrO2 nucleation layers (D-ZrO2) exhibited superior remanent polarization (2Pr = Pr+ − Pr− = 29 μC/cm2) compared to that of similar thin films (12 μC/cm2) crystallized without a ZrO2 nucleation layer (w/o) when the HZO film thickness was 10 nm. Epitaxial-like grain growth of the HZO film was observed on the surfaces of both the top- and bottom-ZrO2 layers, while there was almost no significant difference in the crystal grain size of the HZO film in all samples, as determined by cross-sectional transmission electron microscopy images. Consequently, the ferroelectric orthorhombic, tetragonal, and cubic (O/T/C) phase ratio of the HZO film was significantly increased by using the ZrO2 nucleation layers. It was furthermore confirmed that the 2Pr values were strongly correlated with the O/T/C phase ratio of the HZO film. Therefore, it is clear that the top- and bottom-ZrO2 nucleation layers play an important role in the formation of the ferroelectric HZO film. These results suggest that the HZO film fabrication technique using a nanocrystalline ZrO2 nucleation layer is a promising candidate for next-generation device applications.
