Takanori Mimura

Formation of (111) orientation-controlled ferroelectric orthorhombic HfO2 thin films from solid phase via annealing

0.07YO1.5-0.93HfO2 (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In2O3(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiOx/SiO2/(001)Si substrates, and (111)ITO/(111)Pt/TiOx/SiO2/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ–2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiOx/SiO2/(001)Si was an (111)-oriented uniaxial textured film with ferroelectric orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiOx/SiO2/(001)Si substrate, which does not contain ITO. Polarization–hysteresis measurements confirmed that the films on ITO covered substrates had s...

Fabrication of (110)-one-axis-oriented perovskite-type oxide thin films and their application to buffer layer

BaCe0.9Y0.1O3−δ (BCYO) and SrZr0.8Y0.2O3−δ (SZYO) thin films of perovskite-type oxides were deposited on (111)Pt/TiO x /SiO2/(100)Si substrates. X-ray diffraction patterns showed that the (110)-oriented BCYO and SZYO thin films were grown on (111)Pt/Si substrates directly without using any buffer layers. Thin films of SrRuO3 (SRO), a conductive perovskite-type oxide, were also deposited on those films and highly (110)-oriented SRO thin films were obtained. We believe that this (110)-oriented SRO works as a buffer layer to deposit (110)-oriented perovskite-type ferroelectric oxide thin films as well as a bottom electrode and can modify the ferroelectric properties of the oxide thin films by controlling their crystallographic orientations.

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 0.07YO1.5-0.93HfO2 (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 (Pr) and saturation polarization (Ps) were observed. Thickness dependence of the coercive field (Ec) is also small, and this behavior does not resemble that of conventional ferroelectric films such as Pb(Zr,Ti)O3. Additionally, non-oriented polycrystalline YHO7 films are reported to have similar thickness dependence of Ec and almost the same Ec 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 Ec.

Dynamic observation of ferroelectric domain switching using scanning nonlinear dielectric microscopy

Local response signals in scanning nonlinear dielectric microscopy during domain switching in ferroelectric materials were studied. Periodic response signals corresponding to domain switching were observed in single-crystal LiTaO3 samples under alternating bias voltage applications. This approach was subsequently applied to ferroelectric HfO2 films, showing different response signals depending on the film orientation and the conditions of film formation. These results suggest that the proposed method is useful for obtaining detailed information concerning domain switching in the nanoscale region, such as the pinning-site effect, backswitching, and 90° switching.