Effect of Ce/(Hf + Ce) ratio on ferroelectric and piezoelectric properties and effect of film thickness on ferroelectricity for thick CeO<sub>2</sub>–HfO<sub>2</sub> films deposited by sputtering method without substrate heati

The dependence of ferroelectric properties on composition and film thickness was investigated for CeO 2 -HfO 2 films with various ratios x=Ce/(Hf+Ce), deposited on polyethylene terephthalate coated with an amorphous indium tin oxide layer (amorphous ITO/PET) substrates without substrate heating.Additionally, the dependence of composition on piezoelectric properties was examined.X-ray diffraction (XRD) analysis showed that the films consisted of atetragonal phase (T.) and/or orthorhombic (O.) phases with (111) and {100} out-of-plane orientations for the films with thicknesses ranging from 440 to 910 nm at x=0.23.In addition, the remnant polarization (P r ) increased from 6.0 to 11.7 C/cm 2 with the increase in the film thickness.To investigate the composition dependence, CeO 2 -HfO 2 films with a thickness of 800-1000 nm and x values of 0.17, 0.18, 0.23, and 0.28 were prepared.XRD showed (111) and {100} orientations in all films.Clear P-E hysteresis loops and switching currents were observed for x=0.18 and 0.23, with P r exceeding 10.0 C/cm 2 , even in films deposited on amorphous ITO/PET without substrate heating.Moreover, these films exhibited piezoelectric properties consistent with P-E loops, showing their potential for flexible piezoelectric applications.