Large remanent polarization of Bi4Ti3O12-based thin films modified by the site engineering technique

The site engineering approach based on site-selective substitutions was utilized to improve the ferroelectric properties in Bi4Ti3O12 thin film. Thin films of (Bi4−xNdx)(Ti3−yVy)O12 with both A- and B-sites substitutions were deposited on (111)Pt/Ti/SiO2/Si substrates at 600 °C by metalorganic chemical vapor deposition. Although the films substituted for the A site by Nd, (Bi4−xNdx)Ti3O12, showed no significant improvement in ferroelectricity, additional substitution for the B site by V contributed to a large ferroelectricity. Superior properties compared to (Bi4−xLax)(Ti3−yVy)O12 were confirmed for (Bi4−xNdx)(Ti3−yVy)O12 films. We also showed orientation control using Ru-based substrates. (104)-preferred orientation was obtained on (111)Pt/Ti/SiO2/Si substrates, while (110) and (111) orientations with an advantage for large polarization were stabilized on (001)Ru/SiO2/Si substrates and actually a larger ferroelectricity was obtained; the remanent polarization (2Pr) and coercive field (2Ec) of the (Bi3.35Nd0.65)(Ti2.87V0.13)O12 film were 34 μC/cm2 and 290 kV/cm, respectively. No fatigue phenomenon was also observed for the (Bi3.35Nd0.65)(Ti2.87V0.13)O12 film up to 109 switching cycles.