Charge-Compensative Ion Substitution of La3+-Substituted Bismuth Titanate Thin Films for Enhancement of Remanent Polarization

Ferroelectric properties of La3+-substituted bismuth titanate (BLT) films were modified by Ti-site substitution using higher-valence ions than the Ti4+ ion. Thin films of V5+-, W6+-, Zr4+- and nonsubstituted BLT, i.e., (Bi3.24La0.75)(Ti2.97V0.03)O12 (BLTV), (Bi3.23La0.75)(Ti2.97W0.03)O12 (BLTW), (Bi3.25La0.75)(Ti2.97Zr0.03)O12 (BLTZ) and (Bi3.25La0.75)Ti3.00O12, respectively, were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by chemical solution deposition. These films consisted of isotropic granular structures without a preferred crystal orientation. Remanent polarizations (P r) of the BLTV and BLTW films (13 and 12 µC/cm2, respectively) were larger than those of the BLT and BLTZ films (8 and 9 µC/cm2, respectively), while those films had similar coercive fields (E c) of approximately 120 kV/cm. BLTV and BLTW films also had lower leakage current densities (approximately 10-8 A/cm2 at 100 kV/cm) than that of BLT film (approximately 10-6 A/cm2 at 100 kV/cm). As no obvious difference was found in the crystal orientation or the microstructure, the enhancement of the P r value and suppression of the leakage current density could be achieved on a BLT film by the charge compensation using higher-valence ions than the Ti4+ ion.