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)O-12 (BLTV), (Bi3.23La0.75)(Ti2.97W0.03)O-12 (BLTW), (Bi3.25La0.75)(Ti2.97Zr0.03)O-12 (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 muC/cm(2), respectively) were larger than those of the BLT and BLTZ films (8 and 9 muC/cm(2), 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/cm(2) at 100 kV/cm) than that of BLT film (approximately 10(-6) A/cm(2) at 100 kV/cm). As no obvious difference was found in the crystal orientation or the microstructure, the enhancement of the Pr 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.