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., (Bi_3.24La _0.75)(Ti_2.97V_0.03)O₁₂ (BLTV), (Bi_3.23La_0.75)(Ti_2.97W_0.03)O ₁₂ (BLTW), (Bi_3.25La_0.75)(Ti _2.97Zr_0.03)O₁₂ (BLTZ) and (Bi _3.25La_0.75)Ti_3.00O₁₂, 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 12μC/cm², respectively) were larger than those of the BLT and BLTZ films (8 and 9μC/cm², respectively), while those films had similar coercive fields (E_c) of approximately 120kV/cm. BLTV and BLTW films also had lower leakage current densities (approximately 10^-8 A/cm² at 100kV/cm) than that of BLT film (approximately 10^-6A/cm² at 100kV/cm). As no obvious difference was found in the crystal orientation or the microstructure, the enhancement of the P_rvalue 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.