Ferroelectric Properties of Tungsten-Substituted Bi₄Ti₃O₁₂ Thin Film Prepared by Sol–Gel Method

Bi₄Ti₃O₁₂ (BIT) and tungsten-substituted Bi₄Ti₃O₁₂ (BTW) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel method. There are differences in the ferroelectric properties and grain strucure between BIT and BTW thin films. The crystal structure and the surface grain morphology were characterized by scanning electron microscopy and X-ray diffraction. Grains of BIT were grown with c-axis preferred orientation, while these of the BTW were randomly distributed. The ferroelectric properties and polarization fatigue characteristics were confirmed by the P-E hysteresis loops. The BTW thin film was measured to have remanent polarization (2P_r) of 27 µC/cm² and a coercive field (2E_c) of 130 kV/cm. The dielectric constant and loss tangent at 1 MHz were measured as 210 and 0.05, respectively. On adding a small amount of tungsten in Bi₄Ti₃O₁₂, the remanent polarization increased and fatigue resistance improved.