Effects of annealing sequences on ferroelectric properties of Nb-doped bismuth titanate thin films

Nb-doped Bi₄Ti₃O₁₂ (Nb-BIT) ferroelectric thin films were prepared on Pt/Ti/SiO₂/Si substrates by metalorganic solution deposition (MOSD) method. A nonionic block copolymer was used in the preparation of the precursor solutions in order to give a random orientation of crystal grains. Two annealing methods of conventional furnace annealing (CFA) and rapid thermal annealing (RTA) were compared to investigate differences in microstructures, phase formations and ferroelectric properties of the crystallized Nb-BIT thin films. Also, the effects of pre-heating at 500 °C by RTA before the final annealing steps at 700 °C were studied. The film crystallized at 700 °C by CFA with pre-heating at 500 °C by RTA showed good ferroelectric properties with random orientation and remanent polarization P_r = 26 μC/cm² at a maximum applied field of 200 kV/cm. The pulse polarizations (ΔP = P* - P∧) decreased about 30 % of initial value after being subjected to 1.5×10¹⁰ read/write cycles at a frequency of 1 MHz.