The Fabrication Of (Bi, Nd)₄ Ti₃O₁₂ Thin Films By Sol-gel Process And Their Ferroelectric Properties

Recently, rare-earth lanthanides doped Bi4Ti3Oi2 (BIT) with Bi-layered perovskite structure has been studied intensively for potential applications in ferroelectric random access memories (FeRAM) due to its relatively low crystallization temperature, good fatigue endurance and larger spontaneous polarization compared to SrBi2Ta2O9 (SBT)-based films. However, in order to replace the conventional lead-based materials, which are the most widely used material today for FeRAMs, a lower-processing temperature, large remanent polarization and inherent high-fatigue endurance are required.In this thesis, neodymium (Nd)-doped Bi4Ti3O12(Bi3.15Nd0.85Ti3O12, BNT) ferroelectric films have been deposited on Pt/Ti/SiCVSi substrates by a sol-gel process and crystallized in nitrogen, air and oxygen environments respectively at different temperature. We have studied the effect of crystallization environment and crystallization temperature on the structural, surface morphology, electrical, leakage current and fatigue properties of BNT films. The crystallization environment was found to be important in determining the crystallization and ferroelectric properties of the BNT films. The film crystallized in nitrogen at a relatively low temperature of 650 Cexhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr = 63.6uC/cm2, a coercive field of 130 kV/cm and a fatigue-free characteristic. While the films annealed in air and oxygen did not show good crystallinity and ferroelectricity until they were annealed at 710 C and 730 C, respectively. These results indicated that the crystallization temperature is lowered significantly when the BNT films were annealed in N2, compared with those annealed in air or O2.Moreover, the remnant polarization and dielectric constant of the BNT films crystallized in N2, O2, and air environment, respectively, are not a monotonous function of the crystalline temperature, but decrease as the annealing temperature increases after an optimal crystalline temperature reaches for each case. A positive correlation between the remnant polarization and dielectric constant of the BNT films has been observed.