Study On The Fabrication And Characteristics Of Bi₄Ti₃O₁₂ Thin Films For Ferroelectric Memories

Recently, there has been an increased interest in ferroelectric Bismuth Titanate (Bi₄Ti₃O₁2,BIT) thin films for ferroelectric devices, which are compatible for silicon semiconductor integrated circuits. It is important to study the preparations, microstructure and properties of ferroelectric thin films. This disseration present a theoretical and experimental investigation of preparation and properties of Bi₄Ti₃O₁2 ferroelectric thin films deposited on silicon substrate and Pt/Ti/SiO₂/Si substrate. The optimum fabrication conditions of Sol-Gel technique were investigated on the basis of the analysis of the progresses of Bi₄Ti₃O₁2 ferroelectric thin film materials. The patterns of XRD exhibited that there were not any pyrochlore phase or other second phase in Bi₄Ti₃O₁2 thin films deposited on Si substrate being annealed between 600 and 800℃ , it was otherwise in Bi₄Ti₃O₁2 thin films deposited on Pt/Ti/SiO₂/Si substrate when annealing temperature up to 800 ℃. The surface morphology of the thin films examined by SEM showed that Bi₄Ti₃O₁2 ferroelectric thin films with crack-free and compact structure had been successfully fabricated annealed at 650 ℃. It was the first time that the defects in Bi₄Ti₃O₁2 ferroelectric thin films were studied using a slow positron beam technique. The effect of annealing temperature on the defects in ferroelectric thin films was studied. The J-V characteristics of Bi₄Ti₃O₁2 ferroelectric thin films deposited on Pt/Ti/SiO₂/Si substrate was measured through metal-ferroelectric film-metal(MFM) structure. And the rectifying junction characteristics of metal-ferroelectric film and different conductive mechanism in different voltage range were discussed. The annealing temperature and substrate type dependence of ferroelectric properties is displayed through the corresponding hysteresis loops. The annealing temperature affected the size of grain and consistence of charge carrier. The ferroelectric properties of Bi₄Ti₃O₁2 thin films varied with the annealing temperature, which was affected by these facts jointly. The characterization of Bi₄Ti₃O₁2 thin films deposited on Si substrate annealed at 650℃ showed remanent polarization of 11.25μC/cm2,and coercive field of 47.2kV/cm. The asymmetry in hysteresis, lower remanent polarization and higher coercive field were due to the existence of space charge layers.