Preparation Of BET Thin Film By MOD Method And Characterization Of Residual Stress With Raman Spectroscopy

With prominent ferroelectric properties such as high polarization value, negligible polarization fatigue,high Curie temperature and low leakage current, bismuth layered structure materials(BLSF)are proper to apply at high temperature and high frequency conditions,and they have attractive application in ferroelectic memory fields.With the development of micro-electric technology and the tendency of high integration,more and more reseaches are foused on the preparation and properties of BLSF ferroelectric thin films.The ferroelectric properties of ferroelectric thin films and stability ofthin film apparatus depend on their residual stresses.It is important for us to characterize the residual stresses of ferroelectic thin films.In chapter 1 of the master thesis,the general situation and potential application of ferroelectric thin film,preparation methods,the research status for ferroelectric thin film and the theory and application of Raman spectroscopy Were reviewed.On the basis,the dependences on the technology of metal-organic decomposition(MOD) method and the measurement of residual stress of thin films with Raman spectroscopy were proposed.Inchapter 2,the new BLSF Bi_4-xEu_xTi₃O₁₂(BET)thin films with x=0,0.75,0.85, 1 were prepared by MOD method and annealed at 600,650,700,750 and 800℃.The process of preparation and the processing conditions,such as annealing temperature and Eu-doping amount,were introduced in detail.In chapter 3,the effects of annealing temperature and Eu-doping amount on the microstructure of BET(x=0,0.75,0.85,1)were investigated by X-ray,diffraction (XRD),scanning electron microscopy(SEM)and Raman spectra;In chapter 4,the effects of annealing temperature and Eu-doping amount on ferroelectric properties were studied by Precision Workstation ferroelectric tester.The best processing conditions,which were x=0.85 and 700℃annealing temperature, were ascertained.The remanent polarization of BET(x=0.85)thin-film annealed at 700℃is 81.7μC/cm² under 300kV/cm applied electric field,and leakage current density is 1×10^-8A/cm² under 5V applied voltage.After 9×10⁹ switching cycles at±5V,there is no significant 2P_r loss for BET(x=0.85)thin film annealed at 700℃.In chapter 5,the Raman spectra of BET(x=0.85)thin films under applied stresses were measured and analyzed.The residual stresses of BET(x=0.85)thin films were obtained with Raman spectroscopy based on the linear relationship between the stress and the square of Raman frequency.The obtained residual stresses are tensive stress,and increase with annealing temperature.Additionally,the relationships between residual stress,annealing temperature and remanent polarization were discussed.