The Research Of Lithium Tantalate Thin Films By Polymeric Precursor Method

Lithium tantalate (LiTaO₃) ferroelectric thin films were prepared on the Pt/Ti/SiO₂/Si substrates by the polymeric precursor method. Ta-citric acid complex was used as a raw material instead of metal alkoxide in the Sol-Gel method. Precursor sol can be prepared in an aqueous solution, and the problem of using the metal alkoxide such as hydrolyzation, unstable and high price can be solved by using this method.The metal-carboxylate acid complexes were prepared using Ta₂O₅ as raw materials, hydroxyl carboxylic acid such as citric acid as chelating agents. The Li-Ta polymeric gels were prepared using Ta-citric acid complex in an aqueous solution with citric acid (CA) as chelating agent and ethylene glycol (EG) as esterification agent by polymeric precursor method. The research of stability of the precursor sol with different ingredient we have studied. The thermal decomposition of the Li-Ta precursor gels was studied by TG-DTA.Homogeneous Li-Ta precursor solution and gel with no precipitate can be achieved at pH=7 with the molar ratio of metal cations∶CA = 8∶1 and CA∶EG = 1∶2.The chelation between the carboxylic acid and the metal cations was characterized by Fourier transform infrared (FTIR), Raman spectroscopy and carbon nuclear magnetic resonance spectroscopy (¹³C NMR). A possible molecular structure of the metal cations and citric acid complex was proposed. During the process of preparing the films, the viscosity of the precursor sol was fixed at 13MPa·s, the rotating speed of the spin coating was 4500 r·min-1and the rotating time was 20s. The wet films were dried at 200℃, then were calcined at 400℃for 30min and finally were annealed at 600℃for 3h. The morphology and phase composition of the thin films annealed at different temperatures were characterized by scanning electronic microscope (SEM),atomic force microscope (AFM) and XRD. The resalts revealed that there was no intermediate phase formed during the heat-treatment process, which indicated that the composition of the precursor sol was homogeneous. By using this method, a...