Sr TiO Ba Based Waveguide Device _{0.7 0.3 3 Preparation And Optical Properties Of Thin Films}

Barium strontium titanate (BST) has not only excellent ferroelectric, piezoelectric, pyroelectric properties, but also good optical properties, so it has great application potentials for electro-optical and optical waveguide devices. In this paper, aundoped Ba0.7Sr0.3TiO3La-doped and Mn-doped Ba0.7Sr0.3TiO3thin films were prepared in sol-gel process.Transmittance, refractive index, and extinction coefficient of thin films were investigated. It is a theoretical foundation for applying barium strontium titanate ferroelectric thin filmin the field of optical waveguide devices and integrated optics.First of all, preparation parameters of optical BST thin film were optimized. The results show that the sol is clear, stable and suitable for coating when aging temperature is30℃and aging time is72h. When pretreatment temperature is150℃, the thin film has the best continuity, and no apparent porosity and crack exist in films. Annealed at850℃,films exhibita dense, uniform surface morphology.The maximum transmittance of the as-annealed thin film is80.72%.The maximum refractive index of the as-annealed thin film is2.13647, and the minimum extinction coefficient is4×10-5.Based on this, the effect of surfactant PVP on the quality of thin films was investigated too. When surfactant added in precursor nPVP:nTi equals to3:400, the film surface morphology with dense, uniform grain size, and no cracks was observed. The maximum transmittance of thin film with this qualityreaches87.472%.The maximum refractive index is2.3339, and minimum extinction coefficient is3.01×10-5.The experiment results show that both thin film morphology and optical properties can be improved by the optimazed preparation parameters.Secondly, La-doped Ba0.7Sr0.3TiO3films were researched.No significant morphology change was observed when the La doping concentration is low.However, with the increase of La concentration, surface morphology of the thin films gradually deteriorated. The transmittance properties of the films are improved with low La-doped concentrations. Transmittance of both0.5at.%La-BST and1.5at.%La-BST thin films is greater than80%at visible wavelengths, which is higher than intrinsic BST films. Further increase of La doping concentration leads to a decreased transmittance. Maximum refractive index of La-doped BST thin films is2.28433, and minimum extinction coefficient, lower than the intrinsic BST thin film is9.5×10-11.However, when the La doping concentrationincreases as3at.%, the extinction coefficient increases as0.00521.Finally, Mn-doped Ba0.7Sr0.3TiO3films were prepared.Low doping concentration has no significant effect on the surface morphology of thin films. With the increase of Mn doping concentration, surface morphology of the thin films gradually deteriorated. The transmittance property of0.5at.%Mn-BST thin films is greater than80%at visible wavelengths, higher than intrinsic BST films.Further increase of the Mn doping concentration results in a decreased transmittance. Maximum refractive index of Mn-doped BST thin films is2.01646.The minimum extinction coefficient of Mn-doped BST thin films is0.01804, which is bigger than that of the intrinsic BST film.