Characterization of (Pb, La) TiO3 thin films prepared by the sol-gel method
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Pb(1–1.5x)LaxTiO3 thin films were synthesized by the sol-gel spin-coating technique. The films became crystallized when the spin-coated films were annealed at 600 °C and at higher temperature, and became amorphous when annealed at 550 °C. The breakdown voltage, VB, was recorded at around 30 V for 600–650 °C annealed films and varied only slightly with the composition. The VB value of the amorphous films was observed to be higher than that of the crystalline films. The ferroelectric properties of both the amorphous and crystalline films were found to be similar. The dielectric constant, charge storage density and optical index of refraction of the films were ɛr=5–20, Qc=0.12–0.54 μC cm−2 and n=1.6–2.3, respectively. They all increased moderately with La3+ content in the films. One possible reason why the ferroelectric properties are not modified as the amorphous films crystallize, may be that the octahedra are equilateral, whether the films are amorphous or crystalline. Additionally, a possible cause which lowers the breakdown voltage in crystalline film, is the formation of lead vacancies due to lead loss. The electrical properties of films coated on bare silicon become significantly lowered due to interdiffusion between films and substrate. The diffusion of Si4+ ions into-the films can be prevented by coating SrTiO3 on the silicon substrate as a buffer layer. The charge storage capacity consequently becomes substantially enhanced.
KeywordsDielectric Constant Buffer Layer Breakdown Voltage Ferroelectric Property TiO3 Thin Film
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