Ferroelectric properties of flash evaporated barium titanate thin films

Thin films of barium titanate were fabricated by flash evaporation on Pt-coated silicon at 630 C in the thicknesses range from 30 to 300 nm. X-ray diffraction shows that the films are polycrystalline, in the tetragonal phase. Raman Spectroscopy shows the cubic phase in the 30 nut films and the tetragonal phase in the 300 nm films. The values of the refractive index obtained by spectroscopic ellipsometry indicate that the films contain, also, an amorphous phase. We think that the amorphous phase contributes to high resistivity, I-V measurements present typical resistivity values in the range of 10(11) to 10(12) Omega-cm, and that the crystalline phase is responsible of the ferroelectric behavior. The latter was observed in 300 nm thick films, showing unsaturated hysteresis loops. However, 30 nm films present rounded hysteresis loops, due to current leakage. Both cases were demonstrated by a numerical simulation of the ferroelectric capacitor, which fits the experimental measurements. The dielectric constant and loss factor are affected, also, by the amorphous character of the films.