On the formation of an interface amorphous layer in nanostructured ferroelectric Ba0.8Sr0.2TiO3 thin films integrated on Pt-Si and its effect on the electrical properties

The thin films of Ba0.8Sr0.2TiO3 (BST) investigated in this work were produced by pulsed laser deposi- tion at different pulse-repetition frequencies (PRFs). First measurements by X-ray diffraction suggested a crystalline nature of the deposited films. However, scanning transmission electron microscopy and trans- mission electron microscopy images have revealed that a BST amorphous layer of considerable thickness is formed at the interface between the film and the Pt layer in the films deposited at 10 Hz. Moreover, energy-dispersive X-ray spectroscopy shows that the composition of the BST layer is the same in both the amorphous and the crystalline phases whereas Rutherford backscattering spectrometry measurements have revealed a stoichiometry of the films identical to that of the target. A new interpretation is proposed to explain the formation of this amorphous layer, based on the PRF used during the deposition. Finally, measurements of dielectric and electric properties were performed on as-grown and annealed samples. The results of these measurements are explained by a model, where a low-permittivity amorphous layer is connected in series with the crystalline BST layer.