Engineering of the frequency dependence of the ferroelectric properties of thin film Pt/Ba0.5Sr0.5TiO3/Pt structures

Engineering of a frequency dependent permittivity can be of interest for various sensor application. In this work a strong modification of the frequency dependence of the ferroelectric properties is achieved via a controlled diffusion of the metal electrode (Pt) into the ferroelectric layer ((Ba,Sr)TiO3). For this purpose a series of Ba0.5Sr0.5TiO3 layers is deposited onto Pt coated sapphire at various temperatures range from 660 °C to 760 °C. Using an additional Pt top electrode, the electronic properties of the resulting capacitors are investigated via frequency dependent cryoelectronic measurements. The structure and stoichiometry of the layers are analyzed via X-ray and Rutherford backscattering spectrometry, respectively. The analysis of the permittivity and loss tangent shows a strong frequency dependence of the permittivity in a small region of the deposition temperatures (680-710 °C), i.e. the permittivity changes from εeff≃600 at low frequency to εeff≃20 at high frequency. This behavior is caused by a partial diffusion of Pt into the ferroelectric layer and can be explained by the Maxwell-Wagner model.