Diffuse phase transition of BST thin films in the microwave domain

Ferroelectric materials are widely used in the paraelectric phase in order to realize tunable capacitors with reduced losses and low hysteresis effect. Nevertheless, for polycrystalline thin films, the ferro/paraelectric phase transition can be diffuse and some crystallites can exhibit a ferroelectric nature even if the sample seem to be globally in a paraelectric phase. In this case, domain wall motions are responsible for the sensitivity of the dielectric properties to the driving field and are very dissipative phenomena. In this paper, we evaluate, in the high-frequencies band, the ferroelectricity impact on the properties of BST thin films near the phase transition, by measuring the film's dielectric properties as a function of the incident RF power and for different temperatures.