Theoretical Investigation On Dynamic Dielectric Properties Of Ferroelectric Thin Films

Ferroelectric has already attracted the widespread attentions in the world of physics and materials, but since ferroelectric is not easy to make to thin film, and it is not compatible with the semiconductor, it has been no more development. With the advancement of material processing techniques, it is possible to make ferroelectric thin films. We can make ferroelectric into thin film through some special methods. The investigation of ferroelectric materials become to the ferroelectric thin film.Due to the restrictions of the preparing technologies, there will be impurities, defects, interfacial stress in the surface layer of the ferroelectric thin film, it made the thin film show a non-uniform system in the vertical direction on the surface and resulting in the uneven distribution of spontaneous polarization. This surface layer is called the imperfect surface layer. It makes the properties of ferroelectric thin film different from the three-dimensional ferroelectric and the thin film is more practical value.The practical application of ferroelectric thin film has a variety of structures, but the main structure in the form is caught in two electrodes. The electrode can be Metal and semiconductor material. Because the reality of the current is ac electric field generally. Therefore, a single discussion of the dielectric properties of DC electric field can no longer meet the people's needs. This paper is to study the dielectric properties of ferroelectric thin film which contains imperfect surface layer in AC electric field. In the study, we proceed from the soft mode theory in mean-field approximation and the dielectric response theory of ferroelectric thin film. Taking into account the second-order ferroelectric phase transition, we discuss the dielectric susceptibility along with the position, the specific inductive capacity correlative with the frequency of the external electric field and the phase transition temperature in AC electric field.Through theoretical calculation and graphical analysis, we found that when the imperfect surface layer is thick, the dielectric susceptibility distribution curve along with the position is smooth. It is close to the ideal material. The existence of the imperfect surface layer can reduce the specific inductive capacity, with the increase of the thickness of the imperfect surface layer, the dielectric dissipation fraction of the ferroelectric thin film becomes large. And the phase transition temperature has decreased with the increase of the imperfect surface layer's thickness. Therefore, because of the imperfect surface layer, rising the dielectric susceptibility along with increasing the dielectric dissipation.The ferroelectricity can be seen only after considering the interaction, but when the interaction is strong, the specific inductive capacity is low and the phase transition temperature is low too which is detrimental to the stability of the ferroelectric phase.For our investigation, the frequency will be real only after considering the effects of non-harmonic. The damping coefficient reflected the strength of the effects of non-harmonic. The damping coefficient's increment will decrease the dielectric susceptibility.In AC electric field, both the real part and the imaginary part of the specific inductive capacity will change with the temperature's variation. With the increase of the frequency, the dielectric susceptibility will become larger and the phase transition temperature will be lower. When the frequency reaches a certain value, polarization will appear reversal. We should make discussing in the low electric field.Through theoretical investigations, we have concluded that changing parameters will influence the dielectric susceptibility and the specific inductive capacity. It points out that how to get the ferroelectric thin film which has the larger specific inductive capacity, the higher phase transition temperature and the small dielectric dissipation through controlling experimental conditions. It's good for preparation the ferroelectric thin film in experiment. It provides the theoretical foundation in order to get the better experimental data.