Characteristic Crystallization And Properties Of PbMg_1/3Nb_2/3O₃-PbTiO₃ Ferroelectric Film

It is main bottleneck to prepare Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) film with pure perovskite structure on Pt/Ti/SiO2/Si substrate, which restricts to its application. The article foucs on the effect and mechanisms of phase composition of PMN-PT film that deposited on Pt/Ti/SiO2/Si when the TiO₂ as the seed layer. The TiO₂ seed layer was prepared by radio frequency (RF) magnetron sputtering and annealed by rapid thermal annealing (RTA). The PMN-PT films were prepared by RF magnetron sputtering and pulse laser deposition (PLD) technique. The thickness and sputtering ratio of the TiO₂ seed layer was characterized by small angle X-ray scattering (SAXS). The phase composition of the films was characterized by X-ray Diffraction (XRD). The surface morphologies and grain size of thin films were observed by using scan electron microscope (SEM) and atomic force microscope (AFM). In addition, ferroelectric and dielectric properties of the films were also studied. The effect of the TiO₂ seed layer of on ferroelectric and dielectric properties of the film was discussed.The results of X-ray diffraction showed that it is very difficult to deposit PMN-PT film with pure perovskite phase structure on Pt/Ti/SiO2/Si substrate by RF magnetron sputtering. In RF magnetron sputtering methods, the proper parameters such as working gas, target-substrate distance, annealing temperature and time have important effects on the formation of perovskite. With the help of different thickness of the amorphous TiO₂ seed layer, PMN-PT films with the pure perovskite phase structure are formed. The effect of amorphous and crystallized TiO₂ seed layer on phase composition of the film is different. When the TiO₂ seed layer was crystallized, the pure perovskite phases were observed at the annealing temperature of as low as 550℃and the relative intensity of (110) diffraction peak of perovskite phase increased in PMN-PT film.As far as PMN-PT film deposited by PLD is concern, there are no perovskite phases in PMN-PT films without the seed layer at substrate temperature in range of 575⁶50℃. With the TiO₂ seed layer, PMN-PT film with pure perovskite phase structure is obtained at substrate temperature of 575℃.The study found that the pure perovskite phases were obtained by RTA when the thin film deposited at room temperature. The seed layers have an important effect on phase structure for PMN-PT film with different thickness. Without the TiO₂ seed layer, the pure perovskite phase could be obtained in the thinner PMN–PT film while with the TiO₂ seed layer, and the pure perovskite phase was formed in the thicker PMN–PT film.In order to increase the content of perovskite phase in film and decrease crystallization temperature of the film, the article propose a new two step annealing technology for thin film that the films were firstly annealed at low temperature and subsequently annealed at relatively high temperature. The research results showed that as far as the film annealed by two step annealing, without the seed layer, (100)-texture films were obtained at the thickness of below 200nm. With the seed layer, (110) texture-films were obtained at the range of from 200nm to 360nm. The PMN-PT films with the TiO₂ seed layer treated by two step annealing showed highly (100)-textured.AFM results revealed that the TiO₂ seed layer contributed to the decrease of the roughness of the film. The results of SEM showed that whether the RF magnetron sputtered or pulse laser deposited film, crystallized TiO₂ seed layer was helpful to the growth of size of crystalline grain of PMN-PT film and denser than PMN-PT film without the seed layer. The article believed that the TiO₂ seed layer held back the pyrochlore phase by prevent deleterious phase at the interface together with all kinds of phase analysis results of film.Ferroelectric properties measurement showed that pyrochlore phase seriously affected the ferroelectric properties of PMN-PT film. The TiO₂ seed layers increased remnant polarization and decreased coercive field. With the thickness of the film increasing, the remnant polarization also increased. Two step annealing technology leaded to increase of remnant polarization decrease of coercive field.The results of dielectric properties revealed that with the TiO₂ layer dielectric constant increased. Besides, two step annealing technology can improve significantly the dielectric constant.