Studied On The Preparation Of Predominantly (100)-oriented CSBT Thin Film And Its Growth Mode

Bi-layered perovskite structured ferroelectric(BLPSF) thin films have aroused much attention due to their high Curie temperature, low dielectric loss and excellent anti-fatigue property. The four-layer BLPSF, such as SrBi4Ti4O15, CaBi4Ti4O15 and three-layer BLPSF, such as Bi4Ti3O12 have become the common studied objects. Bi4Ti3O12 has a larger remanent polarization and low synthesis temperature, but with poor fatigue performance. Opposite, SrBi4Ti4O15 has good fatigue performance, although its remanent polarization is lower than Bi4Ti3O12, there are no obvious fatigue after 1011 times reversed. So, our group selected four-layer BLPSF as the research fields. At the same time, we compared SrBi4Ti4O15 with CaBi4Ti4O15. For SrBi4Ti4O15, a typical BLPSF material, even though it has lager remnant polarization and excellent anti-fatigue properties, its low curie temperature (Tc～520℃) has limited its potential applications. New ferroelectric materials with high Curie temperature and lager remnant polarization are needed urgently in recent years with the emerging of high temperature ferroelectric devices and the increasing of requirements for the high-temperature applications, On the other hand, CaBi4Ti4O15 with the same structure of SrBi4Ti4O15, has a much higher Tc (～790℃), even though its anti-fatigue properties is not ideal. In this work, we tried to combine their advantages by replacing Sr2+ with Ca2+ in SBT thin films and found that doped SrBi4Ti4O15 thin film with a composition Ca0.4Sr0.6Bi4Ti4O15 exhibits the best ferroelectric propertiesFor ferroelectric thin film in application, the magnitude of polarization is one of the most important factors characterizing its performance. It is well known that ferroelectric thin films with different orientations are very likely to exhibit different ferroelectric properties. As our studied object, Cao.4Sro.6Bi4Ti4O15is a four-layer bismuth perovskite structure materials. Its polarization vector is colser the a-axis direction, so it is very meaningful to prepare the highly a-axis preferred orientation thin film. At the same time, a more systematic study on the growth pattern of the high A-axis preferred orientation ferroelectric thin films will be very meaningful for how to control the growth orientation of the film and improve its ferroelectric performance.In this paper, we prepared the precursor solution using a sol-gel method. We studied the humidity of the environment, the chelating agent and got some conclusion. If we prepare the precursor solution when the humidity at 20% or less, the reaction temperature maintained at 20≤T(℃)<30 and acetylacetone as the chelating agent, the precursor solution will have the highest quality.We use the layer by layer annealing method combined with rapid thermal annealing in our experiment. By studied the DSC-TG of the powder, discussed the annealing temperature, we found that the thin film exhibited the best preferred orientation, the maximum remanent polarization value and the grain size of thin film samples when the thermal decomposition temperature and annealing temperature are 400℃and 800℃, respectively. And, by the test on dielectric properties of the predominantly (100)-oriented thin films, we found that the thin films can also have excellent dielectric properties, especially the capacitance-voltage characteristics in addition to the good ferroelectric properties. We also found that the reaction to change of annealing temperature was an intrinsic characteristics, there was no direct relationship with the substrate.Under the condition of special annealing process which is layer by layer annealing method combined with rapid thermal annealing, the growth patterns of the thin film is the competitive growth and epitaxial growth. By decomposing the whole process of the preparation and exploring the relation between the monolayer thickness (coating number) and the orientation of the thin film, we have known the growth mode. The reason about the appearance of the growth mode, can be attributed to the anisotropic crystal growth of bismuth layered perovskite ferroelectric materials, as well as our special annealing process. The study on the relation between monolayer thickness (coating number) and the orientation of the thin film, provides the strong evidence for our conclusion.