Crystallization, heterostructure, microstructure, and properties of ferroelectric strontium bismuth tantalate films derived from tantalum glycolate solutions

Strontium bismuth tantalate (SBT) films were prepared by chemical solution deposition (CSD) onto Pt/TiO2/SiO2/(100)Si substrates. Nominal chemical compositions of the precursor solutions of SrBi2Ta2O9, SrBi2.2Ta2O9, Sr0.8Bi2Ta2O9, and Sr0.8Bi2.2Ta2O9 were tested for the deposition of the films. Crystallization of the films was carried out by a two-step process (TS) or a single-step process (SS). The TS treatment consisted of thermal treatment of the films in oxygen atmosphere at 550 degreesC for 7200 s, with a heating rate of 8 degreesC/s, followed by a rapid thermal processing (RTP) in oxygen at a temperature of 650 degreesC for 3600 s, using a heating rate of 200 degreesC/s. The SS process was just the RTP treatment of the films. The X-ray diffraction (XRD) patterns of the crystalline films showed the formation of the layered perovskite together with a second phase. Analysis of the films by means of Rutherford backscattering spectroscopy (RBS) showed that this second phase was placed at the interface and it was formed by the reaction of the film and the substrate. Composition and thickness of this interface as well as profile composition of the SBT layer were also analyzed by RBS. These studies indicated that the heterostructure of the films was related with their nominal composition and with the type of thermal treatment used for their crystallization. Both parameters, composition and treatment, also determined the surface microstructures of the films. Dielectric and ferroelectric properties of the films were measured and related with their composition, heterostructure, and microstructure. The best hysteresis loops with the maximum values of remanent polarization, P-r, were obtained for the films with nominal composition of Sr0.8Bi2.2Ta2O9 and crystallized with the SS treatment. These films have a low fatigue up to similar to10(11) cycles, a retention of the polarization over 10(5) seconds, and leakages of <10(-7) muA/cm(2) at 300 kV/cm.