PREPARATION OF FERROELECTRIC THIN-FILMS OF BISMUTH LAYER STRUCTURED COMPOUNDS

Ferroelectric thin films of bismuth layer structured compounds, SrBi2Ta2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions, were formed onto a sputtered platinum layer on a silicon substrate using spin-on technique and metal-organic decomposition (MOD) method. X-ray diffraction (XRD) analysis and some electrical measurements were performed on the prepared thin films. XRD results of SrBi2(Ta-1-x, Nb-x)(2)O-9 films (0 less than or equal to x less than or equal to 1) showed that niobium ions substitute for tantalum ions in an arbitrary ratio without any change of the layer structure and lattice constants. Furthermore, XRD results of SrBi2xTa2O9 films (0 less than or equal to x less than or equal to 1.5) indicated that the formation of the bismuth layer structure does not always require an accurate bismuth content. The laver structure was formed above 50% of the stoichiometric bismuth content in the general formula. SrBi2(Ta-1-x, Nb-x)(2)O-9 films with various Ta/Nb ratios have large enough remanent polarization for nonvolatile memory application and have shown high fatigue resistance against 10(11) cycles of full switching of the remanent polarization. Mixture films of the three compounds were also investigated.