PREPARATION OF FERROELECTRIC THIN-FILMS OF BISMUTH LAYER STRUCTURED COMPOUNDS

Ferroelectric thin films of bismuth layer structured compounds, SrBi2T a2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions, were formed o nto a sputtered platinum layer on a silicon substrate using spin-on te chnique and metal-organic decomposition (MOD) method. X-ray diffractio n (XRD) analysis and some electrical measurements were performed on th e 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 niobiu m 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 e qual to 1.5) indicated that the formation of the bismuth layer structu re does not always require an accurate bismuth content. The laver stru cture was formed above 50% of the stoichiometric bismuth content in th e 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) cycl es of full switching of the remanent polarization. Mixture films of th e three compounds were also investigated.