Sr content dependence of ferroelectric properties in SrBi2Ta2O9 thin films

The effects of Sr deficiency to the ferroelectric properties and microstructure of SBT thin films prepared at 700 or 800 degrees C were investigated. The maximum 2Pr was obtained at Sr deficiency of 20% for both prepared at 700 degrees C and 800 degrees C. We obtained 12.5 mu C/cm(2) of 2Pr for the films with 20% Sr deficiency prepared at 700 degrees C. Films with 20% Sr deficiency showed the most serious polarization fatigue for films prepared at 800 degrees C while capacitors prepared at 700 degrees C were in breakdown at around 10(6) - 10(7) cycles. XRD analysis revealed that the film orientation changed with Sr deficiency and that formation of a 2nd phase was enhanced by Sr deficiency. Both the orientation change and the 2nd phase were thought to be the origin of 2Pr decrease in the range from 20% to 60% Sr deficiency. The grain growth suppression and the void generation of the stoichiometric films were remarkably improved with decrease in Sr content from 1.0 to 0.8. This would contribute to the. 2Pr increase with decrease in Sr content in the range from 1.0 to 0.8. The fatigue properties dependent on Sr content were explained by the Sr defect density in the SBT crystallites.