DIELECTRIC-DISPERSION IN BARIUM STRONTIUM-TITANATE THIN-FILM CAPACITORS WITH IRIDIUM ELECTRODES

Dielectric dispersion or relaxation results in a frequency dependent l oss in capacitance. This reduces the charge storage capacity under DRA M operating conditions. In this work, the dielectric dispersion behavi or of Barium Strontium Titanate (BST) thin films (compositions: Ba0.5S r0.5TiO3 and Ba0.4Sr0.6TiO3) deposited by RF magnetron sputtering on i ridium bottom electrodes was investigated. Using capacitance-frequency measurements on BST films of various thicknesses, electrode-dielectri c interface effects were separated from the bulk of the dielectric fil m. For the BST films used in this study, the dispersion in Ba0.4Sr0.6T iO3 films was interface dominated while that in Ba0.5Sr0.5TiO3 was bul k controlled. Various multi-layered BST capacitors with combinations o f the above compositions and different individual layer thicknesses we re studied to verify the accuracy of the model developed for the films of each composition.