Dielectric dispersion in barium strontium titanate thin film capacitors with iridium electrodes

Dielectric dispersion or relaxation results in a frequency dependent loss in capacitance. This reduces the charge storage capacity under DRAM operating conditions. In this work, the dielectric dispersion behavior of Barium Strontium Titanate (BST) thin films (compositions: Ba0.5Sr0.5TiO3 and Ba0.4Sr0.6TiO3) deposited by RF magnetron sputtering on iridium bottom electrodes was investigated. Using capacitance-frequency measurements on BST films of various thicknesses, electrode-dielectric interface effects were separated from the bulk of the dielectric film. For the BST films used in this study, the dispersion in Ba0.4Sr0.6TiO3 films was interface dominated while that in Ba0.5Sr0.5TiO3 was bulk controlled. Various multi-layered BST capacitors with combinations of the above compositions and different individual layer thicknesses were studied to verify the accuracy of the model developed for the films of each composition.