Effect of bottom electrode materials on the electrical and reliability characteristics of (Ba, Sr)TiO/sub 3/ capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO/sub 3/ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO/sub 2//Ir, Ru, RuO/sub 2//Ru) before and after annealing in O/sub 2/ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500/spl deg/C, after 700/spl deg/C annealing in O/sub 2/ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9/spl times/10/sup -8/ A/cm/sup 2/ at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC//spl mu/m/sup 2/ at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO/sub 2//Ir, Ru, and RuO/sub 2//Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V.