High dielectric materials such as BST, etc. have been investigated widely for use as capacitor dielectrics in Gbit-scale DRAM (Dynamic Random Access Memory). These high dielectric materials require electrode materials because low dielectric layer is formed at interface between dielectric material and semiconductor. Noble metals such as Pt, Ru, etc. and conductive oxides such as $RuO_2$, etc. were widely used for electrode materials. But these electrodes materials have some drawbacks. Recently Ir has become a potential candidate for electrode material of ferroelectric capacitor including PZT, etc.. However Ir has rarely been reported as bottom electrode for BST thin film. Therefore we investigated the possibility of Ir as bottom electrode for BST thin film. Ir thin films were deposited on three different substrates, $SiO_2$, poly-Si & TiN/Ti/poly-Si, by DC magnetron sputtering. The Effects of deposition temperature, working pressure and power on properties of Ir thin film such as crystallinity, orientation, surface morphology, adhesion & resistivity were studied. as a results we obtain the optimum deposition condition, 400℃, 7.5mtorr and 0.09A, of Ir thin film. We investigated the effect of $O_2$ ambient annealing on surface morphology of Ir thin film. With the increase of annealing temperature surface roughness of Ir thin film abruptly increased. BST thin films were deposited at different temperatures by RF magnetron sputtering on optimized Ir bottom electrode using three substrates. Pt/BST/Ir capacitors were annealed at various temperatures in $O_2$ ambient. Pt/BST/Pt capacitor was prepared to investigate the effect of bottom electrode on electrical properties of BST capacitors. It was found that Pt/BST/Ir capacitor had electrical properties similar or superior to Pt/BST/Pt capacitor. All MIM capacitor was annealed at 650℃ in $O_2$ ambient for 30 min. and their electrical properties such as C-V, I-V were measured.
