Structural and Electrical Properties of Ba0.5Sr0.5TiO3 Films on Ir and IrO2 Electrodes

High-dielectric Ba0.5Sr0.5TiO3 (BST) thin films are grown on Ir and IrO2 electrodes by a rf sputtering method. The structural and electrical properties of BST films are investigated. After postannealing at 750° C for 30 min in N2 atmosphere, the interface between BST and IrO2 remains flat and the IrO2 does not show any structural change. On the other hand, a thin IrO2 layer is formed at the interface between the BST and Ir after the same post-annealing. A larger grain size of BST film is obtained on the Ir electrode compared to that of BST film on the IrO2 electrode. Dielectric constants of 36-nm-thick BST films on Ir and IrO2 are 338 and 290, respectively. The leakage current densities of both the Pt/BST/Ir and Pt/BST/IrO2 capacitors are about 20 nA/cm2 at ±1.5 V, which is sufficiently small for application to dynamic random access memory devices.