Evaluation of the (Ba,Sr)RuO3 and (Ba,Sr)RuO3/Ru bilayer as an oxygen diffusion barrier

The (Ba,Sr)RuO3 (BSR) oxide electrode which can enhance electrical properties of (Ba,Sr)TiO3 (BST) dielectric film due to structural and chemical matches with BST, was evaluated as an oxygen diffusion barrier. It was possible to restrain the oxidation of TiN layer under BSR to TiO2 by sequential depositions of amorphous BSR and crystalline BSR, in which the amorphous BSR eventually crystallized into crystalline BSR during the deposition of crystalline BSR. When two-step BSR layers on TiN, however, were annealed in oxygen ambient at 700 °C, oxygen atoms diffused and oxidized TiN layer to TiO2. On the other hand, oxygen could be effectively blocked by the BSR/Ru bilayer. In this system, the Ru sublayer plays a role as an oxygen getter and the bilayer tends to block oxygen diffusion. The blocking effect was more obvious when the thickness of BSR in the bilayer increased. The BST/bilayer showed higher dielectric constant due to the suppression of formation of a low dielectric layer between BST and the bilayer. Although the BST/bilayer showed a slightly higher leakage current density, it was possible to reduce the leakage current density to 10−8 order A/cm2 at 1 V by increasing the BSR thickness in the bilayer.