Effect of bottom electrodes on resistance degradation and breakdownof (Ba,Sr)TiO3 thin films

The influence of bottom electrodes (Pt, Ir, Ru) on the degradation of (Ba,Sr)TiO₃ (BST) thin films under dc stress conditions was investigated. The current-time (I-t) and current-voltage (I-V) measurement results indicated that the BST thin films deposited on Ru have faster degradation than those deposited on Pt and Ir. The degradation was considered to be caused by the deterioration of the Schottky-barrier. Under dc stress conditions, the dielectric relaxation current in the BST dielectric films probably enhances the deterioration. The breakdown time was found to be approximated by an exponential function of an electric field t_B=α exp(-βE)] for dc stress. The value of the exponential factor β for BST deposited on Pt and Ir was about a quarter of that for BST deposited on Ru. The different value of β observed under dc stress indicates that the degradation of BST on Ru would be more serious than on Pt and Ir. The ten years lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir and Ru have longer lifetime over ten years for operation at the voltage bias of 1 V