Resistance degradation in barium strontium titanate thin films

Experimental and modeling results for resistance degradation in thin Ba0.5Sr0.5TiO3 (BST) film capacitors with platinum (Pt) electrodes are reported. The main experimental results are as follows. Under a constant applied voltage, the current density is observed to increase with time until it reaches a maximum value. Once the maximum value is reached, the current density becomes constant with time. The barrier height at the BST/Pt (cathode) interface is observed to decrease after prolonged electrical stressing. The resistance degradation effect is observed to be reversible, particularly at elevated temperatures. Based on the experimental results, a quantitative model for resistance degradation is proposed. In this model, the increase in the current density is attributed to a decrease in the barrier height at the cathode and this decrease is assumed to have a stretched exponential dependence on time. Using experimentally determined parameters, the model calculates the current density as a function of time at various temperatures. The calculated results are verified and the model is shown to be self-consistent. Hence the model provides an accelerated method for determining the lifetime of thin BST films at the operating conditions for advanced memory applications. (C) 1999 American Institute of Physics. [S0021-8979(99)06217-9].