Resistance degradation in barium strontium titanate thin films

Experimental and modeling results for resistance degradation in thin Ba0.5S r0.5TiO3 (BST) film capacitors with platinum (Pt) electrodes are reported. The main experimental results are as follows. Under a constant applied volt age, the current density is observed to increase with time until it reaches a maximum value. Once the maximum value is reached, the current density be comes constant with time. The barrier height at the BST/Pt (cathode) interf ace is observed to decrease after prolonged electrical stressing. The resis tance degradation effect is observed to be reversible, particularly at elev ated 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 ca thode and this decrease is assumed to have a stretched exponential dependen ce on time. Using experimentally determined parameters, the model calculate s the current density as a function of time at various temperatures. The ca lculated results are verified and the model is shown to be self-consistent. Hence the model provides an accelerated method for determining the lifetim e of thin BST films at the operating conditions for advanced memory applica tions. (C) 1999 American Institute of Physics. [S0021-8979(99)06217-9].