Effect of bottom electrode materials and annealing treatments on the electrical characteristics of Ba0.47Sr0.53TiO3 film capacitors

Abstract

The dielectric constant and leakage current density of Ba0.47Sr0.53TiO3 (BST) thin films deposited by radiofrequency magnetron sputtering on various bottom electrode materials (Pt, Ir, IrO2/Ir, Ru, RuO2/Ru) before and after annealing in O-2 and N-2 ambient were investigated. Improvement in crystallinity of BST films deposited on various bottom electrodes was observed with annealing. The refractive index, dielectric constant, loss tangent, and leakage current of the films were also strongly dependent on annealing conditions. A BST thin film deposited on an Ir bottom electrode at 500 degrees C, after 700 degrees C annealing in O-2 for 20 min, had a dielectric constant of 593 +/- 5%, a loss tangent of 0.019 +/- 10% at 100 kHz, a leakage current of (2.1 +/- 13%) x 10(-8) A/cm(2) at an electric field of 100 kV/cm with a delay time of 30 s, and a charge storage density of 53 +/- 5% fC/mu m(2) at an applied field of 150 kV/cm. Based on the dielectric constant, leakage current, and reliability, the optimum material for the bottom electrode with annealing was Ir, Interdiffusion of Ru and Ti at the interface between the BST film and Ru electrode was observed in 500 degrees-700 degrees C annealed samples. The 10 year lifetime of time-dependent dielectric breakdown (TDDB) studies indicated that BST on Pt, Ir, IrO2/Ir, Ru, and RuO2/Ru had long lifetime over 10 years of operation at a voltage bias of 1 V.