Ferroelectric and microstructure properties of Ba1-xSrxTiO3 films grown on different electrodes

Ferroelectric Ba1-xSrxTiO3 thin films were deposited by pulsed laser ablation on SiO2/Si, RuO2/Ta/SiO2/Si and Pt/Ti/SiO2/Si substrates. The films were weakly crystalline in the as-deposited condition and subsequent crystallization was induced by annealing the films in the range of 550-650 degrees C. The BST films deposited on Pt/Ti/SiO2/c-Si substrates presented wide cracks that were promoted during the annealing process due to the thermal expansion mismatch between the BST films (alpha(BST) = 4 x 10(-6) degrees C-1) and the Pt (alpha(Pt) = 9 x 10(-6) degrees C-1). Smooth films showing slightly crackeded areas were obtained on SiO2/c-Si and RuO2/Ta/SiO2/Si substrates. The ruthenium oxide thermal expansion coefficient is alpha(RuO2) = 5.2 x 10(-6) degrees C-1. A cross-sectional analysis at the ferroelectric/substrate interface showed that for the lower annealing temperature (550 degrees C) a mixed amorphous/nanocrystalline microstructure is formed. For temperatures above 600 degrees C a randomly oriented polycrystalline material is obtained. However, an amorphous layer of 4-6 nm still remains on the substrate even after heat-treatments up to 650 degrees C. The dielectric constant of the BST films varied in the range of 30-325.