Effects of growth temperature and film thickness on the electrical properties of Ba0.7Sr0.3TiO3 thin films grown on platinized silicon substrates by pulsed laser deposition

Barium strontium titanate Ba_0.7Sr_0.3TiO₃ (BST) thin films, with different growth temperatures (T_g) as well as different film thicknesses, have been prepared on Pt/Ti/SiO₂/Si substrates by a reactive pulsed laser deposition method. We observed strong dependences of dielectric properties, such as the Curie-Weiss temperature, dielectric constant, loss tangent, dielectric tunability and leakage current, on the T_g and the BST film thickness. With increase of T_g from 630 to 750 °C, the dielectric constant gradually increases due to the increase in the crystallinity and the grain size. However, the dielectric tunability, loss tangent and leakage current characteristics drastically degrade when the T_g increases up to 750 °C, due to the diffuse and rough interface. The BST film grown at 690 °C shows the best overall dielectric properties with a figure-of-merit of 33 (at 400 kV/cm). These results suggest that film growth process could be optimized by systematically investigating the structure-property relationships. Furthermore, as the BST film thickness increases from 250 to 560 nm, the dielectric properties are remarkably enhanced. The film thickness effect is attributed to the interfacial low-dielectric layers (the so-called “dead layer”) between the BST film and both metal electrodes, which is well explained in terms of a series capacitor model. The thickness and the average dielectric constant for the dead layer are experimentally estimated to be 1.9 nm and 20.3, respectively, in Pt/BST/Pt capacitors.