Dielectric properties and microstructure of nano-MgO dispersed Ba0.3Sr0.7TiO3 thin films prepared by sputter deposition

In this study, thin films prepared from the targets of Ba0.3Sr0.7TiO3 (BST), BST/5 mol % MgO, BST/10 mol % MgO, and BST/20 mol % MgO composites, using radio frequency magnetron sputtering, have been reported. As-deposited films were found to be amorphous and began to crystallize after annealing at temperatures of 650 deg. C and above. The addition of MgO in the BST films resulted in the hindrance of crystallization and inhibition of grain growth. MgO was substituted into the BST lattices to a certain degree. High-resolution transmission electron microscopy results revealed some MgO dispersed in the BST matrix. The MgO dispersed in the dense BST matrix was found to be around 25 nm in size. The dielectric constant was estimated to be 90 for the pure BST film annealed at 700 deg. C, and observed to be slightly reduced with the MgO addition. The dielectric losses of the Ba0.3Sr0.7TiO3 (0.006) and BST/MgO films (0.002-0.004) were much less than those of the Ba0.6Sr0.4TiO3(0.013) and Ba0.7Sr0.3TiO3 films (0.11-0.13). The leakage current was smaller for the BST/10 mol % MgO film compared to the pure BST film and this low leakage current may be attributed to the substitution of Mg in the B sites of BST lattices which might have behaved as an electron acceptors