Ba0.6Sr0.4TiO3 (BST) thin films were fabricated on Pt coated Si (100) substrates by sol-gel techniques with molar ratio of (Ba+Sr) to Ti changing from 0.76 to 1.33. The effect of (Ba+Sr)/Ti ratio deviating from the stoichiometry on microstructure, grain growth, dielectric and tunable properties of BST thin films were investigated. TiO2 and (Ba,Sr)2TiO4 were found as a second phase at the ratios of 0.76 and 1.33, respectively. The variation of the ratio reveals more significant effect on the grain size in B-site rich samples than that in A-site rich samples. The dissipation factor decreases rapidly from 0.1 to 0.01 at 1 MHz with decreasing (Ba+Sr)/Ti ratio. The tunability increases with decreasing ratio from 1.33 to 1.05, and then decreases with decreasing ratio from 1.05 to 0.76. The film with (Ba+Sr)/Ti ratio of 1.05 has a maximum tunability of 32% and a dissipation factor of 0.03 at 1 MHz.
