The processing and properties of barium strontium titanate thick films for use in frequency agile microwave circuit applications

Barium strontium titanate (BST) thick films for use in frequency agile microwave circuit applications have been investigated. A potentially cost-effective processing route has been used to make BST thick films from mixed-oxide powders. BST thick films have been press-formed in a single step onto alumina substrates from a viscous polymer tape. Films with thicknesses ranging from 10 to 140 μm have been obtained. The microstructure and dielectric properties of the BST thick films have been characterised. The results show that Ba0.7Sr0.3TiO3 thick films exhibit ∼20% tunability at room temperature under a DC bias field of 5.5 kV/cm. Possibilities for further improvements are discussed in terms of reducing the interactions between the BST films and alumina substrates.