Interactions between barium strontium titanate (BST) thick films and alumina substrates

Barium strontium titanate (BST) thick films have been prepared on alumina substrates using a novel press forming route. The effect of the sintering temperature on the microstructure and dielectric properties of the films has been investigated. Severe interactions between the BST films and alumina substrates has been observed for sintering temperatures >1250 °C, with Ba and Sr ions diffusing into the substrates. The counter-diffusion of Al ions into the films resulted in the formation of strontium aluminate and the destabilisation of the BST solid solution. The use of B2O3 as a sintering aid and MgO as a buffer layer is also reported and discussed. MgO is shown to be effective in preventing inter-diffusion between the films and substrates and, although B2O3 is effective in reducing the sintering temperature and improving the dielectric properties of the films, it is not compatible with the current thick film processing route.