Structural and thermal analyses on phase evolution of sol–gel (Ba,Sr)TiO3 thin films

The thermal decomposition process of barium strontium titanate (BST) xerogel precursors has been analyzed using thermogravimetric analysis, Differential thermal analysis and X-ray diffraction. The results indicate that the precursors are amorphous in nature when annealed below 520 °C, and perovskite BST grains crystallize at 620 °C via a solid-state reaction between (Ba,Sr)CO3 and TiO2. It is revealed that the intermediate phase suppresses the crystallization of perovskite BST grains in films, and results in higher anneal temperature. To minimize the intermediate phase, the first three layers are crystallized prior to the deposition of subsequent layers, and 340-nm-thick perovskite BST films have been fabricated at a process temperature of 625 °C. The low process temperature results in a fine-grained structure in films, producing films that exhibit low dielectric constant and low tunability accordingly.