Microstructure and dielectric properties of sputtered (Ba _0.3Sr_0.7)TiO₃ thin films with amorphous interfacial layers

Crystallization behavior, microstructure and dielectric properties of sputtered (Ba_0.3Sr_0.7)TiO₃thin films have been studied. The crystallization from as-deposited amorphous structure to equilibrium crystalline structure is confirmed as an irreversible, exothermic and first-order transition by differential scanning calorimetry. At a heating rate of 20°C/min, the exothermic peak temperature for crystallization is measured to be 697.3°C. Transmission electron microscopy results reveal layered structures of amorphous and perovskite crystalline phases in the films deposited at temperatures between 450 and 650°C. The amorphous interfacial layer diminishes with increasing substrate temperature and a well-crystallized film is found at 750°C with a dielectric loss of 0.021. Dielectric constant shows an abrupt increase to 187 for the film deposited at 750°C as a result of the fully crystallized structure. The measured dielectric constants at different temperatures are well consistent with those calculated based on the presence of amorphous interfacial layers in the films.