The effect of annealing on the microwave properties of Ba0.5Sr0.5TiO3 thinfilms

Oriented, single phase thin films (similar to 5000 Angstrom thick) of Ba0.5 Sr0.5TiO3 (BST) have been deposited onto (100) MgO and (100) LaAlO3 (LAO) s ubstrates using pulsed laser deposition. The capacitance and dielectric Q ( 1/ tan delta) of as-deposited and annealed films have been measured from 1 to 20 GHz as a function of electric field (0-80 kV/ cm) at room temperature using interdigitated Ag electrodes deposited on top of the film. For films deposited onto MgO, it is observed that, after a postdeposition anneal (10 00-1200 degrees C), the dielectric constant decreases and the dielectric Q increases. For films deposited onto LAO, a postdeposition anneal (less than or equal to 1000 degrees C) resulted in a significant increase in the diel ectric constant and a decrease in Q. The observed dielectric properties of the BST films are attributed to the changes in film stress, which affects t he extent of ionic polarization. (C) 1999 American Institute of Physics. [S 0003-6951(99)03307-0].