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

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Abstract
Oriented, single phase thin films (∼5000 Å thick) of Ba 0.5 Sr 0.5 TiO 3 (BST) have been deposited onto (100) MgO and (100) LaAlO 3 (LAO) substrates using pulsed laser deposition. The capacitance and dielectricQ (1/ tan δ) of as-deposited and annealedfilms 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 filmsdeposited onto MgO, it is observed that, after a postdeposition anneal (1000–1200 °C), the dielectric constant decreases and the dielectricQ increases. For filmsdeposited onto LAO, a postdeposition anneal (⩽ 1000 °C) resulted in a significant increase in the dielectric constant and a decrease in Q. The observed dielectric properties of the BST films are attributed to the changes in film stress, which affects the extent of ionic polarization.