Improvement of dielectric loss tangent of Al₂O₃ doped Ba_0.5Sr_0.5TiO₃ thin films for tunable microwave devices

摘要

AlO doped BaSrTiO (BST) thin films, with different Al2O3 contents, were deposited on (100) LaAlO substrates by the pulsed laser deposition technique to develop agile thin films for tunable microwave device applications. The dielectric properties of AlO doped BST films were determined with a nondestructive dual resonator near 7.7 GHz. We demonstrated that the AlO doping plays a significant role in improving the dielectric properties of BST thin films. The Al2O3 doping successfully reduced the dielectric loss tangent (tan δ) from 0.03 (pure BST) to 0.011 (AlO doped BST). Reduction in the loss tangent also leads to reduction in the dielectric constant and dielectric tunability. Our results showed that the BSTA4 film remains tunability=15.9%, which is sufficient for tunable microwave devices applications. Consequently, the AlO doping improved the figure of merit () for the BST films from =7.33 (pure BST) to =14.45 (AlO doped BST).