Microwave characterization of hydrothermally crystallized barium strontium titanate sol-gel composite thin films using a coplanar waveguide technique

Barium strontium titanate ( BST) and BST doped with 5 at% Mn films have been fabricated on gold-patterned alumina substrates by hydrothermal sol-gel composite recrystallization at < 200 degrees C. A spun-on sol-gel BST composite film is hydrothermally treated in an alkaline aqueous solution at elevated pressure. The dielectric constant and loss tangent between 5 and 40 GHz has been determined using the response of a series of coplanar waveguide spur-line band stop filters. The film shows a maximum dielectric constant between 15-40 GHz of 94 +/- 5 for a film 2.6 mu m in thickness. The loss tangent at 15 GHz is 0.07.