Characterization of doped BST thin films deposited by sol-gel for tunable microwave devices.

BST thin films with various dopants were grown by the sol-gel method on platinized silicon and MgO substrates. Their dielectric properties were investigated at low frequency (up to 1 MHz) on silicon with parallel-plate capacitors and at high frequency (up to 15 GHz) with interdigitated capacitors on MgO substrate. The results depend on the nature of the dopant and show that Mg is a very good candidate to reduce dielectric losses. On the other hand, K is a good candidate as dopant of BST thin film to drastically increase the tunability.