Coating of planar Barium-Strontium-Titanate thick-film varactors to increase tunability

Scaled varactors on a Barium-Strontium-Titanate (BST) thick-film are produced and characterized. The tunability of the scaled varactors is measured at up to 12.5 V/mum effective tuning field-strength in the planar varactors´ air gap. To increase the effective tuning field-strength without breakdown and therefore to increase the tunability of the varactor the planar structure is covered with Parylene. As a result of the Parylene coating, a tuning field-strength of up to 29 V/mum can be applied to the varactors´ gap which results in a capacitance tuning of 44.5 %. The humidity dependency of the quality factor of BST components based on porous thick-film can be eliminated. By sealing the porous surface, the quality factor of the varactors is significantly increased.