Design of a hybrid ferroelectric thin film varactor for tunable microwave applications

A hybrid ferroelectric thin film varactor device architecture is presented that allows for integrating the features of both structures of coplanar and parallel-plate varactors. In the hybrid varactor structure, a high-resistivity ZnO ultra-thin film is used as dc bias bottom electrode and at the same time the electrode does not contribute in the electric field distribution of microwave signal. The frequency response of the proposed hybrid varactor with the outer dc bias structure is characterized and its analysis shows that the high-resistivity thin film layer is serving as a dc bias path for high tunability. The fabricated hybrid barium strontium titanate thin film varactor exhibited low capacitance and improved tunability compared with the conventional coplanar varactor.