Performance of frequency-agile CPW resonators on thin film ferroelectric material

Tunable coplanar stub resonators have been investigated numerically and experimentally in X-band. They are fabricated on KTa_0.5Nb_0.5O₃ (KTN) ferroelectric layers with various thicknesses ranging between 125 nm and 1460 nm. The impact of the KTN thickness on the device performance (frequency tunability and insertion loss) is studied experimentally. A maximum frequency agility of 54% is reached under a moderate DC external electric field (E_bias~80 kV/cm) for the 1100 nm-thick sample. We also show that the global loss of the device can be divided by a factor 3.2 by confining the ferroelectric layer around the stub only, while keeping up a large frequency agility (47%).