A Twofold Approach in Loss Reduction of KTa_0.5Nb_0.5O₃ Ferroelectric Layers for Low-Loss Tunable Devices at Microwaves

Abstract

Ferroelectric oxide films are attractive to design and fabricate reconfigurable and miniaturized planar devices operating at microwaves due to the large electric field dependence of their dielectric permittivity. In particular, KTaNbO (KTN) ferroelectric material presents a high tunability under moderate dc bias electric field. However, its intrinsic dielectric loss strongly contributes to the global loss of the related devices and limits their application areas at microwaves. In this paper, a twofold approach is investigated to reduce the device loss. The intrinsic loss of KTN is first reduced by doping the ferroelectric material with a low-loss dielectric material, namely, MgO. Second, the doped ferroelectric films are confined using an original laser microetching process. Both routes have been implemented here to provide a synergic effect on the total insertion loss of the microwave test device, namely, a coplanar waveguide stub resonator. The experimental data demonstrate a decrease of the intrinsic loss by a factor of ~2 and a decrease of the global loss by a factor of ~4 with a frequency tunability close to 10% at ~10 GHz under a moderate biasing (80 kV/cm).

Frequency-Tunable Slot-Loop Antenna Based on KNN Ferroelectric Interdigitated Varactors

“…This route allows reducing the global loss of antenna because the ferroelectric materials usually exhibit relatively high dielectric loss (their loss tangent tanδ is typically higher than 1%). As previously demonstrated, the global loss was reduced by a factor four by confining the ferroelectric layer into the active areas [25]. To this end, a KrF excimer laser (MLI-200, MLaser, λ = 248 nm) was used to etch the 600 nm-thick KNN layer with a 150 µm × 150 µm laser spot size and an energy of 3 mJ reduced of 45% through an optical filter.…”