KTa0.6Nb0.4O3 Ferroelectric Thin Film Behavior at Microwave Frequencies for Tunable Applications

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Pulsed laser deposited KNbO3_3 thin films for applications in high frequency range

Potassium niobate thin films were grown by pulsed laser deposition on various substrates. Influence of deposition conditions on film characteristics was studied. Structural investigation evidenced that single phase polycrystalline randomly oriented films were grown on sintered alumina whereas epitaxial films were grown on (100)SrTiO$_3$ and (100)MgO substrates. The microstructure was highly controlled by the structural characteristics. Interdigited capacitors built from KNbO3 films on two different substrates (alumina and MgO) showed the strong influence of the structural characteristics on the dielectric behavior. The variation of the equivalent capacitance measured on the interdigital capacitor on MgO was 6.4% at 2.5 GHz while it was 1.5% on alumina, in both cases for a moderate applied field of $\sim$15 kV cm$^{-1}$. The results show the potentiality of these ferroelectric materials for use in frequency agile microwave electronics

Study of ferroelectric/dielectric multilayers for tunable stub resonator applications at microwaves

International audienceTunable coplanar waveguide stub resonators deposited on various ferroelectric/dielectric heterostructures are studied in the 10-GHz band. A frequency tunability of up to ~ 45% is achieved under a moderate biasing field (Ebias < 100 kV/cm) when the resonator is printed on KTa0.5Nb0.5O3 (KTN) ferroelectric thin film alone: this comes from the large permittivity agility of the KTN material (εr(KTN) varies from ~ 700 to ~ 200). Nevertheless this also leads to significant insertion loss due to the dielectric loss of the ferroelectric material itself (tanδr(KTN) ≈ 0.15-0.30 at 10 GHz). In this paper, an original route has been considered to reduce the device loss while keeping up a high frequency tunability. It consists in associating the KTN film with a dielectric film to elaborate ferroelectric/dielectric multilayers. The Bi1.5Zn0.9Nb1.5O7−δ (BZN) oxide material is selected here for two main reasons, namely its low dielectric loss (tanδr(BZN) ≈ 0.005-0.0075) and its moderate relative permittivity (εr(BZN) ≈ 95-125) at 12.5 GHz. The relevance of this approach is studied numerically and experimentally. We compare numerically two different heterostructures for which the ferroelectric film is grown on the dielectric film (KTN/BZN), or vice versa (BZN/KTN). A stub resonator printed on the most relevant heterostructure has been fabricated, and experimental data are discussed and compared to the numerical results

Loss reduction technique in ferroelectric tunable devices by laser micro-etching. Application to a CPW stub resonator in X-band

International audienceFerroelectric materials are known to be lossy at microwaves. A local microetching technique based on laser ablation is implemented here to reduce the insertion loss of highly tunable devices fabricated on KTa1-xNbxO3 (KTN) ferroelectric thin films. The relevance of this approach is studied in X-band by comparing numerically and experimentally the performance of a frequency-tunable coplanar waveguide stub resonator before and after KTN microetching. The experimental data demonstrate a large loss reduction (by a factor 3.3), while keeping a high-frequency tunability (47%) under a moderate biasing static electric field (80 kV/cm). This approach paves the way for the design of ferroelectric reconfigurable devices with attractive performance in X-band and even beyond

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