K _x Na_1−xNbO₃ perovskite thin films grown by pulsed laser deposition on R-plane sapphire for tunable microwave devices

K _x Na_1−xNbO₃ thin films with x = 0.5 and x = 0.7 were deposited by pulsed laser deposition onto R-cut sapphire substrates to be suitable for microwave applications. The 500–800-nm-thick films present a preferential (100) orientation. The ω-scans show a weak mosaicity (full-width at half-maximum equal to 0.36° and 0.60° for x = 0.5 and x = 0.7, respectively). In addition to this texture, the in-plane ordering evidenced by X-ray diffraction φ-scan for the (100) orientation is in agreement with an epitaxial-like growth in spite of the high lattice mismatch between K _x Na_1−xNbO₃ and sapphire. The dielectric characteristics and the frequency tunability at microwave frequencies were obtained from coplanar waveguide devices (transmission lines and stub resonators). For the K_0.5Na_0.5NbO₃ and K_0.7Na_0.3NbO₃ compositions, high dielectric permittivity ε_r values of 360 and 250 and loss tangent tanδ values of 0.36 and 0.43 without biasing were retrieved from the transmission line measurements at 10 GHz, respectively. Frequency tunabilities of 15 and 12% have been assessed under 80 kV/cm biasing from stub resonator measurements for the K_0.5Na_0.5NbO₃ and K_0.7Na_0.3NbO₃ compositions, respectively. K_0.5Na_0.5NbO₃ composition is therefore a promising solution for miniaturized tunable devices at microwave frequencies.