K x Na1−xNbO3 perovskite thin films grown by pulsed laser deposition on R-plane sapphire for tunable microwave devices

K x Na 1-x NbO 3 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-x NbO 3 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 0.5 Na 0.5 NbO 3 and K 0.7 Na 0.3 NbO 3 compositions, high dielectric permittivity e r values of 360 and 1 250, and loss tangent tanδ values of 0.36 and 0.43 without biasing were retrieved from the transmission lines 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 0.5 Na 0.5 NbO 3 and K 0.7 Na 0.3 NbO 3 compositions, respectively. K 0.5 Na 0.5 NbO 3 composition is therefore a promising solution for miniaturized tunable devices at microwave frequencies.