Thin films and multilayers based on KTN ferroelectric and BZN dielectric oxides for microwave devices
This work aims to develop, in thin film form, integrated structure based on tunable materials such as ferroelectrics and relaxor dielectrics for microwave devices. These applications require materials with large permittivity, low dielectric loss, low leakage current and high tunability (variation of the permittivity associate to the applied electric field). The work focused on the ferroelectric material KTa1-xNbxO3 (KTN) which have shown potentialities to be integrated in such devices and a relaxor dielectric material Bi1,5-xZn0,9-yNb1,5O7-d (BZN). The study was first dedicated to the structural, microstructural and physical characterizations of each material separately. Dielectric properties were measured at low frequencies (100 kHz) and high frequencies (1 GHz to 67 GHz) on undoped and MgO doped KTN. A structural and microstructural dependence of the dielectric and optical properties of BZN thin films was shown. Finally, the two materials were associated on multilayer heterostructures by two deposition methods (pulsed laser deposition (PLD) and chemical solution deposition (CSD). Dielectric measurements performed on these BZN/KTN/substrate multilayers evidenced that the dielectric losses were reduced by 76 % at low frequencies and 21 % at high frequencies. These multilayers present a tunability closed to 3 % at 22 kV/cm, i.e. a higher value than the one measured on other ferroelectric materials at the same electric field.