Investigation of BZT thin films for tunable microwave applications

BZT thin films have been investigated as a prospective material for tunable microwave applications. The thin films were deposited by RF magnetron sputtering from a Ba(Zr0.3Ti0.7)O3 ceramic target on MgO single crystal substrates. By means of Rutherford backscattering (RBS), scanning electron microscopy (SEM) and X-ray diffraction (XRD), the composition, thickness and crystallinity of the thin films were analyzed, respectively. Using interdigital capacitors (IDC) with Au electrodes on thin films, the dielectric constant and loss tangent were measured as a function of bias electric field (0–7 kV/mm) and temperature (−140 to +160 °C) at low frequencies up to 1 MHz. The influence of post-annealing on the tunable dielectric properties of the thin films was studied. Tunability, defined as τ = [ɛ(0) − ɛ(Emax)]/ɛ(0), can be significantly increased by increasing the annealing temperature. A tunability of 76% at Emax = 7 kV/mm and a loss tangent of 0.0078 have been achieved for the sample annealed at 1100 °C, measured at 1 kHz and room temperature. In addition, BZT thin films were also characterized at microwave frequencies up to 26.5 GHz by measuring coplanar waveguide (CPW) resonators.