Improvement of Ba0.5Sr0.5TiO3 Thin Films Microwave Properties using Codoping with Mg-W and Al-W

Codoped (Al-W and Mg-W) Ba0.5Sr0.5TiO3 (BST-0.5) thin films are deposited on ceramic alumina (Al2O3) substrate by pulsed laser deposition (PLD). Al-W and Mg-W doped target are prepared by using a piece of material (Al2O3 and MgO respectively) placed on a 10%wt WO3 doped BST-0.5 target, undoped BST-0.5 thin films are fabricated using a pure BST-0.5 target. After the deposition, crystallization of the films is carried out in a furnace. X-ray diffraction and Scanning Electron Microscope characterizations are used to accurately measure the lattice parameter and analyze the surface morphology of the films. Microwave properties (dielectric constant, loss tangent and tunability in the GHz range) of the films are characterized by two complementary diagnostics that use coplanar devices patterned on the samples: coplanar interdigital capacitors and thru-reflect-line analysis. The Al-W and Mg-W codoped BST-0.5 are polycrystalline and show respectively 0.03 tangent loss with 19% tunability and 0.03 tangent loss with 25% tunability (at 40 kV.cm(-1)) compared to 0.055 tangent loss and 33% tunability for optimized undoped BST-0.5 films. These microwave properties demonstrate that codoping, especially with Mg-W, can improve the figure of merit of BST by more than 40%.