Properties of compositionally graded (Pb,Sr)TiO3 thin films for tunable microwave device application

Multilayered (Pb 1-x Sr x )TiO 3 thin films consisted of uniform PST(x) and sandwich-like compositionally graded PST80- 60-80 were fabricated on Pt/Ti/SiO 2 /Si substrates by coating the solutions with different Sr contents(60≤Sr(mol%)≤80), respectively. Their structural and dielectric properties were investigated. Both uniform and compositionally graded films crystallized into a perovskite structure with no second phase found after post-deposition annealing. Among uniform films, the PST60 films showed the highest dielectric constant and tunability, but low figure of merit(FOM) due to relatively higher dielectric loss. For the sake of bringing down the dielectric loss, the PST60 thin films were sandwiched by PST80 thin layer, resulting in a decrease in dielectric loss and slight decrease in tunability. Besides the improvement of FOM, the temperature stability of graded PST80-60-80 thin films was also enhanced.