Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/ Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba0.5Sr0.5TiO3 (BST) /Bi1.5Zn1.0Nb1.5O7 (BZN) multilayer thin films have been prepared on Pt/Ti/SiO2/Si substrates by a sol-gel method. The multilayer thin films were deposited alternatively by spin coating technique and crystallized by rapid thermal annealing. The structures, morphologies of BST/BZN multilayer thin films were studied. The XRD results showed that the cubic pyrochlore BZN phase was observed in the multilayer thin films annealed at 650 oC, but there was no phase of perovskite BST at the same annealing temperature. With increasing annealed temperature over 700 oC, the peaks of the perovskite BST phase can be observed in the multilayer thin films. No measurable reaction between the BST and BZN phases during the annealing process was detected. The surface of multilayer thin films is compact and crack-free. The BST/BZN multilayer thin films annealed at 750 oC exhibited a medium dielectric constant around 147, a low loss tangent of 0.0034 at 10 kHz, and a relative tunability of 12 % with a dc bias field of 580 kV/cm. Meanwhile, the FOM (defined as a ratio of tunability over loss tangent) of BST/BZN thin films is 35.3. The relative low loss tangent and high FOM suggest that BST/BZN multilayer thin films have potential applications for tunable microwave devices.