The effect of Bi1.5Zn0.5Nb0.5Ti1.5O7 cover layer on the dielectric and tunable properties of Ba0.6Sr0.4TiO3/Bi1.5Zn0.5Nb0.5Ti1.5O7 bilayered thin films

• The BZNT cover layer significantly improved the leakage current and the dielectric loss of BST/BZNT bilayered films.
• The BST/BZNT-50 thin film gave the high FOM of 33.48 with the upper tunability of 55.38%.
• It was found that the internal field across the BST/BZNT bilayered films produced the asymmetric electrical behavior.

Bi1.5Zn0.5Nb0.5Ti1.5O7 (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba0.6Sr0.4TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces.