Dielectric properties of ZnNb₂ O ₆ -TiO ₂ mixture thin films

Abstract

ZnNb₂O₆-TiO₂ mixture thin films with multilayer structures were fabricated via a sol-gel spin coating process. TiO₂ layers were deposited on the pre-crystallized ZnNb₂O₆ layers in order to suppress the formation of the ixiolite phase which always forms in the bulk system. The phase constitution of the thin films, confirmed by X-ray diffraction (XRD), could be controlled by the annealing temperatures, which, in turn, influenced the dielectric properties of the thin films. TiO₂ layers crystallized as the anatase phase and then transformed to the rutile phase at temperatures higher than 725^∘C. Dielectric constants of the mixture thin films, measured at 1 MHz with an MIM (metal-insulator-metal) structure, increased from 27 to 41 with dielectric losses below 0.005 as the annealing temperature increased from 700^∘C to 900^∘C. The increase in the dielectric constants was understood to originate from the increasing amounts of the rutile phase. Temperature coefficients of capacitance (TCC) were also measured between 25^∘C and 125^∘C, which showed a decreasing manner from positive values to negative values with increasing annealing temperatures. When annealed at 850^∘C, the TCC of the thin films could be tuned to be approximately 0 ppm/^oC with dielectric constant and dielectric loss of 36 and 0.002, respectively.