Dielectric properties of ZnNb2O6-TiO2 mixture thin films

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.