Dielectric properties of TiO$_{2}$ and Zr-doped TiO$_{2}$ thin films

The leakage current and photocatalytic performance of TiO$_{2}$ can be improved by properly doping Ti with other transition metal cations. For example, Zr$^{4+}$ doping for Ti$^{4+}$ can significantly improve the desired properties. We have studied the properties of pure TiO$_{2}$ and Zr-doped TiO$_{2}$ thin films prepared by MOD technique and annealed from 650 to 950$^{\circ}$C. Both XRD and Raman spectra show TiO$_{2}$ to be mostly in anatase form below the annealing temperature of 850$^{\circ}$C and in rutile phase above 850$^{\circ}$C. However, the Zr doping does not lead to rutile phase formation. We have studied I-V characteristics and frequency dependence of dielectric constants of pure and Zr-doped TiO$_{2}$ in the frequency range of 100Hz--1MHz. We find an improvement in leakage current with increasing annealing temperature from 650 to 950$^{\circ}$C for both TiO$_{2}$ and Zr-doped TiO$_{2}$, but no appreciable improvement in the leakage current upon Zr doping. The dielectric constant of pure TiO$_{2}$ films improves from 30 to 80 with increasing annealing temperature, whereas that of Zr-doped TiO$_{2}$ is independent of annealing temperature and its value is $\sim$50 at 30 kHz. This may be attributed to the persistence of anatase phase of TiO$_{2}$ over wide range of annealing temperatures for Zr-doping. These properties and their implications for different applications will be discussed.