Dielectric relaxation and conduction mechanisms in sprayed TiO₂ thin films as a function of the annealing temperature

The electrical properties of TiO₂ thin films deposited by chemical spray pyrolysis onto Si substrates were investigated in the metal–oxide–semiconductor (MOS) configuration using current–voltage characteristics and impedance spectroscopy. The electrical properties were analyzed in relation to the changes in microstructure induced during annealing in air up to a temperature of 950 °C. Anatase to rutile transformation started after annealing at 800 °C, and at 950 °C, only the rutile phase was present. The dielectric relaxation strongly depended upon the microstructure of TiO₂ with the dielectric constant for the anatase phase between 45 and 50 and that for the rutile phase 123. Leakage current was reduced by three orders of magnitude after annealing at 700 °C due to the densification of the TiO₂ film. A double-logarithmic plot of the current–voltage characteristics showed a linear relationship below 0.12 V consistent with Ohmic conduction, while space-charge-limited conduction mechanism as described by Child’s law dominated for bias voltages above 0.12 V.