Room-Temperature Preparation of ZrO2 Precursor Thin Film in an Aqueous Peroxozirconium-Complex Solution

We report a deposition method for room-temperature preparation of ZrO2 thin film using an aqueous solution. ZrO(NO3)2·2H2O was dissolved in a solvent mixture composed of H2O2 and ammonia. The dissolving reaction produced a colorless, transparent peroxozirconium-complex solution which was unstable; decomposition occurred even at room temperature. Amorphous, transparent, dense ZrO2 precursor thin films of up to 500 nm thick were prepared on a cleaned P-type Si substrate. The film showed good adhesion to the substrate as peel-off was not found after either sonication or a Scotch-tape peel-off test. The asdeposited thin film was of high purity with a composition of ZrO1.4(OH)1.2. No peroxo groups were present in the as-deposited film. Annealing caused crystallization of the amorphous film into tetragonal ZrO2 at 500 C and phase transformation from tetragonal to monoclinic ZrO2 at higher temperatures. Both films showed very flat surfaces consisting of nanoparticles with homogeneous size of tens of nanometers in diameter. The optical band gap of the amorphous film was 5.0-5.75 eV, whereas it was 5.65 eV for the crystalline ZrO2 thin film