Supercritical fluid deposition of compositionally uniform yttria stabilized zirconia films

We report the formation of yttria stabilized zirconia (YSZ) thin films by supercritical fluid deposition (SFD) in carbon dioxide at 20 MPa and a stage temperature of 300 °C via hydrolysis of zirconium(IV) hexafluoroacetylacetonate and yttrium(III) hexafluoroacetylacetonate. Post-deposition annealing of the films at 800 °C yields crystalline films having the expected fluorite structure as evidenced by X-ray diffraction. Such films are suitable for the fabrication of electrolyte thin films for micro-solid oxide fuel cells (μ-SOFC). We show that a cyclic co-deposition process in which aliquots of precursor are introduced sequentially enables the depostion of YSZ thin films with uniform composition as evidenced by X-ray photoelectron spectroscopy. In each cycle, the mixed precursor solution in CO2 is introduced to the reactor and then purged following a short reaction interval. By contrast, simple batch SFD processes that employ hydrolysis of the mixed precursors introduced at the onset of the depositions lead to non-uniform distributions of the cations throughout the thickness of the films. The cyclic deposition approach extends supercritical fluid deposition to materials such as multi-cations oxides for which precise control of stoichiometry is required.