Multistep magnetron sputtering process and in-situ heat treatment to manufacture thick, fully oxidized and well crystallized YSZ films

Abstract

In this work, yttria stabilized zirconia electrolyte layers were deposited by reactive pulsed DC magnetron sputtering on various substrates (i.e. silicon wafer, glass plates, NiO/YSZ cermets). The sputtering process was studied by following the cathode voltage and gas pressure evolutions with the reactive flow rate. The substrate temperature was found to play a role on the transition between the elemental and reactive sputtering modes. The influence of the sputtering parameters and deposition conditions on the film properties was investigated. Thick (about 2 μm) and dense deposits were manufactured both in elemental and in reactive sputtering modes. Ex-situ and in-situ heat treatments were applied to promote crystallization and oxidization of the deposits. The oxygen content was evaluated by Rutherford backscattering spectroscopy before and after heat treatments which confirmed that fully oxidized material was obtained. Optical transmission measurements on deposits synthesized on glass slides were also performed for a cross check of the oxidation state. X-ray diffraction technique revealed that heating of the substrate is necessary to get a crystallized as-deposited film. However, further annealing is required to synthesize the desired YSZ cubic phase. It has been proved that with the proposed multistep process including in-situ short heating steps, thick YSZ films could be synthesized without any stress cracking as usually observed after complete oxidation. Those films have shown very low leakage rate (6.67 × 10−4 mbar·l·s−1) which is required for the application.