Impact of substrate material and annealing conditions on the microstructure and chemistry of yttria-stabilized-zirconia thin films

Si-diffusion from Si-based substrates into yttria-stabilized-zirconia (YSZ) thin films and its impact on their microstructure and chemistry is investigated. YSZ thin films used in electrochemical applications based on micro-electrochemical systems (MEMS) are deposited via spray pyrolysis onto silicon-based and silicon-free substrates, i.e. Si_xN _y-coated Si wafer, SiO₂ single crystals and Al ₂O₃, sapphire. The samples are annealed at 600°C and 1000°C for 20 h in air. Transmission electron microscopy (TEM) showed that the Si_xN_y-coated Si wafer is oxidized to SiO_z at the interface to the YSZ thin film at temperatures as low as 600°C. On all YSZ thin films, silica is detected by X-ray photoelectron spectroscopy (XPS). A particular large Si concentration of up to 11 at% is detected at the surface of the YSZ thin films when deposited on silicon-based substrates after annealing at 1000°C. Their grain boundary mobility is reduced 2.5 times due to the incorporation of SiO₂. YSZ films on Si-based substrates annealed at 600°C show a grain size gradient from the interface to the surface of 3 nm to 10 nm. For these films, the silicon content is about 1.5 at% at the thin film's surface.