Sol−Gel Fabrication and Electrical Property of Nanocrystalline (RE₂O₃)_0.08(ZrO₂)_0.92 (RE = Sc, Y) Thin Films

Dense, crack-free, and homogeneous nanocrystalline (RE 2 O 3 ) 0.08 (ZrO 2 ) 0.92 (RE = Sc, Y) thin films (≈0.58-μm thick) on monocrystalline silicon (100) wafers were fabricated by a simple sol−gel spin-coating method under reduced annealing temperature and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), and impedance studies. Some key correlative processing parameters such as coating solution composition and gel-firing temperature have been optimized. XRD results indicate that the as-fabricated (Sc 2 O 3 ) 0.08 (ZrO 2 ) 0.92 thin films can achieve good crystallization in a pure cubic phase at a relatively low annealing temperature not exceeding 800 °C in 2 h and the nanocrystal size grows with elevation of the annealing temperature. AFM and SEM micrographs show that the (RE 2 O 3 ) 0.08 (ZrO 2 ) 0.92 nanocrystals after undergoing annealing at 950 °C for 2 h are uniform in the size range of 50−60 nm. AES profile analysis suggests that the (Sc 2 O 3 ) 0.08 (ZrO 2 ) 0.92 thin films are fairly pure with good composition homogeneity in the depth range of 75−500 nm. Impedance measurements reveal that the oxide ion conductivity of the nanocrystalline thin films is 10 times higher than that of the respective bulk material at temperatures beyond 600 °C. A decrease of grain boundary resistance related to interfacial effects is predominately responsible for this electrical conductivity enhancement.