(157c) Atomic Layer Deposition of Yttria-Stabilized Zirconium Using Cp-Type Precursors and Water Vapor for Fuel Cell Applications

Thin films of yttria-stabilized zirconium oxide (YSZ) were successfully deposited via atomic layer deposition (ALD) using metal CP-type precursors Tris(isopropyl-cyclopentadienyl)yttrium and tris(dimethylamino)cyclopentadienylzirconium with water as the oxygen donor for use in solid oxide fuel cells (SOFC’s). In order to characterize the ALD process, the growth rate of individual oxides was measured as function of precursor dosage, water vapor dosage, number of cycles and reactor temperature in a custom-designed and built hot wall ALD reactor. It was found that the ZrO₂ process has a growth rate of ~0.7 Å/cycle while for Y₂O­₃ the growth rate is ~1.4 Å/cycle. An overlap of the individual ALD windows was found from 250 to 280°C; this overlap is ideal for the ALD of the composite YSZ films. The normalized cycle ratio defined as the cycles of yttrium precursor/total cycles was changed to investigate the tunability of the process. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the composition of as-deposited YSZ. It was found that the normalized cycle ratio and the yttrium atomic percentage (Y atoms / metal atoms) have a linear relationship implying excellent tunability. Transmission electron microscopy (TEM) along with electron energy loss spectroscopy (EELS) was performed to characterize the crystalline structure and to determine the stoichiometry of the deposited films. TEM results show that the atomic percentage of yttrium in the YSZ films strongly influence the film crystallinity. For instance, films with 8% atom of Yttrium are polycrystalline with small amorphous grains while films with an atomic % of yttrium higher than 10% are polycrystalline with no amorphous regions.