Deposition and properties of yttria-stabilized zirconia thin films using reactive direct current magnetron sputtering

Yttria-stabilized zirconia (YSZ) thin films were deposited by reactive magnetron sputter deposition from a composite Zr-Y target in Ar-O₂ mixtures. Hysteresis was observed as a function of oxygen flow rate f. For a discharge current of 0.4 A and a total pressure P of 5 mTorr, for example, the target oxidized at f > 2.3 ml/min, with the reverse transition from an oxidized to a metallic target surface occurring at 1.95 ml/min. The deposition rate was 2.7 um/h in the metallicmodeandO.l,um/h in the oxide mode. Fully oxidized (Y₂O₃)_0.1 (ZrO₂)_0.9 was obtained for f > 2.0 ml/min, even in the metallic mode. While films deposited with P = 3−20 mTorr were continuous, for P > 20 mTorr crazing was apparent as expected for a ceramic film in a tensile stress state. For P < 3 mTorr, the films delaminated due to excessive compressive stress. X-ray diffraction and electron microscopy results showed that the films were polycrystalline cubic YSZ with a columnar structure and an average grain diameter of 15 nm. Fully dense films were obtained at a deposition temperature of 350°C. Temperature-dependent impedance spectroscopy analysis ofYSZ films with Ag electrodes showed that the oxygen ion conductivity was as expected for YSZ.