Structural characterization of yttria stabilized zirconia thin film deposited by magnetron sputtering

Abstract

Yttria stabilized zirconia (YSZ) thin film is of great interest as an ionconductor for the electrolyte-electrode sandwich in solid oxide fuel cell (SOFC) applications. YSZ electrolytes have several advantages, but its applicability has been mainly limited because of the inability to synthesize YSZ films at low temperatures due to its high melting point. One way to overcome such limitation is to establish the YSZ structure by optimizing the percentage of crystallinity and densification of the thin film. The current study was focused on the comparative evaluation of crystallization and densification of dense-thin YSZ film for electrolyte in SOFC. The oxygen flow rate (0-50 sccm), substrate bias voltage (0-120 V), substrate temperature (200-300°C), and deposition time (30-120 min) were evaluated in order to develop dense-thin YSZ film with high crystallinity at low substrate temperatures by radio frequency (RF) magnetron sputtering. The deposition parameter controlled the general morphology and the film thickness, whereas the annealing parameter (300- 600°C) affected the crystal orientation in thin films. The current study also determined the effects of the selected deposition parameters on the properties and structures of YSZ thin films. The produced thin films were characterized by glancing angle X-ray diffraction (GAXRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Based on the results, a dense-thin YSZ film was produced with an average thickness of approximately 200 nm without oxygen flow. The GAXRD pattern of YSZ thin film revealed the existence of a columnar structure (cubic phases) with preferred growth along (200) lattice orientation. YSZ thin films grown at 120 V exhibited good homogeneity and uniformity (100 nm thick and 10-12 nm crystallite size) accompanied by a large microstrain along (111) lattice orientation. The sample obtained at the highest substrate temperature (300°C) revealed the lowest microstrain (0.028%) and the highest crystallinity (43%) with a non-columnar structure. The main effect of the deposition time (60 min) had the strongest effect on the lattice microstrain and the thickness of the YSZ thin film. In conclusion, the combined effects of the substrate temperature (300°C) and annealing factor (400°C) were successful in the development of dense-thin YSZ film with high crystallinity (60%) for potential electrolyte use in SOFCs.