Influence of bias voltage on the crystallographic orientation and morphology of sputter deposited yttria stabilized zirconia (YSZ) thin films

ZrO₂-8% mol. Y₂O₃ (8YSZ) thin films were deposited onto silicon [100] and AISI 304 stainless steel substrates by r.f (13.56 MHz) multi-target magnetron sputtering. To improve the adhesion of a YSZ monolayer to the stainless steel substrate, a buffer layer of A1 ₂O₃ was incorporated too. Crystal structure and Infrared (IR) absorption bands of YSZ were investigated as functions of substrate bias by X-ray diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR), respectively. The influence of the bias voltage on the roughness, grain size, and microstructure of deposited thin films was determined by AFM and SEM. XRD results show the presence of a tetragonal phase with [111] and [200] orientations. On the other hand, FTIR spectra exhibit the 2E_u and F_1u modes as two broad bands in the frequency range of 450 ∼ 550 cm^-1 and 550 ∼ 650 cm^-1, corresponding to the tetragonal and cubic phases of ZrO₂, respectively. In this work we present the systematic influence of the bias voltage on the crystalline structure, the presence of the tetragonal phase and morphology of the YSZ thin films. The XRD, FTIR, and AFM results indicate that when the bias voltage increases from -20 V to -60 V the preferential crystallographic orientation of YSZ tetragonal phase changes from [111] to [200], and the percentage of the tetragonal phase diminishes, as well as the grain size of deposited films from (560 ± 5) to (470 ± 5) nm.