Effect of the dopant content on the physical properties of Y2O3-ZrO2 and CaO-ZrO2 thin films produced by evaporation and sputtering techniques

This paper describes the preparation and the characterization of zirconia-d oped yttria (or calcia) produced by reactive thermal evaporation (RTE) and r.f. magnetron sputtering (R.F.MS) methods. The crystallographic, microstru ctural and optical properties of the deposited films were investigated as a function of dopant concentration in the ZrO2 matrix. X-ray diffraction (XR D) analysis permits the study of the stabilization process, lattice paramet er and residual stress. XRD patterns show a gradual change in the crystalli ne structure from a monoclinic phase to a single cubic phase with increasin g Y2O3 (or CaO) mole percentage (mol%). The cubic lattice parameter seems t o increase with increasing dopant mol%. A merely indicative stress study in stabilized samples shows tensile stress in the ZrO2-Y2O3 system obtained b y co-evaporation. Residual stresses were highly compressive in ZrO2-Y2O3 (o r CaO) systems deposited by the sputtering technique. Scanning electron mic roscopy (SEM) revealed a columnar structure for the overall films. Sputtere d zirconia-based films show smooth surface topography with smaller crystall ite dimensions. The film refractive index, the packing density and the abso rption coefficient are determined in the wavelength range 350-800 nm from t he measured reflectance and transmittance at normal incidence. All doped Zr O2 films exhibit high optical transmission over most of the visible and nea r infrared spectrum. The refractive index decreased with increasing dopant content and agreed reasonably well with published values for ZrO2 films. Bu lk like refractive index with nearly unity packing density have been obtain ed for the samples containing 4-7 mol% Y2O3, deposited by the sputtering me thod. The results suggest that the physical constant of ZrO2-based films ar e principally determined by the crystallographic form rather than by the na ture or amount of the added cation. (C) 1999 Elsevier Science S.A. All righ ts reserved.