Growth and characterization of doped ZrO2 and CeO2 films deposited by bias sputtering

Abstract

The deposition rate, chemistry, microstructure, and optical and electrical characteristics of rf sputter deposited Y2O3-doped ZrO2 films have been investigated as a function of applied substrate bias VS. Some preliminary results on Y2O3-doped CeO2 are included. All films were deposited in Ar at a pressure of 20 mTorr (2.67 Pa). The deposition rate of both materials initially increased with VS and then decreased as VS/VT exceeded ∠0.08, where VT is the target voltage. In the doped ZrO2 films, the O/Zr ratio, microstructure, and ionic conductivity activation energy were dependent upon VS. For VT=−500 V, deposited films were approximately stoichiometric at VS?−70 V, while films grown at −VS<60 or ≳80 V were oxygen deficient. Films grown at −VS?40 V had a very columnar microstructure, while films deposited with −VS≳60 V appeared quite dense with little structure visible in fracture cross-section electron micrographs. Electrical measurements indicated ionic-transference numbers within 1% of unity at temperatures T?180°C. Linear Arrhenius plots of measured film resistance versus T in the range 150–550°C yielded activation energies in the range 0.9–1.15 eV and indicated a single-conduction mechanism. All doped ZrO2 and CeO2 films exhibited high optical transmission over most of the visible and near-infrared spectrum. The refractive index decreased with increasing oxygen content and agreed reasonably well with published values for pure ZrO2 films.