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

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 V/sub S/. 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 V/sub S/ and then decreased as V/sub S//V/sub T/ exceeded approx.0.08, where V/sub T/ is the target voltage. In the doped ZrO2 films, the O/Zr ratio, microstructure, and ionic conductivity activation energy were dependent upon V/sub S/. For V/sub T/=-500 V, deposited films were approximately stoichiometric at V/sub S/approx. =-70 V, while films grown at -V/sub S/<60 or >80 V were oxygen deficient. Films grown at -V/sub S/< or =40 V had a very columnar microstructure, while films deposited with -V/sub S/>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> or =180degreeC. Linear Arrhenius plots of measured film resistance versus T in the range 150--550degreeC 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