Techniques for the thin film growth of La_1-xSr _xCrO₃ for solid state ionic devices

Thin films of LaCrO₃ and La_0.8Sr _0.2CrO₃ were prepared using RF magnetron sputtering, electron beam evaporation and pulsed laser deposition (PLD). The films were prepared from both oxide targets and from targets consisting of Cr metal and lanthanum and strontium fluorides. Subsequent anneal of the fluoride/metal composite films in humidified Ar produced an oxide film. Direct growth of the perovskite from oxide targets via sputtering was usually accompanied by second phases with Cr in valance states higher than 3+. Single-phase La-Sr-Cr-O films could not be prepared from a single oxide target electron beam evaporation. However, thick, stoichiometric films were prepared at 400 °C using an electron beam/thermal evaporation dual source method but inconsistently. Single-phase lanthanum chromate films, based on the limited results obtained in this work, could not be prepared using PLD from either oxide or fluoride precursors under conditions similar to those used in the other techniques. However, films prepared by the intermediate fluoride process via off-axis RF magnetron sputtering process produced high quality thin films with density, microstructure and phase purity very similar to bulk La_0.8Sr _0.2CrO₃ using a film growth temperature as low as ambient (T_sub<100 °C). The deposition rate was typically low at approximately 1500 Å/h. SEM analysis showed that the morphology of films produced via fluoride sputtering was nearly identical to bulk La _0.8Sr_0.2CrO₃ prepared by sintering ceramic powders at 1650 °C in air and, based on previous work, should be suitable for mixed potential sensor applications.