Growth of (Sr,La)-(Ta,Ti)-O-N perovskite oxide and oxynitride films by radio frequency magnetron sputtering: Influence of the reactive atmosphere on the film structure

• Oxide and oxynitride films were deposited by reactive RF magnetron sputtering.
• (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 film is (110) epitaxially grown on MgO substrate.
• (Sr0.99La0.01)(Ta0.99Ti0.01)O2N films are preferentially (001) oriented on MgO substrate.
• Nitrogen-substoichiometric films are deposited with low dinitrogen content in plasma.

In the search for new dielectric and ferroelectric compounds, we were interested in the perovskite (Sr1-xLax)2(Ta1-xTix)2O7 solid solution with ferroelectric end members Sr2Ta2O7 (TCurie=−107 °C) and La2Ti2O7 (TCurie=1461 °C). In order to achieve a Curie temperature close to room temperature, the formulation with x=0.01 was chosen and synthetized as thin films by reactive radio-frequency magnetron sputtering. In oxygen rich plasma, a (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 film is deposited, characterized by a band-gap Eg=4.75 eV and an (1 1 0) epitaxial growth on (0 0 1)MgO substrate. The use of nitrogen rich plasma allows to synthesize (Sr0.99La0.01)(Ta0.99Ti0.01)O2N oxynitride films, with band gap Eg~2.10 eV and a polycrystalline, textured or epitaxial growth on (0 0 1)MgO substrate. Nitrogen-substoichiometric oxynitride films with larger lattice cells are produced for low dinitrogen percentages in the sputtering plasma.