Deposition and dielectric characterization of strontium and tantalum-based oxide and oxynitride perovskite thin films

We have synthesized the composition x = 0.01 of the (Sr_1-xLa_x)₂(Ta_1-xTi_x)₂O₇ solid solution, mixing the ferroelectric perovskite phases Sr₂Ta₂O₇ and La₂Ti₂O₇. Related oxide and oxynitride materials have been produced as thin films by magnetron radio frequency sputtering. Reactive sputter deposition was conducted at 750 °C under a 75 vol.% (Ar) + 25 vol.% (N₂,O₂) mixture. An oxygen-free plasma leads to the deposition of an oxynitride film (Sr_0.99La_0.01) (Ta_0.99Ti_0.01)O₂N, characterized by a band gap E_g = 2.30 eV and a preferential (001) epitaxial growth on (001) SrTiO₃ substrate. Its dielectric constant and loss tangent are respectively Epsilon' = 60 (at 1 kHz) and tanDelta = 62.5 × 10⁻³. In oxygen-rich conditions (vol.%N₂ ≤ 15%), (110) epitaxial (Sr_0.99La_0.01)₂(Ta_0.99Ti_0.01)₂O₇ oxides films are deposited, associated to a larger band gap value (E_g = 4.55 eV). The oxide films permittivity varies from 45 to 25 (at 1 kHz) in correlation with the decrease in crystalline orientation; measured losses are lower than 5.10⁻³. For 20 ≤ vol.% N₂ ≤ 24.55, the films are poorly crystallized, leading to very low permittivities (minimum Epsilon' = 3). A correlation between the dielectric losses and the presence of an oxynitride phase in the samples is highlighted.