Lanthanum titanium perovskite compound: Thin film deposition and high frequency dielectric characterization

• Lanthanum titanium oxide films were deposited by reactive magnetron sputtering.
• A La2Ti2O7 chemical composition is proposed, with an unusual orthorhombic cell.
• At 10 GHz, the dielectric losses are lower than 0.02.
• No variation of the dielectric constant is observed under DC electric biasing.

Perovskite lanthanum titanium oxide thin films were deposited on (001) MgO, (001) LaAlO3 and Pt(111)/TiO2/SiO2/(001)Si substrates by RF magnetron sputtering, using a La2Ti2O7 homemade target sputtered under oxygen reactive plasma. The films deposited at 800 °C display a crystalline growth different than those reported on monoclinic ferroelectric La2Ti2O7 films. X-ray photoelectron spectroscopy analysis shows the presence of titanium as Ti4 + ions, with no trace of Ti3 +, and provides a La/Ti ratio of 1.02. The depositions being performed from a La2Ti2O7 target under oxygen rich plasma, the same composition (La2Ti2O7) is proposed for the deposited films, with an unusual orthorhombic cell and Cmc21 space group. The films have a textured growth on MgO and Pt/Si substrates, and are epitaxially grown on LaAlO3 substrate. The dielectric characterization displays stable values of the dielectric constant and of the losses in the frequency range [0.1–20] GHz. No variation of the dielectric constant has been observed when a DC electric field up to 250 kV/cm was applied, which does not match a classical ferroelectric behavior at high frequencies and room temperature for the proposed La2Ti2O7 orthorhombic phase. At 10 GHz and room temperature, the dielectric constant of the obtained La2Ti2O7 films is ε ~ 60 and the losses are low (tanδ < 0.02).