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

International audiencePerovskite 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 degrees 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 Cmc2(1) 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 epsilon similar to 60 and the losses are low (tan delta < 0.02