Reactive sputtering deposition of perovskite oxide and oxynitride lanthanum titanium films: Structural and dielectric characterization

摘要

Perovskite lanthanum titanium thin films were deposited on Nb-doped (001) SrTiO_3 substrates by reactive RF magnetron sputtering using a La_ 2Ti_2O_7 target. Oxynitride LaTiO_2N films were obtained using N_2 rich plasma; they display a variation of their dielectric constant as a function of DC bias in the low frequency range but not in microwaves. The dielectric constant (epsilon) values are high with, for example, epsilon = 325 at 100 kHz. The oxide films, obtained in O_ 2 rich plasma, are composed of an unusual La_2Ti_ 2O_7 phase with an orthorhombic cell. The films are (101) epitaxied on Nb:SrTiO_3 substrates. The dielectric constant value of films is around 77 with losses ～0.076 at 100 kHz; no agility of epsilon in low and high frequencies is detected. Composite and bilayer films, with oxynitride and oxide phases, exhibit a variation of epsilon under DC bias in low frequencies with, for example, an agility of 15% at 100 kHz with a maximum applied field of 40 kV/cm for the LaTiO_2N (200 nm)/La_ 2Ti_2O_7 (250 nm) bilayer.