Deposition and Characterization of Ferroelectric Pb[(Mg1/3Nb2/3)xTi1-x]O3 Thin Films by RF Magnetron Sputtering

Abstract

Ferroelectric Pb[(Mg_1/3Nb_2/3) _x Ti_{1- x} ]O₃ (PMNT) thin films with a well-developed perovskite structure were prepared on Si(100) and Pt/Ti/ SiO₂/Si(100) substrates by rf magnetron sputtering deposition at high substrate temperatures of 480–650° C. The effect of substrate materials was investigated by X-ray diffraction analysis. The substrates that were topped with a Pt/Ti electrode exhibited a significant effect on reducing the perovskite phase formation temperature of PMNT films; in addition, the TiO₂ rutile phase was found to be formed at the interface between the PMNT film and Pt electrode. It was discovered that the TiO₂ rutile phase would degrade the dielectric and ferroelectric properties of the PMNT films. The 0.5-µm-thick perovskite PMNT films of x=0.3–0.5 exhibited a high dielectric constant (k) of 1000–1300, and a dissipation factor less than 0.04 at 1 kHz. Moreover, the films showed satisfactory ferroelectric characteristics. The remanent polarization (P _r) or coercive field (E _c) ranged from 23.5 µ C/cm² and 82.5 kV/cm, respectively, for 10 PMNT (x=0.1) to 10.2 µ C/cm² and 49 kV/cm for 50 PMNT (x=0.5) thin films. Due to the formation of a relatively thick TiO₂ interface layer at a high deposition temperature, the 70 PMNT (x=0.7) films did not show satisfactory dielectric or ferroelectric properties. However, by adding 3 mol% La on the PMNT to reduce the perovskite formation temperature, a 0.5-µm-thick Pb_0.97La_0.03Mg_0.235Nb_0.44Ti_0.325O₃ (PLMNT) film was prepared on the Pt/Ti/ SiO₂/Si substrate, and results of P _r=8.5 µ C/cm², E _c=46 kV/cm with k=1220 and tan δ<0.04 were obtained.