Crystallization resistance of barium titanate zirconate ultrathin films from aqueous CSD: a study of cause and effect

Abstract

Ultrathin BaZr_0.8Ti_0.2O₃ films (t < 30 nm) on SiO_x/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Though the precursor crystallized into cubic perovskite powder at 600 °C, ultrathin films only crystallized at 950 to 1000 °C, even after addition of excess Ba to compensate for loss of Ba. Films with thickness above 100 nm, on the other hand, crystallized readily around 650 °C. The crystallization is related to film thickness, affecting the crystallization activation energy, and to silicate formation by reaction with the substrate, exerting its largest influence in ultrathin films. Barium deficiency, silicate formation, carbonate secondary phase and the high activation energy for crystallization resulted in the amorphous nature of the ultrathin films, which strongly affects the observed k value (∼ 15). The paper contributes insights with implications for the application of BaZr_0.8Ti_0.2O₃ as an alternative high-k gate dielectric.