Aqueous chemical solution deposition of LuFeO3 ultra high-k films

Abstract

Ultra high-k materials are very attractive for the use in applications such as thin-film capacitors. Due to their extremely high dielectric constant (k>10000), they can possibly be used for the miniaturization of the energy storage devices and the increase of their energy density. For orthorhombic LuFeO3 (LFO) ceramics, a dielectric constant of 10000 (frequency ≤ 1kHz) has been reported at room temperature. Nevertheless, literature on the deposition of LFO thin films, indispensable for the thin film applications envisaged, is only scarcely available, especially when it comes to wet chemical deposition. We prepared a stable aqueous Lu/Fe multimetal ion precursor by mixing citrato complex-based Fe and Lu solutions in the desired ratio. Prior to thin film deposition, the thermal decomposition and crystallization behavior of the bulk material were studied. It was shown that phase-pure orthorhombic LFO could be formed at 900°C, indicating the need of high temperatures for the phase formation. By studying several parameters of the deposition process, including the substrate choice and anneal, we were able to obtain thin orthorhombic high-k LFO films on Si3N4. Electrochemical impedance spectroscopy showed a dielectric constant of more than 10000 at room temperature (frequency ≤ 1kHz) for these layers, thus confirming to be ultra high-k films.