Aqueous chemical solution deposition of ultra high-k LuFeO3 thin films

Thin orthorhombic ultra high-k LuFeO3 (LFO) films on Si3N4/SiO2/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Prior to thin film deposition, the precursor synthesis, thermal decomposition and crystallization behavior of the bulk material were studied. It was shown that phase-pure hexagonal LFO powder could be formed at 650 °C while a higher temperature of 900 °C was required to obtain the orthorhombic phase. Deposition on SiO2/Si resulted in the development of silicates in this temperature range, thus preventing the formation of the orthorhombic LuFeO3 phase. The use of Si3N4/SiO2/Si as the substrate shifted the silicate formation to higher temperature, allowing the synthesis of phase-pure orthorhombic LuFeO3 as a thin film at 1000 °C. Impedance spectroscopy analyses confirmed its associated ultra high dielectric constant (>10,000) at room temperature for frequencies lower than or equal to 1 kHz.