Fabrication of Ferrite Thin Films using Low Pressure Metalorganic Chemical Vapor Deposition
thesisposted on 20.06.2014 by Yi Yang
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Several ferrite thin films were fabricated using low pressure metalorganic chemical vapor deposition (MOCVD). Three single metal oxides-iron oxide, bismuth oxide and nickel oxide were studied to obtain the processing parameters which were crucial in deposition of two binary metal oxides-bismuth ferrite and nickel ferrite. BiFeO3 (BFO) was known to be the only single phase multiferroic material which exhibited magnetoelectric (ME) coupling effect at room temperature. This coupling effect provided an extra degree of freedom for designs of whole new devices and applications never thought to be possible before. We introduced a novel liquid iron precursor, n-butylferrocene, delivered into the reactor by heating the precursor canisters at certain temperatures for growing BFO thin films. Other crucial MOCVD conditions (reactor’s pressure, reactor’s temperature, substrates…) were also discussed and optimized. Characterizations for the film composition, crystallinity, ferroelectricity, ferromagnetism and the magneto-dielectric coupling effect were analyzed in detail. The results confirmed that BFO film had multiferroic properties and could be potentially used in future tunable high-frequency devices. Heterostructures such as bilayered/multilayered thin films, nanoparticles/nanopillars embedded in different materials and nanowires became more promising for the future on-chip integration applications because the coupling in such structures was many orders of magnitude stronger. Another research we interested in was the heterostructural magnetostrictive NiFe2O4 (NFO) with piezoelectric materials. NFO was a promising magnetic phase for ME heterostructures due to its low anisotropy, high permeability with high resistivity, low eddy current losses and smaller coercive field. In this study, the nickel ferrite thin films had been deposited using computer controlled MOCVD setup in both co-deposition mode and cyclic-deposition mode. Conditions for CVD process were discussed and optimized for growing NFO thin film. The thin films showed NFO composition, uniformity in chemical states and thickness, trevorite crystalline form, free from carbon contamination and similar magnetic property as other literature reported.