Nickel–zinc ferrite films by rapid thermal processing of sol–gel precursors

A photo-assisted, wet-chemical method (sol–gel) has been developed for the deposition and formation of soft-magnetic nickel–zinc ferrite films on thermally oxidized silicon substrates. A SiO2–FeOx buffer layer eases the thermal expansion mismatch between SiO2 and the ferrite film and provides a nucleation base for the ferrite formation. Upon irradiation by a UV-lamp or rapid thermal processing, the Fe(III) species are reduced to Fe(II) species in the precursor film, which induces the formation of the ferrite film. Local ferrite deposition can be induced by selective UV-irradiation of the wet ferrite precursor film. The SiO2–FeOx buffer layer and the ferrite film have been characterized for their crystallinity and OH content which can be related to the magnetic and optical properties of these films.