Ferrite plating on GaAs for microwave monolithic integrated circuit

Ferrite plating can potentially fabricate a ferrite non-reciprocal component on a microwave monolithick integrated circuit (MMIC); It can make crystalline spinel film in an aqueous solution below 90°C, compatible with the low heat resistance of GaAs devices. To show this, we have electro-plated or electroless-plated Fe3O4films on GaAs substrates. The film electroless-plated by "spray-spin-coating" method on a SiO2intermediate layer (formed by CVD on GaAs) had a mirror plane and a strong adhesion to the surface, though limited in thickness (≤ 0.8). A microstrip junction circulator has been composed of a NiZn-ferrite (Fe2.47Ni0.28Zn0.25- O4, Ms=478 emu/cc, Hc=37 Oe) film plated on a glass substrate. A circulator action has been observed at 4.0- 4.4 GHz, though very weak (0.6 dB isolation), because the ferrite film (0.8 μm) was much thinner than the substrate (500 μm). The Fe3O4and NiZn-ferrite films were polycrystalline with a columnar structure perpendicular to the surface. The magnetization did not exhibit anisotropy, lying in the plane of the film.