High-rate low-temperature (90°C) deposition of Ni-Zn ferrite films highly permeable in gigahertz range

Ni-Zn ferrite films have been prepared by spraying a reaction solution of FeCl₂ + NiCl₂ + ZnCl₂ (pH = 6.8) and an oxidizing solution of NaNO₂ + CH₃ COONH₄ + NH₄ OH (pH = 6.8-9.2) simultaneously onto rotating glass substrates at a substrate temperature of 90°C. The deposition rate increased with the pH value of the oxidizing solution, and a maximum deposition rate of 67 nm/min was attained at pH = 8.4. The film surface observed by scanning electron microscopy was smooth, and a high value of saturation magnetization M_s = 482 emu/cm³ with a low value of coercivity H_c = 17 Oe were measured. The film showed a high static permeability μ\´ = 70 and very high magnetic resonance frequency f_T of about 900 MHz. The imaginary part of the permeability μ" was greater than 30 over a wide frequency range from 300 MHz to 3 GHz. Ni-Zn ferrite films prepared in this study should be useful not only for planar inductors but also as shielding materials for electromagnetic interference suppressions.