2005 Volume 5 Issue 4 Pages 161-164
Previously we revealed that spin-sprayed ferrite films are usable for GHz-range noise suppressors. For actual use, the films must retain excellent characteristics after the reflow soldering process. In this study, we investigated how changing the compositions of films influences their electric resistivity and the noise suppression effects obtained after annealing at 260° C. We plated 3-μm-thick ferrite films #1 (Ni0.2Zn0.1Fe2.7O4) and #2 (Ni0.4Zn0.3Fe2.3O4) onto polyimide sheets. The resistivity of film #1 decreased markedly, from 4 × 102 Ω cm to 1 × 100 Ω cm as a result of the annealing. On the other hand, film #2 exhibited a smaller decrease, from 6 × 104Ω cmto2 × 104 Ω cm. The reflection parameter S11 and transmission loss Δ Ploss measured on a microstrip line for film #1, especially below 1 GHz, were increased by the annealing. This is unfavourable for use of film #1 in lowpass filters that are required to absorb noises only in the GHz range. On the other hand, S11and Δ Ploss for film #2 were not significantly affected by the annealing. This film exhibited Δ Ploss of 40 ‰ at 10GHz.Moreover, the value of S11for the film below 10 GHz was sufficiently weak, less than -12dB.Thus, we succeeded in fabricating aGHz-rangenoise suppressor, with excellent heat resistance.
