Operation characteristics of a buck/boost converter using a layered inductor with high resistive Fe(CoFe)-M-O (M=Hf,Zr,rare-earth) films

Fe(CoFe)-M-O (M=Hf,Zr,rare-earth) films have excellent soft magnetic properties at a high frequency for their high electrical resistivity. Layered inductors using the magnetic films have a low loss at a high frequency. Accordingly, the DC-DC converter using these layered inductors exhibit a high efficiency for the high frequency drive. A layered inductor using nanocrystalline Fe₆₁Hf₁₃ O₂₆ film and Co₄₄Fe₁₉Hf₁₅ O₂₂ film exhibit the Q of 8.4 and 12.3 at 5 MHz. The micro DC-DC converter using nanocrystalline Fe₆₁Hf₁₃ O₂₆ film and Co₄₄Fe₁₉Hf₁₅ O₂₂ film exhibit the maximum efficiency of 83.5% and 86% in the boost converter driving at 5 MHz. Furthermore, thin film inductor using Fe₅₅Hf₁₁O₃₄ film which size of 3.5 mm² exhibits L of 950 nH and Q of 6.6 at 5 MHz. Then, they are evident that high resistive nanocrystalline, Fe(CoFe)-Hf-O films are effective for the high frequency micro DC-DC converter