Application of magnetic metal thin films to EMI noise filter

We demonstrate the applicability of magnetic metal thin films to an electromagnetic interference (EMI) noise filter. We examine the magnetic loss of three kinds of thin films consisting of roll-pressed Ni-Fe, sputtered Ni-Fe and roll-cooled amorphous Co-Fe-Si-B. Impedance measurement reveals that the magnetic loss of these metals becomes higher as their permeability increases. The noise reduction characteristic of thin film filters is evaluated by the S-parameter measurement technique. We can obtain the same noise reduction as a conventional ferrite filter with a thin film filter of 1/30-1/7 its volume. These results indicate that the use of magnetic metal thin films is advantageous with regard to minimizing noise filter size.