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◆ Recently, electric devices have been miniaturized rapidly. Developments of magnetic elements and circuits for miniaturizing have been done actively and they are expected to operate under a high frequencyHowever, eddy current . loss is the most important problem under a high frequency. To reduce the loss is the key to the development of high performance magnetic devices. Therefore, it is needed to grasp the fundamental characteristics of the mag-netic materials and its differences by changing the device parameters. In these backgrounds, we are trying to de-velop high performance magnetic cores.

◆ To reduce the eddy current loss dramatically under a high frequency, we studied the structures of the magnetic core which have very narrow slits act as the eddy current suppressor in it as shown Fig. 1. The slit widths are 1.5 micrometer to 5 micrometer. The LIGA process, that is composed of deep X-ray lithography using synchrotron radiation (SR) and Ni electroforming, was used in this study because this is the best way to fabricate highest as-pect ratio structure. The PMMA walls are so high aspect ratio and long structure that the walls can not stand by itself. Therefore mechanical supports are set up on the walls periodically. Two types of the mechanical sup-ports (absorption type and fixation type supports) are adopted as shown in Fig. 2. Absorption type supports are set up for absorb stretch of PMMA walls during the PMMA developing (Fig. 2(a)). Fixation type supports are set up for prevent PMMA walls from bending by stretch of PMMA walls (Fig. 2(b)). As the result, the Ni mag-netic cores have the very narrow slits with 100 micrometer-height, 1.5 micrometer-width, 4 millimeter length in maximum aspect ratio of 66 were fabricated.

◆ It is thought that the magnetic core applied to the integrated thick film inductor and a transformer in a micro dc-to-dc converter and so on.

Fig.1　Schematic view of the thick magnetic film structure.

＿＿＿＿＿＿＿＿＿＿＿＿Close-up＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿ Close-up (a) Absorption type support ＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿(b) fixation type support

Fig.2　SEM images of magnetic core after Ni electroforming. PMMA walls with 100 micrometer-height, 3 micrometer-width, 4 millimeter-length in maximum aspect ratio of 33.