Appeal No. 1997-2046 Page 2
Application No. 08/059,350
inductor for such a choke coil achieves miniaturization, it
suffers several drawbacks. Because the inductor uses an
amorphous alloy ribbon
having a high permeability as a ferromagnetic ribbon, the
inadequate magnetic characteristics of the ribbon produce poor
DC superposition characteristics. In turn, the poor DC
superposition characteristics reduce inductance, making
control difficult and lowering the efficiency of a DC-to-DC
converter to which the planar inductor is applied. Even if
the DC superposition characteristics can be improved, a high-
frequency loss of the ferromagnetic ribbon limits the
efficiency of the applied DC-to-DC converter.
In practice, the planar inductor is coated with a mold
resin. If the amorphous alloy ribbon has a positive
saturation magnetostriction, when the surface of the planar
inductor is coated with a liquid mold resin and the resin is
hardened, contraction of the mold resin applies a compressive
stress to the ferromagnetic ribbon. An inverse
magnetostrictive effect decreases effective permeability, thus
reducing an inductance.
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