Abstract
For miniaturization of magnetic devices, it is necessary to increase the operating frequency. We have studied thin-film micro-inductors to realize a high operating frequency and reduce the iron loss. In this paper, we propose a thin-film micro-transformer with high operating frequency achieved by application of a multilayered magnetic film to the core. The magnetic core is made of amorphous CoFeSiB monolayer film or a CoFeSiB/SiO2 multilayered film. The induced magnetic anisotropy is controlled so that the exciting direction of the coil is along the hard axis. The total thickness of the magnetic layer is 3μm and the size of the core is 0.6 mm × 2.3 mm. The experimental transformers show that a multilayered core is useful for improving the transmission loss of transformers at high operating frequency. A thin-film transformer whose transmission loss is 2.7 dB from 100 MHz to 250 MHz has been developed. This value is smaller than the 5.3 dB of the monolayer core.
