For miniaturization of magnetic devices, it is necessary to increase the operating frequencies. We have studied a thin film micro inductor in order to realize a high , operating frequencies and reduce iron losses. In this paper, we propose a thin film micro transformer with high operating frequency achieved by application of multilayered magnetic film to the core. The transformer is designed to be able to obtain a high coupling coefficient. The magnetic core is made of amorphous CoFeSiB film or CoFeSiB/SiO2 multilayered film. The induced magnetic anisotropy is controlled so that the exciting direction of the coll is along the hard axis. The total thickness of the magnetic layer is 3 mum and the size of the core is 0.6 mm x 2.3 mm. The experimental transformers show that a multilayered core is useful to improve transmission loss of the transformer at high operating frequency. A thin film transformer whose transmission loss is 2.7 dB from 100 MHz to 250 MHz has been developed, and this value is smaller than the 5.3 dB of the monolayer core.
