Study of thin film micro transformer with high operating frequency and coupling coefficient

For miniaturization of magnetic devices, it is necessary to increase the operating frequencies. A thin film microinductor is studied in order to realize a high operating frequency and reduce iron losses. A thin film microtransformer is proposed, with high operating frequency achieved by the 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 of CoFeSiB/SiO₂ multilayered film. The induced magnetic anisotropy is controlled so that the exciting direction of the coil is along the hard axis. The experimental transformers show that a multilayered core is useful to improve the 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 is developed