Preparation and core loss of CoZrMo/polyimide stacked thin-film core

Abstract

A stacked thin-film core for large amplitude rf magnetization is fabricated. The soft magnetization characteristic and loss is measured and the application of the core is discussed by comparing it with other types of cores. The core is formed by depositing a 2-μm thick CoZrMo film on a 12.5-μm thick polyimide film using an opposing target sputtering system. When the target ratio of Co:Zr:Mo was 82.2 percent:5.7 percent:12.1 percent, the saturation magnetic flux density Bs was 0.32 T. Even without thermal treatment, a core with a small coercive force (Hc) = 4.8 A/m (0.06 Oe)) is obtained. The hysteresis loss was close to that of a 5-μm thick crystalline permalloy wound core but is one order of magnitude higher than that of amorphous (FeCoCr)75(SiB)25 thin-film ribbon. This indicates that the core should be heat-treated to improve the hysteresis property. When the maximum magnetic flux density Bm was 0.1 T at 10 MHz, the core loss was about 8 J/m3, which was close to that of 3.8-μm thick amorphous (FeCoCr)75(SiB)25 thin-film ribbon, which provides the lowest core loss. When Bm = 0.02 T at 10 MHz, the core loss was one-third that of the supermalloy wound core and one-tenth that of MnZn ferrite. At 4 MHz, the loss was lower than that of a 5.3-μm amorphous (FeCoCr)75(SiB)25 thin-film ribbon. The frequency dependence of the core loss was less than that of other cores because the eddy current loss was low. The proposed core can be applied for a high-amplitude rf magnetization if the hysteresis loss is reduced.