Batch-fabricated microinductors with electroplated magnetically anisotropic and laminated alloy cores

Although many integrated inductors have been made by integrated circuit and electronic packaging batch-fabrication techniques, their magnetic characte ristics are inferior to their discrete counterparts, in part because of the relatively poor magnetic properties of integrated magnetic cores. If the p ermeability of an integrated magnetic core can be increased, the magnetic c haracteristics of microinductors based on these cores will improve. To addr ess this issue, batch-fabricated, integrated magnetic devices incorporating electroplated magnetically anisotropic cores and electroplated copper coil s are investigated. These devices are made by micromachining and electropla ting techniques at low temperature, Three different geometries of inductors , each possessing two different core materials [permalloy (NiFe) and superm alloy (NiFeMo)] are presented, The cores have been rendered magnetically an isotropic by application of a magnetic field during electrodeposition, resu lting in easy and hard axis orientations. In addition, some cores consist o f a two-layer electrodeposit separated by a polyimide thin-film lamination, At low frequencies (less than several hundred kHz), the easy-axis devices have higher inductance than the hard-axis devices. However, the hard-axis d evices have better performance at higher frequencies because of a far less steep falloff of material permeability as a function of frequency in the ha rd axis direction.