Contents I. Introduction
There is an ever-increasing demand for the on-chip power management in a portable electronic equipment to boost performance and reduce package size. Several on-chip voltage regulators using thin-film inductors have recently been demonstrated [1], [2]. NiFe, CoNiFe, and amorphous CoZrTa and FeGaB films have been adopted into the magnetic core to reduce the inductor size [2]–[5]. The requirements of such magnetic cores typically include high , high permeability, low coercivity, and proper operational frequency. In addition, a thick magnetic core is very helpful to increase inductance and power density, so high resistivity is a clear merit to reduce the eddy-current loss for both the single-layered and laminated magnetic cores. It is well known that nanogranular magnetic FeCo––O or FeCo––N films ( denotes a nonmagnetic element, such as Si, Hf, Al, and Ti) have both excellent high-frequency soft magnetic properties and relatively high resistivity [6], [7] and, therefore, are very suitable for magnetic cores [8]–[10]. Although thermal stability is a concern with nanogranular films, recent studies show that it can be improved by several techniques, for example, oblique sputtering or thermal annealing after preparation [11], [12].
