The authors reported laminated multilayer magnetic planar inductors for sensitive magnetic field detection, which consist of two serially connected sandwich planar inductors (i.e., FeCuNbSiB/micro planar coil/FeCuNbSiB/micro planar coil/FeCuNbSiB). When ac current is applied to coils, the greatly increased inductance by the incorporated high permeability magnetic material and enlarged mutual-inductance among coils significantly improve the sensor sensitivity to the dc magnetic field. The demagnetizing field is also found to affect the performance severely when the shape and the number of magnetic layers vary. The investigation indicates that the proposed laminate can provide an inductance ratio of 665% at the frequency of 1 kHz. By connecting the sensor with a capacitor, the sensor output with varying dc magnetic fields is obtained by tuning the resonant frequency shift. The study indicates that the proposed sensor can provide a sensitivity of about 3.57 kHz/Oe with a resolution of 28 nT between 2 Oe and 60 Oe, which outperforms most of the magnetic sensors with frequency shifting output.

Magnetic characteristics and the frequency dependence of permeability for Fe-B-N thin films have been studied. Among the compositions investigated, Fe 94.9 B 1.3 N 3.8 exhibited excellent soft-magnetic properties: High saturation induction, B sϳ 20.6 kG, and low coercivity, H cϳ 0.1 Oe. An anomalous change of the incremental permeability ratio ͑PR͒ curve as a function of external magnetic field for the films measured above 4 MHz was observed, indicating a considerable variation in the magnetic softness in the high-frequency region. The changes of PR in low external fields seem to be useful for the evaluation of the magnetic softness in thin-film-type materials.

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