Thin film magnetic field sensor utilizing Magneto Impedance effect

Recently, the Magneto Impedance effect found in amorphous wires with soft m agnetic properties is noticeable as a new principle for sensing magnetic fi led. According to this effect, the impedance of the wire in the range of hi gh frequencies over 10 MHz changes remarkably with the external magnetic fi eld. This effect is expected to be promising for magnetic field sensor with high sensitivity. Therefore, we have attempted to introduce this effect in to amorphous thin films to extend application fields, and a novel thin film sensor sensitive to small magnetic field based on the Magneto Impedance ef fect has been proposed. The sensor consists of half bridge of the individua l detecting element with FeCoSiB/Cu/FeCoSiB multi-layer, which exhibits the large impedance change ratio more than 100% when an external magnetic fiel d is applied. By the optimization of the operating point due to bias field and the signal processing with a synchronous rectifier circuit, no hysteres is, good linearity and good stability against temperature variation as well as high sensitivity in the sensor characteristics have been achieved. The variation of the sensor output with the temperature is largely reduced to o ne-third, compared to the conventional thin film sensor we developed former ly. The detection resolution of 10(-3) Oe order higher than those of any ot her conventional thin film sensors is obtained. (C) 2000 Elsevier Science S .A. All rights reserved.