Abstract
A high-frequency carrier-type (HFC-type) thin-film magnetic field sensor (or giant magneto-impedance, GMI, sensor) needs a bias magnetic field of Oe order for magnetic field measurement. In this report, a thin-film magnetic bias with coplanar layout is proposed for dc bias supply. The merits of the coplanar thin-film magnetic bias are as follows. Magnetic property degradation caused by both lamination of magnetic thin-films and heat treatment is avoided. The heat treatment is indispensable for realizing uniaxial anisotropy in a Co85Nb12Zr3 amorphous sensor element. Since a thin-film fabrication process is suitable for creating a coplanar pattern with precise dimensions, a precise dc bias field is obtained. An additional new structure proposed in this report uses a low-resistivity thin-film magnet for the current path of the sensor element. An SmCo5 amorphous thin-film magnet was proposed for this structure. This conductive metal bias magnet with coplanar layout is suitable for both the return path of the carrier current, which simplifies the sensor structure, and the impedance-matching ground plane for high-frequency carriers. We confirmed the properties of these proposed structures by experiment. The temperature property and 85°C 85% RH treatment property of the sensor were also measured. The results show the effectiveness of coplanar magnetic bias in an SmCo5 amorphous thin-film magnet.
