偶関数型GMRを用いた超高感度磁界センサ

抄録

High-sensitive magnetoresistance (MR) sensors have attracted much attention as an Internet of Things sensor. To improve the sensitivity, a new high-sensitive magnetic sensor which is referred to a symmetric response magnetoresistance (SRMR) sensor is proposed. This sensor uses giant magnetoresistance (GMR) elements which have symmetric field response. An ac magnetic field with frequency f is applied to the GMR elements in order to modulate a small detecting magnetic field. Due to the symmetric response of the MR element, a carrier signal of the ac magnetic field is converted to 2 f and the detecting signal is converted to f. By using a full bridge circuit, where two pairs of GMR elements have opposite phase of the applied ac field, the 2 f components can be eliminated at the differential output terminal of the bridge. Since this system converts the frequency range of the detecting magnetic field to higher one, its noise level, which is dominated by the 1/ f noise, can be decreased. The effect of noise reduction and carrier signal suppression were confirmed by a circuit simulation. Moreover, the SRMR sensor with the antiphase ac modulation bridge was fabricated. It was confirmed that the detectivity of the magnetic field was obtained around 75 pT at 60 Hz. Improvement of the noise reduction and the magnetic field concentrator system, a perspective of the sensitivity less than picotesla might be possible.