Development of optical probe current sensor with Kerr effect for power electronics

A novel magnetic thin film with large anisotropy magnetic field and good thermal stability has been developed for optical probe current sensor using Kerr effect of the magnetic film. Also a sensor module has been fabricated, and its basic characteristic has been evaluated. A fabricated optical probe current sensor module consisted of a polarizer, half-wavelength plate, prism beam splitter and periodically-arrayed Fe-Si/Ru magnetic strips with a large uniaxial magnetic anisotropy field of 16 kA/m. Such large magnetic anisotropy was due to a high aspect ratio (over 1000) rectangular shape of the film. In addition, since the shape magnetic anisotropy field corresponding to the demagnetizing field in the width direction is proportional to the saturation magnetization of the film, temperature independent anisotropy can be realized at least when the ambient temperature is much lower than Curie temperature T_c of the film. In case of Fe₈₉Si₁₁ (at.%) with T_c of 700 degree-C, temperature coefficient of the anisotropy magnetic field was 0.03 %/degree-C small. Therefore thermal stable Kerr effect can be realized and will be useful for mobile applications such as EV/HEV. The fabricated sensor module exhibited a good linear relation between sensor output and the external magnetic field in the ranging from -16 kA/m to 16 kA/m.