Fabrication of symmetrical meandering NiFe/Cu/NiFe film sensors and study of the effects of field direction and film thickness on giant magnetoimpedance

Sandwich NiFe/Cu/NiFe film sensors with symmetrical meandering structure are fabricated by Micro-Electro-Mechanical-System (MEMS) technology, the longitudinal, transverse, and perpendicular giant magnetoimpedance (GMI) effect have been investigated comprehensively. The correlation between film thickness and GMI effect are analyzed thoroughly. The experimental results show that the alternating current (AC) frequency of maximum GMI ratio decreases gradually with the increasing of magnetic layer thickness, but the conducting layer exhibits an opposite tendency. The NiFe and Cu layer both show a GMI ratio tendency from increasing to decreasing along with the increase of film thickness. It is observed the longitudinal, transverse and perpendicular GMI effect share a common characteristic: the AC frequency of maximum GMI ratio increases with the increase of external field intensity. However, there is a notable difference between them, it is demonstrated that the higher GMI ratio and sensitivity can be obtained in the longitudinal direction. The longitudinal GMI ratio reaches the peak value 191.2 % at f _AC = 6.5 MHz under H _L = 17 Oe in six turns sample with the Cu and NiFe thickness of 6 and 7 μm, respectively.