Micro-patterned NiFeMo Magnetoimpedance Multilayer for Magnetic Sensor Application
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Micro-patterned NiFeMo Application
Magnetoimpedance
Multilayer
0906-HH01-09.1
for Magnetic
Sensor
Duhyun Lee, G.H. Jeong, J.H. Kim, Y.S. Kim, and S.J. Suh AMPIT, Dept. of Advanced Materials Engineering, Sungkyunkwan University, 300, Chunchun-dong, Suwon, 440-746, South Korea
ABSTRACT As an alternative to the magnetoimpedance (MI) devices made from amorphous ribbon or wire, this study proposed a thin film type MI device composed with Ag conductive core and soft ferromagnetic NiFeMo sandwich layers. Obtained optimum sandwich structure was Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm/ Ag 900 nm/ Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm, and the width of Ag as 20 µm and the width of NiFeMo as 100 µm. It was patterned by using photolithography and lift-off process. The sandwich structure showed the maximum MI ratio about 40% at the 15 MHz. The impedance change was linear and nearly reversible at the external magnetic field region below the anisotropy field.
INTRODUCTION The impedance of soft ferromagnetic material is very sensitive to the external magnetic field. To apply this phenomenon to magnetic field sensor, for example triaxial compass in mobile electronics, magnetoimpedance material must be integrated into a chip. However the most promising MI sensors of Co-based amorphous wires [1-3] or ribbons [4, 5] are not compatible with semiconductor process due to their shape. Thus, this study adopted the sandwich-type NiFeMo multilayer which could be deposited by using sputtering and patterned by using conventional photolithography. NiFeMo is known as supermalloy and shows the permeability as high as 1,000,000 [6]. This soft ferromagnetic material also has lower resistivity than the amorphous materials. The sandwich-type multilayer is composed with conductive core and soft ferromagnetic shell, which is an ideal structure to obtain the promising MI property. The magnetoimpedance effect strongly depends on the material shape. In this study, thus, the shape and the thickness of conductive layer and the magnetic layer were varied and the resultant optimum shape was deduced.
EXPERIMENTAL The sandwich-type multilayer of Ta 5 nm/ NiFeMo 100-300 nm/ Ta 5 nm/Ag 100-900 nm/ Ta 5 nm/ NiFeMo 100-300 nm/ Ta 5 nm was deposited on the silicon substrate with sputtering, where the Ta is for isolation layer, NiFeMo for magnetic sensing layer and Ag for conducting layer. Substrate was oxidized thermally prior to deposition to prevent RF current leakage. The composition of NiFeMo was Ni79-Fe16-Mo5 wt.%. During the magnetic layer deposition, insitu magnetic field of 300 Oe was applied to transverse direction. Photolithography and lift-off were carried out for micro-patterning. The negative photoresist of Futurrex 6000PY was used
0906-HH01-09.2
Magnetic layer
AC I
H
L
ex
W
Conductive layer
Figure 1. The shape of photolithographically patterned magnetoimpedance sandwich. The left shows top view of the element and the right shows cross-sectional view of it. The lengths of magnetic layer and conductive layer were fixed and the widths of the layers we
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