Huu Duc Nguyen

High-sensitivity planar Hall sensor based on simple gaint magneto resistance NiFe/Cu/NiFe structure for biochip application

The planar Hall effect (PHE) sensor based on a simple giant magneto resistance (GMR) trilayer structure NiFe/Cu/NiFe has been designed and fabricated successfully using conventional clean room fabrication methods. The PHE sensor is integrated by 24 sensor patterns with dimensions of 50 × 50 μm. Influence of individual layer thickness to sensitivity of sensor has been investigated. Sensitivity and planar Hall voltage increases with the decrease of Cu-layer thickness. The results are discussed in terms of the reinforcement of the antiferromagnetic interaction between NiFe layers and shunting current through the layer Cu. The optimum configuration has been found in the structure with the Cu-layer of 1 nm. In this case a single planar Hall effect sensor exhibits a high sensitivity of about 8 μV Oe−1 and a maximal of the signal change as large as ▵V ~ 55 μV. These values are comparable to those of the typical PHE sensor based on complex GMR spin-valve structure. With a high sensitivity and simple structure, this sensor is very promising for practical detection of magnetic beads and identifying multiple biological agents in the environment.

Influence of CoFe and NiFe pinned layers on sensitivity of planar Hall biosensors based on spin-valve structures

This paper deals with the magnetization, magnetoresistance and planar Hall effect (PHE) of NiFe(10)/Cu(1.2)/NiFe(tp)/IrMn(15) (nm) and NiFe(10)/Cu(1.2)/CoFe(tp)/IrMn(15) (nm) spin-valve structures with various thicknesses of pinned layer tp = 2, 6, 9, 12nm and a fixed free layer NiFe of tf = 10nm. Experimental investigations are performed for 50◊50µm junctions fabricated using lithography technique. The results show that the thinner the pinned layers, the higher is the PHE sensitivity obtained in both systems. In addition, in the spin-valve structures with the same pinned layer thickness, the CoFe-based system exhibits higher magnetoresistive ratio, but lower PHE sensitivity with respect to those of the FeNi-based system. The results are discussed in terms of the spin twist as well as the coherent rotation of the magnetization in the individual ferromagnetic layers. The highest PHE sensitivity S of 110µV(kAm 1 ) 1 has been obtained in the FeNi-based spin-valve structure with tp = 2nm.