A Self-biased Anisotropic Magnetoresistive (AMR) Magnetic Field Sensor on Flexible Kapton

Abstract

Magnetic sensors have attracted extensive attention due to their highly sensitive, e.g., navigation, [1] medical diagnosis (magnetoencephalography, magneto-cardiography, etc.), [2–4] and data storage. [5] Flexible substrates have received a great deal of attention due to their outstanding portability and wearability. A great fabrication of magnetic sensors on flexible substrates can make a big difference in our lives. AMR magnetic sensor has a simple structure and high sensitivity, when magnetization M and current density J are parallel $( \mathrm {R}_{//})$, the resistance of Permalloy is at maximum and when magnetization M and current density J are perpendicular with each other $( \mathrm {R}_{\# })$, [6] the resistance is at minimum. In this work, we fabricated a self-biased anisotropic magnetoresistive (AMR) magnetic field sensor on flexible Kapton and it shows excellent stability and sensitivity even in the case of larger deformation. Here, we designed the Wheatstone bridge and barber pole structures, the current flow can be rotated by an angle of 45° or 135° with respect to the magnetic easy axis. We made AMR magnetic sensors on flexible Kapton by lift-off. First, the flexible substrates were cleaned by sequentially rinsing in acetone and ethanol. Then, we made a specific size of the pattern on the substrate by photolithography. Permalloy, Gold, Pt layers were sequentially deposited by sputtering method with base pressure $< 10 ^{-7}$ torr. The magnetoresistance effect is characterized using typical four point probe resistivity measurement, as shown in Figure 1. Figure 1 shows that when there is an applied magnetic field, the resistance of the magnetoresistive sensor will change, the AMR ratio is probably 1.2%. Figure 2(a) shows that when the applied magnetic field is 114 Oe, the resistance of the magnetic field sensor varies with the angle of the magnetic field with a bending radius of 5 mm. Figure 2(b) shows that when the same magnet passes over the sensor at a same height, the resistance of the sensor have a different change with a different bending radius. In summary, we fabricated flexible AMR sensors on Kapton substrates. It shows excellent stability and sensitivity with a bending radius of 5 mm. With a great advantage of high sensitivity, excellent flexibility, and stability, the flexible AMR sensor provides a platform capable where wearable electrics for navigation, medical diagnosis and health monitoring can be realized.