Enhancing the Linearity of Giant Magnetoresistance Sensors by Magnetic Anisotropic Design and Low Temperature Annealing

Giant magnetoresistance (GMR) sensors have been widely used in current detection, compass, automobile, and Internet of Things. The linearity of GMR sensors relies on a magnetic annealing process above the blocking temperature of the antiferromagnetic layer, which causes the same magnetization directions in the free and pinned ferromagnetic layers. Here we construct an orthogonal magnetic anisotropic structure by using a relatively low annealing temperature of 145 °C, where the magnetization direction of the free layer is perpendicular to that of the pinned layer so that a linear output can be realized. Quantitative magneto-optical kerr microscope (MOKE) is used to investigate the vector distribution of the magnetic domains, showing that an orthogonal anisotropy is established by the low temperature annealing process. GMR magnetic field sensor with a sensitivity of 0.78 mV/V/Oe and a measurement range of −20 to 20 Oe is demonstrated, which provides an effective method to enhance the linearity of the magnetic sensors with spin valve structures.