A Sensitive 2-Axis Magnetic Sensor Based on Anisotropic Magneto-Resistance Effect

Nowadays, the detection of the ultra-weak magnetic field (< 1 mOe) in micro- or nano-scope (< 100 nm) is a hot research field. The magnetic sensor based on the principle of anisotropic magneto-resistance effect is attractive in the application of detecting the ultra-weak magnetic field in a contactless manner. In this paper, a sensitive, 2-axis magnetic sensor based on anisotropic thin-film structure is proposed and fabricated. As the sensor's induction layer, the anisotropic film of permalloy Ni (80%) Fe (20%) is deposited by means of magnetron sputtering. Seed layer under the NiFe layer is used to control the NiFe grain size, which is an important parameter for magneto-resistance. In order to obtain good performance, tantalum is deposited as the seed layer, making the NiFe layer with <111> crystallographic texture with suitable grain size. The characterizations are conducted on the prepared layer, including surface roughness by atomic force microscope (AFM). Based on the characterized results, the magneto-resistance related to the anisotropic effect is demonstrated and analyzed. The influence of the thickness of the anisotropic film on the characteristics of the magnetization and the dynamic range of the sensors, as well as the range of the magnetic field sensitivity, are studied and analyzed in the paper. The deposited film with 20 nm thickness shows obvious anisotropy with low coercivity, resulting in high sensitivity and outstanding detecting ability in the weak magnetic field. In addition, the structural parameters of the sensor are optimized by the results of current density obtained by finite element simulation.